Reddit reviews Principles of Helicopter Aerodynamics with CD Extra (Cambridge Aerospace)
We found 3 Reddit comments about Principles of Helicopter Aerodynamics with CD Extra (Cambridge Aerospace). Here are the top ones, ranked by their Reddit score.
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In terms of rotary aerodynamics, there is a factor called the Disk Loading (literally Thrust per unit Disk Area). It's not quite as easy to see from basic physics (which is why I like your explanation better), but it's usually the real non-starter for lots of VTOL aircraft whether you're talking ducted fans or open-blade rotorcraft.
It turns out that the efficiency of your thrust production runs inverse to the disk loading. So if you have a very high disk loading (a very small rotor for instance) then it takes a lot more shaft power to produce the same amount of thrust. When you have a turbine spinning the shaft you've got some wiggle-room. When it's a person with a much worse energy density it becomes perilously tight.
You're absolutely right -- everything you do is to make gains in efficiency. Every Watt of power you can take in from the pilot/engine and not waste is more thrust. And using a smaller rotor -- regardless of how fast you can spin in -- will always require more power. Ducting it can increase efficiency, but in this case I'm sure was not worth the additional weight.
It then becomes an issue of what the optimum rotor and structural weight is. You're looking for that global maximum power-to-weight ratio where increasing the rotor area might generate more thrust, but not enough to counter the additional weight.
If anyone's interested in the deeper theory, Principles of Helicopter Aerodynamics by Leishman is excellent and is my go-to reference.
I like Principles of Helicopter Aerodynamics by Leishman. Starts out very understandable, and then gets as complicated as you care to learn. Also includes a lot of history.
A good book on the basics of helicopters and how they work:
http://www.amazon.com/Principles-Helicopter-Flight-W-Wagtendonk/dp/1560276495
A good textbook directed at engineers studying helicopters:
http://www.amazon.com/Principles-Helicopter-Aerodynamics-Cambridge-Aerospace/dp/0521858607/ref=sr_1_1?ie=UTF8&qid=1372342685&sr=8-1&keywords=leishman