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post #16 of 203
We're all assuming that the plane is a jet, not a prop plane.

The answer is yes, it will take off. I'm not going to explain why. Think it over yourself.

On another forum I'm a part of, every time an "airplane/conveyer belt" thread comes up, it gets locked. Everyone already knows the answer.
post #17 of 203
Quote:
Originally Posted by Mrvile View Post
We're all assuming that the plane is a jet, not a prop plane.

The answer is yes, it will take off. I'm not going to explain why. Think it over yourself.

On another forum I'm a part of, every time an "airplane/conveyer belt" thread comes up, it gets locked. Everyone already knows the answer.
Why would it be different with a prop vs turbofan/turbojet or even rocket?
post #18 of 203
meh, i don't buy it; regardless of all the air being drawn through the engines, you don't have the air flowing around the wings

unless i'm missing something, it's the same as if the wheels of the plane were in rollers so they just kept spinning, yes? if so, i would think no, even with the engines pulling air, there's not enough air flowing over the wings because it's not moving forward

grrrrrrrrrrrr
post #19 of 203
Quote:
Originally Posted by Mrvile View Post
I'm not going to explain why. Think it over yourself.
bite me; you explain it oh mighty one


anyway, the critical issue is, if i'm not mistaken, that enough air is moving over the wings to create lift; in this case all that air would have to be pulled by the engines, and none of it given by moving forward through the air, so yes, maybe, it could take off, but i would think that the engines would have to be pulling vastly more air, and the air being pulled would have to be dispersed over the wing to provide lift; which of course is the very reason that planes speed up to take off, the air being pulled over the wing because of the forward momentum of the plane obviously is critical to flight; so i'd say yes, theoretically if the engines could pull enough air without the added benefit of air flowing over the wings by forward momentum, it could take off, but i doubt that any real plane could pull that much air over the wings, and the air would mostly just be going through the engines rather than over the wings anyway, so it would take such monumental power as to be practically impossible i would think, the engines basically have to create a wind tunnel for the plane to lift off in; so be it

rollers, conveyor belt, frictionless surface, all the same

you'd be better off putting a ginormous fan in front of the plane

just pulling air THROUGH THE ENGINES, does NOTHING, the engines must pull enough air OVER THE WINGS themselves, yes? no? whaeva; to many math monkeys about
post #20 of 203
Quote:
Originally Posted by uzziah View Post
just pulling air THROUGH THE ENGINES, does NOTHING, the engines must pull enough air OVER THE WINGS themselves, yes? no? whaeva; to many math monkeys about
you presume that the jet engine is powerful enough to make the plane lift off in a normal situation. the only difference is the conveyer belt, which exerts a backwards force, but this force is very small, because the wheels are free to spin on its axle (depends on how much friction is on the wheel axle), so at any given speed, the forward force of the air pushing the plane forward is much greater than the conveyer belt pulling the plane backward
post #21 of 203
Patience!

Patience!

All the pilot has to do is wait for a nice gale coming from the direction he is facing. A gale force wind or hurricane will provide sufficient lift at the wings, no?

Laz
post #22 of 203
Yes, it will take off. The wheels will just be spinning about twice as fast as normally. The wheels will essentially be 'freewheeling'.

People have to remember that the wheels don't have anything to do with the propulsion. It's not a car!

Quote:
Originally Posted by Another site
A car's wheels are its means of propulsion--they push the road backwards (relatively speaking), and the car moves forward. In contrast, a plane's wheels aren't motorized; their purpose is to reduce friction during takeoff (and add it, by braking, when landing). What gets a plane moving are its propellers or jet turbines, which shove the air backward and thereby impel the plane forward. What the wheels, conveyor belt, etc, are up to is largely irrelevant. Let me repeat: Once the pilot fires up the engines, the plane moves forward at pretty much the usual speed relative to the ground--and more importantly the air--regardless of how fast the conveyor belt is moving backward. This generates lift on the wings, and the plane takes off. All the conveyor belt does is, as you correctly conclude, make the plane's wheels spin madly.
post #23 of 203
Quote:
Originally Posted by Happy Camper View Post
The engine does not create the air movement over the wing. The thrust moves the body through the air until the speed creates the difference in pressure to force lift on the bottom of the wing. Carriers have to gain speed into the wind to generate easier lift. It is alot harder for a plane to take off on a windless day. They can though because of the thrust of the catapult in addition to the engine. I have seen planes drop on initial departure from the deck. The plane's speed will eventually gain lift.

