On Sun, 04 May 2014 14:19:28 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

fired this volley in
:

I've run a few "audio" tachometer applications on PC and
smartphone.Dead accurate on one engine, and way off on another
virtually identical engine (with different exhaust), and not even
close on another engine. If sensing (non audio) vibrations the same
thing can happen - a different engine mount stiffness, and the tach is
way off. Getting them tuned can be a challenge


Pffft! We're talking about a one-lung model airplane engine with a
straight pipe! Even if it were a twin or a radial, it would represent
the same sort of vibration profile, which is almost always power-stroke
induced. Just more of them per rev.

I've used a lot of vibration tachs, too, and never had one misrepresent
the correct RPM on a single-cylinder engine.

Lloyd
"model aircraft" engines run the gamut from 2 stroke compression
ignition mosquitos to 4 stroke spark ignition singles and twins, to 3
and 5 cyl rotary and radial 4 strokes, and wankels.

Our local RC club flies them all. Twin engines too (and even a 4
engine monster) Vib tachs don't work very well to sync twin engines.

And they go nuts when an (2 stroke) engine starts "4 stroking". If a
spark ignition 2 stroke doesn't 4 stroke coming off load, it's running
too lean.. Don't know (or pretend to know) about a glow engine but I
know my old enya 4 stroked unloaded when it was running properly.(WAY
too many years ago)