Here's a good question for discussion...

The Fuzz

The Fuzz

New member
A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."

The question is: Will the plane take off or not? Discuss. (this is very much like the 'if a tree fell in the woods...' question)
 
You must be on the same chail letter list some other people I know are on. This is a topic of discussion on a couple boards I visit.

Picture this: The plane is tethered to something 50 yards in front of it. The runway is moving backwards and the plane stands still. As the plane is reeled in it would definitely move forward. I don't believe that the backwards moving runway could overcome the thrust from the jet no matter how fast it went. It would only overcome the thrust if it was a wheel driven vehicle. If the power were to the wheels then it would never be able to get off the runway until the wheels were spinning faster than the backwards moving ground. Where the thrust would be independant of the wheels, it wouldn't be an issue. It would just need to create enough thrust to overcome the friction of the bearings and the tires and then it would fly.
 
If, theoretically of course, the conveyer really could keep up with thrust of the plane, then the plane would NOT take off. The overall speed of the plane RELATIVE TO THE AIR would be 0 m/s, while a lot more than that is required for a plane to generate enough lift. But the problem in the first place is extremely flawed.
 
There would be wind resistance if the jet were able to overcome the friction from the wheels on the runway.
 
There would be wind resistance if the jet were able to overcome the friction from the wheels on the runway.....NO......the conveyer would compensate for this forward movement ....speeding up creating a NO lift situation again.
Remember:
"This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."



This sounds like the one that goes,

If you were driving a bus and picked up three people on the first stop, dropped off 2 and picked up 4 more people at the second stop, at the third stop you picked up 3 more people, at the forth you dropped off 2 and picked up 5 more people.

What color are the bus drivers eyes?
 
The thing you are forgetting is that the wheels aren't the driving force. If it were a car we were talking about here then we know it would stand still. The ramp moving the opposite direction that thrust is applied would have no impact on a vehicle on wheels. No matter how fast the conveyor was moving backwards it wouldn't hold the jet in one place. It would still push forward because the driving force has nothing to do with the wheels.
 
this is like the chicken and egg riddle. What came first, The chicken or the egg?

Who knows if it would take off. I sure don't.
 
TrueDetailer said:
this is like the chicken and egg riddle. What came first, The chicken or the egg?

Who knows if it would take off. I sure don't.
Click to expand...
That one is easy

The chicken (only if she injoyed it)
 
Jngrbrdman said:
The thing you are forgetting is that the wheels aren't the driving force. If it were a car we were talking about here then we know it would stand still. The ramp moving the opposite direction that thrust is applied would have no impact on a vehicle on wheels. No matter how fast the conveyor was moving backwards it wouldn't hold the jet in one place. It would still push forward because the driving force has nothing to do with the wheels.
Click to expand...

Your right but the wheels are driven by the force of the plane, or the inertia of the forward force of the plane.
 
The plane will take off just the same as it would on a stable runway. The only difference is that the wheels of the plane will be turning twice as fast as long as they are touching the moving runway. If the runway speeds up so will the the wheels only 2X. The driving force, being either props or jets, has no connection to the wheels or the runway, therefore not relative.
 
stewsco said:
The plane will take off just the same as it would on a stable runway. The only difference is that the wheels of the plane will be turning twice as fast as long as they are touching the moving runway. If the runway speeds up so will the the wheels only 2X. The driving force, being either props or jets, has no connection to the wheels or the runway, therefore not relative.
Click to expand...



what he said.

i ran this question on my physics teacher today while i was catching up on some needed work in college, and he agrees. although he had to think about it for a while as his first answer was no because of the wind resistance.

cool guy. he also loves to detail his roadster.

yumm!
 
Beercan31 said:
Your right but the wheels are driven by the force of the plane, or the inertia of the forward force of the plane.
Click to expand...

That wouldn't make any difference. The thrust from the engine would push the plane forward even if the wheels were rolling backwards. The engine doesn't care what the wheels are doing. It just means it has to thrust harder and longer to get off the ground. The rubber would probably just burn up with all the speed and friction, but eventually you would have take off when the plane broke free of the friction from the tires and accelorated like normal.
 
TrueDetailer said:
this is like the chicken and egg riddle. What came first, The chicken or the egg?
Click to expand...
If you believe in evolution, then the egg came first, as dinosaurs were around before chickens, and dinosaurs laid eggs. A-HA!
 
thinking way to much about this SOOOOOOOOOOOOOOOOO

The wheels are NOT the driving force to get the air craft moving/flying, like you have in an automobile the jet thrust or the propellers are, the jet propulsion will push/pull the fuselage which in turn pull the wheels along the conveyer. The conveyer will in turn cancel out the "wheels only" not the forward movement of the air craft. The wheels have no effect on the forward movement of the air craft.

Think of it this way
same scenario
you have one of your kids pull-toys. as long as you pull the string on the conveyer the toy will move forward.
if you did the same with a wind up toy car, the car would sit still and the conveyer would equal out the force from the wheels.

The Plane will fly.


Now I have a Headache.
 
I must be dumb, cause this one seems easy.
1. Plane needs opposing wind.
2. Conveyor belt moves plane, but causes no wind.
3. No flying plane.
 
I don't think that it will take off.

While the plane is on the ground it is no different than a jet powered car, if you move the roadway under a jet car in the opposite direction at the same identical speed, it will still stay in one spot, so why would a plane be any different. (equal and opposite forces will canel each other out)
In order to have forward movement you need a fixed point.

"J"
 
It will take off, the wheels will be moving at twice the speed of the plane at all times then there is motion. The wheels are merely there to allow the plane to gain the air resistance needed to create lift, as the conveyor accelerates it accelerates the wheels which are only there to keep the plane upright, that's all that the conveyor's force is acting upon. If you think about how a plane works it acts through friction with the air to accelerate, this has nothing to do with wheel friction. Just for fun, try putting a tethered balloon car on a treadmill, if the wheels are spinning and you let the pressure out of the balloon the car moves forward.
 
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