Can a Plane on a Treadmill Take Off? [Archive]

Ron Garret

February 4th 06, 03:02 AM

In article . com>,
"cjcampbell" > wrote:

> Saw this question on "The Straight Dope" and I thought it was amusing.
>
> http://www.straightdope.com/columns/060203.html
>
> The question goes like this:
>
> "An airplane on a runway sits on a conveyer belt that moves in the
> opposite direction at exactly the speed that the airplane is moving
> forward. Does the airplane take off?" (Assuming the tires hold out, of
> course.)
>
> Cecil Adams (world's smartest human being) says that it will take off
> normally.

He's right.

rg

jesse

February 4th 06, 03:03 AM

Ok, so all of us do not comment on his site, or well maybe that would
be better, does this guy really not have any sense to know that the
ground speed is completely irreleveant to aerodynamics(thinking of the
threads about 152s with 0 or negative ground speed)? whatever....
airspeed is zero, no lift, no fly.
Jester

Paul Tomblin

February 4th 06, 03:33 AM

In a previous article, "jesse" > said:
>Ok, so all of us do not comment on his site, or well maybe that would
>be better, does this guy really not have any sense to know that the
>ground speed is completely irreleveant to aerodynamics(thinking of the
>threads about 152s with 0 or negative ground speed)? whatever....
>airspeed is zero, no lift, no fly.

Hopefully the people commenting on his site aren't as stupid as you.

--
Paul Tomblin > http://xcski.com/blogs/pt/
#define sizeof(x) ((int)rand()*1024)

Doug

February 4th 06, 03:58 AM

Actually, this has a real world parallel. A Seaplane taking off (or
landing) on a river. There are three speeds here. The speed relative to
the conveyer belt (river), the speed relative to the non-moving ground
(riverbank), and the airspeed. Put in some wind and you can get some
complicated scenarios.

Jim Logajan

February 4th 06, 04:14 AM

"cjcampbell" > wrote:
> Saw this question on "The Straight Dope" and I thought it was amusing.
>
> http://www.straightdope.com/columns/060203.html

Seems Cecil Adams is compounding the confusion by having the page's title
begin:

"An airplane taxies in one direction...."

So is the plane attempting to taxi or take off? The page's title says one
thing, the person posing the question is stating another. The hypothetical
pilot of the taxing plane would presumably not let the the airspeed go to
takeoff speed, while the pilot of the plane taking off would want to
accelerate to rotation speed. So on that basis alone, we can say a taxing
plane isn't going to take off!

;-)

jesse

February 4th 06, 04:21 AM

when you walk on a treadmill, do you have any significant
airspeed(minus wind and fans)? you are moving forward relative to the
treadmill belt only, your airspeed is zero, sure your legs are moving
at say three miles per hour, and the treadmill belt is moving three
miles per hour the opposite way, but without airspeed you have no
lift(assuming your arms were airfoils). its not that complicated
people. the thrust of the airplane is only used in most cases, to
provide a movement of air over the wings to cause lift. if the supposed
airplane is stationary to the air, regardless how much thrust is being
used to "keep up" with the treadmill, no lift will be created, try it
with an rc plane on a real treadmill if you dont believe me. Im not
calling anyone stupid, but didnt everybody learn in PP ground school
that ground speed has nothing to do with airspeed and the associated
lift? thats one of the first things, the most basic of things that i
was taught. im done with this topic. enjoy, let the roasting begin!
Jester
PP-ASEL
A&P

Doug

February 4th 06, 04:28 AM

What is keeping the airplane's speed up with the conveyor belt? The
propeller. Said propeller moves air. Air causes lift. The problem is
more complicated than it seems to be at first read.

Morgans

February 4th 06, 04:42 AM

"Doug" > wrote in message
oups.com...
> What is keeping the airplane's speed up with the conveyor belt? The
> propeller. Said propeller moves air. Air causes lift. The problem is
> more complicated than it seems to be at first read.

Another way to say it; it had better be a long conveyer belt, cause the prop
is pulling the plane forward, without caring how fast the wheels are going.
That will make the necessary airspeed to lift off.
--
Jim in NC

jesse

February 4th 06, 05:17 AM

experiment, go run with a kite(in a no wind situation) untill it flies,
measure the speed youre running. get on a teadmill and run that speed
that it took to make the kite fly. does the kite fly when youre on the
treadmill? no... same thing as the airplane on the conveyor belt. i
know i said i was done but i cant keep my hand out of this.
jester

Doug

February 4th 06, 05:22 AM

There will be airspeed felt by the plane in the area of the propellor
wash. Out of the prop wash, since the plane is not moving relative to
the surrounding air, there will be no relative wind felt by the
airplane. The airplane MIGHT take off, but it will not be a normal
takeoff, at least not for a normal airplane with 36' wingspan and a 6'
propellor. I really don't think there is enough information to know the
answer for sure. Too many unknowns.

This is one of these "frame of reference" problems.

The Flying Scotsman

February 4th 06, 05:29 AM

I dont know what all the fuss is about. The plane will not takeoff for
the reason that the all the plane is doing is keeping stationary. In
actual fact the trust thats produced is not producing thrust, its only
compensating from the drag thats pull the aircraft back. (treadmill) in
order to take off the plane must superexceed the opposing force and
establish that trust actually does exceed drag. hence the the plane
must build up momentum (in the correct direction)

correct ?

Barry...

Doug

February 4th 06, 05:40 AM

Taxi is just nomenclature for the airplane moving along the ground.
"Takeoff run" would be more correct I guess, but in this case things
are so weird, as it is ambiguous whether the plane is going to takeoff
or not.

The Flying Scotsman

February 4th 06, 05:43 AM

Ok, in relevance to Dougs post... we are both correct !!! apart from
the down wash from the small propeller, they will not be any airflowing
over the rest of the wings... why ??? Because the airplane is not
moving !!!! its only compensating for the exstreem backward force, as i
said its only standing still, and standing still doesnt get you
anywhere. you need momentium.

It however, would be possible if you have a plane with an exceedingly
small wing span, very low stall speed and a big propeller to generate a
downwash to cover the entire wing. As you know your aillerons are
situated at the outer section of the wings, if you have no downwash
over them it will stall and not turn leading to a temporary lift and
then crash.

Barry

Jim Macklin

February 4th 06, 05:46 AM

If the treadmill is stationary and the belt speed is equal
to the required take-off speed, the airplane will have zero
airspeed if it is "moving" in relation to the belt, the
airplane is moving, the prop has thrust and is balancing the
rearward movement of the belt. The tires are rolling, but
the airplane is stationary and there is no airspeed or lift.

--
James H. Macklin
ATP,CFI,A&P

--
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But government sees it as an obstacle to be overcome.
some support
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"Doug" > wrote in message
oups.com...
| Taxi is just nomenclature for the airplane moving along
the ground.
| "Takeoff run" would be more correct I guess, but in this
case things
| are so weird, as it is ambiguous whether the plane is
going to takeoff
| or not.
|

muff528

February 4th 06, 05:47 AM

First I'm not a pilot.... But the engine is providing thrust, not driving
the wheels like a car. The airplane is gonna move regardless of what speed
the wheels are or are not turning. What the wheels do is only slightly
relevant if at all unless you're holding the brake....and even that wouldn't
matter if you're on a treadmill. Second.....are we talking about a
treadmill or a conveyer belt? The treadmill may or may not move at all
relative to the world if it's the "classic" kind ... (i.e. non-motorized).
Depends on whether the wheels or treadmill has better bearings.

"Morgans" > wrote in message
...
>
> "Doug" > wrote in message
> oups.com...
> > What is keeping the airplane's speed up with the conveyor belt? The
> > propeller. Said propeller moves air. Air causes lift. The problem is
> > more complicated than it seems to be at first read.
>
> Another way to say it; it had better be a long conveyer belt, cause the
prop
> is pulling the plane forward, without caring how fast the wheels are
going.
> That will make the necessary airspeed to lift off.
> --
> Jim in NC
>

Jim Macklin

February 4th 06, 05:55 AM

See Custer Channel-wing [Google] and reaction controls.

"The Flying Scotsman" > wrote in
message
ups.com...
| Ok, in relevance to Dougs post... we are both correct !!!
apart from
| the down wash from the small propeller, they will not be
any airflowing
| over the rest of the wings... why ??? Because the airplane
is not
| moving !!!! its only compensating for the exstreem
backward force, as i
| said its only standing still, and standing still doesnt
get you
| anywhere. you need momentium.
|
| It however, would be possible if you have a plane with an
exceedingly
| small wing span, very low stall speed and a big propeller
to generate a
| downwash to cover the entire wing. As you know your
aillerons are
| situated at the outer section of the wings, if you have no
downwash
| over them it will stall and not turn leading to a
temporary lift and
| then crash.
|
| Barry
|

Damian

February 4th 06, 05:55 AM

Paul Tomblin wrote:
> In a previous article, "jesse" > said:
>> Ok, so all of us do not comment on his site, or well maybe that would
>> be better, does this guy really not have any sense to know that the
>> ground speed is completely irreleveant to aerodynamics(thinking of the
>> threads about 152s with 0 or negative ground speed)? whatever....
>> airspeed is zero, no lift, no fly.
>
> Hopefully the people commenting on his site aren't as stupid as you.
>
>
Paul...dont look now, but that airplane is NOT flying off the ground
until the AIRSPEED is up...the treadmill is only moving the TIRES, that
means diddly squat to an airplane.

Damian

jesse

February 4th 06, 06:21 AM

My friend and i were discussing this. There is not enough information
in the orginal question to determine anything. Depending which way you
argue the various variables, it could work either way. The people who
are saying the plane will fly are saying that the prop pushes against
the air and thus will eventually fly, the people who are saying that
the plane will not fly are assuming that the prop(or jet) is only
giving enough thrust to equalize the resistance on the wheels bearings
etc, thus the plane will stand still. define some variables, define
speed(wheel speed, ground speed, air speed) the original poster(at
cecils site) didnt give us enough info, and used the term speed and
move in more than one way. he also a plane standing on a runway, then
it moves, but then the conveyor moves. which is it buddy? if the plane
starts to move, it will take off. uh oh, here i go again, getting lost
in the details, now i think it will take off. its almost akin to
asking, if you fire a gun into a crowd will you kill someone. a lot of
people would say yes. what if the bullet went between people, what if
it was a blank, what if it was a blank and then some guy had a heart
attack, what if superman stopped it. define variables and argue it
either way, the answer is yes and no, it depends, and thats the
wonderful thing about these questions, it gets us to think, thats why
we are the top of the food chain. animals might have said, i dont care
weather it takes off or not, im outta here so it doesnt eat me. other
animals might have tred to eat it. aluminum or wood or fiberglass or
steel is not very edible to us, so we talk about it. its a great world
isnt it! if you need to be right to prove your intelligence, go on
jeopardy. to me, i gotta go flying, and i havent seen any conveyor
belts at OUN, so im outta here!
Jester

alexy

February 4th 06, 06:24 AM

"jesse" > wrote:

>when you walk on a treadmill, do you have any significant
>airspeed(minus wind and fans)? you are moving forward relative to the
>treadmill belt only, your airspeed is zero, sure your legs are moving
>at say three miles per hour, and the treadmill belt is moving three
>miles per hour the opposite way, but without airspeed you have no
>lift(assuming your arms were airfoils). its not that complicated
>people. the thrust of the airplane is only used in most cases, to
>provide a movement of air over the wings to cause lift. if the supposed
>airplane is stationary to the air, regardless how much thrust is being
>used to "keep up" with the treadmill, no lift will be created, try it
>with an rc plane on a real treadmill if you dont believe me. Im not
>calling anyone stupid, but didnt everybody learn in PP ground school
>that ground speed has nothing to do with airspeed and the associated
>lift? thats one of the first things, the most basic of things that i
>was taught. im done with this topic. enjoy, let the roasting begin!
>Jester
>PP-ASEL
>A&P

some people apparently have a hard time reading.

"a conveyer belt that moves in the
opposite direction at exactly the speed that the airplane is moving
forward."

When the conveyor belt is moving backwards at 80mph, how fast is the
plane moving? Hint: there is no mention of how fast the plane is
moving relative to the conveyor belt. If the plane is moving forward
at 80mph, is it likely to have enough airspeed to fly?

If you are still confused, when the plane is moving forward at 80mph,
the conveyor will be moving backwards at 80mph, and a speedometer that
measures off of tire rotation would indicate the plane's speed (before
getting airborne) as 160mph, the speed relative to the conveyor.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

[email protected]

February 4th 06, 06:27 AM

cjcampbell wrote:
> "An airplane on a runway sits on a conveyer belt that moves in the
> opposite direction at exactly the speed that the airplane is moving
> forward. Does the airplane take off?" (Assuming the tires hold out, of
> course.)
>
> Cecil Adams (world's smartest human being) says that it will take off
> normally.

Here's my read...

The propeller or jet provides thrust to move the plane forward through
the air mass. The prop wash on a propeller aircraft will not itself
generate sufficient airflow over the wings to lift the plane. Nor will
a jet engine. The purpose of these devices is to accelerate the whole
aircraft into the air mass. Once the plane is moving forward through
the air the wings will begin to generate lift... but you need positive
airspeed, not just propeller wash.

So, IF the plane is stationary in the air mass it WILL NOT take off.

The complete problem description states that the treadmil's control
system tries to counteract forward movement of the plane by speeding up
the treadmil. It's a flawed idea as the plane's thrust is mostly
decoupled from its wheels. Unless the wheel bearings are superheating
with friction and actually providing a braking force the plane is going
to move forward into the air mass... regardless of the rolling ground.

So the plane will trivially overcome the treadmill, accelerate away and
WILL take off.

.... unless the wheels melt.

Finally...

If, as the plane's prop runs up, a headwind is encountered which
perfectly cancels out the thrust then the plane will be accelerating
into an oppositely accelerating air mass all the way up to take-off
speed. Neither the plane not the treadmill will never have moved
relative to the ground, but the wings are getting all the airflow they
need. The plane WILL take off (like an elevator until equilibrium is
lost).

Regards,
Paul.

Robert M. Gary

February 4th 06, 06:27 AM

> and a speedometer that
> measures off of tire rotation would indicate the plane's speed (before
> getting airborne) as 160mph, the speed relative to the conveyor.

While an airspeed indicator would indicate zero.

-Robert, CFI

Robert M. Gary

February 4th 06, 06:28 AM

> What is keeping the airplane's speed up with the conveyor belt? The
> propeller. Said propeller moves air. Air causes lift

By that logic, a pilot doing a full static runup at the runup area will
levitate.

-Robert, CFI

alexy

February 4th 06, 06:28 AM

"Doug" > wrote:

>What is keeping the airplane's speed up with the conveyor belt? The
>propeller. Said propeller moves air. Air causes lift. The problem is
>more complicated than it seems to be at first read.

Not at all complicated. The propulsion system is irrelevant. The given
fact is that the airplane's speed (not it's speed relative to the
conveyor) is equal to the conveyor's speed, but in the opposite
direction. When that speed is sufficient for flight, it will fly.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

jesse

February 4th 06, 06:31 AM

even cjcampbell's version of the question and the poster at the web
site are different. if it sits on a conveyor belt that moves at the
speed the airplane does, then is the belt moving when the aiplane gets
on it, or does it start to move by it self?. if, in that exact
question, the airplane starts to move forward, the belt moves backwards
at an equal rate, but the plane doesnt care, the wheels spin at the
combined speed of the airplane and the belt, the plane keeps moving
forward, off the end of the belt and away into the sunset, it might
take a thousand years depending on the resistance of the wheels(if they
were very resistive i suppose it would move backwards, but then if that
were the case, it would never have moved at all, and everything would
still be stnading still), oops, even if you try to simplify that one,
it doesnt work, oh well... my plane will even jump its chocks if you
try hard enough. are there chocks on the belt... what about tie
downs.... is it made of a really sticky tar? OMGosh, see, everybody is
right, and everyone gets a cookie!!! we can all think for ourselves!
thats what being a human is all about!... all right.... ummm, can
someone turn this thing off so i dont keep wasting avgas trying to get
off this thing?... is it wide enought to turn around so i can get a
boost?... this is fun!

alexy

February 4th 06, 06:33 AM

"The Flying Scotsman" > wrote:

>Ok, in relevance to Dougs post... we are both correct !!! apart from
>the down wash from the small propeller, they will not be any airflowing
>over the rest of the wings... why ??? Because the airplane is not
>moving !!!!

Reread the stated problem:

"a conveyer belt that moves in the
opposite direction at exactly the speed that the airplane is moving
forward."
Seems a pretty direct contradiction to the claim that it is not
moving. In fact, it very explicitly says that the plane is moving
forward, and at the same speed as the conveyor. So when the conveyor
is moving at takeoff speed, so will the plane, and the sound of the
tires will be that of a plane moving twice takeoff speed (the speed of
the plane relative to the conveyor.

> its only compensating for the exstreem backward force, as i
>said its only standing still, and standing still doesnt get you
>anywhere. you need momentium.
>
>It however, would be possible if you have a plane with an exceedingly
>small wing span, very low stall speed and a big propeller to generate a
>downwash to cover the entire wing. As you know your aillerons are
>situated at the outer section of the wings, if you have no downwash
>over them it will stall and not turn leading to a temporary lift and
>then crash.
>
>Barry

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

[email protected]

February 4th 06, 06:37 AM

LOL :-)) Or do an Indian rope trick! ;-)

Prime

February 4th 06, 06:37 AM

"Doug" > posted the exciting message
oups.com:

> What is keeping the airplane's speed up with the conveyor belt? The
> propeller. Said propeller moves air. Air causes lift. The problem is
> more complicated than it seems to be at first read.
>
>

Well, if it only took the propeller then you could set the brakes, apply
full power, and lift off at zero ground speed.

jesse

February 4th 06, 06:40 AM

man this post took off like a rocket. a rocket? would a rocket get off
the conveyor?... hmmm, who cares! but it is a great mental workout...
anyone who comes up with an answer has made assumptions. but we have to
assume things in order to live, you have to believe that when you take
that next step that the ground will be there. in schrodingers cat(sp?)
the cat both lives and dies. in our world that cant be at the same
time.... its like minority report... this q is similar in a way to the
cat in the box with the poison with the degrading material. it can be
both ways, depending how you look at it. quit debating and go pet a
dog!

alexy

February 4th 06, 06:41 AM

"Robert M. Gary" > wrote:

>> and a speedometer that
>> measures off of tire rotation would indicate the plane's speed (before
>> getting airborne) as 160mph, the speed relative to the conveyor.
>
>While an airspeed indicator would indicate zero.
>
>-Robert, CFI
Only if there is an 80 mph tailwind.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

[email protected]

February 4th 06, 06:59 AM

If you restate the problem as follows the aircraft will obviously NOT
fly.

The aircraft is on a conveyor belt.

The conveyor is programmed to move in such a way as to maintain the
aircraft at an airspeed of zero as measured at the pitot.

propwash?

No - It's a Skymaster and the examiner cut the front engine.

Oh-wait - It's a jet...

a.

cjcampbell wrote:
> Saw this question on "The Straight Dope" and I thought it was amusing.
>
> http://www.straightdope.com/columns/060203.html
>
> The question goes like this:
>
> "An airplane on a runway sits on a conveyer belt that moves in the
> opposite direction at exactly the speed that the airplane is moving
> forward. Does the airplane take off?" (Assuming the tires hold out, of
> course.)
>
> Cecil Adams (world's smartest human being) says that it will take off
> normally.

Morgans

February 4th 06, 07:12 AM

"jesse" > wrote in message
oups.com...
> My friend and i were discussing this. There is not enough information
> in the orginal question to determine anything.

I think jesse has earned his way into my "not worth the effort" file.
Anyone else have him strike you that way?
--
Jim in NC

alexy

February 4th 06, 07:12 AM

wrote:

>If you restate the problem as follows the aircraft will obviously NOT
>fly.
>
>The aircraft is on a conveyor belt.
>
>The conveyor is programmed to move in such a way as to maintain the
>aircraft at an airspeed of zero as measured at the pitot.

Absolutely, if you CHANGED the problem, and restated it as above, then
it wouldn't fly. Another way to state your entirely different problem
is to say that the conveyor is set up to always move at a speed that
maintains the wheel speed of the plane as the same as the conveyor
speed.

Or to parallel the original problem, "a conveyer belt that moves in
the opposite direction to the way the plane is pointed, at exactly the
speed that the airplane' wheels are moving, so that the plane is not
moving"

This will require a VERY fast conveyor, since once power is applied
and the brakes are released, it will have to move fast enough that the
rolling friction of the tires and bearing friction in the wheels
offset any thrust provided by the plane's propulsion system. Sounds
about as possible as any other conveyor belt runway!

>cjcampbell wrote:
>> Saw this question on "The Straight Dope" and I thought it was amusing.
>>
>> http://www.straightdope.com/columns/060203.html
>>
>> The question goes like this:
>>
>> "An airplane on a runway sits on a conveyer belt that moves in the
>> opposite direction at exactly the speed that the airplane is moving
>> forward. Does the airplane take off?" (Assuming the tires hold out, of
>> course.)
>>
>> Cecil Adams (world's smartest human being) says that it will take off
>> normally.

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Morgans

February 4th 06, 07:17 AM

"alexy" > wrote

> Reread the stated problem:
>
> "a conveyer belt that moves in the
> opposite direction at exactly the speed that the airplane is moving
> forward."

