How good of a rational thinker are you?

[BerserkerCatSplat]

A plane (747 passenger jet) is sitting on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the plane's linear speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

The question is:

Will the plane (747 passenger jet) take off or not?

Why?

 

[andyhui01]

No becase for a plane to take it... it needs a very high velocity because the lift effect is by the wings where turbulence is created because of the distance travelled by both winds is different, therefore creating lift.
If the conveyor belt is moving in the opposite direction, the plane will therefore not move at all thus having zero velocity will not take off

 

[BerserkerCatSplat]

OK, then I ask you this: How does a 747 move forwards?

 

[///M]

There's probably some velocity needed for the plane to take off.

If you have the conveyor belt moving in the opposite direction at the same velocity, and I'm not good with frames of reference so correct me if I'm wrong here, but in the earth's frame of reference, the resultant velocity is zero. And a plane generally won't take off if it's standing still, relative to the ground.

 

[watto]

OK, then I ask you this: How does a 747 move forwards?

Thrust. Air is sucked into the engines and spat out the back at a much faster rate than it entered.

 

[BerserkerCatSplat]

OK, then I ask you this: How does a 747 move forwards?

Thrust. Air is sucked into the engines and spat out the back at a much faster rate than it entered.

Exactly. Now, tell me: How would the conveyor belt stop the plane's jet thrust from moving the aircraft forwards?

 

[mmap]

Allrighty, Might make an ass of myself but I do think that the plain could theoretically take off.

Simply because it isn't driven from the wheels and therefore it doesn't matter whether there is a conveyor or not. The wheels can be spinning into whatever direction they want it will not have an effect on the direction the plain is going. Once the thrusts exceeds a set amount the plain will move forwards regardless of the conveyor.

That's one point of view anyways, I can't quite wrap my head around this properly

Edit: was pondering this for a while didn't see BerserkerCatSplat's latest reply...

 

[abhishek2]

Trick question.. :?

 

[andyhui01]

OK, then I ask you this: How does a 747 move forwards?

Thrust. Air is sucked into the engines and spat out the back at a much faster rate than it entered.

Exactly. Now, tell me: How would the conveyor belt stop the plane's jet thrust from moving the aircraft forwards?

why not... the plane has wheels which touch the conveyor belt... so even if you have 4 jet thrust engines, it isn't a Harrier jet, it still needs to move... which is can't because the conveyor belt is going in to other direction and the plane has zero velocity.
Its just the same, weather it is a Bugatti Veyron or a Smart car or a bike, it would not move if it was on that converyor belt

 

[///M]

Doesn't the plane just transfer the energy from the jet engine into forward movement at the wheels?

It's like saying how could the conveyor belt stop air from entering a car's engine. You're going to have combustion, and like the thrust, the energy has to go somewhere. It ends up in the wheels.

 

[bone]

Allrighty, Might make an ass of myself but I do think that the plain could theoretically take off.

Simply because it isn't driven from the wheels and therefore it doesn't matter whether there is a conveyor or not. The wheels can be spinning into whatever direction they want it will not have an effect on the direction the plain is going. Once the thrusts exceeds a set amount the plain will move forwards regardless of the conveyor.

That's one point of view anyways, I can't quite wrap my head around this properly

Edit: was pondering this for a while didn't see BerserkerCatSplat's latest reply...

i voted no, but i think you're right

 

[andyhui01]

Allrighty, Might make an ass of myself but I do think that the plain could theoretically take off.

Simply because it isn't driven from the wheels and therefore it doesn't matter whether there is a conveyor or not. The wheels can be spinning into whatever direction they want it will not have an effect on the direction the plain is going. Once the thrusts exceeds a set amount the plain will move forwards regardless of the conveyor.

That's one point of view anyways, I can't quite wrap my head around this properly

Edit: was pondering this for a while didn't see BerserkerCatSplat's latest reply...

i voted no, but i think you're right

I still don't understand... a plane has to has wheels and has to roll on a flat surface to gather enough speed for the turbulence between the top and bottom of the wing to take off... if the conveyor belt is preventing the plane from moving anywhere, when the plane is on the ground, the power from the jet engines is transfered to the wheels

 

[watto]

Andy's correct. The plane can't take off if the conveyor belt is always matching the "speed" of the plane.

Although thrust would still be present, air flow over the wings would not thus not allowing the plane to create any lift.

The plane can't take off.

 

[BerserkerCatSplat]

Alright, imagine yourself doing this:

You have rollerblades on, and you stand on a treadmill going 5 MPH. If you rollerblade at 5 MPH, your will have a linear velocity of zero.

Now, instead of skating, (you still have rollerblades on), this time you are wearing a jet pack designed to push you 5 MPH forwards. The wheels on the blades will still turn with the conveyor. Do you see yourself remaining motionless, or would the jetpack propel you into the front of the treadmill? Assume that the wheels cause next to no friction.

It's the same principle, just on a smaller scale.

 

[flyingfridge]

The speed of the wheel rotation doesn't matter shit to a plane. Airspeed is the answer. The plane will still accelerate because the ground has no bearing on airspeed.

 

[andyhui01]

no but then if you have a jetback and get propelled to the front of the treadmill on wheels, wouldn't the conveyor belt just go faster so you end up going the same speed?

 

[DJ]

Air moving over and below the wings lifts the airplane up. Therefore, the ONLY relevant relative speed is the one between air and the wings.

In this case that speed is equal to zero. The 747 remains on the ground.

(if you had synched conveyor AND wind tunnel the 747 would take off and would appear to be floating to a outside observer)

 

[BerserkerCatSplat]

no but then if you have a jetback and get propelled to the front of the treadmill on wheels, wouldn't the conveyor belt just go faster so you end up going the same speed?

What is propelling you? The jetpack, or the wheels? Does the treadmill affect the thrust put out by the jetpack?



(Why am I asking a lot of questions? This is about rational thought, I don't just want to give you the answer! )

 

[BerserkerCatSplat]

Air moving over and below the wings lifts the airplane up. Therefore, the ONLY relevant relative speed is the one between air and the wings.

In this case that speed is equal to zero. The 747 remains on the ground.

Why is the speed zero? Is the airplane driven by the wheels?

 

[andyhui01]

the airplane isn't driven by wheels... but because the airplane is still on the ground, the energy from the jet engines are transfered to the wheels. Where can it be transfered to, remember Einstein's Equation E=mc2?... it states that Energy cannot be destroyed, just transfered.