A little engine trouble

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.

"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

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.

"Peter Duniho" wrote in message
...
"Dan Luke" wrote in message
...
Sorry, Pete; you fly a ...?

Lake Renegade (turbocharged model).

Did you happen to look at the tach or MAP during any of these events?

No. Of course, in hindsight that might have provided useful information.
But even when the takeoff is going smoothly, I'm a "eyes outside" kind of
person (once the proper reading of the gauges has been confirmed during
the
takeoff roll, of course).

In this particular situation, my mind was focused on where on the water
would be acceptable for a landing (though, frankly, the Tacoma Narrows are
not generally amenable to seaplane landings in any case, due to strong
currents through there), and on a possible landing back at TIW.

Maybe I could have had my front-seat passenger watch the gauges, to try to
correlate them with the noise. But I personally didn't have the attention
to spare. I would have either have had to keep my eyes on the engine
gauges
until the noise occurred, or I would have had to hope to be able to shift
my
attention quickly enough to evaluate the gauges in the short period during
which the sound occurred. Neither would have been practical to do, IMHO.

It's a pretty good argument for a data-recording engine monitor. I'll
have to think about getting one of those.

Pete

Any idea of what your passengers were doing at the time. In my airplane (an
RV-6) there is a noticable change in the tone and volume of cockpit noise
(and vibration) either the pilot or passenger shifts his/her feet on the
floor. I know when I move my feet, so it doesn't surprise me, but when I've
got a "shifty" passenger, s/he will put me on edge for a few seconds here
and there.

Getting back to your situation, is it possible that a passenger found a neat
way to rest a hand/arm/foot/etc. that created an unusual resonance? I
realize this wouldn't have caused a power loss.

One other thing to consider is a stuck valve. Your description sounds
similar to my understanding of the symptoms of a stuck valve.

KB

"Kyle Boatright" wrote in message
...
Any idea of what your passengers were doing at the time. In my airplane
(an
RV-6) there is a noticable change in the tone and volume of cockpit noise
(and vibration) either the pilot or passenger shifts his/her feet on the
floor.

No, no idea. But I've never experienced anything like that before, and I
have often flown with passengers over the years.

The one "passenger-induced emergency" in my airplane I'm aware of is that
the front seat passenger can actually push on the yoke lever with their
feet. Oddly enough, the one passenger to show this to me (unintentionally,
of course) was the same one that a few years earlier kept messing with my
elevator trim on a nighttime flight, by repeatedly alternating the position
of his seat back (it was a clear night, he was in the back seat in a 182RG,
and he kept lowering the seat back so that he could look at the stars, and
then raising it again to look out the side and front).

One other thing to consider is a stuck valve. Your description sounds
similar to my understanding of the symptoms of a stuck valve.

Unfortunately, that's the best conclusion I've been able to come to as well.
I've never experienced a stuck valve with this engine, so I don't know what
sort of power loss to expect. I'd *think* it'd be more significant than
what I noticed, but I don't really know.

The engine just got all new exhaust valves and guides a few years ago, so if
it's an exhaust valve problem, I'll be sorely disappointed. I suppose it
could be an intake valve problem, even though they don't get the kind of
wear and tear the exhaust valves do.

Pete

"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

"Peter Duniho" wrote in message
...

much snipped

The one "passenger-induced emergency" in my airplane I'm aware of is that
the front seat passenger can actually push on the yoke lever with their
feet. Oddly enough, the one passenger to show this to me
(unintentionally,
of course) was the same one that a few years earlier kept messing with my
elevator trim on a nighttime flight, by repeatedly alternating the
position
of his seat back (it was a clear night, he was in the back seat in a
182RG,
and he kept lowering the seat back so that he could look at the stars, and
then raising it again to look out the side and front).

Pete

Hijacking the thread here, but...

We had a fatal accident in an Ercoupe in the local area last year that
possibly/probably involved accidental control manipulation by the passenger.
Apparently, the aircraft ran out of fuel and the pilot had lined up for a
landing in a field. Most likely survivable, possibly even a field he could
have flown out of after adding fuel. However, the airplane went in almost
vertical at the "approach end" of the field. Speculation is/was that the
passenger used his feet to brace himself for the off-field landing and
unknowingly used the elevator control linkages in the footwell as a place to
brace. The harder he braced, the more the airplane pitched nose down...
Right into the ground. Two fatalities in an accident that shouldn't have
even resulted in injuries.

KB

On Mon, 14 Jun 2004 16:39:51 -0700, "Peter Duniho"
wrote in Message-Id:
:

I've never experienced a stuck valve with this engine, so I don't know what
sort of power loss to expect.

It's not only a specific engine that characterizes the nature of a
stuck valve. The magnitude of the effect of a stuck valve can vary
depending the position in which the valve sticks. If it sticks wide
open, it could contact the piston possibly with catastrophic results.
If it just sticks open a smidgen occasionally, it would obviously be
less severe.


--

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

On Mon, 14 Jun 2004 16:49:49 -0700, "Peter Duniho"
wrote in Message-Id:
:

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.

I would suggest that you attend his inspection, and take a mechanic's
stethoscope with you. That way you'll know what he did and did not
check, and can delve a little deeper into the issue. Someone with a
personal interest and a keen sense of concern can often suggest
relevant procedures beyond those of an average A&P. At least you'll
be able to watch the gages while he runs it up.

I have had experienced mechanics completely overlook subtle nuances of
anomalous behavior that only the owner, who regularly experiences the
machine in its nominal state, can readily discern.


--

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