Soldato
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Where would it get lift from if it was stationary?
Earth spinning
- Thread starter mollymoo
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Where would it get lift from if it was stationary?
Ahem
Because of how that question was worded, in that case it would not fly. It would result in some combination of infinite speeded wheels and treadmills, melted wheel bearings and a whole lot of hurt for the passengers, but it wouldn't fly.
Don
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Why in the hell would it stay stationary??!?
Jeeeze, you are wrong... Don't try and argue it.... Why did I even reply to that question!!
Don
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Ahem
Because of how that question was worded, in that case it would not fly. It would result in some combination of infinite speeded wheels and treadmills, melted wheel bearings and a whole lot of hurt for the passengers, but it wouldn't fly.
WHHAAATT?
The wheel-speed is un-important?!?
This is the popular (and completely wrong) counter argument
http://bleddyn.co.uk/forums/plane.png[IMG][/quote]
LOL, whoever thought that up should go let Airbus know that RR is selling them faulty products. These engines provide no thrust!! May as well have some empty cylinders hanging from the wings right?
I've had long arguments with friends about this, thankfully none of them were as stupid as that though :D
Soldato
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Because the treadmill is stationary, the plane isn't moving forward so no air is passing under/over the wings to create lift.
Why do they have massive fans in front of rolling roads to keep engines cool?
Why do they have massive fans in front of rolling roads to keep engines cool?
You are confused. The original treadmill question was would a plane fly if a treadmill matched the planes forward speed. In this case I, along with the majority of people, agree that it would take off.
If however the treadmill is matching the speed of the wheels then it is physically impossible for the plane to move. You say wheel speed is unimportant, that is wrong. The plane requires it's wheels in order to move. If the treadmill is matching the speed of the wheels exactly there will be no movement. In this situation both the treadmill and wheels will rapidly accelerate to a speed at which either the force from the bearing friction in the wheels balances the push of the engines or the wheels melt/explode/disentegrate.
Soldato
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Yes, but the plane isn't moving to create the air resistance to gain lift. The reason I mentioned the rolling road is that the car isn't moving either, so there is no air resistance hence they put a huge fan in front to keep the engine cool.
Agreed. But the plane still requires the wheels in order to allow it to move forward.
Unless its on water
Soldato
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I don't understand how a plane could possibly take off. They did it on mythbusters but the plane was clearly moving forwards not stayin in one spot like it they inferred it would, the conveyor belt was moving much slower than the plane. (aka they did the wrong experiment so the plane did take off)
My friend did his physics coursework on effects of lift on plane wings using different shaped wings on some scales and blowing a leafblower over it to measure lift. Not the best of experiments but it worked. Surely if a plane could take off on a treadmill that would be like moving this single wing along on an RC car at say 5mph, on a treadmill set to 5pm and it actually creating some lift when surely it stays in the same relative position and has no airflow over it?
My friend did his physics coursework on effects of lift on plane wings using different shaped wings on some scales and blowing a leafblower over it to measure lift. Not the best of experiments but it worked. Surely if a plane could take off on a treadmill that would be like moving this single wing along on an RC car at say 5mph, on a treadmill set to 5pm and it actually creating some lift when surely it stays in the same relative position and has no airflow over it?
There is a fatal flaw in the treadmill vs plane argument, the treadmill cannot match the wheel spin speed, it's is a physical impossibility due to the fact that the plane will always have enough thrust (because it is generated independantly of the wheels/treadmill) to move forwards (and thus the wheels either turn faster than the treadmill or there is no contact between them) unless you add in a negative airspeed component that matches the planes thrust.
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That's moving the car relative to the ground, though, which is completely different to moving a plane relative to the air.
I'm going to leave this thread now as I'm supposed to be revising for my Engineering Mechanics exam this afternoon
surely aslong as you jump upwards and the bus is moving forwards the bus continues moving forward whilst you are still jumping upwords.
plane vs treadmill is stupid because a planes wheels are free rolling it doesnt take much force for the plane to move forwards even if the wheels are spinning backwords as the plane builds up thrust the friction generated by the wheels on the treadmill will become less and less.
the plane will still be able to acheieve enough airspeed to lift off aslong as the treadmill is long enough.
its not hard to comprehend a planes wheels will spin freely and they do not power the airplane, its like saying if you were stood under a flying plane spinning its wheel backwords it would make the plane slow down
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Don
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The problem is that there is 2 versions of the question. The original question stated...
"If a plane on a treadmill tried to take off but the treadmill matched the forward speed of the plane would it fly?"
In this case the answer is yes, it would. As has been pointed out there would be nothing to stop the plane from moving forward through the air and it would take off at it's normal speed. In this case the treadmill would be travelling at the same speed and the wheels would be spinning at twice this speed. Because of this there would be some extra drag from the increased bearing resistance in the wheels so the plane would take longer to get to it's takeoff speed.
The second version of the question stated that the treadmill matches the wheelspeed of the plane. In this case it is impossible for the plane to move. In order for the plane to move the wheels must be moving at a different speed to the treadmill, hence breaking the rules of the question. What would happen is as the plane tries to move forward it's wheels turn, this movement is exaclty matched by the treadmill and so the treadmill and wheels will rapidly accelerate to a ridiculous speed. Given indestructable wheels and a super treadmill, eventually a speed will be reached where the force being emparted onto the plane through the wheels from the insanely highspeed treadmill will balance the thrust from the engines. Although like I said, this is impossible to test in reality. Whats more likely to happen in reality is that the wheels will melt or explode.
"If a plane on a treadmill tried to take off but the treadmill matched the forward speed of the plane would it fly?"
In this case the answer is yes, it would. As has been pointed out there would be nothing to stop the plane from moving forward through the air and it would take off at it's normal speed. In this case the treadmill would be travelling at the same speed and the wheels would be spinning at twice this speed. Because of this there would be some extra drag from the increased bearing resistance in the wheels so the plane would take longer to get to it's takeoff speed.
The second version of the question stated that the treadmill matches the wheelspeed of the plane. In this case it is impossible for the plane to move. In order for the plane to move the wheels must be moving at a different speed to the treadmill, hence breaking the rules of the question. What would happen is as the plane tries to move forward it's wheels turn, this movement is exaclty matched by the treadmill and so the treadmill and wheels will rapidly accelerate to a ridiculous speed. Given indestructable wheels and a super treadmill, eventually a speed will be reached where the force being emparted onto the plane through the wheels from the insanely highspeed treadmill will balance the thrust from the engines. Although like I said, this is impossible to test in reality. Whats more likely to happen in reality is that the wheels will melt or explode.