New answers tagged aerodynamics
The tip speed of a rotor blade has to remain subsonic, as you say. Also the forward speed of the aircraft subtracts from the speed of the backward-moving rotor, and adds to the speed of the forward-moving one. Most of the lift comes from the end of the rotor, because lift is proportional to airspeed squared. Each rotor can only carry so much weight, as a ...
Try the wondrous internet: https://archive.org/stream/nasa_techdoc_19670028324/19670028324_djvu.txt http://www.scribd.com/doc/39708901/Helicopters-Calculation-and-Design-Volume-I-Aerodynamics-September-1-1967-From-www-jgokey-com This next one is more about cross-sections. http://www.helistart.com/RotorBladeDesign.aspx
I doubt if anyone has come up with a complete explanation, but some laboratory simulations have created similar patterns. They happen if the central and surrounding areas in a flat, circular disk of fluid have different velocities. Emily Lakdawalla at The Planetary Society covers it at this site. She also explains how other patterns (triangles & ...
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