John Barrett wrote:

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

John, I believe that an in-flight test of the emergency nose gear extension system is a better test than just measuring the operating force of the gas spring because it verifies capability of the entire system to function as needed. Any binding of the linkage or pivot points in the nose gear can keep even a fully pressurized gas strut from extending the gear. This has happened a couple of times as a result of hard landings that bent/damaged the nose gear strut assembly, although this usually manifests itself as inability to retract the gear on takeoff when the hydraulic system is working against the gas strut for retraction, instead of with it for extension. With no hydraulic pressure, the gas spring has to extend the gear against the force of the wind in flight, and this is what dictates the minimum gas pressure required. My personal cutoff is 120 KIAS although my gear extends and locks down consistently at 140 KIAS. I plan to actually measure the gas spring pressure/force at the coming annual, so will advise if it's deteriorated at all since installation.

I agree with John on the IV hydraulic reservoir configuration. I removed the rod that attaches the pump to the bottom of the tank and plugged this hole with a short bolt and sealing washers. I made a split circular clamp out of 1/2" Delrin that clamps around the neck of the reservoir and used small bolts to attach the pump base to this clamp. Has worked like a champ for 6+ years; no leaks at all.

Bob