Hey, I said I was being stupid in the example, NOT in real life.

John Stricker

PS: No guts, no glory.

quote Originally posted by Wolfhound: Strickter, If your landing downwind in an 80 knot wind I,m not flying with you.

quote Originally posted by jstricker: No you won't. If you could, you could take off by doing a full power runup and you can't even come close. John Stricker

I guess you are right. It can't force enough air over the wings to give it lift.

quote Originally posted by fierofetish: I think you must all re-read the description !! It will not take off!! The conveyor belt is controlled to provide the same rearward motion of the conveyorbelt, as the forward motion of the plane.That means, if the plane's motive power would move the plane forward at say 120 mph, the conveyor belt would compensate by running at 120mph rearwards, thereby maintaining the plane in the same position...motionless!! The wheels would be spinning at 120 mph, the conveyor belt would be running in the other direction at 120 mph. There would be no air passing over the wings, because the plane is motionless with regard to ground/air.The best equivalent I can give, is running on a training mill. Except you run at a speed to match that of the treadmill. In this case, it is the treadmill running to match the speed of the aeroplane's forward motion. Nick

Your treadmill comparison is flawed. Your running feet are propelling your body along the treadmill, giving you a relative speed of zero.

Try this:
Hold a skateboard on top of a treadmill. Turn on the treadmill and the wheels of the skateboard will turn. No matter how fast you run the treadmill, you will always be able to push the skateboard forward just by moving your hand. Because the skateboard wheels are not driven, the backward speed of the treadmill is irrelevant to the forward speed of the skateboard.

The plane will take off.

Excellent analogy.

This theory will not apply in this case.Your theory requires the motive force to be projected into the skateboard from a fixed stationary grounding ie your feet would be exerting a force on the skateboard from a plane unaffcted by the motions involved. In reality, you must consider it this way, and then you will see why you are wrong.You are providing propulsion to the skateboard, by exerting a force exerted against the ground on which you are standing. The skateboard isn't standing on the same ground, it is on the treadmill.So for this instance, you would have to be standing on the skateboard, and pushing against thin air for motivation.The other argument about the propeller giving enough airflow to lift the plane is also flawed. An example as to why.
You have a sailboat, with its sails fully up. There is no wind. You put a powerful fan on the dock behind it, and the sails will fill, and the boat move.Because the fan is pushing air towards the sails, but is anchored to the dock.The anchorage of the fan enables it to move air by its inertia relevant to the ground it is fixed to. Now, if you were to put the fan in the back of the boat, pointing forward toward the sails, the sails would fill with air, but the boat would stand still. Why?Because the fan is not anchored to an imoveable base.And therefore, the action of the fan pulling air toward the sails, would be compensated by the blades of the fan pulling the inert air behind it.So, the pull of the fanblade trying to go backward, would compensate for the wind created trying to push the sails forward.Because it is mounted on the boat, it will not move the boat forward.
Nick

quote Originally posted by Gary W: Your treadmill comparison is flawed. Your running feet are propelling your body along the treadmill, giving you a relative speed of zero. Try this: Hold a skateboard on top of a treadmill. Turn on the treadmill and the wheels of the skateboard will turn. No matter how fast you run the treadmill, you will always be able to push the skateboard forward just by moving your hand. Because the skateboard wheels are not driven, the backward speed of the treadmill is irrelevant to the forward speed of the skateboard. The plane will take off.

OK, Your in a float plane on a river.
Which is more important?
Taking off down stream, or taking off into the wind?
Same thing!, it's all about air speed.

[This message has been edited by Wolfhound (edited 12-02-2005).]

Except completely wrong!! read above!!

quote Originally posted by Taijiguy: Excellent analogy.

quote Originally posted by Gary W: Your treadmill comparison is flawed. Your running feet are propelling your body along the treadmill, giving you a relative speed of zero. Try this: Hold a skateboard on top of a treadmill. Turn on the treadmill and the wheels of the skateboard will turn. No matter how fast you run the treadmill, you will always be able to push the skateboard forward just by moving your hand. Because the skateboard wheels are not driven, the backward speed of the treadmill is irrelevant to the forward speed of the skateboard. The plane will take off.

But you have to excert enough force to propell it forward enough to break that friction point.

