Mythbusters/airplane on a treadmill.

Hammered said:
HAHAHAH someones gonna loose some money. :o


If its a JET I dont think it will take off because of the lift on the wing issue. ...if its a prop plane it is possible it could pick itself up but would probably need to be a 2 or 4 prop... not a cessna single engine.

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Are you saying you would like to make a quick $300?
I'll bet any plane (single , multi, jet engines) that is capable of flight will take off from a conveyour just the same as it would take off from a standard runway. the conveyour or treadmill will have no effect on the plane taking off.
 
Well I just reread the ? and am now changing my point of view. If the ? is simpley .... can a plane take off of a conveyour belt .. well of course it can.
 
goodburbon said:
BTW sean your explination is ass backwards.

100 mph groundspeed into a 50 mph headwind is 150 airspeed
100 mph groundspeed with a 50 mph tailwind is 50 airspeed
:dunce:
You are right, I was am a bit backwards.
BTW, I just found my expired ground school certificate cleaning out my file cabnet today,
<sigh> Some day I will finish, like they say third time is a charm....

It will fly
 
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Above is a simplification of the problem. There is no doubt about the condition of the runway surface affecting take-off performance.

X is the wheel speed in whatever unit you care for. Y is the speed of the treadmill support below that conveniently matches the size of the wheel to remove any question about the frame of reference here.

I won't bother a proof, but if you argue, please argue against the assumptions first, and then so on.

Assume: X > Y for the aircraft to move. (Humor me)

A: "X = Y"

P: "The airplane is stationary"

...Anyway, I was about to try and actually apply some logic but I got lost.

If you require that A is true, then P is true as well. That's why so many people immediately conclude it won't fly. It isn't moving. It is also the flaw to the whole problem.

The treadmill cannot keep up!

If P is not true, then neither is A. The aircraft moves AND the treadmill can't match the speed.

It's a problem of control. If X > Y, then Y is increased by way of this mythical treadmill design. That increase is immediately given to X as well, and it remains X > Y.
 
Are you saying the plane WONT fly?
I agree with your A, X, Y and P formulas, BUT, what you arent addressing is the fact that the treadmill speed is totally irrelevant to whether or not the plane moves forward and therefore flys. Removing friction from the problem, the treadmill could be going the speed of light or better, and the plane would still take off. Even if the treadmill was not capable of matching the planes wheel speed, it would still take off.
 
Ray H said:
Are you saying the plane WONT fly?
I agree with your A, X, Y and P formulas, BUT, what you arent addressing is the fact that the treadmill speed is totally irrelevant to whether or not the plane moves forward and therefore flys. Removing friction from the problem, the treadmill could be going the speed of light or better, and the plane would still take off. Even if the treadmill was not capable of matching the planes wheel speed, it would still take off.

My conclusion is in bold. I don't need to address whether the moving aircraft will eventually fly. That is up to factors outside of the problem definition, such as the aircraft, pressure altitude, temperature, weight, tire limiting speeds, etc. Address the premise that a treadmill matches speed.

p.s. if you remove friction then the wheels can just slide. Just pulling a Capt Ron on you. :dunce:
 
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kubtastic said:
My conclusion is in bold.
I don't need to address whether the moving aircraft will eventually fly.

p.s. if you remove friction then the wheels can just slide. Just pulling a Capt Ron on you. :dunce:

Ok, I see.
Really not much difference between simply "sliding" or freely rolling. captain.;)
 
There's another way to define the problem I suppose.
The treadmill (Y) turns at the same speed as what the aircraft's groundspeed is (G). In this case, X = 2Y instead, leading to X > Y and the airplane moves.
 
Ray H said:
Are you saying you would like to make a quick $300?
I'll bet any plane (single , multi, jet engines) that is capable of flight will take off from a conveyour just the same as it would take off from a standard runway. the conveyour or treadmill will have no effect on the plane taking off.
I'm saying keep your money. As well I'm agreeing with the fact of: No travel, no air speed = no lift on the wings. I'm not sure if you had enough propellers on a wing... If it would create the air speed over the wing to give it lift at high engine speed. and the bigger the prop the more air it would move - Just as with the OSPREY image I posted. But they can obviously angle the wings / propellers.

if it is a center (nose tip) single prop plane or a jet. (not creating wind over its own wings. And if treadmill speed equals aircraft speed (vehicle is standing still) it will not leave the tread mill. -thrust = forward movement = air creates lift on wings = lifting the airplane.


