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Plane Problem
- Thread starter Mr.Russian
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wtf is all this about friction, wheel bearings etc.? this is a total red herring - the question is basically asking - "If a jet moves at top speed but a device X (they call it a treadmill) renders its speed relative to the ground and, by inference the air, zero, will it take off?"
The answe is "No"
The answe is "No"
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You're the one that needs to head back to school.
The ENGINES push the plane. Ever stand behind a running jet engine? No, because they'd blow you away.
If you have a treadmill, take a model plane and push it on the treadmill. Set the treadmill to the fastest speed. No matter how fast the treadmill goes, the plane will still move forward as long as you are pushing it. Same principle applies to the engines: The ENGINES push the plane forward, causing it to take off. Now if the wheels were what were causing the plane to lift off, then yes, you would be right.
You seem to think the treadmill affects the air. It doesn't.
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Yes, but if the tread mill can accelerate at exactly the same speed as the wheels. All the jet's engines are going to do is keep the plane steady on the mill. Once the speed of the mill matches the capability of the jet's engines. The plane will never move forward, or take off. It will sit there until the wheels blow up, the engines break, or it runs out of gas.
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No, because all the wheels do is support the plane.
Okay then, question: IF you're correct, how does an airplane accelerate in mid flight? No wheels there!
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Correct.
Relative speed of the plane towards the ground = 0 --> no lift ==> no take-off
Relative speed of the plane towards the ground > 0 --> lift ==> take-off
It's inded that simple, however, the nerd question is whether the treadmill would be able to
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It uses the thrust of the engine. The only resistance against it is the air.
We are talking about the plane on the runway. The runway is ALWAYS moving in the opposite direction of the plane. At the exact same speed. The plane is moving forward, but not in relation to the air around it. Therefore it can never generate lift.
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it doesnt matter how fast your treadmill is moving, accept it. the weels will go twice as fast as the plane goes if it matches the exact speed of the plane.
lets say the plane needs to have 400km/h to take off, the weels will spin with 800km/h. and the treadmill goes with 400km/h.
lets say the plane needs to have 400km/h to take off, the weels will spin with 800km/h. and the treadmill goes with 400km/h.
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People, people! You're thinking in terms of cars! Airplanes aren't cars! Now a CAR would never accelerate on said treadmill! Why? Because it gets its thrust through the wheels! Airplanes would! Why? Because the ENGINES are PUSHING AIR causing the plane to move!
Again, I ask, if you all are so damn right, how the hell does a plane accelerate in mid flight?
Again, I ask, if you all are so damn right, how the hell does a plane accelerate in mid flight?
The runway has nothing to do with how the plane moves! NOTHING! It will be moving in relation to the air around it because the engines are pushing the plane through the air! It's the exact same damn thing as flying except you're on the ground instead of in the sky! Nothing changes except for speed!
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Haha, take a hairdryer to drive your sailing boat!
Anyway, that makes room for another interesting experiment:
* hairdryer
* toy sailing boat
* toy car
* duct tape
* a long scarf or something that's plain and you can pull back.
Attach boat to car using the duct tape.
Place it on scarf, use the dryer to blow the sail.
Now pull the scarf back and see what direction the car/boat moves.
That is about the same as the plane/treadmill thing.
Comes down to friction between car's wheels (which arent's used for propelling, btw!) and the scarf...
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Let's say that the turbine moves air faster at the rate of X^2 (or X+1).
The speed of the plane is X.
The speed of the mill is -X.
The combined speed of plane and treadmill is 0, but since the engine accelrates at increasing speed, the plane will speed up and take off.
I don't know how turbines work but I suspect that's the case.
The speed of the plane is X.
The speed of the mill is -X.
The combined speed of plane and treadmill is 0, but since the engine accelrates at increasing speed, the plane will speed up and take off.
I don't know how turbines work but I suspect that's the case.
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Then why is it easier to take-off of a forward-moving CV than of one standing still or even moving backwards?
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cause the plane has as initial speed the speed of the carrier + the wind blowing into the wings.
carrier moving with 20km/h + wind blowing with 20km/h that means it has allready a lift equal to 40km/h movent before it even started its engine.
carrier moving with 20km/h + wind blowing with 20km/h that means it has allready a lift equal to 40km/h movent before it even started its engine.
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I'm unsure of the acronym "CV", I'm assuming it's some sort of aircraft carrier, and the answer is simple: If the carrier is moving forward, wind is moving toward the aircraft, therefore, less speed is needed to generate the lift required to cause the plane to lift off.
An analogy to the treadmill case, if the treadmill is moving the plane backwards before the engines engage, it will take that much longer to cause the plane to accelerate and lift off, especially if the wind is coming from behind the plane. But the plane will still take off, since, again, it's the engines pushing the airplane, not the wheels.
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I already answered that. The jet increases thrust and accelerates. Like putting your foot down on the throttle in a car. Every action has an equal and opposite reaction.
In this case however, the jet's thrust is being neutralized by the mill. The jet is moving forward. The runway is moving backward at the SAME speed. The plane can not out accelerate it because if the plane moves at 400 MPH. The treadmill is going 400 MPH in the opposite direction. All the plane can do is keep up with the treadmill. The wheels do affect the plane because they are attached to it. If they can't move forward because the runway is keeping them stationary. The plane can't either because it is being held in place by the wheels.
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A jet plane accelerates by throwing more air, faster out of the back of its jets - there is a Newtonian equal and opposite reaction causing it to move forwards faster. This it does, because it has no treadmill under it when its in mid air.
Basically the treadmill situation is this: engines chuck air out of the back with force equal to X this provides force equal to X but opposite (-X) to push the plane forwards but the tread mill counteracts that.
This means that the only thing moving in the entire scenario is lots of air rushing thru the engines. The air on the wings - what actually does the lifting - is stationary with respect to the wings.
This certainly is not like a car - that much is true. Nor, however, is it like a rocket. I repeat - a plane takes off because of the lift provided by air MOVING over its wing surfaces. No air moving over those surfaces no takeoff ensues.
Simple as that.
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Again, take a treadmill, put a toy car on it, and make the treadmill run as fast as possible while pushing the car forward. You will see the wheels spinning VERY FAST but guess what! The car will accelerate as long as you are pushing it.
Same damn principle applies. The wheels support the plane, that is all. A force completely seperate from the wheels, and the ground, is pushing the plane. All that matters is how fast the air is moving and how much force the engines are pushing.
If the plane is moving 400 mph then the air around the plane is moving 400 mph and IT WILL TAKE OFF. Treadmill can't stop it.
None of you have any idea how an airplane works. There are no different physics acting on the plane when it's on the ground or when it's 100,000 feet off the ground.
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