A Puzzler

[kompressaur]

As you know im ever such an interesting person and so well liked amongst my peers. anyhow here's a 'puzzler' for you. How can you live without it?

A plane is sat on a runway. The runway is like a rolling road, as the plane moves in one direction, the runway acts like a conveyor belt and moves in the opposite direction - it can do this instantly and exactly matches the speed that the plane's wheels turn.

The question is:

Will the plane take off or not?

[Tom Sawyer]

surely the plane needs its engine prepulsion to take off.

[ONEDUNME]

No it won't. The plane needs the flow of air under it's wings to force it upward and make it take off. It doesn't matter what speed it's doing on the rolling road, if it isn't going forward and forcing air under the wings then it ain't going anywhere.

[raven]

It would take off. Thrust comes from the engine or prop and isn't transmitted directly to contact areas unlike a car's engine->driveshaft->wheels on road.

k, there's some friction from the wheels but the speed of the wheels turning is largely irrelevant. Thrust moves the air.

Look at it like this - the wheels are basically only there to keep the plane from the tarmac.

[ONEDUNME]

I don't believe it. Surely the aircraft has got to move forward for any air to get under the wings. No matter how must thrust is coming from the engine (unless it's a jump jet) the plane is not actually moving anywhere and therefore can't get any forward momentum to get the desired uplift by going through the air.

[ONEDUNME]

Looking through the internet it seems that the opinion of the scientists is that it is theoretically possible which has told me

Theory and reality are two different things though. To quote one source

And there you have it, at least on paper. Bear in mind that for a plane to reach that point of decoupling would require two things above and beyond the pale of normal engineering. First, a remarkable amount of power -- far more than any jetliner, and probably any military plane, is capable of developing. The illustration on Pogue's blog is of an Airbus A320; some sort of rocket plane would be more appropriate. Second, no existing aircraft tires could take such abuse. The rotational velocity required before reaching the friction limit would have them bursting within seconds, causing the plane to be flung backward

[Beanie]

I had a look on the net earlier and yeah, it seems the scientists aren't 100% agreed, in which case i'd be fucking amazed if TDP comes up with the answer

[ONEDUNME]

Yeah I've just read some more stuff that says it's not possible Beanie.


I still can't get my head around the question, If no air is flowing under the wings then how can it get lift? It can't can it?

[Seen]

Surely it all depends on whether it's a magic plane or not?

[Doc]

The wheels aren't driven - they freewheel. The only reason they turn normally is because of the friction of the ground. In this case the ground is moving backwards, causing the wheels to spin faster, but that won't make the plane move per se (if you ignore the internal friction). The thrust from the engines will cause the plane to move though.

In reality the tyres would burst and the bearings sieze - so the plane might get off the ground, but it certainly wouldn't land easily again

[traeth]

like odm, i believe that you need forward motion
to get airflow over the wings
to get lift required to fly

but i've always had doubts at how helicopter fly
they do as i've seen them , so my aeronautical knowledge is limited

[ONEDUNME]

In theory, it's impossible for a humming bird to flap its wings fast enough to enable it to fly.

Just shows what the "experts" know.

[madaxeman]

Originally Posted by ONEDUNME

In theory, it's impossible for a humming bird to flap its wings fast enough to enable it to fly.

Just shows what the "experts" know.

I've read the same about bumble bees. Physics will come up with the answer at some point.
Aeroplanes cannot fly without lift. Lift is generated by air moving under the wings. A 'plane on a rolling road will generate no lift, therefore will not fly.

Anything else anyone would like to know?:groucho

[Seen]

Who the hell has voted "yes"?

The bottom line is that the plane is not moving AT ALL (bar the wheels). Unless there's a plane which can take off vertically from a motionless position (ie a helicopter) then it's impossible.

[ONEDUNME]

Yes there is Seen. It's called a VTOL.



Ignore the thickies who voted yes. They probably open their boiled eggs the wrong way too