You place a skateboard on a treadmill by itself and it will just move with the treadmill and fall off. You can hold it in place with your hand, as you say and no matter what speed the treadmill is going, you keep it in place or even move it forward. But the faster that treadmill goes, the more force you have to apply to keep that skateboard stationary. The wheels may just spin, but there is friction involved and that what makes it more difficult to keep it in place as the speed increases.

The plane doesn't have to surpass the speed of the conveyor, it just have to have enough thrust to surpass the friction drag on it's wheels.

quote Originally posted by fierofetish: Except completely wrong!! read above!!

Think outside of the box Nick. It's exactly right. The conveyor doesn't have any effect on air speed because it's functioning as the GROUND. Does a plane stop flying when the wheels leave the ground? So why would the movement/lack of movement/relative speed of the wheels keep it from lifting off?

[This message has been edited by Taijiguy (edited 12-02-2005).]

quote Originally posted by Wichita: But you have to excert enough force to propell it forward enough to break that friction point.

This is also true, but I figure we were letting that slide (no pun intended)

Friction of turning the wheels is about >0001% percent of the equation!! You can only exert force on the skateboard, by pushing against an inert base,,the ground! The forward motivation is exerted, on an aeroplane, by an engine which is mounted on the plane.Therefore, the only inert component involved in flying an aeroplane is the air it suspended in.If the plane is on a conveyor belt that is running at the same speed backwards, as the engine is trying to propel the plane forward, it will stand still!! The air isn't moving against the wings; the plane has to move forward, in stationary air, to create the lift required to raise the plane from the ground.The forces required to move the plane forward, are exerted by the forward motion in the air. If the plane cannot move forward, relative to the ground and air,it cannot fly.As the conveyor belt is absorbing the power created by the plane's engines by moving backward at the same speed, it will stay where it is..until the engine blows up!! The relevant, and most significant point given in the information, is that the conveyor belt is tracking forward motion of the plane, and keeps it standing still by accelerating the rearward motion at the same rate as the engines try to pull the plane forward.
Nick
Edit to add...Thinking inside my box, in this case is correct..and I am staying here!!

[This message has been edited by fierofetish (edited 12-02-2005).]

You're missing the point, Nick.

An airplane's motive force is indpendent of the ground and has nothing to do with it. If it did, it would be a short flight indeed.

If the airplane is stationary as compared to the relative wind, then the airplane will not fly, but the conditions of the example don't say anything that would lead me to believe that whatever the aircraft used for thrust would be interrupted.

John Stricker

quote Originally posted by fierofetish: Friction of turning the wheels is about >0001% percent of the equation!! You can only exert force on the skateboard, by pushing against an inert base,,the ground! The forward motivation is exerted, on an aeroplane, by an engine which is mounted on the plane.Therefore, the only inert component involved in flying an aeroplane is the air it suspended in.If the plane is on a conveyor belt that is running at the same speed backwards, as the engine is trying to propel the plane forward, it will stand still!! The air isn't moving against the wings; the plane has to move forward, in stationary air, to create the lift required to raise the plane from the ground.The forces required to move the plane forward, are exerted by the forward motion in the air. If the plane cannot move forward, relative to the ground and air,it cannot fly.As the conveyor belt is absorbing the power created by the plane's engines by moving backward at the same speed, it will stay where it is..until the engine blows up!! The relevant, and most significant point given in the information, is that the conveyor belt is tracking forward motion of the plane, and keeps it standing still by accelerating the rearward motion at the same rate as the engines try to pull the plane forward. Nick

The conveyor belt is irrelivant. If the engine is on then it is the props that propel the plane forward. From the statements that I am hearing the plane will not takeoff, most you must not know how a plane works. And by your theories, explain to me how a seaplane takes off, it has no wheels.

EDIT: to point out nick's flaw. The wheels are on ball bearings, there is no way in hell that a conveyor belt could spin fast enough against the wheels to create enough pull to equal the thrust of the engine. Period.

[This message has been edited by MDFierolvr (edited 12-02-2005).]

I guess you guys may be right... Instead of trying to grip physics, I'd rather have an example everyone can follow.

Everyone remember those wind-up rubber band airplanes with the little plastic wheels?

Okay, if you wound those things up enough, you could get them to take off from a standing start on the ground (like a real plane).

Now imagine putting a large piece of paper underneath it (conveyor belt). Start pulling when you have someone let go of it, and it will still take off. The only difference is, the wheels will spin twice as fast.

