Will it take off?

Originally posted by orca71

Originally posted by Mayet
Without looking at all the other replies, yes.. cos the plane could be like a jump jet with vertical take off...

It doesnt have to be a jump jet. Any kind of jet or propellor will get it moving forward. The conveyor belt increases friction to higher than normal levels because the wheels are moving twice as fast as usual but it has no effect whatsoever on thrust, and hence propulsion. People are getting confused because they are used to wheels being the source of thrust as in cars or motorcycles.

With so many getting confused by a simple brain teaser its no wonder that con artists are able to raise money for anti-gravity and warp drive schemes.

Although I have to admit that while thinking it would take off when I first read the problem, I definitely had the reason WRONG. Guess I'd fall into the category of those suckers.

Originally posted by av8or
can we PLEASE stop arguing about this. It's getting on my nerves the number of people trying to 'scientifically prove that it will fly'. I won't bother trying to prove again that it won't fly because my responses have been over-simplified or over analysed. It's simple. the plane won't fly. take a step back, look at the bigger picture, the question is quite simple, as is the answer. CAN SOMEONE PLEASE CLOSE THIS TOPIC. it is going around in tight little circles with people who now what they are talking about being continuely bombarded with people adament to debunk well established laws and theories of physics and aerodynamics. face it people, this thread has copped way too much attention for what it is. PLEASE CLOSE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

You can stomp your feet all you like, but it won't change things.

The only thing stopping it taking off will be wheel bearing friction or the tyres exploding, and the max tyre speed for the Bombardier Q400 Dash8 is about 180kts, while the rotation speed is around 90 kts, so it may well take off.


Newtons 2nd law is a fairly well established law in physics - but your totally ignoring it.

Originally posted by ghost
[q
Waynos,

Unless I misunderstand you, I think I see why we can't seem to agree!

Now according to the laws of physics, when two oppisite forces of Equal strength act on the same object, but in oppisite directions, they cancell each other out. This makes the Net Force equal to ZERO. With a net force of Zero acting on the plane, it will remain stationary(Newton's First Law of Motion, A.K.A Inertia).

No you haven't misunderstood me and that is exactly where we disagree tim

I haven't read the many posts that have appeared after yours yet but here's my take on that point.

What you state above is exactly correct but my view is that the two opposing forces are not equal. Yes, the weight is on the wheels but this is mitigated by the castoring nature of those wheels, for instance much less force is required to manually push the plane forward than would be required to lift it up, a bit like the ancient Britons moving the huge blocks for Stonehenge on wooden rollers, however many were required to push them they would never have lifted them (oh no, another analogy! ). Coupled with the fact that the driving force is an independantly acting airscrew, this 'rollering' is what allows the propeller to pull the plane forward more quickly than the belt can push it back, in my view. However if the wheels were driven, like those of a car, then your statement would apply absolutely. I guess this is where we will have to disagree.

In fact heres an equivalent. When a family car is tested it is put on rollers which act in the same way as this theoretical belt and the car is 'driven' as quickly as possible but never moves. However when an aircrafts engine is tested it is not done this way. The aircraft is tethered firmly down because if it wasn't it would pull or push itself forward and off any rollers it might be sitting on.

[edit on 17-2-2006 by waynos]

The planes engines pushes it forward.

The drag of the wheels on the convayer hold it back.

If you read the question and get it to mean that the drag on the plane is enough to negate the force of the engine then the plane isn't going to move and therefore won't take off.

However that would have to be one damn fast convayor.


[edit on 17-2-2006 by Nacnud]

What is so hard for people to understand. Who cares about the ground??? Forget the ground the wheels, the conveyor. The airplane engine makes the plane move forward. It does not care what surface (if any) the plane is physically sitting on. So if the conveyor is wheeling backwards, what does it matter??? It has no effect on the forward thrust of the engines, the plane will move forward normally and take off normally. Stop thinking the conveyor is holding the plane back. Unless the damn brakes are on, nothing is holding the plane back from accelerating forward. There is no equal force on the tires. The tired spin freely.

forget it 80 % of you are ignorant and lack fundamental understanding of physics.

Have fun with your non flying plane idea

Some people are definately having a hard time with the concept that the wheels are free-spinning, and completely independant of the thrust, thats why the conveyer cannot cancel out the thrust.

The prop's interaction with the surrounding air is where the thrust is generated and, unlike a car, this is completely independant of the wheel's torque against the conveyer belt.

The conveyer belt's negative force against the plane is "lost" (for all practical purposes) in the wheels by only causing them to spin faster in the same direction.

Thus, the belt has no effect on cancelling any thrust because it is not generated at the wheels, but instead, is a completely independant system.

Ok I am so confused.

Here is the Original question:

"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?"

Now looking at the question we see several things:
1. The plan starts out standing still on the moving runway.

