Stall Switch Clean

[Costa Leite]

Fellow Mooniacs,

The Stall Switch of our 1998 M20J Allegro is being stuck because of some bug or dust that got inside the system. If I spray some lubrification it momentary solves the problem, but after 30mins it’s again stuck and somehow “glued” to something...

I already tried to apply silicone spray, contact cleaner, etc, and nothing is solving the problem. Til now, normal WD40 was the best result since it improved the switch movement a bit more than the other options I tried...

Does anyone know what kind of product should I try to apply to solve this situation? I am trying to solve this by the outside since removing and open this switch is really hard as I understood on other topics!

Thanks in advance for your help!

Cheers

Fredi

 

[Guest]

Which stall switch do you have installed.  The original Safe Flight or the Mooney version?

Clarence

[Costa Leite]

We never changed it, so I believe it is the original part

Edited June 19, 2021 by Costa Leite

[PilotX]

I found mine stuck midway through its range of motion because it had been bent and was rubbing. I grabbed the vane and bent it outward and that solved the problem. Sounds like your problem might be slightly different but check for freedom of movement. Mine was also sticking and the mechanic sprayed anti-seize early on but that has been a few months. 

[carusoam]

There are a couple of threads around here that have pics of the switch and other details…

including disassembled reasssembled switch…

And heated vanes that are not very sturdy…

The actual switch is an industrial part that should outlast the plane… so expect proper cleaning or calibration to help…

Too bad it is so hard to reach…

pp thoughts only, not a mechanic…

Best regards,

-a-

[PT20J]

Be very careful if you want to attempt bending the vane.

[PilotX]

I guess I could have hammered the part of the pre-stall circuit (or the wing) that was preventing the vane from moving. Don’t see any explicit prohibition on that. 

[Costa Leite]

Thanks for your comments. 
Ours switch is not properly stuck. It can move completely from bottom to top and I can clearly listen the switch working fine at almost on the top end.
The problem is that it feels that the mechanism has some kind of glue inside because it gets stick to and it requires added force to unstick and move the switch. Also on the flare I cannot listen the stall warning any more… but we tried a stall in flight on last weekend and the horn sounded very near the aerodynamic stall, but it kept buzzing for a few seconds, even after pitch down attitude, because the switch probably got sticked to the top. 
Will try to spray with different products before trying to service the switch…

Edited June 21, 2021 by Costa Leite

[carusoam]

Some notes about the vane…

1) They are hardened… which keeps the idea of bending it to a minimum… 

2) They are adjustable in relation to the split line…

3) The objective of adjusting it… so it gets activated as the split line moves down the leading edge…

4) the vane is a mechanical connection to a simple switch…

5) The operation of the vane should be very light… a couple of grams moves my vane up or down…

6) Compared to the force of the wind going by… a few grams is very little…

7) Not much has changed over the years…. It’s possible that they can be purchased pre-flown…

8) If you haven’t added the stall warning switch to the pre flight check list….  Now is a good time to do so… 

9) I once went six months without hearing the stall warning…  I’m not that good of a pilot…

10) Expect that the vane parts can get damaged… it is possible to walk into it accidentally. Probably leaves a nice bruise too…

PP thoughts only… not a CFI…

Best regards,

-a-

[PT20J]

If it were me, I would take it apart and figure out what's going on. Spraying things into switches is usually only a temporary fix if it works at all.

Skip

[Costa Leite]

On 6/22/2021 at 2:40 AM, carusoam said:

Some notes about the vane…

1) They are hardened… which keeps the idea of bending it to a minimum… 

2) They are adjustable in relation to the split line…

3) The objective of adjusting it… so it gets activated as the split line moves down the leading edge…

4) the vane is a mechanical connection to a simple switch…

5) The operation of the vane should be very light… a couple of grams moves my vane up or down…

6) Compared to the force of the wind going by… a few grams is very little…

7) Not much has changed over the years…. It’s possible that they can be purchased pre-flown…

8) If you haven’t added the stall warning switch to the pre flight check list….  Now is a good time to do so… 

9) I once went six months without hearing the stall warning…  I’m not that good of a pilot…

10) Expect that the vane parts can get damaged… it is possible to walk into it accidentally. Probably leaves a nice bruise too…

PP thoughts only… not a CFI…

Best regards,

-a-

Thanks Carusoam for your tips, but I am deeply aware of this vane  behavior and switch mechanism.
The thing is that, throughout these 20years of ownership, I never tried to solve things by myself on the plane, and so I am more or less afraid of dissembling parts and doing owner maintenance work… I am afraid of mixup something… but year after year, and work after work, I am getting more confident of getting hands dirty and do some minor maintenance by my self after studying the topics here in MS… On last years I improved a bit on this matter, doing quick maintenance by myself, and I saved some money on maintenance shop bills and also got even deeply on our aircraft systems!!

Edited June 26, 2021 by Costa Leite

[Costa Leite]

Yesterday I was able to remove the access panel and dissemble the stall switch. I found it very easy to get to the switch, maybe because our M20J Allegro is a late model and has the access panel right close to the switch?

Anyway, when I pulled out the switch I noticed it is probably the Mooney version and not the Safe Flight switch (according to other topics on MS where I saw that the Safe Flight switch it is a totally enclosed mechanism).

I then realized that the switch was totally clean and the problem was with the screw on the movement axis of the vane. The screw was so tight that implied huge strength to move the vane. I loosened a bit the screw and it got again with free (gravitical) movement. I reassembled everything again and did a test flight and everything got back to normal. Today I did another test flight and just right on exterior inspection I confirmed the vane was still with free movement, and so it didn’t got stuck after a few hours like before. Also, on today’s flight the stall horn sounded on flare as before. 
I will post pictures for reference and help on future visits to this topic. 
thanks to all for your help. 
Cheers

Fredi

Edited June 26, 2021 by Costa Leite

[carusoam]

Great pics and details Fredi!

Thanks for sharing them.

Best regards,

-a-