How about we look at this in reverse with the following scenario:

Let's say we have a plane sitting on a giant conveyor belt that is trying to move the plane FORWARD at full speed (assume that the brakes are not being applied to the wheels). At the same time, the reverse thrusters on the jet engine are being applied at full power (in this case we'll say that "full speed" of the conveyor and "full power" of the jet engines are equal). What will happen??

 

duh! the plane willl take off, backwards!

 

Okay...so let's make it an air boat. What happens??

Let's say you are trying to go up river against a river that is flowing at 40 mph. If you throttle up your air boat so that the speedometer shows a speed of 40 mph then how fast are you going in relation to the banks of the river?

0 mph. Surely you can agree with that.

Now, given that, let's say that every time you apply more throttle to go faster, the current speeds up to exactly match whatever throttle you set the boat at. What is the result?

Again, 0 mph.

It is EXACTLY the same with the airplane on the conveyor.

 

Kinda like this thread.............

 

never said it didnt match the speed, just that the direction was opposite per the problem statement. again, that is MY interpretation to it.

i agree the plane would NOT fly if the conveyor belt were to be moving from behind you as you tried to speed up. everytime the wheels try to move the belt would not allow it because it catches up to the wheels instantaneously to make the speed zero, and since the belt never moves unless the wheels do the result would be no airflow over the wings of the plane, and no flight. the wheel and belt would effectively be locked together holding the thrust that is put on the wheel/belt interface, assuming no drag of the wheel happens. its like keeping the brakes on, the plane doesnt move no matter how much engine power is produced. i agree 100% with that. definitely out-of-the-box thinking.

BUT being as the statement said "belt rotates to match the speed of the wheel but opposite direction of rotation" i ASSUMED the rotation of the belt was opposite the rotation of the wheel (when viewed from ground next to the runway), thereby making the runway appear to be coming from the front of you as you take off. the wheel is allowed to speed up because its free to rotate, in this case, and the wheel and belt act as a gear mesh. and the plane is allowed to gain air/ground speed and fly.

its in the interpretation of "opposite direction of rotation"...

 

and how come this thread isnt rated 5 stars?

 

no airspeed

 

I hear ya. I'm done with this one. I love a good debate, but at some point I guess you just have to agree to disagree.

Besides, I'm all out of analogies and illustrations.

Back to concrete bedliners...

 

Good Lord ... I was 5 pages behind !!!

Let's stick to the scenario that was originally presented ...

1. You are looking at a picture of this plane on your computer screen, OK ? The plane is sitting still on the belt with the nose pointing to the left of the screen and the tail to the right. Nothing is moving ... not the plane,not the wheels and not the belt. With me so far ??

2. The plane engine spins up and produces enough power to propel a normal jet of that size .... this causes the jet in the picture to start moving to the left ... agreed ?

3. With this movement, the wheels on a normal jet located on the ground, would start to turn in a counter-clockwise direction (watch a car driving by right to left and see for yourself). The wheels on THIS plane would do that too except for the fact that the conveyor belt starts to move to counter the wheels rotation and make the wheels NOT turn.
To do this ... the belt would have to move from right to left ... CORRECT ? Yes, that is correct. And this is the same direction that the plane is moving as stated above.

4. If the plane captain mashes on the go-pedal and tries to make the plane build up to take off speed, conditions 2 & 3 will happen again with the same results.

5. Now ... the plane is at full thrust, moving right to left at a high rate of speed ........ and so is the conveyor belt (because we proved that in #3). The wheels are stationary .... also proved in #3).

6. At this rate of speed, there is going to be air movement around the wings and this is what will cause the lift.

I can't spell it out any more than that.

PISTOL

 

but the belt cant move unless the wheels do. catch 22. so the plane wouldnt fly in this condition. no wheel speed, no belt speed, no speed for lift.

*i* assume the belt is moving from left to right. it doesnt say the belt has to rotate in such a fashion to not allow the wheels to rotate. just opposite direction of rotation at the same speed. being as though the word "rotation" was thrown in, here we are.

a play on words...

this one is going down in history!

 

this is where you're getting confused. the belt in this case will be moving clock-wise. "opposite direction" as the brain teaser said. this will hold the plane in place

"Imagine an airplane is on the beginning of a massive conveyor belt, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation."

 

if you are traveling to the left in your plane. and the runway acts in the opposite direction, then which way does it go? to the right.

in order for the wheels not to rotate as you are traveling in your plane to the left, the runway would need to move to the left as well. but that isnt opposite. neither linear direction nor rotation direction.

 

OK Everybody!!! READ THIS: THE ANSWER
Scroll Down to where is says "Conveyor Runway"

 

They did not actually test it like they claim they did. Who would make a 3,000 foot runway and spend the money to program it to match the speed of the plane just to prove a hypothetical situation??

 

It was an interesting argument, but as things progressed, more rational heads prevailed, pointing out that the airplanes do not apply their thrust via their wheels, so the conveyor belt is irrelevant to whether the airplane will takeoff. One guy even got one of those rubber band powered wood and plastic airplane that sell for about a buck, put it on the treadmill someone foolishly donated to the Lounge years ago, thinking that pilots might actually exercise. He wound up the rubber band, set the treadmill to be level, and at its highest speed. Then he simultaneously set the airplane on the treadmill and let the prop start to turn. It took off without moving the slightest bit backwards.