” A plane is standing on a runway that can move

2. The Plane begins to move down the “runway”

The plane moves in one direction,

3. The Runway moves in the opposite direction

while the conveyer moves in the opposite direction.

4. The Runway can track the exact speed of the aircraft and match it

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).

5. Can the plane take off.

Why are we discounting the frictional restraints on the wheel axles. The plane would never fly and would most likely suffer gear failure and collapse into a big fireball. Ever seen someone slip on a treadmill…well you would get the same result.

I know there will be a bunch of claims of this and that, but they are all nonsensical. You can not add items such as frictionless wheel bearings and such. As the question makes no such allotment, we are stuck with only the verbiage of the question. And the answer is definitively….NO. It will begin to move but the gear will slag well before reaching rotational speed. Therefore it will not TAKE OFF.

We could alter one or two things and it would work, but that would not be the question. If you want to change the question…fine but that would be silly. You would have then made up an entirely new question, to suit your desired answer, just to be right.


So in summation IA’s answer is Parts and pieces could become airborne….right after the big “Die Hard” explosion! LOL

No, read it again. The plane is standing still on a runway that can move, not one that is moving already. That is an interpretation you have added, which you just said we should not do.

The runway tracks the planes speed and matches it exactly, therefore the plane moves before the runway does, even if only fractionally, therefore the biggest obstacle to its progress, inertia, has already been overcome.

Your assumption that the gear will 'most likely' collapse is no more valid than my assumption that it wont and so in theory, which is all this can ever be, it will fly.



[edit on 17-2-2006 by waynos]

Landing gear can take some extreme punishment, it won't fail from this at all. The plane doesn't have hardly any rolling resistance, the engines can overcome any extra due to the increased speed of the wheels the plane will take off.

the plane is shut off, no engine running..

the conveyor is on and running backwards, ie the direction of travel is from the planes nose towards the tail.

Does the plane move back along the conveyor.. yes

even though the plane is sitting on "wheels" yes

The mass of the plane of the wheel axles pushes the plane into the conveyor, with no power input from the plane the plane moves along the conveyor, after the initial start up due to the rocking of the planes mass there would be little if any opposite roll in the planes wheels, the plane would simply move along in the direction of the conveyor

Now add some input power from the planes engine, now instead of the plane moving along at the same speed as the conveyor the plane is moving slower in the same direction as that of the conveyor, meaning it is still moving back along the conveyor but not at a 1:1 rate, as now the wheels on the plane have positive forward rotation.

Add more power and the plane slows in the rate that it is moving back along with the conveyor until such time that the plane is moving forward at the same rate that the conveyor is trying to take the plane backwards. The wheels are only turing at the rate given by the forward speed of the plane which when equal to the counter speed of the conveyor become only the speed of the equallizing counter speed ie the conveyor since the wheels are only being physically driven on one side, which is the one in contact with the conveyor surface.

The plane has no positive forward speed at this point and thus has no lift, therefor it can not fly.

The bogus idea of the static boundary area off of the conveyor belt does not exist as air does not operate this way, the speed at which the conveyor is traveling to counter the forward motion of the plane would create a small vaccum pocket over the surface and create a swirling chaos of air above it, which is not conducive to produce "ground lift"

Air molecules are actually moving in the reverse of the direction of the conveyor belt as the unaffected air density in front of the air mass ahead of the conveyor (which is not affected upon) acts as a wall the momentarily moving forward air particles slam into this air wal and are repelled back, thus if you were taking a point on the conveyor and traveling with it in the same direction the air over it would appear to be going the opposite direction not in seq with it. Therefore it would not be capable of creating ground lift


www.grc.nasa.gov...

To make things more confusing, the boundary layer may lift off or "separate" from the body and create an effective shape much different from the physical shape. This happens because the flow in the boundary has very low energy (relative to the free stream) and is more easily driven by changes in pressure.


(me)
The air mass is low energy having no velocity of its own and as there is no wing being driven forward into it or a wall traveling along on the conveyor to pressurize the air mass about it, then it would be considered to have very low energy and thus the boundary air above the conveyor would be considered turbulent and therefore more then likely would have “separation issues” with the moving conveyor surface.



[edit on 17-2-2006 by robertfenix]

I'll repeat my earlier explination, with pictures this time as apparently the "it will not fly" crowd chose to ignore me.

The argument has been raised that with 2 equal forces acting in opposite directions, forward momentum will not be achieved.

I give you two equal forces acting in opposite directions, and convieniently linked by a strong chain. Neither the red truck nor the blue car will move, despite both being on a hill and placed in neutral.

However, once the aircraft's brakes are released, there is no mechanical linkage tying aircraft directly to the runway.

For this reason, we can assume both vehicles are still in neutral, but the chain has been removed. The conveyer belt (red truck) is free to roll down the left side of the hill as fast as it will, but it will not prevent the airplane (blue car) from rolling down the other side.

Forgive me if this has been asked already, as I haven't read all the posts...

