----- Original Message -----
From: Paul <rotaryeng@earthlink.net>
Sent: Tuesday, April 25, 2000 6:55 PM
Subject: Cyclic loads - Noise

Bulent Aliev wrote:

I already had it in my plans to do the same modification if I could.  It

is so

simple in theory, I can not believe it Burt did not do it. Moving the

prop hub

couple inches higher or lower will prevent the prop blades entering the

wing wake

along the full length of the blade at the same time.
In a two blade prop is even worse. Both blades unload and load

simultaneously.

Bulent

An interesting footnote.  Most of the stress and noise mentioned

here is

related to *radial* wakes.  If the wake is along a radial of the

prop shaft

then the affects are awful.  Simply moving the wake a few inches

(the more

the better) off radial will make the wake *sweep* across the prop

blade

instead of impacting it all at once.  The difference is remarkable.

At

Moller moving a strut once resulted in a 20 dB noise reduction.

This

means you too Perry, stay away from radial struts.  Also, look at

the

Aerospatial (sp?) helicopters sometime with the buried tail rotor.

The

struts are in the form of an H.  Most other buried rotors use

similar methods.

Jeff Spitzer

Wow. That IS interesting. So those Rutan designs have the thrust line
at wing level. Moving the engine up a few inches will make it
quieter. That will give more room under the engine for the rad too.

Paul Lamar

Richard Sohn wrote:

Pitch mechanism failure on a  CSP has occured on tractor AC too. One of the
first CSP from Hoffmann had the pin come loose in the early sixties. The AC
was a KL 207, all wood four place low wing, crashed on approach. The test
pilot of the AC manufacturer was severly injured.
This aerea(pitch pin) should receive special attention when designing a new
prop.
Richard.

Ours is pressed into the steel hub and it is locked in place
by the other hub. Even if it comes loose it cannot come out of 
its hole. The pitch change will still work. Perhaps the blade
will be a bit loose but it can be preflighted by feel.

Paul Lamar

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