Would the plane take off?

[BoostedXT 0]

Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.
Can the plane take off?

Joe

For long as you live and high you fly and smiles you'll give and tears you'll cry and all that you touch and all that you see is all your life will ever be.
Pedro Offers you his Protection.

[Lindercles 0]

So you're saying that the wheels are moving, but there is no air flowing over the wings?

[Rebecca 0]

Um, no.

you've got to ask yourself one question: 'Do I feel loquacious?' -- well do you, punk?

[shropshire 0]

what have you been drinking? Can I have some?


NO...Once the a/c gets to take off speed, the motive force would stop (a/c would try to leave the conveyor) so would sink .. thus it would not really fly (unless it has an engine too)

(.)Y(.)
Chivalry is not dead; it only sleeps for want of work to do. - Jerome K Jerome

[BoostedXT 0]

Why do you say that?

I think it would...

For long as you live and high you fly and smiles you'll give and tears you'll cry and all that you touch and all that you see is all your life will ever be.
Pedro Offers you his Protection.

[sundevil777 94]

Yes, it would take off.

But, your scenario is a little weird, if it were to try to match the speed at any time, then it would actually try to keep the initial state, a zero rotational speed of the wheels. That assumes it can respond instantaneously. Even if it were opposite, to rotate the wheels faster, unless there is a lot of friction from the wheel bearings, it doesn't matter. The motive force is not from the wheels.

The only thing holding the plane back that has to do with the wheels is the rolling friction from the tires and the wheel bearing friction. Those effects are likely to be slight.

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[Loonix 0]

it is impossible to design such a belt. If the plane moves forward, the belt cannot match its speed, since when the belt increases speed, it also increases the speed of the wheels.

[BoostedXT 0]

My thought exactly...the plane doesnt get its force from the wheels. Its not like a car. I looked at it as this....Wheel speed can be determined in 2 ways...RPM and MPH. The plane uses thrust to move...NOT the wheels.

Joe

For long as you live and high you fly and smiles you'll give and tears you'll cry and all that you touch and all that you see is all your life will ever be.
Pedro Offers you his Protection.

[Lindercles 0]

Ok, I need some clarification here.

Is the conveyor belt:

1. moving from the front of the plane toward the back such that it turns the wheels but the plane itself occupies the same point in space the whole time

or

2. Moving toward the front of the plane such that the point of contact between the conveyor belt and the wheels stays the same, and the wheels don't move but the belt is actually moving the plane forward in space

In option 1. the wheels are moving but no air is flowing over the wings. In option 2. the wheels aren't moving but the plane is, so there is air flowing over the wings.

[CrazyL 0]

Is ther a high cliff at the end of the a/c launch point?

[BoostedXT 0]

The plane uses the wheels for support and nothing else. If the plane thrusts forward using the turbines the wheels roll...not the wheels rolling and driving the plane to air speed to take off.

Joe

For long as you live and high you fly and smiles you'll give and tears you'll cry and all that you touch and all that you see is all your life will ever be.
Pedro Offers you his Protection.

[Loonix 0]

i think you misunderstood me.. I said that the belt can not match the speed of the wheels when the plane is pulled forward, so its an impossible task

[BoostedXT 0]

#1: The belt runs from Nose to Tail.

Wheel speed and rolling resistance comes into play, but the plane doesnt use Wheel speed to take off.

The wheels can spin at 5000rpms or 2rpms...if enough forward speed of the plane it self is created it will leave the ground because of lift, not because the wheels spun.

joe

For long as you live and high you fly and smiles you'll give and tears you'll cry and all that you touch and all that you see is all your life will ever be.
Pedro Offers you his Protection.

[CrazyL 0]

Are you talking of a device similar to a catapult used on Aircraft Carriers?

[billvon 2,434]

>Can the plane take off?

Of course. Indeed, it would take off faster, since the belt would remove some rolling friction.

In fact, if you locked the brakes, shut down the engines and had the belt accelerate the plane to a speed greater than rotation speed, it could then take off. (If the engines remained off, it would then land pretty quickly, of course!) Or you could hook the front wheel to the belt - in which case you'd have a catapult similar to an aircraft carrier's.

Some aircraft have actually used a somewhat similar arrangement - namely, a dolly that rolls with the aircraft until takeoff speed then is left behind. A few WWII rocket and jet powered aircraft used this, including some kamikaze aircraft. (No need for landing gear!)

[davedlg 0]

The thing that determines whether the plane will take off is the airspeed over the wings. The RPM of the wheels is completely insignificant. Theoretically, you could balance a wheel-less plane on a tripod, send it down the runway on your contraption and it would take off. I dont know how you would land that kind of plane though.