Good explanation, Ryan.
Or lay a bottle rocket on a conveyor belt.

[This message has been edited by Wolfhound (edited 12-02-2005).]

quote Originally posted by Gary W: Hold a skateboard on top of a treadmill. Turn on the treadmill and the wheels of the skateboard will turn. No matter how fast you run the treadmill, you will always be able to push the skateboard forward just by moving your hand. Because the skateboard wheels are not driven, the backward speed of the treadmill is irrelevant to the forward speed of the skateboard. The plane will take off.

Your analogy is flawed. Perhaps read the original post again.

quote 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).

No matter what, the plane will not gain ground speed in this scenario. Therefore it will not lift off.

Sorry to disagree John.The relevant fact in the stated question, is that the conveyor belt would accelerate to match the increasing theorectical speed of the plane.If the plane engines cause the plane to move forward, the conveyor belt would increase its speed to negate that forward motion.The forward motion of the plane has to be such that the stationary air it is trying to use for lift is being passed through at sufficient speed to create lift. If the plane is not passing through the air, it cannot lift.Look at it this way, if you like.The engines are flat out.the conveyor belt is moving backward at the optimum speed to match the theoretical forward motion caused by the engines. So, the conveyor belt is moving backward at 120 mph, and the engines are keeping the plane moving forward at 120 mph. Shut the ngines off, and keep the conveyor belt running at the same speed backwards.the plane would now slow down, but the 'Ground' is still running backwards at 120 mph. The plane would start going backwards, and eventually move to the end of the belt, and fall off.

quote Originally posted by jstricker: You're missing the point, Nick. An airplane's motive force is indpendent of the ground and has nothing to do with it. If it did, it would be a short flight indeed. If the airplane is stationary as compared to the relative wind, then the airplane will not fly, but the conditions of the example don't say anything that would lead me to believe that whatever the aircraft used for thrust would be interrupted. John Stricker

I don't care how fast your conveyer is moving the plane will move forward (relative to the air) and take off

quote Originally posted by fierofetish: WoooHooo!!! Somebody has read the neccessary and relevant information given!!! Well done Patrick!!!

Nick, isn't it weird how certain aspects of the proposed scenario are simply ignored (or missed) by a lot of people. The scenario itself may be flawed, but working with what we're given, this plane will not take off.

By the way, why are so many of you convinced that this plane has a prop?

...

EDIT: duh, I am being stupid, my own training is acting against me... ARGHH!

[This message has been edited by MDFierolvr (edited 12-02-2005).]

quote Originally posted by fierofetish: Friction of turning the wheels is about >0001% percent of the equation!! You can only exert force on the skateboard, by pushing against an inert base,,the ground! The forward motivation is exerted, on an aeroplane, by an engine which is mounted on the plane.Therefore, the only inert component involved in flying an aeroplane is the air it suspended in.If the plane is on a conveyor belt that is running at the same speed backwards, as the engine is trying to propel the plane forward, it will stand still!! The air isn't moving against the wings; the plane has to move forward, in stationary air, to create the lift required to raise the plane from the ground.The forces required to move the plane forward, are exerted by the forward motion in the air. If the plane cannot move forward, relative to the ground and air,it cannot fly.As the conveyor belt is absorbing the power created by the plane's engines by moving backward at the same speed, it will stay where it is..until the engine blows up!! The relevant, and most significant point given in the information, is that the conveyor belt is tracking forward motion of the plane, and keeps it standing still by accelerating the rearward motion at the same rate as the engines try to pull the plane forward. Nick Edit to add...Thinking inside my box, in this case is correct..and I am staying here!!

I wouldn't call friction .00001% What is keeping the airplane from flying is drag and weight. If it has enough thrust and lift to overcome drag and its weight, it flys. Drag is an aerodynamic force, but the force of the conveyer is applied to its wheels. All the plane has to do is have enough thrust to overcome that friction and its potential energy at rest and it will move forward. Albiet slowly, but it will get there.

People use the dyno test as an example of the aircraft standing still, but that is because the car wheels are turning the dyno wheel with the same force that is applied, which will cancel each other out. But the conveyor is moving on its own. The Aircraft is not propelling the conveyor. If the conveyor is moving at 120mph, and the aircraft has a thrust that will propel it 120mph, it can overcome the conveyor.

