----- Original Message -----
From: "Marvin Kaye" <marv@lancaironline.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, October 30, 2002 7:32 AM
Subject: [FlyRotary] Re: sanity check - tension bolt issue


> Posted for Mr dan ruggirello <dan_ruggirello@yahoo.com>:
>
> I posted earlier (@ flyrotary) that I was skeptical
> that the tension bolt issue was vibration since my gut
> feel was the bolt was much stiffer than 110hz (6500
> rpm).  Well, I just estimated the 1st mode natural
> frequency and low and behold, I calculated a frequency
> of 150hz.  Too close for comfort!!!
>
> Dan

Don't forget that resonant components can respond to harmonics as well.  My
cruise rpm is in the range of 4500 to 5200 rpm.  This equates to a frequency
range of 75 - 86Hz.  The second harmonic would be 150 - 173 Hz.  This isn't
close, it's dead on!

Having said that, I am fairly confident that damping the bolt near the
center will eliminate the problem.  Tune in again in a few years when I
again hit the hour mark where my tension bolt failed.

Interestingly, my old engine had the early bolts which had a shank necked
down to a smaller diameter than the threads.  These bolts had almost twice
as many hours (not even counting the hours in the car) as the brand new full
diameter shank bolts in my current engine.  The old engine never had a bolt
failure in 856 hours of flight.

Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com