TBM Landing Gear Hydraulics Problem

[Cvairwerks]

Duncan: Two more things to verify correct operation of...make sure the main pressure controller is operating correctly and also verify the unloader valve is fully closing. An unloader that is not completely closed can bypass just enough fluid and pressure to prevent the gear from going up. It completely seats when you get that little pressure transient when the flap valves snap closed. A sticky pressure relief valve can bypass enough fluid that the gear side of the system can't build enough pressure to fully retract.

Something else to try if you haven't yet, is pump the gear up via the hand pump. If it behaves like it does in flight, you've narrowed the problem down a bit more.

[duncan]

PR May- THANK YOU for the additional full-color diagram. Those really help. Wish we had an original color service manual. Our landing gear/flap selector is much as you show, but with an additional mechanical interlock over the small gear up lever which checks for the "squat" position. I don't have time to get a picture and send as I am leaving for Oshkosh on Saturday in my C-185 Skywagon - not in the TBM Although camping in Vintage area, I will undoubtably be wandering the Warbird area and asking the same stupid questions.

Cvairwerks - the manual pump will work when "gear" selected. It is just a lot easier to simply select "down" then "up" again We are thinking about adding an electrical hydraulic pump in parallel with the manual pump. Besides reducing pilot work load under "emergency" conditions, but electrical power is available, this would also help the poor pilot out when spreading wings, etc. when engine is shut down! Guess I am not tough enough to be a WWII Navy Pilot. But I am not 20 years old either.

Our unloader valve is built into the hydraulic pump, like on a T-28. The pump was replaced earlier this year as our first thought about this problem.

[BTBackseater]

First let me say I am no airplane mech. I have been helping and learning on WWII planes while a member of the CAF and my father has assisted me as he has worked on Corsairs and Bearcats before becoming a Flight Engineer on C-121's and C-130's and is also the crew chief on the CAF's Corsair. I have, however, been a auto mechanic for 30 years and as such am familar with hydraulics and was wondering if anyone has checked the hoses going to the gear cylinders. I think you said it was operating normal and then developed the problem I have known hoses to seperate internally and act as a check valve. This may be an example of this as I know in a brake system it can cause the caliper piston to stick appling the brakes constantly. Another thing is (if they have them) is the check valve on the hydraulic cylinder itself. I know it is a different application but hydraulics function the same and I have heard of this happening on a trim cylinder on a boat ( pressure up and pressure down). While looking at the fluid diagram I see that pressure comes from the thermal relieve valve to the flap / gear controller and the return also comes from the flap / gear controller straight back to the reservoir. If the other systems on that pressure circuit are functioning normally then maybe there is a problem with the gear / flap controller. I am not trying to second guess anyone here just adding my comments from a different perspective. My field is mainly eletrical / electronic (automotive related) but from what I can tell the flow of electrons and hydraulic fluid are simular and just as confussing or frustrating.
Please let me know when you find the problem and what it was.

[duncan]

Thanks for ideas BTbackSeater. We have flushed thru those hoses ok and replaced the gear position switch/valve as first thing. It "might" be possible to have replaced with a bad unit, but... We also capped off the lines to the retraction actuators and checked pressures ok - this means the actuator cylinders are not leaking past.

The thermal relief valves for each system are all in a single manifold which you noted on the (very nice) color schematic posted earlier. We just replaced this manifold last week. Now we are having problem where the system pressure is only 700 PSI, whether we use the engine-driven pump, emergency hand pump, or electric-driven "mule". Another set-back.

[BTBackseater]

Oh well thought I had a good idea should have known you guys would have thought of that but one thing I have learned over the years is just because it is new does not mean it is good.

Good luck

[duncan]

John Lane's crew at Airpower Unlimited in Jerome ID chased this problem for about six weeks. Lots of small adjustments to the gear selector and a new bypass return line routed from the pump to the fluid reservoir have finally fixed it. THANK YOU JOHN.

Last edited by duncan on Mon Nov 19, 2007 8:14 am, edited 1 time in total.

[Hal B]

Thanks for letting us know how this turned out. Sounds like a combination of small problems instead of one large one...

[CAPFlyer]

Great news that it got fixed. A lot of those problems can be hard to find on any aircraft or vehicle.

[spookythecat]

hi,

i'm more of a lurker than a poster around here but i thought this picture of bud granley flying the olympia flight museum's avenger would fit into this thread. after a few sharp turns i noticed the wheel hanging out a bit. not sure if it's the exact issue but that's how it stayed for the rest of the flight.

[duncan]

That's exactly the scenario we were fighting for almost a full year. The TBM has mechanical gear indicators, so an observant pilot "should" notice that they are not fully "up". It is also surprisingly noticable in lower speed for same throttle/prop settings. In our case, another "gear down" and "gear up" cycle would clear it - USUALLY. We missed five airshow events while working to fix this before it became a real, can not extend gear, problem. When was this photo taken? Thank you SpookyTheCat!

Another thought is that some TBMs have had their mechanical up-locks removed (worth a whole other WIX thread!). Thus the gear are only held up with hydraulic pressure. It "might" be that this one got them all the way "up" but then had some pressure leak down and no uplocks present.

[spookythecat]

i took this back in june of this year.

bud really works these planes out when he flies. i know it was up earlier in the demo and it only happened to the one side.