Stupid plane on a treadmill question

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Texasspilot

Texasspilot

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didn't get much sleep but i've been arguing this question on another forum and then this hit me.

tell me what i got wrong here/

damnplane.jpg
 
For your diagram to work the acceleration is solely coming from the treadmill - making it like a catapult on an air craft carrier.

If the wheels are going + at the same speed the treadmill is going - then you are going nowhere.
 
TROLL... sorry :)

Ive never seen the question worded like that, the few times I've heard it debated the treadmill was going the otherway, making people think it was holding the plane back (through wheel friction or whatever stupid people think). Your example looks as if its eliminating the need to spin up the wheels and thus helping the airplane get up to flying speed even quicker.
 
I_Money said:
For your diagram to work the acceleration is solely coming from the treadmill - making it like a catapult on an air craft carrier.

If the wheels are going + at the same speed the treadmill is going - then you are going nowhere.
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no theres acceleration from the engine causing the wheels to spin.

the treadmill is spinning in the opposite direction causing zero wheel speed.

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Hypothetical question from another forum....

A plane is standing on a runway that can move like a giant conveyor belt. The plane applys full forward power and attempts to take off. This conveyer has a control system that tracks the plane's wheel speed and tunes the speed of the conveyer to be exactly the same but in the opposite direction, similar to a treadmill.

The question is:

Will the plane take off or not?
 
If they do it at the same speed v=0

And the wheels will be move - otherwise it will go off the end of the treadmill!
 
You need to think about it as 2 seperate objetcs -

The airplane when it accelerates on ground, and then think of of the consequences of the ground moving.
 
Relative motion: Relative to the tread mill surface, if the engines are producing enough thrust to overcome the static and rolling resistance in the wheels then the plane moves forward on the treadmill surface. If that surface is moving in the same dirrection of the aircraft then the velocity of the aircraft would be it's speed plus the tread mills speed. If the treadmill spins opposite the dirrection of the aircraft then you just subtract the treadmill speed. If the aircraft forward speed = the treadmills reverse speed then relative to the outside world the aircraft is still ie. zero ias. The wheels would still turn at the same speed as the treadmill though.
 
What if someone went out and bought all the leafblowers and fans in town and blasted them at the airplane on the treadmill?
 
EDUC8-or said:
What if someone went out and bought all the leafblowers and fans in town and blasted them at the airplane on the treadmill?
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But that wouldn't help, because then it would have relative wind. Of course the plane would take off, that one is easy.

My feeble brain just can't understand how an airplane with zero movement over the ground (ie on treadmill that matches it's speed) can produce any relative wind.
 
The key point, thrust for the plane is not caused by the wheels but by the output of the engines. The plane doesn't care of the wheels are spinning forward or backward. There will still be movement of the aircraft in a forward motion.
 
Or planes on skis... how does THAT work? :) :sarcasm:

Especially with a massive headwind... ;)
 
MDPilot said:
Lock the brakes on an icy runway and go full throttle on the engine. Will the plane move?
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I would think so. The brakes may be locked, but the tires which normally 'grab' on the pavement would be sliding once the engine kicks in. I guess it always depends on how icy....Sheer ice, and it would move. :confused:
 
I can't believe I'm finaly getting suckered into this damn discussion. It seems so clear to me but there are so many (seemingly) intelligent people that are pretty evenly split on this one that I second guess myself. Maybe I'm missing something.

wheelsup said:
My feeble brain just can't understand how an airplane with zero movement over the ground (ie on treadmill that matches it's speed) can produce any relative wind.
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The plane doesn't care what the wheels or the ground does just how much air flows over the wings. Imagine a plane flying at 100 K. into a 100 K. headwind. No relative movement over the ground but plenty over the wings right.
And in the normal example where the treadmill is going the other direction; the same thing. The wheels don't push the plane the engines push the air so the plane would still take off at the normal indicated airspeed. Higher wheel speed but, friction notwithstanding, everything else is normal.
Where did I go wrong?
 
sharkey said:
The plane doesn't care what the wheels or the ground does just how much air flows over the wings. Imagine a plane flying at 100 K. into a 100 K. headwind. No relative movement over the ground but plenty over the wings right.

And in the normal example where the treadmill is going the other direction; the same thing. The wheels don't push the plane the engines push the air so the plane would still take off at the normal indicated airspeed. Higher wheel speed but, friction notwithstanding, everything else is normal.
Where did I go wrong?
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So, you're saying the airplane will just lift off the treadmill, or will it roll down the treadmill and rotate? I can see the latter happening (because the airplane is rolling down the "runway" gathering IAS) but not the former. However, that would require the wheels be rotating faster than the treadmill is going.
 
sharkey said:
And in the normal example where the treadmill is going the other direction; the same thing. The wheels don't push the plane the engines push the air so the plane would still take off at the normal indicated airspeed. Higher wheel speed but, friction notwithstanding, everything else is normal.
Where did I go wrong?
Click to expand...

Bingo!! You are entirely correct.
 
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