Folks
I am dealing with a vexing problem which has plagued me
throughout my phase 1 testing and that is, I can’t get rid of vibration from
my engine prop combination. I am running a Lycoming IO360/Slick Mags
(non-counter weighted crank) with a new Hartzell HC-C2YK-1BF/F7666A.
The prop was dynamically balanced on the ground at 23” map
and 2400rpm to 0.05ips. Interesting thing is the vibration increases
significantly to 0.25ips at 2500RPM on the ground. When flying, I can
see the ASI needle vibrate a little (+/- 0.5mm) at high power settings
>19Inches and any RPM. I have not been able to measure
the vibration in the air since it is difficult to mount an accelerometer in
the vertical plane under the cowl but I do see the stick vibrate a little from
side to side when I let it go.
Some additional background:
1.
The engine has accumulated 44 hours since new
2.
The crank was dynamically balanced at the factory
3.
When the engine was built it was tested with a club and found to
be vibration free
4.
The prop has a 4” extension by Sabre Industries
5.
The balancing weight was mounted to the flywheel in the form of
an AN3 bolt/nut (20 grams)
6.
The spinner is solidly fixed to the prop and back plate and is
centered
7.
The crossover exhaust and tailpipes are fixed to the engine
only
8.
The cylinders are 9:1 compression
9.
All cylinder compressions are even and in the 70s
10. The engine
mount bolts are torqued correctly to 40-45ftlb
11. The engine does
not/cannot touch the cowl
When I tested the aircraft at 17,500 feet, I noted the
vibration was significantly less pronounced or non-existent due to the low
power output. I noticed the same thing in cruise decent at 18 inches or
lower. Talking to the prop balancing mechanic, he stated that it is
unusual for balance to be ok at 2400 RPM but to be significantly different at
2500RPM+.
I would be very grateful for any help and assistance from
anybody with knowledge or experience in correcting vibration issues such as
the one I described above
Thanks
Tom