All it is, is a trick question, aimed at testing your reading and
comprehension ablility. The plane moves off in exactly the same manner as
on a regular runway. The moving belt is a distracter.
--
Jim in NC

Morgans

February 4th 06, 07:19 AM

"Doug" > wrote in message
oups.com...
> There will be airspeed felt by the plane in the area of the propellor
> wash. Out of the prop wash, since the plane is not moving relative to
> the surrounding air, there will be no relative wind felt by the
> airplane. The airplane MIGHT take off, but it will not be a normal
> takeoff, at least not for a normal airplane with 36' wingspan and a 6'
> propellor. I really don't think there is enough information to know the
> answer for sure. Too many unknowns.
>
> This is one of these "frame of reference" problems.

Re-read it, Doug. The plane is not getting its motion from the wheels, so
it matters not what the wheels or wheel speed is doing.
--
Jim in NC

jesse

February 4th 06, 07:48 AM

Of course! the plane does take off! revelation!! if you kept the
throttle low enough to equalize drag on the wheels from the belt, you
wouldnt go anywhere. Firewall it, youre outta there! like a touch n go,
if you have the throttle retarded when you touch down, your in a
similar state, wheels spinning, add throttle you accelerate, even
though the runway increases the speed of the wheels. doesnt matter if
you start out at zero KIAS, KTAS, GS or any other. the prop applies a
force to the surrounding air, the wheels spin freely underneath you, of
a take off occurs... ok, its so simple. if the conveyor matches the
wheel speed so what, youre off still. if it matches air speed, so what
youve got rollers to get you off that spinning track! cool, i get it
now... my bad ....

The Flying Scotsman

February 4th 06, 08:00 AM

Look..... for all you people that think that the plane will take off.
Whats the point in having CAT Launching systems on aircraft carriers
priced at billions of dollars a piece... they could just pop down to
wallmart and buy a treadmill and the aircraft will not need to use any
runway what so ever........

DONT BE STUPID....

IT CANNOT BE DONE !!! IF IT CAN BE THEN SOME CLEVER BUGGER 50 YEARS AGO
WOULD OF DONE IT BY NOW..

plus, has anyone thought what will happen to that aircaraft if i does
manage to generate enough lift..... ITS GOING TO HAVE NO AIRSPEED,
stall and fall out of the sky like a brick.

Simple physics lads...

jesse

February 4th 06, 08:17 AM

Wow, this is too hard to stay away from. New scenario. Same conveyor.
Instead of airplane, i hold in my hand a toy car with freespinning
wheels. If you can agree that thrust from the prop/turbine would be
akin to my hand pulling on the toy car then this will work. It is a
force acting outside of the conveyor. I start to pull the toy car, the
conveyor starts moving backwards at an equivilant speed. so what? my
hand is still pulling the car forward at say one MPH, the belt moves
back wards at one MPH... the belt is only putting a slight amount of
resistance on the car through the friction of the wheels, but nothing
that my hand(or prop etc) cant over come.... i keep accelerating the
car and the belt does too, the wheels see 2 X my forward speed, i can
increase this accelration until the wheel fall off, or untill the car
grows wings or whatever. if the car can accelrate with my hand, so can
the plane using thrust against the air. there it is. one of the amazing
things about this is that some very intelligent people have completely
different views of this. Have yall checked out the boards at straight
dope?

another example, say im on a skate board facing bakwards with a fan....
same thing, the fan pushes against the air and forth do go I.
weeeeeeeeee!

what force exactly does the conveyor hold you back with? the only force
i see is the friction in the wheels, and a negligible amount of power
from even a O-320 will overcome that. really... that and wind
resistance is the only force keeping you in one spot. If your thrust is
greater than that, newton prevails....

it just took me a while to sort it all out... have fun, stay up too
late!
Jester

pilot

February 4th 06, 08:47 AM

Michael Ware

February 4th 06, 09:36 AM

Yes.
The problem states '..moves in the opposite direction at exactly the speed
that the airplane is moving
forward..' So the plane is moving forward, thus it will fly. The wheels
are just spinning at 120mph instead of the usual 60mph.

"pilot" > wrote in message
oups.com...
>
> cjcampbell wrote:
> > Saw this question on "The Straight Dope" and I thought it was amusing.
> >
> > http://www.straightdope.com/columns/060203.html
> >
> > The question goes like this:
> >
> > "An airplane on a runway sits on a conveyer belt that moves in the
> > opposite direction at exactly the speed that the airplane is moving
> > forward. Does the airplane take off?" (Assuming the tires hold out, of
> > course.)
> >
> > Cecil Adams (world's smartest human being) says that it will take off
> > normally.
>

Peter Duniho

February 4th 06, 10:43 AM

"Damian" > wrote in message
...
> Paul...dont look now, but that airplane is NOT flying off the ground until
> the AIRSPEED is up...the treadmill is only moving the TIRES, that means
> diddly squat to an airplane.

Damian, don't look now but Paul is exactly right (except for his rude
nature, of course).

The treadmill is irrelevant to the airplane's motion. If the airplane is
stationary on the treadmill, it's because it has a headwind the same speed
as the treadmill and enough thrust to fly into the headwind at the same
speed as the treadmill. Of course, the wheels will be turning on the
treadmill, but only because the treadmill is rotating them against the
air-based stationary nature of the airplane.

Without a suitable headwind for the airplane to fly into, the treadmill
would just push the airplane backward. Airplanes don't use their wheels for
transmitting power to forward motion (most don't, anyway :) ).

Pete

Peter Duniho

February 4th 06, 10:47 AM

"The Flying Scotsman" > wrote in message
ups.com...
> Look..... for all you people that think that the plane will take off.
> Whats the point in having CAT Launching systems on aircraft carriers
> priced at billions of dollars a piece... they could just pop down to
> wallmart and buy a treadmill and the aircraft will not need to use any
> runway what so ever........

No, they couldn't. Or, put another way, a scenario in which an airplane
launching from a carrier could remain stationary on a treadmill would rely
not on the treadmill, but on the presence of a suitable headwind. Of
course, in the presence of a suitable headwind, the treadmill is not needed.
But that's the whole point to this trick question: the treadmill is a red
herring.

> DONT BE STUPID....

You should think a little harder before throwing the "stupid" word around.

> IT CANNOT BE DONE !!! IF IT CAN BE THEN SOME CLEVER BUGGER 50 YEARS AGO
> WOULD OF DONE IT BY NOW..
>
> plus, has anyone thought what will happen to that aircaraft if i does
> manage to generate enough lift..... ITS GOING TO HAVE NO AIRSPEED,
> stall and fall out of the sky like a brick.

The airplane can't generate lift without airspeed. It's absurd to claim
that it would have "no airspeed". If it has enough lift to fly, then by
definition it has airspeed.

> Simple physics lads...

Yes, it is. But the physics only give you the correct answer if you apply
them correctly.

Pete

Bob Martin

February 4th 06, 12:25 PM

Jim Macklin wrote:
> If the treadmill is stationary and the belt speed is equal
> to the required take-off speed, the airplane will have zero
> airspeed if it is "moving" in relation to the belt, the
> airplane is moving, the prop has thrust and is balancing the
> rearward movement of the belt. The tires are rolling, but
> the airplane is stationary and there is no airspeed or lift.

Let's take this to a logical extreme. The purpose of a wheel is to
reduce friction, right? (Well, excluding steering and braking, since we
aren't using the brakes here) Anyways, let's now assume that the
airplane is sitting on the conveyor belt, and there is no friction
between it and the belt. For all intents and purposes, you now have an
antigravity device as your landing gear. Now run the engine up. If
there is no friction between the airplane and the belt (and
consequently no way to transmit force), how is the belt going to keep it
stationary? Remember, sum of forces=mass*acceleration, and the sum of
the forces in the horizontal plane is now mass*acceleration=thrust-drag
(where drag is a function of airspeed squared). No force from the
conveyor belt.

Now let's put the wheels back on. Certainly, if a wheel's purpose is to
try and reduce friction as much as possible, you aren't going to
suddenly have some wheels that drag on you with as much thrust as your
prop exerts...

if it comes down to it, I'll write a Matlab simulation of this, and show
the results to everyone.

Tony

February 4th 06, 01:54 PM

Exactly right.

In the end we'd have to say it's a nicely phrased question. My first
instinct was to say the ariplane had zero speed relative to the ground
the moving belt is on, but that is NOT the condition the problem
stated.

So, under the usual circumstances (not having a significant tail wind,
for example) you'd lift off assuming the wheels are not going to self
distruct turning at twice their usual takeoff speed.

Gary Drescher

February 4th 06, 02:19 PM

"Tony" > wrote in message
oups.com...
> Exactly right.
>
> In the end we'd have to say it's a nicely phrased question. My first
> instinct was to say the ariplane had zero speed relative to the ground
> the moving belt is on, but that is NOT the condition the problem
> stated.
>
> So, under the usual circumstances (not having a significant tail wind,
> for example) you'd lift off assuming the wheels are not going to self
> distruct turning at twice their usual takeoff speed.

The plane would take off from the treadmill even if there were a tail wind
equal to Vr (though in that case, the wheels would be turning at *four*
times their usual speed).

--Gary

muff528

February 4th 06, 02:33 PM

"cjcampbell" > wrote in message
oups.com...
> Saw this question on "The Straight Dope" and I thought it was amusing.
>
> http://www.straightdope.com/columns/060203.html
>
> The question goes like this:
>
> "An airplane on a runway sits on a conveyer belt that moves in the
> opposite direction at exactly the speed that the airplane is moving
> forward. Does the airplane take off?" (Assuming the tires hold out, of
> course.)
>

AH! ...here's the problem! Are the airplane and the belt moving at equal
speeds in opposite directions
relative to the world? (-X mph for the belt & +X mph for the plane = eg.
airspeed of 100mph &
wheel speed of 200mph) If so the airplane could take off. The answer to this
question would be easy --
is the airspeed high enough or not?

......OR relative to each other? If so, there could be just enough thrust
applied to overcome frictional
forces and the airplane doesn't move relative to the world so airspeed is 0.

BUT WAIT!!! .... ANY two objects can be said to be moving (or not) at equal
speeds relative to each other. A point
on the conveyer belt moving east at 4mph and a jet moving west at 600mph
each have a relative velocity of 604
with respect to each other and there could be an observer who sees each
object moving in opposite directions
at 302mph. The only real question is how fast is the airplane moving with
respect to the air(world).

Thrust is an external force applied to the conveyer belt/airplane system.

> Cecil Adams (world's smartest human being) says that it will take off
> normally.
>

He likely had a little more information than is available in the OP.

Robert M. Gary

February 4th 06, 02:55 PM

> Only if there is an 80 mph tailwind.

If the plane is rolling 80mph against a conveyor going 80mph back the
difference would be zero.

-Robert

alexy

February 4th 06, 03:24 PM

"Robert M. Gary" > wrote:

>> Only if there is an 80 mph tailwind.
>
>If the plane is rolling 80mph against a conveyor going 80mph back the
>difference would be zero.

True. But I was referring to the problem stated, that the conveyor was
moving the same speed and opposite direction to the speed and
direction that the plane was MOVING, not this different scenario in
which the conveyor was moving the opposite direction and same speed to
that at which the plane's tires were turing.

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Michael Ware

February 4th 06, 03:31 PM

"muff528" > wrote in message
news:OW2Ff.179$DV2.5@trnddc07...
>
.....OR relative to each other? If so, there could be just enough thrust
> applied to overcome frictional
> forces and the airplane doesn't move relative to the world so airspeed is
0.

That would have to be either a very underpowered airplane, or wheels with a
lot of friction.
>
> BUT WAIT!!! .... ANY two objects can be said to be moving (or not) at
equal
> speeds relative to each other. A point
> on the conveyer belt moving east at 4mph and a jet moving west at 600mph
> each have a relative velocity of 604

But there's the trick. A treadmill belt isn't really moving at all, it's
turning.
Try this for a brain scrambler. Think about a tire on your car, driving down
the highway. At the point where the tire contacts the ground, it's speed is
zero. 180° away, at the top, it is moving forward at twice the speed of the
car.

Kpi$LyLcEhRo

February 4th 06, 03:38 PM

Gary Drescher wrote:
> The plane would take off from the treadmill even if there were a tail wind
> equal to Vr (though in that case, the wheels would be turning at *four*
> times their usual speed).

SMALL corrections:
*First of all, a plane doesn't take off at Vr but at Vlof (lift off
speed). Vr is the speed at which you lift the nosewheel from the ground
and this speed is smaller than Vlof which is the speed at which the
plane lifts off the ground. So: "The plane would take off from the
treadmill even if there were a tail wind equal to Vlof". But you
probably meant it right.
*Second, in the case of a tailwind equal to Vlof, when the plane leaves
the ground, the wheels would spin at a speed 3 times their usual speed
and not 4. Actually this entire question and solution is about adding
and substracting velocity vectors and a perfect example of Einstein's
relativity theory. It all depends on what you take as a reference (the
ground, the tredmill or the air). As some other folks said here, the
question was not clear enough and there was not enough info! So
obviously we were dealing with a communication problem here. Anyway,
since that is solved now, let me get into adding and substracting
velocity vectors to explain you the case of a tailwind.

<----------(4) <----------(2) <----------(1) vectors in
reference to the conveyor belt
---------->(1a) vector in ref
to the airplane
_____________________________conveyor belt

the plane moves from right to left in the above drawing and the
conveyor belt from left to right.
(1a) is the speed (let's call it "x MPH") at which the conveyor belt
moves

NO WIND CONDITION:
*Engines not running:
Assuming perfectly frictionless wheels, the plane's speed relative to
the surrounding ground (Ground Speed or GS) will be zero. Since there
is no wind, the speed relative to the air (True Air Speed or TAS) is
also 0. However, the conveyor belt moves at a speed x in reference to
the plane (vector 1a) and the wheels will spin at a speed x (vector 1)
and this is also the speed at which the plane moves forward in ref to
the belt.
Briefly:
GS=0 TAS=0
Tire speed=x >>not taking off!

*At takeoff thrust and the plane has reached Vlof=x MPH:
The engine thrust is pushing the aircraft away from the air behind it
to put it in simple words. In other words, we are now moving at an
airspeed (TAS) of x MPH=Vlof and since there is still no wind,
groundspeed is also x MPH BUT the plane is now moving at a speed equal
to 2x in ref to the conveyor belt. Twice the usual speed.
Briefly:
GS=x TAS=x
Tirespeed= 2x >>Plane lifts off!

I'll have to make an additional post since I reached max number of
characters . To be continued...

Kpi$LyLcEhRo

February 4th 06, 03:52 PM

....continue my previous post
TAILWIND equal to x MPH:
*Assume a tailwind has suddenly come up! Suddenly means that the plane
didn't have time to react to it and since the tailwind equals Vlof this
means that your entire true airspeed drops away! So airspeed now is 0!
But your groundspeed for the moment remains x MPH as in previous case
and so does the tirespeed/tredmill speed which is 2x.
Briefly:
GS=x TAS=0!
Tirespeed=2x >>plane would not anymore takeoff!! WINDSHEAR,
WINDSHEAR!! Dangerous condition which can happen in real life!

*Now assume the plane has overcome the tailwind and the airspeed has
recovered and is again equal to x MPH. Good! Now the groundspeed will
be 2x and the tirespeed 3x! Because vector 2 is counteracted by an
opposite and equal in magnitude wind vector, there is now a new vector
4 (see drawing previous post). Oh God, maybe I should have drawn that
sketch a little differently! I'm not going to go through all this
again. Anyway, would you now do me a favor and CLOSE THE DISCUSSION
PLEASE!!

In short, the article from the first post is correct! End discussion,
"point final", over and out!!

PS:If you would like to know, I'm an engineer and an airline pilot!
Jeeeeezus!

muff528

February 4th 06, 04:00 PM

"Michael Ware" > wrote in message
. ..
>
> "muff528" > wrote in message
> news:OW2Ff.179$DV2.5@trnddc07...
> >
> .....OR relative to each other? If so, there could be just enough thrust
> > applied to overcome frictional
> > forces and the airplane doesn't move relative to the world so airspeed
is
> 0.
>
> That would have to be either a very underpowered airplane, or wheels with
a
> lot of friction.

Yes!..that's why I said "COULD be just enough thrust..." More thrust than is
necessary
to overcome friction would result in the airplane moving forward relative to
the air. Then
it's only a question of how much thrust would be necessary to move the plane
forward fast
enough through the air to overcome gravity :-) A little less thrust would
result in the airplane
going backwards but not as fast as the conveyer. In any case the relative
velocities of the
plane to the conveyer would be equal to observers on either object but NOT
to an observer
standing on dirt.

> >
> > BUT WAIT!!! .... ANY two objects can be said to be moving (or not) at
> equal
> > speeds relative to each other. A point
> > on the conveyer belt moving east at 4mph and a jet moving west at 600mph
> > each have a relative velocity of 604
>
> But there's the trick. A treadmill belt isn't really moving at all, it's
> turning.

Again, Yes....but that's why I said "a POINT on the conveyer.." not the
conveyer
system itself.

The trick is that the original question as posted asks a question (will the
plane take off) and gives just enough info
to cause assumptions that aren't specified.

> Try this for a brain scrambler. Think about a tire on your car, driving
down
> the highway. At the point where the tire contacts the ground, it's speed
is
> zero. 180° away, at the top, it is moving forward at twice the speed of
the
> car.

Yes, but only for a very brief instant in time. And since velocity is
measured as a function of
time, is that point on the tire really moving at all at that one brief
instant when the measurement
is taken? :-)
>
>

Travis Marlatte

February 4th 06, 04:10 PM

As posed by the question, I agree that the belt is a distracter. However, it
is not irrelevant as the thrust applied to achieve flying speed must
overcome not only the normal tire rotation friction but twice that. That the
plane will fly presumes that there is enough excess thrust to do just that.

--
-------------------------------
Travis
"Morgans" > wrote in message
...
>
> "alexy" > wrote
>
>> Reread the stated problem:
>>
>> "a conveyer belt that moves in the
>> opposite direction at exactly the speed that the airplane is moving
>> forward."
>
> All it is, is a trick question, aimed at testing your reading and
> comprehension ablility. The plane moves off in exactly the same manner as
> on a regular runway. The moving belt is a distracter.
> --
> Jim in NC

Travis Marlatte

February 4th 06, 04:13 PM

The propulsion system is irrelevant as long as it is independant of the
treadmill.

--
-------------------------------
Travis
"alexy" > wrote in message
...
> "Doug" > wrote:
>
>>What is keeping the airplane's speed up with the conveyor belt? The
>>propeller. Said propeller moves air. Air causes lift. The problem is
>>more complicated than it seems to be at first read.
>
> Not at all complicated. The propulsion system is irrelevant. The given
> fact is that the airplane's speed (not it's speed relative to the
> conveyor) is equal to the conveyor's speed, but in the opposite
> direction. When that speed is sufficient for flight, it will fly.
> --
> Alex -- Replace "nospam" with "mail" to reply by email. Checked
> infrequently.

Gary Drescher

February 4th 06, 04:15 PM

"Kpi$LyLcEhRo" > wrote in message
oups.com...
>
> Gary Drescher wrote:
>> The plane would take off from the treadmill even if there were a tail
>> wind
>> equal to Vr (though in that case, the wheels would be turning at *four*
>> times their usual speed).
>
> in the case of a tailwind equal to Vlof, when the plane leaves
> the ground, the wheels would spin at a speed 3 times their usual speed
> and not 4.

Suppose the plane lifts of at an airspeed of 30 knots, and suppose a 30 knot
tailwind. At takeoff, the plane then has a 60 knot ground speed. By
stipulation, the treadmill moves backward as fast as the plane moves
forward, hence at 60 knots too. Thus, the wheels are turning at 120
knots--four times the usual speed.

> Actually this entire question and solution is about adding
> and substracting velocity vectors and a perfect example of Einstein's
> relativity theory.

No, this is strictly Galilean relativity (from four centuries ago);
Einstein's relativity has no bearing on this discussion.

--Gary

Travis Marlatte

February 4th 06, 04:16 PM

No. The plane is moving forward at 80mph. The wheels are the only thing
feeling the 160mph effect of the treadmill. This isn't a ground propelled
vehicle.

--
-------------------------------
Travis
"Robert M. Gary" > wrote in message
ups.com...
>> and a speedometer that
>> measures off of tire rotation would indicate the plane's speed (before
>> getting airborne) as 160mph, the speed relative to the conveyor.
>
> While an airspeed indicator would indicate zero.
>
> -Robert, CFI
>

Travis Marlatte

February 4th 06, 04:21 PM

Taken to the extreme, it might be considered ambiguous but that is only
nit-picking the puzzle. The general answer to the riddle is: if the plane
has enough excess thrust to overcome the additional drag of friction of the
wheels turning at twice the liftoff speed, the plane will fly. It will
accelerate slower and require a longer run due to the excess friction, but
it will fly.
--
-------------------------------
Travis
"Doug" > wrote in message
oups.com...
> Taxi is just nomenclature for the airplane moving along the ground.
> "Takeoff run" would be more correct I guess, but in this case things
> are so weird, as it is ambiguous whether the plane is going to takeoff
> or not.
>

Travis Marlatte

February 4th 06, 04:29 PM

Peter, I think you lost the relative perspective. Given the original riddle,
the treadmill only moves backward at the same rate the plane moves forward.
If the plane was developing exactly enough thrust to counteract the
headwind, it will not move and neither will the treadmill.

