Airplane on a treadmill

[Electric Monk]

Poll question: Airplane on a treadmill

A plane is standing on a large treadmill or conveyor belt. The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the plane take off?



Spoilers: http://www.airplaneonatreadmill.com/

[anarch]

1. other - depends on the wind

[uppityperson]

2. Ground speed means nothing, air speed is what gets it off the ground.

[cherokeeprogressive]

7. It is actually "lift" generated by the wing that gets it off of the ground.

Some of the largest planes in the world have incredibly slow takeoff speeds because of the amazing amount of lift their wings generate.

[uppityperson]

28. True, I was just typing fast.

[trof]

31. 2 and 7 are correct. (airline pilot for 30+ years)

Although it's not necessarily true that
"Some of the largest planes in the world have incredibly slow takeoff speeds because of the amazing amount of lift their wings generate."

The heavier (larger) birds generally need higher take-off speeds.

You could get a 747 up to 300 mph on a treadmill and it still wouldn't fly until the AIR-speed (air moving over the wings) got to around 130 knots.

[givemebackmycountry]

3. Other...

The plane and the treadmill are hit by birds and both crash into the Hudson River.

[tridim]

4. Fuck off

jk :)

[IDemo]

5. Ambiguous

Not specified is whether "plane speed" means ground speed, air speed, or even "conveyor speed" if the conveyor is itself in motion.

[mike_c]

6. lift is not generated by the wheels turning....

It depends upon laminar flow velocities across the airfoil surfaces. Assuming a fixed wing aircraft, if the plane is stationary any lift would be from the wind, and would be the same as for a plane sitting on the runway with its engines off. Otherwise, no.

[tridim]

9. My RC planes can take off at zero ground speed.

Because the prop, motor and wing are massive relative to actual airplanes.

I can hold the plane in my hand, gun the engine and drop it. It takes right off.

[mike_c]

11. as you say...

...that's because the prop moves enough air across the airfoils to create "static lift." In that case, the condition of the "treadmill" becomes meaningless. I don't think it produces enough lift to fly aircraft of most commercial designs though. If it did, we could save a lot of time on the runway!

[tridim]

13. Right, but the question doesn't say anything about which type of aircraft to use.

I really hate the question BTW, it's even more poorly posed than the "viral" math question. It's meant just to burn bandwidth and make people fight with each other.

[Electric Monk]

14. As you may have guessed, reviving this classic in a poll was inspired by that other one

http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=439&topic_id=982937&mesg_id=983812

[madinmaryland]

32. Uhhmmm! Isn't that the point of DU. Someone posts something and everyone fights

over it??

[tridim]

8. "Wheel speed" was the wording in the original question, not "plane speed"

[krispos42]

10. Since the wheels of the plane are unpowered...

...and can free-wheel at any reasonable speed (okay, if the treadmill is moving at 300mph, a tire might blow and crash the plane), the the treadmill-induced drag via the wheels will be minimal.

The propeller will push air backwards, causing a reaction force forwards irrespective of how fast or slow the wheels are spinning. It should race down the treadmill and take off.

So I'll go vote for that, then check the link.

[Electric Monk]

15. That is my answer as well. It's really that simple, imho

though some people seem to enjoy making it much more complicated than it needs to be.

[jberryhill]

29. That's the main thing - you can't hold the plane stationary on the treadmill anyway

But I don't think people get that from the way the problem is posed to make you think the treadmill is not moving.

A better way to word it is - "An airplane is flying one foot above a treadmill that is going 500 miles in the opposite direction. Does it matter? No. And it doesn't matter if the wheels touch the runway either."

[On the Road]

12. Is This Your Way of Asking for a Divorce?

[backscatter712]

16. Mythbusters actually tested this myth. Yes, the plane can take off.

I wrote this without clicking the spoilers. Bear in mind that the plane, unlike a car, doesn't derive its forward motion by applying torque to its wheels, but by spinning a propeller and creating forward thrust by spinning blades through the air. The spinning speed of the landing gear wheels, and the speed of the conveyor becomes irrelevant - the speed of the aircraft is determined by thrust from the propeller and drag from air friction.

And yes, the Mythbusters tested this, and yes, the plane took off.

[Electric Monk]

25. and yet, 45% of DUers (so far) say No

nt

[hifiguy]

27. You beat me to it

Science sez the plane will take off and for just the reasons you (and Jamie and Adam) set forth.

[tkmorris]

17. The plane will move

The plane will move exactly the same as if it were on a fixed runway. The wheels will turn faster to reflect the added speed of the treadmill but the planes movement is not dependent upon the wheels turning speed nor the movement of the ground beneath it. Planes move due to their interaction with the air around them in some fashion (various means to accomplish it but the point remains). The treadmill underneath becomes irrelevant; it merely forces the wheels to spin faster than they otherwise would as the plane itself speeds merrily along.

In my opinion. Someone tell me why I'm an idiot :)

[joshcryer]

20. Correct, the driving force for a plane is the air, not friction with the ground.

A plane will take off even if it's sitting on a perfectly frictionless surface.

[joshcryer]

18. Oh my god. DU. Seriously. This is the second poll...

...c'mon!

[tkmorris]

19. Problem?

[joshcryer]

21. This and the math poll...

...is really disappointing. :rofl:

[Electric Monk]

23. This was inspired by the math poll, and, to be honest, I'm even more disappointed in the answers

to this one. So far it's 42% yes, 48% no, and 9% other.

(I ate the other percentage point)

[joshcryer]

24. Yeah, I refused to participate in that post, but this one was at least funny.

Didn't mean to come off wrong at all.

(BTW it's tied as I post this.)

[moondust]

22. Is it an Osprey?

:)

[Gabi Hayes]

26. nevermind

http://mythbustersresults.com/episode97

[Canuckistanian]

30. Not unless the conveyor belt moves the whole of the Earth's atmosphere with it

And what happens when the wheels lose traction with the belt?

[ReggieVeggie]

33. I'd have to see that Mythbusters ep

I don't see how the plane could take off if it is stationary. You need lift and you don't get lift without airflow.

[Electric Monk]

34. Re-read the OP. It does not say the plane stays stationary.

It says "The plane moves in one direction, while the conveyor moves in the opposite direction."

[ReggieVeggie]

35. oh, so its a trick question

because if the plane remains stationary it will not take off

But I thought the implication in the OP was that the plane speed was being synched with the conveyor speed. That would mean the plane wasn't moving relative to the ground.

[Incitatus]

36. This is the episode

The conveyor belt does not seem to be holding the plane in place. The plane moves along the ground before it takes off. In their experiment, they just accelerated in opposite directions.

http://www.youtube.com/watch?v=YORCk1BN7QY&feature=related