Airplanes and Conveyor Belts - Mythbusters

[ContestID67]

Question: Can a conventional powered airplane take off from a conveyor
belt which is moving at the same speed but in an opposite direction?

I was surprised at people's range and passion of answers when I asked
this of my glider club. People were absolutely sure it wouldn't work
or it would work. I guess that goes to show that performing this as a
thought experiment is not easy even for pilots.

Please make your own guess before you watch these Youtube videos (in
order) for the final answer.

http://youtube.com/watch?v=KSBFQOfas60 < Start
http://youtube.com/watch?v=S377HwOthjo
http://youtube.com/watch?v=0ul_5DtMLhc < Finish

What I am really surprise about is that the "test" pilot in this video
of the airplane had the wrong answer before his attempt and was very
surprised afterwards. Well, maybe not surprised, he was a light sport
pilot after all. Personally, I knew the correct answer from the get-
go. Hint: The answer is in the wheels.

- John

[Werner Schmidt]

Hallo ContestID67, Du schriebst am 01.05.2008 07:18

> Question: Can a conventional powered airplane take off from a conveyor
> belt which is moving at the same speed but in an opposite direction?

rather simple question.

Two possibilities:

1.) If the conveyor belt is already moving at the beginning of the
experiment (driving the airplane backwards), it just takes more time for
the airplane to accelerate and reach its appropriate airspeed for
takeoff. The wheels just turn faster than "usually" (take-off speed plus
conveyor belt speed).

2.) If both begin to accelerate at the same time, it makes no
significant difference to a usual start. The rolling drag of the
undercarriage wheels pulls the airplane a *little* backwards, but this
effect is negligible. - The wheels just turn faster (as above).

The higher rotation speed of the wheels *could* be a problem, if
bearings become too hot and lock.

Regards
Werner

[Phil Jeffery]

Seeing as it's not soarable today or only briefly between showers, here's my
guess prior to looking at the videos:--

Yes, with a minor reduction in acceleration due to the extra friction from
the wheels needing to rotate faster and possibly some sort of reduction in
actual ground speed required due to the air tending to be dragged towards
the aircraft by the moving belt. A bit like an inverted conventional ground
effect.

Now I'll look at the videos and then try to get out more.


"ContestID67" > wrote in message
...
> Question: Can a conventional powered airplane take off from a conveyor
> belt which is moving at the same speed but in an opposite direction?
>
> I was surprised at people's range and passion of answers when I asked
> this of my glider club. People were absolutely sure it wouldn't work
> or it would work. I guess that goes to show that performing this as a
> thought experiment is not easy even for pilots.
>
> Please make your own guess before you watch these Youtube videos (in
> order) for the final answer.
>
> http://youtube.com/watch?v=KSBFQOfas60 < Start
> http://youtube.com/watch?v=S377HwOthjo
> http://youtube.com/watch?v=0ul_5DtMLhc < Finish
>
> What I am really surprise about is that the "test" pilot in this video
> of the airplane had the wrong answer before his attempt and was very
> surprised afterwards. Well, maybe not surprised, he was a light sport
> pilot after all. Personally, I knew the correct answer from the get-
> go. Hint: The answer is in the wheels.
>
> - John
>

[toad]

On May 1, 1:18 am, ContestID67 > wrote:
> Question: Can a conventional powered airplane take off from a conveyor
> belt which is moving at the same speed but in an opposite direction?
>
> I was surprised at people's range and passion of answers when I asked
> this of my glider club. People were absolutely sure it wouldn't work
> or it would work. I guess that goes to show that performing this as a
> thought experiment is not easy even for pilots.
>
> Please make your own guess before you watch these Youtube videos (in
> order) for the final answer.
>
> http://youtube.com/watch?v=KSBFQOfas60 < Starthttp://youtube.com/watch?v=S377HwOthjohttp://youtube.com/watch?v=0ul_5DtMLhc< Finish
>
> What I am really surprise about is that the "test" pilot in this video
> of the airplane had the wrong answer before his attempt and was very
> surprised afterwards. Well, maybe not surprised, he was a light sport
> pilot after all. Personally, I knew the correct answer from the get-
> go. Hint: The answer is in the wheels.
>
> - John

Pilots (well most of them) do not understand aerodynamics. This is
proven during every hangar flying session.

