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#338455 - 08/22/07 11:07 AM Re: The case of the plane and conveyor belt [Re: Rocnat4]  
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 Originally Posted By: Rocnat4
It depends. What airline carrier are we talking about?

No matter, their sure to blame the delay on "weather in Chicago".




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#338457 - 08/22/07 11:15 AM Re: The case of the plane and conveyor belt [Re: Rocnat4]  
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 Originally Posted By: Rocnat4
It depends. What airline carrier are we talking about?

No matter, their sure to blame the delay on "weather in Chicago".


boy, isn't that the truth
everything that goes wrong here at Lindburgh Airport is blamed on "weather in Chicago",
i was starting to suspect it was just a big joke amongst the fine workers at our airport,
does it really ever get that rainy or snowy in Chicago ?


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#338476 - 08/22/07 12:00 PM Re: The case of the plane and conveyor belt [Re: FatDog]  
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 Originally Posted By: FatDog

does it really ever get that rainy or snowy in Chicago ?
A couple of times a year.


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#338493 - 08/22/07 01:01 PM Re: The case of the plane and conveyor belt [Re: BillyB]  
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I have been on boards where this has gone on for hundreds of replies. Engines do not produce lift, they produce thrust. They can be used to augment lift, such as some STOL concepts, but unless the engine produces more thrust than the mass weight of the plane, it will not take off. An aircraft carrier has to get a minumum wind speed to launch aircraft, even with the tremendouc thrust produced by the jets and the power of the catapaults. If the engines were all that was needed, why have the wings?


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#338498 - 08/22/07 01:16 PM Re: The case of the plane and conveyor belt [Re: seadog]  
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 Originally Posted By: seadog
I have been on boards where this has gone on for hundreds of replies. Engines do not produce lift, they produce thrust. They can be used to augment lift, such as some STOL concepts, but unless the engine produces more thrust than the mass weight of the plane, it will not take off. An aircraft carrier has to get a minumum wind speed to launch aircraft, even with the tremendouc thrust produced by the jets and the power of the catapaults. If the engines were all that was needed, why have the wings?


I was on a physics message board in which this topic rolled on for 550 pages.


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#338512 - 08/22/07 01:58 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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To quote Robin Williams (and the pilot of that plane on the conveyor belt attempting to take off in an aircraft generating no forward motion):

"Oh $#**, gravity works!"


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#338514 - 08/22/07 02:00 PM Re: The case of the plane and conveyor belt [Re: Rocnat4]  
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If the effect of the conveyor is that there is insufficient air movement over the wings to provide lift, the plane will not lift into the air. If there is sufficient air speed/movement of air over the weing surfaces, then the plane will lift off of the ground. Why do you think that light planes are tied down at their airports instead of just having their wheels chocked?


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#338516 - 08/22/07 02:13 PM Re: The case of the plane and conveyor belt [Re: Bowline]  
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I guess I am confused at how people think a conveyer belt will prevent an air plane from moving. Also, if the conveyer belt did move the air to prevent the plane from moving, it would have to be moving enough air over the plane to negate the surface pressure on the props, and therefore would create lift on the wings. It would/could go up, but wouldn't move forward.


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#338528 - 08/22/07 02:43 PM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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Again I agree w/ WaterMutt. Yeah, the engine doesn't provide lift, but the the engine turns the propeller, which pulls the airplane through the air, like a prop pushes a boat through water, the subsequent air movement over the shape of the wings lifts the plane into the air.


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#338535 - 08/22/07 03:17 PM Re: The case of the plane and conveyor belt [Re: athiker]  
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I see a future episode of Myth Busters with the biggest conveyor belt ever built!


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#338539 - 08/22/07 03:28 PM Re: The case of the plane and conveyor belt [Re: BillyB]  
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Or a small plane....


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#338541 - 08/22/07 03:36 PM Re: The case of the plane and conveyor belt [Re: BillyB]  
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Al Offline
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There are three things necessary for an airplane to fly. Thrust, lift, and drag.

Thrust is required for the aircraft to have FORWARD MOTION, and is accomplished by the engine.

Lift is required for the aircraft to GET OFF THE GROUND, and is accomplished BY AIRFLOW ACROSS THE WINGS.

Drag is required to keep the nose of the aircraft in front of the tail, so that it does not do a loop-de-loop. The tail surfaces create drag in comparison to the nose, thusly keeping the nose pointed forward.

Lose one of these three properties and the plane will not fly.

If the plane is on a conveyor, and the conveyor is going into reverse the same speed that the engine is pulling the airplane forward, so that the airplane does not move on the ground......

There is then no airflow across the wings, which means there is no lift generated by the wings, and then no fly. If otherwise, you would not need wings.

