IFACN
Topic Author
Posts: 149
Joined: Sun Nov 20, 2005 7:14 am

Questions About Stalling

Mon Oct 01, 2007 9:20 pm

A question for test pilots, from a student pilot that did some stalling practice on a C172 and on a CAP 10: how is stalling an airliner and recovering it from a stall? I dont' mean how to stall it, but what does the pilot experience while stalling and recovering...

Thanks,
A.
 
113312
Posts: 583
Joined: Sat Apr 16, 2005 9:09 am

Questions About Stalling

Tue Oct 02, 2007 1:26 am

Airliners have a stall warning system installed. Most are called a "stick shaker" because the stall warning system activates a device to vibrate the control column/stick. Most airline training for stall entry and recovery involves increasing angle of attack to the first indication of a stall which most often is stick shaker. Since this activates several knots prior to an actual aerodynamic stall, the recovery is begun prior to an actual stalled condition.

Since most stalls would be encountered during low speed operation close to the ground, stall practice and demonstration is usually simulated between 5000 and 10,000 feet in clean configuration, takeoff, and landing configurations and in turns. The standard recovery is to add maximum thrust and accelerate out of the stall with minimum or zero loss of altitude.

While it might be valuable to train and practice high altitude stalls or full aerodynamic stalls and recoveries without power, these are rarely done by the airlines.
 
pilotboi
Posts: 711
Joined: Thu Sep 06, 2007 8:16 am

Questions About Stalling

Tue Oct 02, 2007 2:18 am

Quoting 113312 (Reply 1):
Most are called a "stick shaker" because the stall warning system activates a device to vibrate the control column/stick.

A note: the reason airliners use stick shakers is because unlike a C172 or other small aircraft that physically shake while stalling, an airline will not do this. In fact, an airline won't even 'correct itself' like a C172. If you've ever tried it - you can stall a C172, and simply let go...and it will correct itself. But airliners will not, and will stay at the same angle of attack. So the stick shaker lets the pilot know that he must do something to correct the situation. If not corrected, the plane will start to descend and literally 'fall out of the sky', but the nose will still point up. If left uncorrected even further, a spin could be induced, making the situation even worse. So moral of all that...when flying an airliner and the stick is shaking - fix it!
 
User avatar
tb727
Posts: 1744
Joined: Thu Jun 30, 2005 1:40 pm

Questions About Stalling

Tue Oct 02, 2007 9:19 am

We practice stalls in the plane when we are doing initial training and doing our recurrent and upgrade checkrides in our jets. I am a training Captain on the Falcon 20 and we don't have a stick shaker system but we do have a stall warning system that has a warning beep and in certain configurations the Air Ignitors fire automatically along with the beep. Usually the controls get mushy and you get the horn and recover. Sometimes with a forward CG with not much fuel on board it is nearly impossible to get a good stall out of the plane for training purposes. It's a very easy recovery in a jet, just push the throttles up and fly your profile and recover. What we practice is a clean stall, an approach stall with Gear Down and 25 degrees of flaps in which we recover and stay in that config, and then a landing stall with Gear down, 40 degrees of flaps with recovery to clean configuration. The airplane will fly surprisingly slow for a midsize jet in the 20,000+ pound range, I've seen about 100 KIAS, maybe upper 90's when we hit the stall. On the other hand, the Learjet has a stick shaker system and stick pusher and I hate it!
Too lazy to work, too scared to steal!
 
roseflyer
Posts: 9606
Joined: Fri Feb 13, 2004 9:34 am

Questions About Stalling

Tue Oct 02, 2007 9:51 am

I have seen videos of 777s and 747s stall which is really interesting. The nose falls, but it does not fall anywhere as much as a Cessna. You can see the tail shaking and vibrating near the stall speed. Full thrust and a level nose attitude gets out of the stal.

A Boeing plane takes somwhere near 70lbs of force on the yoke to stall the plane, so it is a lot of work to stall to begin with. Airbus planes will not allow the pilot to stall them. Airbus planes will increase power and lower the nose on their own if they are near a stall instead of use the stick shacker that Boeing uses. This is the difference in the philosophies of the two different companies.
If you have never designed an airplane part before, let the real designers do the work!
 
