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# Will it take off?

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posted on Feb, 13 2006 @ 02:30 PM
OK, this is not necessarily an aircraft project related thread, but it is an interesting exploration of logic, physics, et.

Here is the problem:

A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"

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posted on Feb, 13 2006 @ 02:37 PM
No, unless there is sufficient wind (highly unlikely). The airspeed over the wing is virtually zero.

[edit on 13-2-2006 by planeman]

posted on Feb, 13 2006 @ 02:38 PM
Without looking at the answer, I would say no, unless perhaps you had a VERY strong wind happening.

I looked just now, and I disagree with the authors official answer, wings need air rushing past to create lift. If the plane is still in relation to the air, where is the lift?

posted on Feb, 13 2006 @ 02:42 PM
I would say that the aircraft is basically stationary, so unless there's a headwind equal to or exceeding normal take off speed, then it ain't gonna happen - probably a good thing too - wouldn't wanna be on it when this was tried

posted on Feb, 13 2006 @ 03:33 PM
It will take off.

The thing to remember is that the wheels aren't directly connected to the propulsion system. They're essentially frictionless meaning what happens to them has no effect on what happens to the rest of the plane.

Think of it this way. Say the plane is moving forwards at 100kph. That means the conveyer is moving 100kph in the opposite direction. The wheels would move at what would feel like to them to be 200kph. Because the wheels are frictionless there is no effect on the plane itself. To the wheels there is no difference between this situation and the plane travelling at 200kph on a fixed ground. The wheels in this situation only support the weight of the plane, they have no effect on the forces in the x direction. It's as if they weren't even there. In fact it doesn't matter what speed the conveyer is travelling at.

From my picture above the plane is providing force in one direction from the engines. The conveyor is providing force in the other direction and because the wheels are frictionless there's no connection between the two.

In reality there is some friction in the wheels so if the conveyer is travelling at 100kph the plane is travelling forwards at 90kph. It would make the beginning (low speed) difficult but at takeoff speed the effect would be negligible.

It does get confusing and is very counter intuitive but once you realise that a planes wheels don't provide the propulsive force like a car it starts to make sense.

P.S. ph34r my l33t dr4w1ng sk1llz

posted on Feb, 13 2006 @ 03:42 PM
I agree with Dragon here, that the conveyer's speed is largely irrelevent. The plane might not take off if the doubling of the speed on the wheels causes them to violently explode and cause damage, but that is beyond the scope of the original question.

posted on Feb, 13 2006 @ 03:59 PM
By Jiminy ( Slaps forehead in disbelief at own stupidity) I think you guys may be right!

Still wouldn't like to be on it though - "She canna take any more, Captain" with referrence to the tyres.................

posted on Feb, 13 2006 @ 06:10 PM
I don't think this plane would take off at all.

Think of it this way....

If I'm running on a treadmill, my body is stationary relative to the ground and the surround atmosphere. In other words, no matter how fast I run, there will be no "breeze" in my face. The air around me is traveling at the same speed as the TREADMILL.

Now think of the plane. The place can accelerate as fast as it likes, but if it's speed relative to the air around it's wings remains at zero, there will be no lift generated, and the plane will NOT take off. It doesn't matter if the thing uses wheels, tracks or a sled, if the air isn't traveling over the wings at a fast enough speed to generate lift, the plane will not take off.

That being said, if you put a powerful enough fan in front of the plane, and tether the plane to something so that it won't roll away, the wind going over the wings (from the fan) could generate enough lift to raise the plane off the ground without the engines (on the plane) even being on.

posted on Feb, 13 2006 @ 07:29 PM
I feel like taking a sledgehammer to the head of that person with the illustration trying to say it would take off. I am in such disbelief right now.

That plane aint going nowhere man. The speed of the plane relative to the conveyor is the same as the conveyor relative to the plane. But the plane is stationary relative to an observer on the ground. Hence, no ground speed, no plane motion. No wind, no wing speed, etc etc, plane remains grounded. Such a stupid topic if you ask me.

Train

posted on Feb, 13 2006 @ 07:36 PM
haha oh man this age old Argument again I don't think it will take off though I always like this argument

[edit on 13-2-2006 by Thug69]

posted on Feb, 13 2006 @ 07:52 PM
The plane will take off just as if there was no conveyer. The wheels on a plane have little to do with how fast it can move, they aren't the driving force, the prop is.....

posted on Feb, 13 2006 @ 08:08 PM
There needs to be airflow over the wings, you can spin the tires and rev the engines, but if the plane is not moving forward, it is not going to fly. Unless it is an F-15.

posted on Feb, 13 2006 @ 09:34 PM
If the plane was dropped from the sky so that it fell strait down, and the engines were fired up, it would go forward.
Therefore the plane would go forward on the treadmill too, and it would take off.

