Dan,
A -550 "thumper" in a Legacy will generate vibration...that and noise are what you spend all the gas money for... Now, a little Rotax might not win at Reno, but you'd likely have less vibration... :-)

But seriously, the engine is a source of vibration, no matter how good the balance. At certain frequencies, it can resonate with other airframe components to be truly annoying, even dangerous. Check your flight control hinges, attachments and any other moveable parts of the airframe for security and free play. Ditto for the flight control linkage. Any of these can be "excited" by the big thumper engine you have up front.... Get rid of any "free play" whatsoever in these components.

Bob

-----Original Message-----
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Dan Ballin
Sent: Monday, November 25, 2013 8:09 AM
To: lml@lancaironline.net
Subject: [LML] Vibration

I am trying to figure out the source of a vibration in a fixed gear Legacy with an IO-550.  The plane had a recent condition inspection and raced at Reno- vibration present before Reno but maybe worse now.
It is RPM related with the worst being about 24-2500 RPM better at 26 to 2700 RPM.  Somewhat speed related - worse with higher speed, but mostly it is RPM that determines the severity.  The prop has been balanced dynamically and I actually hooked it up to another instrument just to see if the equipment was OK.

We have looked for anything rubbing or loose including engine mounts and isolators, baffling.  All EGT and CHT's are fine and close together - haven't done an in flight mag check, but will soon.
Compressions are fine on all cylinders.  All the wheel pants and struts look good and nothing was seen vibrating on close inspection in the air.

So one question is can the vibration be engine related if the prop balance is good or does that pretty much rule it out.

Any thoughts or suggestions would be appreciated.

Dan Ballin

--
For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html