Quote:
Originally posted by BlueSky:
You guys are a trip. Let me start by not even pretending to have read this entire thread, so if this is old news, forgive me.

The airplane wouldn't fly, and it doesn't matter that the engines move the plane as opposed to the wheels. In the original post, it said the belt has a control system that matches the PLANE'S speed - not the WHEELS' speed. Very important distinction because if that happens, the plane's wheels can spin at any speed but the plane's speed relative to the surrounding air remains zero.
You're so very close here, until you conclude that the plane's speed is zero. If the conveyor could *magically* keep the plane in a single position, the plane would have no speed. But wait- if the plane has no speed, then the conveyor must also have no speed, as stipulated by the problem.
Quote:
Originally posted by BlueSky:

If the plane doesn't move forward, there's no airflow (so-called relative wind) over the wings. No airflow, no lift; no lift, won't fly.

It wouldn't move forward because of the old "every action has an equal and opposite reaction" and the related laws of flight: lift must overcome gravity and thrust must overcome drag.

In our scenario, the "action" of the engines still produces the usual reaction (thrust) but not the usual result because a vital element is missing: the friction of the tires against the pavement. Take away this drag and the tires are still rolling on the conveyor belt but the result is different because the surface is not stationary.
Whoa-hold up here. Wheels are a means of reducing friction while attempting to move an object-yes? The tires-on-pavement do extraordinarily little to create friction without brakes applied. The plane still moves because it moves air, and there's nothing the conveyor can do about that.
Quote:
Originally posted by BlueSky:

The airplane will not move forward, so no lift will be generated and so gravity wins - the plane won't fly.

Now here's a new one for you:

Assume we're talking about a fixed-wing aircraft (i.e. not a helicopter) that is not a Harrier jet.

The plane's airspeed is 60 MPH but it is flying into a 60 MPH headwind. What is its speed over the ground?
The plane on the conveyor will create forward motion and achieve lift, because it's using friction against something that has nothing to do with the conveyor.

Imagine roller skating on a long treadmill that matches your speed exactly. There's a taut rope directly overhead within easy reach. As you move forward, the treadmill acts to keep you in the same place. If you grab the rope and start using it to push yourself forward, hand over hand, and your wheels are just touching the treadmill, will the treadmill be able to stop you from propelling yourself forward using the rope? No, because you're applying force to the rope and your wheels are reducing friction with the treadmill.

Of course an aircraft with a 60 knot headwind and 60 KIAS will have a groundspeed of zero. I've seen a plane with a 140 knot headwind remain motionless 6000 feet over an airport for about five minutes before I asked him if he thought he was going anywhere. When he realized he wasn't, he turned around and got home in a hurry.