A little engine trouble

On Sun, 13 Jun 2004 00:04:25 -0700, "Peter Duniho"
wrote in Message-Id:
:

Well, we'd only climbed a few hundred feet when something in the airplane
started making a very strange noise. My friend's wife heard it too. It was
sort of a rapid "growling" sound, lasting a second or two at a time, with
maybe five or ten seconds between. It seemed most likely to be coming from
the engine, but it was subtle enough I couldn't rule out some sort of
airframe flutter.

From the description of the noise, it would be consistent with some
sort of vibratory resonance. Having actually experienced it, can you
rule that out?

It might have been my imagination, but it seemed like
whenever I heard the sound, there was a little deceleration from the
airplane.

As another has suggested, the tach/MP gage should help in diagnosing
any loss of power associated with the noise.


--

Irrational beliefs ultimately lead to irrational acts.
-- Larry Dighera,

"Larry Dighera" wrote in message
...
[...]
From the description of the noise, it would be consistent with some
sort of vibratory resonance. Having actually experienced it, can you
rule that out?

Probably. Resonance can happen in a variety of ways, and can sound and feel
like a wide range of things. But my experience has been that when resonance
happens, it amplifies an existing frequency, rather than introducing a new
one. I think resonance with something is unlikely in this case.

I did forget to mention that in addition to hearing the noise, I could feel
the "rumble" in my seat. It wasn't just a noise; there was a definite
(though equally subtle) vibratory component.

As another has suggested, the tach/MP gage should help in diagnosing
any loss of power associated with the noise.

Yup, hindsight is 20/20. Given the conflicting priorities (diagnose or
maintain control? ), I'm seeing a new reason for one of those fancy
engine monitors that I never thought of. They are always touted as being
useful for diagnosing hard-to-diagnose engine problems, but I never really
thought about the problem of watching engine gauges and dealing with
potential emergencies at the same time.

Pete

I once had a mysterious noise like that which turned out to be a nylon strap
from a bag which had gotten shut in the door and was hanging out of the
plane a few inches and vibrating in the airflow. I had no idea what it was
until someone who had seen me taxi away with a strap hanging out mentioned
it to me.

"Peter Duniho" wrote in message
...
"Larry Dighera" wrote in message
...
[...]
From the description of the noise, it would be consistent with some
sort of vibratory resonance. Having actually experienced it, can you
rule that out?

Probably. Resonance can happen in a variety of ways, and can sound and
feel
like a wide range of things. But my experience has been that when
resonance
happens, it amplifies an existing frequency, rather than introducing a new
one. I think resonance with something is unlikely in this case.

I did forget to mention that in addition to hearing the noise, I could
feel
the "rumble" in my seat. It wasn't just a noise; there was a definite
(though equally subtle) vibratory component.

As another has suggested, the tach/MP gage should help in diagnosing
any loss of power associated with the noise.

Yup, hindsight is 20/20. Given the conflicting priorities (diagnose or
maintain control? ), I'm seeing a new reason for one of those fancy
engine monitors that I never thought of. They are always touted as being
useful for diagnosing hard-to-diagnose engine problems, but I never really
thought about the problem of watching engine gauges and dealing with
potential emergencies at the same time.

Pete