Safe Flight Lift Detector: A Guide, A Rant

[Blue on Top]

I wandered up the wrong alley.  This one's full of IAs  

I should be finding out the TSO information soon.  Thanks all.

[Blue on Top]

12 hours ago, EricJ said:

What is a "Stall Warning Instrument"?  It isn't defined in the TSO, and the SAE document is not publicly available that I can find.   Whatever it is, I've never seen anything in a GA airplane compliant with B.2.v which says there must be a positive indication, readily discernible under any lighting, that the "stall warning instrument" has lost power.   There's also nothing in the Mooney SMM that says any of the components have to meet TSO-C54.   I can't find any reference in the SMM or IPC for my M20J of any TSO at all for anything.   

An instrument that is used to show compliance to the stall warning certification regulation.  The losing power is in reference to the heating device.  IOW, if the probe/sensor loses power, it is considered inop to go into icing conditions.

The problem is that IA/A&Ps and Engineers often discuss from very different perspectives.  A good example is replacing instrument post lights with an LED strip light.  To an IA, this is a minor change (from what I have been told).  To an Engineer this is uncertifiable (and makes the airplane unairworthy) because the post lights were used to show compliance to a certification regulation.  With that said, the LED lights could be much better than the post lights, but they have not been through the certification process. 

[EricJ]

On 2/12/2021 at 11:37 PM, Minivation said:

A bit of light reading if you're bored over the weekend.

TL;DR: Stall switch failed on me, and the $2500 price tag for a new replacement is downright stupid.

It was my turn in the barrel to take a swing at this, and thanks to @Minivation 's excellent and informative post I was reasonably well-armed to take a crack at it.  My stall horn had gotten intermittent, and initially seemed fixed after replacing the Sonalert, but then got intermittent again.   Fiddling with the vane made it pretty obvious that this time it was the switch.

In my opinion the only things that were difficult were getting it in and out (ARG!!) and getting the switch halves separated.   Thanks to the supplied and very clear diagram in the original post in this thread, I figured I'd take a crack at just driving the retaining pins in with a pin punch from a watch repair kit.   That worked reasonably well, but did break one of the retaining bosses on the lid, which I repaired with cyanoacrylate (super glue) as well.   Once the pins were through it pretty much fell into two pieces without any more effort. 

Two of the pins I recovered for re-use, but one drove way into the lid and wasn't accessible or removable.    That one I drove a bit further in so that it'd create a recess for a new pin.   The existing pins are 0.040", so I made a new one out of a tiny chunk of 0.041" steel safety wire, and that worked well.

I think in my case the intermittence was caused by a bunch of corrosion in the screw socket in the common connection, so it's possible that I didn't even need to really take it apart.    As difficult as it is to get in and out, I didn't want to take a chance on having to do it again, so disassembled it just to get some contact cleaner in there and inspect it.   It was very clean inside, but I soaked with contact cleaner, anyway.

Having a watch repair kit around was good for the small pin punches to remove the vane pivot pin as well as driving the retaining pines through and back in.   I also have a small work vice that was handy for pressing the pivot pin back in.   I don't think it was really necessary to remove that other than for thorough cleaning, etc.

The most difficult part of the whole process is getting it back in and fastened.   I have long, reasonably skinny arms, but it was still a total b!tch to reach in there to hold the self-locking nuts while tightening the screws from the outside.   Since you have to do it by feel I'm not sure a second set of hands would really help unless you really work together well.      I put some tape around the rim of the access hole to keep from scraping more skin off than necessary, but it was still very unfun.  The top screw can be reached with a long extension from the access panel, which is how I got it out, but it's still not easy.    For the bottom fastener removal I punted and drilled the head off the old screw.   That's definitely the way to get that job done in my estimation. 

Anyway, just a long post to add a little bit more info to potentially make it easier for the next guy, and to verify that disassembly isn't that bad if one needs to be repaired.   Totally do-able.

[carusoam]

Great details shared, Eric!

Best regards,

-a-

[Will.iam]

On 7/25/2021 at 8:12 PM, EricJ said:

It was my turn in the barrel to take a swing at this, and thanks to @Minivation 's excellent and informative post I was reasonably well-armed to take a crack at it.  My stall horn had gotten intermittent, and initially seemed fixed after replacing the Sonalert, but then got intermittent again.   Fiddling with the vane made it pretty obvious that this time it was the switch.

