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The Great Debate

Old 04-14-2006, 09:51 AM
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Default The Great Debate

This has inspired quite a bit of debate on our local board, so I thought I'd copy it over.

Originally Posted by Abneriel
I've been on MW where a question was posted (months ago) that has been brought back up...here's the question:

Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyor belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.
Can the plane take off?
most of the people on there (including some pilots) are saying that yes the plane will fly, but myself and a few other "idiots" are saying that it will not. The people saying that it will fly are arguing that the plane's thrust causes the forward motion, not the wheels...(which is true). My argument has nothing to do with what causes thrust or movement, but how the question is phrased and how it makes it impossible for the plane to take off. Here was my equation:
you guys are forgetting the key to the equation...the WHEEL speed and the BELT speed always exactly match.

in a real situation, the plane would move forward, but the wheel speed would have to be going whatever the plane speed is + the belt speed. This is not the question the original poster presented.

A= plane speed
B= wheel speed (rotation)
C= belt speed

if A = 300 mph and C = 300 mph (in the opposite direction) then B must= 600 mph (rotation)

600 mph does not = 300 mph

in order to get B to equal C, A must be at a stop.

in other words

if A = 0 mph and C = 300 mph, then B must also = 300 mph

here we see that B and C are equal, which is what the original poster placed as the constant in the equation.

to get B to = C, A must be at 0, which in this case A = the plane, which = no flight
can anyone shed any further light on this? I'm terrible at math, but after reading it over a few times it still makes sense to me...

what do you guys think? anything I'm overlooking?


I'm with the Pilots on this one, I believe the plane will take off every time.
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Old 04-14-2006, 10:05 AM
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Somebody put a wind up plane ( the one with the rubber band) on a treadmill going full speed and the plane flew off the end of the treadmill like it was nothing.
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Old 04-14-2006, 10:59 AM
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In aeronautics(sp?) what causes a plane to fly is lift (aka wind/airspeed underneath the wings). So if there is no airspeed the plane will not take off.

-Mark

Last edited by Bitemark46; 04-14-2006 at 11:10 AM.
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Old 04-14-2006, 11:08 AM
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Originally Posted by 04 Terminator
Somebody put a wind up plane ( the one with the rubber band) on a treadmill going full speed and the plane flew off the end of the treadmill like it was nothing.
I don't think that is going to be a valid experiment comparing it to a commercial jet liner. lol. If you want to get techincal a wind up plane's tail sits lower than the prop so already the propulsion is already angled upward so the wind from the prop has resistance to push against (the ground) helping it achieve lift. Jet liners propulsion is linear so they rely in airspeed. Look at a Harrior Jet (VTOL). Vertical Takeoff Over Land. The jets are turned upward so the thrust pushes agains the ground causing the plane to rise. -Mark
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Old 04-14-2006, 12:42 PM
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All you'll end up with is the wheels spinning faster as it takes off normally.
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Old 04-14-2006, 01:59 PM
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Originally Posted by Wnt2Go10o
if this goes on for more than 2 pages, i feel sorry for all who think the plane wont take off.
Oh really? Then explain on how the plane will generate airspeed when the plane itself is not moving only the wheels.

No airspeed = no lift = a grounded aircraft

It isn't rocket science. -Mark
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Old 04-14-2006, 04:19 PM
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Originally Posted by Wnt2Go10o
because the riddle starts with the conveyor belt matching the speed of the wheels in the opposite direction. wheels are not powered there for the only result would be a false ground speed reading. air speed wouldnt change and the plane would take off.
I saw this post on another board too. There is no question.

Thrust from a jet or pull from the prop is what moves a plane. It is irrelivant what the speed of the tires are so long as the plane is moving forward. In this scenerio which "is" different than the original post (but doesn't change the result) the plane will take off. Even if the conveyor moved in reverse as fast as the plane goes (which would keep the wheels stationary) the plane would lift do to drag on the top of the wings. Wheel speed has nothing to do with a plane taking off other that allowing the plane to move freely as the thrust or prop moves the plane.

A plane is capable of taking off from water where the plane doesn't even use wheels anyway.
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Old 04-14-2006, 04:21 PM
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Make the scenerio a tail wind factor that matches the speed of the plane and then you have a grounded plane.
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