Stall horn on my Jab sounding all the time

[G-OMER]

Hi, when I bought my Jab 450ul, the stall warning horn was under the seat in the storage area un connected. I fitted it up behind the flap plate and plugged it in. the following week when I flew I had this odd noise all the time then realised it wass the horn, so I unplugged it.

 

My question is what IAS should it sound at, what pressure would this bee if connecting a compressor to it and how do you tweak them to only sound at this pressure

 

Cheers

 

Gary

 

 

[old man emu]

The thing that makes the noise is just like a clarinet reed, but it is made from palstic in a plastic surround. I'd suggest that the one you found in your plane is broken. You could try to replace it with the noise maker from a party toy. You know the ones, they are a coiled paper tube and when yoou blow on them, the tube fills with air and unrolls.

 

Failing that, just get a replacement. I've got a couple on hand and postage would be at normal letter rate.

 

Anyway, aren't you frozen in at the moment?

 

OME

 

 

[Ultralights]

it should work at a set Angle of Attack, not airspeed. and that will be dictated by the small vent in the wing leading edge.

 

 

[old man emu]

I had a thought ...

 

Perhaps someone has had the squeaker out at some time and put it back in rrrs-about. Try taking it out and putting it in the opposite way.

 

OME

 

 

[jetjr]

Assuming its not broken or back the front, theres a small tab on the leading edge of the wing which you bend up or down to vary stall warning speed

 

You can just gently suck on the hole in the wing tip to test its working, it should come on suddenly and loudly.

 

Id suggest the stall warning should come on as you approach stall speed? ~ 45-50kts?

 

In the construction manuals on the Jabiru site is how to install and set it up.......somewhere

 

 

[J170 Owner]

Hi, when I bought my Jab 450ul, the stall warning horn was under the seat in the storage area un connected. I fitted it up behind the flap plate and plugged it in. the following week when I flew I had this odd noise all the time then realised it wass the horn, so I unplugged it.My question is what IAS should it sound at, what pressure would this bee if connecting a compressor to it and how do you tweak them to only sound at this pressure

Cheers

 

Gary

The answer to your first question is in the POH. My stall horn sounds when I gently suck (not blow) through the vent on the leading edge of my wing. (J170).

 

P.S. Don't get caught sucking the wing as people may not understand:bounce:

 

 

[G-OMER]

it was a little chilly yesterday, took off in -6, its due to warm up a bit this week, today its warmer but covered in mist so will sit it out n wait. I will look at the plate on the leading edge to see if it needs a tweak down a bit then. as it was sounding on climb out 70+ knots.

 

if I suck the horn it sounds so the horn is working, must be adjustement req'd by the plate.

 

could do with a better heater in the jab as the 1 fitted is usless, no heat at all

 

 

[G-OMER]

I re fitted the warner, adjusted the plate under the wing intake down a bit and went flying today. the horn started sounding at 85 knots again. i unplugged the horn and air was blowing out the pipe not sucking in? so what is the next move?

 

Cheers

 

Gary

 

 

[eightyknots]

Does this stall horn indicate wing stall or Jabiru engine stall?

 

 

[Jaba-who]

OK Back to some reality. Easy enough to work out the problem with some thought and background of how it should function.

 

Superficially this sounds like the reed is in backwards. But generally you can't install it backwards because it is enclosed in a plastic flute that precludes this. But maybe the reed has come out of the flute at some point and someone has just pushed it back in but backwards. (Bit of trivia for you - where did Rod Stiff get the noise making device for the original stall warning? Answer: From the squeaker out of a rubber duck's bum! :-)

 

The Squeaker works by SUCKing air through it from cabin to wing. When the wing is at flying angle the air flow/pressure tries to flow into the Stall warning inlet but can't. The entire stall warning device is very simple: - a hole in the wing leading edge, a small angled plate set up with a lip angled forward and down under the hole, a funnel /connector joining the inlet to to a length of hose (going into the cabin) and a reed device enclosed in a small plastic funnel.

 

When air tries to blow INTO the wing inlet the one way reed blocks shut (no airflow, no noise) When stall is imminent the inlet plate disrupts the flow of air causing a negative pressure at the inlet and it SUCKs air from the cabin out to the leading edge through the reed and it squeaks.

 

Nothing very technical so far.

 

The technical bit is the angle of the plate must correlate with the Angle of Attack you want to achieve so the air flow gets disrupted and the stall warning comes on.

 

So first thing to check is that the sqeaker is in the correct orientation or that it isn't cracked or split.

 

Install the sqeaker as you have it then suck and blow gently into the wing inlet. If it squeaks on blowing and won't let you suck - It's in backwards

 

If it Squeaks on both blowing and sucking - the reed is broken and needs replacing

 

If it sqeaks on suck but not on (gentle) blow then the reed is OK.

 

Next- check the tubing for leaks - just in case what you are hearing is a leak through a split in something other than the reed. Take off the reed and clamp/tape up the tubing inside the cabin to ensure a seal. Then go to wing and blow and suck into inlet. If you still hear squeeking there is a split in the tubing and it's making some whistling which has tricked you. Bad news is that getting tubing out to replace is a fairly tricky task.

 

Assuming tubing is OK that only leaves the inplate angle.

 

Get the manual to check the angles and start carefully adjusting it.

 

(But I'll put my money on a reversed or damaged reed.)

 

Jaba

 

 

[fatmal]

What happens when you actually stall? Does the stall warning stop?

 

If it does, then (as suggested above) the reed is likely in backwards.

 

 

[G-OMER]

I think the horn is buggered, as it sqeeks when I suck and blow. thanks for the education on how it works, appreciated. Will go to the £1 store and look for a candidate

 

Gary

 

 

[G-OMER]

OK I got 3 for a £1. then it was a decision to use the bone, mouse or ball. the mouse got it, popped it out of its bottom and installed it to the horn, so now I have the reed working 1 way only in the right direction. next thing is to re bend the plate back and do some trial in a couple of weeks to get it to sound at 45 knots? or 40 knots?

 

 

[G-OMER]

forgot to say the jab stalls at 35 knots

 

 

[old man emu]

the mouse got it, popped it out of its bottom and installed it to the horn,

I'm told that the A380's is a horse's arrrs.

 

OME

 

 

[Jaba-who]

On an entirely different note - just curious. what does the 450 tas at at various RPMs.?

 

Interested to compare it to the 430. My stall speed is in mid 50s no flaps and 48 with flaps.

 

At 2900 rpm it sits on 120 kts tas.

 

 

[Jaba-who]

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