Would the plane take off?

[BoostedXT 0]

I personally think the plane will take off because there is the rotational force like stated before. Say the airplane makes 200,000 pounds of thrust and force to take off, the bearings, wheel on treadmill, and other frictional requirements involved, lets say and ALL other factors create 10,000 pound of negative force there is still 190,000 pounds of positive thrust that would need to be over come by the treadmill.

I think the plane would take off in the end and all you would have to do is over power the level of drag created by all metal goods with pure forward thrust by the motors.

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]

But you can't take off with forward thrust alone, you need lift. And without air flowing over the top of the wing, you have no lift, and thus no take off.

[sundevil777 102]

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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??

He didn't say it would match the speed of the plane, it would match the speed of the rotating wheels.

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

[davedlg 0]

Basically it breaks down to the question of whether the plane physically moves.

The answer is of course it would. Simple physics tells us it would...you know, the whole balance of forces principle? Basically on a plane you have the engines producing a whole bunch of thrust. Unless something is counteracting the thrust, the plane will accelerate. The wheels and conveyer you are talking about would simply act like low friction ball bearings, reducing the force which opposes the thrust from the jets.

Consider what happens on a frozen lake. You have a difficult time running across it because of the lack of friction with the ice (this is essentially what would happen if a car tried to drive on your conveyer). Now imagine what would happen if you added a source of thrust, say a 300 SF canopy in a brisk wind. You better believe that you would go somewhere!!

In your hypothetical situation, the jet would take off more or less at the same time it would otherwise....regardless of the speed of the tires.

edited to add...one more thing. The conveyer is what would determine the speed of the tires, not the thrust or airspeed of the jet. The wheels are going to move at the differential speed between the conveyer and the plane and it would have no impact (outside of some minor friction) on the plane. The conveyer in actuality would have no true refrence for the speed of the wheels.

[CSpenceFLY 1]

I'm not going to read every post but the answer is yes.The aircraft does not get it's propulsion from the ground it gets it from the air.The conveyor would have no effect.

.

[yamtx73 0]

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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

Ok, the belt is exactly matching the speed of the wheels, going in the opposite direction of rotation. Since the wheels aren't used to propel the aircraft the rotation of the belt should have no affect on forward motion so the wheels would wind up spinning faster as the propellor pulls the body forward. The wheel bearings may burn up but the aircraft should be able to take off.

The only naturals in this sport shit thru feathers...

[champu 1]

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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!!!

This is the correct answer. And better berrings in the wheels will just make them get to a faster rotational rate before they explode.

The engines of the plane are designed to take air from in front of the plane, and throw it behind the plane to make the airframe move forward relative to the air. Once the airframe builds up enough speed relative to the air (force of lift = force of gravity) the plane will leave the ground. It doesn't matter what the engines or the wheels are doing, all that matter is what the airframe is doing relative to the wind.

And here's the part people are missing...

Even though the plane does not use the wheels to drive itself forward, as long as the plane is sitting on the ground and using the ground for support, it's forward speed along the ground (and thus it's airspeed because there is no wind) is bound to the rolling speed of the wheels.

Four forces acting on the airframe.

1) force of gravity holding it down
2) normal force from the belt holding it up
3) force of thrust from the engines pushing it forward
4) force of friction from wheel bearings pushing it backward as the belt spins them faster and faster

they all cancel, the plane's not going anywhere, at least not until, as pjc says, the wheels explode and the plane flies off the back of the belt.

[davedlg 0]

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And here's the part people are missing...

Even though the plane does not use the wheels to drive itself forward, as long as the plane is sitting on the ground and using the ground for support, it's forward speed along the ground (and thus it's airspeed because there is no wind) is bound to the rolling speed of the wheels.

Four forces acting on the airframe.

1) force of gravity holding it down
2) normal force from the belt holding it up
3) force of thrust from the engines pushing it forward
4) force of friction from wheel bearings pushing it backward as the belt spins them faster and faster

they all cancel, the plane's not going anywhere, at least not until, as pjc says, the wheels explode and the plane flies off the back of the belt.

