Stall Warning
Thread Starter
Joined: Oct 2013
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From: Auckland, NZ
Stall Warning
Hi all,
Have recently been asked a question that I can't find the answer to anywhere. It is:
Why do we only have one stall warning sensor when we have 2 wings?
I thought it could be to do with one wing stalling first but have been told that is not the case.
If anyone knows the real reason it would be awesome.
Have recently been asked a question that I can't find the answer to anywhere. It is:
Why do we only have one stall warning sensor when we have 2 wings?
I thought it could be to do with one wing stalling first but have been told that is not the case.If anyone knows the real reason it would be awesome.
Joined: Aug 2013
Posts: 73
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From: YMMM
Stall warning is not designed to sound at the stall AoA, rather in most cases 5-10 knots above the stall speed (actually whatever AoA that corresponds to).
So a stall warning only gives you a 'ballpark' warning that you're approaching the critical AoA, So in theory neither wing should be stalled at the point it sounds.
It's purely a warning device.
So a stall warning only gives you a 'ballpark' warning that you're approaching the critical AoA, So in theory neither wing should be stalled at the point it sounds.
It's purely a warning device.
Joined: Oct 2012
Posts: 85
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From: Australia
On light aircraft, I can see a few reasons:
(1) Cost - installation and maintenance. You'd want them to be calibrated so that they go off at exactly the same angle of attack; otherwise the left one might go off first even though the right wing is actually closer to a stall.
(2) Weight. It isn't much weight, but every kilogram counts.
(3) If one wing is in a stall, the other wing is probably very close to a stall. Not much point warning about a stall on the left wing and then warning about the right wing half a second later.
(4) How to indicate it? The planes I've been in use a light and/or a buzzer. If there are two different warning tones (one for each wing) then that's just going to confuse people. If there are lights, by the time you've actually identified which wing is close to stalling, the other one is probably stalling too.
In bigger aircraft, where the computers might be able to do something sensible even if the pilots can't, there might be a good reason for it - but if the computers are in control then the plane will never get anywhere near a stall on either wing.
(1) Cost - installation and maintenance. You'd want them to be calibrated so that they go off at exactly the same angle of attack; otherwise the left one might go off first even though the right wing is actually closer to a stall.
(2) Weight. It isn't much weight, but every kilogram counts.
(3) If one wing is in a stall, the other wing is probably very close to a stall. Not much point warning about a stall on the left wing and then warning about the right wing half a second later.
(4) How to indicate it? The planes I've been in use a light and/or a buzzer. If there are two different warning tones (one for each wing) then that's just going to confuse people. If there are lights, by the time you've actually identified which wing is close to stalling, the other one is probably stalling too.
In bigger aircraft, where the computers might be able to do something sensible even if the pilots can't, there might be a good reason for it - but if the computers are in control then the plane will never get anywhere near a stall on either wing.
Joined: May 2013
Posts: 1,126
Likes: 2
From: have I forgotten or am I lost?
statye .....nonsense.
in a lightie it is usually on the left wing because we do left turn circuits and the left wing is occasionally slower.
your point 3 WTF!! you would want the stall warning to come on if either wing was about to stall. think about it!
avconnection. the stall angles as you call them are 'trips' to induce stalling on the inboard end of the wing while keeping the ailerons flying.
in a lightie it is usually on the left wing because we do left turn circuits and the left wing is occasionally slower.
your point 3 WTF!! you would want the stall warning to come on if either wing was about to stall. think about it!
avconnection. the stall angles as you call them are 'trips' to induce stalling on the inboard end of the wing while keeping the ailerons flying.
Joined: Oct 2009
Posts: 497
Likes: 2
From: In the doghouse
Go out to your local training area, and do some stalls. Really take notice of whats happening (if you have some SCT cloud above even better for vis ref)
Power to idle
Maintain height with steady app of BP
eventually you will have a..
High nose attitude and You will start to gently yaw left (usually stopped with rudder-clouds as a backdrop help to see this)
Low and reducing airspeed
Reduced control effectiveness
5-10kts above the stall-Stall warning
Control buffett around the stall(high wing or low wing will determine exactly when this happens)
CoP moves rearward, nose drops and if you do absolutely nothing the aircraft will try to recover.
In the app config the stall occurs at a lower nose attitude and tends to be stronger stall with the possibility of a WD, and the vast majority of wing drops are to the left.(why?higher power setting, lower airspeed)
I cant find any written evidence as to why the stall is designed on the left wing, but I doubt it is due to left CCTS.
Id say it is more to do with aerodynamic issues approaching and during the stall as most SE AC have a tendency to yaw left at low speed due slipstream/torque (yes it still has an effect at idle particularly at low speed).
A number of AC if they have electric stall warning will share same circuit as pitot heat and or lights(usually on the left as well) Although this seems less of a deciding factor, but then again a lot of twins are the same with the vanes on the left?....
