Hi Paul-

Apparently a rotary in full song is not very subtle.  We were running
today to continue the tuning exercise & attracted visitors from all over
the airport.   A friend of ours heard the engine from inside his hangar
1/2 a mile away and knew we must be up and running again.  We dropped
the fuel pressure to 38psi, and reduced the injected amount of fuel by
some amount (Tracy neglected to count the number of steps).  We had the
engine running beautifully smoothly at ~4000rpm for 5 - 10 minutes or
so.  We had to knock it off when oil temp went over 205F.  Happily water
temp came up to around 190F and stayed there.  Mixture map is all over
the place, so any other rpm required leaning or enriching to run
smoothly.  I'm still not happy with the throttle behavior - it remains
much touchier than I like, but we'll see how it does once we start
getting the map values more consistent.  I'd like to talk directly to
Mike Wills -- tuning is clearly going to take a while & any tips he
might have would be welcome.  We would have tried running the
auto-mapping function, but the oil hadn't cooled enough from the earlier
run & was back up at 205 after a few minutes at 4500.

One strange behavior -- when we shut down, we seem to always have a
single 'backfire' around 1 second after everything stops moving.  I'm
guessing we're super rich at the bottom end or something.

Mark (Rocky Mtn High)

You can quiet it a bit with something like this. If it melts
it is not likely to plug up the exhaust and cause a loss of power.
Use about .090 or .125 thick 321 SS. 5 minutes at 4000 RPM oil
temp 205 is not that bad. What kind of manifold pressure are you
seeing at 4000 RPM?

Paul Lamar

Hi Mark,

looking at your exhaust, in my humble opinion, the exit from your muffler or
expander, is way too big in cross section. For noise reduction, this exit
should not be bigger but smaller then one exhaust pipe from the engine. I do
not know how much smaller in your particular case.
On my single rotor, also PP port, the inlet into the expansion chamber is 1
1/2" and the outlet is 1 1/8". I can stand next to the running engine all
day long without a problem. Under certain condition, the prop noise beats
the engine noise. My muffler is totally empty.
A couple of years ago we did a test at Tracy's test stand with a resonator
chamber on one of his 13B engines. The resonator did not do very much, but
when we put a 1 1/4 ID piece of pipe to the outlet, the subjective judgement
of about 30 poeple was "wao it is quiet". The RPM loss with this ad-hoc
meassure was 200 at 6000 RPM.
I know it is not very scientific, however, even in cars, the larger tail
pipe makes a vehicle louder.
FWIW.

Richard Sohn
N2071U