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Date: Sun, 08 Jan 2006 22:45:34 -0500
From: Ernest Christley <echristley@nc.rr.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] More single rotor running
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Russell Duffy wrote:

>
> If you start at 2200 rpm, and slowly increase the throttle, all is 
> well until about 2500 rpm, then a high frequency vibration starts. The 
> vibration increases in frequency, and amplitude as the rpm increases, 
> right up to 3100 rpm. At 3100, as you increase throttle, initially 
> nothing happens, but then the engine will suddenly jump to 3300-3400 
> rpm, and be smooth. It’s just like someone flipped a switch to get rid 
> of the vibration. This vibration is pretty severe, and you can see 
> things like the air filter shaking until they’re just a blur.
>

I was reading about harmonic virbrations during the development of the 
BD-5 on a website somewhere that described this exact same problem. They 
determined that the resonance would absorb all the energy that the 
engine could put out (until things broke!), and not allow the engine to 
accelerate. Every now and then, they engine would be able to break out 
of the resonance and then would run fine at other RPMs. Well, at least 
you know for sure where your resonant frequency is.

-- 
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."