I've done it with an RC plane. I know it won't work with a regular full size, but you do generate some real value of lift. It's not the primary issue of the problem, I agree. But it's physically possible and there is nothing wrong with discussing alternative solutions.

So Jedi doesn't have to post another picture:

YES I AGREE THAT THIS IS NOT THE SOLUTION, 100%. IT IS NOT BECAUSE THE LIFT GENERATED BY THE ENGINES. I WILL WRITE IT ON A CHALKBOARD 1000 TIMES. I'm just discussing another way to look at the problem, not saying ANYTHING wrong with the primary solution,

Hello:

I think you`re attacking problem from the wrong side.

The facts of plane moving forward, and taking off are separate, after all.

For the simple Gedanken experiment, let`s replace plane with a firework rocket.

Small conveyor, small trolley and rocket are not hard to procure/make, I believe, if someone wants to make this experiment.

So, let`s put trolley on the conveyor, tie rocket to it, and start cranking the conveyor backwards, as the rocket ignites.

As the thrust of rocket has nothing to do with rotation of wheels, it will propel trolley with rocket forward, off the conveyor. (Or, more likely, will send it tumbling around, due to friction between trolley wheels and conveyor.)
In any case, trolley with rocket won`t stay in place.


__________________________________

Thus, getting back to plane on conveyor - it will move forwards and take off in a more or less ordinary way, despite the conveyor movement.

On a side note, I have to note, that main purpose of jets is to provide a thrust forward, not to change air pressure around the wing.
Examine jets, which have engines mounted on the tail, and ordinary gliders with no engine at all.

Except that if the rocket was properly attached to the trolley it wouldn't tumble.

Uh. It would. If trolley is high enough, and conveyor&trolley wheels are poor enough, friction and possible jams in wheels could`ve, combined with rocket`s thrust, create a spinning moment enough to veer the trolley or even flip it off it`s wheels.

trolley height does not matter if it is designed by someone who knows there stuffs. Also, why would you put crappy wheels on a rocket powered trolley?

Because, I`m suggesting a home experiment.

And in the limits of home budget, quality stuff is quite hard to come by.

In fact, I was thinking, that maybe roller-skate (Old one with two rows of wheels, not the new rollerblades.) might do the trick.

I'm sorry, I was thinking of a real experiment where you don't introduce unnessecary variables.

Ha, you can minimise them, but they still be there to account for, if you want an experiment.

"Real", as you put it, will have to be Gedanken, since there are no absolutely hard bodies and frictionless rolling in real life.

This thread is ridiculous. it's 90% people stating the same thing over and over again in reply to other people who are also saying the same thing, and 10% completely unrelated and quite pointless observations.

Are not all threads like this?

Honestly, it probably should be locked, since the initial answer was already answered profoundly.

WRAR! I'm a dinosaur CHOMP! CHOMP!

Do I get to play with big gun, then? ^_^

no, we don't give guns or scissors to people like you


Edit:

Okay guys listen up.

The plane will take off. If you're still skeptical it doesn't matter, because I decree that the plane would take off and you should accept everything I say on blind faith. :pope:
On a conveyor belt the plane would take off normally (as in, it would reach takeoff speed without any additional strain on the engines) but the landing gear wheels would spin at twice the speed they normally would (which they are designed to handle, contrary to what Alice Whatever has been saying all along).

There. Problem solved.

Heh..on a rather random note...I've seen a glider that had actually broke free of its takedowns and wound up in the trees because it was so windy...

That happens - it has the same capabilities as a sail, and often behaves as such.

If you're still not convinced, replace the landing gear with skis, and make the conveyor belt made of ice (assume idealistic conditions, ie, the ice won't melt before the plane takes off). The will be a little bit of sliding friction (read, little), but once the plane overcomes it, it accelerates freely and is able to take off.

I have glider time and powered fixed-wing time in my logbook. I have an idea of how things work.