411A
Posts: 1788
Joined: Mon Nov 12, 2001 10:34 am

Questions About Stalling

Tue Oct 02, 2007 10:28 am

Quoting Pilotboi (Reply 2):
the reason airliners use stick shakers is because unlike a C172 or other small aircraft that physically shake while stalling, an airline will not do this. In fact, an airline won't even 'correct itself' like a C172. If you've ever tried it - you can stall a C172, and simply let go...and it will correct itself. But airliners will not, and will stay at the same angle of attack. So the stick shaker lets the pilot know that he must do something to correct the situation. If not corrected, the plane will start to descend and literally 'fall out of the sky', but the nose will still point up.


All very interesting, Pilotboi, and from your comments you seem to have actually fully stalled a jet airliner?
Yes?

If, not, what are your references?

Now, I HAVE fully stalled two types of jet transport aircraft during acceptance flights, the B707 and the L1011.
Oddly enough, neither behaved as you described.
Different types behave differently, of course.

Gosh, what an absolute surprise.

[Edited 2007-10-02 03:45:52]
 
pilotboi
Posts: 711
Joined: Thu Sep 06, 2007 8:16 am

Questions About Stalling

Tue Oct 02, 2007 10:44 am

Quoting 411A (Reply 5):
All very interesting, Piloiboi, and from your comments you seem to have actually fully stalled a jet airliner?
Yes?

If, not, what are your references?

Nope, not at all. (Other then FS)

My references are my professors.   ERAU doesn't just give you a license remember.  

Quoting RoseFlyer (Reply 4):
Airbus planes will increase power and lower the nose on their own if they are near a stall instead of use the stick shacker that Boeing uses. This is the difference in the philosophies of the two different companies.

This is why there is that famous Airbus crash into the forest.

[Edited 2007-10-02 03:46:19]
 
User avatar
Starlionblue
Posts: 17085
Joined: Fri Feb 27, 2004 9:54 pm

Questions About Stalling

Tue Oct 02, 2007 12:24 pm

Quoting Pilotboi (Reply 6):
Quoting RoseFlyer (Reply 4):
Airbus planes will increase power and lower the nose on their own if they are near a stall instead of use the stick shacker that Boeing uses. This is the difference in the philosophies of the two different companies.

This is why there is that famous Airbus crash into the forest.

No. The causes of the Mulhouse crash don't have a lot to do with stall characteristics, although the behavior during the final stages of flight is strongly influenced by the stall protection on the aircraft. The stall protection on the aircraft prevented a stall. And so the plane crashed wings level. The crash itself was unavoidable more or less from the time the pilots started the flypast.

A Boeing product flown into the same low energy, low power, low altitude situation would also have crashed. However, it probably would have stalled before hitting the ground. A difference in detail at most.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
pilotboi
Posts: 711
Joined: Thu Sep 06, 2007 8:16 am

Questions About Stalling

Tue Oct 02, 2007 1:28 pm

Quoting Starlionblue (Reply 7):
A Boeing product flown into the same low energy, low power, low altitude situation would also have crashed. However, it probably would have stalled before hitting the ground. A difference in detail at most.

This is correct. I say we blame it on the pilot's thinking that their aircraft was capable of doing anything.  Silly
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

Questions About Stalling

Tue Oct 02, 2007 6:43 pm

Quoting Pilotboi (Reply 8):
Quoting Starlionblue (Reply 7):
A Boeing product flown into the same low energy, low power, low altitude situation would also have crashed. However, it probably would have stalled before hitting the ground. A difference in detail at most.

This is correct. I say we blame it on the pilot's thinking that their aircraft was capable of doing anything.

Pilotboi, I must agree with 411A. I have done numerous acceptance flights on 757/747/747-400 aircraft and they are no where near what you describe.

In fact, during the acceptance flights the stick shaker c/b is pulled (both systems). Next you go into the performance data with the gross weight and altitude. You then come up with an initial buffett speed. The tolerance is +1/-0 KIAS. A stalled aircraft if you let go of the controls will do exactly as a 172 will do, it's trimmed for that speed and it will seek it. Now in a fully developed aft stick stall, you're correct. But Airliners don't do those kind of stalls because of the damage that would be caused by the violend airframe buffetting!


