WILL IT FLY?

Jotaru

Jotaru

shinobi-no-mono
FC/Active Member
Soo... some of you who browse different forums may have seen this debate heating up all over the place lately, its a relatively old question, but seems to be gaining interest lately. I figured I'd ask here to see who thinks what ;) Disclaimer: Kalia I know you know! So don't spoil it! :tounge-1:

A jet plane is sitting on a runway, ready to take off. However, the runway is more like a giant treadmill, and has a system in place to constantly monitor the exact speed of the airplane on it. As the plane moves forward, the treadmill moves rearward, in the opposite direction the plane is moving, at the same speed.

plane-on-treadmill.jpg


So, assuming there is no error in the control system for the treadmill (i.e. no cheap 'lawl the system is wrong' answers) and constantly matches the speed of the aircraft, but in the opposite direction, will the aircraft take flight?

:tounge-3::tounge-3::tounge-3::tounge-3::tounge-3::tounge-3::tounge-3::tounge-3::tounge-3::tounge-3::tounge-3:

LET THE DEBATE BEGIN! :p
 
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As a sidenote, I have less expectations for lulz in this thread than I have seen because generally the people that play FFXI aren't inbred retards, to a certain extent. Sure, there's your morons, but I have more faith in most of you than the general fodder found on other forums ^^; Which sadly equates to less lol-factor :(
 
The entire question is one of lift under the wings of the aircraft. I am not a physicist but I wouldn't think you could build lift when the aircraft isn't actually moving forward.

-benny
 
I think I agree with the same thing Benny just said. It looks as if the only thing the demonstration above is accomplishing is testing the speed that the landing gear can handle. I think it could "fly" if that condition were a windtunnel instead. I don't think any lift is being generated.

The only real world example I could apply it to would be to have a car in that same condition on a set of rollers and sticking my hand out the window. I'm pretty sure that when I stick my hand out of the window, it won't have anything forcing it upwards.
 
The only real world example I could apply it to would be to have a car in that same condition on a set of rollers and sticking my hand out the window.
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Think on this a bit more. ;)
 
Think on this a bit more. ;)
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I'm essentially stationary and only moving the wheels of the car on the rollers (like in those oil commercials). I'm not actually moving so there's not any generated lift being applied to my hand. The only thing different is the fact that you have the runway providing that for you instead of the car's tires (well that and the fact that the plane's engines generate thrust against air, providing the lift instead of how fast you can accelerate via the ground). Isn't it kind of independent?

In either case I still do not think you are generating lift.
 
The plane would have no movement, so no real speed. As speed is needed for take off. It is somewhat similar to the idea if you are on a train going the speed of light, and you run down the hall, are you going faster than the speed of light?
 
My guess would be yes, the plane will take off. My reasoning is so: the plane is moving at x kph (or mph), its relative speed to the ground (not the treadmill) is still x kph as the aircraft is moving. The position of the aircraft does NOT change because it is being put back into place with the treadmill which is running at -x kph (using the initial plane position as a frame of reference and forward as the positive plane) and such its relative velocity would be 0 to the ground. An aircraft generates lift from the air passing under and over each wing, as the speed of the aircraft is still increasing but its position and thus velocity (these are vector measurements while speed is a scalar) are still zero, it will genereate enough lift at a certain point to take off. The displacement may be zero, but the distance those wheels have travelled will still increase with time.

You may not realize it, but a jet taking off the opposite direction a carrier is moving in the ocean is same idea.

Velocity = displacement / time
Speed = distance / time

Displacement = 0, the plane's position is not changing
Speed = x kph
 
Edit: Nvm. Gonna wait and see what more people say, is a pain in the butt to not really be able to reply xD
 
The angle which the wind vector over the wing has to be correct. If there is no wind, there is no flight.

Doesn't matter how fast the tires go, is there any wind?

(Not to mention it looks like even if your plane did manage to get some wind, doesn't look like it would fit through that hole~)
 
The plane will definitely take off. The engines push the plane forward as usual. The moving treadmill does not matter because the wheels aren't driving the plane forward. The wheels are only there to keep the fuselage off the ground. So even though the treadmill is moving backwards as fast as the plane is going forwards, it just means the wheels are turning twice as fast as if the ground is stationary. The plane still moves down the runway, generates lift, and takes off.
 
Planes are too often generalized to cars, but Varda is right, the wheels are only there to keep the plane stable before takeoff on the ground, the turbines and propellers generate the air flow required for lift. Notice how a plane can take off at an airport regardless of what the wind is doing.
 
