Going the same speed in the opposite direction is not the same thing as negating forward motion...unless the wheels are propelling the vehicle, I believe... It just means the wheels will have to spin alot faster than normal when taking off.

 

how would the conveyor negate the forward thrust of the engines? Or by "conveyor" do you mean "a chain attached to the plane and a post in the ground"? The conveyor thing only works if you are pushing against it for forward movement. Since all airplanes must be able to maintain forward thrust while thousands of feet of the ground, the conveyor here is a red herring. Obviously, if there is no air moving over the wings, there is no lift, but nowhere in the stupid question was there any mention made of impeding the plane's forward motion. The plane would merely drive right off the conveyor, airborn or not. Look at a damn airplane. What do you think the engines do? Drive the wheels at 30,000 feet, when they are folded up inside the body? Is a prop just for show, a bit of old-school bling? The kind of ignorance present in this thread is scary.

If a bird is sitting on a conveyor belt that "matches its forward movement," can it take off? If you say no, please don't post it here.

 

yeah, I think it is a myth that people can't grasp the irrelevance of a conveyor belt to an airplane :/

 

This thread is hilarious.

I can see why this would be confusing for car guys. You're thinking it's like a dyno, where the car's wheels turn, the dyno's drum rotates in the opposite direction, and the car doesn't move anywhere. That makes sense on a car, where the driving wheels turn the drum.

It doesn't work that way in a plane. In a plane, airspeed and groundspeed are independent. The plane's prop/jet is driving the aircraft by moving air, NOT by driving the wheels. The conveyor belt can spin the opposite way as fast as it wants to...it doesn't matter. The plane WILL take off exactly as it would on a conventional runway.

In order to keep the plane stationary, the headwind would have to match the thrust being produced by the engine(s). The plane would STILL take off and fly, but it would appear to hover, even though the airspeed indicator in the cockpit would show a high forward airspeed.

 

It has been...there's a HUGE thread about it on the Discovery channel website.

 

if the plane's engines push against air and not against the conveyor belt, how exactly would the belt negate their thrust?

If you put a 747 on a dyno designed for measuring hp output of RWD cars, what would the peak hp output on the dyno chart (assume 60,600 pounds-force thrust per engine)?

 

OHHHHHHHHHHHHHHHHHHHHHHHHHHHHH i get it. its a trick question kinda. the plane IS moving forward

 

I'm not an aeronautic engineer, but this sounds the most plausible. If the conveyer keeps matching the speed of the wheels, the airplane will be in the same spot no matter how fast or slow it may be traveling, hence no lift required for it to take off. Only the wheels and conveyer would be moving while the plane would be stationary.

 

i was thinking the whole time the plane would be standing still in a fixed location on the ground. this whole principle is the same a how a hydroboat can take off in the water, or how a plane on skis can take off over ice. the wheels are just there to hold up the wieght of the plane and alow it slide on the ground. the speed of the wheels spinning have not bearing on the airspeed. got it now. i've had a revelation!

 

No "kinda" about it...it IS a trick question. And a very non-intuitive one. My initial reaction was "Um, no." Something didn't jive in my head though, so after a minute or two of thinking about it, I saw the light. I actually posed the question to two other engineers at work today (one with a PhD), and both got it wrong. Once I pointed out the pushing-on-air thing, they both went , but that's the trick that you have to understand.