The "Plane on a Treadmill" Question

[Griff]

Originally Posted by MaggieL

..not currently flyable.

... as it was mistakenly parked on a treadmill.

[MaggieL]

I'm still trying to envision a treadmill that applies as much force to an aircraft through friction at the wheel bearings as the engines do grabbing at the air.

Without setting fire to the wheelbearings.

Especially interesting in the case of a rocketplane like the Bell X-1, which not many people know was capable of a runway takeoff.

I wonder how fast the treadmill would have to go...:-)

[MaggieL]

Originally Posted by Griff

... as it was mistakenly parked on a treadmill.

Nah, it was just left out in the weather for like forever.

[Happy Monkey]

Originally Posted by lumberjim

i read the question....thought about it..decided that the rotation of the wheels nullified the movement of the treadmill..then i decided to wait to see what Happy Monkey would say, and knew i was right when he agreed.

Heh, thanks.

[Happy Monkey]

Originally Posted by Flint

There is no "right" answer.

The right answer is the one that requires no magic treadmill. The plane takes off.

[skysidhe]

Originally Posted by hideouse

You are a good sport Sky.

[Torrere]

I think I'm getting a clearer picture of the car / plane confusion. The wheels on a car rotate, grab the road (with friction), and 'push the road back'. Since the road doesn't move, the car moves forward instead. So, you could change the speed of the car relative to the earth by moving the road like a treadmill.

With a plane, however, the the only purpose of the wheels is to keep the plane above the ground and reduce friction. The plane pushes itself forward by pushing the air back (hence it is easier to take off in a headwind).

Probably the only way to keep the plane from flying would be to immerse it in a tailwind that matched the plane's velocity, or to lash it down and prevent it from rolling.

I also think that people might be confusing velocity and force. Only force can keep the plane from moving, and the treadmill cannot apply enough force.

[lookout123]

If you replace the word "force" with "Chuck Norris" you may be on to something.

[xoxoxoBruce]

Originally Posted by lumberjim

rotating 200 mph, yes. moving 100 mph as the plane carries them

Oh, gotcha. Yes, of course.

That channel wing would be very difficult and expensive to build, although with composites it might be feasible. But, like Maggie said, heavy.

[tw]

Originally Posted by Torrere

With a plane, however, the the only purpose of the wheels is to keep the plane above the ground and reduce friction. The plane pushes itself forward by pushing the air back.

Probably the only way to keep the plane from flying would be to immerse it in a tailwind that matched the plane's velocity,

As was posted previously:

Originally Posted by tw

So that velocity of a plane is totally irrelevant to ground. Wheels will spin as slow or as fast as necessary so that velocity of the runway and velocity of plane stay totally independent.

Posting by Torrere is that airplane wheels make that plane 'separate from' (independent of) both runway and treadmill. Treadmill only affects how fast those wheels spin. As MaggieL posted, otherwise those wheels would burn up; function instead like brakes.

Meanwhile, tailwind does not change the problem. Remember the two items that a force - the engine - applies between. Engine force pushes between airplane and air. Tailwind or headwind - still that engine applies same force causing the airplane to have a same velocity relative to air (also called airspeed). Still that same F=ma equation applies. No matter how fast the tailwind is blowing, F=ma makes the plane move a defined speed faster than air because same force (F) is remains between air and the airplane.

Airplane speed relative to runway is speed of airplane created by its engine plus speed of air created by tailwind.

[xoxoxoBruce]

Headwind/tailwind changes the airspeed by the velocity of the wind. A tailwind will make it harder for the plane to reach the airspeed necessary to lift off. And a headwind will make it easier.

[Torrere]

It only took us 18 pages, but lookout123 has solved the problem. The giant supernatural treadmill is irrelevant; only Chuck Norris prevent the airplane's movement. Since the problem did not specify that Chuck Norris was holding it back, the airplane flies.

[Dancing Mango]

Imagine the treadmill is powered by a jet engine. One thrust cancels out the other one. Nothing flys.

[lumberjim]

Originally Posted by Dancing Mango

Imagine the treadmill is powered by a jet engine. One thrust cancels out the other one. Nothing flys.

wrong, and misspelled. (flies)

the runway could be powered by chuck norris and clint eastwood and labrat's ass put together. the rotation of the wheels nullifies it's effect. up up and away.

[MaggieL]

Originally Posted by tw

Treadmill only affects how fast those wheels spin. As MaggieL posted, otherwise those wheels would burn up; function instead like brakes.

I think they're in danger of burning anyway. Their friction is the only path for the treadmill to transfer energy to the airplane, and they've been specifically designed *not* to do that, whereas the engines are designed specifically to do exactly what they're doing. So the proposed takeoff failure scenario has a power transfer through friction in the wheel bearings equal to the power output of the engines (less engine system losses, of course). So even in a smallish airplane we're talking 100-200 horsepower...which is about 150 kilowatts. How long before the wheel bearings fail from heat?