Thrust/Lift um, Perpetual energy?

[FakePilot]

Hi All!

I searched for "thrust lift energy" and didn't find a posting, so I ask:

Ok, this is killing me. For years and years I have always wondered, How can an airplane generating 100,000 lbs of thrust lift 700,000 lbs of weight?????? Approx 777, I think?

I understand if you have a rocket which weighs 5 lbs and produces 5 lbs of thrust it will hover. Ok fine.

The best way to illustrate the problem is as follows:

You have a car with a propeller on it, which is the sole method of propulsion. The wheels are just free spinning.

You have a wing on top connected to a generator. The wing lifts up, falls down, lifts up.

The generator drives the motor for the propeller.

Now, wouldn't it therefore be possible at the right speed to just keep cruising forever?

I understand that there's loss of efficienty because of the motor, generator and mechanical wing mechinism, but hey at like 5:1 lift/thrust ratio, that should cover it?

Thanks!

[Josh10524]

The engines are not the lifting force. The wings are. Were the engines vectored straight down, the force would not lift the aircraft off the ground. The thrust, facing rearward, accellerates the aircraft at an angle horizontal to the force of gravity, and when enough energy has been put into forward motion, the wings can harness this energy in the form of lift from air moving over them. It's not a perfect comparison, but think of them as gears, much as a car with a power to weight ratio with an excess of weight can move forward.

[parris50]

Yes, that's the key to it. The plane has to have a certain amount of kinetic energy to get airborne. In level filght, the engines only replace the energy lost through drag, and the generation of lift,

At zero thrust, the plane doesn't drop out the sky but it's speed generates enough lift to enable it to glide down.