But if the plane did not move forward it would not take off.

So what if we are all right?

OK, I guess it would 'take off, eh?'

posted on Feb, 13 2006 @ 09:48 PM
the wheels will get hot, maybe more than they are designed for...

Possible failure of wheels and tires, otherwise no effect on takeoff ability.

posted on Feb, 13 2006 @ 10:08 PM
It would only affect the wheels, not the engines.

It would take off.

posted on Feb, 13 2006 @ 10:15 PM

Originally posted by BigTrain
I feel like taking a sledgehammer to the head of that person with the illustration trying to say it would take off. I am in such disbelief right now.

That plane aint going nowhere man. The speed of the plane relative to the conveyor is the same as the conveyor relative to the plane. But the plane is stationary relative to an observer on the ground. Hence, no ground speed, no plane motion. No wind, no wing speed, etc etc, plane remains grounded. Such a stupid topic if you ask me.

Train

Problem Train with that logic. Will not the airplane roll of the tread mill is it stops moving forward therefore creating a backwards flow of air over the wings. So the plane leaving the tread mill creates movement the plane must be moving to stay stationary relative to the human eye. Propulsion still has to be used to create movement. The plane will fly!

posted on Feb, 13 2006 @ 10:29 PM
The plane will move forward, the engines are totally separate from the wheels.

The wheels would move doublespeed plus the speed of the engine thrust and the plane moves forward.

So the wheels move well over double speed, the over-double is forward movement creating lift.

Remember the wheels are not the engines.

posted on Feb, 13 2006 @ 10:51 PM

Originally posted by BigTrain
I feel like taking a sledgehammer to the head of that person with the illustration trying to say it would take off. I am in such disbelief right now.

Ouch!

Your think that what would happen with a car would happen to an airplane. A car moves forward buy providing a force against the ground. No matter how fast the car goes the conveyor will go the same speed giving the appearance that the care is stationary.

The plane moves forward by providing force against the air. The wheels are completely unrelated to the act of moving forward. They provide NO force along the axis of the motion. It's like the plane is on an air cushion. The plane takes off. Get over it.

There is another version of this question which says the conveyor moves at the same speed as the wheels which doesn't even work.

posted on Feb, 13 2006 @ 11:18 PM
As stated before "take-off" is dependent upon lift. Lift is generated by the Bernoulli Effect resulting from air moving at higher speed over the top of the wing; thus creating an area of lower pressure Above the wing. the relatively higher pressure under the wing thus "lifts" the plane into the air.

Thrust, provided either by a propeller or jet exhaust, serves to push the wing through the ambient air at the speed required to generate sufficient lift.

If a sufficient volume of air does not flow around the airfoil of the wing with sufficient velocity (ie.: take-off speed), there will not be suffiecient lift generated to allow the plane to fly.

Speed is measurement of velocity relative to another object, generally speaking, that object is the ground. Which, although the Earth (the "ground" in this case) spins at some 3000 MPH, I believe, is generally perceived of as being stationary (Except sometimes in California!).

In the thought excercise given, the forward velocity of the plane is exactly countered by the "treadmill runway" thus negating the forward velocity of the plane. The plane would have the same velocity, therfore , if its wheels were locked and unmoving.

Consider: A plane, when parked on the runway is still "moving" at close to 3000 MPH due solely to the spin of the planet it's parked on; yet it is not airborn. Why not? Because it's Relative velocity to the surrounding air, which is Also moving at the same relative speed as the ground, and therefore, to the plane parked on the ground, is 0 MPH.

Depite the vast volume of air (the entire atmosphre) available, the failure of that volume, no matter how vast, to flow about the plane's wings to generate lift will leave the plane earth-bound.

The plane's engines do not generate lift; they generate thrust, which is translated into velocity relative to environment, which results in lift. No matter how much thrust an engine produces (nor the means by which it produces said thrust), if there is no Velocity (or if that velocity is countered in some way, say by a moving runway) there will be no Lift.

As a "backwards" example consider what can happen to a plane, parked on a airport tarmac, in a high wind.

A large volume of air, at sufficient velocity (no engines involved, no forward speed on the part of the plane) and yet the hapless, pilotless plane becomes disaterously airborn.

posted on Feb, 13 2006 @ 11:22 PM
It takes off. the plane is still moving forward, because the force exerted is from the props or jet engines. It simply takes off with double the wheel speed!

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