Been scratching my head on this one, a mechanical intermittent problem that happens occasionally, and happened again this morning.  Main landing gear will not retract.  Nose gear goes up, not mains.  Recycle gear, everything retracts like a thing of beauty.  Months go by, no problem, then it happens again.

 

Twice we have jacked the airplane up, carefully adjusted the rack and pinion clearance and cylinder stroke positioning relative to the rack gear and the plastic down stop, and yesterday it happened on take off.  Grrrrr.  Slow flight, 110 knots, cycle down, up, down, up, no problem.  Back to airport for total of 5 landings, no problem.  

 

This morning filled the cabin with pork, took off for a fly in breakfast, no problem with gear retraction, landed there with heavy braking to get off the runway fast with an airplane behind us on short final, enjoy breakfast, depart a couple of hours later, mains would not come up.  Grrrr.  Recycle, no problem, slick as custard in July.  

 

I have been working this problem with a fellow engineer with much experience in hydraulics . Current theory: Down lock pistons and pins constitute assemblies in the hydraulic cylinders that may get jammed in position after years of wear (estimate about a thousand landing cycles) and application of larger than normal side loads on the locking pins from, for example, heavy breaking.  Piston/pin assembly jams due to side load and wear, select gear up, piston does not rise due to jam, no hydraulic fluid can thus pass to the main gear cylinder.  Cycle the gear, changing forces on the main gear pistons clears the jam with some wiggles and bangs as you recycle the gear, raise gear, no problem.

 

Right now our plan is to order O-rings (requested o-ring kit or list of part numbers for main gear from Lancair), pull the cylinders and rack as an assembly out of the airplane, disassemble, inspect, look for scores, side load wear or whatever we can see.  We will deal with whatever we find.  While out in the boondocks of Western  Australia, the area is agricultural with the regional center town nearby having a surprisingly large number of hydraulics and machine shops due to all the ag machinery within a 200 mile radius.  So we can probably get parts made, bore cylinders, machine inserts, or whatever. 

 

But all this assumes we have diagnosed the problem correctly.

 

We know you encounter problems waiting to raise gear due to air loads as the airplane accelerates.  That is NOT the problem as it has occurred even raising the gear handle at 20 feet/95 knots shortly after rotation.  

 

Any insights, history, observations, advice or theories would be most welcome. 

 

Head Scratching Fred Moreno, going bald