Mark,

 

If I tried I am sure I could find LML emails from a few years back (maybe many) that discussed various landing gear failures because Lancair never made it clear that the actuator push rods must be fully extended at gear down but they are not to not put undue pressure on the over center links.  The full extension should only hold the over center links from reversing in a snug way but not add forces to the links. 

 

In the case of main gear, if the extended actuators are not bottomed out but are under much pressure against the link, a slight misalignment can cause the push rods to bend (been there, done that) and perhaps jam on the next gear cycle.  Furthermore, this pressure puts an up force on the inboard link pivot bolt retaining block that is "attached" to the lower main spar cap.  If one also adds hard tires, hard main gear suspension donuts and a bad landing with some side force, that pivot block can delaminate from the spar. Lancair's fix was to put a phenolic block between the pivot block and the upper spar cap.

 

In the case of the nose gear, the most common failing was to cause the actuator fuselage mounting block to delaminate from the top of the wheel well - you have added another failure mode.

 

The proper method for adjusting the actuators is first set them for full extension to the actuator mechanical stop under hydraulic activation so that the over center link is snugly held in place - no more.  Then set the up-stops by whatever means possible, including re-making the stops, adding washers to the push rod between the too short up-stop and the cylinder, etc. 

 

If one is unsure of the actuators end stops, at the next condition check or sooner and with the plane up on jacks:

 

Nose gear - (the most difficult) - without any hydraulic pressure, disconnect the link at the leg and note that the gas spring should push the link-leg attach hole down about a half inch or a bit more than the receiving hole in the leg tab.  This is to insure that the gas spring will hold the over center link from collapsing.  Then disconnect the gas spring at the over center link and activate gear down hydraulics.  One should be able to reconnect the link to the leg with only some snugness since now the actuator is only to hold the link from collapsing.  If the actuator isn't adjusted right, fix it and re-do the up stops as well.  Check for other looseness in the linkage as the bolt through the tab and the link may wear where the threads turn into the bolt - i.e. use a long enough bolt even though it may require adding a few washers under the castle nut.

 

Mains - Without any hydraulic pressure, remove the leg/link bolt and the rat trap spring.  Then, with the gear down hydraulics activated, one should be able to insert the leg/link bolt with some resistance.  If the holes don't line up because the link hole is way too low, adjust the rod end so that the leg is held firmly in place and re-adjust the up-stop.  Check for looseness and fix it if there is too much.

 

 Scott Krueger

320

 

PS: LOBO - this should be added to the 200/300 maintenance check list for landing gear.

 

 

It seems my nose gear failure was at least partially caused by an overcenter link that was never properly adjusted.

To be more precise, the cylinder extension put down pressure on the link when down and locked.

Combine this pressure with the air spring and lots of landings over 20 years - and it failed with one firm landing in gusty wind.

 

Chris Zavatson suggested I look into the extension length and pressure - thank you very much.

And, Angier Ames told me he solved the problem by disassembling the cylinder and putting a shim inside to limit the down travel.

Thanks for that too.

 

Does anyone else have another suggestion.  I've measured my linkage already and am planning to add a shim.

 

I can see where this problem might develop if the locknut that holds the rod end becomes loose.  This would allow the cylinder rod to unscrew itself in time making the extended length greater.  This locknut is completely hidden when assembled.

 

be safe,

 

Mark Ravinski  LNC2  1484 hrs