airplane riddle (taken from another board)

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One of the posts on that physics forum cracked me up:


"Those who think that the airplane will take off are REALLY REALLY freaking ignorants and should not be on this forum."

​
 
I'm not a physics major...but I'll chime in.

I'll say the airplane will not fly. My thinking...taxi an airplane up an inclined plane. Use just enough power to keep it stationary...i.e. not rolling backwards. Let's say it takes 2000 rpm just to keep it from rolling back down the inclined plane. The airplane is still stationary...no way it can take off.

If the airplane is stationary on the conveyor...and while there's lots of work going on below the wing...there's no work being done on the wing.

I see no flying machine in this scenario.
 
B767Driver said:
I'm not a physics major...but I'll chime in.

I'll say the airplane will not fly. My thinking...taxi an airplane up an inclined plane. Use just enough power to keep it stationary...i.e. not rolling backwards. Let's say it takes 2000 rpm just to keep it from rolling back down the inclined plane. The airplane is still stationary...no way it can take off.

If the airplane is stationary on the conveyor...and while there's lots of work going on below the wing...there's no work being done on the wing.

I see no flying machine in this scenario.
Click to expand...

Bzzzt! Thanks for playing. Better luck next time, and be sure to visit our sponsors! :D

(j/k)

Rick Durden talks about this scenario in this week's AvWeb. See his article here.

:)
 
SteveC said:
Rick Durden talks about this scenario in this week's AvWeb. See his article here.
Click to expand...


Okay the author has lost me with this info

[/quote]

My comment: Notice that the question does not state that the conveyor's movement keeps the airplane over the starting position relative to the ground, just that it moves in the direction opposite to any movement of the airplane.

[/quote]

...so is the airplane advancing forward on the conveyor? If so...this is a poorly worded deal.
 
B767Driver said:
Okay the author has lost me with this info


My comment: Notice that the question does not state that the conveyor's movement keeps the airplane over the starting position relative to the ground, just that it moves in the direction opposite to any movement of the airplane.



...so is the airplane advancing forward on the conveyor? If so...this is a poorly worded deal.
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It's not poorly worded. The treadmill will match the planes speed. So when the plane is at rest the treadmill will not be going. However, when it reaches 1mph, the treadmill will be going 1 mph in the opposite direction. Result? The plane is still going 1 mph forward but the wheels are spinning at 2 mph. When the plane accelerates up to 100 mph, the wheels are now going 200 mph.

It's not that hard people
 
By some peoples theories, the plane would never move. So if you were coming in to land at 100 mph, on a treadmill going 100mph backwards, would you stop instantly? NOPE! you would continue your normal landing roll excpet your wheels are going twice as fast. Your roll may be shortened by the added friction effects in the wheel bearings, etc but you get the big picture (hopefully)
 
Check this out (stolen from another forum):

plane.jpg
 
okay

but the conveyer belt is changing its speed in order to keep the plane in the same position. true, if the plane can move forward and produce lift over the wings, enough for takeoff then yes it will get off the ground. however, if the plane does not move forward, which is what i gather from the riddle, then no, it will not take off.
 
BUT...at which point would you overspeed the tires as you are rotating with whe wheels spinning at twice the normal rotation speed?
 
KLB said:
but the conveyer belt is changing its speed in order to keep the plane in the same position. true, if the plane can move forward and produce lift over the wings, enough for takeoff then yes it will get off the ground. however, if the plane does not move forward, which is what i gather from the riddle, then no, it will not take off.
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But the plane IS moving forward!!!! The prop or the jet produces thrust with no involvement from the ground. The wheels are there to decrease friction, that's all. A plane does not produce thrust like a car (ie: the tires grip the road and the force causes acceleration). You could spin the wheels 1,000 mph and the plane would still take off. This is because the thrust system is independent of the wheels.

If you were roller blading down a hill your velocity would be your mass times accelration, correct? Now, if the ground was matching your speed in the opposite direction, what would happen? Your velocity and acceleration would still be the same as before but your wheels would be spinning twice as fast. Same concept! Again, because your thrust (gravity) is independent of the wheels. the wheels are frictionless for all intents and purposes, as are the aircrafts wheels. Whew! Anyone get all that?
 
OldTownPilot said:
BUT...at which point would you overspeed the tires as you are rotating with whe wheels spinning at twice the normal rotation speed?
Click to expand...

By overspeed do you mean when would the tires fly apart? If so then that is up to the company that makes them and how they engineered them.
 
This thread is crazy....so i see for all intensive purposes that we are assuming that outside variables are not a factor such as friction....but the question i think is still a little misleading....i do agree and believe it will takeoff given the explanations i have recieved in this thread...but the original question does state that the conveyor is matching the airplanes speed so technically if the aircraft is propelling forward and the conveyor picks up that and cancels it out all's i can see happening is the conveyor keeps accelerating as does the planes wheels and sooner or later something just gives out..

i dont know if that was easy to follow...it just seems that both the aircrafts wheels and the conveyor would just have to keep "auto-speeding" up to try and cancel out the never ending thrust from the plane...it doesnt make since to me saying that the aircraft will gain forward momentum and take off if the question itself says that the conveyor cancels any forward movement....therefore just leaving an ever-accelerating device.


-Seth
 
skywestseth said:
<snip>.. if the question itself says that the conveyor cancels any forward movement....therefore just leaving an ever-accelerating device.
-Seth
Click to expand...
It doesn't say that the conveyor will cancel any forward movement. It simply says that it will run the same speed (as the plane) but in the opposite direction.
 
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