Dynavibe consultation?

[ERushing]

Last year, I had my Hartzell 2 blade dynamically balanced with an ACES and then checked with a Dynavibe. The prop is balanced to 0.05 IPS. I still feel an annoying vibration and may try a different orientation.

But before I do that, I wanted to get an informed opinion of where the spike at 1/2 per might be coming from. Any ideas? The prop is on an RV-10 with a IO-540D4A5 with a Lightspeed ignition on one side and a standard mag on the other. Dynavibe output is attached.

Thank you!

 

[ERushing]

Any Dynavibe or prop balancing experts on here that would be willing to do a phone consultation? I'm absolutely willing to pay for your services (with appropriate qualifications, of course...) PM me if you're willing.

I really want to figure out what might be causing large spikes at ~1/8 per and about 1/2 per...

Thank you!

 

[Walt]

Copied from Dynamic Solutions Systems ‘theory’ page. (This is the balancer I use).
http://www.dssmicro.com/theory/th_recip_vibs.htm

ps: lots of 10 owners have had success re-clocking.) 1/8 is probably just ground induced vibrations.

1/2 Order Vibrations

It turns out that if all of the pistons produce nearly identical combustion pulses, the 1/2 order vibration will be very small, .1-.3 IN/S. When any one cylinder produces less power than the rest, the 1/2 order vibration will increase from .3 IN/S on up to over 1 IN/S for a misfire. Mechanics know very well what can cause one cylinder to be weak. Plug misfire, bad plug, plugged injector, broken ring, leaky valve, low compression, bad magneto, worn cam, collapsed lifter, etc. Any of these things can cause a higher than normal 1/2 order vibration.

1/2 order vibration are especially troublesome as they can be felt in the cabin by the pilot. Low frequency vibrations are not well isolated by most engine mounts, and the vibration will shake the entire aircraft. If not taken care of, a 1/2 order vibration can loosen rivets, hinges, and pivots all over the airframe, as well as causing premature pilot fatigue. This is a serious safety issue

 

[ERushing]

Copied from Dynamic Solutions Systems ‘theory’ page. (This is the balancer I use).
http://www.dssmicro.com/theory/th_recip_vibs.htm

ps: lots of 10 owners have had success re-clocking.) 1/8 is probably just ground induced vibrations.

1/2 Order Vibrations

It turns out that if all of the pistons produce nearly identical combustion pulses, the 1/2 order vibration will be very small, .1-.3 IN/S. When any one cylinder produces less power than the rest, the 1/2 order vibration will increase from .3 IN/S on up to over 1 IN/S for a misfire. Mechanics know very well what can cause one cylinder to be weak. Plug misfire, bad plug, plugged injector, broken ring, leaky valve, low compression, bad magneto, worn cam, collapsed lifter, etc. Any of these things can cause a higher than normal 1/2 order vibration.

1/2 order vibration are especially troublesome as they can be felt in the cabin by the pilot. Low frequency vibrations are not well isolated by most engine mounts, and the vibration will shake the entire aircraft. If not taken care of, a 1/2 order vibration can loosen rivets, hinges, and pivots all over the airframe, as well as causing premature pilot fatigue. This is a serious safety issue

Thanks for the help, Walt! I appreciate it. I'll continue investigating.

I've got excellent compression. Borescope indicates that my #3 cylinder exhaust valve might be getting burnt after only 200 hours. Going to do another set of borescope photos at the next oil change. Definitely feel vibration in the cabin. Again, appreciate the help!