Treadmill redux

[Chairboy]

On the AOPA forums, the airplane vs. treadmill debate has flared anew.  Mythbusters _is_ doing an episode where they'll test this, I've seen a teaser video.  A canvas tarp a few hundred feet long will be rolled out on the runway and be towed by a truck at 40-50mph while the plane throttles up.  Obviously, the treadmill is a red herring and has no real bearing on whether the plane takes off, but it's disheartening to see so many folks over there who are pilots getting this one wrong.

Unless...   are there people here who think the plane on a treadmill won't take off?  That'd be fun.

[Chairboy]

For any AOPA'ers, here's the most recent thread:

http://forums.aopa.org/showthread.php?t=37492

[AKIron]

Originally posted by Chairboy
On the AOPA forums, the airplane vs. treadmill debate has flared anew.  Mythbusters _is_ doing an episode where they'll test this, I've seen a teaser video.  A canvas tarp a few hundred feet long will be rolled out on the runway and be towed by a truck at 40-50mph while the plane throttles up.  Obviously, the treadmill is a red herring and has no real bearing on whether the plane takes off, but it's disheartening to see so many folks over there who are pilots getting this one wrong.

Unless...   are there people here who think the plane on a treadmill won't take off?  That'd be fun.

Depends on how fast the treadmill will go of course. We've been there and done that more than a few times.


Reread, of course under the conditions given the plane will takeoff easily, but not before hitting the end of the tarp I bet.

[Chairboy]

It...  really doesn't matter how fast the treadmill goes.  The friction of the bearings in the wheels is insignificant compared to the thrust of the propeller.

[eskimo2]

Like I said in the other thread, give the treadmill unlimited speed and strength and the wheels and bearing unlimited strength and the treadmill will keep the plane in place.  It will have nothing to do with bearing friction and everything to do with loading kinetic rotational energy into the wheels at a rate equal to the thrust output of the motor.  

Mythbusters will prove that a plane can take off if the treadmill matches the plane’s speed.  

A treadmill that matches the plane’s wheel’s speed, however, would be impossible to build or test because it would need to achieve speeds beyond what could be built by man.

[AKIron]

Originally posted by Chairboy
It...  really doesn't matter how fast the treadmill goes.  The friction of the bearings in the wheels is insignificant compared to the thrust of the propeller.

Easy enough for you to test since you have your own plane. Next time you prepare to take just hold your brakes as hard as you can and see if you can take off with those tires not rolling but skidding down the runway.

[Chairboy]

Why in the world would you think that the bearing friction of having wheels free spin twice as fast would be as much as applying full brakes?

[Chairboy]

AkIron, hope this helps ya visualize the physics, I may be using unclear language:
http://www.straightdope.com/columns/060203.html

and then the following when you're ready to leap up from your chair in fury:
http://www.straightdope.com/columns/060303.html

[AKIron]

Originally posted by Chairboy
Why in the world would you think that the bearing friction of having wheels free spin twice as fast would be as much as applying full brakes?

Phrased that way of course they would not. The debate long ago though led to the question as to what the belt was actually matching in speed. As the question was then phrased and possibly on the board you are now visiting it meant that the belt would spin ever faster attempting to match the speed of wheel. So long as the plane was moving even slightly forward the belt would have to accelerate to infinite speed which would of course freeze the wheel bearings long before a black hole would be created.

[john9001]

Originally posted by AKIron
Easy enough for you to test since you have your own plane. Next time you prepare to take just hold your brakes as hard as you can and see if you can take off with those tires not rolling but skidding down the runway.

the runway is covered with ice.

[AKIron]

Originally posted by john9001
the runway is covered with ice.

I play the global warming card and melt your puny runway ice.

[Gunslinger]

I don't get it.  lift is achieved by air flow over the wings.......the wheels have nothing to do with it

[Chairboy]

Originally posted by Gunslinger
I don't get it.  lift is achieved by air flow over the wings.......the wheels have nothing to do with it

Bingo.

[Gunslinger]

Originally posted by Chairboy
Bingo.

so what's the big deal again?

[AKIron]

There's two ways to interpret the wheel/belt thing.

1. Does the surface of the belt match the airspeed of the plane but in the opposite direction

or

2. Does the belt surface match the speed of the surface of the spinning tire but in the opposite direction

If #1, the plane takes off easily. If #2, and the belt isn't constrained by realistic mechanical properties but the tires are then the tire will quickly blow due to speed of the belt.