Ernest Christley wrote:

But what's a fella to do with the flashing light? What are you
checking and what's it all mean?

I mean the engine's going to have this 74" diameter prop on it and
it's bound to vibrate some. How do you tell what's normal and what
isn't?

Corky Scott

I like that timing light idea. With my laptop and a simple program I
can have a lot more range than is possible with the RatShack thing I have.

Corky, the strobe will slow down any flexing due to vibrations to the
point where you can clearly see it. Sorta makes it slow motion. I
would say that if you can clearly distinquish the flexing in a motor
mount or other supporting part, then it is way too much, and you should
consider a redesign. It may not tell you anything interesting at all,
it's just an easy way to see what and where the vibration are and how
much they are shaking what. But you are right, just because it's moving
doesn't mean it's coming apart. I'll counter that you can decide what
is normal for yourself once you see it moving, and I'll bet dollars to
donuts that if you do see a lot of movement you'll be an expert on what
is normal before the engine leaves the ground 8*) (Yes, that was a long
winded way of saying, "I don't rightly know.")

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber

"I don't rightly know", either, Earnest, but it's fun to play with.

Right on about the motion, and with the vibration of the engine
running there is visible motion.

A guitar string on a guitar that is waving back and forth will move -
back and forth. But the string is still straight. It is just waving
back and forth with the guitar - way below it's resonant frequency.

When plucked, it "bows". Flexes into a new shape. The string is
resonating at some frequency based on the length, tension, and
the string's physical properties (cross section, material, windings?)

When the moment is frozen with the strobe, you can see the curvature.


So the apparent motion of the engine mount tubes is just normal
vibration.

But if there is detectible curvature or flexing, there is a resonant
response.

The thing about the variable frequency strobe is that it makes it
easy to look at different response frequencies on the test article.

Like the choke cable where it looped around the front of the engine -
unsupported.

Dumb.


Richard