--
-------------------------------
Travis
"Peter Duniho" > wrote in message
...
> "Damian" > wrote in message
> ...
>> Paul...dont look now, but that airplane is NOT flying off the ground
>> until the AIRSPEED is up...the treadmill is only moving the TIRES, that
>> means diddly squat to an airplane.
>
> Damian, don't look now but Paul is exactly right (except for his rude
> nature, of course).
>
> The treadmill is irrelevant to the airplane's motion. If the airplane is
> stationary on the treadmill, it's because it has a headwind the same speed
> as the treadmill and enough thrust to fly into the headwind at the same
> speed as the treadmill. Of course, the wheels will be turning on the
> treadmill, but only because the treadmill is rotating them against the
> air-based stationary nature of the airplane.
>
> Without a suitable headwind for the airplane to fly into, the treadmill
> would just push the airplane backward. Airplanes don't use their wheels
> for transmitting power to forward motion (most don't, anyway :) ).
>
> Pete
>

Travis Marlatte

February 4th 06, 04:33 PM

How about this, you chain the plane to the ground with a 120kt headwind and
six 600HP engines mounted on a 172 all developing max thrust. Will it fly?

The answer, of course, is yes because no tiedown at any airport I've ever
seen would keep that on the ground. By the way the tires and wings are
irrelevant to the puzzle.
--
-------------------------------
Travis
> wrote in message
oups.com...
> If you restate the problem as follows the aircraft will obviously NOT
> fly.
>
> The aircraft is on a conveyor belt.
>
> The conveyor is programmed to move in such a way as to maintain the
> aircraft at an airspeed of zero as measured at the pitot.
>
> propwash?
>
> No - It's a Skymaster and the examiner cut the front engine.
>
> Oh-wait - It's a jet...
>
> a.
>
>
> cjcampbell wrote:
>> Saw this question on "The Straight Dope" and I thought it was amusing.
>>
>> http://www.straightdope.com/columns/060203.html
>>
>> The question goes like this:
>>
>> "An airplane on a runway sits on a conveyer belt that moves in the
>> opposite direction at exactly the speed that the airplane is moving
>> forward. Does the airplane take off?" (Assuming the tires hold out, of
>> course.)
>>
>> Cecil Adams (world's smartest human being) says that it will take off
>> normally.
>

Kpi$LyLcEhRo

February 4th 06, 04:34 PM

My dear Gary, how could I forget that in post number1 there is a line
saying "An airplane on a runway sits on a conveyer belt that moves in
the opposite direction at exactly the speed that the airplane is moving
forward..." so in other words, the belt adapts it's speed to the
forward motion of the plane?? Another communication problem I guess.
I'm not surprised though, after 55 freakin' posts this topic is
becoming off limits in my personal opinion! But I do hope that now
everyone agrees that the explanation on that website is correct. It's
just a matter of explaining the question properly with all details and
eliminating possible communication problems, right?

>No, this is strictly Galilean relativity (from four centuries ago);
>Einstein's relativity has no bearing on this discussion.

I don't agree completely. But your right that Galilean blabla has to do
with this but then saying that it's all about Newton's laws would also
be correct. So does Einstein! May I remind you of one of Einstein's
many mind experiments... The one about a train moving at a certain
speed, an observer inside the train walking to the front of the train
and an observer outside the train, standing still... As I said, it all
depends on what reference you take! To the observer outside the train,
the train may be traveling at 100km/h and the guy inside the train will
be walking at 105km/h! But to the guy inside, the train seems
stationary, while he himself is going at 5km/h and the guy outside to
him appears to be going backwards at 100km/h! It all sounds very
complicated and silly but relativity (and communication problems) is
all this topic is about! Now why don't y'all go and get a nice cup of
coffee and then start another topic.
No hard feelings I hope!

RST Engineering

February 4th 06, 04:37 PM

Actually, it is Newtonian relativity, but I'm not here to pick the flyspecks
out of the pepper.

Jim

>
> No, this is strictly Galilean relativity (from four centuries ago);
> Einstein's relativity has no bearing on this discussion.
>
> --Gary
>

Kpi$LyLcEhRo

February 4th 06, 04:41 PM

>But to the guy inside, the train seems
>stationary, while he himself is going at 5km/h and the guy outside to
>him appears to be going backwards at 100km/h!
105km/h instead of 100!
Sorry, my mistake

RST Engineering

February 4th 06, 04:44 PM

Cecil Adams (world's smartest human being) is correct to a first
approximation. The correct answer to a second approximation is that it will
take off normally less some small correction factor for the increased
friction of the tires, wheels, and wheel bearings.

Note the "trick" of the question. It does not say that the conveyor keeps
the AIRPLANE at zero speed relative to the real world, just that it rotates
at a speed equal to the airplane moving forward. The question itself
supposes forward velocity of the aircraft relative to the earth and the only
thing the conveyor belt does is spin the wheels twice as fast.

Jim

"cjcampbell" > wrote in message
oups.com...
> Saw this question on "The Straight Dope" and I thought it was amusing.
>
> http://www.straightdope.com/columns/060203.html
>
> The question goes like this:
>
> "An airplane on a runway sits on a conveyer belt that moves in the
> opposite direction at exactly the speed that the airplane is moving
> forward. Does the airplane take off?" (Assuming the tires hold out, of
> course.)
>
> Cecil Adams (world's smartest human being) says that it will take off
> normally.
>

Kpi$LyLcEhRo

February 4th 06, 04:51 PM

Sure, it's all connected to eachother. Einstein didn't invent
everything you know, he just used the tools and perfected them. This is
getting insane. Call it whatever you like. Happy now?
Byebye, I'm going flying now while you guys can continue the
discussion!
Have fun!

Gary Drescher

February 4th 06, 05:18 PM

"RST Engineering" > wrote in message
.. .
>> No, this is strictly Galilean relativity (from four centuries ago);
>> Einstein's relativity has no bearing on this discussion.
>>
> Actually, it is Newtonian relativity, but I'm not here to pick the
> flyspecks out of the pepper.

Newtonian mechanics incorporates Galilean relativity.

--Gary

Doug

February 4th 06, 05:30 PM

The whole problem is confusing because
"An airplane on a runway sits on a conveyer belt that moves in the
opposite direction at exactly the speed that the airplane is moving
forward."

Moving forward with respect to what? The conveyor belt? (you gt the
answer that it WONT take off), or the air? (you get the answer that it
WILL take off).

AMBIGUOUS!!!

(Cecil's answer assumes with respect to the air, and that is also how
he gets the tires going at twice the speed of the plane through the
air).

Peter Duniho

February 4th 06, 06:51 PM

"Travis Marlatte" > wrote in message
hlink.net...
> Peter, I think you lost the relative perspective.

No, I didn't.

> Given the original riddle, the treadmill only moves backward at the same
> rate the plane moves forward.

The rate at which the treadmill moves is entirely irrelevant. An airplane
does not transmit any force through it's wheels. They simply rotate
whatever speed is required to account for whatever speed the airplane has
relative to the surface the wheels are in contact with.

It doesn't matter one bit WHAT speed the treadmill moves, according to the
original riddle or otherwise.

> If the plane was developing exactly enough thrust to counteract the
> headwind, it will not move and neither will the treadmill.

The headwind is just an example. The actual wind could be anything. Yes,
if the headwind is exactly the same speed as the airspeed, the airplane
won't move. My only reason for setting the headwind equal to airspeed, as
an academic point of reference, is that if it's not, the airplane isn't
going to stay sitting on the treadmill for very long, making the "riddle"
even less interesting.

Pete

Gary Drescher

February 4th 06, 06:55 PM

"Kpi$LyLcEhRo" > wrote in message
oups.com...
>"Gary Drescher" > wrote in message
> . ..
>> "Kpi$LyLcEhRo" > wrote in message
>> oups.com...
>>> Actually this entire question and solution is about adding
>>> and substracting velocity vectors and a perfect example of Einstein's
>>> relativity theory.
>>
>>No, this is strictly Galilean relativity (from four centuries ago);
>>Einstein's relativity has no bearing on this discussion.
>
> I don't agree completely. But your right that Galilean blabla has to do
> with this but [...]
> So does Einstein! May I remind you of one of Einstein's
> many mind experiments... The one about a train moving at a certain
> speed, an observer inside the train walking to the front of the train
> and an observer outside the train, standing still...

That's a classic thought experiment in support of Galilean relativity. Of
course Einstein was familiar with it, but it's part of a theory much older
than Einstein's.

> Sure, it's all connected to eachother. Einstein didn't invent
> everything you know, he just used the tools and perfected them.

Einstein invented quite a bit, including special and general relativity. But
those theories of relativity are not involved in the simple vector-addition
problem under discussion.

--Gary

Peter Duniho

February 4th 06, 06:56 PM

"RST Engineering" > wrote in message
.. .
> Actually, it is Newtonian relativity,

Galileo: 1564-1642
Newton: 1643-1727

As Gary already noted, Newton's work built on Galileo's. The concepts here
were observed by Galileo.

> but I'm not here to pick the flyspecks out of the pepper.

Uh, yeah, right. Sure you aren't.

Tom Conner

February 4th 06, 06:58 PM

"Morgans" > wrote in message
...
>
> "jesse" > wrote in message
> oups.com...
> > My friend and i were discussing this. There is not enough information
> > in the orginal question to determine anything.
>
> I think jesse has earned his way into my "not worth the effort" file.
> Anyone else have him strike you that way?

Jesse needs to learn how to capitalize, punctuate, and separate his
sentences into paragraphs in order to make his posts readable.

Morgans

February 4th 06, 07:01 PM

>
> Jesse needs to learn how to capitalize, punctuate, and separate his
> sentences into paragraphs in order to make his posts readable.
\
Yep. That would be a very good start. There is more to it than that,
though.
--
Jim in NC

Darrell S

February 4th 06, 07:03 PM

Flyingmonk

February 4th 06, 07:11 PM

The answer is an obvious YES. I don't know how this thread got as big
as it did :^)

The Monk

Peter Duniho

February 4th 06, 07:13 PM

"Darrell S" > wrote in message
news:rT6Ff.24873$jR.14387@fed1read01...
> [...] For a car the situation would be completely different since it
> produces forward motion by the tires which contact the moving conveyer
> belt. The car wouldn't move at all.

It might. As "Doug" points out, the presentation is ambiguous as to the
reference point for the speed of the vehicle. If one uses the ground (and
stationary portions of the treadmill) as a reference, then the car would
move, just as the airplane does (it would have to in order to comply with
the description given in the problem), and the car's speedometer would
register a speed twice its actual speed relative to that reference.

Pete

Bob Martin

February 4th 06, 07:49 PM

Robert M. Gary wrote:
>>Only if there is an 80 mph tailwind.
>
>
> If the plane is rolling 80mph against a conveyor going 80mph back the
> difference would be zero.

BUT-what is the total friction force from the wheels? Certainly it's
less than the thrust from the engine--I mean, that's what wheels are
designed for, to have as little rolling friction as possible. So let's
add this up... forces acting on airplane are thrust, aerodynamic drag,
and an essentially negligible amount of drag from the wheels. Add it
up, and since the thrust is greater than the drag (as it would be on a
normal takeoff) the airplane accelerates. As I said in another post,
since wheels are designed for minimal friction, just pretend that they
are frictionless, and therefore not even there (anti-gravity airplane).
What is the conveyor belt going to push against now?

The Flying Scotsman

February 4th 06, 07:50 PM

Why dont we look at it from another direction !!!

If the treadmill is moving at 60 MPH in one direction and the trust is
set to pull 60 MPH in the oppisite direction, the plane would be
neither moving forward or back.

so the only thing that is moving is the wheels, the wings are not
generatring any lift becuase they are not moving in a positive
direction, the wings dont know that the wheels are going like a bat out
of hell !!! the wings still things its standing still. you WILL NEED TO
HAVE FORWARD MOMENTIUM to generate lift.....

the only lift the wings will get is downwash from the prop.

and i used the word STUPID not to offend anyone, but i am right in what
i said about the aircraft. but its really fun to talk about this after
over 75 messages posted... :)

Michael Ware

February 4th 06, 07:58 PM

Because it is interesting, and evokes thought.

"Flyingmonk" > wrote in message
oups.com...
> The answer is an obvious YES. I don't know how this thread got as big
> as it did :^)
>
> The Monk
>

Jim Logajan

February 4th 06, 08:01 PM

"cjcampbell" > wrote:
> "An airplane on a runway sits on a conveyer belt that moves in the
> opposite direction at exactly the speed that the airplane is moving
> forward. Does the airplane take off?"

One critical detail is missing that makes in impossible to say "yes" or
"no":

Is the forward speed of the plane above the stall speed?

The plane could, after all, being moving forward at 10 mph. Nothing in the
problem statement above precludes that speed, or any other. HOWEVER, the
question on the web site asks "_Can_ the airplane take off?" The answer to
that one is, using the most common meaning of the word "can," essentially
"yes". What a difference substitution of one word makes!

;-)

muff528

February 4th 06, 08:09 PM

"Flyingmonk" > wrote in message
oups.com...
> The answer is an obvious YES. I don't know how this thread got as big
> as it did :^)

Obviously, the answer is not so obvious! What surprises me is that there are
more than TWO opinions!!! :-)
You would think that the airplane would either take off or it wouldn't!?!
Anyway, reading/participating in this
thread is much more interesting than reading the usual flames in various
newsgroups. It's surprising and refreshing
that this thread, with so many posts, hasn't (yet) degraded into a
flame-fest. :o)
>
> The Monk
>

Morgans

February 4th 06, 08:11 PM

"The Flying Scotsman" > wrote
>
> so the only thing that is moving is the wheels, the wings are not
> generatring any lift becuase they are not moving in a positive
> direction, the wings dont know that the wheels are going like a bat out
> of hell !!! the wings still things its standing still. you WILL NEED TO
> HAVE FORWARD MOMENTIUM to generate lift.....

Man, you are about as dumb as a fence post, or bag of rocks, or.......PLONK
--
Jim in NC

Michael Ware

February 4th 06, 08:31 PM

"The Flying Scotsman" > wrote in message
ups.com...
> Why dont we look at it from another direction !!!
>
> If the treadmill is moving at 60 MPH in one direction and the trust is
> set to pull 60 MPH in the oppisite direction, the plane would be
> neither moving forward or back.

You are implying that because the treadmill is spinning the wheels at 60mph,
that the treadmill is therefore exerting a force equal and opposite the
thrust generated by the propellor neccesary to propel the plane forward at
60mph. That is incorrect.
The force that the treadmill is capable of exerting on the mass of the
aircraft through the wheels is negligible.

> you WILL NEED TO
> HAVE FORWARD MOMENTIUM to generate lift.....

WOW, I must have missed that in ground school.
You need airflow across the wings to generate lift. Which, because the plane
is moving forward as stated in the question, is present.

>
> the only lift the wings will get is downwash from the prop.
>
> and i used the word STUPID not to offend anyone, but i am right in what
> i said about the aircraft.

Apparently you are the only one that thinks so.

alexy

February 4th 06, 08:32 PM

"The Flying Scotsman" > wrote:

>Why dont we look at it from another direction !!!
>
>If the treadmill is moving at 60 MPH in one direction and the trust is
>set to pull 60 MPH in the oppisite direction, the plane would be
>neither moving forward or back.
Why. What's keeping it from moving forward if the thrust is set for a
thrust that would normally move it forward at 60mph. And besides, you
just said that the plane is moving neither forward nor backward. The
statement of the problem is that the conveyor moves at the same rate
and opposite direction as the plane. Since you say the plane is not
moving, I guess neither is the conveyor. Do you really think that is
what the poser of the question intended? <g>

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Ron Rosenfeld

February 4th 06, 08:34 PM

On Sat, 04 Feb 2006 16:10:16 GMT, "Travis Marlatte"
> wrote:

>As posed by the question, I agree that the belt is a distracter. However, it
>is not irrelevant as the thrust applied to achieve flying speed must
>overcome not only the normal tire rotation friction but twice that. That the
>plane will fly presumes that there is enough excess thrust to do just that.

So long as the bearings don't melt or seize, there's not much (if any)
extra "rotation friction" at double the normal takeoff speed.
Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Flyingmonk

February 4th 06, 08:36 PM

>It's surprising and refreshing
>that this thread, with so many posts, hasn't (yet) degraded into a
>flame-fest. :o)

Amen to that!

The Monk

alexy

February 4th 06, 08:43 PM

"Doug" > wrote:

>The whole problem is confusing because
>"An airplane on a runway sits on a conveyer belt that moves in the
>opposite direction at exactly the speed that the airplane is moving
>forward."
>
>Moving forward with respect to what? The conveyor belt? (you gt the
>answer that it WONT take off), or the air? (you get the answer that it
>WILL take off).
>
>AMBIGUOUS!!!

Yes, the problem could have been made uninteresting by removing any
ambiguity. But as stated, it is very common (almost universal) to
speak of movement of a terrestrial object with respect to the surface
of the earth. If another frame of reference is intended, it is almost
always specified. Two movements are mentioned in the problem. Is
there any reason to suspect that one is movement relative to surface
of the earth (the conveyor) and the other is movement relative to the
first object? Why not th other way around, in which case the conveyor
is just an ordinary runway?

If you are not willing to resolve that ambiguity by assuming
conventional frames of reference, you might as well assume that one is
speaking of velocities relative to a solar system frame, in which case
the plane may be going very very fast forward, backward, sideways, up,
or down, depending on time of day and orientation relative to the
earth. The problem makes a lot more sense assuming conventional use
of "moving".
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Michael Ware

February 4th 06, 08:44 PM

jesse

February 4th 06, 09:05 PM

All,
I read some of my posts in response to comments made about me. The
spelling, punctuation, and grammar mistakes are all because of my
blatant laziness, and excitement to get my post out. The comments I
made about the gun and the crowd seemed a bit disturbing to me when I
read through them. I should have picked a better example. Please do not
take those comments as some subconscious plea. I have been through
several hefty background checks in at least two states and the latest
for the Department of Defense that went back to when I was a teenager.
I admit that I was wrong initially about the answer to the question.
After working through it via the posts, discussions with my friend, and
my own reasonings, I changed my mind. I hope that in the future if you
all see my posts you will not regard me as some crazy loon. I have been
following r.a.s since late 2000 and think it is a priceless source of
information and support. Many people helped my as I was going through
my private pilot training, and I appreciate that. I hope that when I
begin my instrument training that people will be just as kind and
helpful. Thank-you.
Jesse

P.S. I could always chalk it up to the chemicals at work. Maybe my Mom
dropped me on my head when I was a baby, you never know!

muff528

February 4th 06, 09:13 PM

>
> Yes, the problem could have been made uninteresting by removing any
> ambiguity. But as stated, it is very common (almost universal) to
> speak of movement of a terrestrial object with respect to the surface
> of the earth. If another frame of reference is intended, it is almost
> always specified. Two movements are mentioned in the problem. Is
> there any reason to suspect that one is movement relative to surface
> of the earth (the conveyor) and the other is movement relative to the
> first object? Why not th other way around, in which case the conveyor
> is just an ordinary runway?
>
> If you are not willing to resolve that ambiguity by assuming
> conventional frames of reference, you might as well assume that one is
> speaking of velocities relative to a solar system frame, in which case
> the plane may be going very very fast forward, backward, sideways, up,
> or down, depending on time of day and orientation relative to the
> earth. The problem makes a lot more sense assuming conventional use
> of "moving".

Yes, the frame of reference has everything to do with the answer ...and the
riddle!
Since the original post refers to an airplane taking off you should conclude
that
"air" (the atmosphere) has to be included in the mix and that an airplane
does it's
flying relative to the world/atmosphere. Then it is not unreasonable to
assume that the riddle
implies that the most logical reference frame is the planet and that the
conveyor and the plane
are moving in opposite directions with respect to that stationary observer.
The only requirement
then is that the airplane move fast enough to take off and that the conveyor
move fast enough "backwards"
to match the airplanes speed (only to satisfy the specified initial
conditions even though the speed of
the conveyor is entirely irrelevant to whether or not the airplane takes
off.) It doesn't even matter if the wheels
need a bearing job or if the plane is on skids or if the brakes are set.
Either the engine generates enough thrust
to overcome resistance and accelerate the plane to take off or it doesn't.

Scott Skylane

February 4th 06, 09:21 PM

Kpi$LyLcEhRo wrote:
/snip/
>
> PS:If you would like to know, I'm an engineer and an airline pilot!
> Jeeeeezus!
>

Q: How do you know if there is an (airline pilot/engineer) at a party?

A: Oh, he'll tell you!

Happy Flying!
Scott Skylane

Dave Doe

February 4th 06, 09:42 PM

In article >,
says...
>
> "muff528" > wrote in message
> news:OW2Ff.179$DV2.5@trnddc07...
> >
> .....OR relative to each other? If so, there could be just enough thrust
> > applied to overcome frictional
> > forces and the airplane doesn't move relative to the world so airspeed is
> 0.
>
> That would have to be either a very underpowered airplane, or wheels with a
> lot of friction.
> >
> > BUT WAIT!!! .... ANY two objects can be said to be moving (or not) at
> equal
> > speeds relative to each other. A point
> > on the conveyer belt moving east at 4mph and a jet moving west at 600mph
> > each have a relative velocity of 604
>
> But there's the trick. A treadmill belt isn't really moving at all, it's
> turning.
> Try this for a brain scrambler. Think about a tire on your car, driving down
> the highway. At the point where the tire contacts the ground, it's speed is
> zero. 180° away, at the top, it is moving forward at twice the speed of the
> car.

Negative - yer forgetting centripetal force.

http://www.wordiq.com/definition/Centripetal

--
Duncan

Tony

February 4th 06, 10:31 PM

Let' say it this way. The airplane is moving forward at 60 kts. Does
that make it more clear?

The airplane is moving forward at 60, the belt, using the model in the
OP, is moving backwards at 60. The wheels are turning at 120 kts. If
it's a 172 it'll lift off into, on a calm day, 60 kts of airspeed over
the wings.

