plane on a conveyor belt?

[FBplmmr]

picture this --- on the majic belt get the belt moving to however fast you want backwards but the plane is not moving forward -- now retract the gear ! what happens?


apdrone beat me to it

[Donzo]

Originally posted by FBplmmr
yes briefly, my stance is that without air passing over the wings the plane can't achieve flight.


if the plane is in effect staionary(either by a belt or lockdowns) and the thrust being produced is parralell to the  ground the plane will remain stationary.  when released from eitherfrom  the belt or the lock downs the plane will begin forward and will not acheive flight untill sufficient airflow goes over the wings to allow it.

to be honest trying to visulize a conveyour under a jet on a catapault made my head bleed =)

Yes, without air passing over the wings the plane will not fly.

What is stopping the air fom passing over the wings?

The conveyor under the plane on the catapult is the same as a plane sitting on a conveyor runway.  Think of the "thrust" that will propell the plane forward as being the catapult itself.  
Once the button is pressed and the catapult is fired, what will stop the plane from going forward....the fact that it's wheels are on a conveyor that matches the wheel speed in the oppostite direction?  Think about that.

[Donzo]

Originally posted by APDrone
The catapult is an external force in relation to the conveyor belt.

The thrust produced by the engines has the same effect as the catapult would....both move the plane forward regardless of what the ground under the wheels is doing.

[Kurt]

The funniest thing here...  Is that 5 posts into this thread, a link was posted that explained exactly why the airplane does fly... But so many didn't read it... Here it is again for those of you who are just here to argue..

http://txfx.net/2005/12/08/airplane-on-a-conveyor-belt/


I will try one more time, and then I'm jumping out of this discussion because the utter lack of understanding is really depressing.  I suppose some of you believe if a tree falls in the forest and no one is there, then it really doesn't make a sound?

Ok...  3rd Law of Motion... For every action there is an equal an opposite reaction..

So you use a fan to act on the air.  We agree?  Good.

The fan does not act on the ground at all... This is why planes keep flying even when the ground stops touching the plane.

Since your motive force is acting in the medium of air, that is where the reaction will occur, this moves the plane.  The conveyor simply isn't part of the math, well, perhaps to a negligible amount due to the tiny friction, but these are wheels on ball bearings, the brakes are not applied, they are simply rolling at whatever speed they roll at, they have no relationship to the thrust being created by the propeller.

Above, and also in the linked article, the analogy of a string tied to the plane are used, this is a great example... You put a toy plane on a piece of paper, you pull the string one way (thrust) you move the paper the other way (conveyor) and the distance and speed that the plane travels is the distance and speed that the string pulled it, it has nothing to do with the movement of the piece of paper.  Just like in the full size experiment, it has nothing to do with the conveyor.

By contrast, the action of moving the conveyor has the opposite reaction of moving the wheels of the plane, but nothing more.  So maybe it adds 40 pounds of friction.. Thats not going to prevent the accelleration of the airplane.

[FBplmmr]

Originally posted by Donzo
Yes, without air passing over the wings the plane will not fly.

What is stopping the air fom passing over the wings?

The conveyor under the plane on the catapult is the same as a plane sitting on a conveyor runway.  Think of the "thrust" that will propell the plane forward as being the catapult itself.  
Once the button is pressed and the catapult is fired, what will stop the plane from going forward....the fact that it's wheels are on a conveyor that matches the wheel speed in the oppostite direction?  Think about that.

omg! let me have another cup of coffee, I see I was focused on what I thought the probelm was trying to say (that the belt was just there to create a scenario where the plane would not move)as opposed to what would happen if you actually did it.  

doh

[hitech]

Boy I'm glad some of you were not involved in the conservation of energy conversations we had concerning the torque of jet engines a few years back.

HiTech

[lukster]

The tires will spin too fast causing them to blow taking out the elevator and killing everyone on the plane, but it did get off the ground.

