Think of it this way, it is always air speed when using any kind of airdrive. The wheels do not have ANY practical effect on movement.

I had this discussion with a normally intelligent guy last week. The only way I got him to understand what is happening was to ask him if the conveyor would be able to effect forward motion on my hovercraft, of course it cannot. Then ask him what hew thought would be the effect of hovering over the conveyor and setting down on wheels and ask him if he thought that somehow I would not be able to accelerate after the craft was off cushion and resting on the wheels. This was tough for him but he finally got it.

Picture a plane landing on a conveyor, do you think if the small plane was going 70 mph when landing on a conveyor going 70 mph in the opposite direction that the plane would come to an abrupt stop? the answer is it would not, in fact you could do a touch and go.

quote Originally posted by Formula88: Answer my question. What's going 120 in your example? Air speed = 0 Ground speed = 0 Plane speed = 120

[screaming=damn loud]Answer the question[/screaming]


Even Tattoo knows!!!

quote Originally posted by Gokart Mozart: How can a plane that has a max speed of 120 counter a 1000 reverse motion? It would be going 880 mph in reverse. It would need to move faster than the conveyor by 120 mph in order to lift off.

Wrong.

Once again, the wheels are free-wheeling, and are not really connected to the plane. The wheel bearings are the only drag.

The reason I brought torque into this conversation, is that torque is the only force that the conveyor belt can act upon on the plane. The only way for the conveyor belt to have any impact on the plane, is that the plane would need to transfer it's power by torque through it's wheels to ground. However, the plane doesn't. It transfers it's power by thrust to the air. In order to stop the plane, you would need a way to counteract the thrust in the air that's being generated by the planes engines.

Opposing thrust, not opposing torque would be the only way to stop that plane. What is the only force being generated by the conveyor belt?.......Torque! Since torque can't stop that plane, neither will that conveyor belt.

[This message has been edited by AJ7 (edited 01-01-2008).]

quote Originally posted by Red88FF: Think of it this way, it is always air speed when using any kind of airdrive. The wheels do not have ANY practical effect on movement. I had this discussion with a normally intelligent guy last week. The only way I got him to understand what is happening was to ask him if the conveyor would be able to effect forward motion on my hovercraft, of course it cannot. Then ask him what hew thought would be the effect of hovering over the conveyor and setting down on wheels and ask him if he thought that somehow I would not be able to accelerate after the craft was off cushion and resting on the wheels. This was tough for him but he finally got it. Picture a plane landing on a conveyor, do you think if the small plane was going 70 mph when landing on a conveyor going 70 mph in the opposite direction that the plane would come to an abrupt stop? the answer is it would not, in fact you could do a touch and go.

The hovercraft is sitting on a river that flows at 20 mph. If the hovercraft wants to go upstream, the amount of thrust needed would be more than what's needed to go 20 mph.

quote Originally posted by Gokart Mozart: The hovercraft is sitting on a river that flows at 20 mph. If the hovercraft wants to go upstream, the amount of thrust needed would be more than what's needed to go 20 mph.

Incorrect. The speed of the flow of water under the hovercraft has NO, none, zip ,zero, effect on the speed of the hovercraft. This is one of the reasons I got into hovercraft design and construction. I live on the Skykomish river and it is the ultimate river cruiser.

I can be going along next to a regular boat, we are both going 40mph (mine does 50! :-) ) we enter a shoot where the river is flowing at 10mph, his boat will slow down by the speed of the flow, 10mph, while I will maintain an even 40mph. The water in theory could be going 100 and it would make little difference to my forward speed.

quote Originally posted by Red88FF: Incorrect. The speed of the flow of water under the hovercraft has NO, none, zip ,zero, effect on the speed of the hovercraft. This is one of the reasons I got into hovercraft design and construction. I live on the Skykomish river and it is the ultimate river cruiser. I can be going along next to a regular boat, we are both going 40mph (mine does 50! :-) ) we enter a shoot where the river is flowing at 10mph, his boat will slow down by the speed of the flow, 10mph, while I will maintain an even 40mph. The water in theory could be going 100 and it would make little difference to my forward speed.

Now, you know your experience with the real thing has no bearing on anything.

quote Originally posted by Red88FF: Incorrect. The speed of the flow of water under the hovercraft has NO, none, zip ,zero, effect on the speed of the hovercraft. This is one of the reasons I got into hovercraft design and construction. I live on the Skykomish river and it is the ultimate river cruiser. I can be going along next to a regular boat, we are both going 40mph (mine does 50! :-) ) we enter a shoot where the river is flowing at 10mph, his boat will slow down by the speed of the flow, 10mph, while I will maintain an even 40mph. The water in theory could be going 100 and it would make little difference to my forward speed.

