M20C - hand pump flaps not staying in down position

[rwabdu]

Wondered if anyone has some insights on this: yesterday I put my flaps down to take off, when I applied power, the air pressure on the flaps caused them to retract as I was on take off roll / just becoming airborne. I made it around the pattern and put the flaps down on short final, had to pump them continuously to keep them down, fortunately the breaks worked... I did have some hydraulic work done a few flight hours ago because the parking break was leaking fluid. My mechanic replaced the seals to the parking break and hydraulic cylinder. He also said he added a easier method to fill cylinder from the cowl (some sort of pipe) instead of having to go behind the firewall. Anyone with thoughts about what might be wrong? 

[N201MKTurbo]

There has been hundreds of posts about this. Search away! Don’t make us write it again….

[rwabdu]

10 minutes ago, N201MKTurbo said:

There has been hundreds of posts about this. Search away! Don’t make us write it again….

Fair enough, sorry 

[AdamJD]

Start here.  

I haven't had this issue yet, but fly a lot and have hydraulic flaps.  So these are a good read for me too.

 

 

[RLCarter]

1 hour ago, N201MKTurbo said:

There has been hundreds of posts about this. Search away! Don’t make us write it again….

Having a bad there? LOL

[M20F]

Your flap pump needs to be overhauled.  Could just be gaskets (cheap) or the plastic house the bearings sit in is worn out.  If it is the latter good look finding the replacement plastic piece (Maxwell had a gunsmith making them but no more) or a pump that works.  
 

[Ragsf15e]

Also check that your selector  lever is going down all the way.  Mine works perfectly as long as it’s firmly down, but doesn’t take excessive pushing… not so much if I’m weak with it.

Edited July 6, 2023 by Ragsf15e

[Utah20Gflyer]

3 hours ago, M20F said:

Your flap pump needs to be overhauled.  Could just be gaskets (cheap) or the plastic house the bearings sit in is worn out.  If it is the latter good look finding the replacement plastic piece (Maxwell had a gunsmith making them but no more) or a pump that works.  
 

This certainly could be the case but since the flaps worked properly right before work was done on the system I suspect air was introduced into the hydraulic lines.  The system might just need to be bled.  

[N201MKTurbo]

Sorry I was short with you before, but there is a lot written about this.

If they are coming up, it is most likely the ball on the back behind the flow screw. It needs to be re-coined. This sounds fancy, but it is just putting the pump in a vice and whacking the ball with a punch. This will re-form the seat to the ball. What was wrong with the pump before? What problem were you trying to fix?

[47U]

3 hours ago, Utah20Gflyer said:

since the flaps worked properly right before work was done on the system I suspect air was introduced into the hydraulic lines.  The system might just need to be bled.  

If the hydraulic system was opened up for parking brake mx, and the addition of plumbing for servicing, it’s possible that some debris was introduced and is preventing the ball from seating allowing fluid to leak past and the flaps retract.  You might try flushing the system from the bottom up, i.e., flap cylinder forward.  

If there’s air in the flap system, the first few pumps on the flap handle will be soft.  Bleeding the flap system fixes this, but it should not be a reason for the flaps to not stay down.

How old is your flap-retract Bowden cable?  It pulls to retract and pushes for flaps down, right?  If the cable needs lubrication, pushing the lever on the panel down (or knob in) might not fully actuate the lever on the pump.  When I got my C, someone had added a spring at the pump end to help push the cable on the pump lever to the closed position.  I thought, WTH???  Very shade-tree.   

 

[rwabdu]

Thanks for our help! i should have realized others have had this problem before and looked it up more. Hopefully its just flushing the system or replacing seals then re-coining the ball behind the flow screw and go from there. I have 4 hours on the airplane since the hydraulic cylinder and brakes were worked on (for a leaking parking break) before the problem with the flaps started. I bet my flap retract cable is as old as the airplane... 1968. Thanks a again for the advice. 

[M20F]

The 2 HE1516 springs are different.  One is a strong spring and one is weaker.  They look pretty much the same but need to go in the right way or flaps no workie.  