It's a nicely phrased question that caught me at first as well.
Substitute real speeds into what had been posted and the answer becomes
clear to me, although a lawyer in the group might find a (ground) loop
hole.

Michael Ware

February 4th 06, 10:49 PM

"Dave Doe" > wrote in message
. nz...
> In article >,
> says...
At the point where the tire contacts the ground, it's speed is
> > zero. 180° away, at the top, it is moving forward at twice the speed of
the
> > car.
>
> Negative - yer forgetting centripetal force.

? Negative what? Talking about a point on the surface of the tire, not the
wheel as a whole. Centripital force has nothing to do with the forward
velocity of that point (how it travels in one axis).
>
> http://www.wordiq.com/definition/Centripetal
>
> --
> Duncan

Robert M. Gary

February 4th 06, 11:28 PM

> What is the conveyor belt going to push against now?

The conveyor belt is pushing against the force of the prop through the
air but we don't care. The problem stated that they are doing 80mph, we
shouldn't worry about how the plane is able to do 80mph on the belt.

-Robert

Peter Duniho

February 5th 06, 12:41 AM

"alexy" > wrote in message
...
> Yes, the problem could have been made uninteresting by removing any
> ambiguity. But as stated, it is very common (almost universal) to
> speak of movement of a terrestrial object with respect to the surface
> of the earth. If another frame of reference is intended, it is almost
> always specified.

Very amusing.

According to you:

On the one hand, the problem is uninteresting if one removes the ambiguity
in the phrasing.

On the other hand, there is no ambiguity, because if a different frame of
reference were intended, "it is almost always specified".

So, the logical conclusion you arrive it in your post is that the problem is
uninteresting.

For an uninteresting problem, it sure generated a lot of traffic.

Pete

AES

February 5th 06, 12:58 AM

If you tie a 100 foot rope to the tail of an airplane (or some other
part of the airframe), attach it to a good strong post, and run the
propellor up to whatever rpm is available, is anyone claiming the
airplane can then lift up say a feet off the ground?

(Assuming the tail doesn't tear off)

(and, a conveyor belt under the airplane is optional)

Michael Ware

February 5th 06, 01:12 AM

Are you saying 1) the rope is tight, or are you saying 2) you are giving the
plane a 100' running start?

"AES" > wrote in message
...
> If you tie a 100 foot rope to the tail of an airplane (or some other
> part of the airframe), attach it to a good strong post, and run the
> propellor up to whatever rpm is available, is anyone claiming the
> airplane can then lift up say a feet off the ground?
>
> (Assuming the tail doesn't tear off)
>
> (and, a conveyor belt under the airplane is optional)

Flyingmonk

February 5th 06, 01:22 AM

>If you tie a 100 foot rope to the tail of an airplane (or some other
>part of the airframe), attach it to a good strong post, and run the
>propellor up to whatever rpm is available, is anyone claiming the
>airplane can then lift up say a feet off the ground?
>
>(Assuming the tail doesn't tear off)
>
>(and, a conveyor belt under the airplane is optional)

Depends on the airplane, certain lpanes are built in such a way that
they can actually attain enough lift just from the prop wash alone.

The Monk

Flyingmonk

February 5th 06, 01:25 AM

>If you tie a 100 foot rope to the tail of an airplane (or some other
>part of the airframe), attach it to a good strong post, and run the
>propellor up to whatever rpm is available, is anyone claiming the
>airplane can then lift up say a feet off the ground?

>(Assuming the tail doesn't tear off)

>(and, a conveyor belt under the airplane is optional)

Depends on the airplane, if a plane is built in such a way that it can
actually attain enough lift just from the prop wash alone than yes.

The Monk

BillJ

February 5th 06, 01:53 AM

Jim Logajan wrote:
> "cjcampbell" > wrote:
>
>>Saw this question on "The Straight Dope" and I thought it was amusing.
>>
>>http://www.straightdope.com/columns/060203.html
>
>
> Seems Cecil Adams is compounding the confusion by having the page's title
> begin:
>
> "An airplane taxies in one direction...."
>
> So is the plane attempting to taxi or take off? The page's title says one
> thing, the person posing the question is stating another. The hypothetical
> pilot of the taxing plane would presumably not let the the airspeed go to
> takeoff speed, while the pilot of the plane taking off would want to
> accelerate to rotation speed. So on that basis alone, we can say a taxing
> plane isn't going to take off!
>
> ;-)
The earth is a treadmill. Goes about about 900 knots (at equator). Does
that bother your takeoff? Suppore treadmill stopped (rotation stopped).
Takeoffs any different, assuming you aren't launching into orbit?

Bob Moore

February 5th 06, 02:04 AM

BillJ > wrote
> The earth is a treadmill. Goes about about 900 knots (at equator).
> Does that bother your takeoff? Suppore treadmill stopped (rotation
> stopped). Takeoffs any different?

You forgot one major difference....in the case of the earth, the
airmass is travelling at the same 900kts, ignoring any localized
wind effect....not so in the treadmill case.

Bob Moore

Dave Doe

February 5th 06, 02:12 AM

In article >,
says...
>
> "Dave Doe" > wrote in message
> . nz...
> > In article >,
> > says...
> At the point where the tire contacts the ground, it's speed is
> > > zero. 180° away, at the top, it is moving forward at twice the speed of
> the
> > > car.
> >
> > Negative - yer forgetting centripetal force.
>
> ? Negative what? Talking about a point on the surface of the tire, not the
> wheel as a whole. Centripital force has nothing to do with the forward
> velocity of that point (how it travels in one axis).

Are you talking about a round tire or not - are you then talking about a
big long flat tire of say infinite length. Sorry bud, can't make the
initial assumption that's been made - as it's on a tire, and yep, even
that point, at that time - has the centripetal force.

--
Duncan

Private

February 5th 06, 02:34 AM

"cjcampbell" > wrote in message
oups.com...
> Saw this question on "The Straight Dope" and I thought it was amusing.
>
> http://www.straightdope.com/columns/060203.html
>
> The question goes like this:
>
> "An airplane on a runway sits on a conveyer belt that moves in the
> opposite direction at exactly the speed that the airplane is moving
> forward. Does the airplane take off?" (Assuming the tires hold out, of
> course.)
>
> Cecil Adams (world's smartest human being) says that it will take off
> normally.
>

When this question was raised on Sci.aeronautics it lasted 14 replies, (as
archived by Google groups, but I think that some other posts were dropped by
the news servers.)

http://groups.google.ca/group/sci.aeronautics/browse_thread/thread/e344b133e57880a0/57a2a6789dd92bf6?lnk=st&q=(treadmill)+group%3Asci.aeronautics&rnum=1&hl=en#57a2a6789dd92bf6

One of the posters raised the issue of what would happen when the aircraft
returned for landing.

we are up to about 110 replies here on r.a.s, r.a.p.

A similar question was posed in the Airliners.net forums, what a great
discussion it was! See here:
http://www.airliners.net/discussions/tech_ops/read.main/136068/ over
400 replies!

I am quite surprised that this question has received the amount of
consideration that it has. Must be a slow news month or maybe is an
indication that there are more people thinking about flying than there are
actually doing it.

Dave Doe

February 5th 06, 02:56 AM

In article >, rmoore16
@tampabay.rr.com says...
> BillJ > wrote
> > The earth is a treadmill. Goes about about 900 knots (at equator).
> > Does that bother your takeoff? Suppore treadmill stopped (rotation
> > stopped). Takeoffs any different?
>
> You forgot one major difference....in the case of the earth, the
> airmass is travelling at the same 900kts, ignoring any localized
> wind effect....not so in the treadmill case.

So when a treadmill runs the wind starts blowing ? OK... wot are yer
saying then?

--
Duncan

Michael Ware

February 5th 06, 03:34 AM

"Dave Doe" > wrote in message
. nz...
> In article >,
> says...
> >
> > "Dave Doe" > wrote in message
> > . nz...
> > > In article >,
> > > says...
> > At the point where the tire contacts the ground, it's speed is
> > > > zero. 180° away, at the top, it is moving forward at twice the speed
of
> > the
> > > > car.
> > >
> > > Negative - yer forgetting centripetal force.
> >
> > ? Negative what? Talking about a point on the surface of the tire, not
the
> > wheel as a whole. Centripital force has nothing to do with the forward
> > velocity of that point (how it travels in one axis).
>
> Are you talking about a round tire or not
What other kind of tire is there?
.. Sorry bud, can't make the
> initial assumption that's been made -
I'm not your bud,. And what assumption are you talking about?
as it's on a tire, and yep, even
> that point, at that time - has the centripetal force.

We aren't talking about the forces at work on the wheel or tire, we are
talking about the forward velocity. I can see this concept is lost on you.
>
> --
> Duncan

BDS

February 5th 06, 03:49 AM

"cjcampbell" > wrote

> The question goes like this:
>
> "An airplane on a runway sits on a conveyer belt that moves in the
> opposite direction at exactly the speed that the airplane is moving
> forward. Does the airplane take off?" (Assuming the tires hold out, of
> course.)
>
> Cecil Adams (world's smartest human being) says that it will take off
> normally.

Maybe he's not so smart after all :>)

On a calm day you can run and feel a wind on your face because you are
moving across the ground as well as through the air. But, if you run on a
treadmill there will be no wind because you are not moving through the air -
the air is calm so it has no relative motion with respect to the ground.
Neither do you when you run on a treadmill.

Assume the airplane is on the conveyor and there is a 10 kt headwind, and
assume we need 60 kts for takeoff. The only way to generate the additional
50 kts of airspeed is by moving across the ground at 50 kts. If the
airplane is standing still because the conveyor is moving backwards at the
same speed that the airplane is moving across the ground at, then the
airspeed will still be 10 kts.

If the conveyor keeps the airplane standing still relative to the ground,
then it cannot take off. If it could, then we'd all have problems during
run up because the brakes do the same thing that the theoretical conveyor
does - prevent motion across the ground.

BDS

Michael Ware

February 5th 06, 03:56 AM

"BDS" > wrote in message
t...
>
> Maybe he's not so smart after all :>)
>
> On a calm day you can run and feel a wind on your face because you are
> moving across the ground as well as through the air. But, if you run on a
> treadmill there will be no wind because you are not moving through the
air -
> the air is calm so it has no relative motion with respect to the ground.
> Neither do you when you run on a treadmill.
>
Yes, but an airplane isn't propelled by its feet.

Jeff Shirton

February 5th 06, 04:04 AM

"BDS" > wrote in message
t...

> 50 kts of airspeed is by moving across the ground at 50 kts. If the
> airplane is standing still because the conveyor is moving backwards at the
> same speed that the airplane is moving across the ground at, then the
> airspeed will still be 10 kts.

But the airplane *isn't* standing still (as others have pointed out).

Since the wheels are able to spin freely, the reverse thrust by the
conveyor belt is *not* transferred past the wheels to the plane's
fuselage, and so the only remaining applied force is the unbalanced
forward force of the thrust of the engine.

The conveyor *doesn't* "drag" the plane backwards to compensate
for the engine's thrust. All it does (as others have pointed out) is
spin the wheels faster.

> If the conveyor keeps the airplane standing still relative to the ground,

It doesn't.

(Don't worry... I didn't understand it at first either.)

> BDS

Jeff Shirton (PP-ASEL)

jesse

February 5th 06, 04:18 AM

"One of the posters raised the issue of what would happen when the
aircraft
returned for landing."

If the belt were moving backwards at the speed of the aircraft when it
touched down, it would be similar to landing with that much tailwind,
basically, your ground speed would double you airspeed at touch down.
Jester

alexy

February 5th 06, 04:27 AM

Dave Doe > wrote:

>> Try this for a brain scrambler. Think about a tire on your car, driving down
>> the highway. At the point where the tire contacts the ground, it's speed is
>> zero. 180° away, at the top, it is moving forward at twice the speed of the
>> car.
>
>Negative - yer forgetting centripetal force.
>
>http://www.wordiq.com/definition/Centripetal

Well, I'm impressed that you know of the existence of centripetal
force. But in what possible way do you think it negates the comment
about the speeds (relative to the ground) of points at the top and
bottom of the tire on a moving car?
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

alexy

February 5th 06, 04:33 AM

"Peter Duniho" > wrote:

>"alexy" > wrote in message
...
>> Yes, the problem could have been made uninteresting by removing any
>> ambiguity. But as stated, it is very common (almost universal) to
>> speak of movement of a terrestrial object with respect to the surface
>> of the earth. If another frame of reference is intended, it is almost
>> always specified.
>
>Very amusing.
>
>According to you:
>
>On the one hand, the problem is uninteresting if one removes the ambiguity
>in the phrasing.
>
>On the other hand, there is no ambiguity, because if a different frame of
>reference were intended, "it is almost always specified".
>
>So, the logical conclusion you arrive it in your post is that the problem is
>uninteresting.
>
>For an uninteresting problem, it sure generated a lot of traffic.

True. Which really surprised me. When I first saw CJ's post, I thought
it was too obvious to draw in this kind of activity.

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

alexy

February 5th 06, 04:39 AM

"BDS" > wrote:

>Maybe he's not so smart after all :>)
Maybe not, but smart enough to see this one.
>
>On a calm day you can run and feel a wind on your face because you are
>moving across the ground as well as through the air. But, if you run on a
>treadmill there will be no wind because you are not moving through the air -
>the air is calm so it has no relative motion with respect to the ground.
>Neither do you when you run on a treadmill.
True. Irrelevant, but true.
>
>Assume the airplane is on the conveyor and there is a 10 kt headwind, and
>assume we need 60 kts for takeoff. The only way to generate the additional
>50 kts of airspeed is by moving across the ground at 50 kts.
Right so far.

> If the
>airplane is standing still
Hold that thought...
> because the conveyor is moving backwards at the
>same speed that the airplane is moving across the ground at
Skip back up to see what speed you say the airplane is moving across
the ground. Then go back to the original question and figure out what
speed the conveyor must be moving when the airplane is not moving.

>
>If the conveyor keeps the airplane standing still relative to the ground,
>then it cannot take off.
Yeah, but the original statement of the problem made no such claim.

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Flyingmonk

February 5th 06, 04:45 AM

>Maybe he's not so smart after all :>)
>
>On a calm day you can run and feel a wind on your face because you are
>moving across the ground as well as through the air. But, if you run on a
>treadmill there will be no wind because you are not moving through the air -
>the air is calm so it has no relative motion with respect to the ground.
>Neither do you when you run on a treadmill.

D*mn you're dumb. Oh sorry, was I thinking out loud? A thousand
pardons. :^)

The plane is NOT powered at the wheels! In this case the plane will be
going 60kts forward relative to the surrounding air and 120kts forward
relative to the treadmill. Think about it.

The Monk

Dave Doe

February 5th 06, 04:50 AM

In article >,
says...
>
> "Dave Doe" > wrote in message
> . nz...
> > In article >,
> > says...
> > >
> > > "Dave Doe" > wrote in message
> > > . nz...
> > > > In article >,
> > > > says...
> > > At the point where the tire contacts the ground, it's speed is
> > > > > zero. 180° away, at the top, it is moving forward at twice the speed
> of
> > > the
> > > > > car.
> > > >
> > > > Negative - yer forgetting centripetal force.
> > >
> > > ? Negative what? Talking about a point on the surface of the tire, not
> the
> > > wheel as a whole. Centripital force has nothing to do with the forward
> > > velocity of that point (how it travels in one axis).
> >
> > Are you talking about a round tire or not
> What other kind of tire is there?
> . Sorry bud, can't make the
> > initial assumption that's been made -
> I'm not your bud,. And what assumption are you talking about?
> as it's on a tire, and yep, even
> > that point, at that time - has the centripetal force.
>
> We aren't talking about the forces at work on the wheel or tire, we are
> talking about the forward velocity. I can see this concept is lost on you.

There is no forward velocity - there *is* a change in angular momentum
though. Do you not understand that concept?

--
Duncan

alexy

February 5th 06, 04:59 AM

Dave Doe > wrote:

>> We aren't talking about the forces at work on the wheel or tire, we are
>> talking about the forward velocity. I can see this concept is lost on you.
>
>There is no forward velocity - there *is* a change in angular momentum
>though. Do you not understand that concept?

I proudly profess to not understand that a point on the top of a tire
does not move at twice the velocity of the axis of the wheel on which
that tire is mounted.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Don Tuite

February 5th 06, 05:21 AM

On 4 Feb 2006 20:45:34 -0800, "Flyingmonk" > wrote:

>The plane is NOT powered at the wheels! In this case the plane will be
>going 60kts forward relative to the surrounding air and 120kts forward
>relative to the treadmill. Think about it.

I reckon that's true, given the question posed in "The Straight Dope,"
(I've been too lazy to read it myself, but I gather from the other
responses that what you say above is what Adams had in mind.) but what
is the point of the original question in that case? Is it just to
trap a sloppy reader into thinking it's all about a crackpot VTOL
methodology?

The more interesting question is whether you could land real short by
using the treadmill.

Don

Michael Ware

February 5th 06, 05:24 AM

I undertand that, for any one given point on a wheel, mounted on a vehicle,
traveling horizontally, more or less, there is a forward velocity (not
constant) for exactly one half the time, and a rearward velocity (not
constant) for exactly half the time, in relation the wheels' point of
rotation. The average of this constantly changing velocity just happens to
be the same as the forward speed of the vehicle.

> There is no forward velocity - there *is* a change in angular momentum
> though. Do you not understand that concept?
>
> --
> Duncan

Flyingmonk

February 5th 06, 05:43 AM

>The more interesting question is whether you could land real short by
>using the treadmill.

The treadmill is irrelevant; it is the relative wind that matters.
Whether you are standing on solid ground or on a treadmill, if you have
a head wind of 60kts, you will be airborne period.

The Monk

Morgans

February 5th 06, 07:45 AM

"jesse" > wrote

> I read some of my posts in response to comments made about me. The
> spelling, punctuation, and grammar mistakes are all because of my
> blatant laziness, and excitement to get my post out. \\

Jesse, is that you? I didn't recognize you!

You will find that you will be taken more seriously around here, if you
continue you attempts at correctly (minus a few typo's) written posts. The
small mistakes will always creep in, it seems, no matter how hard we all
try. In this case, a small one was there,

>Many people helped my as I was .....

but I'm almost sure there is a mistake in me post. It is a rule, I was
told. <g>
--
Jim in NC

Morgans

February 5th 06, 08:03 AM

>>For an uninteresting problem, it sure generated a lot of traffic.
>
> True. Which really surprised me. When I first saw CJ's post, I thought
> it was too obvious to draw in this kind of activity.

Indeed. If it was not a well recognized name posting, it would be a post
more worthy of a troll.

Dang you, CJ! Please refrain, next time!

Or if your post was moving backwards at twice the speed of light, did it
ever appear at all, and did it erase all of the activity before it? <g>
--
Jim in NC

Morgans

February 5th 06, 08:06 AM

"Flyingmonk" > wrote

> Depends on the airplane, certain lpanes are built in such a way that
> they can actually attain enough lift just from the prop wash alone.

How many buckets of prop wash would it take?

Peter Duniho

February 5th 06, 08:39 AM

"Flyingmonk" > wrote in message
oups.com...
> Depends on the airplane, certain lpanes are built in such a way that
> they can actually attain enough lift just from the prop wash alone.

Other than the ones we call helicopters, I've never heard of such a thing.

Care to elaborate?

Peter Duniho

February 5th 06, 08:41 AM

"jesse" > wrote in message
ups.com...
> "One of the posters raised the issue of what would happen when the
> aircraft
> returned for landing."
>
> If the belt were moving backwards at the speed of the aircraft when it
> touched down, it would be similar to landing with that much tailwind,
> basically, your ground speed would double you airspeed at touch down.

All that would happen is that the wheels would have to turn faster to
accomdate the treadmill. Just as they do at takeoff. There's not really
any difference between the two scenarios.

Flyingmonk

February 5th 06, 01:35 PM

>Other than the ones we call helicopters, I've never heard of such a thing.
>
>Care to elaborate?

Already rephrased my statement.

The Monk

Gary Drescher

February 5th 06, 02:01 PM

"Don Tuite" > wrote in message
...
> but what
> is the point of the original question in that case? Is it just to
> trap a sloppy reader into thinking it's all about a crackpot VTOL
> methodology?

I think the more interesting point is to notice the implications of not
transmitting force through the wheels. Even people who know that planes and
cars differ in that way may fail (at least at first) to draw the appropriate
conclusion about what happens to the treadmill plane when it applies takeoff
power.

--Gary

John T

February 5th 06, 02:14 PM

"cjcampbell" > wrote in message
oups.com
>
> "An airplane on a runway sits on a conveyer belt that moves in the
> opposite direction at exactly the speed that the airplane is moving
> forward. Does the airplane take off?" (Assuming the tires hold out, of
> course.)

The conveyor belt is simulating groundspeed. How many of you fly airplanes
by reference to groundspeed?

--
John T
http://sage1solutions.com/TknoFlyer
Reduce spam. Use Sender Policy Framework: http://spf.pobox.com
____________________

Gary Drescher

February 5th 06, 02:23 PM

"Morgans" > wrote in message
...
>
> You will find that you will be taken more seriously around here, if you
> continue you attempts at correctly (minus a few typo's) written posts.
> The small mistakes will always creep in, it seems, no matter how hard we
> all try. In this case, a small one was there,
>
>>Many people helped my as I was .....
>
> but I'm almost sure there is a mistake in me post. It is a rule, I was
> told. <g>

Yup. :) In addition to writing "you attempts" and "me post", you misspelled
"typos" (apostrophes are not used to form nonpossessive plurals). Also, the
comma in the first sentence is incorrect. It indicates that the dependent
clause is parenthetical, but in fact that clause is integral to the sentence
(the sentence means something substantially different if the clause is
removed). The Chicago Manual of Style gives these examples to illustrate the
distinction:
She ought to be promoted, if you want my opinion.
We will agree to the proposal if you accept our conditions.

