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plane question

#82
Tom Crofts said:
The engines are pushing the plane forward whilst it's wheels spin twice as fast as the plane, but it still moves which is causing air to move over the wings.

As I understand it.

:ninja:
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Thanks. Spinning wheels on an airplane have nothing to do with getting the plane airborne. Wind over the wings at the correct speed to generate lift will.
 
#83
bmc said:
Where is the airflow coming from?
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From the engines accelerating the aircraft relative to the air. There is a very small deceleration caused by the conveyor through the friction in the wheel assembly, but it is mostly irrelevant (unless the wheels spin so fast that they are destroyed or something).

The wheels can be spinning at whatever speed they want, all that matters is how fast the plane is going relative to the air. In strong winds some small aircraft can take off at very low ground speeds, but the airspeed for takeoff is always the same. In this case the ground speed relative to the conveyor will be twice the airspeed assuming that there is no other wind.
 
#84
Geoff St. Germaine said:
From the engines accelerating the aircraft relative to the air. There is a very small deceleration caused by the conveyor through the friction in the wheel assembly, but it is mostly irrelevant (unless the wheels spin so fast that they are destroyed or something).

The wheels can be spinning at whatever speed they want, all that matters is how fast the plane is going relative to the air. In strong winds some small aircraft can take off at very low ground speeds, but the airspeed for takeoff is always the same. In this case the ground speed relative to the conveyor will be twice the airspeed assuming that there is no other wind.
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I told my Dad I fell for this, he's ex- Air Force and an Engineer, I think he's still laughing.:rollno:
 
#87
fr0me0 said:
A plane is standing on 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: Will the plane takeoff?
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No. The plane requires air moving over the wings to provide lift. On a conveyer moving at exactly the same speed as the plane, no air moves past the wings.
 
#88
Disco_Gee said:
No. The plane requires air moving over the wings to provide lift. On a conveyer moving at exactly the same speed as the plane, no air moves past the wings.
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Correct. And to add to the discussion, the airspeed indicator is not attached to the wheels. It is a ram air tube, usually hanging off of a wing. It's called a pitot tube. If you place you lips over it and blow, you can activate the airspeed indicator. When you are on a takeoff roll, you watch your airspeed indicator for the right speed to rotate and lift off. A small single engine Cessna can rotate around 70 mph. Using the conveyor belt discussion, unless there is an adequate wind over the wings, the plane will go nowhere.
 
#89
Disco_Gee said:
No. The plane requires air moving over the wings to provide lift. On a conveyer moving at exactly the same speed as the plane, no air moves past the wings.
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How do you, based on the original question, reach the conclusion that no air will move over the wings? Where does it say that the plane will not move?

And: If the conveyor "..tracks the plane speed and tunes the speed of the conveyer to be exactly the same..." - how will the conveyor move if the plane stands still?
 
#90
erik II said:
How do you, based on the original question, reach the conclusion that no air will move over the wings? Where does it say that the plane will not move?

And: If the conveyor "..tracks the plane speed and tunes the speed of the conveyer to be exactly the same..." - how will the conveyor move if the plane stands still?
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Read the original post:

The plane moves in one direction, while the conveyer moves in the opposite direction.

You ask: "Where does it say that the plane will not move?"

Original post:
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).

Both the plane and conveyor working to equalize each other.
..........................

You ask: And: If the conveyor "..tracks the plane speed and tunes the speed of the conveyer to be exactly the same..." - how will the conveyor move if the plane stands still?[/QUOTE]

The conveyor moves at the same speed as the plane does. If the plane tries to move forward at 50 mph while standing on a conveyor belt moving in the opposite direction at the same speed. The plane is stationary with it's wheels spinning. If it's stationary, it is not moving. If it is not moving, there is no wind over the wings. No wind over the wings, no flight. No flight, go home and practice your bass.
 
#91
Brad Barker said:
stop right there. :D :p

aerospace stuff isn't my thing, but gard's right. engines themselves aren't what cause planes to fly--it's relative motion between the planes and the air. the engines just allow for a sufficient rate of motion for flying.

and in any reference frame that's worth a damn, that plane on that hypothetical conveyor belt isn't moving an inch!


next problem!
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So, did you discount my thoughts on the matter solely due to my lack of physics teaching?


Having come back to the thread....it appears my thoughts, though not necessarily correct, had solid bases of reasoning behind them....which I expected from the beginning....hence I posted them.



ESPECIALLY on a hypothetical question....I don't think it's best to immediately discredit someones thoughts just because they don't have a physics degree.
 
#93
bmc said:
Read the original post:

The plane moves in one direction, while the conveyer moves in the opposite direction.

You ask: "Where does it say that the plane will not move?"

Original post:
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).

Both the plane and conveyor working to equalize each other.
..........................

You ask: And: If the conveyor "..tracks the plane speed and tunes the speed of the conveyer to be exactly the same..." - how will the conveyor move if the plane stands still?

The conveyor moves at the same speed as the plane does. If the plane tries to move forward at 50 mph while standing on a conveyor belt moving in the opposite direction at the same speed. The plane is stationary with it's wheels spinning. If it's stationary, it is not moving. If it is not moving, there is no wind over the wings. No wind over the wings, no flight. No flight, go home and practice your bass.
Click to expand...


What you are saying would only be true for vehicles such as cars which accelerate themselves through the wheels. The plane accelerates itself through the thrust of it's engines, not through the wheels. The only difference between the plane on the conveyor, and a plane taking off normally will be that the plane on the conveyor will have a wheel speed that is twice what it would normally be and will take slightly longer to take off, due to the small decellerating force caused by the wheels spinning faster than they would have been normally. The plane will have the exact same air speed, which is all that matter to an aircraft.
 
#94
Geoff St. Germaine said:
The conveyor moves at the same speed as the plane does. If the plane tries to move forward at 50 mph while standing on a conveyor belt moving in the opposite direction at the same speed. The plane is stationary with it's wheels spinning. If it's stationary, it is not moving. If it is not moving, there is no wind over the wings. No wind over the wings, no flight. No flight, go home and practice your bass.
Click to expand...


What you are saying would only be true for vehicles such as cars which accelerate themselves through the wheels. The plane accelerates itself through the thrust of it's engines, not through the wheels. The only difference between the plane on the conveyor, and a plane taking off normally will be that the plane on the conveyor will have a wheel speed that is twice what it would normally be and will take slightly longer to take off, due to the small decellerating force caused by the wheels spinning faster than they would have been normally. The plane will have the exact same air speed, which is all that matter to an aircraft.[/QUOTE]


So...have you been touched by his noodly appendage?
 
#95
This is a good analogy:
lump said:
If it were a submarine with wheels sitting on a conveyor belt on the bottom of the ocean, would it move forward? Sure it would, as it pulls itself through the water with its screws. Air is less dense than water, but the physics are the same. The wheels are irrelevant to the equation.
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Yup. The plane will pull itself through the air with its airscrew(s). The conveyor will just make the wheels spin faster, with negligible effect on the plane's movement.
 
#98
Gotta side with Geoff on this one. The plane will roll forward til it reaches it's airspeed, and then take off. The only difference is the wheels will be spinning twice as fast as they would without the conveyor.
 
#100
First of all, "momentum" doesn't enter in the occasion. You mean airspeed, or velocity with the surrounding air as the frame of reference.

What makes you think that a conveyer rolling backwords will quell the planes forward velocity? The wheels are not connected via a driveshaft. They just rotate freely.
 

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