Stall Warning
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As they say there are no dumb questions when it involves aviation especially if yr airborne!:-)
Part of the original Q says 'we have two wings'......well technically that's correct for say a modern day A/C but essentially there is only one wing just interrupted by the body of the machine. What about a parasol wing? That's just one wing from tip to tip uninterrupted so it could be said for aerodynamic purposes there's only one wing not withstanding the other associated issues with this common arrangement such as parasite drag or interference drag.
Typically having the only stall warning device on the L/H side as for say Cessna means the PIC whom usually sits in the L/H seat can see the probe for a variety of reasons. Obviously a low wing machine doesn't have this feature.
Both wings (if you want to call them that for clarity) in a perfect world would stall at the same time as they are considered as one being equal lift either side of the body but obviously one side of the wing will stall first due all sorts of reasons such as bank angle etc but for simplicity of design in light A/C there's only one stall warning device.
Lots of good answers here.
'GG' the original poster re computer controlled planes is quite correct & that's exactly why modern day planes like the Airbus won't allow under normal law a pilot to exceed the planes set parameters,keeping it from stalling being just one of them, hence that comment computers are in control is essentially correct & not the dumbest Q.
Wmk2
Part of the original Q says 'we have two wings'......well technically that's correct for say a modern day A/C but essentially there is only one wing just interrupted by the body of the machine. What about a parasol wing? That's just one wing from tip to tip uninterrupted so it could be said for aerodynamic purposes there's only one wing not withstanding the other associated issues with this common arrangement such as parasite drag or interference drag.
Typically having the only stall warning device on the L/H side as for say Cessna means the PIC whom usually sits in the L/H seat can see the probe for a variety of reasons. Obviously a low wing machine doesn't have this feature.
Both wings (if you want to call them that for clarity) in a perfect world would stall at the same time as they are considered as one being equal lift either side of the body but obviously one side of the wing will stall first due all sorts of reasons such as bank angle etc but for simplicity of design in light A/C there's only one stall warning device.
Lots of good answers here.
'GG' the original poster re computer controlled planes is quite correct & that's exactly why modern day planes like the Airbus won't allow under normal law a pilot to exceed the planes set parameters,keeping it from stalling being just one of them, hence that comment computers are in control is essentially correct & not the dumbest Q
.Wmk2
Last edited by Wally Mk2; 15th Oct 2013 at 00:47.
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FAR 23.207 provides some useful background.
As always, one needs to read the relevant AC to find out what the rule might actually mean in practical FAA-speak. AC 23-8C indicates -
4. § 23.207 Stall Warning.
a. Explanation.
(1) Purpose. The purpose of this requirement is to ensure an effective warning in sufficient time to allow a pilot to recover from an approach to a stall without reaching the stall.
(2) Types of Warning. The effective warning may be from either aerodynamic disturbances or from a reliable artificial stall-warning device such as a horn or a stick shaker. The aerodynamic warning is usually manifested by a buffet, which vibrates or shakes the airplane. The type of warning should be the same for all configurations.
(3) Artificial Stall Warning. Stall warning devices may be used in cases where there is inadequate aerodynamic warning. The warning signal from the devices should be clear and distinctive and not require the pilot's attention to be directed inside the airplane. A stall warning light by itself is not acceptable. If a stick shaker is installed, the warning should be unmistakable even if flying hands off.
(4) Margin. The stall warning margin, as defined in the rule, is applicable with speed reduced at a rate of one knot per second for §§ 23.201 and 23.203(a)(1).
b. Procedures.
As always, one needs to read the relevant AC to find out what the rule might actually mean in practical FAA-speak. AC 23-8C indicates -
4. § 23.207 Stall Warning.
a. Explanation.
(1) Purpose. The purpose of this requirement is to ensure an effective warning in sufficient time to allow a pilot to recover from an approach to a stall without reaching the stall.
(2) Types of Warning. The effective warning may be from either aerodynamic disturbances or from a reliable artificial stall-warning device such as a horn or a stick shaker. The aerodynamic warning is usually manifested by a buffet, which vibrates or shakes the airplane. The type of warning should be the same for all configurations.
(3) Artificial Stall Warning. Stall warning devices may be used in cases where there is inadequate aerodynamic warning. The warning signal from the devices should be clear and distinctive and not require the pilot's attention to be directed inside the airplane. A stall warning light by itself is not acceptable. If a stick shaker is installed, the warning should be unmistakable even if flying hands off.