Todd Smith
3S

[[email protected]]

>
> > Question: Can a conventional powered airplane take off from a conveyor
> > belt which is moving at the same speed but in an opposite direction?
>
> > I was surprised at people's range and passion of answers when I asked
> > this of my glider club. * People were absolutely sure it wouldn't work
> > or it would work. *I guess that goes to show that performing this as a
> > thought experiment is not easy even for pilots.
>
> > Please make your own guess before you watch these Youtube videos (in
> > order) for the final answer.
>
> >http://youtube.com/watch?v=KSBFQOfas60*< Start
> >http://youtube.com/watch?v=S377HwOthjo
> >http://youtube.com/watch?v=0ul_5DtMLhc< Finish
>
> > What I am really surprise about is that the "test" pilot in this video
> > of the airplane had the wrong answer before his attempt and was very
> > surprised afterwards. *Well, maybe not surprised, he was a light sport
> > pilot after all. *Personally, I knew the correct answer from the get-
> > go. *Hint: The answer is in the wheels.
>
> > - John

Relativity!!

The misunderstanding probably derives from the fact that the question
is inadequate in not specifying whether the plane is to be regarded as
moving as the same speed (but opposite direction) as the conveyor
relative to the belt or relative to the ground/nil wind airmass. The
motor vehicles in the videos are moving oppositely at the same speed
relative to the belt - i.e. stationary relative to the ground/
airmass. The propeller aeroplane is moving oppositely relative to the
ground/airmass and so obviously should have no great difficulty in
taking off - it is, however, at take off, moving at about twice the
speed relative to the belt as the belt is relative to the ground. The
fact that the freewheel/propeller derived thrust characteristics of an
aeroplane allow it to achieve take does not negate the fact that at a
lower power setting it could be set up such that it remained
stationary relative to the ground (like the cars) in which case it
would not take off - and this is what many people would probably
assume was meant by the question.

The question not logically valid as it implies two possible but
different hypotheses.

John Galloway

[Michael Ash]

Werner Schmidt > wrote:
> 2.) If both begin to accelerate at the same time, it makes no
> significant difference to a usual start. The rolling drag of the
> undercarriage wheels pulls the airplane a *little* backwards, but this
> effect is negligible. - The wheels just turn faster (as above).

In standard Newtonian dynamics, rubbing (or rolling) friction is
independent of speed, so long as you're moving at all. So the extra speed
of the wheels is no penalty at all, barring problems with extra heat as
you mentioned.

--
Michael Ash
Rogue Amoeba Software

[Kloudy via AviationKB.com]

ContestID67 wrote:
>Question: Can a conventional powered airplane take off from a conveyor
>belt which is moving at the same speed but in an opposite direction?

Absolutely.

The propulsion of the aircraft is provided by the prop and not the wheels.
If it were the other way around then the ship will remain stationary in
relation to the ground.

--
Message posted via http://www.aviationkb.com

[Werner Schmidt]

Hallo Michael Ash, Du schriebst am 01.05.2008 17:42

> Werner Schmidt > wrote:
>> 2.) If both begin to accelerate at the same time, it makes no
>> significant difference to a usual start. The rolling drag of the
>> undercarriage wheels pulls the airplane a *little* backwards, but this
>> effect is negligible. - The wheels just turn faster (as above).
>
> In standard Newtonian dynamics, rubbing (or rolling) friction is
> independent of speed, so long as you're moving at all. So the extra speed
> of the wheels is no penalty at all, barring problems with extra heat as
> you mentioned.

But same friction at higher speed releases more energy (=>heat).

Why does a spaceship need a heat shield and a ASK13 doesn't? And special
gearboxes do need cooling (air may suffice). Bearings become hot if
rotation speed is high and cooling not adequate. A too hot bearing may jam.

Regards
Werner

[noel.wade]

Ugh, this old topic again? :-P

I understand why you say "the answer is in the wheels". But that's
exactly the wrong attitude to take, and it illustrates why so many
pilots (IMHO) don't fly well.

The answer is in the wing!!! :-)

The answer is ALWAYS *the wing* when it comes to flying!
(OK, some smartass will point out that its sometimes *the tail* - but
that's really just another wing!)

