Technically, aerodynamic principles govern the conversion of temperature and pressure in the combustion chamber into exhaust velocity as the propellant travels through the nozzle.

Actually, helicopter rotors are typically symmetric, meaning they produce zero lift/thrust at zero angle of attack. The amount of lift/thrust they get is directly dependent on the pitch of the rotor blades, and the "profile" or camber of the blades is only to prevent flow separation on the suction side of the blade at higher angles of attack.

You mention the "tilting of the rotor", which I suspect is a serious misunderstanding of how a helicopter works. Helicopter rotor blades pitch up and down to produce more or less lift/thrust, but the rotor disk itself does not move in relation to the attitude of the helicopter The disk is fixed. If the helicopter wants to move forward, the entire craft, rotor disk, fuselage and all must pitch forward to change the direction of thrust.

It pitches the swashplate such that the rotor blades currently at the front of the disk have a low or negative angle of attack, while those at the back have a high angle of attack. This shifts the center of lift/thrust rearward with respect to the center of mass, causing the helicopter to pitch forward. Now that the whole craft, including the rotor disk, is pitched forward, the lift/thrust vector tilts rearward, and the rotor now produces forward thrust.

Just how does a propeller work, if not aerodynamically?

ALL rotorcraft fly by thrust only, and that thrust is produced by aerodynamic surfaces, following aerodynamic principles.

The average system efficiency may be that low, when you account for transmission losses and off-design operation.

Yes. The point was this "fantastic maneuverability" of quadrotors as seen on youtube videos is nothing special. It's merely a function of the squared-cubed law allowing for very high thrust to weight ratios, and traditional helicopter designs offer a no less impressive display.

Eh, what? The aerodynamic principles governing subsonic flight have been known for a century and a half, and they're the same regardless of whether you have fixed or rotating wings, and fixed or variable pitch.

People have been developing drone helicopters since the 90s, and they have seen active military use for several years.

That's because any asshat with $300 can go buy an AR Drone and make a nuisance of themselves. As I've explained, fixed propellers, electric motors and batteries have lowered the barrier for entry to rotorcraft and opened it up to a much larger audience. Just because they're widely available does not mean they're efficient or performant.

Excluding transmission losses, modern automotive gasoline engines are typically in the low 30s.

Engines small enough for RC aircraft are typically 2-stroke, which significantly increases your power-to-weight ratio, but roughly halves your energy efficiency. They also typically run on alcohol and nitromethane blends, which have low energy density but high power outputs. Four stroke gasoline engines on the order of a couple cubic inches are used on large scale models, and some rough power and fuel consumption estimates from manufacturers puts them around 0.45-0.5 lb/hp*hr, which is on the high side of what you see in automotive engines.

Just how light do you think enough battery for an hour long flight is? Hint, it's going to weigh more than the IC engine and a comparable amount of fuel.

Those videos show the performance of an unloaded quadcopter. If you try to put any significant payload on one, you will see something very different. I suggest you watch some youtube videos about 3D aero helicopters.

In terms of thrust per unit power, larger disk area is always better than smaller. That's why turbofans use less fuel than turbojets. That's why props use less fuel than turbofans. That's why helicopters can lift so much weight, but propeller aircraft can very rarely accelerate vertically.

Electric motors typically operate at around 90% efficiency, while combustion engines are closer to 30%. On the other hand, that combustion engine will use fuel with an energy density some 40x better than the best batteries we have. If you expect to have any significant loiter or range, you're going to need a lot of energy storage, and that very quickly means your battery powered aircraft simply won't cut it. This is why we don't have battery powered aircraft.

Who cares? First, the whole purpose of drones is supposed to be that they're disposable. They're cheap enough to source and operate that you're not supposed to care too much if you lose one. Besides, in this application, carrying medical supplies, the payload is going to be valued at far far more than the aircraft itself.

Also, you're fooling yourself if you think a several kg object made of plastic and impacting at 30m/s is going to survive. This is real hardware, not your RC toy.

You're going to have to explain your logic on this one to me. On a quad copter, you vary the RPM of your independent motors to shift the center of thrust. On a traditional helicopter, you change the pitch of your swashplate to vary the angle of attack of your rotor and shift the center of thrust. The only difference I can see between the two different control systems is that the quad copter requires an additional matrix mixer on its outputs, and reacts more slowly since it has to fight inertia.

If you could simply delete it, because you weren't using it, your system was never vulnerable and in need of fixing anyway.

That's why head tracking demos that allow you to shift your head to get a slightly different viewpoint on screen are so effective.

Use it with a bunch of stationary devices? Two-way broadcast communication should only be used for mobile devices.