Electric stall warners
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Electric stall warners
My current aeroplane has one of these. it is the "vane" type, which you can test on the ground (with the power on) by moving it backwards, and the buzzer duly sounds. No power, no buzzer.
My question is this. What happens if you have a complete power failure ? I know all about stall buffet, but .... Is this not a serious design flaw ? My last plane had a simple but highly effective "pressure activated" system which required no power ...
FF
My question is this. What happens if you have a complete power failure ? I know all about stall buffet, but .... Is this not a serious design flaw ? My last plane had a simple but highly effective "pressure activated" system which required no power ...
FF
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I test mine by moving it forwards...........
How did your 'pressure activated' system get its important message across to you?
Does a little red flag with 'stall' written on it unfurl in your line of vision.?
Safe (but fast enough) flying.
Cusco
How did your 'pressure activated' system get its important message across to you?
Does a little red flag with 'stall' written on it unfurl in your line of vision.?
Safe (but fast enough) flying.
Cusco
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Dependant on the aircraft, would you not still feel the buffeting over the tail as the wing starts to stall at the root? so you still have an indication...
The vane type you are talking about is indeed off battery power and if that is totally dead it will not work, BUT the amount of current it draws, the battery would have to be seriously flat to not operate it.
The vane type you are talking about is indeed off battery power and if that is totally dead it will not work, BUT the amount of current it draws, the battery would have to be seriously flat to not operate it.
Last edited by NutLoose; 11th Jul 2007 at 11:43.
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hi fully flapped,
as nut loosed says...what do you mean by complete power failure..??
if you have alternator failure ( and of course doing regular cruise checks you will have noticed this before you run out of battery power ), then you will still have probably at least ( depending on the condition of your battery ) 45 minutes and possibly a lot more ( especially if you pull circuit brakers ...or switch off all non essential equipment )...so no problem as you will still have power to run your stall warning..and make arrangements to land at the nearest suitable airfield..
in any event..i am sure you would pay close attention to your airspeed indicator on approach anyway..so why should it be such a problem even if you lost the electric stall warning...? in the average small plane getting close to the stall is so noticeable in attitude, wind noise, buffeting..( some may vary a little and may not have all three ) that it is difficult not to recognise the onset of the stall. this is why on flight test some of the stalls given ( not the fully developed ) you are asked to recover ' from the first indication of stall '....that is for the examiner to see that you can recognise the early symptoms ...and initiate the recovery from that point..
good you should wonder ' what if '...but i do'nt see it should be a problem for you.
fly safe..
the dean.
as nut loosed says...what do you mean by complete power failure..??
if you have alternator failure ( and of course doing regular cruise checks you will have noticed this before you run out of battery power ), then you will still have probably at least ( depending on the condition of your battery ) 45 minutes and possibly a lot more ( especially if you pull circuit brakers ...or switch off all non essential equipment )...so no problem as you will still have power to run your stall warning..and make arrangements to land at the nearest suitable airfield..
in any event..i am sure you would pay close attention to your airspeed indicator on approach anyway..so why should it be such a problem even if you lost the electric stall warning...? in the average small plane getting close to the stall is so noticeable in attitude, wind noise, buffeting..( some may vary a little and may not have all three ) that it is difficult not to recognise the onset of the stall. this is why on flight test some of the stalls given ( not the fully developed ) you are asked to recover ' from the first indication of stall '....that is for the examiner to see that you can recognise the early symptoms ...and initiate the recovery from that point..
good you should wonder ' what if '...but i do'nt see it should be a problem for you.
fly safe..
the dean.
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Ah, good to see the usual cross-section of Proon replies (i.e. some helpful, some wildly assumptive, some trotting out good-old standard cliches, and just a little sprinkle of "smart-arse" thrown in for good measure - although Mr. "little red flag" has obviously never seen a vacuum-activated system, and should restrain his smart-arsery until he's done a little more reading!).
OK, here's the background : a few days ago, I lost all electrical power within no more than 10 minutes of take off, despite taking down everything as quickly as possible once I'd noticed a continuous discharge. We lost everything, including radio, flaps, and - and here's the reason for the question - undercarriage. No 45 minute grace : could be the battery is duff, I don't know yet.
I deployed the undercarriage manually, but there is no way of knowing whether it's actually down and locked without power. I took us off to the longest hard runway I could find, made sure my wife was briefed and secure as possible, and then attempted the gentlest landing I've ever made : which means as slow as safely possible.
Down and safe, all's well that ends well etc. But it only occurred to me afterwards that once I'd got the speed nailed, and then cut the power for the hold off (as low as I dared), that I never heard the stall warner go off at all ... (didn't notice at the time, but I was kind of busy !
)
Never mind, just wondered because you'd kind of expect them to have picked this up at design time ...
FF
OK, here's the background : a few days ago, I lost all electrical power within no more than 10 minutes of take off, despite taking down everything as quickly as possible once I'd noticed a continuous discharge. We lost everything, including radio, flaps, and - and here's the reason for the question - undercarriage. No 45 minute grace : could be the battery is duff, I don't know yet.