--Gary

BDS

February 5th 06, 02:57 PM

"Michael Ware" > wrote
> >
> Yes, but an airplane isn't propelled by its feet.

This is where everyone who seems to think that the airplane will fly is
getting confused.

The method of propulsion doesn't matter. You can drive an airplane down the
runway by driving its wheels just like a car and it will still reach takeoff
airspeed and fly briefly. The propeller is only important once you are
airborne, because you need something to pull you through the air.

The bottom line is this - you cannot take off without first moving across
the ground unless the wind (airmass movement relative to the ground) is
blowing hard enough to give you sufficient airspeed to fly without moving.
In this case, once you take off your airspeed will immediately begin to
decrease unless you are using a prop to pull you through the air, or a
tether to hold you there (relative to the ground).

Example - a floatplane is sitting in a river that is moving at 30 mph (hey,
it's a fast river!). There is also a wind blowing down the river at 20 mph.

If the floatplane is anchored and facing into the wind, it has an airspeed
of 20 mph. If you release the anchor and use enough engine power to get the
plane going through the water upstream at 30 mph you will be standing still
with reference to the shore, and your airspeed will be 20 mph. If the river
was flowing at a rate in excess of the maximum speed of your airplane, then
you could never move forward going upstream with reference to the shore, and
your airspeed would never exceed 20 mph, even at full throttle. If you
fully understand this then you would know that you could shut your engine
down, face downstream, and take off and fly briefly.

BDS

BDS

February 5th 06, 02:59 PM

"alexy" > wrote

> >If the conveyor keeps the airplane standing still relative to the ground,
> >then it cannot take off.
> Yeah, but the original statement of the problem made no such claim.

Alex - here is what the statement said:

> "An airplane on a runway sits on a conveyer belt that moves in the
> opposite direction at exactly the speed that the airplane is moving
> forward. Does the airplane take off?" (Assuming the tires hold out, of
> course.)

The plane cannot move forward - that means that it is standing still to me.

BDS

Michael Ware

February 5th 06, 03:16 PM

"BDS" > wrote in message
m...
>
>
> > "An airplane on a runway sits on a conveyer belt that moves in the
> > opposite direction at exactly the speed that the airplane is moving
> > forward. Does the airplane take off?" (Assuming the tires hold out, of
> > course.)
>
> The plane cannot move forward - that means that it is standing still to
me.
>
> BDS
>
>
You are taking the statement 'a conveyer belt that moves in the opposite
direction at exactly the speed that the airplane is moving
forward' to mean that somehow there is a force being applied to the mass of
the aircraft, equal and opposite the thrust generated by the propellor. The
only place the treadmill can exert any force an the airplane is the only
place the treadmill is touching the airplane: the wheels. Any motion of the
treadmill belt will be translated into rotation of the wheels. This will not
prevent the aircraft from moving forward, through the air and taking off.

BDS

February 5th 06, 03:17 PM

"BDS" > wrote

> This is where everyone who seems to think that the airplane will fly is
> getting confused.

Nevermind - I finally get it.

DUH!!

BDS

Michael Ware

February 5th 06, 03:23 PM

"BDS" > wrote in message
m...
>
> "Michael Ware" > wrote
> > >
> > Yes, but an airplane isn't propelled by its feet.
>
> This is where everyone who seems to think that the airplane will fly is
> getting confused.
>
> The method of propulsion doesn't matter. You can drive an airplane down
the
> runway by driving its wheels just like a car and it will still reach
takeoff
> airspeed and fly briefly. The propeller is only important once you are
> airborne, because you need something to pull you through the air.

And all this time, I thought it was the propellor that made the airplane
move across the ground. I stand corrected.
>
> The bottom line is this - you cannot take off without first moving across
> the ground unless the wind (airmass movement relative to the ground) is
> blowing hard enough to give you sufficient airspeed to fly without moving.
> In this case, once you take off your airspeed will immediately begin to
> decrease unless you are using a prop to pull you through the air, or a
> tether to hold you there (relative to the ground).

What do you mean, 'unless you are using a prop to pull you through the air'?
How does your airplane work?
>
> Example - a floatplane is sitting in a river that is moving at 30 mph
(hey,
> it's a fast river!). There is also a wind blowing down the river at 20
mph.
>
> If the floatplane is anchored and facing into the wind, it has an airspeed
> of 20 mph. If you release the anchor and use enough engine power to get
the
> plane going through the water upstream at 30 mph you will be standing
still
> with reference to the shore, and your airspeed will be 20 mph. If the
river
> was flowing at a rate in excess of the maximum speed of your airplane,
then
> you could never move forward going upstream with reference to the shore,
and
> your airspeed would never exceed 20 mph, even at full throttle. If you
> fully understand this then you would know that you could shut your engine
> down, face downstream, and take off and fly briefly.

This is not an anology. With the wheels turning on the treadmill, friction
(and thus the force exerted) are negligible. The force exerted by the
running water on the floats is much greater.
>
> BDS
>
>
>
>

muff528

February 5th 06, 03:39 PM

"BDS" > wrote in message
m...
>
> "Michael Ware" > wrote
> > >
> > Yes, but an airplane isn't propelled by its feet.
>
> This is where everyone who seems to think that the airplane will fly is
> getting confused.
>
> The method of propulsion doesn't matter. You can drive an airplane down
the
> runway by driving its wheels just like a car and it will still reach
takeoff
> airspeed and fly briefly. The propeller is only important once you are
> airborne, because you need something to pull you through the air.
>
> The bottom line is this - you cannot take off without first moving across
> the ground unless the wind (airmass movement relative to the ground) is
> blowing hard enough to give you sufficient airspeed to fly without moving.
> In this case, once you take off your airspeed will immediately begin to
> decrease unless you are using a prop to pull you through the air, or a
> tether to hold you there (relative to the ground).
>
> Example - a floatplane is sitting in a river that is moving at 30 mph
(hey,
> it's a fast river!). There is also a wind blowing down the river at 20
mph.
>
> If the floatplane is anchored and facing into the wind, it has an airspeed
> of 20 mph. If you release the anchor and use enough engine power to get
the
> plane going through the water upstream at 30 mph you will be standing
still
> with reference to the shore, and your airspeed will be 20 mph. If the
river
> was flowing at a rate in excess of the maximum speed of your airplane,
then
> you could never move forward going upstream with reference to the shore,
and
> your airspeed would never exceed 20 mph, even at full throttle. If you
> fully understand this then you would know that you could shut your engine
> down, face downstream, and take off and fly briefly.
>
> BDS

BUT... the initial condition, as stated in the OP, is that the
river(conveyor) is moving at the same
speed as the airplane but in opposite directions. So, with a 30 mph
river(conveyor) and a
20 mph headwind the airspeed would be 50 mph. The plane is moving at 30 mph
in the opposite
direction with respect to the shore(runway). The airplane would then be
travelling upstream at 60 mph
relative to the rivers surface. The only difference between the river
example and the conveyor example is how firmly the airplane is
coupled to the conveyance. The floats/river scenario would require more
thrust to overcome the resistance
than the wheels/conveyor example. Same mathmatics, different numbers. The
floatplane just needs a bigger motor.

Helen Woods

February 5th 06, 04:06 PM

Nice article explaining this:

http://www.avweb.com/news/columns/191034-1.html

601XL Builder

February 5th 06, 04:43 PM

Flyingmonk wrote:
>> If you tie a 100 foot rope to the tail of an airplane (or some other
>> part of the airframe), attach it to a good strong post, and run the
>> propellor up to whatever rpm is available, is anyone claiming the
>> airplane can then lift up say a feet off the ground?
>
>> (Assuming the tail doesn't tear off)
>
>> (and, a conveyor belt under the airplane is optional)
>
> Depends on the airplane, if a plane is built in such a way that it can
> actually attain enough lift just from the prop wash alone than yes.
>
> The Monk
>

Yeah Monk that airplane is called a helicopter.

Mark

February 5th 06, 04:53 PM

"The Flying Scotsman" > wrote:
>
> DONT BE STUPID....
>
> IT CANNOT BE DONE !!! IF IT CAN BE THEN SOME CLEVER BUGGER 50 YEARS AGO
> WOULD OF DONE IT BY NOW..
>
> plus, has anyone thought what will happen to that aircaraft if i does
> manage to generate enough lift..... ITS GOING TO HAVE NO AIRSPEED,
> stall and fall out of the sky like a brick.
>
> Simple physics lads...
>

Ok, now suppose the treadmill is on the moon. . .

(ducks)

Mark

February 5th 06, 04:55 PM

However the airspeed-vs-wheel-rotation argument works out,
I think it is worth pointing out that all this time on the treadmill
should result in a _significant_ loss of weight for the aircraft,
resulting in more useful load.

Jim Macklin

February 5th 06, 04:55 PM

Category and class of aircraft...
aircraft includes all types of flying machines.

AIRPLANE does not include helicopters, see FAR Part 1

ASEL ASES AMEL AMES the A means category airplane and the
rest is the class
AMEL B747 includes the type.

Rotorcraft is the category and helicopter is the class.

--
James H. Macklin
ATP,CFI,A&P

--
The people think the Constitution protects their rights;
But government sees it as an obstacle to be overcome.
some support
http://www.usdoj.gov/olc/secondamendment2.htm
See http://www.fija.org/ more about your rights and duties.

"601XL Builder" <wrDOTgiacona@coxDOTnet> wrote in message
news:43E62B1E.6080403@coxDOTnet...
| Flyingmonk wrote:
| >> If you tie a 100 foot rope to the tail of an airplane
(or some other
| >> part of the airframe), attach it to a good strong post,
and run the
| >> propellor up to whatever rpm is available, is anyone
claiming the
| >> airplane can then lift up say a feet off the ground?
| >
| >> (Assuming the tail doesn't tear off)
| >
| >> (and, a conveyor belt under the airplane is optional)
| >
| > Depends on the airplane, if a plane is built in such a
way that it can
| > actually attain enough lift just from the prop wash
alone than yes.
| >
| > The Monk
| >
|
| Yeah Monk that airplane is called a helicopter.

alexy

February 5th 06, 04:55 PM

"BDS" > wrote:

>
>"alexy" > wrote
>
>> >If the conveyor keeps the airplane standing still relative to the ground,
>> >then it cannot take off.
>> Yeah, but the original statement of the problem made no such claim.
>
>Alex - here is what the statement said:
>
>> "An airplane on a runway sits on a conveyer belt that moves in the
>> opposite direction at exactly the speed that the airplane is moving
>> forward. Does the airplane take off?" (Assuming the tires hold out, of
>> course.)
>
>The plane cannot move forward - that means that it is standing still to me.

If the plane does not move forward, how fast is the conveyor moving?
Hint: "a conveyer belt that moves in the opposite direction at exactly
the speed that the airplane is moving forward."

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

RK Henry

February 5th 06, 04:57 PM

On Sun, 5 Feb 2006 00:39:47 -0800, "Peter Duniho"
> wrote:

>"Flyingmonk" > wrote in message
oups.com...
>> Depends on the airplane, certain lpanes are built in such a way that
>> they can actually attain enough lift just from the prop wash alone.
>
>Other than the ones we call helicopters, I've never heard of such a thing.
>
>Care to elaborate?
>

I've been told that a Maule will do that. With a little wind, just
apply power and it jumps into the air instantly. Similarly, in wind
it'll land vertically. But then the Maule pilot who told me this was
from Alaska, where airplanes routinely perform mythic feats.

RK Henry

JJS

February 5th 06, 05:09 PM

"Peter Duniho" > wrote in message ...
> "Flyingmonk" > wrote in message oups.com...
>> Depends on the airplane, certain lpanes are built in such a way that
>> they can actually attain enough lift just from the prop wash alone.
>
> Other than the ones we call helicopters, I've never heard of such a thing.
>
> Care to elaborate?
Tilt wing... Osprey?
Ducking and running! :' )

Joe Schneider
8437R

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alexy

February 5th 06, 05:12 PM

"Gary Drescher" > wrote:

>"Don Tuite" > wrote in message
...
>> but what
>> is the point of the original question in that case? Is it just to
>> trap a sloppy reader into thinking it's all about a crackpot VTOL
>> methodology?
>
>I think the more interesting point is to notice the implications of not
>transmitting force through the wheels. Even people who know that planes and
>cars differ in that way may fail (at least at first) to draw the appropriate
>conclusion about what happens to the treadmill plane when it applies takeoff
>power.

Totally irrelevant. The answer is the same for a glider being towed to
take-off by a ground vehicle (except that you would want to change the
rear end or wheel size of the vehicle to cut the final drive ratio in
half, so that it could attain the doubled wheel speed necessary to
attain the needed forward speed.)
>
>--Gary
>

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

BDS

February 5th 06, 05:22 PM

The mistake is in not realizing that the air that the propeller acts upon is
unchanged regardless of the speed of the conveyor belt. Therefore, the
propeller will be able to pull the airframe forward on the conveyor
regardless of how fast the conveyor moves, because it is putting a force on
the airframe relative to the air, not relative to the conveyor belt.

The same thing would happen if you attached a rope to the nose of the
airplane and stood on the ground ahead of the conveyor so that you were not
standing on the moving belt. Start the conveyor and the airplane stands
still while the wheels spin with the conveyor belt. Now pull on the rope
and you can move the airplane forward even though the conveyor is moving
backwards and the wheels are spinning like crazy.

The mistake I made in comparing it to a seaplane on a river is that the
floats are attached to the airframe - where they go, the plane goes. No so
with wheels. Wheel rotational speed has nothing to do with how fast the
airframe moves in this scenario.

BDS

muff528

February 5th 06, 05:22 PM

"Helen Woods" > wrote in message
...
> Nice article explaining this:
>
> http://www.avweb.com/news/columns/191034-1.html

C'mon Helen! .....How can reading that article in 5 minutes possibly
be as much fun as arguing about the problem in a public forum over the
course of 2 days??? ....Huh?!?

Omigod! ....What's happened to me!?! :~(

Gary Drescher

February 5th 06, 05:42 PM

"alexy" > wrote in message
...
> "Gary Drescher" > wrote:
>>I think the more interesting point is to notice the implications of not
>>transmitting force through the wheels. Even people who know that planes
>>and
>>cars differ in that way may fail (at least at first) to draw the
>>appropriate
>>conclusion about what happens to the treadmill plane when it applies
>>takeoff
>>power.
>
> Totally irrelevant. The answer is the same for a glider being towed to
> take-off by a ground vehicle (except that you would want to change the
> rear end or wheel size of the vehicle to cut the final drive ratio in
> half, so that it could attain the doubled wheel speed necessary to
> attain the needed forward speed.)

I don't think we're in disagreement. My point is just that (even assuming
frictionless wheels) you have to make some changes (such as the ones you
proposed) to a typical ground vehicle to imagine it running normally at
twice its usual speed (even if the relative wind is merely at the usual
speed). The airplane, in contrast, just takes off normally from the
treadmill without needing to be modified.

--Gary

Darrell S

February 5th 06, 06:25 PM

AES wrote:
> If you tie a 100 foot rope to the tail of an airplane (or some other
> part of the airframe), attach it to a good strong post, and run the
> propellor up to whatever rpm is available, is anyone claiming the
> airplane can then lift up say a feet off the ground?
>
> (Assuming the tail doesn't tear off)
>
> (and, a conveyor belt under the airplane is optional)

That completely changes the situation. The plane couldn't take off with a
regular runway if you secured it to a fixed post.

--

Darrell R. Schmidt
B-58 Hustler History: http://members.cox.net/dschmidt1/
-

Montblack

February 5th 06, 06:28 PM

("Michael Ware" wrote)
> You are taking the statement 'a conveyer belt that moves in the opposite
> direction at exactly the speed that the airplane is moving forward' to
> mean that somehow there is a force being applied to the mass of the
> aircraft, equal and opposite the thrust generated by the propellor. The
> only place the treadmill can exert any force an the airplane is the only
> place the treadmill is touching the airplane: the wheels. Any motion of
> the treadmill belt will be translated into rotation of the wheels. This
> will not prevent the aircraft from moving forward, through the air and
> taking off.

THE AIRPLANE WILL NOT MOVE. (That's my vote)

The rotating wheels + gravity (Thank you Sir Isaac!) ANCHOR the plane to the
treadmill. Plane/prop move forward, treadmill/wheels fall back. The plane is
attached to the wheels. Try it in front of you with a ruler and a magic
marker.

That airplane is doing 150 mph down that runway, only the runway is really a
treadmill which is matching that speed. End result is = to an Olympic
sprinter on the same treadmill - I can stand next to him for his entire 10
second (27 mph) race.

Montblack 83.7
(I thought some of double-digit people needed to be heard from. <g>)

alexy

February 5th 06, 07:17 PM

"cjcampbell" > wrote:

>"An airplane on a runway sits on a conveyer belt that moves in the
>opposite direction at exactly the speed that the airplane is moving
>forward. Does the airplane take off?" (Assuming the tires hold out, of
>course.)

Now, there are two references to motion in the problem, and the
correct (IMHO) solution is based on both of those motions being from a
consistent frame of reference, i.e., relative to the ground.

The incorrect (IMHO) solution seems to depend on reading these two
motions as related to inconsistent frames of reference, to wit: "An
airplane on a runway sits on a conveyer belt that moves relative to
the surface of the earth in the opposite direction at exactly the
speed that the airplane is moving relative to the surface of the
conveyer [Not sure how those who read it this way fit the word
"forward" into their interpretation.] This reading leads to the
conclusion that the plane is standing still, but flies in the face of
what really would happen if such a device were built, given how a
plane's propulsion is provided -- i.e., this reading of the problem
assumes facts inconsistent with what conceivably could happen were
such a device built. (BTW, many seem to focus on this practical aspect
of propulsion, but that misses the pure logic of the thought
experiment, it seems to me.)

But think about the opposite inconsistent reading of the statement:
"An airplane on a runway sits on a conveyer belt that moves, relative
to the airplane, in the opposite direction at exactly the speed that
the airplane is moving forward relative to the ground." That
inconsistent frame of reference seems just as justifiable as the
other, and is in fact MUCH easier to imagine actually implementing!

I think we should do something to make sure that all future airports
are built with runways that work like this third interpretation of the
stated problem! <g>
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Jon Woellhaf

February 5th 06, 08:19 PM

BDS, aren't you glad you used initials rather than your name?

"BDS" wrote

> Nevermind - I finally get it.
>
> DUH!!
>
> BDS

AES

February 5th 06, 08:27 PM

In article >,
"Michael Ware" > wrote:

> Are you saying 1) the rope is tight, or are you saying 2) you are giving the
> plane a 100' running start?
>
>
> "AES" > wrote in message
> ...
> > If you tie a 100 foot rope to the tail of an airplane (or some other
> > part of the airframe), attach it to a good strong post, and run the
> > propellor up to whatever rpm is available, is anyone claiming the
> > airplane can then lift up say a feet off the ground?
> >
> > (Assuming the tail doesn't tear off)
> >
> > (and, a conveyor belt under the airplane is optional)

Didn't think of that -- and maybe your response is tongue
in cheek -- but I had in mind "rope is tight".

Peter Duniho

February 5th 06, 09:09 PM

"Flyingmonk" > wrote in message
oups.com...
> Already rephrased my statement.

Sorry, I missed that. Even having been told it exists, I still can't find
the post with the rephrasing, but I'll assume it essentially retracts the
claim that an airplane can fly from prop wash alone.

Brien K. Meehan

February 5th 06, 11:04 PM

It's one of those strange Usenet phenomena.

How do start a big argument on Usenet? Ask a simple question.

Michael Ware

February 6th 06, 01:03 AM

"Brien K. Meehan" > wrote in message
oups.com...
> It's one of those strange Usenet phenomena.
>
> How do start a big argument on Usenet? Ask a simple question.
>

It would be fun to see this worked out on 'Mythbusters'.

Mike

jesse

February 6th 06, 01:43 AM

If the belt were moving backwards at the speed of the aircraft when it
> touched down, it would be similar to landing with that much tailwind,
> basically, your ground speed would double you airspeed at touch down.

Oops, my bad. I meant apparent (to the conveyor) groundspeed.
Jester

cjcampbell

February 6th 06, 02:56 AM

cjcampbell wrote:
> Saw this question on "The Straight Dope" and I thought it was amusing.
>
> http://www.straightdope.com/columns/060203.html
>
> The question goes like this:
>
> "An airplane on a runway sits on a conveyer belt that moves in the
> opposite direction at exactly the speed that the airplane is moving
> forward. Does the airplane take off?" (Assuming the tires hold out, of
> course.)
>
> Cecil Adams (world's smartest human being) says that it will take off
> normally.

I confess to having difficulty understanding the difference between a
conveyer belt and a treadmill, although it seems important to some
folks.

Cecil does not seem to be arguing that prop wash or jet thrust are
generating enough lift by providing downwash over the wings. He claims
the airplane will take off normally -- that is, the airplane will move
forward just as in a normal takeoff, developing airspeed as it goes. He
also claims that this will not take any extra thrust.

He likens the situation to someone on rollerblades on a treadmill who
is holding onto a rope fixed to an object at the front of the
treadmill. No matter how fast the treadmill is moving, it takes the
same energy to pull yourself to the front of the treadmill as it would
if the treadmill was stopped. The only difference is that the wheels
would turn twice as fast.

