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Will it take off?


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Discussion Starter #1
Repost from another forum but the responses were very interesting so I'm curious what comes out of this group. I have my answer but would like to see what you think.

A plane is standing on a movable runway( something like a conveyor).as the plane moves the conveyor moves but in the opposite direction.the conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction.

The question is, will the plane take off or not?
 

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Discussion Starter #4
SAR_Squid79 said:
No way. A plane HAS to move, so that air will pass over, and under the wing to create lift.
Nobody said the plane won't move, just that if the plane is moving 10mph one direction the conveyor is moving 10mph the other.

I say it takes off.
 

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Discussion Starter #6
Sisyphus said:
If the plane remains in the same spot, there is no airspeed under the wings. The only way the plane could take off is if it was VTOL capable. Even with a STOL kit on a Husky its not possible.
Nobody said the plane stays in the same spot.

The way I see it is the plane accelerates against the air around it and the ground speed is irrelevant. Once the plane starts moving, and it will, the wings will create lift and the plane takes off. The wheels do nothing more than keep the belly of the plane from dragging. The wheels don't drive the plane, they just spin.
 

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CHRINTHEDESTROYER said:
no it would not according to the laws of lift, But if the conveyor stopped suddenly the plane would have a catapult effect like on a carrier
The engines aren't driving against the ground so ground speed means nothing to the plane. If the conveyor stopped the wheel speed of the plane would be cut in half but wouldn't really affect the plane other than the small amount of drag in the bearings and minor friction against the ground.
 

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CHRINTHEDESTROYER said:
no it would not according to the laws of lift, But if the conveyor stopped suddenly the plane would have a catapult effect like on a carrier
Nope, the wheels would just stop turning, or it might creep forward an inch or two.

10mph isn't very fast, much less approaching catapult speed.

Now if it was a vehicle whose power was turning the conveyor, then yes... similar to a car jumping off a dyno.

In this case, the conveyor is simply turning the wheels.
 

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SteveO said:
The engines aren't driving against the ground so ground speed means nothing to the plane. If the conveyor stopped the wheel speed of the plane would be cut in half but wouldn't really affect the plane other than the small amount of drag in the bearings and minor friction against the ground.
Steve, the plane's ground speed is zero.

The measured wheelspeed would be rotating at a rate of 10mph, but it wouldn't matter.

It's not like a moving car whose occupants are moving at the same speed of the car... the conveyor negates any true motion, although it gives a sense of motion.
 

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so you don't think that the plane would move forward on the ground? also dont you think the thrust would push the plane forward since the thrust force is pushing the plane forward the wheels might just turn twice as fast. Just a thought since the friction on the wheels would probably be less than say a car (or truck).
 

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He didn't say the engines were running, but I guess by saying "as the plane moves the conveyor moves" one could assume the engines are on.

If the engines are off, I'm right.

If the engines are on and at full throttle, the plane will take off because it is being propelled by thrust, and no power is being applied to the wheels, therefore the conveyor would either not move, or if it had little friction/resistance it would actually probably roll in the same direction the plane was headed due to the rolling resistance of the tires.
 

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ok, the plane moves, the air speed needs to be x to lift. say x = 150mph.
well the wheels will turn 150mph on a static runway. so if the runway has to counteract the wheel speed of the aircraft rolling down the runway, then the conveyor must run at 2x mph. so at liftoff the plane will be moving at 150mph airspeed, but wheelspeed will be running 300 mph.

my question is, where can you find a conveyor that is as long and wide as a runway and that can move at 300 mph???
 

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Discussion Starter #16
valkyrie said:
Can't happen brother.

Wheelspeed has nothing to do with lift over the wings.

Brush up on Bernoulli's law. :)
I think you guys are misunderstanding. If you put a jet on a dyno (or any rollers) and throttled it up would the plane move? Of course it would. The motion of the wheels has nothing to do with the movement of the plane.
 

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Discussion Starter #17
The plane is generating thrust out th eback of th engines but when the plane moves at say 50mph forward the conveyor is moving 50mph backwards. Their would be motion and the wheels would turn twice as fast as the forward motion of the plane. As long as the plane move realtive to the air around it the wheelspeed/ground speed means nothing.
 

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Discussion Starter #18
KyleT said:
ok, the plane moves, the air speed needs to be x to lift. say x = 150mph.
well the wheels will turn 150mph on a static runway. so if the runway has to counteract the wheel speed of the aircraft rolling down the runway, then the conveyor must run at 2x mph. so at liftoff the plane will be moving at 150mph airspeed, but wheelspeed will be running 300 mph.

my question is, where can you find a conveyor that is as long and wide as a runway and that can move at 300 mph???

That's what I'm thinking.
 

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Yeah, I figured out that I had it wrong. Initially, I thought you meant that the conveyor was moving and the engines were off.

However, if it was throttled up, how would it generate airspeed over the wings if it didn't travel?

The fact that the ground doesn't move makes the wheels turn due to the thrust.

I'm gonna go home and have beer.
 
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