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My writing got "edited" somehow; it should have read:
The other related variable on prop blades is "runout" or "blade tracking." Although it's NOT as severe as that caused by different blade pitch angles, significant variation between blade tracking can also be a cause of vibration. Always worth checking as part of these checks.
This is relatively easy to do by removing the plugs so you can rotate the engine easily without moving the airplane around in the process. Place a fixed work stand/stool in front of the prop and clamp a ruler or straightedge to it so it extends back toward the prop to just touch the leading edge, about 4" or so from the tip. Adjust the position of the straightedge as you rotate the prop blades past it until it just touches the closest one, then measure the "gap" between each other blade and the straightedge. Ideally there is no gap, but it's almost impossible to produce/maintain this standard. Different prop manufacturers specify the allowable gap; anything less than 0.20" will likely produce little/no vibration; the amount increases with the increase of tracking run-out. To make it more complex, it's almost impossible to measure this at anything but fine pitch--or the pitch stop setting for our variable-pitch props--in the field. Truly accurate runout measurements require the tools of a proper overhaul shop.
Bob
-----Original Message-----
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Robert R Pastusek
Sent: Friday, July 26, 2013 1:23 PM
To: Lancair Mailing List
Subject: [LML] Re: Potential Problem-Engine Vibration
The other related variable on prop blades is "runout" or "blade tracking." Although it's as severe as with different pitch angles, ;but significant variation between blade tracking can also be a cause of vibration. Always worth checking as part of these checks.
Bob
-----Original Message-----
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Craig Schulze
Sent: Friday, July 26, 2013 12:48 PM
To: lml@lancaironline.net
Subject: [LML] Re: Potential Problem-Engine Vibration
It sounds to me that you may have an issue with your prop hub not changing the pitch exactly the same on all the blades. The vibration you are feeling is one blade taking a larger bite of air and then causing everything to wobble. It settles in sometimes but when you change the power setting the pitch on the prop is adjusted by the hub unevenly. Blue Skies,
Craig Schulze
Lancair N73S
On Jul 25, 2013, at 1:22 PM, "Steve Colwell" <mcmess1919@yahoo.com> wrote:
In the first 40 hours I had vibration so severe it caused stick shake. This has continued intermittently more or less for almost 400 hours.
First I found and fixed several Cowl Interference locations, then adjusted and notched the hat section of the nose gear door.
At about 50 hours I paid Barrett to tear down the engine to replace the Performance pistons (prematurely worn top rings) with stock ECI pistons.
Also found a cracked case.
We had the Kelly Alternator balanced and rebuilt at a shop recommended by Bill Bainbridge of B & C. Sorry I can't remember the name, the Legacy file is in Texas. I rounded the leading edges of the elevator counter weights when building so I temporarily squared them off to go back to the stock shape for testing.
All gear doors were checked in flight with video camera. The pitch trim hinge pin had play, I replaced it per Chris Zavatson's web page.
Along the way the prop was balanced twice.
I could not get more that the usual vibration (which always seemed to be too
much) on test flights. Then, unpredictably, vibration magnitude would increase with power reduction on some later flight. I say unpredictably because I could not get increased vibration by attempting to duplicate previous conditions. Let's hope a solution surfaces at Airventure.
Steve Colwell Legacy RG IO550-N with Hartzell 3 Blade
-----Original Message-----
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Paul Miller
Sent: Thursday, July 25, 2013 7:22 AM
To: lml@lancaironline.net
Subject: [LML] Re: Potential Problem-Engine Vibration
Ed Martin's legacy is smooth. Mine has had a lot of annoying vibes as you describe but virtually all have been removed with lots of cowling interference fixes and plug change. Many pilots forget the alternator can be a wicked source of vibration and it is almost in the same plane as the prop.
The problems I had originally were in that freq range and visible at the wingtip also.
Paul
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