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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.
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