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The Myth: As the plane accelerates the conveyer belt accelerates to an equal speed in the opposite direction keeping the plane stationary preventing it from taking off. Is the conveyer capable of keeping the plane stationary?
True/False?
I know the answer to this one, but I figure I'll open it up to debate here as its a good one. Please post before reading the answer. I post this because it generated a huge thread on another forum with all sorts of wild answers. I wanna see if other people think the same way.
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What is your point of reference? In the plane or on the conveyer belt or looking from somewhere else?
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moliver Wrote:What is your point of reference? In the plane or on the conveyer belt or looking from somewhere else?
This being a real world application, assuming we could build a conveyer belt long enough.
The point is the plane starts on the belt at 0, and as it tries to accelerate the belt matches the planes speed in the opposite direction. Will the plane take off?
The premise is based around a jogger on a treadmill.
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or like a car on a dyno, kinda, no it wont take off. Unless im missing some way in which lift could be created. But since the delta velocity would be zero i dont see how it could take off
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good call, the wings have to have air passing over and under them to have lift. Plane isn't going to take off.
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i believe that since the plane uses thrust to propell it instead of wheel spin that the conveyor would have little to no effect on the plane taking off no matter how fast it spins
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but if the conveyor spins as fast as the plane moves then there can be no air passing past the plane. If the plane is not moving itself i dont see how it could take off even if the turbines were pushing it a thousand mph if it isnt traveling any distance, no lift can be created
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I think the plane would still take off. If it it a prop, the lift is generated by the prop moving air over the wings, if its a jet, thrust would get it airborn. I saw a display at the museum of science and industry where you "fly" a plane that is a static model and wind simulates the prop and it rises up.
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ya but the prop doesnt create all the lift. I guess if i knew how much prop speed factored in the take off i could better guess what would happen. But if a plane could create lift from its own props alone we wouldnt have runways
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Good point. So it has to be a propellor plane, because we all know that jet planes use thrust and can take off from moving aircraft carriers, and that missles can fly just fine from a horizontal stand still.
So watch Mythbusters tonight and find out.
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A plane does not use its wheels for thrust. I dont care what the wheels are doing, if there is thrust from either type of engine prop or jet the plane is going to move forward threw the air and cause lift. I guess what im saying is that a conveyer alone cant keep a plane stationary.
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well a jet wouldnt be able to take off either, the big thing is that it is not moving relative to the earth.
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How do you explain this though. This plane is generating all of its lift from the single prop.
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MX_KEVIN Wrote:A plane does not use its wheels for thrust. I dont care what the wheels are doing, if there is thrust from either type of engine prop or jet the plane is going to move forward threw the air and cause lift. I guess what im saying is that a conveyer alone cant keep a plane stationary.
but the big reason that it gets into the air is because at higher speeds the wings creat lift, here there is not velocity. itd be the same if u picked it up off the ground and held it stationary; saying that it would be able to take off with no velocity is the same as saying that it would be able to hover. No lift no take off
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In the video, the plane is stationary and hovering, yet has plenty of lift. So theoretically as long as the motor and prop speed were high enough it would lift off of the conveyor and move forward.
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mikeh Wrote:How do you explain this though. This plane is generating all of its lift from the single prop.
because of the position of the prop. The army has some new hybrid planes in development that work off the same concept. Doing that with the plane is basically turning it into a helicopter. The props are designed to push air past the plane and accelerate its motion to the point where it can use the air from the propeller and its velocity in whatever direction it is traveling to create lift. i doubt you would be able to get a real plane to do that. If the thrusters on a jet pointed downward or a the prop pointer upward then yes it could do it. Then again thats basically a helicopter
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I thought the question was "Is the conveyer capable of keeping the plane stationary?"
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as in from taking off. It says that the conveyor belt will keep the plane stationary no matter how fast it is going, per second line of the question
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Thirdgen89GTA Wrote:This being a real world application, assuming we could build a conveyer belt long enough.
The point is the plane starts on the belt at 0, and as it tries to accelerate the belt matches the planes speed in the opposite direction. Will the plane take off?
The premise is based around a jogger on a treadmill.
If the wheels could maintain traction equal to the force being genertaed by the engines, and the belt could match the speed (thrust) created by the engines, the plane would not have forward movement. No forward movement, no lift from the wings, no takeoff.
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mikeh Wrote:How do you explain this though. This plane is generating all of its lift from the single prop.
Planes hang on the prop because they push enough air to overcome the weight of the craft. Without some way of moving into the vertical attitude, the plane on the belt conveyor could never lift it's nose, unless it was a vectored thrust system (Harrier, etc.). Real prop planes cannot just full throttle, pull back on the stick, and take off vertically. Some fighter jets could if you set them on an incline and launched them. They have more thrust than weight so they can climb vertically (essentially a rocket).
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Well here is the answer as I see it. I wanted to wait for a few posts to get in the thread.
Certainly if you use the Jogger on a treadmill scenario then the plane could NOT take off as there would be no airflow over the wings. Consider this, for a Jogger, or a Car on a dyno the primary means for acceleration is through the ground. The power is applied as either steps forward, or rotating tires to propel a person or car.
With a plane acceleration is not provided by the wheels on the ground but thrust given by a prop or an engine. So if you go with that then the friction generated by the wheels is not enough to stop the plane and hold it in place. Even if the tread mill is moving at 150mph it doesn't require the same amount of thrust as a plane traveling 150mph on a runway because the treadmill does not have any wind resistance.
So the plane will still accelerate, even though the tread mill is slowing the plane down the plane would still have sufficient thrust to overcome the extra friction by the treadmill and attain enough speed to generate lift.
BTW, this is what tonights Mythbusters is about.  And i'm positive that it will be able to take off.
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I still say a conveyer wont keep a plave stationary. The wheels can roll forward, backwards all they want. On a conveyer a plane will still have forward motion which will generate lift.
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Thirdgen89GTA Wrote:Well here is the answer as I see it. I wanted to wait for a few posts to get in the thread.
Certainly if you use the Jogger on a treadmill scenario then the plane could NOT take off as there would be no airflow over the wings. Consider this, for a Jogger, or a Car on a dyno the primary means for acceleration is through the ground. The power is applied as either steps forward, or rotating tires to propel a person or car.
With a plane acceleration is not provided by the wheels on the ground but thrust given by a prop or an engine. So if you go with that then the friction generated by the wheels is not enough to stop the plane and hold it in place. Even if the tread mill is moving at 150mph it doesn't require the same amount of thrust as a plane traveling 150mph on a runway because the treadmill does not have any wind resistance.
So the plane will still accelerate, even though the tread mill is slowing the plane down the plane would still have sufficient thrust to overcome the extra friction by the treadmill and attain enough speed to generate lift.
BTW, this is what tonights Mythbusters is about. And i'm positive that it will be able to take off.
Ya, what I said. LOL 
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but ideally if the treadmill holds it from advancing its motion in any direction it will not take off. you asked for the answer in an ideal situation
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I didn't write the myth correctly.
The treadmill would have to move awful fast to keep a plane at full thrust stationairy. I don't think any tires could hold up at those speeds.
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