In my opinion the only things that were difficult were getting it in and out (ARG!!) and getting the switch halves separated.   Thanks to the supplied and very clear diagram in the original post in this thread, I figured I'd take a crack at just driving the retaining pins in with a pin punch from a watch repair kit.   That worked reasonably well, but did break one of the retaining bosses on the lid, which I repaired with cyanoacrylate (super glue) as well.   Once the pins were through it pretty much fell into two pieces without any more effort. 

Two of the pins I recovered for re-use, but one drove way into the lid and wasn't accessible or removable.    That one I drove a bit further in so that it'd create a recess for a new pin.   The existing pins are 0.040", so I made a new one out of a tiny chunk of 0.041" steel safety wire, and that worked well.

I think in my case the intermittence was caused by a bunch of corrosion in the screw socket in the common connection, so it's possible that I didn't even need to really take it apart.    As difficult as it is to get in and out, I didn't want to take a chance on having to do it again, so disassembled it just to get some contact cleaner in there and inspect it.   It was very clean inside, but I soaked with contact cleaner, anyway.

Having a watch repair kit around was good for the small pin punches to remove the vane pivot pin as well as driving the retaining pines through and back in.   I also have a small work vice that was handy for pressing the pivot pin back in.   I don't think it was really necessary to remove that other than for thorough cleaning, etc.

The most difficult part of the whole process is getting it back in and fastened.   I have long, reasonably skinny arms, but it was still a total b!tch to reach in there to hold the self-locking nuts while tightening the screws from the outside.   Since you have to do it by feel I'm not sure a second set of hands would really help unless you really work together well.      I put some tape around the rim of the access hole to keep from scraping more skin off than necessary, but it was still very unfun.  The top screw can be reached with a long extension from the access panel, which is how I got it out, but it's still not easy.    For the bottom fastener removal I punted and drilled the head off the old screw.   That's definitely the way to get that job done in my estimation. 

Anyway, just a long post to add a little bit more info to potentially make it easier for the next guy, and to verify that disassembly isn't that bad if one needs to be repaired.   Totally do-able.

Chock me up as the next one in the barrel to have to do this procedure I also want to thank both @Minivation and @Eric J for their details on disassembly. One thing i will point out to whom ever the next person is to tackle this project on, use a voltmeter to test the resistance on the switch terminals every step of the way as it saved me from having to disassemble the block switch box that both minivation and eric broke and had to superglue the pieces back together. I laughed when they said watch out for the plunger as it could fall out.  my plunger this was not the case. In fact mine was so gummed up from dirt and grim i even think i pulled out a blade of grass stuck around the plunger that i had to use tweezers to get the plunger out. I was reading 1.5 - 0.5 ohms at the beginning but after getting all the junk off the plunger and trying it again i was getting 0.5- 0.2 ohms. I then read about how eric had trouble with one of the 3 pins holding the case on and i decided to just squirt (flush) deoxit down the plunger hole for a good 5 seconds. I then put the plunger back in and low and behold i got 0.0 ohms. As much as i wanted to check out the internal guts i didn’t want to risk cracking the case and i was getting great continuity so i put it all back together and it works like a new switch! very sensitive from the moment the switch starts up and gets louder until it’s blaring at 7/8 travel. The last 1/8 to the top is no change. Since i took a sharpie marker and marked the stall plate before i took it off the wing i knew exactly where to put it back and tighten down. I went out and test flew it today and it works better than when i got the plane. Now i get a faint sound at 67 or so that grows louder until full blast at 63 the plane buffeted at 61 and nose dropped at 60. I was happy with that. Special thanks for the watch repair kit tip from eric. It made getting the pin out of the switch vane very easy as well as pushing out the rivets after i ground off the heads. We will see how long this cleanup lasts since I didn’t open up the actual switch to clean it but if it goes more than three years I’ll just do that again as it only took me an hour to do and i was triple checking my work and having to drill out rivets which i replaced with screws and nuts so should be way faster to clean in the future. My A/P was impressed it worked so well he asked if i wanted a part time job to help him with other planes. 

[EricJ]

Nicely done!   It's definitely better if you can rehab it without splitting the halves apart, so I'm glad that worked for you.

[carusoam]

Great pics Will.i 

-a-

[Will.iam]

2 hours ago, EricJ said:

Nicely done!   It's definitely better if you can rehab it without splitting the halves apart, so I'm glad that worked for you.