Thanks for the real life stats. I'd rather have that info than to specutale.
If you want to stay at the same spot on the river, what do you do? I know it's not the same thing as if you are on land.
This is a good tangent but the fact is there's no real contact to the river.

quote Originally posted by Gokart Mozart: This is a good tangent but the fact is there's no real contact to the river.

Sure there is. Friction from the air. It aint much gut then niether are free spinning round objects. I think they are called wheels.

quote Originally posted by Gokart Mozart: Don't break the example up. it distorts the truth.

I almost choked on a cracker.

[This message has been edited by pokeyfiero (edited 01-01-2008).]

quote Originally posted by Gokart Mozart: Don't break the example up. it distorts the truth.

Fine.

quote Originally posted by Gokart Mozart: Which theory are you talking about? I want to be sure what you're rebutting. air speed 0 plane speed 120 tire speed 240 conveyor speed -120 ground speed 0

Now answer the question. What's going 120?

quote Originally posted by Formula88: Now answer the question. What's going 120?

you'd have to be an idiot to not figure that out...

Gokart, I figured out a way for that conveyor belt to stop that plane..................put both in a vacuum chamber!

Vacuum chamber = no air.
No air = no thrust.
No thrust = no forward movement of the plane.

No thrust or forward movement of the plane means that it can be subject to whatever forces you'd like to impose on it. Like the torque imposed on it from a conveyor belt. Now, in a vacuum, if you had a plane on a conveyor belt and turned it on; the plane would start to move backwards. It won't start moving backwards as the same speed of the conveyor belt; as it would only move as fast as the friction imposed by the wheel bearings.

I've never seen anyone try so hard to be so wrong before. It's quite entertaining!

quote Originally posted by Deabionni: \I've never seen anyone try so hard to be so wrong before. It's quite entertaining!

yep

quote Originally posted by Deabionni: Gokart, I figured out a way for that conveyor belt to stop that plane..................put both in a vacuum chamber!

Like everything else in this thread, that's already been covered, in this case Here.

quote Originally posted by Gokart Mozart: Thanks for the real life stats. I'd rather have that info than to specutale. If you want to stay at the same spot on the river, what do you do? I know it's not the same thing as if you are on land.

Well in a sense you can't, you might be able to pull it off in a fast current with enough of a headwind to hold the craft stationary against the power of the airdrive. Without the headwind you will be moving forward. A headwind slows you down and a tail wind speeds you up. These are the only things that can effect your thrust,,,,,, well a side wind on the prop can do things too but that does not enter into our experiment.

quote Originally posted by Gokart Mozart: This is a good tangent but the fact is there's no real contact to the river.

Here in is the misunderstanding. Using wheels instead of an air cushion on a prop driven craft the same thing happens as I explained above. Granted there is more friction with wheels because there is only minute friction due to skirt drag on a hover, but with an airdriven wheeled vehicle the friction is not exponentially increased with speed, there is but a moment force of moving the mass and once this is overcome it takes even less than the initial force to keep the movement going.

I think someone explained this already but if it takes say 20 pounds of thrust to overcome the crafts weight and friction from wheel movement on the conveyor and your airdrive (like mine) puts out in excess of 100 pounds and you goose the throttle, you are gone. Remember, the friction factor does not increase with speed to any notable degree. The thrust air is all that matters.

If you are interested, here is a linky a pic of my hovercaft. It is an older pic and does not show the bigger lift engine or the hardtop installed.

http://www.seanet.com/~dave...4-18hp/page0002.html

There's where a major difference between the two vehicles are. In a plane all you have to do is hit the brakes and stop and you're in the same spot because the ground isn't moving.

i didnt read the hole 7 pages but i think the plane will fly, when they pull the tarp/tredmill the wheels will just spin since the prop will grab air not the tarp.

quote Originally posted by slinger: i didnt read the hole 7 pages but i think the plane will fly, when they pull the tarp/tredmill the wheels will just spin since the prop will grab air not the tarp.

See, he gets it! What was so hard about that?

For those of you that don't know, I work in a KC-130 squadron. We are fortunate to have a handful of Lockheed Martin Representatives that work with us to help with the new J-model conversion. I asked each one of them about this discussion. Once they got over the absurd nature of the question and thought about it, they came to the same conclusion as most of us. Three of them have over 40 years experience in the field. Another retired as an E-9 Flight Engineer.

