🚀 go-pugleaf

maddog@kuhub.cc.ukans.edu writes:
>One last shot on the "silent helo" thing.  Now, this was a few years back, and
>I have NO idea if anything became of it, but there was one additional theory.
>There for a while, they were toying with the idea of using accoustic drivers
>to offset the "hellacious" noise helos produce.  By utilizing the "wave 
>addition" principles, they were hoping to eliminate noise. . .or at least
>bring it to a minimum.
>
>They were going to have sensing mics in various places beneath the blades,
>sample the noise and create an "opposite" or inverted signal at the same
>amplitude.  Theoretically, anyway, it would significantly reduce the noise.
>(It can't eliminate it since the sources do not have the same point of
>origin.  But, it's a helluva lot better than nothing!)  :-)
>
>Sooooooo, anybody heard about this?  Or am I spewing hot air, as usual?

There's a project here at Purdue that would do active noise cancellation
of helicopter sound.  However, the system is a fixed set of speakers at
the airfield and not on the helicopter.  It has something to do with
appeasing the people who move into homes near an airport........

Rob U
--
-       Rob Unglenieks             REAL race cars DON'T wear BOWTIES       -
-  "It is the foreign element that commits our crimes.   There is no       -
-   native criminal class except Congress."  [Samuel Langhorne Clemens]    -
-  (Don't look at me, I DIDN'T vote for Clinton.  Will Engineer For Food)  -

Yes, some people (like myself) are working on an active noise control system
for many things, one of which is a helicopter.  Your summary of how it works
is pretty accurate.

Andy Entrekin
GTRI-CC/AERO (Aeroacoustics)
Aero Eng Student, Ga Tech