Can a Plane on a Treadmill Take Off?

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.

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

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

"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.

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!

"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

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

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

"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.

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!

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