Steve,
Thanks for the offer. Actually I think it
would be great if you could conduct a test. I had thought about a block off
plate that could be pulled into place with a long wire. This would allow a
high power test run with a sudden blockage. It’s the only way I can come
up with to create a not so dramatic reinactment. Your test stand would be a
better platform then the airplane. The engine was popping and shaking when the
failure occurred. As best I can remember my wideband O2 was off the scale lean
but I’m not certain. Speaking of wideband O2’s. My wideband has always
jumping around a few 10ths or more. My EM3 get’s a narrowband output from
the wideband. The EM3’s mixture bar appears stable. Could the wideband be
seeing a injector bounce associated with the injector delay? As an example when
leaned for cruise, say 13.2 it’s often switching rapidally between 13.1
and 13.3. At this point the engine seems reasonable smooth. The larger the
bounce the less smooth the engine becomes. Have you done any of your testing
with a wideband?
Bobby
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Steven W. Boese
Sent: Sunday, March 20, 2011 4:44
PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Forced
Landing.
Bobby,
You are to be commended for getting down
safely and for proceeding with caution afterward.
I did some exhaust back pressure tests
with my engine stand which is a NA 13B. Increasing the exhaust back
pressure was accomplished by partially blocking the outlet. An increase
in back pressure from 23” to 34” of Hg resulted in about a 20%
decrease in HP. The thing that was interesting is how small the outlet
was when the HP decreased by that 20%. I didn’t measure it, but it
was less than one square inch. I would expect that blocking off more of
that small remaining area would have had a dramatic effect. I can test
the effect of more completely blocking off the outlet with the engine stand if
it would be of interest to you. It will take something more substantial
than a banana to do the job, though ;>)
During an extended below zero cold spell
here, I had a friend who had his muffler completely fill with ice because of
driving to work and back just a short distance. After the muffler was
completely blocked, the engine would start, run for a second or two, and the
die. He had the car towed to the dealership and warming it up in the
heated repair shop fixed the problem.
Steve
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Bobby J. Hughes
Sent: Sunday, March 20, 2011 5:03
PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Forced
Landing.
It’s supercharged. My EGT’s
never get over 1540F. Most of the time they run in the 1400’s. I am also
not 100% convinced the muffler was to blame. But it seems to fit the symptoms.
I can’t confirm the muffler was blocked after landing while trying to
taxi. One theory is the exhaust pressure was enough to keep all the little
pieces in place until after shutdown. Then towing the plane shook everything
loose. Wonder if I could talk Mark S. into sticking a banana in the tail pipe
on a full power ground run to duplicate the problem? This is my second HP-2
muffler in about 100 hours of engine time. It may have 25 hours of flight time.
The first one was inside the cowl and angled down and back. It lost all the
mesh and cone material. The angle may have helped some of the loose material
exit the muffler. But it’s all speculation.
Bobby