(4) Margin. The stall warning margin, as defined in the rule, is applicable with speed reduced at a rate of one knot per second for §§ 23.201 and 23.203(a)(1).
b. Procedures.
The stall warning tests should be conducted in conjunction with the stall tests required by §§ 23.201 and 23.203.
I'll leave it to those interested to research older versions for any differences applicable to a specific Type/Model Certification.
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while the stall is not related to speed, merely angle of attack, the angle of attack that leads to a stall is most often encountered in slow flight.
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Stall is irrelevant to speed
For quasi-steady flight conditions, on the other hand, we all use speed as a useful guide to what's what in the aeroplaning world. Different matter when it starts to get more dynamic ...
For quasi-steady flight conditions, on the other hand, we all use speed as a useful guide to what's what in the aeroplaning world. Different matter when it starts to get more dynamic ...
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Stall is very relevant to speed seeing as it's the only indicator a pilot has (apart from any aural or buffeting effect) That's why they have a white arc on the speedo, the lower end of which represents the stall speed in a certain flap config for Eg.
AoA is the dynamics of the actual stall (as has been mentioned)with regards to wing shape & any delaying devices used, the leading up to it is only shown to the pilot by the speedo:-)
It is my opinion that the speedo is the single most important inst in a plane, that plus the other important commodity, height of course
Good to see healthy discussion here about a killer disease & good ref by 'JT':-0)
Wmk2
AoA is the dynamics of the actual stall (as has been mentioned)with regards to wing shape & any delaying devices used, the leading up to it is only shown to the pilot by the speedo:-)
It is my opinion that the speedo is the single most important inst in a plane, that plus the other important commodity, height of course
Good to see healthy discussion here about a killer disease & good ref by 'JT':-0)
Wmk2
The Pitot and Stall sensors are positioned to allow minimum disturbance from things such as prop wash or other localised airflow.
On large aircraft this is on the forward fuselage.
For aircraft with nose-mounted engines this is not as easy so outboard on a wing is where they go.
Piper must have found that the left wing is less prone to disturbance so it was all packed in that area. Since most of the small Piper twins have build commonality with the single version the sensors were kept in a similar place.
The Navajo has the stall warning fitted to the right wing for something different.
On large aircraft this is on the forward fuselage.
For aircraft with nose-mounted engines this is not as easy so outboard on a wing is where they go.
Piper must have found that the left wing is less prone to disturbance so it was all packed in that area. Since most of the small Piper twins have build commonality with the single version the sensors were kept in a similar place.
The Navajo has the stall warning fitted to the right wing for something different.
Last edited by 43Inches; 15th Oct 2013 at 06:00.
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Stall is irrelevant to speed.
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you can if the attitude is correct.
I've seen a stall in a cessna 150 with warning blaring at something like 100 knots. ....vertically down after a flick stall.
it was done to demonstrate and prove just that.
I've seen a stall in a cessna 150 with warning blaring at something like 100 knots. ....vertically down after a flick stall.
it was done to demonstrate and prove just that.
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why can i activate the stall warning at cruise speed while still straight and level, or even in a dive, just by pulling sharply on the stick?
Does this clear the previous statement up?
The fact that reference to speed above aerodynamic stall for pusher activation is mentioned in AFM's of slightly more sophisticated aircraft than a 172 would indicate that it's a reasonable datum measure.
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Fuji, my stall warning is also on the right (low) wing. Being a tab/microswitch type, it's vulnerable to all sorts of 'precision' adjustments by well-meaning folk. Currently set very conservatively, but it barely matters: to get into trouble in most flight regimes you'd have to work hard to induce a stall, and then consciously ignore the aerodynamic signs. But I guess it's possible. Stats for RH/LH wing drop (if it happens) on power off stalls are about equal (checked after trim tab adjustments).
Incidentally, I notice the LSA version of the aircraft doesn't have a stall warning - and they don't seem to be dropping from the sky.
At least the tab type switch is checked without the suck test. I see a lot of people sucking vigorously on C172 etc reeds without the obligatory barrier hanky. Obviously don't have spiders like the ones in our hangar!
Incidentally, I notice the LSA version of the aircraft doesn't have a stall warning - and they don't seem to be dropping from the sky.
