airplane riddle (taken from another board)

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Okay, after consulting with my roommate, we figured out where the difference lied. I was assuming the tire speed was being matched by the treadmill, not the airplane's speed.

Can you confirm that if the tire speed was being matched by the treadmill, the airplane would not take off, yes? :)
 
Philip said:
it wouldn't matter. Tire speed and aircraft speed are in no way related.
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Exactly, if the tires are spinning 200 MPH forwards and the treadmill is spinning 200 MPH backwards, the plane is stationary. That's what I got hung up on, I was looking at the tire speed being matched, not the airplane speed. But it makes sense that if the airplane is moving 10 MPH forward and the treadmill moving 10 MPH backwards, the tires are moving 20 MPH, I agree. And that's how the riddle is worded. But I'm asking a separate question.

If the tire speed is matched by the treadmill, the airplane remains stationary and cannot takeoff... I'm fairly certain :)

BTW Steve, thanks for the patience (although I saw you were losing it towards the end) and remember that I was just trying to get clarification, not arguing over your physics knowledge. Now get cracking on how a spring gets heavier when stretched :p
 
Chris_Ford said:
Exactly, if the tires are spinning 200 MPH forwards and the treadmill is spinning 200 MPH backwards, the plane is stationary.
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No, not if there is thrust being applied to overcome the friction of the tires spinning.. the body moves on... You can spin the tires backwards, forwards, hell, sideways. it's not going to make a whole lot of difference.
 
Here's the answer and if someone thinks I am wrong, please prove it to me...

While there are the 4 forces of flight which act upon an airplane, the thrust is what is needed to propel the aircraft into relative wind. Without relative wind, there is no possibility of the aircraft to stay aloft. An exception to this is an R/C airplane which with a powerful enough engine can remain inverted while hovering for an extended amount of time. Granted, the propellar on a full scale airplane is a small contribution to the relative wind in order to create lift, it's way too small to make enough wind to cover all of the wing's surface area to make Burnoulli's principle start workin'.

The thrust is there but the treadmill prevents the most important force involved: LIFT. Now, if there is a strong enough headwind that is at or above Vs or whatever speed you choose to stay aloft (without stalling the aircraft) then the aircraft will take off. That's the ONLY way it would.

Without relative wind, air will not rush over and under the wing surface area and not generate lift, PERIOD (period-------->.<-------period)

FOIL.gif
 
JaceTheAce said:
Here's the answer and if someone thinks I am wrong, please prove it to me...

While there are the 4 forces of flight which act upon an airplane, the thrust is what is needed to propel the aircraft into relative wind. Without relative wind, there is no possibility of the aircraft to stay aloft. An exception to this is an R/C airplane which with a powerful enough engine can remain inverted while hovering for an extended amount of time. Granted, the propellar on a full scale airplane is a small contribution to the relative wind in order to create lift, it's way too small to make enough wind to cover all of the wing's surface area to make Burnoulli's principle start workin'.

The thrust is there but the treadmill prevents the most important force involved: LIFT. Now, if there is a strong enough headwind that is at or above Vs or whatever speed you choose to stay aloft (without stalling the aircraft) then the aircraft will take off. That's the ONLY way it would.

Without relative wind, air will not rush over and under the wing surface area and not generate lift, PERIOD (period-------->.<-------period)
Click to expand...
lots of talking, none of it really related to the problem at hand :p
 
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? Will it be able to run up and take off?
Click to expand...

Okay it looks like after two pages of this going on the main question was sort of lost....it says in the question quoted right above here ...that the "plane" or aircraft speed would be identically matched by the treadmill...

so the answer is no it will not take off or accelerate....


by jacetheace
Here's the answer and if someone thinks I am wrong, please prove it to me...

While there are the 4 forces of flight which act upon an airplane, the thrust is what is needed to propel the aircraft into relative wind. Without relative wind, there is no possibility of the aircraft to stay aloft. An exception to this is an R/C airplane which with a powerful enough engine can remain inverted while hovering for an extended amount of time. Granted, the propellar on a full scale airplane is a small contribution to the relative wind in order to create lift, it's way too small to make enough wind to cover all of the wing's surface area to make Burnoulli's principle start workin'.

The thrust is there but the treadmill prevents the most important force involved: LIFT. Now, if there is a strong enough headwind that is at or above Vs or whatever speed you choose to stay aloft (without stalling the aircraft) then the aircraft will take off. That's the ONLY way it would.

Without relative wind, air will not rush over and under the wing surface area and not generate lift, PERIOD (period-------->.<-------period)

FOIL.gif
Click to expand...




In my opinion Jacetheace spelled it out right here....
 
If a helicopter is on the surface of a giant elevator descending at 150 fps, the pilot moves the collective to produce a 150 fps climb, will it remain on the elevator, hover, or climb at 150 fps?

The same logic applies to the airplane question.
 
skywestseth said:
Okay it looks like after two pages of this going on the main question was sort of lost....it says in the question quoted right above here ...that the "plane" or aircraft speed would be identically matched by the treadmill...

so the answer is no it will not take off or accelerate....


by jacetheace





In my opinion Jacetheace spelled it out right here....
Click to expand...



uhhhhh what does the speed that the wheels are spinning have to do with anything?
Why do you think the airplane isn't going to move just because the treadmill matches the speed?
 
Doug Taylor said:
If a helicopter is on the surface of a giant elevator descending at 150 fps, the pilot moves the collective to produce a 150 fps climb, will it remain on the elevator, hover, or climb at 150 fps?

The same logic applies to the airplane question.
Click to expand...
logic, psh.
 
Doug Taylor said:
If a helicopter is on the surface of a giant elevator descending at 150 fps, the pilot moves the collective to produce a 150 fps climb, will it remain on the elevator, hover, or climb at 150 fps?

The same logic applies to the airplane question.
Click to expand...

It will slowly stop descending, then hover, then ascend up via the 150 fps...

BUT!

...........that is a helicopter who's lift is created 100% by it's thrust. It doesn't need relative wind. An airplane needs relative wind.

Here's another question: Will an airplane take off with a special humungous fan that creates a tailwind always exceeding it's stall speed? Keep in mind the fan adjusts the wind speed to exceed the airplanes ability to go faster than the relative wind.
 
Philip said:
uhhhhh what does the speed that the wheels are spinning have to do with anything?
Why do you think the airplane isn't going to move just because the treadmill matches the speed?
Click to expand...

The treadmill would have to have an infinite speed in which case the airplane's tire would blow at one point anyway :)
 
Wait a minute... I'm actually thinking right now. The treadmill won't be able to defy the forces of propellar thrust; only the force created by a car's engine propelling a wheel to try to counteract the treadmill's force.

Propellar thrust is associated with relative wind (which is at a standstill and not affected by the treadmill) whereas a car wheel is directly affected by the treadmill (because it's directly planted onto it). Since the airplane's wheel is not associated with the counteracting forces of the treadmill, it will takeoff!

So basically the only way this would work is if there's the tailwind fan analogy I made above (to counteract against the thrust).

Oh man I feel like a dumba$$ lol.
 
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