I found something relevant to the exhaust noise and muffler problem.
I found an aircraft I've never seen before, a Lockhead YO-3 Quiet
Star which was used as an observation aircraft in Vietnam flying
unheard at just 200 ft. It used a slow turning prop and a very thin
fuselage as well as a very long muffler seen here. Would a muffler
running the length of the fuselage and enough exhaust pipe ahead of
it to allow EGT to cool along with a heat shield to keep unwanted
heat out of the cabin work?
Ken Cohagen
They made a rotary version of this.
Yes.
Looks a lot like our coax muffler :)
Paul Lamar
Hi!: I'd say that as stated by Mazda when presenting the 87
13B series, an important part of the exhaust noise is that the
way exhaust port opens leads to exhaust gases reaching
supersonic speeds; reducing noise from this origin was formerly
attempted by having three small exhaust ports instead of only
one, but bigger in size, and also, as pointed in SAE papers
841017 and 870446, besides that a multi-chamber exhaust port may
greatly reduce exhaust noise, the length of exhaust ducts, and
the back pressure in the exhaust port, have a lot of influence on
the engine's performance in relationship to the rpm, and also on
the BMEP, SFC, and other issues.
For the use most writers in
this site seem doing, powering aircraft, a short, low back
pressure duct would give best performance above 4000 rpm, adding
length to the exhaust duct may ease the last portions of tube
not being too hot, but no noticeable changes would probably
result in the temperature in the first part of exhaust duct. I
can't imagine an approach to exhaust duct having a safe
temperature besides cooling it, this can be accomplished by an
external duct around the hot exhaust tube, in the style of
Suzuki RE-5, but some kind of forced air blowing in the tubular
chamber around the hot inner tube would be needed, and this
would require power use. Liquid cooling of the first part of
exhaust duct sounds not practical. Thanks for your attention,
I'd like having your feedback about this.
Best regards.
Salut Jose Gros-Aymerich Madrid, Spain
The best 2 inch diameter pipe length for a 13B p-port is 32 inches.
Of course tuning is a function of pipe length AND diameter.
The larger the pipe the lower the exhaust gas speed.
Mazdatrix built an RX8 engine with 13B rotor housing yielding
three exhaust ports per rotor. It did sound different.
Paul Lamar
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