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 11-05-12, 10:34 PM

Herb, the video raised a couple of questions.
1. did you have a torque arm bolted to the pump to stop it spinning on the end of the drill?
2. The vortex generators in front of the wheel wells, do these come with the kit & do they help?

hharney · #8 11-06-12, 11:16 AM

I am not following your question about the torque arm spinning on the end of the drill. The pump is removed and the drill provides the energy to run the pump. Just hold it in hand to operate

The VG's are part of the Horton STOL kit. Not sure on the effectiveness but must provide some benefit in stability at slow speed. Originally from the R-STOL system and copied by Horton

hew · #9 11-06-12, 07:40 PM

OK, I guess the hoses and a strong hand prevents the pump spinning on the end of the drill. I'll try it and see.

hharney · #10 11-06-12, 08:34 PM

Yes, there is enough support on the pump to stabilize it for the process. You will need an input gear to fit the pump shaft. Available from Aviation Enterprises

hew · #11 11-11-12, 10:19 PM

Thanks Herb, the electric drill works a treat and all you need is a 15mm 1/2" drive socket on the drill to fit on over the pump splines. Pressures could be monitored by inserting a Tee and gauge on the outlet side of the pump. We didn't do that as we have decided that the slow door closing is probably because the power pack needs overhauling and pressures re-adjusting in the process.

hew · #12 10-02-13, 09:58 PM

Quote:

Originally Posted by hew

Thanks Herb, the electric drill works a treat and all you need is a 15mm 1/2" drive socket on the drill to fit on over the pump splines. Pressures could be monitored by inserting a Tee and gauge on the outlet side of the pump. We didn't do that as we have decided that the slow door closing is probably because the power pack needs overhauling and pressures re-adjusting in the process.

The latest findings on the gear door issue. Here is what happens. Gear goes up, handle stays up, doors remain open. Move handle back to neutral, orange light comes on indicating all up-locks are in. Move handle to up position, doors close, handle drops back to neutral.
When cycling the gear on jacks using an electric drill on the front pump the cycle works perfectly. (pressures are probably lower)
I have readjusted all the up-lock switches & replaced one. No permanent change.
The doors will close (but not 100% reliable) when I overfill the hydraulic oil. Power pack has been serviced, all pressures as per specs.
This suggests to me that the gear is going up past the up-locks (or at least one of them). When the handle is returned to neutral the pressure is released and the gear drops back into the up-locks and completes the electrical circuit.
My solution so far has been to 1. overfill the hydraulic fluid daily. 2. make as a standard procedure, return the handle to neutral then re-cycle up if doors don't close within 5 seconds of gear retraction.
The best investment so far has been a $4 convex mirror attached to the landing light shield and angled so I can see the rear doors and gear during the cycle.

hew · #13 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 · #14 08-10-14, 09:31 PM

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

hew · #15 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.