----- Original Message -----

From: Tracy Crook

To: Rotary motors in aircraft

Sent: Tuesday, September 08, 2009 7:48 PM

Subject: [FlyRotary] Re: Muffling

The Spintech was flown for about 200 hours with no problem.  Guts stayed intact and it was slightly more effective than the Hushpower II was when new (before the packing departs).  But it was heavy (can't remember the number) and the boxy profile cost me about 4 mph in cruise.  If the Hushpower gets fried on the -8 (likely) I will give the Spintech a try again.
BTW, I'm going to try a 1.75" reducer on my -4 (and maybe the -8 too).  The test results we did on the test stand with a 1" reducer were amazing.  VERY quiet and the engine only dropped 200 rpm at static WOT.

BTW, the 20B with turbo 13B rotor housings running through the Hushpower II is not as loud as the Renesis with the same (but probably internally damaged) muffler.  I haven't had the guts blow out yet on the -8 but it is likely to happen when I get into the high power settings.

Tracy

On Tue, Sep 8, 2009 at 10:01 PM, Mike Wills <rv-4mike@cox.net> wrote:

For Tracy,

 

 Can you refresh my memory on what happened with the Spintech experiment? I seem to recall some issues with weight and drag? But I wasnt subscribed to the list when you replaced it so I'm not sure what happened.

 

 At this point I think I'd be willing to accept both penalties to get an acceptible muffler. But I dont want to buy another muffler that doesnt work any better than the one I made.

 

 Spintech wants $375 for a custom muffler made from 321 SS. The same muffler in aluminized mild steel is $116. I'm tempted to buy the cheapie and try it out before committing the $375.

 

Mike Wills

RV-4 N144MW 

----- Original Message -----

From: Lynn Hanover

To: Rotary motors in aircraft

Sent: Tuesday, September 08, 2009 5:39 AM

Subject: [FlyRotary] Muffling

The fish tail muffler has been in service for years on motorcycles and other machines.

 

Its poor service life behind a rotary is due to the shock wave dropping to subsonic by applying its energy to the flat sides of the design. It is both a rflective and an impinging design.

 

If saw cuts are made into the long axis of the fish tail shape and bits of metal are welded in place to prevent the flexing (and fatigue death) of the pieces, this design might be found quite effective.

 

Years ago I tried one of the big Suitcase Flowmaster mufflers on the racer. A reflective design and very effective. In one session of 45 minutes, all of the baffles were hammered loose and piled up at the exit pipe and the sides of the muffler swelled up like a giant pillow. The reflective design was changed to an impinging design. I was far from home at Sebring Florida so I cut open the Flowmaster and flatened the sides. I welded the baffles back in place with more than a spot weld here and there. I drilled through both sides behind each baffle and installed solid 1/4" rods to keep the flat sides from spreading open again.

 

I moved it to the very rear of the body where the heat load would be reduced.

 

That muffler lasted the rest of the season. It was sinfully heavy and really too big for anything but a big GM car, but it worked great on the rotary.

 

The Spintech or similar I think will fill the bill. More likely a combination of two styles, or one style behind another. Any system that does not include equal length headers leave a bunch of HP on the table.

 

Lynn E. Hanover