rbridges

Tips to bleeding flaps?

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Last thing left on annual.  We changed o-ring with kits for master brake cylinder and flaps from lasar.  IA is having trouble getting pressure. He's bled the lines a lot with little luck. I'm going to call Cole on Monday if nothing improves. I've also read some old threads. Just wondering if there's a trick to it. 

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Pre-load the pump portion of the hydraulic unit to prime it before installation in the aircraft.  Otherwise, it takes forever to get it pumping.  Bleeding it by the book doesn't prime the pump, it only gets air out of the flap actuator.

Once you get it pumping, you'll find it takes more pumps than usual to lower the flaps.  That eventually decreases after cycling the system 15-20 times.  Over the course of the next few months, it will slowly allow air bubbles out so eventually it will take the normal 4 1/2 pumps.

Good luck, let us know how it works out.

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10 minutes ago, Andy95W said:

Pre-load the pump portion of the hydraulic unit to prime it before installation in the aircraft.  Otherwise, it takes forever to get it pumping.  Bleeding it by the book doesn't prime the pump, it only gets air out of the flap actuator.

Once you get it pumping, you'll find it takes more pumps than usual to lower the flaps.  That eventually decreases after cycling the system 15-20 times.  Over the course of the next few months, it will slowly allow air bubbles out so eventually it will take the normal 4 1/2 pumps.

Good luck, let us know how it works out.

So, it will be mushy but gets better with time?

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Yes, once you actually get it to pump, then you can bleed it forward from the back cylinder like the book says.  It will slowly get better over time, but to be signed off I would want it to be 5 pumps or less to get full extension. 

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Here is the way I have done mine in the past

Remove the filler plug on the reservoir on the firewall and screw in a barb fitting for ¼” hose, fold the vent line on top the reservoir over and zip tie together (pinch it off), attach a 48” length of clear hose to the barb and run the other end of the hose into catch can, let it hang off to the side of the aircraft and sit the catch can on the ground. Get a hose fitting to go one the “T” at the flap cylinder (see photo, only the black pieces will be used). Attach a hose from the pressure pot to the tapered hose fitting, force fluid through the system from the bottom, you can see the fluid coming out of the reservoir through the clear hose while under plane, when all the air bubbles are gone from the clear hose from the reservoir you are ready to seal the system back up, have the cap ready to be installed as soon as the hose fitting is removed from the “T”. Allow the fluid to drain from the clear hose and then pump the flaps down, while there is pressure on the system loosen the nut on the “T” and allow any air to bleed out, this also lowers the fluid level in the reservoir so the barbed fitting can be removed, recheck the fluid level and go fly

300-3S.jpg

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^^^^^^^This....  If the search function worked better, I'd link a step by step write up, but I can't find it as of yet.

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48 minutes ago, Andy95W said:

Yes, once you actually get it to pump, then you can bleed it forward from the back cylinder like the book says.  It will slowly get better over time, but to be signed off I would want it to be 5 pumps or less to get full extension. 

If the check valve is in the flaps up position, the back filling the system from the bottom should fill everything.  I have only worked on a couple of these systems, but every one of them took exactly (and I mean exactly) 4 pumps from no flaps to full flaps. 1, 2, 3, 4, hydrolock...

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Taken from the thread above...

The next thing is to ensure the system is properly bled (this is where most fail). 

 

My "12 step" program is as follows and is based on starting with the flap system drained of fluid:

 

1) Loosen the set screw (as I've already stated above).

 

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

 

3) Remove the plastic blocking plate from the T shaped AN fitting on the ACTUATOR (lowest point in the system) and attach a pressure pot filled with the specified hydraulic fluid.

 

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

 

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

 

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

 

7) Plug overflow hose and reservoir vent.

 

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

 

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

 

10) 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...

 

11) 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).

 

12) 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...

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Step 13). Use caution the first time releasing the flaps while in flight...

On the ground, the return is set for 10 seconds... the forces of air pressure on the flaps may cut that time down significantly...

You will want to know how much before your first real go around...

My old M20C got its flap return rate set based on something other than the MM...  probably based on normal progression time... but done without any inflight forces.

The first time being used, they just about snapped back in a couple of seconds...

You really feel the loss of lift in that case...

PP thoughts only, not a mechanic...

Best regards,

-a-

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4 hours ago, rbridges said:

thanks the help.

I'd urge you to read the post I linked that Sven started. He took pictures of the hardware that I listed in th procedure and cataloged the process.

Edited by Shadrach

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13 minutes ago, Shadrach said:

I'd urge you to read the post I linked that Sven started. He took pictures of the hardware that I listed in th procedure and cataloged the process.

I did!  I also forwarded the link to my IA. 

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13 hours ago, carusoam said:

Step 13). Use caution the first time releasing the flaps while in flight...

On the ground, the return is set for 10 seconds... the forces of air pressure on the flaps may cut that time down significantly...

You will want to know how much before your first real go around...

My old M20C got its flap return rate set based on something other than the MM...  probably based on normal progression time... but done without any inflight forces.

The first time being used, they just about snapped back in a couple of seconds...

You really feel the loss of lift in that case...

PP thoughts only, not a mechanic...

Best regards,

-a-

I read many of your posts in may different threads describing the flap system in your old M20C.  I am convinced that it was not properly bled nor was the restrictor properly adjusted.  Once set, flap retraction speed should not change. Also,  IIRC you stated that in your old M20C, the first pump did nothing to move the flaps. That is not how the system should operate if in proper working order.  When the system is properly bled, there is no lag in the system. Even the smallest actuation of the handle results in an actuation of the flaps.

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2 minutes ago, rbridges said:

I did!  I also forwarded the link to my IA. 

Let us know how it works out.  If any issues remain, feel free to PM me.

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On my 68 M20g I have overhauled the pump. Now the flaps are bleeding back up after pumping them down.  Any wisdom out there on the adjustment.  Getting very proficient at panel and screw removal.  Last night the flaps stayed full right up to the flare then started coming up—- not the best landing. Any tips would be appreciated.

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@hoot777- it almost sounds like the on/off lever isn't rigged correctly, like the throw isn't far enough.  Perhaps try disconnecting the push/pull rod from the arm, and see if you can manipulate it by hand to see when it holds.

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Hoot,

you are describing the hydraulic fluid leaking back out... to allow the pressure to decay...

This happens if the valve control isn’t closing and staying closed... that is an easy external check/fix...

The other ways of leaking fluid internally is losing the seals... remember the steal balls, springs and Teflon (washer like) part?

what did the Teflon part look like when you saw it last?  When new it is like a tube with 90° ends when cut off...

after they get used they assume the shape of the steel ball... if is scratched, chipped, or broken... you know you have a leak...

If it is leaking externally... the hydraulic oil will be drying up on the belly panel... turning to jelly before collecting a lot of dirt...

expect one of three things to be happening...

1) mechanical valve control / cable challenge...

2) internal leak

3) external leak

Whatever the cause is... it wants to be fixed... the pilot doesn’t want to have the stall speed change Unexpectedly during the landing phase...

PP thoughts only, not a CFI or mechanic...

Best regards,

-a-

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