Intermittent Stall Warning

[chrisk]

My plane has recently developed a problem with the stall warning horn.  It is intermittent when in a stall condition.   Basically, it seems to randomly sound during a pre-flight when the stall vane is lifted.  When the horn does not sound, I can hear a faint click.  Just curious if anyone else has had this problem.  

 

My mechanic seems to think it is a loose ground on the stall vane.  I guess I should find out some time this week.

[DrBill]

The 75 F model at my airport recently had this problem and after measuring the voltage at the sound device it was clear that the device was defective.   Proper voltage was there but no sound.

That happened after they took out the switch ( a LOT of work) and it checked out OK.  The stall horn is easier to get at and check.

BILL

[larryb]

I just answered the same question, but for an autopilot beep.... The sonalert is likely bad. Nice that they are cheap. http://www.alliedelec.com/search/productdetail.aspx?SKU=70186814 The gear warning one is sc628p and stall/autopilot beep is sc628. I replaced all of mine this year when the autopilot no longer beeped. They do age and become intermittent.

[chrisk]

I'll definately order a new stall horn and get that installed first.

[bnicolette]

Ive been having the same issue. Ive tried cleaning and tightening the ground at the stall switch but that didn't help. Im going to order the Sonalert also as its certainly a cheaper try than the switch. Does anybody have a good source for the switch in the event the Sonalert isn't the problem?

[KSMooniac]

Try spraying some electrical contact cleaner into the switch assy from the front and back (ie inside the wing) and exercising the switch a bunch of times before you go replacing the sonalert.

[bnicolette]

Try spraying some electrical contact cleaner into the switch assy from the front and back (ie inside the wing) and exercising the switch a bunch of times before you go replacing the sonalert.

 

I did try that Scott and my intermittent problem is still there.  However, it is hard to get to the inside (back) of that sucker.  I did douse it fairly good with a long spray straw and then worked the switch for quite a while.

[Bill_Pyles]

I had a similar issue on my J.  At pre-flight the stall warning horn would just stay on.  The fix was to enlarge the aperture through which the tab protrudes so the switch can fully open (tab goes down).  Somehow in the 34 years of the airplane's life, the stall switch location must have moved relative to the aperture in the leading edge of the wing.  Atlantic at KDVT fixed it for me.

[chrisk]

For the last few flights the stall warning horn has worked during pre-flight and when landing.   I will probably install a new sonalert when the plane comes up for annual, provided it continues to work.  If not, the new sonalert is already at the hanger.

[KSMooniac]

I had a similar issue on my J.  At pre-flight the stall warning horn would just stay on.  The fix was to enlarge the aperture through which the tab protrudes so the switch can fully open (tab goes down).  Somehow in the 34 years of the airplane's life, the stall switch location must have moved relative to the aperture in the leading edge of the wing.  Atlantic at KDVT fixed it for me.

 

If that happened, then your stall vane is no longer in the correct position!  You should've restored it to the proper location instead of enlarging the cutout.

[KSMooniac]

I did try that Scott and my intermittent problem is still there.  However, it is hard to get to the inside (back) of that sucker.  I did douse it fairly good with a long spray straw and then worked the switch for quite a while.

 

You have to access the back of it thru the bottom of the wing, and yes, it is difficult.  Doing so fixed my problem.

[bnicolette]

Update: I did replace the sonalert and my horn is working consistently now. Thank goodness it wasn't in the stall switch.

[chrisk]

The sonalert was also replaced in my plane too.  Since then the stall horn has be working, so it seems to have fixed the problem.