It won't!! The propeller will be exerting enough force to keep the plane in a fixed position!! It will use the air to keep the plane stationary to the ground on which the conveyor belt is mounted. And the relative speed of the air to that ground is nil, unless there is a headwind of enough speed to give the wings lift.The engines are using the air to counteract the rearward motion of the conveyorbelt, and therfore the plane,therby keeping the plane in a stationary position, relevant to the surrounding ground, and therefore the stationary air.the engines only supply power to the plane by pulling the air through it.They do not provide lift. Only by moving forward, at the neccessary speed to create lift ON THE WINGS from the air. The engines provide ONLYforward motive power.The forward motion then allows the stationary air through which the wings are passing to flow over the wings, giving lift. If the engine provided LIFT as well as forward motion, the wings would not be neccessary.
Nick

------------------
fierofetish.PFF'S self-confessed Snowbird!!

Responsibility: the solution for our World's Dilemmas..
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quote Originally posted by fierofetish: WoooHooo!!! Somebody has read the neccessary and relevant information given!!! Well done Patrick!!! Nick

Someone has no concept of how an aircraft flies. Groundspeed has nothing to do with how an aircraft flies.

Here is how it would work with a car:

The engine is started and the wheels begin to turn against the conveyer belt. They push backwards against the belt at 10 mph. The belt moves at 10 mph in the other direction (matched to the speed of the car). Since the wheels are pushing against the belt at the same speed as the belt is moving in the other direction, the car's motion is 0 mph.

Here is how it would work with an airplane:

The engine is started and the propeller is turning through the air. It pushes air backwards and the plane begins moving forward at 10 mph. The conveyor belt moves 10 mph in the other direction. (matched to the speed of the aircraft). Since the propeller is pushing against the air to propel the aircraft forwards, what would cause the aircraft to not move?

[This message has been edited by Steve Normington (edited 12-02-2005).]

"There's only one way to find out....."

quote Originally posted by ryan.hess: "There's only one way to find out....."

What I was thinking. A good test for the Mythbusters.

http://videos.streetfire.net/player.aspx?fileid=35E964D9-38DB-4EFD-BE8D-D6BA1A43A06B

^ Evidence to back up my statement

The airplane is already freely moving basically... The propeller is pushing air back around the wings, causing air to flow over the wings. Also, the air from the treadmill of sorts, is also moving over the wings. Now, the wheels aren't wasting much energy, just a little bit of friction causing loss of some mild kinetic energy. So in theory, the plane will fly. Or at least overcome the treadmill and then crash and burn.

The way the question is worded, doesn't take into account several different instances: How long is the treadmill, and is it grooved so that it generates some slight airflow? How heavy is the aircraft (It'd have to be pretty heavy for it to matter)? Are the wheels rotating at the full potential with no acts of friction on them (IE: bearings would be eliminated, and they'd be floating in space per say), and how much friction is acting on the wheels? What's the wing mass/length/width of the airplane? What's the mass overall in relation to weight? How big are the propeller blades (to calculate air flow)?

Say the wheels weren't lubricated and it was causing some heavy friction, and the plane is heavier then normal so it's sitting on the treadmill. Then no, the plane wouldn't take off if the friction is overcoming the amount of velocity that the propelers are moving and there's a lack of a wind.

quote Originally posted by Steve Normington: Someone has no concept of how an aircraft flies.

Someone has no concept of how to read (and follow) the proposed scenario.

As I stated earlier, the scenario itself may be flawed (because the "conveyor belt" wouldn't be able to move nearly fast enough), but working with what we've been told, there would never be enough airflow over the stationary wings to cause lift.

quote Originally posted by fierofetish: WoooHooo!!! Somebody has read the neccessary and relevant information given!!! Well done Patrick!!! Nick

How come he gets props (no pun intended)?! I pointed that out hours ago!!!

...

[This message has been edited by 87FieroGTx (edited 12-02-2005).]

quote Originally posted by JohnnyK: How come he gets props (no pun intended)?! I pointed that out hours ago!!!

No one reads your posts anymore.

The answer is a mix between: It'll go off the conveyer because the wheels spin freely unless friction is introduced in a way in which the kinetic energy equates or is greater then the kinetic energy produced by the propellers. Because the propellers push the air behind the plane, the plane will move forward for sure. It'll hit off the end of the conveyer, where it can then accelerate to take off.

All the conveyer belt would do is make it seem like the wheels were frictionless because the propellers are what moves the plane. The wheels act as a way for it not to drag on the ground.