Cecil appears to be saying that the airplane cannot be prevented by the
conveyer belt from moving forward, no matter how fast the conveyer belt
moves, because the thrust is generated independently from the wheels.
The airplane will accelerate and take off, using the same length of
conveyer belt as it would an ordinary runway. The only difference is
that the wheels will be spinning twice as fast at rotation as they
would otherwise, thus the caveat "assuming the wheels hold out."

I am not sure I understand why Cecil thinks this. If I understand him
correctly, the drag of the treadmill against the wheels does not
increase just because the treadmill is moving. Okay, I guess I can
believe that. Still, it seems counterintuitive to me that if a plane is
sitting on a conveyer that is moving backwards at exactly the same
speed (I assume they mean groundspeed here) as the airplane is moving
forward that the airplane will move forward at the same speed as if it
was not on a conveyer at all.

cjcampbell

February 6th 06, 03:04 AM

Flyingmonk wrote:
> >It's surprising and refreshing
> >that this thread, with so many posts, hasn't (yet) degraded into a
> >flame-fest. :o)
>
> Amen to that!
>
> The Monk

Shockingly, no one has even called anyone a Nazi yet, nor has anyone
called me a troll for posting this and then departing for the weekend
without checking back to see if there were any replies. :-)

darthpup

February 6th 06, 03:08 AM

I hope none of you people are pilots!

RST Engineering

February 6th 06, 04:23 AM

All right, dammit, you're a Nazi and a troll. And I'm taking off for a
couple of days. Satisfied?

{;-)

Jim

"cjcampbell" > wrote in message
oups.com...
>
> Flyingmonk wrote:
>> >It's surprising and refreshing
>> >that this thread, with so many posts, hasn't (yet) degraded into a
>> >flame-fest. :o)
>>
>> Amen to that!
>>
>> The Monk
>
> Shockingly, no one has even called anyone a Nazi yet, nor has anyone
> called me a troll for posting this and then departing for the weekend
> without checking back to see if there were any replies. :-)
>

Greg B

February 6th 06, 05:12 AM

"Jane! Stop this crazy thing!"

Happy Dog

February 6th 06, 05:17 AM

"Montblack" > wrote in message
...
> ("Michael Ware" wrote)
>> You are taking the statement 'a conveyer belt that moves in the opposite
>> direction at exactly the speed that the airplane is moving forward' to
>> mean that somehow there is a force being applied to the mass of the
>> aircraft, equal and opposite the thrust generated by the propellor. The
>> only place the treadmill can exert any force an the airplane is the only
>> place the treadmill is touching the airplane: the wheels. Any motion of
>> the treadmill belt will be translated into rotation of the wheels. This
>> will not prevent the aircraft from moving forward, through the air and
>> taking off.

That's one of the best so far.
>
>
> THE AIRPLANE WILL NOT MOVE. (That's my vote)
>
> The rotating wheels + gravity (Thank you Sir Isaac!) ANCHOR the plane to
> the
> treadmill. Plane/prop move forward, treadmill/wheels fall back. The plane
> is
> attached to the wheels. Try it in front of you with a ruler and a magic
> marker.
>
> That airplane is doing 150 mph down that runway, only the runway is really
> a
> treadmill which is matching that speed. End result is = to an Olympic
> sprinter on the same treadmill - I can stand next to him for his entire 10
> second (27 mph) race.

Lordy. BDS answered this pretty well. But, imagine that the plane is held
still by a rope secured in front of the conveyor. That rope is attached to
a strain guage that measures the force, in kg, say, that the moving conveyor
exerts on the plane. This will increase with the speed of the conveyor, but
let's use a reasonable number and we will see that the force is minimal
since it's only whatever is converted to heat in the wheel bearings.
Probably less than a few hundred watts. The amount of power required to
move the plane forward will be more than required on a stationary runway by
only this much. Dig?

> Montblack 83.7
> (I thought some of double-digit people needed to be heard from. <g>)

moo

www.mensa.org

>

Happy Dog

February 6th 06, 05:21 AM

"cjcampbell" > wrote in message

> Still, it seems counterintuitive to me that if a plane is
> sitting on a conveyer that is moving backwards at exactly the same
> speed (I assume they mean groundspeed here) as the airplane is moving
> forward that the airplane will move forward at the same speed as if it
> was not on a conveyer at all.

Then you may not be ready for this:

http://www.mste.uiuc.edu/reese/monty/monty.htm

moo

Flyingmonk

February 6th 06, 05:24 AM

Who's on first? Third base!

The Monk

John T

February 6th 06, 05:25 AM

"cjcampbell" > wrote in message
oups.com
>
> Still, it seems counterintuitive to me that if a plane is
> sitting on a conveyer that is moving backwards at exactly the same
> speed (I assume they mean groundspeed here) as the airplane is moving
> forward that the airplane will move forward at the same speed as if it
> was not on a conveyer at all.

Why does the conveyor belt speed have anything to do with the airspeed of
the airplane?

--
John T
http://tknowlogy.com/TknoFlyer
Reduce spam. Use Sender Policy Framework: http://spf.pobox.com
____________________

Jon Woellhaf

February 6th 06, 06:46 AM

CJ, please let us know when the light bulb finally goes on.

"cjcampbell" wrote

> Still, it seems counterintuitive to me that if a plane is
> sitting on a conveyer that is moving backwards at exactly the same
> speed (I assume they mean groundspeed here) as the airplane is moving
> forward that the airplane will move forward at the same speed as if it
> was not on a conveyer at all.

cjcampbell

February 6th 06, 10:30 AM

Happy Dog wrote:
> "cjcampbell" > wrote in message
>
> > Still, it seems counterintuitive to me that if a plane is
> > sitting on a conveyer that is moving backwards at exactly the same
> > speed (I assume they mean groundspeed here) as the airplane is moving
> > forward that the airplane will move forward at the same speed as if it
> > was not on a conveyer at all.
>
> Then you may not be ready for this:
>
> http://www.mste.uiuc.edu/reese/monty/monty.htm
>

Now I have a headache. And they call me a troll and a Nazi. :-)

cjcampbell

February 6th 06, 10:38 AM

Jon Woellhaf wrote:
> CJ, please let us know when the light bulb finally goes on.
>

I am not a real fast learner, but I have some reputation, possibly
undeserved, for intelligence. The lightbulb will probably go on in the
middle of the night. Serves me right for even bringing it up. :-)

[email protected]

February 6th 06, 11:27 AM

It WILL take off normally.
The propeller works in the air, not on the ground.
The only problem can be in the tires, that may blow up going twice as
fast as the normal takeoff speed, but i doubt that can happen.

It will surely take off, though.

Piero

DaveB

February 6th 06, 03:58 PM

On 3 Feb 2006 18:27:39 -0800, "cjcampbell"
> wrote:

>Saw this question on "The Straight Dope" and I thought it was amusing.
>
>http://www.straightdope.com/columns/060203.html
>
>The question goes like this:
>
>"An airplane on a runway sits on a conveyer belt that moves in the
>opposite direction at exactly the speed that the airplane is moving
>forward. Does the airplane take off?" (Assuming the tires hold out, of
>course.)
>
>Cecil Adams (world's smartest human being) says that it will take off
>normally.
>
OK you got me thinking, I presently have a work crew making conveyor
so will give a full report soon.

Regards
Daveb

Montblack

February 6th 06, 05:56 PM

("Michael Ware" wrote)
> It would be fun to see this worked out on 'Mythbusters'.

How would wiring a treadmill up to explode solve anything? <g>

Montblack
It blow'd up. It blow'd up real good.

Mike Weller

February 6th 06, 06:31 PM

On 3 Feb 2006 18:27:39 -0800, "cjcampbell"
> wrote:

>Saw this question on "The Straight Dope" and I thought it was amusing.
>
>http://www.straightdope.com/columns/060203.html
>
>The question goes like this:
>
>"An airplane on a runway sits on a conveyer belt that moves in the
>opposite direction at exactly the speed that the airplane is moving
>forward. Does the airplane take off?" (Assuming the tires hold out, of
>course.)
>
>Cecil Adams (world's smartest human being) says that it will take off
>normally.

No it won't.

And I'm surprised that I'm even responding to this.

Mike Weller

BDS

February 6th 06, 06:41 PM

"Mike Weller" > wrote

> >Cecil Adams (world's smartest human being) says that it will take off
> >normally.
>
> No it won't.
>
> And I'm surprised that I'm even responding to this.
>
> Mike Weller

And yet another hapless soul falls into the trap! :>)

BDS

Mike Weller

February 6th 06, 07:08 PM

On Sat, 4 Feb 2006 08:44:24 -0800, "RST Engineering"
> wrote:

>Cecil Adams (world's smartest human being) is correct to a first
>approximation. The correct answer to a second approximation is that it will
>take off normally less some small correction factor for the increased
>friction of the tires, wheels, and wheel bearings.
>
>Note the "trick" of the question. It does not say that the conveyor keeps
>the AIRPLANE at zero speed relative to the real world, just that it rotates
>at a speed equal to the airplane moving forward. The question itself
>supposes forward velocity of the aircraft relative to the earth and the only
>thing the conveyor belt does is spin the wheels twice as fast.
>
>Jim
>

Jim, you've got to realize that it must be a tough job being the
smartest man in the world.

I like being the second smartest. But as George Wallace once put it
after a reporter asked him, "You think that you're the smartest man in
the world?" No he said, "but I'm the smartest man in this room."

Mike Weller

And I'm not a George Wallace fan, for many reasons.

alexy

February 6th 06, 07:11 PM

Mike Weller > wrote:

>On 3 Feb 2006 18:27:39 -0800, "cjcampbell"
> wrote:
>
>>Saw this question on "The Straight Dope" and I thought it was amusing.
>>
>>http://www.straightdope.com/columns/060203.html
>>
>>The question goes like this:
>>
>>"An airplane on a runway sits on a conveyer belt that moves in the
>>opposite direction at exactly the speed that the airplane is moving
>>forward. Does the airplane take off?" (Assuming the tires hold out, of
>>course.)
>>
>>Cecil Adams (world's smartest human being) says that it will take off
>>normally.
>
>No it won't.
>
>And I'm surprised that I'm even responding to this.
>
>Mike Weller

<g>

Let this be a lesson to you: whenever replying to a posted riddle or
puzzle that has over 100 replies, it might be a good idea to read some
of those replies to avoid falling into a well-set trap!

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Mike Weller

February 6th 06, 07:15 PM

On Mon, 06 Feb 2006 14:11:45 -0500, alexy > wrote:

>
>Let this be a lesson to you: whenever replying to a posted riddle or
>puzzle that has over 100 replies, it might be a good idea to read some
>of those replies to avoid falling into a well-set trap!

Yes, and thank you. I've only touched the tip of the ice on this one.

Mike Weller

Gig 601XL Builder

February 6th 06, 07:55 PM

It was a joke James. I'll bet The Monk got it.

"Jim Macklin" > wrote in message
news:UtqFf.75785$QW2.44974@dukeread08...
> Category and class of aircraft...
> aircraft includes all types of flying machines.
>
> AIRPLANE does not include helicopters, see FAR Part 1
>
> ASEL ASES AMEL AMES the A means category airplane and the
> rest is the class
> AMEL B747 includes the type.
>
> Rotorcraft is the category and helicopter is the class.
>
> --
> James H. Macklin
> ATP,CFI,A&P
>
> --
> The people think the Constitution protects their rights;
> But government sees it as an obstacle to be overcome.
> some support
> http://www.usdoj.gov/olc/secondamendment2.htm
> See http://www.fija.org/ more about your rights and duties.
>
>
>
> "601XL Builder" <wrDOTgiacona@coxDOTnet> wrote in message
> news:43E62B1E.6080403@coxDOTnet...
> | Flyingmonk wrote:
> | >> If you tie a 100 foot rope to the tail of an airplane
> (or some other
> | >> part of the airframe), attach it to a good strong post,
> and run the
> | >> propellor up to whatever rpm is available, is anyone
> claiming the
> | >> airplane can then lift up say a feet off the ground?
> | >
> | >> (Assuming the tail doesn't tear off)
> | >
> | >> (and, a conveyor belt under the airplane is optional)
> | >
> | > Depends on the airplane, if a plane is built in such a
> way that it can
> | > actually attain enough lift just from the prop wash
> alone than yes.
> | >
> | > The Monk
> | >
> |
> | Yeah Monk that airplane is called a helicopter.
>
>

Flyingmonk

February 6th 06, 08:13 PM

>It was a joke James. I'll bet The Monk got it.

Even if I didn't I'd pretend that I did. LOL

The Monk

Gig 601XL Builder

February 6th 06, 08:21 PM

"Flyingmonk" > wrote in message
oups.com...
> >It was a joke James. I'll bet The Monk got it.
>
> Even if I didn't I'd pretend that I did. LOL
>
> The Monk
>

Damn straight you would!

Dallas

February 6th 06, 09:13 PM

"alexy"

> avoid falling into a well-set trap!

I wouldn't call this a trap, it's simply a physics question that about 25%
of the respondents picks "won't take off".

Having gone through this once already in another group, the one thing that
stands out in my mind is that intelligence seems to have nothing to do with
how someone will answer. I have seen highly intelligent people insist that
the airplane won't move and they are willing to robustly defend their
position.

I would be at a loss to explain the difference between the minds of both
groups. Rick Durden's article suggests that those with engineering or math
backgrounds tend to side with the "will take off" group. I haven't seen
that correlation at all.

Dallas

cjcampbell

February 7th 06, 02:41 AM

Jon Woellhaf wrote:
> CJ, please let us know when the light bulb finally goes on.
>
> "cjcampbell" wrote
>
> > Still, it seems counterintuitive to me that if a plane is
> > sitting on a conveyer that is moving backwards at exactly the same
> > speed (I assume they mean groundspeed here) as the airplane is moving
> > forward that the airplane will move forward at the same speed as if it
> > was not on a conveyer at all.

Okay, I see why the plane moves forward normally no matter how fast the
treadmill is going and even why it would not work in an automobile.

As for that Monty Hall thing, I see that it works, but I have not
figured out why it works yet.

There are certainly some strange things in the world.

Morgans

February 7th 06, 05:17 AM

> Now I have a headache. And they call me a troll and a Nazi. :-)

That's right, you troll posting, rat bast__d, head banging fascist!
Beginning a thread that *should* be able to be unraveled by a cross-eyed 6
year old, is evil, pure evil. I hope your head inflates to twice it's
normal size, before becoming pink mist! <bfg>

Well, at least the "pure evil" part is true!

This whole thing has been quite amazing. Who would'a thunk?
--
Jim in NC

Tony

February 7th 06, 09:12 AM

176. cjcampbell
Feb 6, 9:41 pm show options

Newsgroups: rec.aviation.student, rec.aviation.piloting
From: "cjcampbell" > - Find messages by
this author
Date: 6 Feb 2006 18:41:35 -0800
Local: Mon, Feb 6 2006 9:41 pm
Subject: Re: Can a Plane on a Treadmill Take Off?
Reply | Reply to Author | Forward | Print | Individual Message | Show
original | Report Abuse

> "cjcampbell" wrote

>Okay, I see why the plane moves forward normally no matter how fast the
>treadmill is going and even why it would not work in an automobile.

Well, not exactly. This dead horse is fun to beat. Suppose I tell you
the car is going forward at 60 mph. That means the belt is going the
other way at 60, right? The speedometer would be indicating 120.

The OP said the belt is moving backward as fast as the <whatever> is
moving forward. When you substitute real numbers into the thing it
becomes more clear.

Or not.

cjcampbell

February 7th 06, 10:54 AM

Tony wrote:
> 176. cjcampbell
> Feb 6, 9:41 pm show options
>
> Newsgroups: rec.aviation.student, rec.aviation.piloting
> From: "cjcampbell" > - Find messages by
> this author
> Date: 6 Feb 2006 18:41:35 -0800
> Local: Mon, Feb 6 2006 9:41 pm
> Subject: Re: Can a Plane on a Treadmill Take Off?
> Reply | Reply to Author | Forward | Print | Individual Message | Show
> original | Report Abuse
>
>
>
>
>
> > "cjcampbell" wrote
>
> >Okay, I see why the plane moves forward normally no matter how fast the
> >treadmill is going and even why it would not work in an automobile.
>
> Well, not exactly. This dead horse is fun to beat. Suppose I tell you
> the car is going forward at 60 mph. That means the belt is going the
> other way at 60, right? The speedometer would be indicating 120.
>
> The OP said the belt is moving backward as fast as the <whatever> is
> moving forward. When you substitute real numbers into the thing it
> becomes more clear.
>
> Or not.

Apparently not to everyone. :-)

The speedometer would indicate 60.

Tony

February 7th 06, 11:33 AM

If the car had an airspeed indicator it would, I agree, indicate 60. In
the model I suggested the car is moving to the north at 60, the
treadmill to the south at 60, and the speedometer will indicate 120.

muff528

February 7th 06, 11:50 AM

Uh-Oh!!.....here we go again!

I vote -- 120
Kinda like an escalator. You can still go up on a "down" escalator
if you run. The treadmill would have to be "set" at the 60 mph speed
so that the car's "input" would not affect it. Then you could move
faster "forward" than the treadmill is moving "backwards". You could
also adjust the indicated speed to less than 60 and the conveyor would
carry the car backwards at less than 60. All relative to the world.
Speedometer says 60 - car is standing still.
Speedometer says 120 - car moves forward 60 mph
Speedometer says 0 - car moves backwards 60 mph

The conveyor is just another stationary road in a different reference frame.
Only this time it's not interacting with another frame's stuff (airmass).
The conveyor could be on another planet....or BE another planet.

"cjcampbell" > wrote in message
oups.com...
>
> Tony wrote:
> > 176. cjcampbell
> > Feb 6, 9:41 pm show options
> >
> > Newsgroups: rec.aviation.student, rec.aviation.piloting
> > From: "cjcampbell" > - Find messages by
> > this author
> > Date: 6 Feb 2006 18:41:35 -0800
> > Local: Mon, Feb 6 2006 9:41 pm
> > Subject: Re: Can a Plane on a Treadmill Take Off?
> > Reply | Reply to Author | Forward | Print | Individual Message | Show
> > original | Report Abuse
> >
> >
> >
> >
> >
> > > "cjcampbell" wrote
> >
> > >Okay, I see why the plane moves forward normally no matter how fast the
> > >treadmill is going and even why it would not work in an automobile.
> >
> > Well, not exactly. This dead horse is fun to beat. Suppose I tell you
> > the car is going forward at 60 mph. That means the belt is going the
> > other way at 60, right? The speedometer would be indicating 120.
> >
> > The OP said the belt is moving backward as fast as the <whatever> is
> > moving forward. When you substitute real numbers into the thing it
> > becomes more clear.
> >
> > Or not.
>
> Apparently not to everyone. :-)
>
> The speedometer would indicate 60.
>

Flyingmonk

February 7th 06, 12:10 PM

>The conveyor is just another stationary road in a different reference frame.

....but an airplane's "reference frame" is ALWAYS the
surrounding/relative air, not the runway beneath it!

The Monk

muff528

February 7th 06, 12:14 PM

"Flyingmonk" > wrote in message
oups.com...
> >The conveyor is just another stationary road in a different reference
frame.
>
> ...but an airplane's "reference frame" is ALWAYS the
> surrounding/relative air, not the runway beneath it!
>
> The Monk
>

Exactly,....that's why the airplane will take off.
Tony brought up the prospect of replacing the airplane
with a car.

alexy

February 7th 06, 01:28 PM

"muff528" > wrote:

>Uh-Oh!!.....here we go again!
>
>I vote -- 120
>Kinda like an escalator. You can still go up on a "down" escalator
>if you run. The treadmill would have to be "set" at the 60 mph speed
>so that the car's "input" would not affect it.
But that would change the problem. In the problem as stated, you would
have to have a device that determined the cars forward speed (NOT its
wheel speed) and feed that input to the speed regulator on the
treadmill.

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

MaulePilot

February 7th 06, 01:43 PM

A plane on a conveyor belt takes off East Bound at 9:15am from Peoria,
Il, while a 747 on a conveyor belt takes off West Bound at the same
time from Hackensack NJ.
What time and at what point will they meet?

NEVER you morons. There is no air moving over the wings to produce any
'lift', much less any forward ground speed. I can't believe the
stupid crap that people talk about here.

Thomas Borchert

February 7th 06, 02:00 PM

Alexy,

> >The conveyor is programmed to move in such a way as to maintain the
> >aircraft at an airspeed of zero as measured at the pitot.
>
> Absolutely, if you CHANGED the problem, and restated it as above, then
> it wouldn't fly.
>

Actually, you couldn't do that - which is another point the question
makes.

--
Thomas Borchert (EDDH)

darthpup

February 7th 06, 02:04 PM

Actually conveyor belt would decrease the length of runways if operated
in the direction of take off???

Flyingmonk

February 7th 06, 02:15 PM

>Actually conveyor belt would decrease the length of runways if operated
>in the direction of take off???

Instead of wasting all that energy to power the conveyor belt, why not
add that power to the plane itself?

The Monk

alexy

February 7th 06, 02:35 PM

"MaulePilot" > wrote:

>A plane on a conveyor belt takes off East Bound at 9:15am from Peoria,
>Il, while a 747 on a conveyor belt takes off West Bound at the same
>time from Hackensack NJ.
>What time and at what point will they meet?
>
>NEVER you morons. There is no air moving over the wings to produce any
>'lift', much less any forward ground speed. I can't believe the
>stupid crap that people talk about here.

There goes another one! <g>

Has anyone counted how many folks have fallen into this "trap"? I
wonder if those who call others "morons" as they fall in tend to have
bigger welts on their forehead when they finally get it and give
themselves a dope slap? <g>
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Flyingmonk

February 7th 06, 02:40 PM

>> >It was a joke James. I'll bet The Monk got it.

