Author Topic: Stall Warning System Question (Read 861 times)

Ralph Portnoy · « **on:** November 30, 2009, 12:06:31 PM »

Hi, I was doing a stall series the other day and my stall warning horn didn't go off prior to wing rock and nose drop and effectively provided no warning of impending stall. It chirped once but it happened just as the nose was breaking. Repeated a couple times and same effect. On deck, the stall warning horn checks fine when the tab is lifted to the stop. It works every time on the ground and I can't get it to not work so don't think there is a wiring or actuator problem. One more piece of data, I had the plane painted and prior to the painting the system worked just fine. So, could it be possible the paint shop installed it improperly and is this something I can adjust? Could it be installed backwards? Or upside down? The tab actuates the horn when when you lift it up and it springs to the down position and turns the horn off. Before I ask someone to bend the tab is there something I could be missing? Thanks for the help.

Mike Bland · « **Reply #1 on:** November 30, 2009, 03:14:49 PM »

Ralph,

Since it works when you lift the tab on the ground and it works in the air but just comes on too late, I would think it is just out of adjustment. Don't bend anything. You have to loosen the screws that hold the vane assembly to the mounting plate, raise the vane assembly slightly and retighten the screws. I can't remember if you have to remove the mounting plate from the wing. There are 4 screws that hold the mounting plate to the wing. Be careful and don't force anything. These things are super expensive. You kind of have to do it by trial & error (adjust-fly-adjust-fly) until it comes on about 6 to 8 knots above the stall speed.

Mike Bland

Bob Andrews · « **Reply #2 on:** December 01, 2009, 07:45:51 AM »

That's good advice from Mike, DON'T BEND ANYTHING. On most stall vane switches there are six screws. The four corner screws hold the unit to the wing and the two center screws may be looosened to move the vane. A 1/4" movement of the vane will change the stall warning by about five MPH of indicated airspeed and the only way to test the accuracy of your setting is to fly the airplane. Moving the vane UP will cause the stall warming to come on EARLIER.

The stall should be made with the gear and flaps up, power off and a deceleration rate of about one mph per second. Ideally, the stall warning should be set to actuate at 5-7 mph prior to a complete stall.

Take someone with you to help look for traffic during all this precision, head in the cockpit flying and carry an extra burp bag.

Bob Andrews

ABS Tech

Ralph Portnoy · « **Reply #3 on:** December 01, 2009, 11:14:16 AM »

Thanks Mike and Bob. I appreciate the advice and I'll make the adjustments this weekend. I'm glad I didn't bend it. Take care.

Ralph

Tom Nelson · « **Reply #4 on:** December 01, 2009, 03:50:46 PM »

Just wondering did they paint the tab?

Ralph Portnoy · « **Reply #5 on:** December 03, 2009, 12:21:55 PM »

Tom,

No the tab itself was not painted. I'm not sure if it was removed and reinstalled prior to paint. I'm not sure why the adjustment is necessary now but hopefully this weekend I'll get it back to where it belongs. Take care.

Ralph