Stall Warner adjustment

[Steevo]

Hi All,

I just wondered if there was any adjustment procedure for the stall warner on a UL-450. I have just taken a new hangar but the only downside is that the farm strip has a very short 370m runway. Now testing it out with my aircraft does not seem to be a problem. I have tried it at MAUW and I can land with quite a bit of runway spare and taking off is even quicker.

The art is obviously to get the approach speed right. At my previous airfield I had a 1000m runway but the aircraft was stored outside and I could easily come in at 60kts, float along the runway a bit and do a gentle touch down.

Coming in slower at my new airfield is not a problem but at about 57kts, the stall warner starts to go off so instinct says to push the nose down a bit. At full flap, the book says that my aircraft stalls around 35kts and trying it in the air, that figure seems to be about right so there is no reason that the stall warner needs to go off 22kts above that speed. I have an EFIS and an analogue ASI and they both agree on the speed so even allowing for a small error in the airspeed reading, this is still way above the stall speed.

I am not sure about other Jabs, but mine seems to have a 2-tone stall warner. It first comes on as a low pitch sound and then goes high pitch when you get very close to the stall (about 5kts or so above). I could just ignore it, but it gets extremely annoying and worrying when it goes off.

Ideally, I would like to come in at about 55kts then maybe move to 50kts just before flare.

I just wondered if there was any adjustment method for the stall warner.

[Garyo]

Steve, the plate on the LH side wing leading edge adjusts the point at which the warner will sound, its in the manual somewhere. this should of been checked and adjusted at permit test flight as I think it is on the list of checks

I use the squeaky bit out of a dog toy in mine, works great, not had to adjust the plate though, mine starts a quiet squeak at about 45 knots then gets louder as the speed drops off. only way to test is to go up and do some stalls, then re adjust when you land

[Steevo]

When I last did the permit, I just wrote down the speeds I got and the LAA accepted it. It's not really been a problem until now as I have always approached my home airfield at about 60kts (sometimes even a little bit quicker). Even then in gusts, I have had the stall warner beep a couple of times.

The stall horn is behind the flap handle. It seems to work ok but just goes off a bit early. Obviously, a warning that goes off too early is a bit pointless as once you start to ignore it, then the one time it goes of for real it could be dangerous.

I did notice there is a very small tab on the plate on the leading edge of the left hand wing. I assume that if I bend it down a little bit the AOA will have to be slightly higher before it sounds. Ideally, it should be about 10kts less than it is at the moment. It is a very tiny flap though.

[Garyo]

yep that's the tab that needs adjusting, if I think on next time im at the field (later
this week for an evening flight) I will take a picture of mine at the angle it is at, if it differs a lot from yours, bend yours in the direction same as mine
G

[diablo]

Here are the instructions for fitting and calibrating the stall warning system. The recommendation is that the tab is trimmed for correct speed.

http://sydney.edu.au/engineering/aeromech/AERO1400/Jabiru_Construction/Manuals/J160/Construction%20Manual/WINGS%20FLAPS%20AND%20AILERONS/Fit%20Stall%20Warning%20to%20wing.PDF

Info can be found in build manual as well...

[dcnfsr]

sorry to jump on this thread, but I have a related qus: where is best place to get a stall warning horn/reed?

(I see a dog toy was referenced!)

looking, I find: CESS STALL HORN REED S2488-1 - http://www.aircraftspruce.eu/cess-stall-horn-reed-s2488-1.htm with the cheapest delivery option making 10euros total.

[Garyo]

that is the same fitting that's in a dog toy, think mine has been in now 3 years. pack of 3 toys from the £1 shop..

[dcnfsr]

thanks garyo. picked one up - unfortunately looks like inflation has run rampant since you got yours, only 1x for £1 now!

[Garyo]

Ah, 99p shop