A little engine trouble

I was out flying the CAP's 172 yesterday when I noticed the same thing. A
growling sound. I determined that it was the soda can air vents getting hit
by the prop wash, or rather, the openings being hit and the cans amplifying
the sound.

What were you flying and could it have been the same thing?

mike regish

"Peter Duniho" wrote in message
...

I hesitated to even bother writing about this, since so far it seems like
pretty much a non-event. But then I figured, what the heck...hardly
anyone
ever actually writes about actual flying, however mundane, in this
newsgroup, so here you go...

"mike regish" wrote in message
news:QRXyc.95474$Ly.16002@attbi_s01...
I was out flying the CAP's 172 yesterday when I noticed the same thing. A
growling sound. I determined that it was the soda can air vents getting
hit
by the prop wash, or rather, the openings being hit and the cans
amplifying
the sound.

What were you flying and could it have been the same thing?

Nope...the Renegade doesn't have those kinds of vents, and of course the
prop wash is entirely aft of cabin venting anyway.

I'm not ready to rule out some sort of aerodynamic effect -- for one, during
the annual inspection the fiberglass tips of the horizontal stabilizer were
replaced -- but it sure didn't seem like one to me at the time. My instinct
was that it was an engine issue.

Also, with ten years of experience flying the airplane, if it IS an
aerodynamic effect, it's almost certainly something new since the annual
inspection. Obviously I can't say that I've seen every single thing the
airplane could do, but I'll bet I've come pretty close over the years,
especially in what are otherwise normal situations such as this one.

Now that I think of it, another thing that's new is that I had them add a
second comm antenna. The sound happened in a climbing left turn, so I
suppose another possibility is some sort of vibration from the antenna.
I'll have to check into that.

I will, of course, post follow-ups to report what, if anything, I eventually
learn.

Pete

In article QRXyc.95474$Ly.16002@attbi_s01, mike regish wrote:
I was out flying the CAP's 172 yesterday when I noticed the same thing. A
growling sound. I determined that it was the soda can air vents getting hit
by the prop wash, or rather, the openings being hit and the cans amplifying
the sound.

Sometimes odd sounds turn out to be nothing to worry about.

A week ago, I was flying my Ka-8 glider over Andreas village, which is
not far from the airfield. I had just got off a winch launch, and was in
about the first or second thermal, trying to get enough altitude to try
and get out of the area.

I then heard amongst the sound of the wind going past the canopy this
"Bbbbrbrbrrrrrr brrrrrrrrrrr brrbrbrbrbrbrb" sound, which
immediately made me think that it was airframe fabric vibrating in the
wind. It went quiet for a bit. Then I heard it again. Getting a bit
concerned that the glider might have hit something on the launch that
had damaged the fabric, I was thinking of levelling out for a short
while to make a decision.

Then I realised what it was. It was the sound of motorcycles
accelerating up the Sulby straight about three or four miles away...it's
amazing how well sound travels when you're above what's making the
sound.

(The nice thing about the Ka-8 is that I can hear powered aircraft in
the vicinity).

--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"

"Peter Duniho" wrote in message
...

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.

Might be the electric hydraulic pump. It will growl if it's flooded with
hydraulic fluid.
Have it checked anyway!
Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/ CFI Retired
For personal email, please replace
the z's with e's.
dhenriquesATzarthlinkDOTnzt

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

You did exactly the right thing.

I aborted a takeoff on my last BFR because "something didn't feel
right" at liftoff. Did a double-check of all systems before launching
again and everything was fine. There's only 1 engine out there, and
my home airport has no decent emergency landing sites within 5 miles.

Could it have possibly been gusts hitting the prop? This would give the
deceleration and some changes in sound, similar to what you describe-at
least with the prop out front. Was it a gusty or thermally day? A little
thermal turbulence will hit the prop from all kinds of angles changing its
sound.

I always look for the simplest (and cheapest) explanations first.

mike regish

"Peter Duniho" wrote in message
...

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

"mike regish" wrote in message
news:37nzc.30974$2i5.23228@attbi_s52...
Could it have possibly been gusts hitting the prop? This would give the
deceleration and some changes in sound, similar to what you describe-at
least with the prop out front. Was it a gusty or thermally day?

Nope, that's not it. It was a little windy that day, but the sound was far
too regular to be any sort of response to wind gusts. Also, I've got plenty
of experience flying this airplane in a wide variety of wind conditions,
including much stronger gusts and winds than existed on this flight, and
have never experienced any sound like this as a result.

[...]
I always look for the simplest (and cheapest) explanations first.

Me too. I'm still hoping for that. But there are a number of "simplest"
explanations I can definitely rule out.

I just heard from my mechanic. He wasn't able to make it over to the
airplane today, but says he should be able to get to it tomorrow morning.
He's going to inspect the airframe and engine, do some full-power run-ups to
see if he can reproduce the sound on the ground. Hopefully I'll know
something more after that.

Anyone have any thoughts on what to do if nothing is found? I figure at
some point, a decision will need to be made as to whether to give up and
completely dismantle the engine, or to just go fly it again to see if the
problem can be reproduced. With my mechanic on board, of course, so he can
hear the noise first-hand.

As an intermediate step, it occurs to me that even though the oil was just
changed, we could change it again, and inspect the filter to see if there's
any metal. Presumably if the engine truly were on the verge of coming
apart, it'd be shedding at least some metal into the oil, right? Or wrong?
I'll be running that question past my mechanic as well, but I figure when
looking for opinions, this is a great place to ask.

Pete