I deployed the undercarriage manually, but there is no way of knowing whether it's actually down and locked without power. I took us off to the longest hard runway I could find, made sure my wife was briefed and secure as possible, and then attempted the gentlest landing I've ever made : which means as slow as safely possible.
Down and safe, all's well that ends well etc. But it only occurred to me afterwards that once I'd got the speed nailed, and then cut the power for the hold off (as low as I dared), that I never heard the stall warner go off at all ... (didn't notice at the time, but I was kind of busy !
)Never mind, just wondered because you'd kind of expect them to have picked this up at design time ...
FF
Last edited by FullyFlapped; 11th Jul 2007 at 11:55.
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Did you recycle the Alternator? I ask, as some of the pilots that fly our Aircraft are unaware of this, I realise you probably had your hands full, but selecting the Alternator off for a brief period of time, ( about 20 seconds) then turning it back on resets the Voltage regulator and brings the alternator back online. This may or may not have worked in your circumstances, or indeed if there was a fault elsewhere, but its worth knowing if you are unaware....... The Battery does sound a bit suspect......
Just as well it wasn't a DA 42, as prior to the Airworthiness Directives that are currenty whistling through, you would have ended up flying a twin engined glider.
Just as well it wasn't a DA 42, as prior to the Airworthiness Directives that are currenty whistling through, you would have ended up flying a twin engined glider.
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I'm learning aerobatics and one thing they teach you is that the stall, more than anything, is associated with stick location. At 0g or +4g, Vs or Vs0 (bottom of the green or white arc) is completely meaningless. So as long as the aircraft is trimmed for a reasonable approach speed and you're not pulling the stick hard into your crotch (in case of a yoke, into your armpits), you can't (or rather, should not) stall.
In the circumstances, what you did sounds perfect. Find a long runway, nail the approach speed to something safely above the stall, flare and cut the power just inches above the runway. Keep pulling until you get strong signs of stalling behaviour, or where you feel that the aircraft is done flying. Then put her down gently.
If you're worried about the undercarriage not being locked, you might actually want to shut the engine(s) down completely while holding off, so that the props are not turning. If the gear fails, at least you're only shearing off one or two prop blades, not all of them, and are not shock-loading the engine. But I admit you have to have the spare mental capacity to do that.
Don't worry about keeping the runway occupied after landing. It's your emergency, not the ones in the circuit.
In the circumstances, what you did sounds perfect. Find a long runway, nail the approach speed to something safely above the stall, flare and cut the power just inches above the runway. Keep pulling until you get strong signs of stalling behaviour, or where you feel that the aircraft is done flying. Then put her down gently.
If you're worried about the undercarriage not being locked, you might actually want to shut the engine(s) down completely while holding off, so that the props are not turning. If the gear fails, at least you're only shearing off one or two prop blades, not all of them, and are not shock-loading the engine. But I admit you have to have the spare mental capacity to do that.
Don't worry about keeping the runway occupied after landing. It's your emergency, not the ones in the circuit.
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I'm genuinely puzzled by this and indeed similar stories recounted at other times.
I cannot see how a battery could fail within ten minutes of takeoff simply because the alternator fails. There must have been enough charge in the battery to start the engine and even a small amount of remaining capacity would be enough supply radios etc for more than 10mins.
For instance even as little as 10% capacity (unlikely for an aircraft in regular use) would still be about 7AH (Ampere hours) which would require a current flow of 42A to completely discharge in 10mins. For the undercarriage retraction to explain that would require very high currents to flow.
Even if some load had discharged the battery, switching off all the avionics, lights and so would allow some recovery in battery voltage, surely enough to work the stall warner which is just a buzzer - 1A or so and probably works down to 6v anyway.
So I'm convinced there must be some other factor in play - a battery fault or an undisclosed load that can handle 50A or so without making a burning smell. Fan belt failure just doesn't meet the facts as described.
I cannot see how a battery could fail within ten minutes of takeoff simply because the alternator fails. There must have been enough charge in the battery to start the engine and even a small amount of remaining capacity would be enough supply radios etc for more than 10mins.
For instance even as little as 10% capacity (unlikely for an aircraft in regular use) would still be about 7AH (Ampere hours) which would require a current flow of 42A to completely discharge in 10mins. For the undercarriage retraction to explain that would require very high currents to flow.
Even if some load had discharged the battery, switching off all the avionics, lights and so would allow some recovery in battery voltage, surely enough to work the stall warner which is just a buzzer - 1A or so and probably works down to 6v anyway.
So I'm convinced there must be some other factor in play - a battery fault or an undisclosed load that can handle 50A or so without making a burning smell. Fan belt failure just doesn't meet the facts as described.
I've had enough experience of rotten old cars (and most light aeroplanes are electrically simpler than them) to know that if there was enough urge in the battery to start the engine, there wasn't that much wrong with it and if you started to conserve electricity as soon as the "low volt" light went on you should be OK fo some time.
I can only assume that the departing belt took an important cable with it .. or dead shorted one.
I can only assume that the departing belt took an important cable with it .. or dead shorted one.