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Lift and Drag
A wing must be at a high enough Angle Of Attack (AOA) to deflect the air downward and produce the desired lift. The pilot uses the elevators to change the angle of attack until the wings produce the lift necessary for the desired maneuver.
Other factors are involved in the production of lift besides the AOA. These factors are relative wind velocity (airspeed) and air density (temperature and altitude). Changing the size or shape of the wing (lowering the flaps) will also change the production of lift. Airspeed is absolutely necessary to produce lift. If there is no airflow past the wing, no air can be diverted downward. At low airspeed, the wing must fly at a high AOA to divert enough air downward to produce adequate lift. As airspeed increases, the wing can fly at lower AOAs to produce the needed lift. This is why airplanes flying relatively slow must be nose high (like an airliner just before landing or just as it takes off) but at high airspeeds fly with the fuselage fairly level. The key is that the wings don't have to divert fast moving air down nearly as much as they do to slow moving air.
As an airplane in flight slows down, it must continually increase its pitch attitude and AOA to produce the lift necessary to sustain level flight. At high AOAs, the top of the wing diverts the air through a much larger angle than at low AOAs. As the AOA increases, a point will be reached where the air simply cannot "take" the upper curve over the entire distance of the top of the wing, and it starts to separate. When this point is reached, the wing is not far from stalling. The airflow unsticks further up the wing as the AOA increases. The top of the wing still contributes to the production of lift, but not along its entire curve.
As the airspeed slows or as the angle of attack, or both, is increased further, the point is reached where, because of this separation, an increase in the AOA results in a loss of lift instead of an increase in lift. Thus, the wing no longer produces sufficient lift and the airplane that the wing is supporting accelerates downward. This is the stall.
Air density also contributes to the wing's ability to produce lift. This is manifested primarily in an increase in altitude, which decreases air density. As the density decreases, the wing must push a greater volume of air downward by flying faster or push it down harder by increasing the angle of attack. This is why aircraft that fly very high must either go very fast like the SR-71, capable of flying Mach 3 (three times the speed of sound), or must have a very large wing for its weight, like the U-2.
 
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Yes, Yes, Yes, We all know lift, drag, weight, thrust.
What some people are missing out on though is that it doesnt matter how fast the conveyor goes, theres nothing to keep the plane from traveling forward. The wheels on a plane have nothing to do with it flying, they just free wheel. Their only purpose is to reduce the friction between the ground and the plane so it can move forward. Planes use other means of reducing friction besides wheels (skis, pontoons). Shis and pontoons dont turn at all, so how do these planes take off? With no friction between the ground and the plane, it doesnt matter what the ground (ie: treadmill) is or the wheels are doing, the plane will still roll.
 
Hammered said:
then that is the question - is the plane STILL or not

It will move. Why would it stay still, its got a prop that pulls it forward and with the wheels free wheeling (brakes released) theres nothing to hold it back.
 
Hammered said:
??? it would say at the same location because the tread mill is equaling out the forward movement. Thats the whole point of the argument.

This is where everyone gets hung up. Its not a car, the wheels are free to turn as fast or as slow as they do and it wont effect the forward motion of the plane.
think about this. You are wearing rollerskates while standing on a treadmill. when the treadmill starts to move, you can still easily pull yourself forward by using the rails and it wont matter how fast the treadmill is going, you can still pull yourself forward. its the same with a plane. It doesnt matter how fast the conveyor is going, the prop will still pull the plane forward.
 
It's also kind of like truck pulls, tug of war style. Once one truck starts spinning, it's essentially hovering. It either needs to gain traction with the wheels to move, or be acted upon by an outside force.

Since a plane doesn't get traction with it's wheels in any real sense, thats not going to happen. But the outside force (thrust from the engines) moves it very easily, because it's hovering. Just like then a truck starts spinning it gets easier to pull it with the other truck, it's hovering.

Or how about like this, whenever you land in a commercial jet they don't hit the brakes. Because the wheels don't have anything to do with stopping the craft at that point. But they do reverse the thrust of the engines, because they are controlling movement of the aircraft... to use tires big enough, with enough braking and traction to stop the craft against the thrust and momentum would probably make the aircraft unable to fly.
 
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98XJSport said:
Or how about like this, whenever you land in a commercial jet they don't hit the brakes. Because the wheels don't have anything to do with stopping the craft at that point. But they do reverse the thrust of the engines, because they are controlling movement of the aircraft... to use tires big enough, with enough braking and traction to stop the craft against the thrust and momentum would probably make the aircraft unable to fly.

Ummm . . . No.

The brakes are used in conjunction with the thrust reversers to slow/stop the aircraft.

Check out a pilot's checklist sometime, where it says "Brakes - As Required"
 
RedHeep said:
Ummm . . . No.

The brakes are used in conjunction with the thrust reversers to slow/stop the aircraft.

Check out a pilot's checklist sometime, where it says "Brakes - As Required"

Yes, brakes as required. As in when they slow down enough for them to be used without making the jet skid out of control.

Talking in the world of big jetlines, of course.
 
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