[Jim Peace]

On 7/5/2023 at 10:38 PM, rwabdu said:

 the parking break was leaking fluid. 

have not tried my parking brake in almost 10 years of ownership.....

[rwabdu]

1 hour ago, Jim Peace said:

have not tried my parking brake in almost 10 years of ownership.....

I never do .. but I think the mechanics do when they did the run up after annual 

[M20F]

2 hours ago, Jim Peace said:

have not tried my parking brake in almost 10 years of ownership.....

My hanger slopes (the ramp portion) so after 35yrs of never using one, use it every flight.  Amazingly it works good.  

[Fly Boomer]

11 hours ago, rwabdu said:

Thanks for our help! i should have realized others have had this problem before and looked it up more. Hopefully its just flushing the system or replacing seals then re-coining the ball behind the flow screw and go from there. I have 4 hours on the airplane since the hydraulic cylinder and brakes were worked on (for a leaking parking break) before the problem with the flaps started. I bet my flap retract cable is as old as the airplane... 1968. Thanks a again for the advice. 

The search function provided by the forum software is not great.  What works better is to employ the search engine in your favorite browser.  You can open a separate tab, and search like this:

site:MooneySpace.com hydraulic flaps

The "site" parameter restricts the search to the MooneySpace.com domain only.  Of course, you can search without the "site" parameter, but you will get a lot more extraneous hits.

[Ragsf15e]

2 hours ago, rwabdu said:

I never do .. but I think the mechanics do when they did the run up after annual 

It can leak without using it.  Mine was leaking on my left foot, so i had the orings replaced even though I don’t use it either.

[Utah20Gflyer]

3 hours ago, M20F said:

My hanger slopes (the ramp portion) so after 35yrs of never using one, use it every flight.  Amazingly it works good.  

The ramp where I park my plane has a very gradual slope to it so I always deploy the park brake before I get out.  Feeling the plane starting to move as you are exiting is not a great feeling even if it’s not moving very far.  I can turn off the brake by reaching in the hatch on the pilots window after I connect the tow bar.   I always use it when I’m getting fuel as well, probably don’t really need to but I don’t see a downside.  

[M20F-1968]

Suffice it to say this system is a bear to work on.   Once it is. working properly it is reliable until you have a leak.   My approach to this system has been to always have an overhauled flap pump known to be good to swap out when the system is not working.   Aside from the flap pump in the rear actuator, everything else is just plumbing and needs to be clean and leak-free.   The flap-pump needs to be overhauled properly and it is. best if you have a test bench to check it before installing it. Of course, no one has these except service centers.   The other thing I did that was helpful is to make up two pressure pots with hoses that terminate with AN fittings that will fit directly into the various connections in the system.   One is a  pressure pot purchased from Aircraft Tool Supply and the other is a approximately quart-sized pressure pot that is. meant to be a sprayer but can be fitted with a hose to be connected to the reservoir fill tube.

 Some people try to fill/purge the system of air from the front,  others do so from the back.   I tried both and neither were completely successful.   The former manager from Lasar  made the only suggestion that worked and that was to disconnect the front hose coming into the flap pump and back-fill it from the pump forward until all the air is out of the line.  There are gyrations in that line that are hard to clear of air.  Then quickly attach to the pump and tighten.  Then fill the line again with the small pressure pot from the brake fluid reservoir fill tube clear to the rear of the system.  Then close the system.  Test it.  You will likely need to fill, bleed and test the system many time filling from the front and letting out air at the rear.  Read the manual on this.  

This is a system that, if it works, leave it alone.  If it does not work, do not try to do anything to it until uou have all the pressure pots, lines, connec tors, flap pumps, sufficient brake fluid, many rags, and a change of clothes that you will need.  You get the picture by now I assume....

John Breda

 

[M20F]

2 hours ago, Utah20Gflyer said:

The ramp where I park my plane has a very gradual slope to it so I always deploy the park brake before I get out.  Feeling the plane starting to move as you are exiting is not a great feeling even if it’s not moving very far.  I can turn off the brake by reaching in the hatch on the pilots window after I connect the tow bar.   I always use it when I’m getting fuel as well, probably don’t really need to but I don’t see a downside.  

