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From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-2958141@logan.com>
Subject: Re: [FlyRotary] Re: Mistral Crash Analysis
Date: Sat, 7 Jun 2008 22:12:09 -0400
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Ernest,  There is no question that using jam nuts to try to restrain the 
"turbine discs" was woefully inadequate - even welding on that small arm 
just prolonged the event as you correctly pointed out.  I still think with 
some work that approach might have ended up with a good working muffler.  I 
think the theory was proven sound - but the fabrication was certainly 
inadequate to the task.

Rosette welds on the outer perimeters would undoubtedly have been much more 
effective.  However, not being a welder (and not going to risk my one good 
eye ball, I am never going to become a welder {:>)) - also should mention 
retired and too cheap to hire one - I decided to abandon the project in 
order to take a whack at some of  other To-Do projects.

Finally finished the software for my AOA (it took me several weeks to 
discover a long vexing problem that turned out to be an unnoticed, not 
readily apparent(is that redundant?) and certainly unintended loop within an 
loop which was throwing off the wave-form timing and therefore shape that I 
used to measure pressure from the pressure transducer used for the AOA.

 So with that problem now solved, I am proceeding on  my single axis 
autopilot using some of the latest (and reasonably priced) MEMS gyros and 
accelerometers- got the board designed, now "just" have to write the 
software {:>).

There is just too many projects and not enough time (even when you are 
retired - or perhaps especially when you are retired {:>).

Ed

> Ed Anderson wrote:
>> The rotary is also pretty sensitive to back-pressure, so what kills the 
>> noise generally does the same to the power.  There was one design I tired 
>> that used 3" dia SS disc in a tube with "Paddles" bent on the outer 
>> permimeter.  The ideal was that the shock wave would see solid metal and 
>> be reflected - but the exhaust gas would cruve and flow around the paddle 
>> blades.
>>
>> It worked (while it worked) , I flew from NC to Florida and it measurably 
>> reduce the exhaust note (by something like 8 db), the problem was the 
>> discs and  the jam nuts I had holding them on a 3/8" dia SS rod (I don't 
>> weld) I had through their center.  At  some point, some of them (I had 5 
>> discs in each tube) worked loose under the pounding .  They then began to 
>> act like a windmilling propeller (yes, they were spinning at high speed). 
>> The effect was to expotentially increase the drag on the exhaust gas and 
>> imped gas flow.
>>
>> Tracy was kind enough to use his arc welder to weld the discs to the rods 
>> (that lasted for about two weeks).
> I think you gave up to early on that one Ed, but I can see how you felt 
> like you did your part with so many others under your belt.  The way I'm 
> seeing it, the 3/8" torque arm was just way to small for the 3" disks 
> torque arm.  What you needed was some rosette welds on the perimeter of 
> the discs to tack them to the will of the tube.
>
> Make the discs last, and we can feed the exhaust through that Swiss 
> muffler that Neil is talking about.
>
> --
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