Electric stall warners
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I was genuinely interested in a pressure active stall warner, having never heard of it.
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I don't have a stall warner......I imagine electric ones stop working in the absence of electrickery.
I would say though that this is a secondary piece of equipment, and not really nescessary in my view, other than for the JAA PPL When I bought my plane, I didn't even notice that it didn't have one to tell you the truth, and I find them slightly annoying, especially if they're constantly chirping away at 5kts about stall. I suppose it can be quite satisfying when you touch down with the thing chirping away, especially on your YouTube vide 
Anyway, not having a dig at anyone here, but I don't even listen for stall warning on landing (partly because I don't have one
) but feel the aeroplane and it'll soon let you know when it wants to stop flying....Just don't be too high at that point!
I would say though that this is a secondary piece of equipment, and not really nescessary in my view, other than for the JAA PPL
When I bought my plane, I didn't even notice that it didn't have one to tell you the truth, and I find them slightly annoying, especially if they're constantly chirping away at 5kts about stall. I suppose it can be quite satisfying when you touch down with the thing chirping away, especially on your YouTube vide Anyway, not having a dig at anyone here, but I don't even listen for stall warning on landing (partly because I don't have one
) but feel the aeroplane and it'll soon let you know when it wants to stop flying....Just don't be too high at that point!
Is this not a serious design flaw?
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!72:
I still don't know what signal the pressure active stall warner gives the pilot to tell him he's about to drop out of the sky, presumably it's not an electrically generated warning..........
I can understand 'on the ground testing' with a French Kiss: presumably it lets out a languid sigh, wiggles its pelvis a tad then drops off to sleep..............
Cusco
I still don't know what signal the pressure active stall warner gives the pilot to tell him he's about to drop out of the sky, presumably it's not an electrically generated warning..........
I can understand 'on the ground testing' with a French Kiss: presumably it lets out a languid sigh, wiggles its pelvis a tad then drops off to sleep..............
Cusco
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Cusco, you came across as a wind-up on your first post. Perhaps that's why nobody took you serious. Call me stupid but I now believe you really have never seen a pressure-activated stall warner. They're common on Cessnas, and the DA-40 has 'em too.
It's nothing more than a hole in the leading edge of the wing, just below the line where the air normally separates itself into a low pressure area above the wing, and a high pressure area below the wing. In other words, in normal flight, there is a high pressure (higher than static, I mean) pushing into the hole. Nothing happens in this case.
As you approach the stall, the line between low and high pressure shifts downward due to the higher angle of attack. The hole is now in the low pressure area (lower than static), and air is sucked out of the hole.
The hole is connected, via a tube, to a sort of whistle in the cockpit, which makes a loud buzz as soon as air is sucked out through it. That's why you french-kiss it as part of your preflight checks: by sucking on it, you should hear the buzz. And yes, that is yuck, so there are little harmonica-like things for sale that do the sucking for you.
The advantage over a vane-type like in the PA-28 or Robin is that this system requires no electrics with all the problems associated with that (like mentioned in this thread). The disadvantage is that sometimes insects fly (or even nest) inside the hole, and it's harder to prevent them from icing over compared to electric vanes.
It's nothing more than a hole in the leading edge of the wing, just below the line where the air normally separates itself into a low pressure area above the wing, and a high pressure area below the wing. In other words, in normal flight, there is a high pressure (higher than static, I mean) pushing into the hole. Nothing happens in this case.
As you approach the stall, the line between low and high pressure shifts downward due to the higher angle of attack. The hole is now in the low pressure area (lower than static), and air is sucked out of the hole.
The hole is connected, via a tube, to a sort of whistle in the cockpit, which makes a loud buzz as soon as air is sucked out through it. That's why you french-kiss it as part of your preflight checks: by sucking on it, you should hear the buzz. And yes, that is yuck, so there are little harmonica-like things for sale that do the sucking for you.
The advantage over a vane-type like in the PA-28 or Robin is that this system requires no electrics with all the problems associated with that (like mentioned in this thread). The disadvantage is that sometimes insects fly (or even nest) inside the hole, and it's harder to prevent them from icing over compared to electric vanes.