Maybe so. ^_^

I don`t have files on hand, so I don`t know. But bleugh, it`s downright unpleasant, when you forget about sail effect for a moment. I`ve got blown into lagoon, once.

Yep. You can also assume it's a seaplane on a river that increases in speed at the same rate as the plane, if you're willing to suspend your curiousity about wtf is going on with this river?

There's more drag, but whatever.

Maybe water in the river is accelerated by secret underwater turbines. ^_^

unless the pontoons have a subsurface cross-section area of zero.

but then it'd sink.

Because I hate myself and want to get flamed, I tried to calculate the lift provided by the engine:

Let's say we have a prop plane, engines on both sides. The dimensions of the propellers are that they have a radius of 1 meter. They generate 160 km/hr of windspeed, stationary. So in one second, they move a cylinder of air 3.14 m^2 * 45 meters long ==> 141 m^3 is the volume of air moved in one second under the wing by the engine.

The weight of air at 10 C is around 12 N/m^3. This gives the "weight" of the moved cylinder of air 1700 N. If the foil deflects the column of air 30 degrees downward, the vertical component of force generated downward is 850 N (cos(60)*1700 N); with both engines working you are back to a force of 1700 N. This is around 400 lbs of force. Yes, as we all know, not enough to lift any real airplane, period. However, 400 pounds of force is not inconsequential on its own. Real world factors included further, especially drag, may decrease it a great deal, but hey it isn't zero or close to it.

Wait, wait. Did you just said, that force is "downward"? Aka one, which presses plane to the ground? Or it`s just awkwardly put?

Damnit I voted no without thinking it through.

It'd be just like taking off on ice.

I didn't think I needed to clear up that since the wing exerts a force downward on the air, the air pushes back up opposite and equally.

Oh, wing. I thought you meant wind pressing wing downwards.

Made me thought if you missed a word, or something.

P.S. Gah, thinko. I seemingly missed whole line. You`re right.

I don't think you understand how aerofoils work

why don't we just call mythbusters and have them try it out.

A. That plane is awesome.
B. It seems a monthly ritual where we have a long thread ending up with someone leaving.
C. Jon.C is pwning.

Sorry, I mean to say the lift provided by the engines acting on the wing, not like a harrier. As opposed to the engines causing thrust, moving the aircraft through the air then causing lift.

Look, is there anything wrong with the psyiks I did? You can read what my point was as clear as day, at least shoot it down that way.

Don`t waste your time, Kuat. Obviously, it`s impossible to logically reason with flamer.

Your calculations are correct, at least in theory. I haven`t checked actual numbers, but you`ve done a good job stringing them up, and it looks correct.

I`m not too sure about the angle of 30, though, and you haven`t accounted for elerons, which add complexity to the calculations, so lifting power might be actually more.

Alice you are not smart go away

Really, I would go on to keep annoying you just by the sheer virtue of getting more images.

I don't think that's a good idea though for my continued existence here on the forum though.

what he said

Isn't the air compressed first then ignited?

Yes, as it is shown in my diagram.

Yes it is... I saw it backwards.

I'm talking about a sort of design in the picture below. The engines would indeed push some air under the wing.

I understand that what you've been saying is correct, unquestionably so. But in a case like the plane pictured, some air would indeed hit the fins on the edges of the wing, deflecting the air and causing some degree of lift. My sole issue is that the lift generated by such a setup would not be negligible, as was argued by others, and could conceivably produce lift if the plane was extremely light or the engines very powerful. Yes, no plane is designed that way. Engines are made to provide thrust. Airfoils aren't made to just deflect the air moved by the engine. I'm just bringing up a point. It never hurts to discuss alternate aspects of a problem? We've all seen this before and know the correct answer, just bringing up another point for discussion, not contention.

That's all I'm saying. Period. Wrangling with you is like wrestling the Juggernaut, I swear. I look forward to the next image of you slaughtering me.

(because I just need an excuse to use this picture)