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Personally I would not rely on a free fall test to check the air strut. Way too much at stake if you're wrong. I would think the nose gear could free fall perhaps without adequate air strut effectiveness. Until someone tests this with multiple air struts that have various strengths I would not trust this.
I like Grayhawk' s and others' comment about undoing the scissor arm at the nose strut either to test the air strut or to compress it for reinstall. If that works for the strut it has the added bonus that you remove the scissor attach point, inspect, clean and lubricate it, which should also be done periodically. I'm thinking if this works I might alternate with strut removal one year and scissors attach point the next. Haven't tried it even though I considered it, but I'm wondering if the hydraulic cylinder allows a enough movement of the scissor to effect a compression of the air strut. Does it work without removing the hydraulic cylinder attachment?
On Bob's discussion of the emergency down pump system, I always thought the design of the reservoir is suspect. It has a thru bolt that comes up through the bottom of the tank with nothing but a rubber gasket to prevent leakage of hydraulic fluid from the very lowest point of the tank. It was a long time ago to recall the details, but I had someone weld the rod into the tank to reduce the risk of losing all hydraulic fluid in the tank with resulting gear up landing. That could mess up your whole day.
My .02.
John
Sent from my iPad
On Apr 7, 2013, at 7:20 PM, Robert R Pastusek <rpastusek@htii.com> wrote:
Dennis wrote:
I know this might not work in a Lancair IV, but in my Legacy, I do an alternate gear extension test in flight, using gravity and the gas shocks, to confirm that I get three down and locked. If it works, I don't think there is any need to remove the gas shock and test it.
Dennis,
As designed by Lancair, the IV/IV-P mains will "free fall" to a trail position when the "up" pressure is removed from the gear retraction cylinder. They will not fully extend and lock down because they have to move forward against the airstream. Because of the design, there is no reasonable way to attach a gas strut to assist this, although some folks have devised various alternative "automatic" extension systems. The Lancair solution was to mount an emergency pump between the front seats to pump the mains down. Works well in all situations except some broken/leaking hydraulic line emergency situations. The reservoir even has a pick up for the emergency pump that is lower in the tank so there is some fluid left after the electric pump starts sucking air. The IV/IV-P nose gear is extended by a gas strut just like the Legacy, and should extend and lock down any time the "up" pressure is removed from the nose gear retraction cylinder. Part of the recommended condition inspection is a flight test to confirm that it will extend at or above 120 KIAS when the hydraulic pressure is depleted--(and that you can also pump the mains down and locked). My nose gear will extend and lock down reliably at 140 KIAS so I have not removed and tested it with a bathroom scale as recommended, but I'm thinking that this year is probably time to do so...
My two cents...
Bob --
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