Has anyone ever tried using a Supertrap on the rotary? Was talking with a guy this last weekend at the local EAA chapter meeting. Said he used to race an RX-7 and swore that the Supertrap quietted the beast and held up under the pressure. I'm skeptical but have had good luck with Supertraps on motorcycles and various hot rods. Maybe a custom built "super Supertrap" with 321 stainless or even Inconel discs? Might be worth a try.

One thing is certain. My "muffler" isnt (a muffler that is). I need something better.

Mike Wills
RV-4 N144MW
----- Original Message ----- From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Saturday, June 07, 2008 2:48 PM
Subject: [FlyRotary] Re: Mistral Crash Analysis

Hey, Al, if it were not for rationalization mode, none of us would be flying "auto" engines {:>).

So, Al, why don't you post a sketch/drawing of your muffler design and give us some details - dimensions/materials etc.  You design may be the answer someone has been looking for.

Sounds like a good muffler design - I have two headers and two mufflers so should one plug up, I have one to come home on.

 When I was expermenting with mufflers, I tried a number of approaches with less than stirling success.  One of the problems is the very powerful shock wave of the exhaust pulse which I have had fatigue SS metal in a matter of a few minues.

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.

I was later told by an observer that my rotary sounded just like a turbine when I took off - (Yeah, Yeah I thought at the time - the poor mans turbine.)  But, later examination showed the dics had indeed been spinning and had burnished the inside of the tube where they spun.  Tracy was kind enough to use his arc welder to weld the discs to the rods (that lasted for about two weeks).

While the disc were stationary they did reduce the exhaust noise by 8 db and did not have any measureable effect on power - however, when they started windmilling - the max rpm I could get out of the engine was 6000 rpm. Fortunately more than enough - but far below my normal max of 6800 rpm.

By that the sixth experiment on mufflers, I sort of lost interest.  So went and got two HushpowerII mufflers and stuck them underneath.  So far they have survived the pounding of the turbo block without any ill effects (about 50 hours on them).

Good words to heed, as usual, Al.

Ed

C'mon guys. You do this every time there's a crash. Instantly go into rationalization mode. It's unhealthy. Greatly increases risk builders won't take action. Increases risk you won't research it thoroughly.

A healthy response would be:" Here's another example of how our engines produce unusually destructive exhaust temperature and pulses. We have a rich history of broken exhaust components. We need to be very thorough when designing and building exhaust."

I designed my own muffler. It had two inlets, two outlets. So if (when) my muffler failed, it could never block both pipes. I also put loose safety wire around my pipes, because on a pusher loosing pipe wipes out prop. So basically, I assume stuff will  fail, then design it to control the way it fails. I've heard of rotary guys doing same type of thing. This is a good time to share those key items.

On your car, they deliberately design products to fail a certain way. They will make a component weak, so it fails first. They do that with wheels and hubs. So when the muffler fails, little pieces come apart, not big sections?

You guys do a great job of sharing successes, design and construction details. This is another opportunity.

-al wick




<No doubt you are on the money, Rusty.  When folks are already predisposed to bad mouth the rotary - this will only be more ammunition. "See! even with umpteen million dollars you can't get one to fly"  {:>). But, I serious doubt it will effect many who have researched the rotary and come to understand its benefits - as for the rest, who cares {:>)

 I'm certain it was a relief to Mistral that the culprit was not one of their engine components.



 Whew! a close one for sure.



 Hi Ed,



 Unfortunately, I bet the majority of people will only hear "Mistral rotary", "lost power", and "crash"  :-(



 Rusty (RV-3 taking forever.)

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