|
|
Lynn,
Thanks for the muffler history lesson. I have six and 1/2 hours
flight time and I'm on my second muffler already. So far, my second
homemade "spin tech" seems to be holding its own, although I have had
to weld up some cracks and beef up where it bolts to the outer shell.
I've been told that it isn't loud (from the ground), but it does seem
pretty loud in the cabin. I find myself yelling into the mic when
talking on the radio. To my knowledge, there haven't been any
complaints from the local citizens, only that it sounds like a chain
saw. I can live with that.
Realistically, I would like it to be quieter. For those that heard
Dennis' RV-7A, that should be the target for us to shoot for. Of
course, it is a Renesis, so he has an advantage before he even starts.
My 20B has the turbo exhaust ports, so it is especially difficult to
muffle. If I had it to do over, I probably would have left the stock
exhaust inserts in the housings.
I would like to try the Flowmaster muffler, but that would require
that I build a new exhaust system. Something I really don't look
forward to doing, but I guess it is inevitable. But for now I will
use what I have, and keep an eye out for cracks.
Mark S.
On Nov 9, 2007 8:22 AM, <Lehanover@aol.com> wrote:
>
>
>
> In a message dated 11/9/2007 7:30:44 A.M. Eastern Standard Time,
> msteitle@gmail.com writes:
> ...but it looks so cool!!!
>
>
> Interesting muffling stories.
>
> Muffling the Mazda race engine.
>
> My first attempt was on a rear engined car. Why not a simple formed glass
> pack that had worked so well on piston engined car? Lasts about 10 miles at
> speed. No glass left in muffler. Sound level back above 105 Db.
>
> The limit at 50 feet. Turned the curved tip tube, down at the track, had the
> driver lift going past the sound equipment. No problems until the last lap.
> The remaining shell melted into two pieces.
> The rear engined car has a short system similar to the aircraft.
>
> Built a muffler from .062 truck exhaust pipe, packed with Lava rock. Its
> heavy but really kills off the sound.
> Got through the next weekend with a warning after the race. Got two hits
> from sound on the last two laps.
>
> No Lava rock in the muffler. Center tube melted at the inlet end.
>
> Rebuilt the muffler with a piece of a house jack as the center tube. Very
> heavy. Replaced the Lava rock with kitchen scouring pads (the real fine
> stuff). Got through the weekend but no pads left in the muffler.
>
> Went back to $8.00 glass packs. Two per weekend. Drop them into the dumpster
> on the way home.
>
> For the front engined car, (full length of the car system) i used a
> Flowmaster (looks like a big suit case) muffler. Very good sound control.
> Went to Sebring. During the race the muffler swelled up like a giant pillow.
> All of the many baffles were at the rear bulkhead blocking much of the flow.
> During the week, I rebuilt the muffler. Cut off the top. Welded in the
> baffles, and installed through pins of 1/2" diameter behind each baffle.
> The already heavy muffler was then really heavy. I moved the rebuilt muffler
> to the rear of the car, behind the axle housing. I built another house jack
> muffler, this time about 40" long. Installed that right at the collector.
>
> Got through the weekend at West Palm Beach. Center tube of the front muffler
> melted in two again.
>
> The current muffler is huge (4" ID center tube) Very heavy, stainless all
> around. Filled with course stainless swarf. The headers are .140" mild
> steel, with a blast tube providing ambient air to the tubes. The engine is
> tuned to maintain EGTs below 1600 degrees. Same exhaust parts for 8 years.
> No problems.
>
> Mild steel is not very strong at 1600-1800 degrees. The supersonic shock
> waves slow to subsonic in the muffler and the pressure spikes inside the
> muffler, will beat it to pieces.
>
> Round mufflers last way longer than flat mufflers.
>
> Mild steel muffler disintegrate with out regard to shape.
>
> Round and stainless works best for life length, but not sound control. Mine
> is just below the new 103 Db limit.
>
> Flat mufflers work best for sound control, but have short lives. The Spin
> Tech looked like a winner with the many fins connecting the top and bottom.
> I would go in that direction even if I have to build a bit of streamling
> onto it.
>
> If it is going to last a long time, it will probably be a bit heavy. Because
> there is no free lunch.
>
> Best sound control was the Flowmaster, with a "V" shaped baffle that splits
> the incoming shock wave into two parts and then aims the two halves directly
> at each other, so as to kill off much of the sound energy while adding
> little resistance to flow.
>
> If it isn't stainless, don't bother. Save your money.
>
> The picture is the Guppy Mazda powered rear engine.
>
> Lynn E. Hanover
>
>
>
>
> ________________________________
> See what's new at AOL.com and Make AOL Your Homepage.
> --
> Homepage: http://www.flyrotary.com/
> Archive and UnSub:
> http://mail.lancaironline.net:81/lists/flyrotary/List.html
>
>
|
|