Will a plane take off on a conveyor belt?

A plane doesn't NEED an engine if it's launched by a conveyer. It could be a glider, like I said before.

 

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Yes, but in the OP the conveyer was running backwards, and the reason for its existence is to stop the airplane, not to throw it.

 

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This brings up an application. A conveyor capable of magically affecting airspeed by touching the wheels without friction could be used instead of that difficult and skill-requiring system of tripwires the Air Force uses on carrier landings.

Simply accellerate a deck conveyor to the plane's airspeed, and have the plane touch down and become motionless anywhere along it. Much easier, for the pilots.

 

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That's the point. But some people don't seem to get it.

 

Temur is right.

You cannot stop the plane from accelerating. Wheels will simply move faster as belt speed increases. The plane still moves forward as the wheels are free spinning. Thus, the plane moves through air, creates lift, and flies.

 

The plane has no relationship with the conveyor, if it were powered by it's wheels then no it couldn’t take off because it wouldn’t generate any forward motion to generate lift.

A plane powered by jet engines, will take off, and will move forward, it doesn’t matter how fast the conveyor is rolling, because it doesn’t affect the output of the engines, which will always be greater than any frictional coefficient with the runway. The plane will also not stay stationary, it will run off the back rolling conveyor at the same speed as it would a runway, only at the end it's wheels will be spinning faster.

 

Simple solution:
Assuming it is a perfect system and our observer is the pilot (I didnt see anyone mentioning that)
then the conveyer belt will always be moving as fast as the wheels spin (while its on the ground.) This is because the wheel's will spin because of two things:
1. the plane moving forward relative to the belt
2. the conveyer moving backward relative to the plane
Now since our observer is the pilot, then those are the same things (both are the belt moving backwards relative to the pilot.)
and therefore, the given scenario would be true without the conveyer belt even moving, and thus is infact the scenario for every pilot taking off a real runway

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this situation would hold true no matter how fast the conveyer belt moved relative to the ground.

-Andrew

 

I know the answer... I just don't know what I was talking about then. Just ignore me. I think I was considering that the conveyor was going significantly faster than the plane such that the friction between the moving wheels and the plane actually matters.

 

If the belt is moving at the peripheral speed of the wheels then the wheel centres won't move forward relative to the ground, yes?
And if the wheel centres, hence undercarriage legs, hence aircraft, doesn't move forward relative to the ground how does the aircraft generate lift?

 

They are ignoring/bypassing/seeing different, the "belt moves exactly as fast as the wheels" part. However that needs to be explained(frictionless or totally in-elastic or whatever blah blah blah) with this crew...the original question is not written well enough.

I can't believe I just posted in this thread again....

 

Wrong, while the wheel centers never move relative to the pilot, the airspeed conveyer, and ground does.
Just think about it:
Your in a car and you look out the window, currently you are at a red light. Your car isnt moving, the ground isnt moving, the wheels are stopped.
Light turns green, you go through the intersection and look again.
The car still isnt moving, the gorund is moving opposite the wheels, and the wheels are turning. Their peripheral speed is the same as the gorund's speed, though in oppoiste direction.

Edit: periphreral speed is cause on the wheels in our system by the torque created from moving a high friction object against the wheels, relative to the rotational center, ie the axal. Thus, that motion is equal to the movement of the plane (or car) relative to the convayer or road. Thus it depends on the observer to tell how much speed each object is contributing to this.

-Andrew

 

Because the ground isn't moving... but the conveyor belt in this case is.
Ever held a speedometer wheel on a stick against a conveyor belt?
I have.
The belt moves backwards, the wheel rotates and the stick (and my hand) do not move relative to the ground.
If I moved that stick/ wheel forward I would have generated a wheel speed greater than the conveyor belt's (and got a false reading of belt speed).
But the OP said that the belt MATCHES the wheel (peripheral) speed.

 

Ah, but in your case you are standing on the ground. Try it while your on the convayer, as the plane is, and your resaults will agree with my argument. The faster you move relative to the belt, the faster the speedometer says, so if you stand still on the belt, it reads 0 no matter how fast the belt moves relative to the ground.

Now the OP never said that the ground was the observer; it didnt specify anyone. Nor did it state the plane was not moving relative to the gournd (indeed, that it what we are trying to figure out.) and I am stating that the pilot in the plane is the observer.

-Andrew

 

If the belt is doing 60 mph backwards then the plane (and wheels) must be doing 60 mph "forwards" to remain in the same relative position to the ground (for example, in the middle of the belt's length). And will generate no lift since it isn't moving forwards relative to the ground (or air).
The pilot cannot be the observer since it is air speed that determines lift. (The air being apart from the belt and should be considered with the ground, not the pilot)
If the plane accelerates to 120 the belt (as stated in the OP) will also do 120 mph backwards - still no relative motion to the air, no lift.

 

Doesn't seem to stop pilots from taking off everyday...
You see, what happens is, the belt is stationary. the pilot does 100mph. and since its form his perspective:
1. the belt is moving 100mph backward
2. the wheels have peripherial motion of 100mph
3. the air and ground are moving 100mph backward
Airspeed is the measurment of the speed of air relative to the plane, so the pilot is actualy the best observer for it in this case.

edit: keep in mind the above was the simples scenario, the conveyer could still be moving relative to the ground.

You keep stating the plane must remain stationary relative to the ground, but it doesnt say that this is a condition at any point in the OP. Indeed, as I said, it is what we are trying to figure out; since groundspeed will = the airspeed in a no wind scenario (as was stated.)

-Andrew

 

okay, listen up.
the props act like screws.
they twist through the air forcing the plane forward.
the only way the plane will not take off is if the plane is chained to the ground.
the conveyor belt has nothing, nada, zip, zero, to do with this scenario.
it can be traveling at mach 50,000 and still not make any difference.

it's a similar situation with jets, but in this case the rearward thrust is matched by the forward motion of the plane.

edit:
another way to look at it is the reverse.
what if the props was blowing forward.
now, can the conveyor belt keep the plane from moving backwards?

whatever you do, do not bet any money that the plane will not take off under the scenario being proposed in the first post.

 

The problem, leopold, was with the fact that the wheel's peripheral speed had to be = to the conveyer speed. People took the ground as a reference point by default, and thus the only way that condition would be possible would be if the plane was stationary relative to the ground (however, only true if the ground is our observer.)

This is because if the conveyer moves 100 mph backwards relative to the ground, the perihperial motion of the wheels must be 100mph relative to the ground, and thus the planes speed must be 0.
Edit: Now if the plane gerates thrust, in a perfect scenario the conveyor would as you say have no effect on its acceleration, and thus it would accelerate. But then the condition that it's peripheral speed matched the conveyors would be impossible since it would be:
peripheral speed=conveyor speed+planes speed
thus if:
peripheral speed=conveyor speed
planes speed MUST = 0

If the plane was generating thrust, then that would simply would not be true, OR it would be an imperfect scenario in which the axels generate eanough friction to slow the plane down. So either its an imperfect scenario with the wheel axels, or the plane is not making thrust. Since we should assume its making thrust, that leaves in imperfect scenario.
But in an imperfect scenario the wheels could slide and allow the plane too move forward... thus the best conclusion would be to take a different observer as I have.

 

People must be making the mistake of thinking of a plane operating like a car. Thinking that the wheels provide thrust, they don't.

The thrust is created by the propeller "screwing" it's way thru the air. The wheels do nothing but allow the plane to move freely on the ground. All a conveyor belt will do is cause the wheels to move faster as the plane is pushed forward by it's engines.

 

But as the wheels move faster, so does the conveyor belt.

 

apparently.