Terrence,

 

In review:

 

0.  Assuming all plumbing is per Lancair specs.

 

1. After any normal gear down condition, fluid is everywhere in the system, all actuators are fully extended and the pump valves are set so that no fluid can flow back to the reservoir from the down-side, even if the fluid pressure is not at the down pressure switch range (power not recently switched on).

 

2. Confirming the above condition, an attempt to unlock the over center link is unsuccessful because the nose gear actuator fluid has no place to go.

 

3. The dump valve is opened so that fluid from the down-side can flow to the up-side and the nose gear is unlocked with the actuator moving down-side fluid to up-side.

 

4. Alas, there is not enough fluid to fill the up-side because the volume requirement is larger since the up-side lacks the space taken up by the actuator push rod on the down-side.

 

5. The fluid needed to satiate the up-side can now come from one of two sources: Either the reservoir thru the pump (up-side valve) or from other down-side actuators (including door actuators that are spring loaded).  I have never observed your problem and would assume that pump valves should have allowed flow from the reservoir to the up-side of the nose gear.  SO, in your case, even though all the aircraft weight (including tail weight) on the mains should have not have allowed them to be drawn in by fluid being sucked from the down-side (I am impressed by the leverage you got thru the nose gear). However, that must have happened in order to supply the needed fluid.  Note that this is extraordinary because fluid needed to fill the main actuators up-side has also got to come from somewhere.

 

6. When you then lowered the nose gear, there would have been excess fluid and it must have flowed back to the reservoir rather than re-fill the down side of the main gear.  Perhaps this was thru the up-side pump valve because the down-side should still not have allowed fluid to flow back out.  Perhaps the pump shuttle valve was not where it was supposed to be.

 

7. "I managed to get the jack in place and raise the wing enough to push the gear in place and pull the over-center strut to lock."  One should never have to "pull" the over center links with the dump valve open as when they reach a certain position, the spring should snap them in place.  Something does not seem right.

 

 

9. Your scenario failed to mention slowing to 87 KIAS (100 mph) before completing the emergency operation.  The free fall situation should succeed whether or not fluid is in the system.  The nose gear gas strut must be exerting 100 psi to push down, lock and keep locked the nose gear and the over center link.  Whatever spring system is used for the mains, it should be able to keep the over center link locked once the gear is down and any yaw maneuver is used to get a sticky main to lock. 

 

Note that getting the gear down with the dump valve open requires less fluid transfer that going the other way.

 

I am sure Chris Z can discuss the valve positions more clearly than I can.

 

Scott Krueger

 

Here's an interesting quirk of the retract system, I think....

Yesterday, spurred by a helpful LML suggestion to increase the preload in my nose strut, I chocked the mains, weighted the tail, and supported the nose with the nosewheel an inch off the ground, in order to rotate the nosegear up a little in order to get an air chuck on the schroeder valve less than an inch behnd #3 exhaust tube.

So I pushed up the over- still locked up. So I opened the free-fall valve. Pushed back the nose strut, chucked my new $22. / 300 psi made-in-china strut pump, on, and put in the max. 

Then lowered the nosewheel to over-center lock, lowered the nose, removed the weight on the tail, and observed 3 inches of strut!

So I pulled the plane out to run an engine idle check, and glanced at the right wing, was shocked to see the gear leaning inward about 10 degrees. !

 

I managed to get the jack in place and raise the wing enough to push the gear in place and pull the over-center strut to lock.

Checked the left gear... and found its over-center strut pushed up, unlocked,  too!

Jacked and pulled it down, and then put the plane back in the hangar and ran a retract-extend check -- after putting the free-fall valve back in closed position.

My guess is that with the hydraulic system closed/normal, in pushing the nosegear over-center lock up and pushing back on the nosewheel I also hydraulic-pressured the main cylinders to pull their over-center locks up.

 

So, if this is true, then here's a scenario to consider:

Gear down, no nose green light.

System pump or solenoid CB pops. 

SO, pull the pump CB, gear switch in Down, valve to free-fall.

Still can't get a nose green light. Just the mains.

 

To land, should the free-fall valve be left open,  or moved to closed? 

 

If it is moved to closed, and the nosegear is not locked over-center... will aft pressure on touchdown unlock the mains too, damaging not only the prop/engine but also the gear and fuselage?

 

Terrence

L235/320 N211AL

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