There is not enough airflow generated by the engine to generate sufficient lift. As I said previously, in the case of a Cessna 172, where the engine is predominately below the wings, there will be more airflow under the wings than over, which generates negative lift, and results in the airplane being sucked to the ground.

Only when there is enough lift generated by airflow to counteract the weight of the aircraft AND negative lift generated by the engine, will the airplane lift off the ground.



So its SUFFICIENT airflow over the wings that creates lift, and the engine cannot produce sufficient airflow. Only FORWARD MOTION OF THE WINGS, BEING IN A WIND TUNNEL or something that creates airflow is what creates lift. If a conveyor in reverse prevents forward motion of the WINGS, in the absence of any other sufficient air flow mechanism, there is insufficient lift.

and lastly, even if there were enough lift created by the engine to get the plane off the ground, its likely there would still not enough air flowing across the control surfaces (and for sure the alerons) to fly it.


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#338542 - 08/22/07 03:43 PM Re: The case of the plane and conveyor belt [Re: Al]  
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Al, I fully understand that no air over the wings = no fly. But explain me this, how does a conveyer with contact only to the tires of the air plane stop it from moving?

Also, in your "No Fly" drawing, what is keeping the prop from pulling the plane forward? The conveyer?


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#338544 - 08/22/07 03:49 PM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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Al Offline
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Well then maybe I am reading the scenario wrong.

I took it that the conveyor is going in reverse at the same speed as the airplane is moving forward, which means that the airplane and wings are stationary.

Is this not the case?

But if it takes 100mph of forward movement for the airplane to generate sufficient lift, and if the conveyor is moving at 25mph to the rear, and the airplane is moving at 125mph, and if the conveyor is a mile and half long, then yes, the airplane will take off, because its relative movement to the surrounding air is 100mph.

But if the airplane is moving 100mph forward and the conveyor is moving 100 miles to the reverse, then there is no forward movement of the wings at all, and there is insufficient lift.


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#338546 - 08/22/07 03:58 PM Re: The case of the plane and conveyor belt [Re: Al]  
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Al Offline
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Maybe I am seeing your point a bit.

You are saying that the airplane will move forward regardless if the conveyor is moving to the rear?

So lets think about.

So its not really about creating lift, but whether or not the airplane would move forward or not when the same energy is applied to the conveyor as is applied to the engine.

1. if the conveyor moves to the rear, and the airplane engine is off, will the airplane move rearward? I would submit that inertia would initially attempt to keep the airplane steady, but friction from contact with the conveyor would result in the airplane moving to the rear.

Anyone who has pushed a wheelbarrow full of dirt knows this to be true. There is nothing moving the wheels, but it still takes much effort to move the wheelbarrow. Gravity causes a tremendous amount of friction to be applied to the wheel.

2. if the airplane's engine is running, and the conveyor is not, it too will have the initial resistance of inertia attempting to keep it from moving forward, but it will slowly move forward. Again, friction will impede this movement.

3. but if the conveyor is moving to the rear with the same energy as the airplane pushing the plane forward, then the intertia will balance out, but its my guess that friction of the wheels spinning backwards will aid the conveyor, and the airplane will move backwards on the conveyor.

This is because for the wheels to stay static, there is no friction involved, just inertia, so the airplane will move rearward with the conveyor. But to just keep the wheels moving forward to match the rearward movement of the conveyor, friction and inertia must be overcome.

So, rearward movement = overcome inertia.
Forward movement = overcome inertia and friction.

This suggests that it takes more energy to move forward than to maintain status quo.

4. but only when the airplane has enough power to overcome the friction of the wheels spinning backwards, and then can move forward at sufficient speed to create lift will it fly.

Regardless, there has to be forward movement in the airplane for this to happen.

A close scenario might be if you had a treadmill and put a marble on it. If the treadmill were flat, the marble would roll off to the rear.

But if you tilted the treadmill forward so that the marble due to gravity was rolling forward, at some point, the forces would cancel out and the marble would roll without movement.

And if you tilted the treadmill even more forward, gravity would overcome the treadmill and the marble would roll forward off the treadmill.

And its my belief that at that point, there is more energy applied to the marble via gravity than in the rear movement of the treadmill, and that is where friction comes in.

My guess then is that if the forces were equal, then friction would be the tie-breaker and the marble would move to the rear. Only when greater force is applied would the marble overcome friction.

At worst case, equal forces might balance the marble in one spot, but to get it to move forward I believe would require an increase in force.

This is an interesting scenario.


