Stalling without stall warner going off
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Stalling without stall warner going off
I did ask this question in another thread, but I thought I would put it in its own place.
Are there circumstances (and I'm talking about your average trainer here, C152 PA28 etc.) when the plane can stall without the stall warner being activated?
For example, a skidding turn where airflow over the wing with the stall warner may be disrupted?
I've often wondered whether you could get into a situation where the stall happens without the warning going off - and I am just talking about the stall warner here, no other signs such as buffet, high nose etc. etc.
Any thoughts gratefully received.
Are there circumstances (and I'm talking about your average trainer here, C152 PA28 etc.) when the plane can stall without the stall warner being activated?
For example, a skidding turn where airflow over the wing with the stall warner may be disrupted?
I've often wondered whether you could get into a situation where the stall happens without the warning going off - and I am just talking about the stall warner here, no other signs such as buffet, high nose etc. etc.
Any thoughts gratefully received.
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<continuing frivolous banter from Spitfire thread!! 
>
I'll have you know that I generally give warning when about to pop!! (and the AB thread about her Remove B4 Flight T Shirt / 2 Lovely Bristols got a happy man feeling very old!)
Also, I've never been pulled by my instructor (not that I'd have really wanted to be - they were mostly old, fat & hairy - and male!!)!!
CB
>I'll have you know that I generally give warning when about to pop!! (and the AB thread about her Remove B4 Flight T Shirt / 2 Lovely Bristols got a happy man feeling very old!)
Also, I've never been pulled by my instructor (not that I'd have really wanted to be - they were mostly old, fat & hairy - and male!!)!!
CB
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Mine can stall without the stall warner being activated - it hasn't got one!
It's not activated by the wing stalling so stall warner is a slight misnomer. It activates when the wing reaches a preset angle of attack. As AoA increases the point at which the airflow divides moves down the leading edge. Once this point goes below the vane it is lifted by the upward airflow and the warning sounds. It's usually adjustable and set to go off prior to the stall so you have enough time to react and do something before the stall actually occurs. Providing the thing is in good working order and not iced up it should consistently go off at the same AoA, which if it is in adjustment should be below the stalling AoA.
However if you were to suddenly pull a lot of G at low speed you could easily leave yourself no time to react.
(Above refers to the vane type, haven't thought about the suction version.)
It's not activated by the wing stalling so stall warner is a slight misnomer. It activates when the wing reaches a preset angle of attack. As AoA increases the point at which the airflow divides moves down the leading edge. Once this point goes below the vane it is lifted by the upward airflow and the warning sounds. It's usually adjustable and set to go off prior to the stall so you have enough time to react and do something before the stall actually occurs. Providing the thing is in good working order and not iced up it should consistently go off at the same AoA, which if it is in adjustment should be below the stalling AoA.
However if you were to suddenly pull a lot of G at low speed you could easily leave yourself no time to react.
(Above refers to the vane type, haven't thought about the suction version.)
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The only aerodynamic situation I can think of is: If you have power (preventing root stall) on are near stall speed and then you use the aileron, the down going aileron can take the wing tip AoA past critical and stall that tip resulting in a sudden wing drop in the opposite direction to the stick.
>>For example, a skidding turn where
>>airflow over the wing with the stall
>>warner may be disrupted?
I don't believe this to be possible as the stall is by definition the stagnation point (point of stationary air that neither goes over the top nor underneath the wing) moving down the leading edge of the wing and pushing the stall flap up. If that is prevented then at least that part of the wing is below critical AoA.
>>For example, a skidding turn where
>>airflow over the wing with the stall
>>warner may be disrupted?
I don't believe this to be possible as the stall is by definition the stagnation point (point of stationary air that neither goes over the top nor underneath the wing) moving down the leading edge of the wing and pushing the stall flap up. If that is prevented then at least that part of the wing is below critical AoA.
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I've always maitained that the first aerodynamic sign of the approach to a stall is an increase in back pressure on the controls.
If you haven't changed the centre of gravity or configuration and the aircraft was trimmed to a certain speed then any increase in back force must be because you are slowing down (increasing pitch attitude).
The next symptom is a reduced effectiveness of the controls.
Then you usually get some kind of airframe buffeting.
How many stall warnings do you need?
If you haven't changed the centre of gravity or configuration and the aircraft was trimmed to a certain speed then any increase in back force must be because you are slowing down (increasing pitch attitude).
The next symptom is a reduced effectiveness of the controls.
Then you usually get some kind of airframe buffeting.
How many stall warnings do you need?
