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 Airplane and Belt Conveyor
A plane is standing on a runway that can move (some sort of belt conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"
If it ain't broke, don't break it.
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i'm going with a i don't think so 
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Nope. It's not a matter of the speed of the wheels turning, but of the rate of airflow over/under the wings that make the plane fly.
Mark & Mary Lou Lawson
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 Originally Posted by MarkLawson
Nope. It's not a matter of the speed of the wheels turning, but of the rate of airflow over/under the wings that make the plane fly.
 Without movement through the air; the wings provide no lift...
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Originally Posted by MarkLawson
Nope. It's not a matter of the speed of the wheels turning, but of the rate of airflow over/under the wings that make the plane fly.
Originally Posted by Bob Denman
Without movement through the air; the wings provide no lift...
They tested this on Mythbusters.
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Depends
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Originally Posted by aeroshots
Hadn't considered that possibility!
Mark & Mary Lou Lawson
Snellville, GA USA
'10 RT-S PE #0031
'10 RT-622 Trailer
'08 Yellow SM5 #2332
'01 Black GL1800A Goldwing #0930
"Remember in the darkness what you have learned in the light." - Joe Bayly
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If it ain't broke, don't break it.
IBA #47122
2020 RT Limited Asphalt Grey
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Originally Posted by ThreeWheels
A plane is standing on a runway that can move (some sort of belt conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"
It doesn't mention HOW it must take off; it just misdirects us, by making us think about the obvious...
We were all drawn to the issue of the wings not having airflow over them...
...While forgetting about the other methods of lift that are available! 
Last edited by Bob Denman; 04-07-2015 at 09:31 AM.
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The plane is accelerating with regard to the runway, moving or not. It does not use the wheels as motive force, rather the acceleration of air through the engines provide thrust which happens regardless of the speed of the wheels turning. The belt movement has no net effect other than the minimal rolling resistance of the wheels.
Yes the plane will take off in normal fashion and will move forward at its normal acceleration and lift rates.
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But it's not moving forward; the conveyer belt is counteracting it's forward speed, by running in the opposite direction.
It'll just sit there... 
Unless it's a Harrier!
https://www.youtube.com/watch?featur...&v=2pweY5y5eRI
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Originally Posted by jcthorne
The plane is accelerating with regard to the runway, moving or not. It does not use the wheels as motive force, rather the acceleration of air through the engines provide thrust which happens regardless of the speed of the wheels turning. The belt movement has no net effect other than the minimal rolling resistance of the wheels.
Yes the plane will take off in normal fashion and will move forward at its normal acceleration and lift rates.
It's not the air through the engine that causes lift, but air moving over the wings. The plane has to move forward through the air in order to achieve lift. It the plane can't move through the air, it won't fly!
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Originally Posted by jcthorne
The plane is accelerating with regard to the runway, moving or not. It does not use the wheels as motive force, rather the acceleration of air through the engines provide thrust which happens regardless of the speed of the wheels turning. The belt movement has no net effect other than the minimal rolling resistance of the wheels.
Yes the plane will take off in normal fashion and will move forward at its normal acceleration and lift rates.
We are not talking about a car where the mode of forward movement is the wheels.
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Originally Posted by Bob Denman
The counter direction conveyer has no effect once the engines are providing enough thrust to overcome rolling resistance of the wheels. It cannot 'counter' the forward acceleration that is the direct effect of the rearward acceleration of the air through the engines. This is nothing like a car that uses the wheels to generate the forward thrust.
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Originally Posted by PrairieSpyder
It's not the air through the engine that causes lift, but air moving over the wings. The plane has to move forward through the air in order to achieve lift. It the plane can't move through the air, it won't fly!
Its the acceleration of the air through the engines that provides the forward movement. The plane DOES move forward regardless of the speed of the conveyor belt. Therefore the plane achieves lift in the normal manner.
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A plane cannot fly without achieving a certain AIRSPEED. The contact with the ground and the speed at which it travels relative to the ground is irrelevant.
Consider a glider. After it is aloft, it gets lift by having air flow over it's wings. An engine is not required. Thrust comes from gravity.
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Originally Posted by PrairieSpyder
A plane cannot fly without achieving a certain AIRSPEED. The contact with the ground and the speed at which it travels relative to the ground is irrelevant.
Consider a glider. After it is aloft, it gets lift by having air flow over it's wings. An engine is not required. Thrust comes from gravity.
I wonder how many forums have had this very same question asked and how many hours have been devoted to arguing about it.
Here's the correct answer:
The wheels under a typical airplane are nothing more than nearly frictionless free spinning wheels. The airplane gets ZERO propulsion from the wheels. The airplane is drug through the air by the thrust created by the propeller. The airplane WILL TAKE OFF!!! If the wind was blowing hard enough an airplane could take off with no groundspeed whatsoever (think about that one for a while). It's all about the air movement NOTHING about the ground affects it.
Added thought here: The belt cannot overcome the forward motion of the airplane AND the conveyor moving in the opposite direction is going to cause a wind to assist in the plane's takeoff.
Last edited by ARCTIC; 04-07-2015 at 12:34 PM.
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Originally Posted by PrairieSpyder
A plane cannot fly without achieving a certain AIRSPEED. The contact with the ground and the speed at which it travels relative to the ground is irrelevant.
Consider a glider. After it is aloft, it gets lift by having air flow over it's wings. An engine is not required. Thrust comes from gravity.
ehh, ok. The conveyor belt does not have any effect on airspeed either. Same point as I previously spoke. The plane achieves lift and forward speed in the normal manner. The conveyor belt is irrelevant.
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You did say plane four times in your question, but I missed the VTOL exemption. I guessed I missed your point in the question. So, what is the answer?
but I'll keep my three wheels on the ground...
its ground speed/(wheel speed if measured) will be 140 Kts GS for the given conditions. I know, there are other factors that relate to GS, but to keep it simple please humor me. In said example with the conveyer belt runway, the runway will correct for the speed of the "plane" (as I understand the riddle). One would need to ascertain if "plane" speed in this riddle is measured at the wheels or at the pitot tube (i.e. airspeed). If at the wheels then when the IAS reaches take off speed of 140 Kts the wheel speed would be 280 Kts because the runway would be matching the wheel speed thereby doubling it again and again to infinity. The airplane still takes off when it reaches 140 Kts IAS.
