Date: Mon, 01 Feb 1999 13:27:27 -0800
From: Paul <rotaryeng@earthlink.net>
To: z <rotaryeng@earthlink.net>
Subject: Strange low frequency vibration.

Kruiswyk, Neil wrote:

Paul,

        I've heard the low vibration first hand flying with Jim.  If I
had to guess, I'd say it was the difference between the engine RPM and
the prop RPM*2...  eg.  5000RPM/2.17 = 2304.  2304*2=4608.
5000-4608=392.  392/60 (for Hz) = 6.5Hz.  This is about the frequancy 

we

hear/feel as a whoa, whoa, whoa sound.  It is VERY pronounced.

        Jim flew over the weekend with my prop (3 blade IVO) and no
vibrations.  I've flown with both 2 blade wood and IVO and have never
heard the low vibrations in my plane, ever.

        It's a strange one...

Neil

What does the muffler look like Neil? Record it on one of
those small casettes and send it to me. I'll put it on
the scope and check the frequency.

Paul Lamar
 
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