Northern Monkey
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Slightly off topic,
Can I legally pull the CB on the stall warner before take off? I find the stall warner on the firefly very irritating when I'm doing aerobatics, and pulling the CB would sort that problem.
NB
Can I legally pull the CB on the stall warner before take off? I find the stall warner on the firefly very irritating when I'm doing aerobatics, and pulling the CB would sort that problem.
NB
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Rather than pull it before TO why not put it in as part of your before and after Aeros checks, then you have it for departure and arrival but not when it is just going to be a nuisance.
(The people who might get funny about this would be the insurance co. if you crashed on departure or arrival, they would probably not consider this a factor so much during aeros)
(The people who might get funny about this would be the insurance co. if you crashed on departure or arrival, they would probably not consider this a factor so much during aeros)
For info, from FAR 23 para 207 at Amdt 23-50:
(f) For acrobatic category airplanes, an artificial stall warning may be mutable, provided that it is armed automatically during takeoff and rearmed automatically in the approach configuration.]
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With you Foxmoth, don't believe that it does apply.
Many of the aerobatic machines that I know have the stall warner C/B out and disabled (taped over) so that it can't inadvertently be selected on and therefore give the poor stick-Ninja the fright of his life!
On my own mount, the audio feed is insufficiently loud to be heard above cruise power, so for take-off it is pretty useless and for landing - it scares me to bits! So the non-cycle type C/B has been changed to the selectable one. With pax, I always have it ON as their weight does make quite a difference!
One young lady recently asked after we'd landed what that siren noise was? I told it her that it was the aeroplane's lie detector. She wanted to know; what was lying? You were, it doesn't believe that you are only eight and a half stone!
Stik
Many of the aerobatic machines that I know have the stall warner C/B out and disabled (taped over) so that it can't inadvertently be selected on and therefore give the poor stick-Ninja the fright of his life!
On my own mount, the audio feed is insufficiently loud to be heard above cruise power, so for take-off it is pretty useless and for landing - it scares me to bits! So the non-cycle type C/B has been changed to the selectable one. With pax, I always have it ON as their weight does make quite a difference!
One young lady recently asked after we'd landed what that siren noise was? I told it her that it was the aeroplane's lie detector. She wanted to know; what was lying? You were, it doesn't believe that you are only eight and a half stone!
Stik
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Miserlou old chap,
Had I wanted to see her again, I'd have taken her to lunch then found somewhere far more comfortable than the front hole in the Pitts to take her upside down!
Stik
Had I wanted to see her again, I'd have taken her to lunch then found somewhere far more comfortable than the front hole in the Pitts to take her upside down!
Stik
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The stall warner on the C150 I learn't in never went off for the whole of my PPL.
Was first shown to suck on it during my walk round ( the stall warner). And quickly thought that was bloody stupid idea so didn't bother.
Did the course and the three instructors never made a comment it not going off during stalls.
On the final practise I was given a new Riddle instructor to break in and show JAR methods to.
He watched me do the walk round and gave me a bollocking for not checking the stall warner. I lied and said i had never been shown how. At which point he gave it a good suck and ended up with 2 months of compacted Love bugs and other beasties in his mouth. At which point he barfed. But give him credit the stall warner did work in the next flight. And to this day i have never felt the urge to find out if the constipated duck works on a pre flight check.
MJ
And to answer the question.
1. High load stall in the cessna after say a spin recovery ie the pilot trys to pull the nose up to hard to stop the plane going through Vne.
2. When the plane stall warner is a wee bit to liable to go off. It has been know for instructors to stick a bit of chewing gum on it after the student has done there walk round to stop it going off on every gust.
Was first shown to suck on it during my walk round ( the stall warner). And quickly thought that was bloody stupid idea so didn't bother.
Did the course and the three instructors never made a comment it not going off during stalls.
On the final practise I was given a new Riddle instructor to break in and show JAR methods to.
He watched me do the walk round and gave me a bollocking for not checking the stall warner. I lied and said i had never been shown how. At which point he gave it a good suck and ended up with 2 months of compacted Love bugs and other beasties in his mouth. At which point he barfed. But give him credit the stall warner did work in the next flight. And to this day i have never felt the urge to find out if the constipated duck works on a pre flight check.
MJ
And to answer the question.
1. High load stall in the cessna after say a spin recovery ie the pilot trys to pull the nose up to hard to stop the plane going through Vne.
2. When the plane stall warner is a wee bit to liable to go off. It has been know for instructors to stick a bit of chewing gum on it after the student has done there walk round to stop it going off on every gust.
Last edited by mad_jock; 3rd Jun 2005 at 13:37.