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Will it take off?


Coytee

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"An airplane engine doesn't exert force on the ground it exerts force on the air and its resulting acceleration and speed is relative to the air. It could care less what the conveyor is doing. It will only add a small amount of drag based on the friction in the bearings of the wheels and the tires' rolling resistance."

I spent a decade or so as an aircraft maintenance inspector. We use to chalk the wheels of fixed wing aircraft and run the engines/props all the time to perform engine analisys.

None of the planes every lifted off the ground.

The props or jet thrust, in itself, can not generate enough lift, to put the plane in the air.

A plane that can not move forward, will never take off.

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Agreed, but we are not talking about a plane that is stopped in relation to everything around it as if it were chocked. This plane is free to move forward by the force from the prop.

Imagine a row of identical trees as a background to said plane. If it never passes a tree, it will never fly. But the fact that the wheels are already rolling on the conveyor doesn't mean the plane is incapable of passing trees, or moving forward. Move forward fast enough, and it should lift off, correct?

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You are correct in saying that a plane that can not move forward will never take off, and that air wash from a prop will not make the plane lift off The post in front of mine was talking about air wash from the prop, not me.

Also, in your tests the the wheels were chocked. The wheels of the plane in question are free to turn.

If you are standing on roller skates, and I pull the rug out from under you, you will not move but the wheels will turn. Same goes here... the conveyor belt imparts no force to the plane except for a small frictional force from the wheel bearings.

OK, how about this.

You are on a bicycle which is on a conveyor. You are holding onto your dogs leash. The dog is not on the conveyor but is on the ground beside the conveyor. You say to your dog, Sit. Stay. The conveyor starts up. Neither you nor your dog are moving, but your tires are spinning. The small frictional force in the wheel bearings is not enough to pull your dog backwards.

Now you throw a ball and say to your dog, Fetch! The dog starts to pull you and your bike. The reverse speed of the conveyor matches your dogs forward speed (who is running on solid ground, not the conveyor) and youre still holding the rope.

Does your dog get to the ball?

The dog pushes on the ground. The airplane engine pushes on the air.

The dog is tied to you by a rope. The engine is tied to the airplane with bolts.

The wheel bearing friction doesnt slow down your dog or the airplane.

The dog gets his ball. The plane takes off.

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Agreed, but we are not talking about a plane that is stopped in relation to everything around it as if it were chocked. This plane is free to move forward by the force from the prop.

Imagine a row of identical trees as a background to said plane. If it never passes a tree, it will never fly. But the fact that the wheels are already rolling on the conveyor doesn't mean the plane is incapable of passing trees, or moving forward. Move forward fast enough, and it should lift off, correct?

CT/BT, I didn' write it, so it's open to some interpretation perhaps. I personally, presumed it to mean that though the plane was NOT chocked, that the conver belt would move "infinately fast" if needed, to 100% offset any forward motion of the plane.

Seems to me that until the plan can obtain forward motion (relative to say, a tree) sufficient to lift it, that it ain't going anywhere. My take on it is, as long as the belt is moving the plane 'backwards' (to keep it in place) that any forward motion would be used to keep it on the same spot.

This strikes me and my peabrain, as one of those things that is probably so simple, folks like me are confusing it up! [:$] I'm never going to let Chops take any of my dogs for a walk near any airports!!

[:P]

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This is a simple Dynamics problem solved using the equation SumF=mA. The fact that the wheels are turning in relation to the the ground only changes the frictional force from a static force to a kinetic force. Acceleration of the aircraft is going to be a function of the resultant forces acting on the aircraft divided by the mass being moved. The landing gears purpose is to support the weight of the aircraft until the point that lift provided by the wings exceeds the weight of the aircraft. the lift generated by the wings is a function of the air moving across the wings. As my dynamics prof used to say "does everbody follow what I say now?" It will fly

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"da plane", "da plane" needs forward motion to allow the wings o generate lift, will not fly on prop or jet thrust alone (VTOL being the exception)

