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From: Robert R Pastusek <rpastusek@htii.com>
To: Lancair Mailing List <lml@lancaironline.net>
Subject: [LML] Nose Gear Emergency Extension
Thread-Topic: [LML] Nose Gear Emergency Extension
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Date: Tue, 9 Apr 2013 02:34:59 +0000
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John Barrett wrote:

Personally I would not rely on a free fall test to check the air strut.  Wa=
y too much at stake if you're wrong.  I would think the nose gear could fre=
e fall perhaps without adequate air strut effectiveness.  Until someone tes=
ts this with multiple air struts that have various strengths I would not tr=
ust 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 scis=
sor attach point, inspect, clean and lubricate it, which should also be don=
e periodically.  I'm thinking if this works I might alternate with strut re=
moval one year and scissors attach point the next. Haven't tried it even th=
ough 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.  D=
oes 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 thro=
ugh the bottom of the tank with nothing but a rubber gasket to prevent leak=
age of hydraulic fluid from the very lowest point of the tank.  It was a lo=
ng 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 resu=
lting gear up landing.  That could mess up your whole day.


My .02.

John

John,=20

I believe that an in-flight test of the emergency nose gear extension syste=
m is a better test than just measuring the operating force of the gas sprin=
g 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 ge=
ar strut assembly, although this usually manifests itself as inability to r=
etract the gear on takeoff when the hydraulic system is working against the=
 gas strut for retraction, instead of with it for extension. With no hydrau=
lic pressure, the gas spring has to extend the gear against the force of th=
e wind in flight, and this is what dictates the minimum gas pressure requir=
ed. 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 pressur=
e/force at the coming annual, so will advise if it's deteriorated at all si=
nce installation.

I agree with John on the IV hydraulic reservoir configuration. I removed th=
e rod that attaches the pump to the bottom of the tank and plugged this hol=
e 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