Stall warning

Cap'n Jack said:
Tom, aren't at least stall warning devices a crude angle of attack indicator? If they were based simply on speed, they wouldn't go off in an accelerated stall.

Also, please note the image below from a Cessna.

stallsw.jpg


Confirming my supposition, I ran into this comment from you:

(found this after I made my post)
Click to expand...

Correct, they work on AoA and actual airflow which makes them even more accurate indicators of stall than the ASI. The other day when I did my BFR I was doing a short field landing and my CFI indicated "we're below the white arc", "you hear a stall horn going off (I knew it worked since we had already done stalls and slow flight)?" "Nope" "We still flying?" "Yep" "then we're fine.":D
 
Tom-D said:
Almost every stall warning device can be adjusted to go off prior to the stall.

If it doesn't contact your A&P and get it fixed.
Click to expand...

If it doesn't what good is it? This is sort of like the brake light on my old mustang that came on after I pushed the pedal to the floor with no affect on my car's speed. (Those of you who know what that light does should no why).
 
Cap'n Jack said:
Tom, aren't at least stall warning devices a crude angle of attack indicator? If they were based simply on speed, they wouldn't go off in an accelerated stall.

Also, please note the image below from a Cessna.

stallsw.jpg


Confirming my supposition, I ran into this comment from you:

(found this after I made my post)
Click to expand...

Yes BUT,

They are set by airspeed under controlled conditions.

For example a Cessna (going from memory so pardon any errors) is set by slowing the plane 1kt/sec strait and level. The warning should sound X kts before the stall under those conditions.

Remember that at a constant load AOA and airspeed will vary together.
 
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all stall warning devices were not vanes.

the Cessna 150 simply is a hole in the leading edge that when the airflow is changed the tweeter makes a noise, all it is, is a baby dolls tweeter it is the least expensive item in the IPC. $.39 at the cessna dealer last I bought one.

you loosen two screws and move the hole to change the stall speed.
 
My Aerostar doesn't have one. The wing gave such ample buffet warning it wasn't deemed necessary during certification.
 
Call me old fashioned.. But.....

I view a stall warning indicator as a crutch for poor piloting skills...It is part of the dumbing down of society.. Similar to the devices they advertise on TV for new cars that have auto braking systems for dumb drivers that don't pay attention.. Etc,Etc,Etc....

If you can't feel the plane's controls getting sluggish and the wing shuddering from the slow airspeed flowing over it, you really should not have a pilots license. IMHO...

Flame suit on...:redface:
 
N801BH said:
Call me old fashioned.. But.....

I view a stall warning indicator as a crutch for poor piloting skills...It is part of the dumbing down of society.. Similar to the devices they advertise on TV for new cars that have auto braking systems for dumb drivers that don't pay attention.. Etc,Etc,Etc....

If you can't feel the plane's controls getting sluggish and the wing shuddering from the slow airspeed flowing over it, you really should not have a pilots license. IMHO...

Flame suit on...:redface:
Click to expand...
I don't disagree with you, however, in most cases we as pilots don't get a choice in whether a particularly airplane has a stall warning or not. That is decision is made during certification by the FAA. As I understand it, whether or not the stall warning is required depends entirely on how the wing behaves during the stall and how much warning it gives. This is why the 1948 170 does not require a stall warning, but the 170B is not airworthy without it. Same basic model, but completely different wing.
 
N801BH said:
Call me old fashioned.. But.....

I view a stall warning indicator as a crutch for poor piloting skills...It is part of the dumbing down of society.
Click to expand...

Couldn't you could say the same about every instrument in the panel...when VFR?

Anyone who flies a 182 for a month or so with the ASI covered will learn a LOT about that airplane.
 
Skylane81E said:
Yes BUT,

They are set by airspeed under controlled conditions.

For example a Cessna (going from memory so pardon any errors) is set by slowing the plane 1kt/sec strait and level. The warning should sound X kts before the stall under those conditions.

Remember that at a constant load AOA and airspeed will vary together.
Click to expand...
That vane in the photo I posted is in the "non-stall position". When parked, taxi-ing, and take off run before the wing is flying, the stall warning doesn't go off.

This suggests there is either a switch on the landing gear system someplace that quiets the stall warning, or that vane doesn't care about speed but rather which side of it has higher pressure (AOA). I suspect that the warning is set by speed a few knows above stall as you suggest, because this produces the desired angle of attack.

Is this set by actually flying the plane, or is there a procedure that allows it to be set on the ground?
 
