Gear doors slow to close

hew · #1 10-31-12, 12:52 AM

When I select gear up the gear retracts then it can take a long time for the doors to close and the handle to return to neutral. Sometimes the handle will return to neutral and the orange light come on but the doors are still open or partially open. Selecting up again closes the doors or pumping on the emergency handle closes them. Is this a pump problem or a power pack problem? (1970 E model with two hydraulic pumps) Is there a pressure relief valve that can be adjusted?

hharney · #2 11-02-12, 02:33 PM

Is this during flight? What is the AOA or have you tried this at level flight? How does it react on jacks on the ground?

hew · #3 11-02-12, 05:31 PM

This does not happen on jacks with the test rig. It also does not happen on gear extension. It happen during climb, usually full power, haven't tried reduced power. Suggests to me three possibilities. 1. Not enough pressure from the pumps but I have two of them. 2. Something in the power pack. 3. The snubbing valve on the main gear actuator needs adjusting.
If anyone else has had a similar problem we might know where to start looking.

hew · #4 11-02-12, 05:49 PM

BTW, in the parts catalog the snubber valve is called a metering pin, #17 on figure 160 p/n 294604-1. Don't want to mess with this if it's not known to cause a problem.

hharney · #5 11-04-12, 12:20 PM

When you test it on jacks on the ground, what is the source of energy? Are you using the engine pumps or a mule? It is very easy to use the engine pumps on the aircraft to test the system. See my video

http://www.youtube.com/watch?v=w67UYBa48Lg&feature=plcp

hew · #6 11-04-12, 08:58 PM

Thanks Herb, yes we used a power pack which may have had a better pressure than the engine pumps. I love your electric drill adaptor to turn the engine pump. Saves a whole lot of hassle. Did you have a pressure gauge on the pump outlet side to see what was going on? What size drill (watts)?
I am leaning toward the hydraulic filters partly blocked or the solenoid sticking or intermittent electrical fault on the up lock switches / up-down switch. We've had a few other problems where soldered connections are broken but held together just enough by the heat shrink insulation.

hew · #7 08-09-14, 07:41 PM

If you have problems with the gear doors as per my previous thread I have solved the problem. Step one, replace both up-lock switches. No more steps!

I replaced one switch which made to problem intermittent, once I had replaced both switches I have had no more problems. The red herring in this issue was that the system worked perfectly well during retract tests and the switches checked out when tested and operated manually. For some reason, vibration in the air was preventing them contacting reliably. Without a complete electrical circuit around all the up-lock switches the doors won't close. At $70 each it's a very cheap fix before you go looking for other problems.

hharney · #8 08-10-14, 09:31 PM

Thanks for the response and glad you got the problem isolated to the switches.

hew · #9 05-29-16, 12:45 AM

Between the door unlock actuator and the unlock hooks there is a bell-crank, one on each side. Hydraulic pressure unlocks the hooks by pulling the bell cranks inwards. A spring inside the actuator pushes the unlocks out to reset them.
The bolt through the fulcrum had been overtightened so sometimes, usually first retreats, the spring only slowly pushed the unlock hooks out. Retracting the gear before the hooks had time to fully move out prevented the unlock switches properly engaging the legs so the doors didn't close.