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However, I agree with Lynn
on the fly wheel being the issue with the torque pulses. My load on the test
stand is direct coupled, via a donut dampener to the load prop. I have the space
in the fly wheel housing to add weight if necessary.
Hi Richard,
Thanks for the comments. I took a look yesterday,
and will be hard pressed to add much weight to the dampener bolt
locations. I can probably add 1-2 large washers at each spot, though from
what Lynn said, this may be more than enough to make a difference.
At
the RPM you are talking about, I do not think there is an engine balance
problem. Even with a badly balanced engine, related vibrations did not show up
below 4000RPM on my engine.
I've had the engine up to about 5000, but couldn't
richen the mixture enough to do much. Still, aside from the odd beat
frequency prop oscillation, I didn't notice any vibration. Once the engine
breaks out of the 2500-3100 rpm vibration pit, it's quite smooth.
As for the prop oscillation thing, I've
come to believe that the prop pitch is way too high for the single rotor.
I'm using a Warp Drive, 68" diameter, 3 blade prop, which is exactly the same as
what I used on the RV-3 initially. When I set the initial pitch, I just
picked a round number, and set the tip angle at 15 degrees, since that number
was stuck in my brain for some reason.
Now
that I looked it up, I found that 15 degrees was the highest pitch I ever tried
on the RV-3, and that was with the turbo, and 5 psi of boost. The 13B had
a 2.17 drive, rather than the 2.85, but still, me thinks I need to back off to
about 10 degrees for now. I even found notes about prop stalling issues
when running that pitch on the RV-3, so with all the obstacles around the prop
on the Kolb, I've almost certainly got some sort of asymmetric stalling issues
going on. I'm just sure this is causing the odd beat frequency vibration,
and prop oscillation. This will
be an easy thing to try, so I'll find out pretty soon if this is
it.
Thanks,
Rusty (Gmail still
working)
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