Airplane physics question

Sorry, saw it - If that Mythbusters episode was a Science Fair project - it would have gotten EPIC FAIL.

 

Don't bother with the 1799, just read the first item - this question isn't the same as the one answered on Mythbusters.

 

Are we a little bored?
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Man am I glad that I wasn't a member here when this thread started.

I have a life and thus will not read 96 pages to see if a conclusion was reached, but the answer is that the plane would fly because the premise of the original question is flawed. The freely rotating wheels introduce a degree of freedom and decouples the plane from the conveyor belt. If you assume the wheels do not have a maximum speed, and that the drag from the bearings in them is negligible, the plane will simply move forward relative to the ground as thrust is developed. The speed of the plane relative to the conveyor belt could be infinite in this scenario, and the plane will still take off once its speed relative to the air/Earth reaches the speed required to generate enough lift to take off.

 

Ad revenue down this month?

 

yes....no.....yes....no....final conclusion: plane will take off.
Don't know if this expanation is a repost, but here it goes:

The forward thrust will move the plane forward.
However any movement of the wheels will be countered by the belt. In fact the wheels will not turn, but the belt will move in the forward direction of the plane (also being the counterdirection as the wheels would want to turn.)

 

For the plane to take off the wheels must spin at a different speed to the speed the belt is traveling (I know you can start talking about angular velocity etc but thats the simple explanation). If the wheels travel at a different speed to the belt then the limits of the original question (flawed or not) have been broken. The only way the question can be correctly answered (for me) is:

"For the plane to take-off the wheels MUST travel faster than the belt is spinning which would happen because the thrust of the aircraft is not connected to the travel of the belt seeing as it does not drive the wheels but pumps air. The only way for the limits of the question to be followed i.e. the wheels must match the belts speed, is for the pilot to ensure, using very gentle thrust, that the plane remains stationary (relative to the air) whilst the belt moves underneath it. In this state the planes wheels will match the speed of the belt (but in the opposite direction) which means the plane will not take off because it isn't moving. The pilot could add thrust and easily take off, but the moment he starts to gain airspeed is the moment he moves out of the limits of the question."

 

But given that the wheels rotate freely on a plane, their driving force is supplied by the belt only - so the wheels cant "skid". As long as the plane has air speed the wheels will always travel faster than the belt. Unless, I guess, the pilot also applies sufficient brakes to match wheel/belt speed - but I would imagine the brakes can cope with holding the aircrafts thrust back - so plane still doesn't take off (I think)

 

Won't fly. Sorry.
http://en.wikipedia.org/wiki/Pitot-static_system

 

No wind = Won't fly.

 

Wind isn't required, it's forward thrust that creates lift.

 

Yes, as long as the thrust of the engines move the airplane forward IN RELATION TO THE ATMOSPHERE OF THE EARTH the speed of the wheels could be 2,000 MPH on the conveyor it would still take off AS LONG AS THERE IS AIRFLOW OVER THE WINGS
No airflow over the wings and the plane will sit there like a rock. PERIOD!!
Wheel speed is irrelevant.

 

Only to those that don't understand the function of a wing

 

Thrust is NOT necessary, just forward motion of the wings through the air.

An airplane sitting stationary WILL fly off the ground if the wind is high enough from the right direction, especially during a storm. Happens all the time.
That's why you see them tied down at airports, not because they don't have E-brakes.

IT'S AIRFLOW OVER THE WING THAT IS THE KEY, not THRUST.
Take a look at a glider sometime, NO THRUST, just forward motion of the craft creating airflow over the wing.

 

If there is forward motion, the plane is moving relative to the conveyor belt. If it is moving relative to the conveyor belt, the tires are rotating faster than the belt is rotating backwards. That breaks the condition of the original question, which says that the conveyor belt matches the tire speed.

At all times that the conveyor belt matches the tire speed, the plane sits still on the conveyor belt. If it sits still, there is no air flowing past the wings to create lift, and it won't take off.

The moment the thrust pushes the plane forward, it is breaking the condition of the question. While the condition is not broken, ie. the engine is producing a very small amount of thrust and the tires' rotation is matched by the belt moving in the opposite direction, the plane will sit there happily and not take off.

While the conditions of the question hold, the plane does not take off. However, those conditions hold for a very, very tiny amount of time. Then the massive power of the plane's engines pushes it forward, causing the wheel speed to exceed the conveyor belt speed in the other direction.

Does the plane eventually takes off? Yes, of course, absolutely. BUT while the conditions of the question apply, however, the plane does not take off. So, the answer to the question is No, the plane does not take off.

The question's conditions hold for a very, very small time, however, and the plane does take off. As you would expect. But the moment it starts moving forward, the question's conditions no longer apply, as the wheel speed is obviously greater than the converyor belt speed (if they were equal, the plane would sit there, if the conveyor belt speed was greater, the plane would move backwards).

 

Agreed, 100% .

 

Note the direction in which the wheels turn when a plane moves forward.
To counter that movement, the conveyor belt would have to move in the forward direction of the plane, agree?

Now, I say the wheels will not rotate. Instead the belt will follow the speed of the plane. The plane will take off.

Since the wheels can rotate freely, I think you could even say it does not matter what the wheels do. They are not moving the plane forward, they are not breaking it. So the forward motion of the plane is independant of the wheels.

 

Downloading the mythbusters episode on this as we speak

 

It's all downhill in a glider...........................................

 

This question has always made me LOL.

No air flow over wing = no fly.

I don't have a degree in anything, yet I get that.

 

I guess 'thrust' was the wrong word to use. What I meant to say was airflow over the wings is what causes lift.

Air current is the key.