REFLECTOR: FW: Chasing Down the Source of a Vibration

Thu Jan 26 13:29:11 CST 2006

Good story Chris.  Sometimes, the obvious is hard to see.  After all,
the first place we go blind is in the eyes.

Chuck Jensen

Do Not Archive

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Christopher Martin
Sent: Thursday, January 26, 2006 11:37 AM
To: reflector
Subject: REFLECTOR: FW: Chasing Down the Source of a Vibration

	From: Christopher Martin
<mailto:christophercmartin at earthlink.net>  

	To: reflector-admin at tvbf.org

	Sent: 1/25/2006 11:53:57 PM 

	Subject: Chasing Down the Source of a Vibration

	I want to share a little interesting problem I had because we
all learn from one anothers mistakes and experiences. It's the nature of
the Reflector and it is a very good thing.

	I have been flying my Velocity XL RG since November of 2000. I
now have 620 plus hours on it and many happy experiences. I used to be a
more frequent contributor to the Reflector and am overdue in making a
contribution. So, it's time to share a story.

	Last May, I was departing Fresno, California on a return flight
to my home base in El Monte , California. I was climbing out in a left
cross wind departure at 3000' AGL. Suddenly, a vibration emanated from
somewhere in the plane. It sounded like a bearing in some engine
component. It lasted for what seemed like a full 20 seconds. I was
debating on wether to return to Fresno or land in Visalia when it, just
as suddenly, disappeared. I climbed on up to 9500' and leveled off in
cruise at 185 KNTS. Suddenly, the vibration appeared again. This time I
tried changing engine RPM and throttle settings. At times the vibration
would shut off and then suddenly reappear. This was a very abrupt
vibration. Meaning it was either on or off. And, when it came on it
lasted for as much as a minute and then might go off for as long as 20
minutes. I concluded that it must be engine related and that I would
debug it back at home. The first thing to check would be the engine oil
and filter. 

	Back home I started the investigation. Engine oil and filter
were fine. So, how about vacuum pump. It was time to rebuild it anyway.
After all, the pump was approaching 600 hours. So, I rebuilt the vacuum
pump. With the rebuilt pump installed, I took off and all was fine. I
flew out to Camarillo and it was perfect. On the return flight all was
well until I started my decent into El Monte and suddenly, the vibration
reappeared. Lasted for a few minutes and then just as suddenly
disappeared. It must be the alternator I concluded. Had to be. I had
nothing else with bearings that could make that noise. I have dual
electronic ignitions so, it's not magnetos. It has to be the alternator.
So, I send the alternator in for new bearings and brushes. After all,
like the vacuum pump, 600 hours is time enough for a rebuild.

	The alternator comes back. I bolt it on. Take off and
immediately hear the vibration. It lasts for 20 seconds and then
disappears. After all of this I am dumbfounded. I can't reproduce the
problem on the ground. It only appears in flight. It is intermittent and
I'm baffled. So, I continue to fly the plane with this occasional
vibration sound. There is no other manifestation of the problem other
than the sound. I conclude that there is only one other possibility.
With 600 hours on the plane and 6 years, the engine is starting to sag
on the mounts. Is it possible that in flight the engine is causing some
vibration to be transmitted to the cowling? Is something hitting the
cowling because the engine mounts are sagging? Ok, I'll change the
rubber bearings. This is expensive and difficult and I really don't want
to do it, but I have time at Christmas when 'I'm doing the annual.

	So, last Christmas, I changed the engine mounts. First of all,
it does look better to once again have the engine sitting squarely in
the engine cowling. The 6 years and 600 hours of use had allowed the
mounts to creep so that the engine had sagged a full 1/2 inch. Now, with
the new mounts, it was back where it was supposed to be; squarely in the
engine cowling. The prop perfectly aligned with the prop opening and
cowling. A piece of sculptural beauty. But, did it solve the problem?

	I took off from El Monte and was just turning down wind when the
vibration appeared. It lasted 20 - 30 seconds and, again, disappeared. I
landed.... I was pissed..... What else could it be...? I am such a
moron..... I can't find this dumb sound..... I decided that I had become
so focused in the chasing down of the vibration that I needed to stop
and walk away. Take 100 steps back and look at the plane entirely. Is
there anything that appears to be out of place..... There wasn't.

	I walked around the plane and checked it again, in total.
Everything was exactly as it was supposed to be. As I completed my walk
around, I passed by the co-pilot side rudder and, almost out of reflex,
straightened the tape I had placed on the rudder gap. You know how we
have talked about the merit of gap sealing the ailerons and the rudders.
Well, I had placed some white electrical tape over my aileron and rudder
gaps. It works great. All of my control surfaces have it. And, I do
think the control surfaces are more responsive and must have less drag.
But, every time I go by this co-pilot side rudder, I need to realign
this piece of tape. It is as if it has come loose at some point and then
reattached itself. Is it possible that this tape is loose in flight and
creating a vibration? I check it out..... It seems that 2 to 3 inches of
the tape is loose and is not adhering well. The rest of the tape is
holding strong. It is very possible that this 2 to 3 inch pi! ece of
tape is trailing in flight. So, I pull off the tape. After all, it is
not flight critical. In fact it is more cosmetic than anything. 

	I take off........ not a sound.... Perfectly quiet..... I can't
believe it! I flew all over the area and and into the desert and back
without a sound! I have now flown 6 hours and not one time has the
vibration reappeared. The problem is solved.....

	As I reflect back on my preflights. I had always checked my
rudders and I had always straightened that same piece of tape on the
co-pilot side rudder. I had been looking at the problem before every
flight and couldn't see it because I was so certain it was engine
related.

	I'm not drawing any other conclusions from this other than :
These planes are very fast and anything that gets into the air stream
that is not tied down is going to flap and vibrate. Appreciate the
aerodynamics and drag associated with everything that is hanging out
there in the breeze. At 185 KNTS a 2 inch piece of tape can generate a
great deal of vibration energy.

	And, that's my little story for "Share Time" today.

	Build it straight and fly it safe....

	Christopher Martin

	christophercmartin at earthlink.net

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.tvbf.org/mailman/private/reflector/attachments/20060126/3cf6c6b8/attachment-0001.htm