I do agree with the final assessment though.
But we're assuming that this conveyer belt is matching the initial forward velocity of the plane....it would have to be the engine forcing air over the wing that generates lift. An airplane does not nessasarily need a moving wind to fly. A great example would be the old X planes. They were dropped from bombers (passively dropped just like a bomb), and then the pilot would fire up its jets while in free fall. There is no forward velocity there: just gravity pulling the airplane downward
post #24 of 203
What kind of plane, what kind of engines, what is the length of the runway, what is the temperature, and what is the altitude?

Seriously: if the wheels can withstand spinning at twice the speed of a normal takeoff then the plane will take off just fine.
post #25 of 203
Quote:
But we're assuming that this conveyer belt is matching the initial forward velocity of the plane....it would have to be the engine forcing air over the wing that generates lift.
No. The thrust from the engines moves the plane forward through the air and generates lift. The conveyor belt and wheels are irrelevant, because the wheels are free-spinning and have nothing to do with the plane's propulsion.

Here's an analogy I heard: Imagine that you're in a pair of rollerblades and that you're standing on a treadmill. When the track starts, you're taken backward with it. Now, hold onto the rails and pull yourself forward. It shouldn't take much effort to do it. It's the same with the airplane. The treadmill is the conveyor, you are the plane, and your arms pulling you up are the engines.
post #26 of 203
My recollection of this problem is that the plane can take off for any normal conveyor belt. The exception is if the conveyor belt is magic and truly matches the speed of the wheels/plane no matter what, in which case, weird stuff happens like things burning from friction.
post #27 of 203
Quote:
Originally Posted by PiccoloNamek View Post
No. The thrust from the engines moves the plane forward through the air and generates lift. The conveyor belt and wheels are irrelevant, because the wheels are free-spinning and have nothing to do with the plane's propulsion.
Well this depends on how this question is phrased. Since this question is saying that the conveyer belt is matching the speed of the plane (and not the wheels), then my point is that there is no forward velocity in this very "magical" and specific example. The wheels don't have anything to do with it, except acting as posts to keep the plane from moving forward (since this very magic conveyor belt can somehow keep pace with the forward velocity of an airplane). Since a plane can generate lift with a downward vector (previous example X plane), I believe the engine would generate enough thrust (in non forward vectors) to lift the wing.

Anyway, since this question is asked all the time, in different forms, there is always going to be more and more debate. I'm just pondering this set of conditions: if the plane can not physically move forward would countering forces (ie gravity) be able to lift it up? Yes, in real life, a plane would take off, because there's no way to have a conveyor belt would match the forward velocity of the plane: thereby canceling out that factor of lift.
post #28 of 203
If the plain leaves the conveyor belt then it will most certainly take off. Thus we investigate if the plain will leave the conveyor belt.


The sum of forces = mass * acceleration

first we define some variables
F(t) = Force exerted by engine(s)
v(t) = velocity relative to air
u(t) = velocity relative to conveyor
a(t) = acceleration

next we define the constants
m = mass of plane
d1 = dragconstant due to air friction (typically 0.5*rho*C*A)
d2 = dragconstant exerted by wheels indepent of velocity
d3 = dragconstant exerted by wheel proportional to conveyor velocity

Inventerisation of forces:
Force exerted by engine(s): F(t)
Force due to airfriction: -d1*v^2
Force due to drag by wheels: -d2+d3*u

thus the sum of forces = mass * acceleration can be rewritten as

F(t) - d1*V^2 - d2 - d3*u = m*a

We assume that the velocity relative to the air is so small that it can be neglected, as long as the plane is on the conveyor belt. So:

F(t) - d2 - d3*u = m*a

Considering there is no propulsion system connected to the wheels (the wheels are allowed to move freely), the constant d3 will be relatively small.
The assumption can be made:

F(t)>>d2 +d3*u, which means

m*a>>0

there will be an acceleration and the plaine will leave the conveyor belt
post #29 of 203
Quote:
Originally Posted by Davesrose View Post
But we're assuming that this conveyer belt is matching the initial forward velocity of the plane....it would have to be the engine forcing air over the wing that generates lift. An airplane does not nessasarily need a moving wind to fly. A great example would be the old X planes. They were dropped from bombers (passively dropped just like a bomb), and then the pilot would fire up its jets while in free fall. There is no forward velocity there: just gravity pulling the airplane downward
Actually, those planes are already moving forward quite fast when dropped and although they only accelerate downward, they already have enough forward velocity (exactly same speed as the plane that dropped them) that they basically glide until the engines kick in.

As for the original question, my logic says the plane doesn't take off simply because a plane flies due to the air above the wings, not below it and since the only moving air is below the wings, it doesn't make sense for it to ever be able to lift off the track.

Of course I could be wrong, I'm no pilot, but I'll ask my buddy who just got graduated from an Aviation university program, he should know
post #30 of 203
Oh no. NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO.

For the Love of God close this thread before the beast awakens!

And the plane will take off. /thread
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