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Erik,
It may be easier to "delete" things. I don't
think it is the engine. By just changing indicated airspeed you
are changing engine parameters only very very slightly. You are
changing prop blade angle. Possible source. And you are changing pressures
on the various parts of the airplane. Gear doors, cowl, etc.
Possible source. If it is indeed RPM sensitive, then the prop would be my first
pick assuming you have ruled out FM. (f***g magic). I will be at Palomar
tomorrow, hope to see you.
Craig Berland
Hi All:
Just
wondering if anyone has an idea on which way to go to start trouble shooting
this problem.
Here are the particulars:
I have a Legacy with
about 120 hrs on it. Performance Engines IO-550 / Hartzell Prop /
Mags.
It has been running exceptionally well, very smooth until just
yesterday when I first noticed a sort of nondescript rumble/vibration after a
long descent at relatively high speed, from 17,500'.
As we slowed to
enter the pattern for landing it cleared up and everything seemed normal.
I went out and flew today to see if it was just an anomaly......apparently it
was NOT.
* A download of all the engine parameters was normal......
nothing out of the ordinary.
* Engine run-up and full power run were
all normal/smooth.
* Takeoff and initial climb out were all normal with
no vibration UNTIL we accelerated through approximately 165kts.
* At
165kts and greater, on three successive flights, we felt a distinct
cyclical type vibration setting up. It's a bit hard to describe in
words but it does NOT seem to be a
steady
vibration (like a gear door) but seems to feel almost like a prop out of
balance.
* Without touching the power or prop we can make the vibration
go away by raising the nose and slowing < 165kts.
* When we do get
the vibration > 165kts..... you can mitigate it somewhat by increasing prop
RPM. The vibration is still there but not has bad.
* The prop is NOT
surging in any way, RPM's are rock steady and remain where they are
set.
* The issue is serious enough, in my mind, that I am DRIVING
tomorrow from San Diego to Las Vegas.......and I HATE driving;)))
So in
summary, it seems this vibration just happened somewhat spontaneously (ie. not
progressively worsened over time) and although were not ruling anything out, it
seems to be Engine/Prop/Speed related.
We would GREATLY appreciate any
ideas, comments, suggestions.... we are kind of at a loss as to which way to
head in troubleshooting/fixing this problem.
Best regards,
Erik
Larson
asw20747@aol.com
(619) 301-7475
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