[eagl]

Torque in a jet engine?  With good bearings there shouldn't be much torque...  Gyroscopic effect though, that can be a big one if the rotating mass is large.  In my training to fly the F-15, we were educated on how much force the engines exert sideways every time the nose rotates up or down.  It's pretty significant and is one source of the infamous "bitburg roll" where pitch, yaw, and roll coupling can cause an F-15 to go out of control after a relatively simple pitch-up.

Torque though... Hmmm...  With good bearings, I'd think that torque stresses shouldn't get passed to the airframe in any large amount.  The force produced by the rotating parts of an engine are mostly passed fore and aft.  Any torque goes into making the engine spin faster or slower and the bearings keep the spinny parts spinning and the engine casing (and airframe) not spinning.

[Meatwad]

Are you trying to crash the oclub with a paradox?

[Kurt]

Originally posted by eagl
the bearings keep the spinny parts spinning and the engine casing (and airframe) not spinning.

A very important feature in modern jets... In the old ones where the plane spun and the fans stood still I used to get awfully sick...

Its like in the old days when they used to spin the radio station and the record stood still.  And everyone wondered why DJ's were weird.

Does anyone remember a few years ago when the Earth blew up, and we moved here... And the government decided not to tell the stupider people because they thought that it might effect....

Oh, I've said too much...

[APDrone]

Originally posted by Kurt
The funniest thing here...  Is that 5 posts into this thread, a link was posted that explained exactly why the airplane does fly... But so many didn't read it... Here it is again for those of you who are just here to argue..

http://txfx.net/2005/12/08/airplane-on-a-conveyor-belt/


I will try one more time, and then I'm jumping out of this discussion because the utter lack of understanding is really depressing.  I suppose some of you believe if a tree falls in the forest and no one is there, then it really doesn't make a sound?

Ok...  3rd Law of Motion... For every action there is an equal an opposite reaction..

So you use a fan to act on the air.  We agree?  Good.

The fan does not act on the ground at all... This is why planes keep flying even when the ground stops touching the plane.

Since your motive force is acting in the medium of air, that is where the reaction will occur, this moves the plane.  The conveyor simply isn't part of the math, well, perhaps to a negligible amount due to the tiny friction, but these are wheels on ball bearings, the brakes are not applied, they are simply rolling at whatever speed they roll at, they have no relationship to the thrust being created by the propeller.

Above, and also in the linked article, the analogy of a string tied to the plane are used, this is a great example... You put a toy plane on a piece of paper, you pull the string one way (thrust) you move the paper the other way (conveyor) and the distance and speed that the plane travels is the distance and speed that the string pulled it, it has nothing to do with the movement of the piece of paper.  Just like in the full size experiment, it has nothing to do with the conveyor.

By contrast, the action of moving the conveyor has the opposite reaction of moving the wheels of the plane, but nothing more.  So maybe it adds 40 pounds of friction.. Thats not going to prevent the accelleration of the airplane.

I did read the article before I posted and I found it to be flawed for this argument.

In order for an aircraft to gain enough speed for flight, it must roll forward on its landing gear.  If you try to push more thrust than the wheels can keep up, you get to where the plane is going faster than the landing gear, and then this happens:



If the wheels cannot spin fast enough to stay under the center of gravity, the plane will attempt to leave the wheels behind.  Remember, if this happens before you have attained stall speed, you have wreckage.

Seems like everybody is so focussed on discussing why such a contraption can't be built, you've lost sight of the possibilities of what would it be like if it did.

As with Kurt, this is my final shot.  Somebody let me know who won.

[Benny Moore]

So are you "won't fly" advocates going to try to build a perpetual motion machine yet?

[Donzo]

Drone,

Just try to visualize the catapult/winch analogy.

The catapult/winch are doing the same thing the engines do to the plane...they move it forward, no matter what happens to the ground under the wheels.

[Kurt]

Its purely hypo-pathetical

[Benny Moore]

http://www.design-simulation.com/WM2D/index.php

Originally posted by hitech
Boy I'm glad some of you were not involved in the conservation of energy conversations we had concerning the torque of jet engines a few years back.

So, which position do you take?