"da plane" does not need wheels to fly, nor does it need a prop, or jet thrust, to generate primary lift.....note glider being pulled by turck or air field winch, will get air borne once the lift created by the forward movement of the planes wings is greater than the weigth of "da plane".

prop or jet enging generates thrust over a portion of the planes wings.

the plane moves forward in response to the thrust

the forward motion results in more air traveling over the wings

this creates lift

the plane begines to get lighter

the prop or jet thrust becomes more effcient since the plane has be come lighter as a result of the thrust, plane move forward faster

faster moving plane generates more lift over the wings

more lift means plane is now lighter

prop or jet thrust becomes even more efficent, plane moves forward even faster

cycle continues until the plane is airborne.

no forward movement of the planes wings, and plane will not fly.

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Think of it this way. A single engine on a jetliner can generate over 50,000 pounds of thrust. If there are four engines that's 200,000 pounds of thrust. In the example, there is no opposing force exerted on the aircraft so the plane accelerates forward moving the wing through the air creating lift force. Using chocks on the tarmac results in an opposing force and there is no forward motion in that case. The conveyor is irrelevant except that the landing gear wheels must spin twice as fast but the plane's airspeed is normal given it's thrust and the plane takes off. The conveyor would also have to be as long as the regular runway.

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I just dont see how the plane can take off with no air flow over the wing to provide lift.

Hell, I'm on my second scotch after a very long work week and I really don't give a .......This is obviously a debate for those people much smarter than I.

Time for another scotch.

If I just had a conveyer belt, dog, ball, bicycle, plane, sheep, vasoline, and a night light, I could get to the bottom of this!

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"

I can't believe that some of the contributors to this thread can't picture this in their heads. Take a while to do so, you will come to the only conclusion, IT WILL FLY. "

picture this...if it would fly....why do we need VTOL capable aircrafts? if it would fly...that means all aircraft would be VTOL capable.....which is certainly not true.

////////////////////////

VTOL is an abbreviaton for Vertical Take-Off and Landing. VTOL describes fixed-wing aircraft that can lift off vertically. This classification includes only a very few aircraft; helicopters, autogyros; balloons and airships are not normally considered VTOL. Some aircraft can operate in VTOL mode in addition to others, such as CTOL (Conventional Take-off and Landing) and/or STOL (Short Take-Off and Landing). Others can only operate by VTOL, due to the aircraft lacking landing gear that can handle horizontal motion.

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I will admit to not having read any of the 3 pages of responses (and it bothers me a bit that there ARE 3 pages of debate over this!) - but the answer is easy!


Using only what was stated and assuming nothing else...You have a case of relative motion where a conveyor moves and the wheels of the plane move correspondingly fast so the plane remains in the same spot.


Let's see, that last I checked, the cause of lift was not wheels turning, but rather the differential velocity of air flowing over a wing generating sufficient lift to make the plane airborne.


Despite the wheels turning, there is no indication that there is any increase in the speed of the air over a wing in the proper direction to cause any lift - in fact there is no indication of any air flow over a wing period.


If you can accelerate the plane (by whatever method you choose - prop, jet, rubberband, gnats superglued to the wings, flatulence...) such that the differential between the air velocity and the wing generate sufficient lift, yes it will fly.


But if you are simply allowing the wheels to turn in a 'frictionless'(ideal) manner such that the plane stands still on a conveyor, then If you can get the plane airborne in this scenario, call me. I would love to be your manager.

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Just because the problem states that the conveyor moves backwards at the same velocity that the plane moves forward does not mean that the plane is stationary relative to a fixed reference (say still air and the ground). That's just thrown in as a red herring to cause a premature conclusion that the plane remains stationary. Without an applied force opposing the thrust of the aircraft, the plane must accelerate forward (relative to the fixed reference of still air) thus moving the wing through the air and creating lift force. The conveyor is irrelevant, it just spins the tires as the plane moves (it could be moving backwards two or three times as fast as the plane moves and not affect the plane's forward acceleration for a normal take off). Yes, since the wheels will be turning faster than normal, you could argue that the frictional force in the wheel bearings increase to oppose the forward thrust but that force will be negligible.

