Unmanned_air_vehicles site rankings:

fluid dynamics (5)
lighter than air (5)
racing cars (10)
cfd (13)
parachutes (15)
propulsion (18)
rotorcraft (18)
uav (20)
wind turbines (22)
aerodynamics (33)
windmills (39)
propellers (57)
aeronautics (75)

subsonic (2)
bml (2)
low speed (3)