Stall horn and annunciator malfunction

[mike_elliott]

On 8/9/2020 at 3:24 PM, Schllc said:

Plane is a acclaim ultra, but the little tab on the leading edge of the left wing is the same device that is on every mooney I have ever seen so I am hoping someone else here has experienced this. 
I took off today in fairly scattered weather and at about 1000 ft agl the Avionic warning voice started to say stall repeatedly, and the stall horn was blaring. 
my air speed was good and all functions were normal, and I was entering imc so I just asked act to level off so I could run through the systems and make sure all was ok. 
long story short we went back into vmc shortly after and I confirmed it was just a malfunction. 
I continued to my destination, landed, jiggled the little tab and it stopped the horn and annunciator.
i took off and flew it again without issue. 
has anyone else ever had this happen?

its baffling because the air pressure required to push the tab back is minimal. 

Sometimes line guys when fueling the pilot's side tank will accidentally lean up against the stall vane and tweak it some, causing it to catch randomly in its travel. Not good if it happens, but I believe can be fixed without the big $ thrown at the problem. Owners never do this of course.

[PT20J]

The stall warning is not listed in the M20V AFM as a G1000 annunciation and the description in section VII  seems to imply that it is a separate system which I believe certification would require. But, I defer to @mike_elliott or @donkaye who are much more familiar with later models. To really understand it you would need to dig into your Service and Maintenance Manual and the detailed schematics therein. The electrical diagrams in the POH are merely representational. 

However, it’s always best when troubleshooting to eliminate the simple stuff, and the  stall warning vane/switch is pretty simple. Here’s what I would do:

1. With master off, move the vane by hand and check that it is free to move and there is no resistance. When released it should freely fall back all the way down. 

2. With master on,  check that the stall warning sounds when the vane is lifted and that it stops when the vane is lowered.

3. Fly it and verify operation. If you encounter further problems, it must either be a short or a bad switch. Disconnect the switch to eliminate that possibility.

Skip  

 

[kortopates]

1 hour ago, PT20J said:

To really understand it you would need to dig into your Service and Maintenance Manual and the detailed schematics therein.

........

The electrical diagrams in the POH are merely representational. 

Absolutely right on both counts. The POH only give an overview of the operation of the system. The OP, or anyone attempting to troubleshoot something on their airframe, really needs the service manual with the real schematics. 

[Schllc]

1 hour ago, PT20J said:

The stall warning is not listed in the M20V AFM as a G1000 annunciation and the description in section VII  seems to imply that it is a separate system which I believe certification would require. But, I defer to @mike_elliott or @donkaye who are much more familiar with later models. To really understand it you would need to dig into your Service and Maintenance Manual and the detailed schematics therein. The electrical diagrams in the POH are merely representational. 

However, it’s always best when troubleshooting to eliminate the simple stuff, and the  stall warning vane/switch is pretty simple. Here’s what I would do:

1. With master off, move the vane by hand and check that it is free to move and there is no resistance. When released it should freely fall back all the way down. 

2. With master on,  check that the stall warning sounds when the vane is lifted and that it stops when the vane is lowered.

3. Fly it and verify operation. If you encounter further problems, it must either be a short or a bad switch. Disconnect the switch to eliminate that possibility.

Skip  

Exactly what I did the day it happened and no more malfunctions on the next leg home. 
Given how it is designed to operate, and the normal function on the ground it is vexing as to how it happened mid flight. 
I guess I’ll just have to wait and see...

[Aspen2013]

Schlc,

I have  a thread that describes the same thing you are experiencing. Wish I would have seen this sooner. There are pictures on there as well. I have Acclaim Type S with G1000. I am sure you have a Safe flight lift detector. If you call them they have a technical department. But they told me that the switches do go bad. There is nothing you can do except send it to them for an "overhaul". You really get a new switch but for a cheaper price. It was tricky to get out. They have it zip tied a couple times. I had to pull the switch forward as much as possible and use an exact-o knife to cut the zip ties. then with some long tweezers or (long needle nose maybe)  grab a hold of the zip tie and pull it out the hole. there is now plenty of excess length to get the switch unplugged. Poor design. There is no panel under the wing to remove that accesses that area. So the only way to get at it was through the hole on leading edge. if zip tie falls inside the wing it may not be retrievable but i don't think a problem.  I did not put the zip ties back on!!!!  I found the switch needs to be pretty much mounted in the full down position and the screws just snug. The switch base plate does not match contour of the wing.

[carusoam]

@Schllc

Aspen above may have an interesting idea of what may be happening for your particular stall vane...

For planes with a FIKI system.... they get the heated stall vane to go with it....

There are a few examples and pics of various heated vanes... that are losing their heater that is affixed to the vane itself...

If the heater part on the vane comes unglued.... it may be causing an oddity to its behavior...

Have a look at your stall vane to see how much of the heater is still left on it...
 

Aspen’s pic shows one in good condition... some show just a stainless blade left behind... others are missing part of the heater and may have some threads flopping about...
 

Got any pics of yours?

PP thoughts only, not a mechanic...

Best regards,

-a-