There is also 4th and 5th degrees of freedom, rotation and torque.

Anything is measurable if you have the right equipment and techniques.
15 years ago or so, I met a couple of guys who marketed their services of
predictive vibration analysis for very large diesels in the oil patch and
marine fields.
They could tell you when a valve guide was beginning to wear.
They smiled big when asked about their fees.

Predictive vibration analysis is well known by turbine aircraft operators.
I decided long time ago that its not economically viable for aircraft
piston engines. I think that the other techniques of predictive
maintenance do just as well. Exception maybe is the front alternator 520.

Really, who is goin' to pay for it?

The first requirement would be to have a well established baseline for a
specific engine.
And if one is taking measurments that have nothing to do with cylinder head
separation, one would not have to account for the percentages of difference
of combustion forces of all the cylinders and the percentage difference in
the other factors, like valve spring pressure, that influence the horizontal
yawing motion a flat opposed aircraft engine undergoes during normal
operations.

Another angle to consider could be......how to describe this? .....is to
ask what musical note the cylinder rings at.
Everything rings at its own frequency and a crack will change it.

Good luck
Kent Felkins
Tulsa Oklahoma





15 years ago or so I talked to some guys who
"Jim Weir" wrote in message
...
I've come across a marvelously cheap vibration sensor that I want to
convert
into an engine vibration instrument for a Kitplanes article. The
electronics
for me is relatively trivial...the mechanics of vibration are a little
harder to
fathom.

From a mechanical engineering point of view on a horizontally opposed
engine,
there are (as with most things) three axes of freedom -- fore and aft,
side to
side, and up and down (longitudinal, lateral, vertical).

The sensor I have reads two axes, and my hit is that fore-aft is the least
interesting vibration mode of the engine. The question is whether to have
a
two-channel meter (which complexes up both the design AND the panel
space), a
single meter switchable between lateral and vertical) or a single meter
with the
two axes summed together.

Comments and thoughts from the technonerds amongst us appreciated.

(It has nothing, repeat NOTHING to do with the fact that such a meter
might have
detected a crack in that cylinder WAY BEFORE it departed the engine on the
way
home from Oshkosh {;-) )


Jim


Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com