Power to idle
Maintain height with steady app of BP
eventually you will have a..
High nose attitude and You will start to gently yaw left (usually stopped with rudder-clouds as a backdrop help to see this)
Low and reducing airspeed
Reduced control effectiveness
5-10kts above the stall-Stall warning
Control buffett around the stall(high wing or low wing will determine exactly when this happens)
CoP moves rearward, nose drops and if you do absolutely nothing the aircraft will try to recover.
In the app config the stall occurs at a lower nose attitude and tends to be stronger stall with the possibility of a WD, and the vast majority of wing drops are to the left.(why?higher power setting, lower airspeed)
I cant find any written evidence as to why the stall is designed on the left wing, but I doubt it is due to left CCTS.
Id say it is more to do with aerodynamic issues approaching and during the stall as most SE AC have a tendency to yaw left at low speed due slipstream/torque (yes it still has an effect at idle particularly at low speed).
A number of AC if they have electric stall warning will share same circuit as pitot heat and or lights(usually on the left as well) Although this seems less of a deciding factor, but then again a lot of twins are the same with the vanes on the left?....
Last edited by Homesick-Angel; 14th October 2013 at 12:56.
Joined: Oct 2009
Posts: 497
Likes: 2
From: In the doghouse
if you have no evidence why do you doubt it?
And..Im reading this on PPrune
Im happy to be proven wrong..
Id like to know definitively as well.
Joined: Apr 2005
Posts: 469
Likes: 14
From: Lost in the space-time continuum
Last time I looked the Aerostar that I use didn't have any stall warning devices of any description installed on the airframe. Go figure!
I suppose Mr.Smith (and the FAA) was of the opinion that the airframe itself gave off enough hints that it was about to stop aviating.
I suppose Mr.Smith (and the FAA) was of the opinion that the airframe itself gave off enough hints that it was about to stop aviating.
Joined: Nov 2008
Posts: 2,890
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From: The Shire
In bigger aircraft, where the computers might be able to do something sensible even if the pilots can't, there might be a good reason for it - but if the computers are in control then the plane will never get anywhere near a stall on either wing.
P.S The computers are never in control. They are merely doing what they are told to do by the Pilot.
Joined: May 2013
Posts: 1,126
Likes: 2
From: have I forgotten or am I lost?
ok
in part of a circuit you are doing a descending turn to the left.
since this is not far from the ground it is important that you dont stall there.
in the descending turn the left wing is flying slower and has a higher angle of attack than the right side wing. thus the left wing is closer to the stall.
so it make sense to place the stall warning on the left wing.
next time you turn finals just remember that the designer did his best to help you avoid stalling in that turn. the rest is up to you.
in part of a circuit you are doing a descending turn to the left.
since this is not far from the ground it is important that you dont stall there.
in the descending turn the left wing is flying slower and has a higher angle of attack than the right side wing. thus the left wing is closer to the stall.
so it make sense to place the stall warning on the left wing.
next time you turn finals just remember that the designer did his best to help you avoid stalling in that turn. the rest is up to you.
Joined: Jan 2008
Posts: 2,296
Likes: 305
From: All at sea
I suspect that in most bugsmashers, the location of the stall sensor is more to do with ease of design, i.e. the wiring and plumbing arrangements for that particular airframe. Simplicity and cheapness are more likely to have been the drivers.
In heavier iron there will be duplicate stall warning systems - one per side. - and all sorts of clever comparitors to prevent false warnings. Many of these sensors are not even on the wing, but are angle of attack 'vanes' situated on each side of the nose.
Which way you normally turn would have little to do with the designer's thought process because he at least knows that the relative speed of the wings in a turn is so small as not to matter. Do the math. On a typical bugsmasher it is so little that it can't be measured with conventional instruments.
As airframes age, stall characteristics can change. I have flown old beat-up aircraft of exactly the same type where in a full-on stall one will drop the left wing first while the other will drop the right wing. One will flick into an incipient spin without notice, the other will stay wings level and buffet and mush in a benign manner.
In heavier iron there will be duplicate stall warning systems - one per side. - and all sorts of clever comparitors to prevent false warnings. Many of these sensors are not even on the wing, but are angle of attack 'vanes' situated on each side of the nose.
Which way you normally turn would have little to do with the designer's thought process because he at least knows that the relative speed of the wings in a turn is so small as not to matter. Do the math. On a typical bugsmasher it is so little that it can't be measured with conventional instruments.
As airframes age, stall characteristics can change. I have flown old beat-up aircraft of exactly the same type where in a full-on stall one will drop the left wing first while the other will drop the right wing. One will flick into an incipient spin without notice, the other will stay wings level and buffet and mush in a benign manner.
Joined: Feb 2006
Posts: 1,697
Likes: 9
From: Melbourne
Last time I looked the Aerostar that I use didn't have any stall warning devices of any description installed on the airframe.