Cusco:
Small port on the left wing leading edge connected to what looks like a kid's plastic 'parp' trumpet, internally just forward and above the doorpost. Works by pressure decrease as the AoA changes approaching the stall. Best tested on the ground by holding a handkerchief over it and sucking (just in case of wasps, etc!).
Edit: Cross-posting - Backpacker beat me to it!
Small port on the left wing leading edge connected to what looks like a kid's plastic 'parp' trumpet, internally just forward and above the doorpost. Works by pressure decrease as the AoA changes approaching the stall. Best tested on the ground by holding a handkerchief over it and sucking (just in case of wasps, etc!).
Edit: Cross-posting - Backpacker beat me to it!
Slightly off the immediate subject, some aircraft, such as the Seneca, have vane-type stall warners that can't be tested on the ground unless the landing gear squat switch is manually operated to give a 'weight off' signal. Annoying as it has two vanes, one dependant on the flap position. Most crew are probably not aware of this, so there is always the possibility of a malfunctioning stall warning system not being detected. Bad design fault in my opinion.
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Stall warner? Looked everywhere and can't find it. Similar problem with the flap lever, pitot heat, fuel pump, low voltage warning light, vacuum pump etc etc. How it flies without them is a complete mystery, that it can still do it 60 years on is a miracle.
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I recently had to replace a battery due to the fact a cell or two was bad.
The symptom was with only a small amount of ground running of electrics I didn't have enough power to turn the engine over. Interestingly, I could tell if I was going to have a problem on my walk around. The lights would come on (strobes, beacon, nav, landing) but when I gave the stall warner a flick - no noise! So at least on my plane it fails at a higher voltage than almost anything else in the plane. But as others have said, there are lots of other warnings of stall than just the electrickey one - so potential lack of stall warning wasn't the issue that got me to replace the battery post haste!
My Bonanza has a 15.5 amp-hr 24 volt battery (70 amp hour seems like a decent size car battery). If FF has similar and threw the belt right as he started his take off roll, with a full suite of avionics and the draw from the gear retraction motor, he could well have had only a little time left. However, 10 does sound like the battery has a weak cell or possibly the belt was dropped at engine start.
The symptom was with only a small amount of ground running of electrics I didn't have enough power to turn the engine over. Interestingly, I could tell if I was going to have a problem on my walk around. The lights would come on (strobes, beacon, nav, landing) but when I gave the stall warner a flick - no noise! So at least on my plane it fails at a higher voltage than almost anything else in the plane. But as others have said, there are lots of other warnings of stall than just the electrickey one - so potential lack of stall warning wasn't the issue that got me to replace the battery post haste!
My Bonanza has a 15.5 amp-hr 24 volt battery (70 amp hour seems like a decent size car battery). If FF has similar and threw the belt right as he started his take off roll, with a full suite of avionics and the draw from the gear retraction motor, he could well have had only a little time left. However, 10 does sound like the battery has a weak cell or possibly the belt was dropped at engine start.
My initial thoughts were that a warning system should be fail safe (loss of power brings the warning on) as with most of the electrical gear I deal with.
However, my next thought was that if it failed/lost power etc and switched on the buzzer, there would be no way to switch the buzzer off until you landed. I reckon that would be pretty distracting - a worse potential hazard than not having a stall warning, especially if the power loss was a widespread multi-instrument power loss as you'd be busy enough dealing with that.
Just a thought.
However, my next thought was that if it failed/lost power etc and switched on the buzzer, there would be no way to switch the buzzer off until you landed. I reckon that would be pretty distracting - a worse potential hazard than not having a stall warning, especially if the power loss was a widespread multi-instrument power loss as you'd be busy enough dealing with that.
Just a thought.
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My personal opinion is that you should know the POH of your aircraft to the extent that you know by instinct what systems fail if one of your base systems fails.
Here's what generally fails in a small aircraft, fixed gear:
Electric system failure: Internal and external lights, electric fuel quantity indicators, all avionics (Intercom, COM, NAV, ADF, DME, autopilot, transponder), electric flaps, electric stall warner, CDI, electric trim and some engine instruments (T&Ps most likely yes, MAP/RPM most likely not, but it does depend on the exact type)
Vacuum system failure: AI, DI
Pitot/static system failure: ALT, VSI, ASI
For a retractable, you have down & locked indicators which rely on electrics, and the gear itself might be electric or hydraulic. Warnings along the line of "MAP below 15" with the gear up and flaps down" (or other combinations of these) will most likely also be based on electrics.