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Just because the problem states that the conveyor moves backwards at the same velocity that the plane moves forward does not mean that the plane is stationary relative to a fixed reference (say still air). That's just thrown in as a red herring to cause a premature conclusion that the plane remains stationary. Without an applied force opposing the thrust of the aircraft, the plane must accelerate forward (relative to the fixed reference of still air) thus moving the wing through the air and creating lift force. The conveyor is irrelevant (it could be moving backwards twice as fast as the plane moves and not affect the plane's forward acceleration for a normal take off). Yes, since the wheels will be turning faster than normal, you could argue that the frictional force in the wheel bearings increase to oppose the forward thrust but that force will be negligible.

I hate smart people

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The thing to remember is that the wheels on the plane's landing gear spin freely and have nothing to do with providing a driving force to move the plane forward or slow it down. Instead of a plane, lets place a car with wings on the conveyor and say that the conveyor moves backwards at the same velocity that is read on the flying car's speedometer. In that case, the car would remain stationary since the car's propulsion system (the drive wheels) are coupled to the conveyor. Just like running on a treadmill. In the case of the plane; however, the propulsion system has nothing to do with the conveyor and the plane flies off into the wild blue yonder.

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couldn't someone build a model airplane that can fly and put it on a conveyor belt?

anyways I think we need to define certain things......

real world and theoretical world (aka physics world)

in a perfect physics world with a 0% friction on the wheels, the only point of reference or motion would be a plane's wheels. The air would be stationary and so would the body. The body is not moving but the wheels/bearing would be.

In real world the friction of the beaing will apply force to the airplane body and thus pushing it backwards......

there might be a relavent question to the conveyor type belt being capable to moving enough air that the plane starts to develope lift? even treadmills do create a tiny amount of air as the friction and the surface of the surface does catch air.

I do believe Bernolli(sp) law was that lift is created when two different pressures are over a two different surfaces (get a piece of paper and put it on your bottom lip and blow over the paper, the higher pressure on top means lower pressure on the bottom and creates lift, the paper will rise) Since we can I guess say that the treadmill will not generate enough wind to have the wings catch it would be just a plane moving a certain speed without the air catching it....

The closest thing I can thing of is a sailplane. A plane that relies on thermals and does not have an engine. The plane is hoisted into the air by a tow airplane and relies on thermals and forward motion in the air. The air in this case does not move to create lift but the sailplane is moving into the wind to create the lift. Since the reference point to the airplane is stationary it should not lift? OK I was jumping everywhere...... I'll be quiet now.....

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First off, the originator of this thread should be tar and feathered. knowing full well what havoc it must have caused on the other forum. [:P] That said, it is fun to watch the different opinions and reasoning.

No one has said the conveyor belt is causing the airflow expected to cause lift at the wing.

So we have a vehicle with wheels (the airplane or me with roller skates on) resting on a (conveyor belt or tread mill). The belt/treadmill can roll as fast as the wheels, so no apparent motion between the two.

I firmly believe that if an outside force (the prop, or you with a broom handle) is applied to the (plane or my buttocks) with enough pressure, the (plane or I) will move forward. Move it or I fast enough, and the plane will fly, and I will surely fall off the front end of the treadmill. [:P]

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For you "it will fly" people... (and I'm asking honestly since I really don't know)

Here's how I see it...

With the plane AT REST, the weight of the plane is on the wheels. The plane can't fly until the weight is transferred from the wheels to the wings.

If/as the engine turns, pulling plane forward, causing treadmill to roll in opposite direction in perfect unison with the wheels & friction & bearings and all that crap, the weight is STILL currently on the WHEELS, is it not?

If not, where is the weight?

If the weight IS still on the wheels, then any 'forward' motion is absorbed/wasted by the conveyor belt working in perfect unision is it not? If it IS absorbed, then how does the plane garner any forward motion over the wings, to transfer the weight from the wheels TO the wings?

Once the weight is transferred to the WINGS, I can see the logic that it WILL fly because then the conveyor/wheel situation is moot.

thoughts?

And as for tarred & feathered.....

gotta catch me first

[:P]

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