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Tom-D said:
all stall warning devices were not vanes.

the Cessna 150 simply is a hole in the leading edge that when the airflow is changed the tweeter makes a noise, all it is, is a baby dolls tweeter it is the least expensive item in the IPC. $.39 at the cessna dealer last I bought one.

you loosen two screws and move the hole to change the stall speed.
Click to expand...
I suspect this is also an AOA device...the air only blows in the hole and blows the whistle at the "correct" range of angles corresponding to a stall or incipient stall. By moving the hole, one is changing the angle at which air blows into the hole, and thus the AOA that sets off the tweeter.

Some of the AOA indicators one can purchase for experimental planes are also pressure based, and basically measure the pressure differential from two inlets set at slightly different angles. The difference in pressure corresponds to a given angle of attack and isn't based on airspeed. I thought it was rather clever.
 
Tom-D said:
all stall warning devices were not vanes.

the Cessna 150 simply is a hole in the leading edge that when the airflow is changed the tweeter makes a noise, all it is, is a baby dolls tweeter it is the least expensive item in the IPC. $.39 at the cessna dealer last I bought one.

you loosen two screws and move the hole to change the stall speed.
Click to expand...

I always call it the party horn. I figured in addition to making that noise it should unroll the little tube in front of the pilot's face.
 
Cap'n Jack said:
That vane in the photo I posted is in the "non-stall position". When parked, taxi-ing, and take off run before the wing is flying, the stall warning doesn't go off.

This suggests there is either a switch on the landing gear system someplace that quiets the stall warning, or that vane
Click to expand...

It's lightly spring loaded to that position in most cases (though it need not be). It indeed measures angle of attack. As the AOA increases that point on the wing goes from being pretty much inline with the relative wind to being above it. Once it is above it the vane flips and the horn goes off.

The party horn style does the same thing. It goes from ram air to being blown across (i.e., negative pressure) which sucks on the reed in the party horn.

Tom-D is right in that it is calibrated by using airspeed, (because there's no real good way not having a wind tunnel to test angle of attack). The stall speed is the point that you exceed the critical angle trying to maintain unaccelerated (level) flight. Airspeed however has no bearing on how the stall warning works, which is fortunate because airspeed has no bearing on stall.

By the way, the wing is "flying" any time there is air moving across it. The stall horn does not sound during taxi (usually) because the aircraft is not stalled. Inadequate lift to counter weight is NOT the definition of a stall.
 
Cap'n Jack said:
That vane in the photo I posted is in the "non-stall position". When parked, taxi-ing, and take off run before the wing is flying, the stall warning doesn't go off.

This suggests there is either a switch on the landing gear system someplace that quiets the stall warning, or that vane doesn't care about speed but rather which side of it has higher pressure (AOA). I suspect that the warning is set by speed a few knows above stall as you suggest, because this produces the desired angle of attack.

Is this set by actually flying the plane, or is there a procedure that allows it to be set on the ground?
Click to expand...

I don't understand what you're saying...

You say the vane is in the "non-stall position" which is correct but then you say "this suggests there is either a switch on the landing gear system someplace that quiets the stall warning".

But, if it's in the "non-stall position" there would be no warning while on the ground. Additionally, "When parked, taxi-ing, and (during the) take off run before the plane is flying, the stall warning doesn't go off" because there is no reverse airflow over the vane. The plane isn't flying in those cases because of low airspeed and not because the angle of attack is being exceeded.

(I see Ron beat me to some of this...sorry for the repeat)
 
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Cap'n Jack said:
That vane in the photo I posted is in the "non-stall position". When parked, taxi-ing, and take off run before the wing is flying, the stall warning doesn't go off.

This suggests there is either a switch on the landing gear system someplace that quiets the stall warning, or that vane doesn't care about speed but rather which side of it has higher pressure (AOA). I suspect that the warning is set by speed a few knows above stall as you suggest, because this produces the desired angle of attack.

Is this set by actually flying the plane, or is there a procedure that allows it to be set on the ground?
Click to expand...

The stall warning doesn't go off on the ground because the aircraft isn't stalled, eg there is no vertical airflow up the leading edge to trigger the switch/suck the reed.
 
We were tipping a few at the club one evening when the skipper of VA 128 (A6 Mother squadron) related a story to us, he asked a young aviator why it required the flares and flashing lights to get him to wave off and go around.

the young aviator told him between the landing gear warning, and the stall warning he couldn't hear the tower tell him his gear wasn't down.