Five hundred points to Varda :) The tricky thing about this question is that everyone thinks about it 'as a car'. Were it a car, and propelled by the wheels (ignoring the fact that it would have no propulsion in the air!) it definitely would not take off, because the entirety of its power source would be getting counteracted by the opposing runway force. However, its a plane! The engines generate the force, and they don't care if the wheels are going 0mph, 100mph, or 200mph (assuming the landing gear doesn't break off and whatnot) The only thing the opposing runway does is cause the wheels to rotate twice as fast at V(r).

In a sense, Archain, you were right - if the plane somehow did remain stationary (i.e. the wheels were powering it, not the engines) there would be no lift and it would not take off. That's the other thing I like about this question, it has three 'potential' answers, or more, and all seem right because they 'prove' one of the others wrong.
 
The problem is, the engines generate THRUST, not lift. The lift is generated by the drag produced as the plane moves forward through the atmosphere. If the plane is stationary, there is no drag. Run in place. Feel the wind hitting your face? No? Average takeoff speed is about 140-155 mph, if there isn't a 140-155mph wind hitting those wings, you're not going anywhere. With that setup, though, it's going to crash right into the front of the treadmill or fall over the front, Cause no force is being applied to the treadmill's track to get it moving.
 
The plane will definitely take off. The engines push the plane forward as usual. The moving treadmill does not matter because the wheels aren't driving the plane forward. The wheels are only there to keep the fuselage off the ground. So even though the treadmill is moving backwards as fast as the plane is going forwards, it just means the wheels are turning twice as fast as if the ground is stationary. The plane still moves down the runway, generates lift, and takes off.
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I've got to go with this as well, I was thinking about this on the way to work. The original scenario took great measures to make sure that the runway (treadmill) and landing gear were irrelevant and would essentially cancel forward motion out.

I was thinking about the plane's propulsion almost the same way that I was thinking about a car. The little analogy I posted was irrelevant because a plane and a car have different means of moving forward (one works against the ground and one works against the air). I was thinking of the plane in the same way that I think of a car and not thinking about the thrust generated by the engines.

If you take the treadmill and contact with the ground out of it you've essentially got the engines acting against the air. I know missiles and VTOL aircraft do it all the time without a runway.

I have to change my answer to "Yes", lol.
 
Archain said:
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If you take the treadmill and contact with the ground out of it you've essentially got the engines acting against the air. I know missiles and VTOL aircraft do it all the time without a runway.

I have to change my answer to "Yes", lol.
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The amount of thrust required to launch a passanger jet from a standstill with an average payload is enormous, you'd need to strap 6 -10 more jet engines and at least 500,000 NOS stickers on it. Not to mention line-locking the landing gear or positioning the plane vertically so you could power the engines up while maintaining a velocity of zero.
 
if the plane is stationary
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That's the whole point - it isn't stationary. Sure, the treadmill runs faster and faster, but the wheels dont care, they spin freely. The plane will accelerate, as will the treadmill, but who cares, and the plane will eventually reach enough IAS to takeoff.

I was thinking about the plane's propulsion almost the same way that I was thinking about a car. The little analogy I posted was irrelevant because a plane and a car have different means of moving forward (one works against the ground and one works against the air)
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A-yup!

The amount of thrust required to launch a passanger jet from a standstill with an average payload is enormous, you'd need to strap 6 -10 more jet engines and at least 500,000 NOS stickers on it. Not to mention line-locking the landing gear or positioning the plane vertically so you could power the engines up while maintaining a velocity of zero.
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You don't have to launch it instantly. As you accelerate, the treadmill will accelerate, to match the speed. This is where people get hung up - read: it doesn't matter how fast the treadmill moves (to a point..) this is the purpose of bearings. The only affect the treadmill vs airplane speed makes is the resistance force due to friction, which is very very very small. You have an enormous outside force (jet engines) propelling you. In a car, the wheelspeed is ENTIRELY important, because its the only way you can move forward. In an airplane taking off, wheelspeed is of no consequence.


Edit: Imagine sitting on a treadmill on a skateboard, and you have a friend holding you from behind so that your speed matches the treadmill's speed (as in this example) and you don't go in reverse. Now he gives you a mighty shove from behind - do people deny that you would move forward? Assume that the treadmill accellerates to match your new speed- sure, it will slow you down due to friction in the bearings of the wheels, and eventually you will match speeds again, but that was because you just got that one instantaneous push. Replay this scenario x 100000 as you turn the instantaneous 'push' force into a continuous 'thrust' force, and you can see why the plane accellerates.
 
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The amount of thrust required to launch a passanger jet from a standstill with an average payload is enormous, you'd need to strap 6 -10 more jet engines and at least 500,000 NOS stickers on it. Not to mention line-locking the landing gear or positioning the plane vertically so you could power the engines up while maintaining a velocity of zero.
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Did you totally disregard the impossible treadmill that would have to be created in order to do this, lol.
 
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