>> Even if I didn't I'd pretend that I did. LOL

>> The Monk

>Damn straight you would!

Damn straight you would! LOL

The Monk

alexy

February 7th 06, 02:56 PM

Thomas Borchert > wrote:

>Alexy,
>
>> >The conveyor is programmed to move in such a way as to maintain the
>> >aircraft at an airspeed of zero as measured at the pitot.
>>
>> Absolutely, if you CHANGED the problem, and restated it as above, then
>> it wouldn't fly.
>>
>
>Actually, you couldn't do that - which is another point the question
>makes.

True, from a practical standpoint. As far as the thought experiment
goes, you could if the conveyer moved fast enough that the rolling
friction of the tires plus the bearing friction of the wheels exactly
offset the thrust of the plane's propulsion system. My initial
calculations indicate that the speed needed for that to happen is
somewhat below the speed of light, but significantly beyond the speed
at which the wheels and tires would disintegrate. <g>
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Gene Seibel

February 7th 06, 03:35 PM

Depends on how long the treadmill is....
--
Gene Seibel
Hangar 131 - http://pad39a.com/gene/plane.html
Because I fly, I envy no one.

[email protected]

February 7th 06, 03:45 PM

>I would be at a loss to explain the difference between the
>minds of both groups.

Well, the difference is simply that someone looks at the tree, someone
else looks at the forest and sees the problem in its integrity.

Everyone that answers "Won't take off" don't think that the runway is
NOT a relevant element to make an airplane take off. The airplane works
in the air whether or not the wheels are on the ground.

Piero

Tony

February 7th 06, 04:25 PM

No one has thought of the other limitation: the airplane could fall off
the edge of the world.

Thomas Borchert

February 7th 06, 04:28 PM

Alexy,

> Has anyone counted how many folks have fallen into this "trap"?
>

What irks me most is how violent people attack those of a different
opinion over this rather trivial matter - all the while being wrong...

--
Thomas Borchert (EDDH)

Thomas Borchert

February 7th 06, 04:28 PM

Darthpup,

> Actually conveyor belt would decrease the length of runways if operated
> in the direction of take off???
>

The point the question makes is that the speed of the belt is completely
independent of the airspeed of the plane, so you just CAN'T make the belt
keep the airspeed at zero.

--
Thomas Borchert (EDDH)

Thomas Borchert

February 7th 06, 04:28 PM

Alexy,

> My initial
> calculations indicate that the speed needed for that to happen is
> somewhat below the speed of light, but significantly beyond the speed
> at which the wheels and tires would disintegrate. <g>
>

Concur. <g>

--
Thomas Borchert (EDDH)

Montblack

February 7th 06, 04:49 PM

wrote)
[snip]
> The airplane works in the air whether or not the wheels are on the ground.

BUT...the AIRplane isn't in the AIR yet!

Gravity, wheels, belt, zero airspeed. Once the wings get some lift under
them, sure...

But just like a plane sitting on the tarmac, our plane is still heavy enough
to rest on those happy little spinning wheels.

It's not a frigg'n blimp!

Montblack 83.7
More from the double-diget crowd.

Tony

February 7th 06, 05:38 PM

Once again: assume the airplane is moving at 60 miles an hour to the
north. The tread mill then by definition is turning so that the belt is
going 60 miles an hour to the south. The wheels are turning as though
the airplane was going 120 miles an hour on the runway. If 60 is enough
airspeed for this airplane to lift off, the pilot just needs to apply
back pressure to the yoke. It's a question nicely phrased to make some
of us draw the wrong inferences: that's how come this is the 197th
response, and I think it's correct but then again others who don't
agree think they are correct as well. They have a right to be wrong
:-)!

Peter Duniho

February 7th 06, 06:48 PM

"Thomas Borchert" > wrote in message
...
> What irks me most is how violent people attack those of a different
> opinion over this rather trivial matter - all the while being wrong...

I find it amusing, *because* of the strong correlation between abusive
language and ignorance.

As you noted, the folks who "get it" have been reasonably polite, while the
people who use the worst language, calling others "idiots" and "morons" etc
are the ones who don't have a clue.

I find this outcome hilarious. I don't mind the name-calling; it's par for
the course on Usenet, and the above-noted correlation holds true nearly all
of the time, not just in this thread. It's an easy way to filter out the
people who really *are* morons.

Pete

Greg Copeland

February 7th 06, 07:19 PM

Actually, I believe you are incorrect. That passage only implies the
belt will move inversely proportional to the wheels on the plane;
meaning the delta is conantly zero. They never actually state the
plane is moving forward. Thus, with a wheel speed of zero, the delta
is still zero. Therefore, I would suggest the only correct answer,
based on that sole passage is, "no".

Now, if we look at the actual question posted on straight dope, the
answer is, "maybe", for many reasons. Having said that, we can
*easily* tear up the explanation provided on straight dope. Simple
fact is, Cecil makes a huge assumption which causes his whole house of
cards to come tumbling down. Simply stated, there is nothing which
precludes the belt from being motorized. Given a sophisticaed enough
implementation, one can absolutely state, the plane would never leave
the ground; assuming no head wind is involved.

Long of the short, there is simply not enough information to provide an
exact answer, other than maybe. If the belt is not motorized, AND the
plane is moving (positive delta), yes, the plane will fly. If the belt
is motorized, and it is intelligent enough to ensure a belt/wheel delta
of zero, no, the plane will never fly.

Greg Copeland

February 7th 06, 07:24 PM

Sorry....the plane would not fly as you described. For if your
statement were true, we would not need wings...only a engine and a
prop. We must have air flow over the wings to generate lift. Propwash
does not generate enough lift, especially for planes wihch have a
centrally located engine/prop between the wings.

Greg Copeland

February 7th 06, 07:28 PM

Only if you make many assumptions. Otherwise, he's wrong. The only
correct answer is "unknown" because of lacking information. The only
way to get off of, "unknown", is to make assumptions, which Cecil
happily did. Therefore, if he's allowed to make assumptions, so are
the rest of us. Which means, the answer is equally, "no".

Either way, he's wrong because he made an assumption or he's wrong
because we are allowed to make assumptions in the other direction,
thusly proving he's wrong.

BDS

February 7th 06, 08:24 PM

"Greg Copeland" > wrote

> Sorry....the plane would not fly as you described. For if your
> statement were true, we would not need wings...only a engine and a
> prop. We must have air flow over the wings to generate lift. Propwash
> does not generate enough lift, especially for planes wihch have a
> centrally located engine/prop between the wings.

Nitpicking aside, I suspect that everyone agrees that in order for the plane
to take off it must move forward along the conveyor. Since the prop applies
a force to the plane which acts independent of what the conveyor and the
wheels are doing, the plane can definitely move forward, and therefore it
can take off.

Tie a rope to the plane and to your car which is parked in front of the
conveyor and not on the belt. Start the conveyor and run the belt at any
speed you wish. The plane sits still on the conveyor as the wheels spin
away. Now, if you drive your car forward the plane will move forward along
the conveyor at the speed that you are driving your car forward, regardless
of how fast the conveyor belt is moving. The conveyor cannot keep the plane
from moving forward, it can only spin the plane's wheels. The example says
that the belt moves backwards at the same speed that the plane moves
forward, but that doesn't mean that the plane must be standing still.

Get rid of the rope and the car and use the prop and the engine to pull you
forward along the conveyor (because it pulls you by exerting a force on the
air) and voila, you're flyin' the friendly skies.

BDS

alexy

February 7th 06, 08:24 PM

"Greg Copeland" > wrote:

>Actually, I believe you are incorrect. That passage only implies the
>belt will move inversely proportional to the wheels on the plane;
What problem are you reading? The one I saw said "An airplane on a
runway sits on a conveyer belt that moves in the opposite direction at
exactly the speed that the airplane is moving forward." I didn't see
anything about wheel speed mentioned or implied. If you inferred it,
I'd suggest that is a product of your inference, not of the author's
implication.

>meaning the delta is conantly zero.
What delta?
> They never actually state the
>plane is moving forward.
That's true. One does have to make the radical assumption that the
question is not about a plane parked on a non moving treadmill.

> Thus, with a wheel speed of zero, the delta
>is still zero. Therefore, I would suggest the only correct answer,
>based on that sole passage is, "no".
>
>Now, if we look at the actual question posted on straight dope, the
>answer is, "maybe", for many reasons. Having said that, we can
>*easily* tear up the explanation provided on straight dope. Simple
>fact is, Cecil makes a huge assumption which causes his whole house of
>cards to come tumbling down. Simply stated, there is nothing which
>precludes the belt from being motorized.
In fact, I would argue that it would need to be motorized to go
backwards at the same speed at which the plane is moving forward. In
what way does that "cause the whole house of cards to come tumbling
down"?

> Given a sophisticaed enough
>implementation, one can absolutely state, the plane would never leave
>the ground; assuming no head wind is involved.
>
>Long of the short, there is simply not enough information to provide an
>exact answer, other than maybe. If the belt is not motorized, AND the
>plane is moving (positive delta), yes, the plane will fly. If the belt
>is motorized, and it is intelligent enough to ensure a belt/wheel delta
>of zero, no, the plane will never fly.
Of course, if it did that, it would assure that the plane did not move
forward, thus meaning that the belt would not move forward, which is
back to your rather uninteresting parked plane analysis. I think it
far more likely that the problem intended what it said, that the
conveyor moves backward at the same rate the plane moves forward,
rather than your different problem statement having to do with wheel
speed.

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Greg Copeland

February 7th 06, 08:43 PM

> What problem are you reading?

The one provided....but I clearly stated that I was replying to a
speciifc section...see message I replied to. What are you reading?
The section is,
> "a conveyer belt that moves in the opposite direction at exactly the speed that the airplane is
> moving forward."

> I didn't see anything about wheel speed mentioned or implied. If you inferred it,
> I'd suggest that is a product of your inference, not of the author's
> implication.

Actually, you're reading into the statement...which is exactly my
point. Yet, after pointing this out, you still completely missed it.
Even funnier, you then turn an imply that I completley missed the boat.
If I state, "when I jump out of a window, I will hit the ground", it
does not mean I'm falling as I type this. It clearly means, when one
happens, so will the other. It in no way, shape, or form, implies that
it's happening or has happened. Which clearly opens the door that the
speed is zero, or at least can be. A plane will not fly with zero air
over it's wings, producing zero lift.

In other words, you ASSUMED that speed was not zero and Cecil ASSUMED
the runway was not driven by it's own motor. Lots of assumptions.
What are you reading?

You then go on to talk about left turns you madel. Simply stated, it
is *all* about wheel speed and lift; depending on wihch assumptions you
want to make. If the plane is moving forward, the wheel is turning
faster than the treadmill.; thusly allowing you to generate lift as
forward motion allows for air over the wings. If the wheel is turning
slower than the treadmill, then you are moving backwards. Thusly, a
delta of zero or less means NO LIFT...NO FLIGHT.

This isn't exactly rocket science...

Greg Copeland

February 7th 06, 08:58 PM

> Nitpicking aside, I suspect that everyone agrees that in order for the plane to take off it must move
> forward along the conveyor.

Which is exactly my point! If you have a motoroized conveyor which
always reduces the plane's forward movement to zero, no lift is
generated, preventing the plane from flying. In other words, the plane
generates lift by moving air over its wings. It moves air over its
wings by moving forward. If you zero out forward movement, by a
motorized conveyor, resulting in a zero delta, no lift is generated.
it's a question of the plane making forward movement.

Specifically, as it relates to your reply, while prop wash would indeed
produce some lift over the wing, it would not be nearly enough to
obtain take off....which is why we have wings. Thusly, if forward
movement is zero and you're full throttle, you're not airbound....which
is exaclty the same thing as a plane with no wings.

BDS

February 7th 06, 09:11 PM

"Greg Copeland" > wrote
> > Nitpicking aside, I suspect that everyone agrees that in order for the
plane to take off it must move
> > forward along the conveyor.
>
> Which is exactly my point! If you have a motoroized conveyor which
> always reduces the plane's forward movement to zero

It doesn't say that the plane has no forward movement - it says that the
conveyor moves backwards at the same speed at which the plane moves
forward - that does not prevent the plane from moving forward.

alexy

February 7th 06, 09:12 PM

"Greg Copeland" > wrote:

>In other words, you ASSUMED that speed was not zero
If one applies power to the plane (and yes, I am assuming that is
implied in the question of whether the plane takes off normally), and
the conveyor only moves backward at the same rate as the plane moves
forward, yes, the plane will move forward.

> and Cecil ASSUMED
>the runway was not driven by it's own motor.
As said before, I saw no such assumption, and in fact would assume the
opposite. I see no way for the conveyer to move without its own power.

> Lots of assumptions.
>What are you reading?
>
>You then go on to talk about left turns you madel. Simply stated, it
>is *all* about wheel speed and lift
Maybe for you. I didn't see anything about wheel speed.

> If the wheel is turning
>slower than the treadmill, then you are moving backwards.

If you are moving backwards, and the conveyer, according to the
statement of the problem, is moving backwards at the same rate as the
plane is moving forwards, what direction is it moving?

>Thusly, a
>delta of zero or less means NO LIFT...NO FLIGHT.

I still don't know what delta you are referring to, but I think we are
in agreement that a plane will not fly backwards. (Jokes about canards
aside).

>This isn't exactly rocket science...
No, it's the wheels that are confusing folks. Make it "rocket science"
and it would become clearer. <g>

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

RST Engineering

February 7th 06, 09:50 PM

Let's do the old Einstein thought experiment. Let's presume a motorized
conveyor belt that is being rotated towards the departure end of the runway.
Let's also presume frictionless wheel bearings in an aircraft sitting at the
departure end of the runway on the conveyor belt.

What happens to the aircraft? Nothing. THe airplane remains motionless
because the aircraft wheels, which are rotating, do not impart any force to
the aircraft to make it move in any direction (F=ma). To a bystander
sitting on the taxi light at the end of the runway, the conveyor belt is
moving left to right, the wheels are spinning in a counterclockwise
direction, and the aircraft itself is motionless.

Now introduce wheel bearing friction. The aircraft will begin to slowly
move left to right as a function of how much friction there is. Fire up the
propeller and give it just enough throttle to overcome wheel bearing
friction. Again, the observer on the taxi light sees the aircraft
motionless.

Now give it full throttle. Not only do we now have enough thrust to
overcome wheel bearing friction, we have more than enough to launch the
aircraft successfully into the air.

If ya can't see this, I give up.

Jim

"BDS" > wrote in message
t...
>
> "Greg Copeland" > wrote
>> > Nitpicking aside, I suspect that everyone agrees that in order for the
> plane to take off it must move
>> > forward along the conveyor.

Jon Woellhaf

February 7th 06, 09:57 PM

As a tribute to CJ Campbell for starting this wonderful thread, I propose
his official RAS and RAP call sign be "La Brea."

Jon

Michael Ware

February 7th 06, 11:15 PM

> Which is exactly my point! If you have a motoroized conveyor which
> always reduces the plane's forward movement to zero, no lift is
> generated, preventing the plane from flying.

That's not what the original problem stated. And we have explained at least
ten times why the conveyor belt CANNOT prevent the plane from moving
forward. My attempt, an earlier post:

You are taking the statement 'a conveyer belt that moves in the opposite
direction at exactly the speed that the airplane is moving
forward' to mean that somehow there is a force being applied to the mass of
the aircraft, equal and opposite the thrust generated by the propellor. The
only place the treadmill can exert any force an the airplane is the only
place the treadmill is touching the airplane: the wheels. Any motion of the
treadmill belt will be translated into rotation of the wheels. This will not
prevent the aircraft from moving forward, through the air and taking off.

Michael Ware

February 7th 06, 11:18 PM

"Greg Copeland" > wrote in message
ups.com...
> Only if you make many assumptions. Otherwise, he's wrong. The only
> correct answer is "unknown" because of lacking information. The only
> way to get off of, "unknown", is to make assumptions, which Cecil
> happily did. Therefore, if he's allowed to make assumptions, so are
> the rest of us. Which means, the answer is equally, "no".
>
> Either way, he's wrong because he made an assumption or he's wrong
> because we are allowed to make assumptions in the other direction,
> thusly proving he's wrong.
>

Bull. The only unknown is the amount of friction due to rolling resistance
of the tires and wheel bearings. Give me that and I'll give you the takeoff
distance.

Matt Whiting

February 7th 06, 11:24 PM

RST Engineering wrote:
> Let's do the old Einstein thought experiment. Let's presume a motorized
> conveyor belt that is being rotated towards the departure end of the runway.
> Let's also presume frictionless wheel bearings in an aircraft sitting at the
> departure end of the runway on the conveyor belt.
>
> What happens to the aircraft? Nothing. THe airplane remains motionless
> because the aircraft wheels, which are rotating, do not impart any force to
> the aircraft to make it move in any direction (F=ma). To a bystander
> sitting on the taxi light at the end of the runway, the conveyor belt is
> moving left to right, the wheels are spinning in a counterclockwise
> direction, and the aircraft itself is motionless.

Actually, that isn't true. You don't need wheel bearing friction to
apply a horizontal force to the wheel at the contact point. The wheel
has inertia and accelerating the wheel will cause a reaction at the
contact point with the belt and the aircraft will begin to move along
the direction of the conveyor. This force will go to zero once the belt
reaches a steady-state speed, but the aircraft will continue to move
along with the belt.

Now if the wheels have no mass as well as no bearing friction... :-)

Matt

Morgans

February 7th 06, 11:53 PM

"Jon Woellhaf" > wrote

> As a tribute to CJ Campbell for starting this wonderful thread, I propose
> his official RAS and RAP call sign be "La Brea."

No, I go the opposite way, and say that his name be "damned for all time!"
<g>

It has been somewhat entertaining, I must admit, but at what cost?

"Oh, the humanity!" <:-)
--
Jim in NC

Tony

February 8th 06, 01:02 AM

Can anyone appreciate the number of electrons that have been very
disturbed because of this thread? One could ask oneself, if an electron
was moving to the left, while someone was pulling the wire to the right
at exactly the migration speed of the electron, would the thread be
extended. One could ask that, but that might start another thread.

Kevin

February 8th 06, 01:24 AM

Travis Marlatte wrote:
> The propulsion system is irrelevant as long as it is independant of the
> treadmill.

No, it doesn't even have to be "independant of the treadmill." Even
if the wheels of the plane were providing the thrust, all that would
happen is that the wheels would be spinning twice as fast by the time
the plane lifted off.

The key is in the wording of the question. The people here who have
gotten it wrong have misinterpreted the riddle to imply that it means
the aircraft is being held stationary. But that's not true. That's
not what it said. It simply said the belt is moving backwards at the
same speed the plane is moving forward. If the belt were moving
backwards fast enough to keep the plane motionless, then you've just
violated the fundamental rule of the riddle. Vbelt != -(Vplane) in
that case.

Picture it this way:

<--- Plane @ 100 mph
Treadmill @ 100 mph --->

Now, what is the TAS of that aircraft? 100 mph. I assure you, it
will fly.

The only braintwister is that one must realize that the WHEELS are
turning at 200 mph, rather than 100 mph.

Kevin.

darthpup

February 8th 06, 03:27 AM

Must consider the wind at time of experiment. If wind is same speed as
conveyor then real problem??

muff528

February 8th 06, 03:36 AM

"alexy" > wrote in message
...
> "muff528" > wrote:
>
> >Uh-Oh!!.....here we go again!
> >
> >I vote -- 120
> >Kinda like an escalator. You can still go up on a "down" escalator
> >if you run. The treadmill would have to be "set" at the 60 mph speed
> >so that the car's "input" would not affect it.
> But that would change the problem. In the problem as stated, you would
> have to have a device that determined the cars forward speed (NOT its
> wheel speed) and feed that input to the speed regulator on the
> treadmill.

OK -- I'll stand corrected on that part of my post. But the car's
speedometer will do just fine. The car's (and the belt's) speed relative to
the ground will be half of the indicated speed if we continue to meet the
"equal speed" condition.

The Flying Scotsman

February 8th 06, 03:50 AM

To : Michael Ware

Maybe you should stop replying, as all you give is negitive feedback to
other people. !!!!!

Travis Marlatte

February 8th 06, 04:44 AM

We are in agreement but you took my reply out of context. I was rephrasing
someone else's post who simply claimed that the propulsion system was
irrelevant (and therefore the plane wouldn't fly). In fact, the propulsion
system would be very relevent to this puzzle if it were relative to the
ground as in a wheel driven plane. As you have pointed out, it would then
need to spin the wheels at twice the speed necessary on a staionary runway.

I am beginning to see why some people struggle and even give up getting
their pilot's certificate. I can also begin to see why experienced pilots
crash when something very minor goes wrong in the air. The realities of
physics finally catches up with them.

--
-------------------------------
Travis
"Kevin" > wrote in message
...
> Travis Marlatte wrote:
>> The propulsion system is irrelevant as long as it is independant of the
>> treadmill.
>
> No, it doesn't even have to be "independant of the treadmill." Even
> if the wheels of the plane were providing the thrust, all that would
> happen is that the wheels would be spinning twice as fast by the time
> the plane lifted off.
>
> The key is in the wording of the question. The people here who have
> gotten it wrong have misinterpreted the riddle to imply that it means
> the aircraft is being held stationary. But that's not true. That's
> not what it said. It simply said the belt is moving backwards at the
> same speed the plane is moving forward. If the belt were moving
> backwards fast enough to keep the plane motionless, then you've just
> violated the fundamental rule of the riddle. Vbelt != -(Vplane) in
> that case.
>
> Picture it this way:
>
>
> <--- Plane @ 100 mph
> Treadmill @ 100 mph --->
>
> Now, what is the TAS of that aircraft? 100 mph. I assure you, it
> will fly.
>
> The only braintwister is that one must realize that the WHEELS are
> turning at 200 mph, rather than 100 mph.
>
> Kevin.

cjcampbell

February 8th 06, 04:52 AM

Tony wrote:
> If the car had an airspeed indicator it would, I agree, indicate 60. In
> the model I suggested the car is moving to the north at 60, the
> treadmill to the south at 60, and the speedometer will indicate 120.