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#338554 - 08/22/07 04:19 PM Re: The case of the plane and conveyor belt [Re: athiker]  
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 Originally Posted By: athiker
Again I agree w/ WaterMutt. Yeah, the engine doesn't provide lift, but the the engine turns the propeller, which pulls the airplane through the air, like a prop pushes a boat through water, the subsequent air movement over the shape of the wings lifts the plane into the air.


Yes but a boat facing upriver in order to stay still must prouduce enough forward thrust to negate the riverflow. 5mph riverflow against 5 mph of forward thrust and the the boat stays still relative to the banks - How fast is the boat going ? Relative to what ? 0 relative to the river bank, 5 mph realitive to the water going behind it.


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#338556 - 08/22/07 04:23 PM Re: The case of the plane and conveyor belt [Re: Al]  
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Is that the static coefficient of friction, or the dynamic coefficient of friction?

All this brings up another thought. If the conveyor has sufficient friction (read roughness), then it could create drag with the air molucules above it causing the air actually to move past the wing of the plane and quite possibly creating lift. But soon after the plane lifted off the conveyor it would get out of this air stream, lose lift and fall again. If the conveyor created enough wind motion about the wings, the plane might begin to hover a few feet above the conveyor.

Are you ready for 550 pages of posts on this subject?


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#338558 - 08/22/07 04:25 PM Re: The case of the plane and conveyor belt [Re: Al]  
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I think it comes down to the energy created by the air plane to move forward, the energy needed to overcome the friction of the "tires" (and we'll call it that for simplicity, but it does include the tire friction, compression of tire, and bearing friction), and the net amount of energy required to get the plane off the ground. Basically, if the air plane can create the energy needed to get to speed to take off while producing an excess amount of energy equal to or more than the energy to over come the tire friction, I feel that it will take off.

If you really simplify and call all tire friction negligible, that plane is flying.

I understand your theory on the plane not running on the conveyer running backwards. Given the laws of physics, it will eventually equal the speed of the conveyer, minus wind resistance effects.

I guess my biggest thing is the air plane uses the air around it as its ability to get traction, where as the conveyer is just the gound. Kind of opposite of being in a car driving into a head wind. Ground isn't moving, but the non essential medium of air is moving creating some resistance, similar to the conveyer for the air plane.

Maybe we get one of those JATO's from the guys with the Hobbie, that'll take care of any extra power needed.


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#338569 - 08/22/07 04:47 PM Re: The case of the plane and conveyor belt [Re: Scott L]  
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Once again I follow WaterMutt...unless typing takes too long!

Scott L wrote:
 Quote:
Originally Posted By: athiker
Again I agree w/ WaterMutt. Yeah, the engine doesn't provide lift, but the the engine turns the propeller, which pulls the airplane through the air, like a prop pushes a boat through water, the subsequent air movement over the shape of the wings lifts the plane into the air.

Scott L:
Yes but a boat facing upriver in order to stay still must prouduce enough forward thrust to negate the riverflow. 5mph riverflow against 5 mph of forward thrust and the the boat stays still relative to the banks - How fast is the boat going ? Relative to what ? 0 relative to the river bank, 5 mph realitive to the water going behind it.


If someone sits in a hydrofoil air chair, that is tied via a line to a fixed point (rock upstream), thus 'standing still' relative to the bank and earth, but the foil (wing) has water flowing over/around it...then I submit the chair will rise in the water (and the plane will rise in the air as the propeller pulls the plane wings through the air). The wing only cares about wind/water flowing over it to provide lift...either via a head wind/current or moving over the surface of the earth through the medium...not a conveyor belt underneath.

The plane example is not quite the same b/c I believe the plane will move forward in relation to the earth as the prop pulls it through the air. The conveyor belt (setting aside residual air flow...which probably will only help...and extreme friction...there are some pretty good ball bearings out there) is inconsequential. The only reason wheels exist on a plane is to decrease the friction of the plane with the earth as the prop pulls it forward. Wheels roll...and if the bearings are good enough to overcome the increased friction then the plane takes off.

Imagine a sea plane attempting to take off pointed upstream in a river. What is the only thing that will keep it from taking off? Too much friction of the pontoons w/ the water that prevents the plane from getting enough airspeed...or moving over the surface of the earth fast enough assuming no weather wind conditions. I say the conveyor belt can spin to it's heart's content as long as the friction isn't too great a factor, the plane takes off!

550 here we come....


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#338571 - 08/22/07 04:51 PM Re: The case of the plane and conveyor belt [Re: athiker]  
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There is insufficient air flow created by the propeller to create lift on the wings.

Who here is an aerospace or aeronautical engineer? Let's see the hydrodynamics of this equation. (BTW, air is another fluid and conforms to fluid mechanics as a "compressable fluid")

It will not fly, but may hover if there is adequate air flow created by the conveyor belt.


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