------------------
"Semper Fiero"

[hijak]

quote Originally posted by Red88FF: If you are interested, here is a linky a pic of my hovercaft. It is an older pic and does not show the bigger lift engine or the hardtop installed.

That looks like fun!

[/hijak]

quote Originally posted by slinger: i didnt read the hole 7 pages but i think the plane will fly, when they pull the tarp/tredmill the wheels will just spin since the prop will grab air not the tarp.

The thing is it isn't a quick pull like the pull the tablecloth trick. It's a slow pull to match the speed of the plane. The plane still needs to roll forward and it can't.

I've stated before how much runway a plane needs to take off. It doesn't matter how much thrust it has, it still needs to roll forward in relation to the runway - meaning non-moving ground and air.

Let me state this again:
If the conveyor is still, the normal speed (lets say 120) is required to take off. The distance would be normal.
If the conveyor is moving forward at 120, the plane would be able to lift off without any power from the plane. It could take off immediately.
If the conveyor is moving backwards at 120, 240 is needed to lift off. The distance would be (basically) normal if the plane goes 240.
If the conveyor matches the speed of the plane, it can't take off.

quote Originally posted by Gokart Mozart: The thing is it isn't a quick pull like the pull the tablecloth trick. It's a slow pull to match the speed of the plane. The plane still needs to roll forward and it can't. I've stated before how much runway a plane needs to take off. It doesn't matter how much thrust it has, it still needs to roll forward in relation to the runway - meaning non-moving ground and air. Let me state this again: If the conveyor is still, the normal speed (lets say 120) is required to take off. The distance would be normal. If the conveyor is moving forward at 120, the plane would be able to lift off without any power from the plane. It could take off immediately. If the conveyor is moving backwards at 120, 240 is needed to lift off. The distance would be (basically) normal if the plane goes 240. If the conveyor matches the speed of the plane, it can't take off.

quote Originally posted by Gokart Mozart: Which theory are you talking about? I want to be sure what you're rebutting. air speed 0 plane speed 120 tire speed 240 conveyor speed -120 ground speed 0

Now answer the question. What's going 120?

quote Originally posted by rogergarrison: I must have missed something in the first thread on this. What exactly, with all the details, is the description of what they are trying to do ? If I understood the original thread, they were supposed to make the plane fly by just spinning its wheels on a treadmill......

I think the whole controversy and confusion over this question has nothing to do with the physics of it, but is entirely over misunderstanding of the specifics of the question itself.

There was a halfway decent animation in another thread to explain the specifics of that given question, but I know I have heard it both ways on here.

quote Originally posted by 86GT3.4DOHC: I think the whole controversy and confusion over this question has nothing to do with the physics of it, but is entirely over misunderstanding of the specifics of the question itself. There was a halfway decent animation in another thread to explain the specifics of that given question, but I know I have heard it both ways on here.

Here's 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's speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Will the plane fly?"

You have to read the question carefully and pay attention to details. The conveyor tracks "the plane's speed." If the plane's speed is anyting other than zero, the plane is moving and can take off.

The assumption people make is that the movement of the conveyor will affect the movement of the plane. It won't. In a car or go-cart, it might, but this isn't a go-cart. It's a plane.

Assume no wind.
Ground speed is the speed of the plane's wings relative to the ground (not the treadmill).
Air speed is the speed of the plane's wings relative to the wind.
Wheel speed is the speed of the plane's landing gear relative to the treadmill, or what a speedometer hooked up to the landing gear would measure.
Treadmill speed is the speed of the treadmill. (shown as negative, since it's in the opposite direction of the plane)

Engine off:
Ground speed = 0
Air speed = 0
Wheel speed = 0
Treadmill speed = 0

Engine on, full throttle to takeoff velocity with treadmill disabled:
Ground speed = 120 mph
Air speed = 120 mph
Wheel speed = 120 mph
Treadmill speed = 0

Engine on, full throttle to takeoff velocity with treadmill enabled:
Ground speed = 120 mph
Air speed = 120 mph
Wheel speed = 240 mph
Treadmill speed = -120 mph

The only thing the treadmill does is make the wheels turn faster.
The treadmill speed is relative to the plane. In order for the treadmill to move, the plane MUST move.
With the common error that the treadmill will keep the plane from moving, you would have the plane stationary and the treadmill going at -120mph. That cannot happen since the plane and the treadmill must be going the same speed (refer back to the original question).

