Nose gear doors opening in flight

MelsML55 · #1 11-13-19, 08:37 PM

A short time after take-off the nose gear doors fall open. Pull them back up, 2-5 mins later....or sooner.....gear doors open. Actuating cylinder has been rebuilt 2 times. Curiously, with your fingernail between the gear doors you can pull them down without any effort. Master switch and landing gear handle in ANY configuration.....same result. You can pull the doors about half way closed, then the resistance will not allow closure. Slight hydraulic film on the belly, likely from over filling the res after refitting the actuating cylinder, no leaks detected under the dash. 1965 337 number 0199.
Fire away.

JAG · #2 11-14-19, 03:11 PM

Do the NLG doors also open on ground if aircraft is sitting??

On my 66, the main thing that holds the actuator in the closed position, is the internal lock on the actuator (small balls internal in actuator). The actuator requires pressure, to unlock it. If I remember correctly, I cannot unlock mine using my fingers - have to pump a few times and build up pressure. If the 65 is the same, then it could be that the either A. The wrong actuator is installed (later models did not have internal locks, B. The balls or mechanism not installed correctly during the rebuild, or C. The actuator is not rigged properly and the doors are bottoming out before the actuator does (least likely, but possible).

Again, on my 66, the only other item in the system is the door vent valve, but that is actually meant to bleed pressure off the door system so that with temperature changes, the pressure in the lines does not build up statically and cause the doors to open. Not sure if that valve being adjusted wrong would cause this problem... If the tolerance was too tight, you would think it would also impact the main gear doors as well then.

On the later models, from what I can tell from the Service Manual, they had actuators without internal locks, and had a Door Close Lock Valve in the LH engine compartment (inbd of battery leading into Nose Wheel-well). That check valve holds pressure in the close line to keep doors closed. When its seals get old, it will cause the pressure to bleed off the lines, and ALL the doors will open. I do not believe this is how the 1965 model is (you can quickly verify by looking in the LH forward cowling and following the lines) - especially given the symptom.

Just some thoughts.
Jeff

n86121 · #3 11-16-19, 10:34 AM

A bazillion years ago when I first got my 'thrasher, sometimes the doors would open.

The design is/was that unless the locks are all engaged and circuit closed, doors open.

This prevents the gear from cycling UP or DOWN with doors closed.

Does your gear UP light go out? If it does, that's your smoking gun.

If the microswitches are 'edgy' they are easy to replace.

MelsML55 · #4 11-16-19, 03:15 PM

The light turns on and stays on even after the doors fall open, when you ground open the doors, all 4(I have the gear door deleted kit), you can halfway close the front gear doors By hand BUT NOT THE 2 REAR DOORS. Something to do with the front actuating cylinder is causing the hold up pressure to bleed off.
Secondly if I resort to pulling the power pack, who’s best for the job?

Kim Geyer · #5 11-16-19, 08:32 PM

Cox Airparts

TomeHill79 · #6 11-17-19, 08:19 PM

Have the front gear door actuator rebuilt by Cox AirParts in Wichita, KS.
It’ll cost you about $650.
It’s very common for a spring to break in the actuator to keep it from retaining the static pressure. They’ll completely overhaul it with new seals, etc..
They’ll pressure test it after completion. Expect about a week turnaround on the repair.

wslade2 · #7 11-23-19, 05:02 AM

similar situation with a rear door. earlier this year purchased plane, it had sat and reservoir required top off. rear door drooped open and could pull until resistance. Topped off again, little drip from belly, several cycles, now holds tight tight. I have talked myself into thinking there may have been some air in system that is now worked out. Was ready to jump in and do cylinder but holding on that.
I am suspecting air got in by sitting, suction line to pumps going dry (have a '70 model with dual engine driven pumps), initial flights and slug of air got sucked in and pumped around system that is now worked out.
Did vacuum test pumps with a rig I set up to be sure pump seals not leaking and sucking in air. I think manual says something about multiple cycles (minimum 5?) to get air out of system (after work etc)....