Author Topic: Will the plane fly? (Brain teaser) (Read 10883 times)

Pride · « **Reply #15 on:** December 29, 2005, 03:51:39 PM »

All that proves is that the paper wasnt being pulled away at the same speed as the fan blowing air...

Here is the key part of the original question:

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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 opposite direction)

Biggles · « **Reply #16 on:** December 29, 2005, 04:48:51 PM »

Let me try and put this in a different perspective.

The plane relies on thrust, through the form of displacing air, to move. Displacing air, has nothing to do with the ground. Right.

Its wheels are there to minimize friction between it and the ground.

Now, replace the airplane with a skatebaord, kinda like Billabond did. It's much like the airplane, only it lacks something to make it move.

And now, replace the runway with a treadmill...pointing almost straight down, with the conveyor moving upwards. That way, the skateboard has something to propel it, namely, gravity, which is also independent of air. If you set the skateboard on it and program it to increase its speed to match teh skateboard's while the skateboard accellerates, it won't stop it.

The wheels can not generate enough friction to counteract the force causing it to accellerate...the plane is designed so that the wheels do not have enough friction to stop it. If you had the treadmill spinning at 30mph, several times the skateboard's downward velocity, the skateboard would still fall.

Thus, the skateboard is moving relative to the air, as would the plane, because there is not enough friction in the wheels to keep it from moving.

Pride · « **Reply #17 on:** December 29, 2005, 05:09:52 PM »

Billabond1 · « **Reply #18 on:** December 29, 2005, 06:40:18 PM »

that is exactly what i was trying to say...thus the plane would move and it would generate lift and therefore it would fly.

Pride · « **Reply #19 on:** December 29, 2005, 08:21:05 PM »

But the plane isnt moving. If you were to stand on top of it.. .it wouldnt go anywhere! And you wouldnt feel any wind.

Biggles · « **Reply #20 on:** December 29, 2005, 08:52:10 PM »

Quote from: "Pride"

But the plane isnt moving. If you were to stand on top of it.. .it wouldnt go anywhere! And you wouldnt feel any wind.

And why is it not moving? The conveyor belt can not create enough friction with the wheels to exert the force needed to keep its engines from moving it, just like the treadmill, no matter how fast it's moving, can not generate enough friction with the skateboard wheels to keep gravity from moving the skateboard like I said above.

.:F3ar0n:. · « **Reply #21 on:** December 29, 2005, 08:54:55 PM »

U guys are all geeks...only fites would discuss such a topic...will agree with Biggles on this one (after taking 10 min to read all the posts for this topic)

Pride · « **Reply #22 on:** December 29, 2005, 09:29:20 PM »

friction has nothing to do with it.

The only thing that lifts a plane off of the ground is air flowing around its wing. the flow of air has to be so fast or the wing wont generate lift.

So unless you have a giant fan blowing air in front of the plane... it wont lift off the ground. I dont get why this is so hard for some of you to comprehend.

The speed of the "treadmill" and the speed of the jet engines are cancelled out in this question... since the treadmill is automatically adjusting to equal the speed of the jet propulsion.

kona · « **Reply #23 on:** December 29, 2005, 10:00:40 PM »

It really doesn't matter if the plane takes off or not.....................the airlines will STILL loose your luggage....................

Biggles · « **Reply #24 on:** December 29, 2005, 10:12:50 PM »

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since the treadmill is automatically adjusting to equal the speed of the jet propulsion.

The velocity of the jet exhaust and the forward velocity of the plane are completely different which matters because...

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This conveyer has a control system that tracks the plane speed

PLANE SPEED meaning forward velocity of the aircraft, not the velocity of the air being thrusted.

Your scenario of the conveyor cancelling out the thrust of the jet engines would work if

1. the conveyor applied an equal force to the aircraft in the opposite direction and
2. if the plane was bolted to the conveyor, so it could apply the force without any loss of energy.

Even if the conveyor IS going as fast as the jet exhaust, it can not apply enough force to the aircraft in the opposite direction because the wheels prohibit it from doing so...the force of the conveyor is being used to spin the wheels, not to push the plane.

That's what friction has to do with it...the wheels reduce friction to the point where there is not enough of it to transfer the force of the conveyor into the airplane.

It's as if you put a car on a dynomometer and drenched the tires in grease...you wouldn't be transferring nearly as much energy into the dyno because there's not enough friction for an efficient transfer of energy.

Billabond1 · « **Reply #25 on:** December 29, 2005, 10:32:52 PM »

/me continues to argue with pride

The plane would actually be moving. The fact that the belt moves the same speed as the plane does not matter. The wheels would just end up spinning faster as the plane moves faster.

A plane isn't driven down the runway because the wheels move, the wheels move because the plane is driven down the runway buy the thrust from the engines.

Pride · « **Reply #26 on:** December 29, 2005, 10:35:09 PM »

define moving....

if I can point at an object for 1 hour and I dont move my finger... is it moving??

sure, the wheels are in motion... but the plane isnt actually moving. lol

Billabond1 · « **Reply #27 on:** December 29, 2005, 10:49:21 PM »

yes the wheels are spinning. The plane is also moving in the direction that the plane is ment to move.

after this thread was started, i found this thread in the quakecon forums. read what they have to say (masteryoda knows what he is talking about).

Biggles · « **Reply #28 on:** December 30, 2005, 01:01:26 AM »

Put simply, the conveyor ain't doing s*** cuz of the whizzles.

good quote from MasterYoda:

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Look at it this way. Stand on a treadmill going full speed while wearing rollerblades, tie a rope around your waste, and have someone standing in front of the treadmill pull on the rope...will you move forward? yes

Pride · « **Reply #29 on:** December 30, 2005, 07:54:34 AM »

The truth is, you guys can argue all day long... but the fact is.. the plane will NOT take off.

I dont know how else to put this...

If the tread is moving backwards at 100 MPH, and the wheels are turning at 100 MPH, the plane is NOT moving.

In order for a plane to lift off of the ground, it must have a significant amount of air flowing over the wing to create the lift when it hits the flap.

If the plane is not actually physically moving, then no air is flowing over the wing.

I think what you are all forgetting is that Jet Engines do NOT create lift. they simply push the air behind them allowing the plane to thrust forward, in turn causing air to flow over the wing, in turn giving lift.

So essentially, the Treadmill is counteracting the Jet Thrust... and in turn the plane is NOT moving!

No plane movement, no air over the wing, no lift.