I agree Mark. I don't think that the rotor would be doing its job
properly if it went supersonic at any part. The aerodynamics would not
suit the subsonic shape of the blade.
However, I believe that the rigidity of the rotor is to blame for the
distinctive beat - this is according to a Hind pilot from the Czech
Republic who once worked for me. Also there are only 2 blades so each
blade is doing more work and is accordingly wider.
What a mailing list eh?
OM content, Gary E took a cool photo of one on a real desert island ...
;-)
Chris
On Saturday, Jun 7, 2003, at 13:59 Europe/London, Mark Marr-Lyon wrote:
I don't know for sure, but I'd guess that helicopter rotors aren't
supersonic, especially in the days of the Huey. Guestimating the
Huey's rotor diameter at, say, 15 meters, the rotor tips travel about
50 meters for 1 revolution. To go supersonic (more than 330 m/s,
ignoring any velocity of the aircraft itself), the rotor would have to
spin 7 times or more in one second, which sounds a lot faster than it
actually does spin (2-3 rev/s, maybe?).
I think the distinctive whop-whop-whop of the Huey is from main-tail
rotor interaction. The main rotor produces tip vortices, just like
those you can occasionally see on a fixed-wing aircraft when
conditions are right. When the tail rotor slices through a vortex, it
makes a whop.
Newer helicopters are much quieter in this regard, so now you hear
mostly engine noise and tail rotor noise.
Mark
<|_:-)_|>
C M I Barker
Cambridgeshire, Great Britain.
+44 (0)7092 251126
ftog at threeshoes.co.uk
http://www.threeshoes.co.uk
http://homepage.mac.com/zuiko
... a nascent photo library.
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