[This message has been edited by Scythe (edited 12-02-2005).]

Yes, it will fly. The plane is creating thrust which will not equal the frictional quality of the wheels on the conveyer. So no matter how fast the conveyer spins, it can't overcome the thrust of the plane because there isn't enough friction on the wheels to keep the plane stationary. The wheels ust spin that much faster. remember, the thrust is a force against the air, not the ground like a car wheel.

Wichita, you have hit the nail on the head, without realising it!!! Where is the lift coming from, if the plane is not moving forward? It isn't!! The theoretical FORWARD speed of the plane RELATIVE TO THE REARWARD-MOVING BELT IS SAY 120 MPH.. that relationship does not transfer to the air around it. The plane is stationary in relation to the EARTH, and therefore to the air.And therefore there is no lift from the wing aerofoil system.
Nick

quote Originally posted by Wichita: I wouldn't call friction .00001% What is keeping the airplane from flying is drag and weight. If it has enough thrust and lift to overcome drag and its weight, it flys. Drag is an aerodynamic force, but the force of the conveyer is applied to its wheels. All the plane has to do is have enough thrust to overcome that friction and its potential energy at rest and it will move forward. Albiet slowly, but it will get there. People use the dyno test as an example of the aircraft standing still, but that is because the car wheels are turning the dyno wheel with the same force that is applied, which will cancel each other out. But the conveyor is moving on its own. The Aircraft is not propelling the conveyor. If the conveyor is moving at 120mph, and the aircraft has a thrust that will propel it 120mph, it can overcome the conveyor.

The plane CAN'T move, that is the basis to the question. Forget the fact he said conveyer, I don't think he was thinking that through when he used that analogy (Of course I'm not him) but, I think I see where he was going with it. I think he simply meant, if ground speed is zero, can the plane take off, but confused himself when he brought the conveyer into the equation.. Well, thats the answer to his question in a nutshell, the conveyer is really irrelevent.

Oh, and the answer is it'll overcome the belt if and only if the plane can already fly in the air before it was put on the belt system.

quote Originally posted by fierofetish: Wichita, you have hit the nail on the head, without realising it!!! Where is the lift coming from, if the plane is not moving forward? It isn't!! The theoretical FORWARD speed of the plane RELATIVE TO THE REARWARD-MOVING BELT IS SAY 120 MPH.. that relationship does not transfer to the air around it. The plane is stationary in relation to the EARTH, and therefore to the air.And therefore there is no lift from the wing aerofoil system. Nick

Yes, this is what he meant I think, to assume that the plane is not moving.

Somebody who doesn't comprehend simple English!! THE PLANE CANNOT MOVE FORWARD RELATIVE TO THE AIR NEEDED FOR LIFT< BECAUSE THE CONVEYORBELT COMPENSATES FOR FORWARD MOVEMENT OF THE PLANE THEREFORE KEEPING THE WINGS STATIONARY IN RELATION TO THE AIR NEEDED TO GIVE LIFT BY PASSING OVER THE AEROFOIL SURFACE OF SAID WINGS!! aaaaaarrrrggghhhhh!!!!!!

quote Originally posted by Steve Normington: Someone has no concept of how an aircraft flies. Groundspeed has nothing to do with how an aircraft flies. Here is how it would work with a car: The engine is started and the wheels begin to turn against the conveyer belt. They push backwards against the belt at 10 mph. The belt moves at 10 mph in the other direction (matched to the speed of the car). Since the wheels are pushing against the belt at the same speed as the belt is moving in the other direction, the car's motion is 0 mph. Here is how it would work with an airplane: The engine is started and the propeller is turning through the air. It pushes air backwards and the plane begins moving forward at 10 mph. The conveyor belt moves 10 mph in the other direction. (matched to the speed of the aircraft). Since the propeller is pushing against the air to propel the aircraft forwards, what would cause the aircraft to not move?

quote Originally posted by Toddster: So no matter how fast the conveyer spins, it can't overcome the thrust of the plane because there isn't enough friction on the wheels to keep the plane stationary.

There would be plenty on friction of the tires on the conveyor belt and within the bearings of the wheels. Remember, there would be NO lift if the plane wasn't moving forward (relative to the ground) and the full weight of the plane would still be on the wheels/tires. And keep in mind there is no limit to how fast this imaginary magical conveyor belt can spin.