|
Message
What G-force and frequency range
are we talking about?
See
attached chart of acceleration limits.
Do you find an RPM of high
amplitude and work there.
The
manual suggests a low cruise setting for the rpm. I'm not sure it matters
much, but you need to reproduce the same rpm from one run to the next for best
results.
What sort of weights do you put on
the prop?
None. You put the permanent weights on the spinner back plate,
but the temporary weights generally go under the spinner attachment screws on
the outside of the spinner. On Lycomings, you can put them
on the flywheel, since there are already holes every 30
degrees.
I assume placement is amount is
trial and error.
Yep, no equipment
required :-) Kidding.
Does this approach work on a
three-blade?
Absolutely.
Any info on how this is done
appreciated
Using the
professional equipment, it's pretty easy. Basically, you set up
one vibration sensor, vertical, as close to the prop hub as you can
get (I've got a bracket that clamps to the nose of the redrive). You also
set up an optical tach, with a piece of reflective tape on one blade. Pick
an rpm, and the analyzer tells you what the peak acceleration reading
is, and how many degrees from the tape mark it occurred at. It then
suggests a temporary weight that should be attached, and tells you what position
to install it.
If you think
about this, you will realize that the distance the sensor is from the prop,
and the distance the weight is from the center of the prop hub both
make a difference on how much weight is required. The program doesn't
know any of these variables up front, and doesn't care. It initially picks
a weight that it knows will make a measurable change, then you install it,
and re-run the test. From the change that was made, using a
known weight, the program can now calculate what the real weight
should be to make the change required. Each time, the old weights are
removed, and the new weight is installed where the program
suggests
The program will
continue to work well, even if you don't do exactly what it says, as long as you
are honest, and tell the program what you really did. For example, if it
says put 15 grams at 355 degrees, and you have a spinner hole at 360, then put
15 grams at 360, and enter that for the actual weight in the
program. If you have a hole at 30 and 60 degrees, and it
wants weight at 39 degrees, you can tell it to split the weight, and
give it the two locations you have available. It will then tell you how
much weight to put in each location to make the equivalent weight.
Pretty handy.
When you get to
.06 ips or less, you have to convert the temporary weights to permanent
ones. For that, you measure the radius the temporary
weights are located, and the radius you want to install the permanent weights,
and the program will tell you how much to adjust the weights for the new
location.
Or maybe Rusty has purchased the
professional equipment by now and wants to rent it out J.
We have
vibration analyzers similar to this for measuring site environmental
qualifications for MRI scanners, and it takes just a few trips on the FedEx
plane to convert a new piece of equipment to junk. In other
words, there will be no
renting, or shipping of equipment, but I can certainly offer a reasonably priced
balance job if you bring your airplane to 2R4. Send all your experimental
Lycoming friends too, since those are
simple :-)
Cheers,
Rusty (fighting
Al's font for control)
|