I disagree. The force of friction will be nowhere near the force of thrust from the engines. The only time this could even be true would be if the brakes were on. If the wheels were free to spin, there would be very little friction in comparison to the thrust from the engines and the plane would accelerate down the runway. The speed at which the wheels spin would be entirely determined by the speed of the conveyer....there is nothing the conveyer could "keep up with"

[ViperPilot 0]

Correct. In a perfectly situation (like this hypothetical one) you'll just get wheels spinning incredibly fast, attached to a stationary aircraft with no air flowing over the wings, thus no lift. In this hypothetical situation, lets say the engines propel the aircraft to it's rotation speed of 170 kts, but then the conveyer runs at the exact same power in the reverse direction, thus the aircraft never gets rolling on its wheels, as the wheels are held in a stationary position. No airflow = no lift. It doesn't matter one bit that the wheels don't provide the thrust.

[champu 1]

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I disagree. The force of friction will be nowhere near the force of thrust from the engines. The only time this could even be true would be if the brakes were on. If the wheels were free to spin, there would be very little friction in comparison to the thrust from the engines and the plane would accelerate down the runway. The speed at which the wheels spin would be entirely determined by the speed of the conveyer....there is nothing the conveyer could "keep up with"

Nope. If you spin a wheel fast enough you can generate enough friction to counter anything, right up to the point where the wheels simply explode.

You forgot one of the conditions laid out in the original post:

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The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.

The only kind of plane that could take off in such a scenario would have to be capable of VTOL

[sundevil777 102]

The conveyor would match the speed of the rotating wheel, but that would not be the speed of the body of the plane.

As I described in my earlier post (#24), even if the conveyor started accelerating before the engine started to provide thrust (I think this is a useful hypothetical), the body of the plane would not be moving as fast as the conveyor, because the wheels would start to spin. If you extend this conclusion, with the engine providing thrust, then the conveyor would provide a rearward push to a small degree, that depends on the rolling friction and rotational inertia of the wheels.

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

[pilotdave 0]

It seems to be a pretty complex problem.

The frictional force is not necessarily proportional to the rotation of the wheels (or the relative speed of the plane vs the belt).

Here's a 231 page discussion on a physics forum about this problem:

http://forum.physorg.com/index.php?showtopic=2417&st=0

And finally, video proof of the "correct" answer (or not, who knows): http://videos.streetfire.net/Comment.aspx?fileid=35E964D9-38DB-4EFD-BE8D-D6BA1A43A06B

Please don't continue this for 231 pages!
Dave

[sundevil777 102]

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It seems to be a pretty complex problem.

The frictional force is not necessarily proportional to the rotation of the wheels (or the relative speed of the plane vs the belt).

Here's a 231 page discussion on a physics forum about this problem:

http://forum.physorg.com/index.php?showtopic=2417&st=0

And finally, video "proof" of the correct answer: http://videos.streetfire.net/Comment.aspx?fileid=35E964D9-38DB-4EFD-BE8D-D6BA1A43A06B

Please don't continue this for 231 pages!
Dave

That link says that the conveyor tracks the 'plane speed' (as opposed to the wheel speed) and makes the conveyor speed the opposite. This is an easier to understand scenario. The video of their experiment is pretty funny, but not exactly going to convince those that think don't agree with the conclusion.

Some of the posts on that site also incorrectly state the scenario to require that the conveyor move such that it forces the plane to remain still. This is not the case, the conveyor is just supposed to move backwards at the same speed at the plane moves relative to the ground.

A skateboard is not such a good example because there is very little deflection of the 'tires' from the weight of the skateboard, so the rolling friction is very low.

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

[sundevil777 102]

One of the posts from the physics forum sums up the incorrect assumption that so many make:

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But as soon as the plane starts to overcome the friction and move forward, the conveyor speeds up to eliminate any forward motion - right?

This is of course wrong! The original problem states that the converyor speed will match the speed of the plane, NOT that the conveyor will move at whatever speed is needed to keep the plane still. The wheels will just be rotating extra fast with some extra 'drag' force that the plane will need to overcome.

It is amazing how so many did not understand the original problem statement.

