Stall warner problem

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SimonH
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Stall warner problem

Post by SimonH »

Just wondered if anyone has had this problem....

Stall warner works fine in test on the ground, but I found on a training flight that it doesn't work when you need it in the air!

Any ideas?

Cheers
Simon
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Fred
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Re: Stall warner problem

Post by Fred »

Hi Simon, are you testing on the ground by blowing air into the stall horn? In the air you are able to reach stall speeds clean or with flaps without hearing the horn?

My Bose A20's N/C do such a great job keeping the plane quiet I have to pay more attention to hear the horn on my DA40. I'm assuming a DA42 has a bit more noise and "maybe" the horn is the same one used on the DA40 and the two engines with a good headset just make it harder to hear.

To make sure I wasn't crazy (still may be a little) I practiced stalls with my headset off and the horn did sound 5-7 knots ahead of the stall every time.

Just a thought.

Cheers, Fred
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SimonH
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Re: Stall warner problem

Post by SimonH »

Hi Fred. Thanks for the reply. It is a DA42 (which is probably not much noiser as the engines are to the side rather than right in front of you!) and doesn't have the same set up as a DA40...it's the metal tab type which I test on the ground by just moving it upwards. I have heard it before quite clearly so I can't blame my Bose headset!

Cheers
Simon
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carym
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Re: Stall warner problem

Post by carym »

Simon, is your plane FIKI? If so, then you may have a stall heat problem (I had to replace mine).
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Re: Stall warner problem

Post by mdieter »

Two thoughts:
1) I believe you have to 'suck' air out of the hole in the wing to properly test the stall warning on the ground.
2) I have also experienced 'good' headphones blocking most of the stall horn sound. I spent literally minutes with the stall horn going off trying to convince the instructor that it was sounding! It kind of blended into the background noise.
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SimonH
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Re: Stall warner problem

Post by SimonH »

That's interesting Cary. It is certified for FIKI. Are you saying that yours didn't work when it was frozen because the heater did not work or because the stall heater malfunctioned causing it not to work at all in any condition?

Mark, the stall Warner on my 42 is differ to to the 40. It's the tab kind rather than the hole in the wing type.
And it was audible before and have the same headset. But thanks for your thoughts as any ideas are always worth considering.

Cheers
Simon
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carym
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Re: Stall warner problem

Post by carym »

Simon,
When the stall heater went out, I did not get a stall warning. But, I never tested it on the ground. I did get a STAL HT FAIL in flight. This is different from the STAL HT OFF notice that is always lit while the plane is on the ground (because of the squat switch), but goes off once the nose gear is lifted off the ground. If the squat switch detecting the nose gear on the ground is not ?closing then you should still see the STAL HT OFF light while in the air and that may disconnect the stall horn from sounding. I'm just speculating here.
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Re: Stall warner problem

Post by SimonH »

Thanks Cary. I'm not getting any failure indication in flight. It's odd that it works on the ground though.
I spoke to my local engineer this evening and he was rally spooked....he's just seen another example yesterday having never seen one before. The other aircraft is several years old and has spent its life outside on the South coast of the UK. He initially put it down to age but now he has heard about mine he's going to look into it further.

I will post when I get a resolution, but it may not be for a few weeks.

Cheers
Simon
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Re: Stall warner problem

Post by Snowy »

I fly a DA42 FIKI too, and also a DA40. I can hear the 40 stall fine, as its the old fashioned type of negative pressure, but the 42 is an electric type. I also have A20 headsets. I noticed that in the stall, in the 42, I could only just hear the stall warner being activated, now it maybe that yours just isn't set up correctly, or it's failing in the air. Perhaps carry out a practice stall, with one ear cup pushed back? (just to discount the cheapest thing first!)
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Re: Stall warner problem

Post by CFIDave »

The stall system on the DA42 is quite different from that of the DA40. It consists of a heated lift switch on the wing leading edge that's electrically connected to a round 28V stall warning "buzzer" mounted just below the PFD on the inside bottom of the instrument panel.

If the stall warning is audible (quite loud) on the ground -- which you test by manually lifting the lift switch tab with the electric master ON) -- then the components are all working. If however you can't hear it in the air, perhaps the lift switch is out of adjustment or sticking (i.e. has too much friction). The lift switch angle of attack can be adjusted by loosening the screws that hold it to the leading edge of the wing; it's supposed to be adjusted to switch ON about 10 knots above actual stall speed.
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