[This message has been edited by Formula88 (edited 01-02-2008).]

How can air speed and ground speed be 120?

[This message has been edited by Gokart Mozart (edited 01-02-2008).]

quote Originally posted by Formula88: The plane moves in one direction, while the conveyer moves in the opposite direction.

Is moves and adjective,noun or verb?

quote Originally posted by Gokart Mozart: How can air speed and ground speed be 120?

You must just be having fun .

[This message has been edited by pokeyfiero (edited 01-02-2008).]

quote Originally posted by Gokart Mozart: How can air speed be 120?

air speed and ground speed are the same because there is no wind.

Since the plane is MOVING at 120 mph relative to the ground, air speed is 120 mph.

Rather than ask a question about the scenario I posted, why do you continue to post while refusing to answer my one question about your scenario?

quote Originally posted by Gokart Mozart: How can air speed and ground speed be 120?

Because none of those speeds are relative to the conveyor at all. It just flails away not able to effect anything in regards to the plane. That is the hook.

quote Originally posted by Formula88: http://dictionary.reference.com/search?q=moves

What an interesting definition.

can't belive this is still being discussed.
or is there something else thrown in?

some important things to considir while trying to understand tghe problem:
1> the plane is NOT powered thru the wheels. the spinning of the wheels is 100% irrelevant.
2> forward motion of the airplane is provided by the engines mounted either on the wings, the nose, the tail. but one common thing: they are mounted in way where the ground is irrelevant.
3> lift of the wings is provided 100% by AIRFLOW. again - the ground is irrelevant.
4> with the proper wheels mounted on the landing gear - you can have the treadmill go SIDEWAYS, and the plane will still take off.

the planes engines will propell the plane forward. unless you tether it down. and it will accellerate to speed and take off. unless you tether it. the treadmill is irrelavant. you can spin it forwards, backwards, sideways - it will do nothing to the forward motion being generated by the engines.

now, the only affects of the treadmill will be: bearing drag on the wheels, slightly hindering getting up speed and possible wind generation - which would help in generating lift, aiding in take off.

A boat is floating down a river going 10 mph.
A man is moving towards the front of the boat going 10 mph.
To someone standing on the shore it looks like the man is going 20 mph.
If the man is going to the back, from the shore it looks like the man is standing still.

quote Originally posted by Gokart Mozart: A boat is floating down a river going 10 mph. A man is moving towards the front of the boat going 10 mph. To someone standing on the shore it looks like the man is going 20 mph. If the man is going to the back, from the shore it looks like the man is standing still.

almost. to someone standing on the shore in #1 - they both look like they are going 10. the boat is moving, the man is moving - the shore is NOT in #2, it'll look like both are moving at 10. to a person standing ON THE BOAT - yes, he'll see the man moving at 20 for #1, and standing still for #2.

in fact - you have just provided a simple and easy to understand way to view the above problem with the airplane & treadmill. water planes with pontoons. their takeoff speed is NOT highly affected by the flow of a river. yes, there is a slight addition of drag, but that is it. they dont need to go extra fast or extra slow to compensate for the speed of the river flow. they take off at the same speed, no matter what the river's current flow rate or direction.

The boat is "connected" to the water, and the man walking is "connected" to the ground. Your above scenario works.

The body of a plane is in no way "connected" to the ground, so what's happening on the ground has no bearing on what the plane can/can't do. (A plane only uses it's wheels to rest/roll on, and for some breaking on landing). Your scenario fails when talking about planes and ground.

[This message has been edited by Deabionni (edited 01-02-2008).]

quote Originally posted by Gokart Mozart: A boat is floating down a river going 10 mph. A man is moving towards the front of the boat going 10 mph. To someone standing on the shore it looks like the man is going 20 mph. If the man is going to the back, from the shore it looks like the man is standing still.

Answer the question. What's going 120 in your example.

quote Originally posted by Gokart Mozart: Which theory are you talking about? I want to be sure what you're rebutting. air speed 0 plane speed 120 tire speed 240 conveyor speed -120 ground speed 0

If he answers the question, then he proves himself wrong.

It's much easier (and more entertaining) for him to dodge the question, and try to prove that physics doesn't work.

quote Originally posted by Deabionni: If he answers the question, then he proves himself wrong. It's much easier (and more entertaining) for him to dodge the question, and try to prove that physics doesn't work.

So you're saying he's either a troll or is stupid?