Yea we will see how long mine last compared to yours. I’m hoping future pilots stuck in this situation will be able to avoid splitting the halves too. When you avoid that the hardest part is getting the rivets out of the case and mounts. Looking back now that i have done it i could have skipped drilling out the rivets to the mount and just did the switch box rivets. At yhe time i didn’t realize the whole base came out of the mount box but it would have been more tricky to file off the rivet heads with the curved wing bracket still attached to the mount. 

[Evelyn Craik]

I have enjoyed the conversation as I also have the lift detector blues.  Someone mentioned that Mooney came out with a replacement.  I have a 1966 M20e Super 21.  The part no is C-46001 if anyone knows if I can replace it.

[Will.iam]

Just to give y’all an update that my lift stall detector is still working buttery smooth like new and very clean loud signal from the stall horn. 

[DCarlton]

My stall warning horn just stuck after my F sat on the ground in the AZ for month getting repaired.  Spent a couple of unplanned hours in the sun Sunday trying to get silenced.  Got it silenced and made the 2.5 hr flight home.  No idea if it's working correctly yet; need to go do a few stalls and check "calibration".  

Has anyone identified a new replacement solution at a reasonable price?  My part manual shows C-46001 too.  I had hoped to just replace it since it's used across several platforms; then found this thread.  

If you spray DEOXIT contact cleaner directly into the vane area under the vane, any idea if it will it reach the switch contacts?  Not exactly sure what Will.Iam meant by spraying cleaner down into the "plunger hole" above.  

Another helpful MS thread.  Thanks.  

[EricJ]

1 hour ago, DCarlton said:

My stall warning horn just stuck after my F sat on the ground in the AZ for month getting repaired.  Spent a couple of unplanned hours in the sun Sunday trying to get silenced.  Got it silenced and made the 2.5 hr flight home.  No idea if it's working correctly yet; need to go do a few stalls and check "calibration".  

Has anyone identified a new replacement solution at a reasonable price?  My part manual shows C-46001 too.  I had hoped to just replace it since it's used across several platforms; then found this thread.  

If you spray DEOXIT contact cleaner directly into the vane area under the vane, any idea if it will it reach the switch contacts?  Not exactly sure what Will.Iam meant by spraying cleaner down into the "plunger hole" above.  

Another helpful MS thread.  Thanks.  

I don't think it'd hurt and it might help, so probably worth a shot.

[DCarlton]

31 minutes ago, bluehighwayflyer said:

Cleaning is definitely worth a shot.  There is a Mooney kit for a relatively affordable replacement, but availability these days is highly questionable. Good used replacement C-46001s are also occasionally available even cheaper.  That is the direction I took when I had the same problem a year or so ago.  My original C-46001 had become intermittent since having the plane repainted. I tried cleaning it but that didn’t work for me.
 

Access is an absolute bear.  My elbow would barely fit in the access panel.   If yours won’t you’ll have to find someone else with skinnier and preferably longer arms to do the job for you.  This job was a no BS test of my patience, but it was ultimately very satisfying to successfully accomplish. 

Yeah a mechanic and I removed it, and reinstalled it, twice on Sunday on a hot ramp to get it working enough to get me home without the horn screaming. Definitely easier with two people.    

[Pinecone]

Maxwell has a quick fix when it goes constant on. It seems the vane gets bent by someone refueling.

Contact them for exact info.  It has to do with pulling on the vane with pliers while bending it slightly.  They did mine in a couple of minutes at Mooney Max. 

[Will.iam]

On 10/23/2023 at 7:21 PM, DCarlton said:

My stall warning horn just stuck after my F sat on the ground in the AZ for month getting repaired.  Spent a couple of unplanned hours in the sun Sunday trying to get silenced.  Got it silenced and made the 2.5 hr flight home.  No idea if it's working correctly yet; need to go do a few stalls and check "calibration".  

Has anyone identified a new replacement solution at a reasonable price?  My part manual shows C-46001 too.  I had hoped to just replace it since it's used across several platforms; then found this thread.  

If you spray DEOXIT contact cleaner directly into the vane area under the vane, any idea if it will it reach the switch contacts?  Not exactly sure what Will.Iam meant by spraying cleaner down into the "plunger hole" above.  

Another helpful MS thread.  Thanks.  

You can’t see the plunger hole until you take the outer case apart and remove the vane that pushes on the plunger down to activate the micro switch inside. You are definitely going to have to take the unit out of the wing to get at it. No way to clean or even get cleaner down that hole without opening up the case. It is after all designed to withstand the elements.