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It is quite common for PFA aircraft to not have stall warners fitted. In my gliding days, I spent large amounts of time tacking up and down and going in circles just above the stall, with no stall warning. Unless your aircraft is unusual in its stall characteristics, or you are not listening to your airframe, you have very little to worry about.
Rod1
Rod1
All those years ago when I was doing my training, it was common practise for my instructor to wait until I was downwind and then slap the black circular rubber sucker over the ASI and I was expected to complete the landing OK without it. (To calls of "Low and slow - lookout below" if I wasn't getting it right). Perhaps for that reason I tend to be heads up looking at the picture as I land, rather than heads down looking at the instruments.
I guess that after all these years and knowing what an aeroplane feels like on the point of stalling (slack controls, the attitude, the right picture and all that) means that the stall warner is one of the "instruments" I rely on least.
I suppose that is what the seat of your pants is for ... how long does it take get the "feel" ??
To digress a bit, one of our instructors in a chat on Saturday morning was saying how bad most airline pilots who want to fly a PA-28 are, as they are no longer instinctive aviators but systems operators, it having been perhaps decades since they flew a light aircraft.
(Hard hat to ON)
I guess that after all these years and knowing what an aeroplane feels like on the point of stalling (slack controls, the attitude, the right picture and all that) means that the stall warner is one of the "instruments" I rely on least.
I suppose that is what the seat of your pants is for ... how long does it take get the "feel" ??
To digress a bit, one of our instructors in a chat on Saturday morning was saying how bad most airline pilots who want to fly a PA-28 are, as they are no longer instinctive aviators but systems operators, it having been perhaps decades since they flew a light aircraft.
(Hard hat to ON)
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My tuppence?
10 mins to a flat battery - got to be something very wrong. In my Terrier we toured for a week without any power generation - although after the first couple of days I did handswing the engine. Got home about 20 hours later and the battery still started us! (but of course fixed gear).
If losing the stall warner is a serious design flaw then most aircraft have a whole raft of issues.
Stall warners are only added for certification purposes when there is not considered to be 'sufficient' natural buffet. What an acceptable level of buffet is has often baffled me. (Especially as differing variants of the same airframe do and don't have them and very frequently the G-reg airframes must have them but the least of the world doesn't need them). That does of course rather ignore the somewhat unnatural attitude that you need to get into to stall the thing in the first place and all those other clues like airspeed, g-loading etc. The same Terrier also had a vane stall warner - I found looking at the sky tended to give me a bit of a clue not the feeble buzzing.
10 mins to a flat battery - got to be something very wrong. In my Terrier we toured for a week without any power generation - although after the first couple of days I did handswing the engine. Got home about 20 hours later and the battery still started us! (but of course fixed gear).
If losing the stall warner is a serious design flaw then most aircraft have a whole raft of issues.
Stall warners are only added for certification purposes when there is not considered to be 'sufficient' natural buffet. What an acceptable level of buffet is has often baffled me. (Especially as differing variants of the same airframe do and don't have them and very frequently the G-reg airframes must have them but the least of the world doesn't need them). That does of course rather ignore the somewhat unnatural attitude that you need to get into to stall the thing in the first place and all those other clues like airspeed, g-loading etc. The same Terrier also had a vane stall warner - I found looking at the sky tended to give me a bit of a clue not the feeble buzzing.
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Worth remembering that some of the most numerous GA types on the planet, eg Cub and associated types have been flown for years without stall warners. The lack of a warner would be a problem in a plane, for example some heavy jets, that doesn't give you fair warning of an oncoming stall!
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I'm really grateful to those who seem to think that I need a lesson on recognising the symptoms of an incipient stall (in my own aeroplane) ...
Where exactly did I say that I needed a stall warner to land the b*****y plane ?
There is no doubt that as I held off, the airspeed reduced sufficiently to make the stall warner go off under normal circumstances. It didn't, because obviously there's no fallback when the power's gone, and that's the only point I was making !
FF
Where exactly did I say that I needed a stall warner to land the b*****y plane ?
There is no doubt that as I held off, the airspeed reduced sufficiently to make the stall warner go off under normal circumstances. It didn't, because obviously there's no fallback when the power's gone, and that's the only point I was making !
FF
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Take a chill pill FF:
Perhaps if you'd posted the circumstances as background information in your original posting you might have avoided some of the irony of subsequent replies.
I was genuinely interested in a pressure active stall warner, having never heard of it.
It does however sound a bit like the 'wire and cork float' type of fuel gauge on some a/c types.
However I'm not about to get the books out every time there is noise on PPRuNe.
Safe (and fully powered) flying
Cusco(aka Mr Smart *rse)
Perhaps if you'd posted the circumstances as background information in your original posting you might have avoided some of the irony of subsequent replies.
I was genuinely interested in a pressure active stall warner, having never heard of it.
It does however sound a bit like the 'wire and cork float' type of fuel gauge on some a/c types.
However I'm not about to get the books out every time there is noise on PPRuNe.
Safe (and fully powered) flying
Cusco
(aka Mr Smart *rse)