Sounds like we have derived the same system.  

[Kesk]

On 7/7/2023 at 11:36 AM, M20F-1968 said:

Suffice it to say this system is a bear to work on.   Once it is. working properly it is reliable until you have a leak.   My approach to this system has been to always have an overhauled flap pump known to be good to swap out when the system is not working.   Aside from the flap pump in the rear actuator, everything else is just plumbing and needs to be clean and leak-free.   The flap-pump needs to be overhauled properly and it is. best if you have a test bench to check it before installing it. Of course, no one has these except service centers.   The other thing I did that was helpful is to make up two pressure pots with hoses that terminate with AN fittings that will fit directly into the various connections in the system.   One is a  pressure pot purchased from Aircraft Tool Supply and the other is a approximately quart-sized pressure pot that is. meant to be a sprayer but can be fitted with a hose to be connected to the reservoir fill tube.

 Some people try to fill/purge the system of air from the front,  others do so from the back.   I tried both and neither were completely successful.   The former manager from Lasar  made the only suggestion that worked and that was to disconnect the front hose coming into the flap pump and back-fill it from the pump forward until all the air is out of the line.  There are gyrations in that line that are hard to clear of air.  Then quickly attach to the pump and tighten.  Then fill the line again with the small pressure pot from the brake fluid reservoir fill tube clear to the rear of the system.  Then close the system.  Test it.  You will likely need to fill, bleed and test the system many time filling from the front and letting out air at the rear.  Read the manual on this.  

This is a system that, if it works, leave it alone.  If it does not work, do not try to do anything to it until uou have all the pressure pots, lines, connec tors, flap pumps, sufficient brake fluid, many rags, and a change of clothes that you will need.  You get the picture by now I assume....

John Breda

 

Yeah it is a pain. Had a leaking HE625, probably had a solid inch of gunk from leaking for so many years. Resealed it and the HE626, no leaks but now they slowly come up once down, tried manually using the cable to actuate the cam. Sometimes it would seal and stay down, but now it never does it. Slowly comes up no matter how far in the closing direction the cam is pulled. Took it apart and resealed + bled it again, same problem.

Think it's a ball valve seat or something else besides an o-ring internally. I'm not aware if it was working before because the owner was not using the flaps as the leakage at the HE625 was so bad they just plain didn't work.

[Ragsf15e]

On 9/1/2024 at 11:56 PM, Kesk said:

Yeah it is a pain. Had a leaking HE625, probably had a solid inch of gunk from leaking for so many years. Resealed it and the HE626, no leaks but now they slowly come up once down, tried manually using the cable to actuate the cam. Sometimes it would seal and stay down, but now it never does it. Slowly comes up no matter how far in the closing direction the cam is pulled. Took it apart and resealed + bled it again, same problem.

Think it's a ball valve seat or something else besides an o-ring internally. I'm not aware if it was working before because the owner was not using the flaps as the leakage at the HE625 was so bad they just plain didn't work.

Isn’t there an adjustment for how fast they come up?  Someone here (@Shadrach) will know…

[47U]

On 9/1/2024 at 11:56 PM, Kesk said:

Think it's a ball valve seat or something else besides an o-ring internally.

It’s leaking somewhere in the internals.  Someone here knows which ball/seat it is, but (pending expert replies) perhaps taking the pump apart and under close visual inspection you can determine what seal/ball is not sealing correctly.

[M20F]

My guess is the Teflon seals HE-1517 are bad for which there is no fix @M20F-1968 is working on making some parts.  

[rwabdu]

So with mine, I had two things going in. 1) started leaking and I had it resealed by my mechanic with the little kit of gaskets Lasar sells. Then 2) the flaps would retract slowly while down and would not stay down in the air. I assumed it was a problem with the valves after his reseal but he found that it was the cable the pulls the flaps down was loose in the underbelly of the airplane. He tightened it a few inches and it solved the problem. My only concern is that if the cable was loose I may have overspread the flaps and I’m lot sure what the integrity of that cable is. 

Edited September 4 by rwabdu