But if you're trying to take off at 100mph for instance, and the wind is also blowing at 100mph in the same direction you are trying to take off... will the plane take off?

I've always thought that planes will take off sooner if they take off INTO the wind. Same with birds. I saw at the San Diego zoo, an animal trainer lady showed us an eagle flying in place (with the help of a fan blowing towards the eagle).

So my opinion would be that the plane on the treadmill won't take off unless a wind is also blowing towards the plane. Perhaps the props produce this wind though?

your little pictures with the cars is not complete, you are forgetting the thrid force which is acting on both sides of the hil.

Gravity, is pushing both cars down equally. Both cars having equal mass will not roll down the hill when connected by the chain because the mass+ gravity is equal on both sides.

It has nothing to do with opposing forces. Gravity is pulling both cars down equall (assuming both are equal mass) and the chain and the hill top become a fulcrum. Just like a scale. with equal mass on both sides the scale arms appear to defy gravity by balancing on the fulcrum of the scale.

Take away the hill and the chain is irrelevant because the cars are not opposing forces only gravity is still puching down on each.

So your example is flawed and does not apply here

This site's section has a nice, full, lengthy explanation of this myth that has apparently been circulating for some time:

There's a new aviation myth running around the Internet. It involves a conveyer-belt runway and misuse of aerodynamics and ... well, it's better if AVweb's Rick Durden explains it all himself in The Pilot's Lounge.....

The Pilot's Lounge


mg

I love how people have resorted to "No, you're wrong for saying it will take off, thus you are ignorant and should just stop". I don't think it's fair to do that because I don't think anyone here has actually run an experiment to be able to say what will happen, until someone actually runs an experiment, we will NEVER know.

And I mean it has to be an ACCURATE experiment, nothing with kites and treadmills or rollerblades and treadmills. A real plane on a real moving runway.

Now to get a runway to move.

Shattered OUT...

Planes take off in a shorter distance into the wind because the airspeed is starting out greater. If the wind is blowing as a tailwind, the plane has a longer takeoff roll to build the speed.

If you had no airspeed at all (ie. the treadmill), it shouldn't take off right?

The treadmill idea would have the same effect of taking off in the same direction of the wind, with the wind being equal to the speed of the plane on the runway.

Originally posted by waynos
No, read it again. The plane is standing still on a runway that can move, not one that is moving already. That is an interpretation you have added, which you just said we should not do.

The runway tracks the planes speed and matches it exactly, therefore the plane moves before the runway does, even if only fractionally, therefore the biggest obstacle to its progress, inertia, has already been overcome.

Your assumption that the gear will 'most likely' collapse is no more valid than my assumption that it wont and so in theory, which is all this can ever be, it will fly.

No I am sorry You are the one that is incorrect the question states that the runway moves exactly the same. Not slight but pretty darn close to, but exactly.

Def. of exactly:
exactly
adverb
In an exact manner.
With precision or absolute conformity.
www.answers.com...&r=67

Nothing in the question indicates a lag between first rotation of the wheel and the first contra movement of the runway. Even if there is a slight lag, the speed of the wheels, prior to rotation, would be well in excess of the rating for the tire. This would increase the friction on the tires heating up the gas inside. Ever seen what happens to a tire that overcooks, it blows up. There would be a systemic failure well before v2 is ever reached.

BTW the main gear do not ”caster” Caster means to pivot not to freely spin. The nose gear can caster though (to a limited degree).

Originally posted by mxboy15u
Landing gear can take some extreme punishment, it won't fail from this at all. The plane doesn't have hardly any rolling resistance, the engines can overcome any extra due to the increased speed of the wheels the plane will take off.

What are you talking about. Correct me if I am wrong but I assumed the “Will” crowd has established that the wheel speed would be extreme, say two times the speed of the airframe. This means that the bearings and tires will not handle the load.


I just want to point out that IF the question allowed for frictionless bearings and tires that can withstand the speed, then Yes the plane would take off. Or if we are talking about a Piper cub or other STOL type airframe, then yes it could. But a 737 and such…no but that is due to material fatigue and has nothing to do with the wheels.

Originally posted by Kruel
If you had no airspeed at all (ie. the treadmill), it shouldn't take off right?

The treadmill idea would have the same effect of taking off in the same direction of the wind, with the wind being equal to the speed of the plane on the runway.

No.

Even if the aircraft had its engines off and was already being taken backwards on a treadmill at a speed equal to it's take-off speed, or -x mph (where x= take off speed), as soon as the engines were fired up it would be able to do so without a problem as long as the engines are capable to generate thrust at take-off speed, i.e., take-off speed is not equal to maximum non-drag-constrained speed.

In other words, the only way the airplane will not take-off is if the airplane either is not normally able to take-off anyway or if it can normally take off and has a drag coefficient of zero.

Which, of course, means it will be able to take off.