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

[jonstark 8]

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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

The plane would accellerate with the conveyer matching the wheelspeed thus the wheels would not need to rotate. This would have no effect on whether the a/c would fly or not. An a/c flies due to the air going over the wings not the speed of the tires.

Now... If you were to introduce a windtunnel and accellerate the air past the a/c as it accellerated the a/c would take-off but wouldn't go anywhere relative to the physical tunnel just the air flowing within it.

And... if there were no atmosphere. Nope it wouldn't fly. It wouldn't even run if it were powered by an internal combustion engine.

sober up yet???

[wildblue 7]

Yeah, it seems pretty simple. Wheel speed doesn't have anything to do with the plane taking off. Heck, you could say the belt makes the wheels spin in the wrong direction, and the plane could still take off. The wheel bearings might melt, but who cares?!

it's like incest - you're substituting convenience for quality

[azureriders 0]

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The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.

Impossible. Let's think of the speed of the wheels in MPH and not RPM. Now consider that when the plane excerts thrust, by means of prop or jet, it is going to be draged, pushed or pulled through the AIR without regard to the ground or wheels. Now if the plane is North boud and belt is spinning South bound, the wheels will always be spinnig at the speed of the belt plus the airspeed of the plane. Therefore if, CB = to the speed of the Converyor Belt, AC = to the airspeed of the Air Craft, and WH = to the speed of the Wheels, then CB + AC = WH. This can only be true if CB or AC = 0 and by your example we know this not to be true.

If it were possible for the belt to match the wheel speed and if the plane would indeed take off, wow, what a break through.

New DZ at my place. My 40 acre track which is only 1320' by 1320' would make a perfect LZ and as for as take off, the otter could just roll out onto the connveryor belt, which would only need to be as long as the plane since it is not going to be moveing anyway, and then mysteriously rise off the ground and proceed to jump run. We could put up a net to stop it on landing, or would landing it back on the belt that is already spinning at above stall speed allow you to set down and come to a stop as the belt matches the deccelarating speed of the wheels until they came to a stop on a 50' run wa...connveryor way.

You think the DZ is a good idea, what do you think this would do to Aircraft Carrier design????

My post probably means nothing but I have been behind this PC and Auto Cad for over 12 hours and it was time for a break

[Lindercles 0]

For god's sake, IT'S A HYPOTHETICAL!

Please, at least read SOME previous posts before replying.

Sheesh!

[azureriders 0]

whoa, please dont yell at me, its been a long day. I did read all the post, that was just my two cents. Didnt really mean anything by it, hope no one takes offense, it wasnt meant to be offensive.

[Lindercles 0]

No worries bro.

If anyone takes offense to a hypothetical intertnet post....well, god help them.

I just think this thread has gone on way too long.

[champu 1]

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Yeah, it seems pretty simple. Wheel speed doesn't have anything to do with the plane taking off.

Sure it does, and here's the problem:

1 - can't generate lift without forward airspeed
2 - can't generate forward airspeed without forward groundspeed (because there's no wind)
3 - can't generate forward groundspeed without the wheels rolling (because you're resting the entire weight of the plane on the ground)
4 - if wheels roll, belt fights back
5 - can't beat the belt unless you beat friction
6 - can't beat friction unless you generate lift
7 - see 1

As they say, "You can't get there from here."

Physical experiments aren't going to demonstrate this properly because a belt that can instantaniously match the speed of a wheel rolling along it is a non-causal system, and is not physically realizable.

Any lag whatsoever in the feedback loop between the sensor that's measuring wheel speed and the motor control that's driving the conveyor will allow the plane to take off. But that's not what the original question is asking.

[Lindercles 0]

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1 - can't generate lift without forward airspeed
2 - can't generate forward airspeed without forward groundspeed (because there's no wind)

Didn't I say this about 9934593874 posts ago??

[champu 1]

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Didn't I say this about 9934593874 posts ago??

Yes, but that's only true if you omit 80% of my post as you have.

[azureriders 0]

was that what you said? I remember it was something about it not working, and then he said it, and she said it, oh and then I said it, yep and then he said it too. I think it has been said, yep, I think it has

[Lindercles 0]

2 = 80% of 9934593874?

I think that's what GW would refer to as "fuzzy math"

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