lml@lancaironline.net Mailing List Archive

Craig, et al,

Interesting ......

A friend with a 600 hr, 6 cyl Continental engine switched from a 2 blade to a 3 blade prop with resulting obnoxious vibration and, after weeks of meticulously ridding the engine compartment of anything that moved from touching the fuselage or cowling, consulted a gray haired A&P who related how the wear pattern against bearings by torque pulses from using a 2-blade and a 3-blade prop would be in different places in the engine. He went back to a 2-blade prop and all vibration disappeared.

There was an example of a change affected by how the engine bearing had worn that definitely resulted in inducing vibration.

Grayhawk

In a message dated 7/28/2013 1:21:29 P.M. Central Daylight Time, craig@skybolt.net writes:

It could be possible for wear or manufacturing process to allow one blade to have more play in pitch operation than the others.

Blue Skies,

Craig Schulze

On Jul 27, 2013, at 5:36 PM, vtailjeff@aol.com wrote:

How is that mechanically possible? All blades are attached to the same pitch change mechanism.

J

Sent from my iPad

On Jul 27, 2013, at 12:34 PM, Steve Colwell <mcmess1919@yahoo.com> wrote:

That is a possibility I had not considered, I will ask Hartzell about it. Another possibility is the movable crankshaft counter weights failing to position correctly.

Steve Colwell

From: Craig Schulze <craig@skybolt.net>
To: Steve Colwell <mcmess1919@yahoo.com>
Cc: "lml@lancaironline.net" <lml@lancaironline.net>
Sent: Friday, July 26, 2013 7:42 AM
Subject: 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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