Now imagine all of the systems that use electricity, to have their own failure indication if the electrics fail. Not only would this require a small backup battery for almost each instrument, but it would also lead to a cacophony of warning signals in the cockpit, all of which need to be cancelled/acknowledged individually...
Here's what generally fails in a small aircraft, fixed gear:
Electric system failure: Internal and external lights, electric fuel quantity indicators, all avionics (Intercom, COM, NAV, ADF, DME, autopilot, transponder), electric flaps, electric stall warner, CDI, electric trim and some engine instruments (T&Ps most likely yes, MAP/RPM most likely not, but it does depend on the exact type)
Vacuum system failure: AI, DI
Pitot/static system failure: ALT, VSI, ASI
For a retractable, you have down & locked indicators which rely on electrics, and the gear itself might be electric or hydraulic. Warnings along the line of "MAP below 15" with the gear up and flaps down" (or other combinations of these) will most likely also be based on electrics.
Now imagine all of the systems that use electricity, to have their own failure indication if the electrics fail. Not only would this require a small backup battery for almost each instrument, but it would also lead to a cacophony of warning signals in the cockpit, all of which need to be cancelled/acknowledged individually...
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Bookworm
Having stated that airmanship should protect a pilot against stall warner failure, let me now play devils advocate when you say "The failure that you're concerned about (stall warner fails to alert pilot to imminent disaster after electrical failure) would require two highly unlikely events: both the failure of the pilot to maintain a proper AoA and the failure of the electrical system."
I could make a strong argument that electrical failure is just the sort of distraction that could cause a single pilot to miss a change in AoA and get into trouble, especially if the pilot was inexperienced - so perhaps the holes in the cheese might align.
Having stated that airmanship should protect a pilot against stall warner failure, let me now play devils advocate when you say "The failure that you're concerned about (stall warner fails to alert pilot to imminent disaster after electrical failure) would require two highly unlikely events: both the failure of the pilot to maintain a proper AoA and the failure of the electrical system."
I could make a strong argument that electrical failure is just the sort of distraction that could cause a single pilot to miss a change in AoA and get into trouble, especially if the pilot was inexperienced - so perhaps the holes in the cheese might align.
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MM Flynn is right to say
, so it was a bad example. The 12v battery in the Warrior -161 is about 30AH according to Concord battery, but even 10% (3AH) remaining would still require 18A continuous drain for a discharge in 10mins.
However I was being very conservative in assuming 10% capacity left. That would only really happen if the battery was already in trouble due to a cell fault (as above), overcranking, master left on, etc. all of which ought to merit some consideration before flight. I suppose it's possible that a discharged battery might cause the belt to throw but that's wild speculation.
More realistically the battery ought to be at 50% capacity after starting and it's very hard to explain where all that current went in 10mins without starting a fire. So my point stands - there must be more to it than just belt failure.
PS Interesting about the stall warner being the first thing to fail. You'd expect the designers to require 6v operation in a 12v aircraft for all the reasons we are discussing. I'm sure a replacement would only be £100 (aviation grade), or £0.30 from Maplins, so maybe a time for a new one?
70 amp hour seems like a decent size car battery
However I was being very conservative in assuming 10% capacity left. That would only really happen if the battery was already in trouble due to a cell fault (as above), overcranking, master left on, etc. all of which ought to merit some consideration before flight. I suppose it's possible that a discharged battery might cause the belt to throw but that's wild speculation.
More realistically the battery ought to be at 50% capacity after starting and it's very hard to explain where all that current went in 10mins without starting a fire. So my point stands - there must be more to it than just belt failure.
PS Interesting about the stall warner being the first thing to fail. You'd expect the designers to require 6v operation in a 12v aircraft for all the reasons we are discussing. I'm sure a replacement would only be £100 (aviation grade), or £0.30 from Maplins, so maybe a time for a new one?
