25 Oct 06
Originally posted by uzlessyou ask for a straight yes or no anser then ask for an explanation.
So, someone give a straight yes or no answer to the question!
A plane is at point X on the runway. The runway begins to move left. The plane begins to move right at exactly the same speed as the runway. Therefore the plane is stationary at point X all the time.
Can someone therefore explain how a plane is supposed to lift off the ground if it isn't moving?
No.
unles sthe air speed generate by the engine/props alone become enough to generate sufficient lift.
But i still say no.
25 Oct 06
Originally posted by KingsBishop"unless the air speed generate by the engine/props alone become enough to generate sufficient lift."
you ask for a straight yes or no anser then ask for an explanation.
No.
unles sthe air speed generate by the engine/props alone become enough to generate sufficient lift.
But i still say no.
So you say the answer is No unless it is Yes? Good thinking there.
PS. The answer is Yes.
25 Oct 06
Originally posted by uzlessThe point is that the plane moves at whatever speed relative to the air, not the ground, because it generates its force against the air. Therefore, it's not stationary relative to the ground.
A plane is at point X on the runway. The runway begins to move left. The plane begins to move right at exactly the same speed as the runway. Therefore the plane is stationary at point X all the time.
Can someone therefore explain how a plane is supposed to lift off the ground if it isn't moving?
If planes were driven through their wheels as cars are, it would be stationary relative to the ground and not take off but that's not how planes are powered.
25 Oct 06
Originally posted by uzlessNo, it'll still take off.
So what I'm gathering here is that the plane will take off it's a propellor plane, but won't take off if it's a jet plane.
All planes move forward as a reaction to the force they apply backwards to the air. This can be done by a propeller or a jet engine.
The analogy of a person running on a treadmill is completely misleading. People move forward by applying a force to the ground, so the movement of the ground matters. Planes don't, so the movement of the ground doesn't matter.
25 Oct 06
The plane is held on the ground by gravity.
Lift will overcome the force of gravity and allow the plane to fly.
Lift is created by relative motion between the wing surface and air.
In the treadmill example there is no relative motion between the wing and the air, so there is no lift.
Without lift, gravity wins.
26 Oct 06
1 edit
Originally posted by mtthwWrong. Jet propulsed artifacts don't need air (atnosphere) surrounding them. They expell the burned combustible thru proper designed nozzles at supersonic speeds. Ideally, the pressure at the exhaust should equal the atmospheric pressure at the high of flying for maximum performance.
All planes move forward as a reaction to the force they apply backwards to the air. This can be done by a propeller or a jet engine.
Why? Simple. The reason is that the nozzle exit should provide the optimum thrust, so the force vectors calculated over the stream lines on the exit portion of the nozzle shoud be parallel (they can converge or diverge, and so the nozzle is called over- or under- "expanded" ).
As long as the exit area of a nozzle can't be easily modified in real time to make it adapted to the exterior atmospheric conditions, when designing the divergent portion of a nozzle one has to make the previtions about at what altitude (and atmospheric pressre) it must deliver more thrust.
Anyway, jet engines are built on the simple base of Newton Law on action/reaction.
- J
26 Oct 06
Originally posted by CrazyLilTingThere are different types of jet engine, but the ones used on planes all take air in at the front, compress it, mix it with fuel and ignite it to create the exhaust gas. If they didn't take in air they would be closed off at the front.
Wrong. Jet propulsed artifacts don't need air (atnosphere) surrounding them. They expell the burned combustible thru proper designed nozzles at supersonic speeds. Ideally, the pressure at the exhaust should equal the atmospheric pressure at the high of flying for maximum performance.
Why? Simple. The reason is that the nozzle exit should provide the op ...[text shortened]... st.
Anyway, jet engines are built on the simple base of Newton Law on action/reaction.
- J
Rockets don't need air as they carry their own propellant.
But yes, they work on Newton's Third Law. As does pretty much any method of moving.