Well, is a jet engine pushing the air back or the gases from the engine are coming out? I think it’s not the same. Propeller engine pushes back air, yes, but air is not a rope you can push or pull to get movement, it’s not homonogeus (a solid object if you will)[/quote]
(Leaving the original question alone as the inevitable result of it being answered thoroughly correctly is repeated insistence of the opposite.)
A rocket produces thrust only from the exhaust gases.
A modern high-bypass turbofan jet engine – as used in airliners today – produces some small percentage of its thrust that way, but the majority of the power developed is used towards driving the “fan” in front, which basically is a many-bladed ducted propeller. Most of the thrust is from air drawn in and pushed back by the fan.
LOL, can we do the Monty Python problem again next?
Other’s seem to have given fine responses, but I’ll add one more thing for those that still don’t get it.
As pointed out, the wheels in the plane are not spun by the motor. The only reason they are even on the plane is to reduce friction with the ground during takeoff. Many mechanisms would work to allow the plane to takeoff without no wheels, ever see a seaplane? Theoretically, so long as the wheel bearing has a coefficient of friction lower than that of the rubber tire with the ground, a plane on a conveyor would not even move when not running (relative to someone on the ground that is, but let’s not get into relativity). This is where the roller skate analogy fits very well. This is also the reason why an icy runway will not affect a takeoff, a landing is a different story, however.
So if a plane was sitting on an apparatus that wouldn’t allow any horizontal motion, with the props/jet engines running, the plane would be able to lift off, correct?
[quote]matko5 wrote:
ucallthatbass wrote:
The simply answer is a plane is not a car, the engine does not drive the wheels.
Tie a rope to a wall, put on roller skates and jump on a moving treadmill. You can still pull yourself toward the front of the treadmill even though the wheels are moving in the opposite direction. Your arms drive you forward just like the plane’s engine or propeller does…kinda
That’s a wrong assumption, and it’s not the same with the rope, tree and rollerskates ;)[/quote]
it’s an analogy not an assumption.
I never mentioned a trees
Propellers work by creating a low pressure zone infront of them, and a high pressure zone behind giving forward thrust.
Engines do the same but with more thrust and power
Your dumb
???
Profit
The shape of the wing creates a lower pressure zone above and high pressure below providing lift.
My analogy was in reference to the wheels on a plane being irrelevant in the conveyor belt scenario, because again the engine/prop and the wings provide lift and thrust, not the wheels.
[quote]Ronsauce wrote:
So if a plane was sitting on an apparatus that wouldn’t allow any horizontal motion, with the props/jet engines running, the plane would be able to lift off, correct?[/quote]
No. The posters claiming no wind=no lift were technically correct. If the plane is physically restrained by a force greater than that of the thrust produced, it will not move forward and will not produce the pressure differential caused by air moving past the wings that is necessary for lift.
The point you must have missed is that even with a conveyor moving in the opposite direction, the plane will still move forward.
[quote]Rocket Scientist wrote:
Of course not! Ground speed is no factor. it’s airspeed and only airspeed, and in this scenario the airspeed is only however fast the wind is blowing, because the aircraft is not moving through the air.[/quote]
Ok it took me a minute to realize that the plane will be moving forward - regardless of any rear moving ground speed. Make sense? The ground won’t inhibit forward progress of the plane. (yeah and I was too lazy to click on any links or pictures which may have been why it took me so long to clock on that)
[quote]matko5 wrote:
I KNOW I KNOW, it has been munched over a thousand times, but I would like to hear your opinion on this.
For all who don’t know what I’m talking about, here’s the original question:
“A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?”[/quote]
the funny thing is at first this seems like an interesting question, partly because its worded kind of strange and partly because most of us dont ever really sit and think about the minute reasons of how a plane works for taking off.
but its kind of funny how simple it really is once its explained; the wheels don’t mean shit except to prevent the plane from scraping against the ground. the only thing that matters is thrust generated by the propellers/turbines