Human-powered helicopter

[JaXanim]

Winged aircraft ie. all aeroplanes, gliders as well as the Gossamer Albatross (GA) get lift from the passage of air over their aerofoiled surfaces.  This is achieved using a propellor or a jet engine to create forward motion through the atmosphere. A reltively slow airspeed can produce quite substantial lift, as evidenced by the peddling man powering GA's large but very light propellor. Helicopters on the other hand get lift from an equal and opposite reaction to downthrust.

Downthrust is created by the rotors (which have a small aerofoil section themselves) compressing air downwards into a relatively small column below the craft. In effect, the rotors press down and the craft rises. I suppose a small amount of lift is generated via the aerofoiled blades but nowhere near that of a formal wing.

As has been said, no man has enough energy to generate a downthrust equal to the combined weight of the craft and himself. No amount of gearing or body weight reduction will change that. Interesting thing is a bumble bee can do it with ease even though the principles of aerodynamics say it shouldn't.

Cheers,

JaX

[JaXanim]

@blobrana

Not sure I understand your point.

Anyway, horizontal flight embraces three major forces:

Mass (gravity) which is down.
Lift (via the aerofoil or reaction to a down thruster) which is up.
Drag (air friction) which is backwards in the case of 'forward' motion through the air.

Provided lift exceeds mass, the craft will hover.
Provided the motive force exceeds the drag, the craft will move horizontally, ie: it will fly.

Aeroplanes get lift from the differential pressure above (low) and below the relatively vast wing aerofoil area. A very slow forward motion through the air will create a lot of lift if the aerofoil is pronounced (as in GA and typical gliders). A man has enough energy to achieve this lift if the total mass is low enough (as in GA). The craft also has to be designed with sufficient streamlining to allow drag to be minimised. Even so, GA flies very slowly, perhaps 10mph.

In the case of hovering, which only helicopters and vectored thrust planes can achieve, there is no drag because there's no motion. All the power of the engine is directed in opposition to the mass. In other words, the downthrust must equal the mass of the craft. The air is simply used as the down thrusting medium in the helicopter. In the Harrier, it's the high pressure exhaust stream.

So, no man has the energy to counterbalance the mass and can never power a hover. He can, however, power just sufficient forward motion, by overcoming the drag, and thereby get a hand from Mother Nature's lift as the air passes over the aerofoil.

As a matter of interest, the tips of a helicoper's rotor break the sound barrier. So yes, the stresses are immense.

Cheers,

JaX

[JaXanim]

@blobrana

I see your argument, but it's a fallacy.

When you propose GA flying in a circle, I guess you mean to simulate a 'copter. The ultimate analogy is GA rotating about its centre.

If GA's wings were given 'opposite' pitch akin to helicopter blades and it was made to rotate about the wings' centre point and with a relative wind speed of say 10mph, it wouldn't hover. Hovering requires downthrust, and there is none in the case of aeroplanes. The wings create lift. The equal and opposite force (as required by Newton's first law) is the mass of the craft.

You could think of the 'copter rotor as an air pump, sucking in air from above and compressing it by altering the pitch of the blades. It's not their aerofoil section which creates lift, it's the downward jetstream against which the rotors react and thereby lift the mass.

When planes turn in too tight a circle they become unstable because the relative airspeed across the wings goes down. The airspeed becomes a vector determined by the angle of turn. At a hypothetical 90 degree turn, airpseed is zero and the plane will fall out of the sky. You've probably seen videos of US and Russian fighters getting into such predicaments.

[EDIT: Flying a plane in circles requires more and more power as the radius decreases. In the GA case, I doubt if it could be made to turn in anything but very big circles, maybe a mile across. The peddling man wouldn't have enough extra energy to do otherwise and remain aloft.]

Now it just might be possible to power a helicopter on dung, but never by a man.

Cheers,

JaX

[JaXanim]

@Vincent

Yep. Remember Mad Max's mate with the autogyro? That was powered by methane derived from fermented pigshit wasn't it? I'm sure it was something like that.

JaX