this problem has nothing to do with lift and everything to do with the wheel speed having no effect on the overall speed of the aircraft.

Theoretically, is the conveyor is matching the EXACT speed and momentum change that means that IF the plane continues to accel then the conveyor will too (I understand that the plane does not accel against friction to the ground). This means the plane technically cannot take off if the conveyor is matching the speed EXACTLY (saying that the ground friction is minimal is not relevant seeing as the conveyor would match speed exactly). I think it is impossible for the conveyor to do such things.

I propose that making an accurate test of this is a myth.

Okay, for the last time, the plane will not remain stationary.

The wheels are not the mode of propulsion for a plane. The bearings only provide a system with which to reduce contact friction between the ground and the airplane. THE WHEELS DO NOT DRIVE THE PLANE FORWARD!

what if it was a flying car?

coltjimclemens, that is correct. Assuming you could build a conveyor capable of super speeds, you could turn the wheels fast enough backwards to create enough friction to hold the plane still.

Considering this is unlikely, the plane will take off.

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NeuroticAg
posted 12:25p, 10/24/07



coltjimclemens, that is correct. Assuming you could build a conveyor capable of super speeds, you could turn the wheels fast enough backwards to create enough friction to hold the plane still.

Considering this is unlikely, the plane will take off.

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Yep

if and when this show airs, it should become mandatory for all posters to watch. that way we dont have to do this again in the future. make it part of the terms of agreement when you sign up.

oh and it will so fly

Will the airplane hover?


Take your props and jets and your f-ing conveyor belt and turn those props perpendicular to the ground.....now, the belt if moving the wheels they fire up the engines. Does the airplane stay stationary or take off?

[This message has been edited by jed1154 (edited 10/24/2007 12:27p).]

I think the bigger myth is the practicality of this experiment.

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traveler1
posted 12:26p, 10/24/07



if and when this show airs, it should become mandatory for all posters to watch. that way we dont have to do this again in the future. make it part of the terms of agreement when you sign up.

oh and it will so fly

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Guarantee there will be a 50 page thread on how mythbusters screwed it up.

Again ...

The conveyor is moot.

nm

[This message has been edited by ryan2010 (edited 10/24/2007 12:29p).]

A conveyor belt capable of creating friction higher than 20,000 lbf of thrust is straight out of la la land.

NA, friction is not increased significantly by turning the wheels faster.

The coefficient of friction between the tire and the road will increase only slightly due to heat.

The friction in the bearing would only increase slightly due to heat.

The only way to create enough friction is to hit speeds that will generate enough heat to melt the bearings and cause them to not turn.

IM pretty sure that with a big enough engine, you can take a RC airplane, tie a string to the tail so that it is effectively stationary and still have it hover once you get enough airflow over the wings......i dont know though, it seems like it would work.

ryan, I assumed that is what they were planning on, but the OP was unclear.

CDUB/MKF, what creates the airflow then that provides the lift from the wings? Not the treadmill, and not the propeller (which may create some, but not nearly enough to provide lift over the entire span of the wings).

The air is static (unless this is a treadmill in a wind-tunnel).

[This message has been edited by agrams (edited 10/24/2007 12:31p).]

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ryan2010
posted 12:28p, 10/24/07



Neurotic, the conditions of the experiment state that the conveyor belt be moving at the same speed of the wheels. Under those conditions, the friction is negligible and the airplane takes-off as normal.

I do understand what you are saying. If you jack the conveyor belt way way up, you will produce enough friction to overcome the thrust of the engines. But that would violate the conditions of this particular experiment.

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I thought it said exact speed of the airplane.

Propulsion from the jet engine or props will accelerate the plane at the same rate regardless how fast the wheels are spinning. The airflow generate during this acceleration is how convention aircraft achieve lift.

grams, you are thinking along the wrong lines, period.

Seems like you guys have been arguing about two different problems for months.

The velocity of the conveyor belt only affects the magnitude of wheel rotation.

The conveyor is moot.



[This message has been edited by IIIHorn (edited 10/24/2007 12:33p).]

So the jet engine pushes the airplane fast enough to make the wind speed be fast enough to lift the plane......????

So, this experiment sucks because it wont take off..because a variable of wind speed has not been met or accounted for in this experiment?

I change my stance. it wont take off, but it has nothing to do with the conveyor belt.

[This message has been edited by jed1154 (edited 10/24/2007 12:34p).]

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The issue with the plane and conveyor is whether or not the conveyor belt's matching the plane's speed will nullify the wind speed at the wing, and the "myth" is probably based on wheel based speed calculations. If I had my car on a conveyor that matched my wheel speed, and I stuck my hand outside the window, I doubt I'll feel any resistance since I am not actually moving anywhere. Now if we are talking about wind speed at the wing, then yeah, the conveyor is gonna be moot since wind speed will be based upon air movement over the wing which is gonna give you the lift you need.

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An airplane does not propell itself the same way your car does. If your car were to become airborn, it will no longer be able to provide itself forward thrust. This would be detrimental to an airplanes flight, and would make it classified as a glider.

The clarification needed here is if the conveyor is to match the ground speed of the airplane, or the rolling speed of the wheels. Since an airplane accelerates by either pulling itself through the air (propellors) or pushing iself forward with large ammounts of hot, high pressure air (jet) the fact that it is on a conveyor will not affect forward motion. (this is why the length of the conveyor matters, if it is too short, the experiment won't work)

If the conveyor matches the rotational speed of the wheels, the conveyor will infinitely increase. As the plane moves forward the conveyor will have ot match itself + the ground speed of the airplane, which is impossible since while 0<x and y!=0, x != x+y. The conveyor will continue to accelerate and friction will eventually overtake the plane's engines.

If the conveyor matches the ground speed of the plane, it is simply that x=x and the plane will take off with just a little added rolling resistance.

[This message has been edited by TexasRebel (edited 10/24/2007 12:41p).]

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So the jet engine pushes the airplane fast enough to make the wind speed be fast enough to lift the plane......????

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do you have any idea why planes have jet engines or props on them to begin with?

Dang it Brennus.

I miss being able to see the 'bombs moon' picture.

Workfilterowned.

yes, and after thinking about my other post, if i tie a string to my airplane, and hold it back, no engine in the world is going to make it hover. The prop and jet pull or push the plane fast enough to achieve lift across the entire wing surface.

hth

This is why I love being an engineer.

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MonkeyKnifeFighter
posted 12:31p, 10/24/07



Agrams: put a skateboard on a treadmill and stand on it. Turn the treadmill on. Now grip the rails and push yourself forward. You still move. That's the whole point.

The rails are the standing air around the plane. They're not attached to the movement of the treadmill.

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However, if the treadmill speads up to the exact speed that you pull the skateboard forward it will stay in place.

Do you see what I am saying; this is impossible though.

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NA, friction is not increased significantly by turning the wheels faster.

The coefficient of friction between the tire and the road will increase only slightly due to heat.

The friction in the bearing would only increase slightly due to heat.

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Exactly. Assuming that you had unmeltable bearings, you could theoretically create enough heat to increase friction to the point where the plane would not take off.