My electric stall horn doesn't work during power-on stalls. It does work during my pre-flight (when I physically lift the metal tab, the alarm sounds) and I think (but need to confirm on my next flight) that it still works during power-off stalls, however during a power-on stall, the alarm doesn't sound.
It seems to me that the metal tab may be bent at an angle where it just isn't 'catching' during pwr-on stalls- and so I wonder whether I should be looking at having an AI bend the tab to be sure the angle is w/in specs - or whether the tab needs to be replaced?
I would not bend the tab, if you look closely this switch is adjustable via mounting slots. You do not want to take the chance by bending the tab as these switches are VERY expensive....
Most likely the contacts are corroded at the switch. If you spray contact cleaner inside the switch while moving the lever back and forth....sometimes that brings them back to life.
Otherwise you are looking at several hundred dollars for a new switch.
Yeah, it is probably not the switch contacts. The switch body should be adjustable within the mount, not by bending the tab, but by sliding the assembly up and down.
You might consider moving the switch assembly slightly up, so that the tab will see more of the flow separation at stall. When the stall occurs the boundary layer flow reverses and pulls the tab up.
I agree with that Rich says re adjustment. Re the explanation, what is going on is that as you increase angle of attack, the stangation line (the line along which no airflow occurs) along the leading edge moves downwards and backwards, causing the vane of the detector to be pushed up by a flow that is now going over the top of the wing. Note that the wing doesn't have to stall to create this effect: it's just a function of AoA, so the vane can be adjusted so that warning occurs at any AoA, the correct option being sufficiently before the stall begins. Moving the vane upwards means that the stagnation line will cross the vane at a lower AoA, and therefore further before the stall.
