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To:  lml@lancaironline.net
Date: Sat, 28 Sep 2013 14:44:51 -0400
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From: "John Richardson" <n16dx@comcast.net>
References: <list-6491326@logan.com>
In-Reply-To: <list-6491326@logan.com>
Subject: Re: [LML] Engine Mount Crack
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Dan

I too inspect this area on my Legacy for cracks because of the same issue 
you suggest....flexing of this weld area when the gear is placed in the down 
position.  I first noticed this in 2007 during my flight test period and 
called Lancair.  They had logged no reports of cracks or bending of the 
engine mount in this area.  Still, it didn't look right so I investigated to 
find the "down" hydraulic pressure in my system peaked out around 800 psi 
even though the pressure switch was set to around 400 psi.  And, in fact, I 
found that setting the "down" pressure switch even lower did not change the 
800 psi reading.  So the nose gear hydraulic cylinder is pulling on this 
welded boss in the gear down position and I could see it flexing forward.

I'm sure Chris Zavatson can add to this, but I believe the design and 
construction of the legacy gear hydraulic systems is such that it is 
difficult to reduce the pressure much below what I measured.  I think this 
is because we have a very small volume system and the lines are rigid  and 
when the current to the pump is shut off by the pressure switch, simply the 
rotational inertia of the pump motor / impeller causes the pump to continue 
turning as as it winds to a stop.  When the pump finally stops turning, the 
pressure is above the switch set point.

Although I am not familiar with hydraulic systems, my take on this situation 
is that some kind of accumulator or pressure relief valve is needed to snub 
this pressure pulse.  I added a pressure relief valve from Circle Seal  and 
have found that around 300 psi gets the gear down reliably and significantly 
reduces the engine mount deflection.  No cracks so far...650 flight hours.

An engine mount modification in this area is probably also a good idea.

In the gear up position, the hydraulic cylinder is pushing on this boss 
against the firewall which is supported by fiberglass structure of the nose 
gear well so no flexing is possible.

You might show your picture to Lancair and by this time perhaps some others 
have reported this condition.

Thanks

John Richardson
Legacy N16DX
Spokane WA

PS  Good job at Reno


----- Original Message ----- 
From: "Dan Ballin" <dballin@gmail.com>
To: <lml@lancaironline.net>
Sent: Thursday, September 26, 2013 9:14 AM
Subject: [LML] Engine Mount Crack


> While doing my condition inspection on my Legacy, I discovered an
> engine mount crack on the nose wheel brace.  It was pretty obvious and
> a little bit unnerving, when I did a gear retract on jacks and looked
> on the right side just above the nose gear door rail, just lateral to
> the over center link bushing.  I have attached a picture, but would be
> happy to send better resolution ones and a small movie to those
> interested.
>
> My concern is that this is a design flaw and/or setup issue.  If the
> hydraulic cylinder is set to put some pressure to keep the nose gear
> overcenter while extended, this puts stress on the nose wheel brace
> plate on the mount.  I would encourage everyone with a Legacy to check
> the area the next time you do a gear retract on jacks.
>
> Dan Ballin
> N386DM LEG2
>
> PS qualified at Reno with David Robinson flying at 292 mph.
> Unfortunately a failed governor kept us from flying the last 2 races,
> but great time was had by all.
>