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Could a plane take off on a conveyor belt?

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Discussion Starter · #1 ·
I know this topic has been beaten to death over the years. I think about it and come to a conclusion but then I change my mind.

“Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway. The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?"

I think it would take off because the wheels have nothing to do with the plane "flying". They are just there to keep the plane off the ground. But something in my mind keeps telling me that it just wouldn't happen.

Indecisive
 

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I know this topic has been beaten to death over the years. I think about it and come to a conclusion but then I change my mind.

“Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway. The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?"

I think it would take off because the wheels have nothing to do with the plane "flying". They are just there to keep the plane off the ground. But something in my mind keeps telling me that it just wouldn't happen.

Indecisive
Hi Zefrik,

The ability for a plane to 'lift off' has nothing to do with how fast the wheels are spinning. It has to do with the airspeed (or groundspeed) and the lift created as the air goes over the surface of the wings. In your scenario this is no air going over the surface of the wings, so no 'lift' is created, and therefore no 'lift off'.
 

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I know they put this theory to the test on the tv show mythbusters. In a small scale and full scale test, both planes were able to achieve lift off on a conveyor belt. It was quite an interesting show. You might be able to find it on discovery.com
 

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Discussion Starter · #7 ·
Hi Zefrik,

The ability for a plane to 'lift off' has nothing to do with how fast the wheels are spinning. It has to do with the airspeed (or groundspeed) and the lift created as the air goes over the surface of the wings. In your scenario this is no air going over the surface of the wings, so no 'lift' is created, and therefore no 'lift off'.
I completely understand that and 50% of the time I agree with that but then I start to think that the wheels are completely independent from the plane. They just roll in the direction the plane is headed. But by the time the plane throttles up the engines are pushing the air frame in a forward position. Won't the plane just start to speed up normally no matter the speed of the wheels? Imagine a a guy with roller blades on and attaching a jet pack on his back with him leaning forward, wouldn't he still go forward even if the ground was moving underneath him?
 

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If I'm picturing this correctly (conveyor belt carries plane in desired direction of flight which forces air over it's wings??) it'll take off. Doesn't mean that it will fly though, you'd obviously need some form of propulsion. Aircraft carrier catapults (and aircraft carriers) work in a vaugely similar way, the ship steams into the wind at full or close to full speed to help create airflow over the aircraft's wings, then the catapult gives it a massive boost in acceleration.

If the conveyor belt is being used some other way feel free to ignore what I just said.
 

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Hi Zefrik,

The ability for a plane to 'lift off' has nothing to do with how fast the wheels are spinning. It has to do with the airspeed (or groundspeed) and the lift created as the air goes over the surface of the wings. In your scenario this is no air going over the surface of the wings, so no 'lift' is created, and therefore no 'lift off'.
+ 1

It's all about airspeed over the wings that causes the lift. If planes didn't need to move to take off why would we have designed them to do so ( I know they use wheels to land but ignore that part for a sec.)

If they didn't need to move it would have been more efficient for us to design them to lift off from a standstill.

Any thoughts?
 

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Children Boogie
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Wheels would be bad on the conveyor belt. Say a plane needs to move 90mph to lift off. So the belt needs to move the plane to that speed but there's this thing, air friction and resistance. The plane on wheels would be pushed back as the belt moves forward so the plane would never reach an optimal speed unless there are brakes on the wheels.
 

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Children Boogie
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+ 1

It's all about airspeed over the wings that causes the lift. If planes didn't need to move to take off why would we have designed them to do so ( I know they use wheels to land but ignore that part for a sec.)

If they didn't need to move it would have been more efficient for us to design them to lift off from a standstill.

Any thoughts?
It takes more energy to lift and stay in the air vertically than horizontally. Think Rocket.
 

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From what I am gathering, he is saying that the plane is throttling up like it is about to take off, but the conveyor belt starts moving to match the plane's effective forward speed so that it stays still. Is that correct?
In this case, no it will not take off. Well, unless there is sufficient headwind. You can play around with smaller cessnas on windy days and get them off the ground with a few guys holding onto it.
For the plane to match the wheel speed of take off, it will be throttled way down. It would be like a car up on blocks running in gear. The wheels will spin like the car is doing 35-40MPH at idle. No wind resistance, no rolling resistance the weight is off the wheels, it isn't operating under normal conditions.
In the airplane, if you ramped up the throttle where it normally is for takeoff, you would start moving forward. Where does the propulsion come from? Once you overcome that small bit of rolling resistance of the wheels and bearings, you will start moving forward, generating lift.
So yes, an airplane can take off from a conveyor belt runway, but if the question were asking if it could take off if the plane was kept stationary, then the answer would be no.
 

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If the plane was a Harrier Jump jet it would :)
 

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I accidentally hit no on the poll, but I meant yes. It actually took me a while to understand it. I had an argument with my dad about it years ago. (He is a mechanical engineer) He eventually swayed me to his way of thinking.

The engines of the plane push against the air, not the ground. The wheels of a plane are just free rolling. Say a plane needs to read 100mph to take off. As it throttled up, the engines would push against the air and it would start moving forward. Even if the conveyer matched the speed, it wouldn't matter, because it touches nothing but the free rolling wheels. The plane would pull itself through the air and take off like normal at 100 mph. The only difference is the wheels themselves would be moving twice as fast, so they would be going 200mph.

Now, some kind of glider that got its propulsion from the wheels before take off wouldn't be able to take off. It would stay stationary. The plane pushes against the air, though, so the ground doesn't matter to it.
 

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Pixel Prestidigitator
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Think about a seaplane.
 

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Myth Busters proved it could. Something about the engine doesn't power the wheels so it still moves forward, unlike a car. Plus the wind under the wings helps lift it or something like that.
 

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I accidentally hit no on the poll, but I meant yes. It actually took me a while to understand it. I had an argument with my dad about it years ago. (He is a mechanical engineer) He eventually swayed me to his way of thinking.

The engines of the plane push against the air, not the ground. The wheels of a plane are just free rolling. Say a plane needs to read 100mph to take off. As it throttled up, the engines would push against the air and it would start moving forward. Even if the conveyer matched the speed, it wouldn't matter, because it touches nothing but the free rolling wheels. The plane would pull itself through the air and take off like normal at 100 mph. The only difference is the wheels themselves would be moving twice as fast, so they would be going 200mph.

Now, some kind of glider that got its propulsion from the wheels before take off wouldn't be able to take off. It would stay stationary. The plane pushes against the air, though, so the ground doesn't matter to it.
This is what happens, the thrust from the engines determines the speed (head/tail-winds not withstanding). This is what creates lift. The speed of the wheels and/or a conveyor belt are completely irrelevant. Do you guys think that if the conveyor was going the opposite direction that suddenly the plane would be crushed to the earth?
 

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Only one way for a plane to fly, air pressure greater under the wings then over them! wheels are only to get the plane to move forward, to get the lift the plane needs to fly! This post is like jumping up in a free falling elevator....won't work!

gary
 

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https://www.youtube.com/watch?v=cT1yvqcDZZw

The jet moves air past the bottom of the wing, creating lift, therefore the airplane doesn't technically have to be moving to lift off. OTOH it would need a helluva lot of lateral thrust to do so.
Hi m00se,

The air goes through the jet engines, hardly any air (if any) is going across the surface of the wings.
 
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