At least the tab type switch is checked without the suck test. I see a lot of people sucking vigorously on C172 etc reeds without the obligatory barrier hanky. Obviously don't have spiders like the ones in our hangar!
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I think that's what the crew of AF447 were thinking as well...
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A case of theory vs practice, I believe. Aircraft manufacturer's POH/FCOM all have references to stall speeds, eg, Vso, Vs1, approach speed Vref = 1.3Vs .. etc.
But yet, PPL training manuals will teach that a stall can occur at any speed when the critical angle of attack is exceeded.
But yet, PPL training manuals will teach that a stall can occur at any speed when the critical angle of attack is exceeded.
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The discussion is going around in aimless circles.
(a) POH information on stall is for quasi steady state - slow reduction of speed (< 1kt/sec) to stall. Whether that be reasonable or not is not for me to say but, at least, it gives repeatable and quantifiable data of use to the certification process. If the aerodynamic warning is inadequate, one needs some artificial warning device.
(b) If you are yanking and banking the devices will respond to inertial and fluctuating airflow effects according to the design and installation. Why is anyone surprised in the slightest ? I'd be more concerned to keep a sensible lid on the yanking bit rather than worrying about spurious stall warning indications.
One can get an accelerated stall (increase/decrease) under g-loading (positive/negative). This should be covered in the principles of flight courses with the usual equation discussions.
.. as well as an unusual animal (usually described as a dynamic stall) where, under quite high pitch rates, the stall generates a short lived vortex which pushes the effective stall angle quite a bit higher than the usual item. Not a well scanned paper - the joys of 1-bit photos - but this gives a bit of information for those interested.
(a) POH information on stall is for quasi steady state - slow reduction of speed (< 1kt/sec) to stall. Whether that be reasonable or not is not for me to say but, at least, it gives repeatable and quantifiable data of use to the certification process. If the aerodynamic warning is inadequate, one needs some artificial warning device.
(b) If you are yanking and banking the devices will respond to inertial and fluctuating airflow effects according to the design and installation. Why is anyone surprised in the slightest ? I'd be more concerned to keep a sensible lid on the yanking bit rather than worrying about spurious stall warning indications.
One can get an accelerated stall (increase/decrease) under g-loading (positive/negative). This should be covered in the principles of flight courses with the usual equation discussions.
.. as well as an unusual animal (usually described as a dynamic stall) where, under quite high pitch rates, the stall generates a short lived vortex which pushes the effective stall angle quite a bit higher than the usual item. Not a well scanned paper - the joys of 1-bit photos - but this gives a bit of information for those interested.
I think that's what the crew of AF447 were thinking as well...
The reason behind focusing on angle of stall in the early theory is to strengthen the mind in relation as to how to recover from a stall and that is to reduce the angle of attack.
You can't really fly an aircraft through all stages of flight with reference to an angle of attack. It does have its place in efficiencies but as soon as you change configuration, gather ice, dirt, dent a wing etc the angles change, including stall angle.
Using speed to reference the basic max weight level stall in ISA gives a speed datum which a well trained pilot can manipulate to find where the minimum place you want to be is. You can then maintain a speed well above that and be safe.
The stall warning is just that and should go off a few knots at least before you stall. Who cares what angle you are at, reduce the attitude and power up to regain some speed ensures you move away from the stall point.
One point to make is that if you get iced up or other form of wing degredation you may stall at an angle and speed prior to stall warning activation.
Another posible reason for the placement of piper switches and pitot is on the opposite side to the cabin doors. Small Pipers are right side doors, left side sensors, PA31 left side doors right side stall sensor. It may have nothing to do with it but this may stop random bending of vanes etc. Also may offset drag caused by handles and probes, switches etc.
Last edited by 43Inches; 15th Oct 2013 at 23:01.
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'JT' it may seem that this subject is going round in circles but I think it's healthy that there are a steady flow of posts on the subject 'cause at the very least it gets some thinking about a subject that has taken many an aviator prematurely possibly thru a little misunderstanding in the first place.
Yr posts are excellent more based on the technical side of things going beyond the original posters query but hey we can never have enuf knowledge about flying as it is a dangerous environment we play in at times
Wmk2
Yr posts are excellent more based on the technical side of things going beyond the original posters query but hey we can never have enuf knowledge about flying as it is a dangerous environment we play in at times
Wmk2