[BoostedXT 0]

The belt it working against the plane...The plane is facing and takine off north bound but the belt is running southbound...
Joe

For long as you live and high you fly and smiles you'll give and tears you'll cry and all that you touch and all that you see is all your life will ever be.
Pedro Offers you his Protection.

[RhondaLea 3]

Thread killer.

If you don't know where you're going, you should know where you came from. Gullah Proverb

[sundevil777 94]

I think his scenario is that the conveyor goes the opposite direction.

I propose that we think of it this way. If you have perfect/idealized wheels/bearings with no friction or rotational inertia, then a plane with the engine off would not move (the wheels would just rotate) as the conveyor accelerated in either direction. Since the wheels are not perfect, they would not start rotating as fast, and would cause the plane to be moved at some rate less than the speed of the belt, so it would be slightly harder for the plane to get up airspeed.

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[billvon 2,434]

>The belt it working against the plane...The plane is facing and
>takine off north bound but the belt is running southbound...

Ah, different story then!

Yes, the plane will still likely take off. The belt will run southbound as the aircraft accelerates northbound. If the belt can run very fast, then the tires will disintegrate as they exceed their ultimate rotational speed. Whether the plane can take off after that happens depends on whether the belt is smooth or not, whether the hubs remain intact, whether the debris from the wheels hits anything etc.

In such a case, it's similar to trying to take off with a 60mph tailwind. It's doable, but the tires take a lot of abuse.

[pjc 0]

The wheels and belt would accelerate infinately until they disintegrate and the whole thing would collapse or the plane would be launched backwards off the belt!!!

[BoostedXT 0]

Quote

I think his scenario is that the conveyor goes the opposite direction.

I propose that we think of it this way. If you have perfect/idealized wheels/bearings with no friction or rotational inertia, then a plane with the engine off would not move (the wheels would just rotate) as the conveyor accelerated in either direction. Since the wheels are not perfect, they would not start rotating as fast, and would cause the plane to be moved at some rate less than the speed of the belt, so it would be slightly harder for the plane to get up airspeed.

The plane cant go anywhere without its motors. The plane gets its drive from its engines not the wheels spinning. Think about a person on a treadmill with rollerskates on holding onto a rope. The treadmill could be going 60mph against them, but if they were holding on to the rope they could still move forward against the treadmill by pulling with their arms. The planes wheels like rollerskate wheels are there to roll NOT propell.


Joe

For long as you live and high you fly and smiles you'll give and tears you'll cry and all that you touch and all that you see is all your life will ever be.
Pedro Offers you his Protection.

[CrazyL 0]

The dolly/ kamikaze take off. Saw some show on History or military channel using such device for the rocket powered a/c. Amazing. The acceleration speed/lift seemed easily attained. Did'nt know such device was used for kamikaze missions.

[sundevil777 94]

Quote

Quote

I think his scenario is that the conveyor goes the opposite direction.

I propose that we think of it this way. If you have perfect/idealized wheels/bearings with no friction or rotational inertia, then a plane with the engine off would not move (the wheels would just rotate) as the conveyor accelerated in either direction. Since the wheels are not perfect, they would not start rotating as fast, and would cause the plane to be moved at some rate less than the speed of the belt, so it would be slightly harder for the plane to get up airspeed.

The plane cant go anywhere without its motors. The plane gets its drive from its engines not the wheels spinning. Think about a person on a treadmill with rollerskates on holding onto a rope. The treadmill could be going 60mph against them, but if they were holding on to the rope they could still move forward against the treadmill by pulling with their arms. The planes wheels like rollerskate wheels are there to roll NOT propell.

I understand everything you stated. It is your scenario that is hard for everyone to understand. I was just proposing a scenario that shows that in an idealized case with perfect wheels/tires (friction between conveyor and tire, but no wheel bearing or rolling friction from tire deformation and no rotational inertia), the conveyor can't move the plane at all, because the wheels would just spin (there is no friction or rotational inertia of the wheels/bearings). As you go away from this idealized case, the movement of the conveyor would make it harder to achieve increasing airspeed.

As others have said, if the conveyor keeps trying to match an ever increasing wheel speed, in part due to the conveyor itself, then it would quickly spin up to an infinite speed, theoretically.

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[Lindercles 0]

If the conveyor belt exactly matches the speed of the airplane (which is obviously impossible, but this is a hypothetical question), then the plane gets no forward movement and thus no airflow over the wings.

So where would the lift come from??