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(I am one who has converted from your point of view....sorry
)
Here's another way (I think) to look at this problem.
The wheels are meerly a support mechanism for the plane while it needs to sit on the ground. If you could levitate the plane (get rid of this bloody conveyor belt) on a set of mag-levs, what will happen when the engines wind up to full thrust. Where will the thrust act....
The plane flies....Try to think about how a VTOL (Harrier) vectors the thrust from the engines to provide forward motion....its a slow process but it works.
Just another thought....when a plane is in motion on the runway, it GAINS speed (both ground and air0 by the thrust of the engines against the air itself
you guys have proved me wrong, but I have a problem. I can't convince my coworkers. They don't think the paper is being pulled at the same speed. I can clearly see now what I was not seeing before. Very interesting topic! You got me. I feel like I have a big clown nose on.
The guys here say that he didn't pull the paper fast enough. The skateboard already had forward momentum that could not be canceled by pulling the paper. I'm really getting now
Take a chill pill there davidinindy. I didn't know that was you in the video. I admitted I was wrong. I was trying to convince my office mates here. I think they are just giving me a hard time for the sake of giving me a hard time. No more explaining is required. I think at this point everyone is on the same page. I'm sure I was not the only one that did not belong to your all knowing engineering club. Can i get a pass?
Nothing was directed at you, Phoxeoy... Maybe it came across too harshly. Just commenting on that video, (it's not me, by the way) and the fact that some people here just aren't getting it.
BTW, I'm not an true engineer...but I did stay at a Holiday Inn recently...
Just kidding... I consider myself a Mechanical Designer, since I don't have more than an AAS degree. I'm a little more than a CAD jockey though. Edited by: davidinindy
<DIV>The plane must move first for the control to sense any movement. This is a velocity feed back loop. The velocity of the plane is independent of the conveyer, driven by the thrust it generates in the air. The conveyer will move -x mph as the ground speed of the plane is x mph. The wheels of the plane will spin a rate equal to 2x. </DIV>
<DIV></DIV>
<DIV>Is there a PRO-wind tunnel ?</DIV>
Maybe the important thing would be to define "airspeed", with a nice graphic showing what it means? Am I right in assuming thattheengines will "pull" enough air under (and over, at a lower pressure) the wings to generate a very high "airspeed" no matter what the plane is doingwith respect to the ground?
So, the pilot is generating "speed" in a sense in which most of us never think of it - the speed is the relative velocity of the air compared to the plane, and has nothing to do with the speed relative to the ground. While the plane was spinning its wheels like mad, what would it feel like if youstuck your hand behind that jet engine? Wouldn't you go flying off behind the plane like a rag doll? Now you'd be feeling the "airspeed", eh? Heck, that oughta be enough power to lift that baby off the ground!
Imaginethe plane is on ice, withthe front of its wings placed against two amazingly strong, tall well-greased posts. Nowthe pilot cranks up the engines. Can't you picture the thingsliding up those posts?
All right, so I jumped in when the thing had been solved, but just thought I'd try to throw in another attempt at visualization.
I think the question was a bit confusing ...no offense israir
Not sure why I threw the ice part in there. Just trying to take the wheels out of the equation altogether, since they're basically a red herring. Forget the ice.
The assumption that the engines pull the
air over the wing is incorrect. As discussed above the engines give the
aircraft a forward airspeed, the wings then change the momentum of the air that
passes over them and in doing so create a lift force. There have been
aeroplanes such as the Custer Channel Wing and the Boeing YC-14 that use the
engines to augment the lift from forward motion in order to improve short
take-off and landing performance, but they still need forward airspeed.
You can grease your pole as much as you like but the plane won't go anywhere.As for an aeroplane in a wind tunnel, it is indeed flying but the airspeed is generated by the dirty great fans blowing air through the tunnel. Turn the tunnel fans off and there is no lift, even if the aeroplane has its own engines doing their thing.
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