If more pilots could think about their aircraft in terms of "what is
the wing doing right now" or "what is the wing __feeling__ right now",
there would be a lot more pilots who were a lot more skilled (and
possibly a lot fewer accidents!)

Take care,

--Noel

[Jim Logajan]

"noel.wade" > wrote:
> I understand why you say "the answer is in the wheels". But that's
> exactly the wrong attitude to take, and it illustrates why so many
> pilots (IMHO) don't fly well.
>
> The answer is in the wing!!! :-)

Maybe it would help by simply saying "The answer is in the air."

[tommytoyz]

> Question: Can a conventional powered airplane take off from a conveyor
> belt which is moving at the same speed but in an opposite direction?

You asked the question wrong. In the Video the question is:

Can a conventional powered airplane take off from a conveyor
belt which is moving at the take off speed of the airplane in the
opposite direction?

[[email protected]]

On 1 May, 20:31, tommytoyz > wrote:
> > Question: Can a conventional powered airplane take off from a conveyor
> > belt which is moving at the same speed but in an opposite direction?
>
> You asked the question wrong. In the Video the question is:
>
> Can a conventional powered airplane take off from a conveyor
> belt which is moving at the take off speed of the airplane in the
> opposite direction?

Exactly.

[Michael Ash]

Werner Schmidt > wrote:
> Hallo Michael Ash, Du schriebst am 01.05.2008 17:42
>
>> Werner Schmidt > wrote:
>>> 2.) If both begin to accelerate at the same time, it makes no
>>> significant difference to a usual start. The rolling drag of the
>>> undercarriage wheels pulls the airplane a *little* backwards, but this
>>> effect is negligible. - The wheels just turn faster (as above).
>>
>> In standard Newtonian dynamics, rubbing (or rolling) friction is
>> independent of speed, so long as you're moving at all. So the extra speed
>> of the wheels is no penalty at all, barring problems with extra heat as
>> you mentioned.
>
> But same friction at higher speed releases more energy (=>heat).

Right, that's why I mentioned extra heat.

> Why does a spaceship need a heat shield and a ASK13 doesn't? And special
> gearboxes do need cooling (air may suffice). Bearings become hot if
> rotation speed is high and cooling not adequate. A too hot bearing may jam.

The comparison with the spaceship isn't quite apt. Aerodynamic friction
increases with the square of the speed so the total rate of generated heat
increases with the cube of the speed. Rolling friction is constant so the
total rate increases linearly. In any case, if the extra heat is enough to
cause problems then that would certainly make a difference, but I think
the original question more or less assumes that it's not a factor.

--
Michael Ash
Rogue Amoeba Software

[Werner Schmidt]

Hello Michael Ash, you wrote at 02.05.2008 05:12

> Werner Schmidt > wrote:
>[...]
>> Why does a spaceship need a heat shield and a ASK13 doesn't? And special
>> gearboxes do need cooling (air may suffice). Bearings become hot if
>> rotation speed is high and cooling not adequate. A too hot bearing may jam.
>
> The comparison with the spaceship isn't quite apt. Aerodynamic friction
> increases with the square of the speed so the total rate of generated heat
> increases with the cube of the speed. Rolling friction is constant so the
> total rate increases linearly.

Correct.

> In any case, if the extra heat is enough to
> cause problems then that would certainly make a difference, but I think
> the original question more or less assumes that it's not a factor.

I just wanted to mention that a jamming wheel bearing (caused by extra
heat due to higher rotation speed) might cause an accident.

Regards
Werner

[Kloudy via AviationKB.com]

Jim Logajan wrote:
>>
>> The answer is in the wing!!! :-)
>
>Maybe it would help by simply saying "The answer is in the air."


The answer


My friend


is blowin' over the wing

--
Message posted via AviationKB.com
http://www.aviationkb.com/Uwe/Forums.aspx/soaring/200805/1

[[email protected]]

On May 1, 12:31*pm, tommytoyz > wrote:
> > Question: Can a conventional powered airplane take off from a conveyor
> > belt which is moving at the same speed but in an opposite direction?
>
> You asked the question wrong. In the Video the question is:
>
> Can a conventional powered airplane take off from a conveyor
> belt which is moving at the take off speed of the airplane in the
> opposite direction?

The wheel steering will get a bit touchy!