If the car's airspeed indicator said 60 then the speedometer will
indicate 120. But the car would then need to expend the same energy to
accelerate to 60 as it would to accelerate to 120 on a stationary road.

An aircraft would need no additional power to accelerate to 60 on a
treadmill.

Travis Marlatte

February 8th 06, 04:55 AM

I'm not sure what negative feedback you are referring to. I just scanned
back through a few of his posts and they seemed pretty reasonable to me. He
also supports the most popular theory - that the plane will accelerate and
fly in spite of the treadmill spinning the tires twice as fast.

I agree.

--
-------------------------------
Travis
"The Flying Scotsman" > wrote in message
oups.com...
> To : Michael Ware
>
> Maybe you should stop replying, as all you give is negitive feedback to
> other people. !!!!!
>

Travis Marlatte

February 8th 06, 05:01 AM

I agree that it would not require much more additional power to overcome the
additional friction drag of wheels spinning at twice the normal speed but it
is not zero.

--
-------------------------------
Travis
"cjcampbell" > wrote in message
oups.com...
>
> Tony wrote:
>> If the car had an airspeed indicator it would, I agree, indicate 60. In
>> the model I suggested the car is moving to the north at 60, the
>> treadmill to the south at 60, and the speedometer will indicate 120.
>
> If the car's airspeed indicator said 60 then the speedometer will
> indicate 120. But the car would then need to expend the same energy to
> accelerate to 60 as it would to accelerate to 120 on a stationary road.
>
> An aircraft would need no additional power to accelerate to 60 on a
> treadmill.
>

alexy

February 8th 06, 05:25 AM

"cjcampbell" > wrote:

>
>Tony wrote:
>> If the car had an airspeed indicator it would, I agree, indicate 60. In
>> the model I suggested the car is moving to the north at 60, the
>> treadmill to the south at 60, and the speedometer will indicate 120.
>
>If the car's airspeed indicator said 60 then the speedometer will
>indicate 120. But the car would then need to expend the same energy to
>accelerate to 60 as it would to accelerate to 120 on a stationary road.
Nope. The same energy as it would take to accelerate to 60 on an
ordinary road, assuming that the mechanical system of the conveyor is
taking care of its motion. The work being done is to accelerate the
same mass to the same velocity in either case. If the car is providing
the energy to move the conveyer (reasonable, if its mass and friction
loads are less than those of the car), how much additional energy it
takes will depend on the conveyer.
>
>An aircraft would need no additional power to accelerate to 60 on a
>treadmill.
True. The same laws of physics apply to the car as well.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

[email protected]

February 8th 06, 05:38 AM

What an inane thread! I am amazed at how many people are arguing about
such a silly subject. Get a life people!

Dean

cjcampbell wrote:
> Saw this question on "The Straight Dope" and I thought it was amusing.
>
> http://www.straightdope.com/columns/060203.html
>
> The question goes like this:
>
> "An airplane on a runway sits on a conveyer belt that moves in the
> opposite direction at exactly the speed that the airplane is moving
> forward. Does the airplane take off?" (Assuming the tires hold out, of
> course.)
>
> Cecil Adams (world's smartest human being) says that it will take off
> normally.

cjcampbell

February 8th 06, 05:56 AM

darthpup wrote:
> Must consider the wind at time of experiment. If wind is same speed as
> conveyor then real problem??

Wind has nothing to do with it. The airplane will accelerate and move
down the treadmill just as it would a stationary runway. It cannot feel
the treadmill at all. The wheels can, but the wheels spin independently
of the thrust generated by an airplane.

Travis Marlatte

February 8th 06, 06:00 AM

Interesting question. Are you suggesting a wind machine that is capable of
creating a wind that matches the conveyor?

Let's start with no wind. The plane must achieve lift off speed relative to
the stable air mass to take off.

airspeed = Vlo
Conveyor moving = - Plane motion relative to ground
Conveyor moving = -xVlo (relative to ground)

airspeed = Vlo = Plane motion relative ground + headwind = xVlo + 0Vlo;
solve for x = 1
Wheels spinning = Plane motion - conveyor motion = xVlo - -x Vlo = 2 Vlo

Plane will liftoff at an airspeed that matches its groundspeed of Vlo. The
conveyor is moving backward also at Vlo. The wheels are spinning at twice
that speed.

Now with a headwind. The plane must still achieve lift off speed relative to
the air mass which is now an accelerating headwind.

airspeed = Vlo
Conveyor moving = - Plane motion relative to ground
Conveyor moving = -x Vlo (relative to ground)
Headwind = Conveyor moving
Headwind = - x Vlo (relative to ground)

airspeed = Vlo = Plane motion relative ground - headwind = x Vlo + x
Vlo; x = 1/2
Wheels spinning = Plane motion - conveyor motion = 1/2 Vlo - -1/2 Vlo =
Vlo

The plane will be able to lift off at 1/2 the ground speed than under normal
circumstances. The wheels are spinning at twice that speed which is just
Vlo. It would be feasible to construct both such a conveyor and the wind
machine.

Now with a tailwind. The plane must still achieve lift off speed relative to
the air mass which is now an accelerating tailwind.

airspeed = Vlo
Conveyor moving = - Plane motion relative to ground
Conveyor moving = -x Vlo
Tailwind = - Converyor moving
Tailwind = x Vlo (relative to ground)

airspeed = Vlo = Plane motion relative ground - Tailwind = x Vlo - x
Vlo; ******** No solution ********

With this simple formula, the plane will never take off but will continue to
accelerate (until the wheels disintegrate) since the thrust of the engine is
acting on the air mass which is accelerating as a tailwind. Very much the
dog chasing his tail.

Assumptions:
As with most things in life, we need a point of reference. Almost any
will do but I chose the ground upon which the conveyor belt is built and we
are standing watching. It is from this reference that the conveyor belt's
velocity (backwards) is derived.

I arbitrarily chose the positive sign of velocity in the direction of
the plane motion.

--
-------------------------------
Travis
"darthpup" > wrote in message
oups.com...
> Must consider the wind at time of experiment. If wind is same speed as
> conveyor then real problem??
>

Travis Marlatte

February 8th 06, 06:02 AM

I would but everytime I start to move toward the edge, this damn treadmill
pulls me back in...

--
-------------------------------
Travis

> wrote in message
oups.com...
> What an inane thread! I am amazed at how many people are arguing about
> such a silly subject. Get a life people!
>
> Dean
>
> cjcampbell wrote:
>> Saw this question on "The Straight Dope" and I thought it was amusing.
>>
>> http://www.straightdope.com/columns/060203.html
>>
>> The question goes like this:
>>
>> "An airplane on a runway sits on a conveyer belt that moves in the
>> opposite direction at exactly the speed that the airplane is moving
>> forward. Does the airplane take off?" (Assuming the tires hold out, of
>> course.)
>>
>> Cecil Adams (world's smartest human being) says that it will take off
>> normally.
>

cjcampbell

February 8th 06, 06:05 AM

alexy wrote:
> Thomas Borchert > wrote:
>
> >Alexy,
> >
> >> >The conveyor is programmed to move in such a way as to maintain the
> >> >aircraft at an airspeed of zero as measured at the pitot.
> >>
> >> Absolutely, if you CHANGED the problem, and restated it as above, then
> >> it wouldn't fly.
> >>
> >
> >Actually, you couldn't do that - which is another point the question
> >makes.
>
> True, from a practical standpoint. As far as the thought experiment
> goes, you could if the conveyer moved fast enough that the rolling
> friction of the tires plus the bearing friction of the wheels exactly
> offset the thrust of the plane's propulsion system.

The question, though, says that the wheels are built to take it. They
must have frictionless bearings. <g>

Travis Marlatte

February 8th 06, 06:20 AM

Accelerating the mass to the same velocity requires the same energy
regardless of what the surface is doing but wheel drag cannot be totally
ignored.

Why did you suggest that the car is providing the energy for the conveyor?
This would imply wheels with normal friction behavior but a frictionless
conveyor with a brake. The conveyor needs to be frictionless for you theory
that no additional energy is needed but a brake to keep it from being flung
backwards preventing forward motion of the car.

Since the same frictionless conveyor would get dragged along under an
accelerating plane, it seems like a strange experimental model.

A conveyor that is motor driven but controlled makes a more consistent
model.

I agree that very little additional thrust is necessary (either from the
wheels of a car or from the propeller of a plane) to counteract the
counter-moving conveyor. But some additional energy will be needed due to
the additional drag provided by the faster spinning wheels (both for the car
and the plane).

--
-------------------------------
Travis
"alexy" > wrote in message
...
> "cjcampbell" > wrote:
>
>>
>>Tony wrote:
>>> If the car had an airspeed indicator it would, I agree, indicate 60. In
>>> the model I suggested the car is moving to the north at 60, the
>>> treadmill to the south at 60, and the speedometer will indicate 120.
>>
>>If the car's airspeed indicator said 60 then the speedometer will
>>indicate 120. But the car would then need to expend the same energy to
>>accelerate to 60 as it would to accelerate to 120 on a stationary road.
> Nope. The same energy as it would take to accelerate to 60 on an
> ordinary road, assuming that the mechanical system of the conveyor is
> taking care of its motion. The work being done is to accelerate the
> same mass to the same velocity in either case. If the car is providing
> the energy to move the conveyer (reasonable, if its mass and friction
> loads are less than those of the car), how much additional energy it
> takes will depend on the conveyer.
>>
>>An aircraft would need no additional power to accelerate to 60 on a
>>treadmill.
> True. The same laws of physics apply to the car as well.
> --
> Alex -- Replace "nospam" with "mail" to reply by email. Checked
> infrequently.

Travis Marlatte

February 8th 06, 06:26 AM

He suggested a wind that is dynamic and tied to the speed of the conveyor
(and therefore also tied to the speed of the plane).

The plane can feel the conveyor - wheels are not frictionless. The friction
is not even insignificant. An amplified example would be trying to take off
in slushy snow. I think you will agree that the plane will feel that drag.

Back to the original puzzle - yes, the plane will accelerate and takeoff but
it will be a longer takeoff roll to overcome the increasing friction of the
wheels turning at twice the normal speed.

--
-------------------------------
Travis
"cjcampbell" > wrote in message
oups.com...
>
> darthpup wrote:
>> Must consider the wind at time of experiment. If wind is same speed as
>> conveyor then real problem??
>
> Wind has nothing to do with it. The airplane will accelerate and move
> down the treadmill just as it would a stationary runway. It cannot feel
> the treadmill at all. The wheels can, but the wheels spin independently
> of the thrust generated by an airplane.
>

Travis Marlatte

February 8th 06, 06:29 AM

It only says that they can take it. It doesn't say why. My plane lifts off
at 60mph. I'm sure the bearings and wheels would handle 120mph but they
aren't frictionless.

--
-------------------------------
Travis
"cjcampbell" > wrote in message
ups.com...
>
> alexy wrote:
>> Thomas Borchert > wrote:
>>
>> >Alexy,
>> >
>> >> >The conveyor is programmed to move in such a way as to maintain the
>> >> >aircraft at an airspeed of zero as measured at the pitot.
>> >>
>> >> Absolutely, if you CHANGED the problem, and restated it as above, then
>> >> it wouldn't fly.
>> >>
>> >
>> >Actually, you couldn't do that - which is another point the question
>> >makes.
>>
>> True, from a practical standpoint. As far as the thought experiment
>> goes, you could if the conveyer moved fast enough that the rolling
>> friction of the tires plus the bearing friction of the wheels exactly
>> offset the thrust of the plane's propulsion system.
>
> The question, though, says that the wheels are built to take it. They
> must have frictionless bearings. <g>
>

Montblack

February 8th 06, 06:42 AM

("Travis Marlatte" wrote)
>I would but everytime I start to move toward the edge, this damn treadmill
>pulls me back in...

I'm going to have nightmares about those darn monkeys in the original Wizard
of Oz books.

Montblack
Arrgh. Wheels!

Peter Duniho

February 8th 06, 06:46 AM

"cjcampbell" > wrote in message
oups.com...
> If the car's airspeed indicator said 60 then the speedometer will
> indicate 120. But the car would then need to expend the same energy to
> accelerate to 60 as it would to accelerate to 120 on a stationary road.

No, not really. Most of the horsepower of a car is used to counteract
aerodynamic drag, at that speed. Unless the treadmill (conveyor belt,
whatever) somehow gets the air above it to move rearward along with the
belt, the car barely has to use more power than it would accelerating to,
and cruising at, 60 mph on a regular road. It absolutely doesn't require
anywhere near as much power as it would to travel at 120 mph on a regular
road.

Pete

[email protected]

February 8th 06, 08:41 AM

>BUT...the AIRplane isn't in the AIR yet!

Ok, there is some friction involved.

Let's say that the airplane will take off in 1010 instead of 1000 feet,
ok?

Piero

Thomas Borchert

February 8th 06, 10:00 AM

Peter,

> I find this outcome hilarious.
>

I agree. Also, I am always amused at how hard people here find it to
just say "Oops, I was wrong, sorry."

--
Thomas Borchert (EDDH)

Thomas Borchert

February 8th 06, 10:00 AM

Greg,

> If you have a motoroized conveyor which
> always reduces the plane's forward movement to zero,
>

Nowhere does it say that in the question.

--
Thomas Borchert (EDDH)

Tony

February 8th 06, 01:02 PM

cjcampbell wrote

If the car's airspeed indicator said 60 then the speedometer will
indicate 120. But the car would then need to expend the same energy to
accelerate to 60 as it would to accelerate to 120 on a stationary road.

An aircraft would need no additional power to accelerate to 60 on a
treadmill.

To which I'll note that you're on the right track, but remember kinetic
energy varies as velocity squared: it takes 4 times the energy (at non
relativistic velocities) to get to 120 as it does to 60: actually a lot
more than that because windage losses and the like are not linear,
either.

alexy

February 8th 06, 02:02 PM

"Travis Marlatte" > wrote:

>Accelerating the mass to the same velocity requires the same energy
>regardless of what the surface is doing but wheel drag cannot be totally
>ignored.

True. Another factor that I ignored as being insignificant (and this
applies to the plane or car) is the extra energy it takes to provide
the angular acceleration of the wheel to higher rotational velocities.
E.g, at speed, one car includes 4 flywheels spinning with rim
velocities of 60mph, while the other car has 4 flywheels spinning with
rim velocities of 120mph. This additional energy need will cause
slower acceleration if the same power is available.

>Why did you suggest that the car is providing the energy for the conveyor?
We've had one recent poster who apparently thought that the power
source for moving the conveyer was key to the problem. I'm not
suggesting THAT the car was providing the energy, but only examining
what IF it did.

>This would imply wheels with normal friction behavior but a frictionless
>conveyor with a brake.
Not needed. As long as the conveyer has less friction and mass than
the car, and has a brake to control its speed, the car can power it.
And how much power that absorbs will determine how much the car's
acceleration is lowed down. At the limit, it is CJ's speculation of
the car's acceleration to 120 (on the speedometer) matching a regular
road acceleration to 120.

>A conveyor that is motor driven but controlled makes a more consistent
>model.
Agreed.

>I agree that very little additional thrust is necessary (either from the
>wheels of a car or from the propeller of a plane) to counteract the
>counter-moving conveyor. But some additional energy will be needed due to
>the additional drag provided by the faster spinning wheels (both for the car
>and the plane).
And to accelerate the wheels to a higher angular velocity, assuming
they are not massless.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

alexy

February 8th 06, 02:05 PM

"Tony" > wrote:

>
>cjcampbell wrote
>
>If the car's airspeed indicator said 60 then the speedometer will
>indicate 120. But the car would then need to expend the same energy to
>accelerate to 60 as it would to accelerate to 120 on a stationary road.
>
>
>An aircraft would need no additional power to accelerate to 60 on a
>treadmill.
>
>To which I'll note that you're on the right track,
Not really. Except for minor factors (having to do with wheel friction
and mass), getting a car to 60 (ground speed) on the treadmill takes
no more energy than getting it to 60 on a regular road.
> but remember kinetic
>energy varies as velocity squared: it takes 4 times the energy (at non
>relativistic velocities) to get to 120 as it does to 60: actually a lot
>more than that because windage losses and the like are not linear,
>either.

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Gary Drescher

February 8th 06, 04:25 PM

> wrote in message
oups.com...
> What an inane thread! I am amazed at how many people are arguing about
> such a silly subject.

There's nothing wrong with being interested in a brain-teaser.

> Get a life people!

Oddly, your own busy life leaves you time not only to read a thread you're
not even interested in, but also to post here announcing your lack of
interest.

--Gary

Flyingmonk

February 8th 06, 05:51 PM

Gary wrote:
>> What an inane thread! I am amazed at how many people are arguing about
>> such a silly subject.
>
>There's nothing wrong with being interested in a brain-teaser.
>
>> Get a life people!
>
>Oddly, your own busy life leaves you time not only to read a thread you're
>not even interested in, but also to post here announcing your lack of
>interest.

It is just another way for Dean to tell us that his life is much more
fulfilling than ours Gary. lol

The Monk

Jim Macklin

February 8th 06, 07:08 PM

An idea that popped into my mind...
ywo subject question lines...
1. Can a plane on a treadmill take off?

2. Can a plane take off from a treadmill?

In the first instance, the airplane is attached to the
treadmill and would have to lift the weight and shape of the
treadmill. In the second, the airplane would behave
differntly depending on whether the treadmill was powered or
just a belt on rollers.
a. If just a belt on rollers, the engine thrust would drive
the airplane forward until it was not on the treadmill
anymore, thus it would have air movement over the wings and
would take-off. If the brakes were not locked, either or
both the tires and treadmill would "roll." If the brtakes
were set, the treadmill would roll and the airplane would
likely come to a stop when it departed the treadmill unless
it was alrady at flying speed.
b. If the treadmill was powered [and everything was timed
in sync] the belt would be accelerating rearward and the
engine thrust would be pulling forward at the same rate,
thus the airframe mounted wigs would have near zero airspeed
and lift and would not fly.
b1. If the treadmill was powered and ran forward, it would
act as a catapult and launch the airplane or at least
assist.

Hey, let's build a really big treadmill and try several
different airplane types, such as a Helio, a Maule, a Cessna
Caravan, and a C5 [a really big treadmill] and see what
happens.

--
The people think the Constitution protects their rights;
But government sees it as an obstacle to be overcome.
some support
http://www.usdoj.gov/olc/secondamendment2.htm
See http://www.fija.org/ more about your rights and duties.

"Flyingmonk" > wrote in message
oups.com...
| Gary wrote:
| >> What an inane thread! I am amazed at how many people
are arguing about
| >> such a silly subject.
| >
| >There's nothing wrong with being interested in a
brain-teaser.
| >
| >> Get a life people!
| >
| >Oddly, your own busy life leaves you time not only to
read a thread you're
| >not even interested in, but also to post here announcing
your lack of
| >interest.
|
| It is just another way for Dean to tell us that his life
is much more
| fulfilling than ours Gary. lol
|
| The Monk
|

alexy

February 8th 06, 08:01 PM

"Jim Macklin" > wrote:

>b. If the treadmill was powered [and everything was timed
>in sync] the belt would be accelerating rearward and the
>engine thrust would be pulling forward at the same rate,
>thus the airframe mounted wigs would have near zero airspeed
>and lift and would not fly.

Just to "set the hook" here, are you saying that it will be possible
to have the conveyer move backwards fast enough that the plane remains
still, even under full power, and with no brakes on?
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Peter Duniho

February 8th 06, 08:08 PM

"alexy" > wrote in message
...
> Just to "set the hook" here, are you saying that it will be possible
> to have the conveyer move backwards fast enough that the plane remains
> still, even under full power, and with no brakes on?

I thought you had already established that it would be possible, and that
the treadmill speed is "somewhat below the speed of light"? You didn't
appear to solve the "materials integrity" aspect of the problem, but that
seems like a minor quibble. :)

Pete

alexy

February 8th 06, 08:18 PM

"Peter Duniho" > wrote:

>"alexy" > wrote in message
...
>> Just to "set the hook" here, are you saying that it will be possible
>> to have the conveyer move backwards fast enough that the plane remains
>> still, even under full power, and with no brakes on?
>
>I thought you had already established that it would be possible, and that
>the treadmill speed is "somewhat below the speed of light"? You didn't
>appear to solve the "materials integrity" aspect of the problem, but that
>seems like a minor quibble. :)
>

No fair; that's the next question, not to be asked out of order!! ;-)

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Jon Woellhaf

February 8th 06, 08:19 PM

Another pilot slips into the tar pit.

"alexy" > wrote in message
...
> "Jim Macklin" > wrote:
>
>
>>b. If the treadmill was powered [and everything was timed
>>in sync] the belt would be accelerating rearward and the
>>engine thrust would be pulling forward at the same rate,
>>thus the airframe mounted wigs would have near zero airspeed
>>and lift and would not fly.
>
> Just to "set the hook" here, are you saying that it will be possible
> to have the conveyer move backwards fast enough that the plane remains
> still, even under full power, and with no brakes on?
> --
> Alex -- Replace "nospam" with "mail" to reply by email. Checked
> infrequently.