Every body except the skipper thought that was funny, skippers have a different sense of humor.
 
My CTSW doesn't have one. Some CTs have AoA indictors through their Dynon displays, mine has a simple pitot so I'd have to change it out to enable AoA.
 
I've owned two without and flown several without. I've been thinking about an AOA indicator but the plumbing would be difficult.
 
flyingron said:
<SNIP>

By the way, the wing is "flying" any time there is air moving across it. The stall horn does not sound during taxi (usually) because the aircraft is not stalled. Inadequate lift to counter weight is NOT the definition of a stall.
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Yep- I never said the wing was stalled, just saying that speed wasn't what set off the stall warning; It seemed the post I replied to implied it was speed based although it is a matter in how the sentence could be interpreted.
 
Henning said:
The stall warning doesn't go off on the ground because the aircraft isn't stalled, eg there is no vertical airflow up the leading edge to trigger the switch/suck the reed.
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Yep. That's pretty much what I was getting at. I replied to a post which could be interpreted (perhaps incorrectly) that speed set off the warning.
 
timwinters said:
<SNIP>

(I see Ron beat me to some of this...sorry for the repeat)
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No prob... I figured that instead of directly challenging someone, I'd ask a question to get a clearer answer. Who knows? Maybe I'll learn something..
 
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This type question goes in the same file as......what type of license plate holder should I acquire and does it hurt to leave a plane outside in the weather. 86.
 
Cap'n Jack said:
Yep. That's pretty much what I was getting at. I replied to a post which could be interpreted (perhaps incorrectly) that speed set off the warning.
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No one said speed set off the warning, just that we use speed to SET WHERE the warning triggers, we aren't worried about what the speed is, just that the warning goes off a set speed before the stall breaks.

Again, under constant load AOA and airspeed are related, More speed less AOA and vice versa.
 
Tom-D said:
Have you flown any aircraft that does not have one?
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Are you referring to the aircraft just quit flying with no hint?
Or the lack of an aural or visual light stall warning device?

most gliders do not have any stall warning device other than the visual, nose high, low airspeed, sloppy controls, wind noise decreases, and if you're lucky maybe a little buzz in the elevator (2-33 or 1-26)
 
BillTIZ said:
Are you referring to the aircraft just quit flying with no hint?
Or the lack of an aural or visual light stall warning device?

most gliders do not have any stall warning device other than the visual, nose high, low airspeed, sloppy controls, wind noise decreases, and if you're lucky maybe a little buzz in the elevator (2-33 or 1-26)
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I didn't refer to any thing. see my last post prior to this.
 
This whole thread and no one has pointed out whether stall warnings are set to go off at an indicated airspeed or a calibrated one. ;)

(Ducking...)
 
Skylane81E said:
No one said speed set off the warning, just that we use speed to SET WHERE the warning triggers, we aren't worried about what the speed is, just that the warning goes off a set speed before the stall breaks.
Click to expand...
Please note what was written in post #27 in this thread

Skylane81E said:
Again, under constant load AOA and airspeed are related, More speed less AOA and vice versa.
Click to expand...
I'm pretty sure I didn't post anything disagreeing with this comment, thank you for confirming my understanding of speed and angle-of attack with a given load.
 
Fearless Tower said:
I don't think I have ever had a stall warning go off that I wasn't expecting with the possible exception of hearing brief chirps in really rough air.
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Did you notice how those brief chirps were at a much higher airspeed?
Brief upgusts of air which effectively increase AoA .
Stall warning systems are set to activate a few kts above stall in normal unaccelerated flight as in a landing flare.
Higher loads on the wings at higher speeds still increase AoA to activate the stall warning.
Regardless of speed.
So it is really all about AoA, and understanding the relationship of speed to AoA.
 
Just because an aircraft has no stall warning system, it doesn't mean it will give you no warning.
All the birds I have fliwn without "party horns" have had some quirk or other- usually pronounced buffeting of turbulent airflow onto the aft fuse and/or empennage-that provided adequate warning that a stall was developing. The two rag and tube frame gliders I have been flying have this characteristic, to the extent that youd have to be asleep to miss it, even if you suddenly yanked and banked either one of them. To a lesser extent I have noticed this feedback with the J3, 7AC, Citabria, C140, and some C150s and C172s with inop horns. In addition to buffeting, theres changes in airflow sound, and of course pitch attitude.
For airplanes in this vein, no horn or ASI is really needed for stall recognition, IMHO.
 
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