Bleeding hydraulic flap system

[Jon]

Slow fluid loss at slave cylinder. Air in system. No flap actuation. What is the best method to bleed system?  We have sent master cylinder of to LASAR twice. 

[Shadrach]

1) Remove the B-nut and plastic cover from the T shaped AN fitting on the ACTUATOR (lowest point in the system) and attach a pressure pot filled with the hydraulic fluid. 

2) Ensure that the small lever is in the "flaps up" position (this is to say needle valve off the cam lobe that opens the check valve).

3) Attach an AN fitting with a 2' hose to the reservoir to act as an overflow. position the hose over a catch can (bucket). 

4) Actuate the pressure pot and watch for fluid at the overflow hose at the front of the aircraft.

5) When you detect fluid coming through the overflow, cut the pressure from the the pressure pot.

6) Plug overflow hose and reservoir vent.

7) This is where it gets messy... remove pressure pot fitting and replace the blocking plate.

8) Remove whatever you used to block the reservoir vent plug (I've used chewing gum). Leave the overflow plug in place.

9) Select "down" position on flap lever and have someone simultaneously pump the the handle (slowly) while you back off the plastic plate on the aforementioned actuator "T fitting" just enough to allow it to leak. You should get fluid only, but possibly a small amount of air and then fluid. Have your pump person maintain gentle pressure. Make sure to only have the bottom of the system open under positive pressure from the pump person. Close it under pressure. If the person pulls up on the flap pump and the system is open it will draw air into the system...

10) With T fitting secure, pump the flaps down. Remove overflow hose, retract flaps and be ready with a rag to catch any overflow. If fluid level is too high in the reservoir , siphon a bit off with a drinking straw (use your thumb not your mouth).

11) close up the system, adjust flap retraction speed set screw so that the flaps take apprx 10 secs to retract, ops check, button everything up and go fly...

 

The above process usually works. on occasion the pump cylinder will not draw in fluid. If that happens, it may be necessary to  pre-prime the pump.

[TPC]

In addition to the end of  Shadrach's instructions:

If your flaps still require more than the 4-5 pumps for full, leave the flaps down half way for a day...just walk away. 

This is advice from a member's previous post and it works.

 

[Shadrach]

29 minutes ago, TPC said:

In addition to the end of  Shadrach's instructions:

If your flaps still require more than the 4-5 pumps for full, leave the flaps down half way for a day...just walk away. 

This is advice from a member's previous post and it works.

 

Flaps should be totally hydrolocked after four pumps. More than that and there is air in the system. I made a short video so folks have a reference for how they should perform when properly set up.

 

 

[47U]

22 hours ago, Jon said:

Slow fluid loss at slave cylinder.

I think this is the issue you must first resolve.  Hydraulic fluid on the belly could be from a number of issues.  Are you absolutely sure it is the actuator (slave cylinder) that is leaking?  It could be a loose or cracked fitting, leaking flare or tapered thread on the fittings, a bad hose, or combination of things.  It’s hard to see what’s going on looking through those little inspection panels in the belly.

As for the flap pump (master cylinder), is the retract arm not closing completely?  It wouldn’t be the first time that the flap control cable on a vintage ‘65 Mooney had trouble closing the retract arm.  

You might also verify the supply hose to the pump isn’t kinked.  I’m not sure why Mooney used SF-193 hose, but that’s what the parts book calls for.  It doesn’t have any wire braid internal reinforcement and could easily be kinked, keeping the pump from drawing fluid.  

Good luck… please keep us updated.  

[Shadrach]

On 12/28/2023 at 2:48 PM, Jon said:

Slow fluid loss at slave cylinder. Air in system. No flap actuation. What is the best method to bleed system?  We have sent master cylinder of to LASAR twice. 

Is the actuator leaking or weeping? The vent hole at the bottom of the cylinder will weep a tiny amount of fluid over time. LASAR sells an overhaul kit for the actuator, but I’m sure the parts could be sourced locally. Several years ago I noticed a leak at the actuator. I took it apart but there was no evidence of a problem. I cleaned and reassembled everything and it’s been tight ever since. A piece of FOD must have entered the system.

[Andy95W]

21 hours ago, Shadrach said:

Flaps should be totally hydrolocked after four pumps. More than that and there is air in the system.

 

Ross knows more about Mooney hydraulic flaps than any A&P I know (myself included).  But 4 and 1/2 pumps is perfectly acceptable, and was for both Mooneys I’ve owned as well as the Owners Manual:

 

[Shadrach]

1 hour ago, Andy95W said:

Ross knows more about Mooney hydraulic flaps than any A&P I know (myself included).  But 4 and 1/2 pumps is perfectly acceptable, and was for both Mooneys I’ve owned as well as the Owners Manual:

 

I never have figured out why the Owner’s manual says that. Every system that I have encountered is precisely 4 pumps IF the system is fully bled. 

[Andy95W]

16 hours ago, Shadrach said:

I never have figured out why the Owner’s manual says that. Every system that I have encountered is precisely 4 pumps IF the system is fully bled. 

The factory probably wasn’t as diligent as you when they were bleeding the system.  They probably got it pretty good and figured, “well, I guess it’s 4 and a half pumps…” 

I think we can agree that between 4 and 4 1/2 pumps is acceptable for airworthiness?

[Shadrach]

2 minutes ago, Andy95W said:

The factory probably wasn’t as diligent as you when they were bleeding the system.  They probably got it pretty good and figured, “well, I guess it’s 4 and a half pumps…” 

I think we can agree that between 4 and 4 1/2 pumps is acceptable for airworthiness?

Yes, I’d say that just being able to fully deploy the flaps is adequate for airworthiness, but I would never leave mine that way. I have become too accustomed to setting flap position based on number of pumps, rather than the indicator position.

[Nokomis449]

On 12/28/2023 at 8:24 PM, TPC said:

In addition to the end of  Shadrach's instructions:

If your flaps still require more than the 4-5 pumps for full, leave the flaps down half way for a day...just walk away. 

This is advice from a member's previous post and it works.

 

This really works!  I tied down the Mooney and left the flaps half-down for the 5 day stay.  I kinda expected the flaps to rise as the air bled out, but upon return to the ramp the flaps were still down.  So I raised them for the preflight, but when I pumped in takeoff flaps they moved immediately.  Thanks for the info!