Stall Horn

[aerobat95]

So I am trying to figure out why my stall horn is not working. I tried opening up the access panel behind it but my question for you is this. How does one reach the stall horn? I cannot get my hand/arm in there far enough. I also bought some contact cleaner and was wondering what you though of this. If this part needs to be replaced how much is the part and how big of a job is it? Is the stall switch a Mooney specific part? Finally in this picture I am assuming that the black circular things are the gear horn and stall horn??

[aerobat95]

Why can I not upload any pictures?? I tried putting one here in this thread and one in my gallery.....just comes back with an error??? Is there some sort of trick?

[laytonl]

In my J model the gear warning horn and the stall warning horn are mounted in the headliner. The most common problem with the stall warning is the horn. The easiest way to check this is to tape the stall warning in the "stall" position and then check to see you have voltage at the horn. If so, then it is the buzzer that is defective, which is the most likely problem. The buzzer is a common item and can be found at Mouser and other electronic parts outlets. Lee

[aerobat95]

I did take a volt meter and saw no voltage at the stall horn in the headliner. I am assuming that the two black circular plastic pieces are the gear and stall horns. I would upload a photo but the site is not allowing it. I am thinking that there is some sort of problem at the stall warning switch. I tried to get my hand into that area today but to no avail. Honestly I am not sure how anyone could get their hand all the way to the leading edge to get to the horn. Tomorrow I am going to try some contact cleaner and some compressed air and hope that takes care of the problem.

[mike28w]

About 5 years ago, I had a similar problem..... I sprayed some electronic contact cleaner ( Radio Shack , I think) on it. I sprayed it from the outside and inside. (I have small arms and hands and can reach inside.) I worked the stall vane up and down a bunch and then sprayed on more cleaner. Did this a couple of times and have had no more problems for at least 5 years....

If I couldn't reach inside, I find a youngster or wife or girlfriend , and bribe him/her to help out !! Jmo, Mike

[takair]

If it is like the E model (I think it is) and you don't have voltage at the horn, then you either have a bad circuit breaker or broken power wire. The stall vane only applies a ground to the ground side of the horn, not power. If you have power on one side of the horn, but don't get a ground when the vane is activated, then you may have a switch problem. You can try contact cleaner and flicking the vane a few times, that seems to help sometimes. You may also have a bad ground out at the vane. As you suggested, it is hard to get to. You almost need another elbow on your arm. I have had both the vane and ground at the vane give me problems.

To get pictures to post, you have to shrink them significantly. I used Paint, and cut the resolution. I'm sure there are more user friendly ways with the right software.

[aerobat95]

Well spent some time out at the hangar today to troubleshoot some more. So I can kinda get my arm up in there (so to speak). The two screws at the leading edge that hold the thing in place have a nut on the inside of the wing (sucks). There are two screws on the switch itself. One appears to be power. The other is definately a ground that attaches to one of the screws that hold the whole assembly to the wing. There appears to be some corrosion on that nut. There are also two rivets that hold the actual switch to the plate that attaches to the wing. So later on today I am going to see if my wife can get her arm better in there. If not I think the only way to get that switch out would be to drill the two rivets out and then remove the switch. If I were to do that (with A&P supervision of course) then accessing the screws and nuts would be somewhat easier. What do you guys think?

[aerobat95]

So this item is required for flight but according to my POH during the preflight step 6 says Pitot tube and stall vane switch--unobstructed

Seems like you would never know if the thing is operable unless you have an approach to stall condition or at annual......kinda crazy seeing as how its required for flight.

[yvesg]

I periodically check the stall warning on a pre-flight by:

Turn the master switch on.

Go outside and push the vane up manually, expect the stall horn to howler.

Run back inside turn off the master swtch.

Yves

C-FQKM

[takair]

As I recall, you don't want to drill the rivets. That is part of the switch assembly. After the first time I removed the switch, I made a backing plate with nut plates and ground all inclusive. Now it is an easy one person job. If you are getting power on one side of the switch, then there must be power at the horn.

I usually cycle the stall vane numerous times every few flights. This seems to keep it working. I think the fact that it is rarely operational in flight causes some oxidation/corrosion on the contacts. Most switches are designed to be self cleaning. However, they rely on rated current going through them at some interval. I'm sure there are many folks flying around with an inop stall warning system, as we speak.

[Hank]

So this item is required for flight but according to my POH during the preflight step 6 says Pitot tube and stall vane switch--unobstructed

Seems like you would never know if the thing is operable unless you have an approach

to stall condition or at annual......kinda crazy seeing as how its required for flight.

My stall horn sounds once every landing. Doesn't yours? Flare, buzz, chirp, chirp.

[Jerry 5TJ]

Another problem in vintage Mooneys arises with use of ANR headsets. My Bose headset does a fine job of suppressing the stall warning tone. I prop one earcup half off as part of my downwind check so I can hear it. Next time I upgrade avionics I will try to route the stall and landing gear warning tones and the audio from the Aera 510 ('warning, terrain") into the intercom.

[DrBill]

_{Had same problem with my Beech. The plunger in the switch was stuck with some VERY fine dust/dirt. After replacing the swirtch, I did failure analysis on the old one. Found that the plunger was stuck "in". Disassembled the switch enough to pull the plunger out and with it came a bunch of fine dust/dirt. "Lubed" it up with some silicone grease and re-assembled. Worked like new.}

_Bill

[skyking]

I just paid $650 to replace my stall warning.

$400 bucks for the part and $250 in labour.

The good news is that it is not a Mooney specific part. My mechanic had one in stock.

[Stefanovm]

My problem is the opposite and may only require an adjustment. My horn comes on 20 kts above an actual stall. It tends to keep me fast on approach, not good in a Mooney for book landing lengths.

[N201MKTurbo]

I've had good luck taking the switch out and washing it in the parts washer, then test it with an OHM meter while actuating it until it starts working, then drying it off with compressed air. Both of my Mooneys have had this problem at one time and I was able to get it working again in both instances.

The switch lives in a pretty harsh place and can easly get full of crud. Giving it a shot of triflow from the wing side at every annual would probably be a good idea.

[Marauder]

I have the complete manual set for our vintage Mooneys. Here is what I found under the stall warning system (hope it helps track down parts if you need to):

[dcastor]

My stall warning horn is showing a different problem...comes on with master and doesn't turn off unless I pull the circuit breaker or turn off the master. It seems like a basic switch, does anyone know what the internals look like?

[jimluper]

Maybe someone can help me with my stall warning problem.

 

On takeoff (using V-R of 75 MPH) it buzzes until I am over 90 mile an hour. Not constant but on and off. It is clearly out of adjustment. I have looked it over and it does not seem bent incorrectly or anything. It also moves nicely.

 

On landing, it goes off but I don't pay too much attention as by then I am over the runway and waiting for speed to bled off for touchdown.