Now if you're talking about the same type of stall training that occurs in GA, then the characteristics are much the same be it a 150/727/747400. 411A has it correct!

Quoting Starlionblue (Reply 7):
No. The causes of the Mulhouse crash don't have a lot to do with stall characteristics, although the behavior during the final stages of flight is strongly influenced by the stall protection on the aircraft. The stall protection on the aircraft prevented a stall. And so the plane crashed wings level. The crash itself was unavoidable more or less from the time the pilots started the flypast.

I disagree. The major cause of the crash was the crew's lack of knowledge of the flight control systems. The aircraft did what exactly it was asked to do. A secondary cause was the lack of spool up by the CFM which was addressed in a later mod.
Fly fast, live slow
 
Bellerophon
Posts: 516
Joined: Thu May 09, 2002 10:12 am

Questions About Stalling

Tue Oct 02, 2007 8:36 pm

Pilotboi

...My references are my professors. ERAU doesn't just give you a license remember....

I should check your notes, and then, if you have correctly reported what they said, I would recommend changing classes or school, because what you've reported them as saying is inaccurate.

Like others, I speak from experience, having stalled 3 and 4 engined jets on air tests.

Regards

Bellerophon
 
User avatar
Starlionblue
Posts: 17085
Joined: Fri Feb 27, 2004 9:54 pm

Questions About Stalling

Tue Oct 02, 2007 8:43 pm

Quoting PhilSquares (Reply 9):

Quoting Starlionblue (Reply 7):
No. The causes of the Mulhouse crash don't have a lot to do with stall characteristics, although the behavior during the final stages of flight is strongly influenced by the stall protection on the aircraft. The stall protection on the aircraft prevented a stall. And so the plane crashed wings level. The crash itself was unavoidable more or less from the time the pilots started the flypast.

I disagree. The major cause of the crash was the crew's lack of knowledge of the flight control systems. The aircraft did what exactly it was asked to do. A secondary cause was the lack of spool up by the CFM which was addressed in a later mod.

I don't think we disagree in substance. I think you are saying that the major cause was the crew not being sufficiently well trained/aware of the stall protection characteristics. Putting it that way, of course stalling characteristics (or lack of them) have a lot to do with it. I expressed myself imprecisely.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
Jetlagged
Posts: 2562
Joined: Sun Jan 23, 2005 3:00 pm

Questions About Stalling

Tue Oct 02, 2007 9:04 pm

Quoting Pilotboi (Reply 6):
My references are my professors. ERAU doesn't just give you a license remember.

I think your professors need educating. Most airliners stall like any other conventional aircraft, complete with accompanying buffet.

The stick shaker ("STALL STALL" audio warning for FBW Airbus) is there to give the pilot advance warning of an impending stall. Stick shake speed is a few knots higher than stall speed itself. Buffet will inevitably also occur, it's an aerodynamic certainty.

Quoting PhilSquares (Reply 9):
Now in a fully developed aft stick stall, you're correct. But Airliners don't do those kind of stalls because of the damage that would be caused by the violend airframe buffetting!

I'm not sure why you qualified your post with that comment. Have you experienced a full stall in such an aircraft? I have seen many flight test traces from airliner full stall tests and most Boeings, certainly the 747-200 and 747-400, exhibit strong nose down pitch at stall with full aft stick, from over 10 deg nose up (AOA over 20) thru zero to beyond 10 deg nose down. Not something you would do on an acceptance flight or in normal operation I entirely agree. However the test aircraft survived the buffet to fly another day. Most training, even in the simulator, is to initial buffet only, sometimes only to stick shaker activation.

However, Airbus aircraft such as the A300 and A320 do tend to "mush" more at full stall from the data I have seen. Very much harder to identify the stall speed (a simulator qualification requirement) without a significant g break or nose drop to mark it. Any g break there is is masked by the stall buffet normal acceleration. Maybe they don't have the elevator authority to fully stall the aircraft in the condition flown?

There is no point in putting a revenue earning aircraft through the punishment of a full stall even on acceptance, but flight test aircraft must be for certification.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

Questions About Stalling

Tue Oct 02, 2007 10:11 pm

Quoting Jetlagged (Reply 12):
I'm not sure why you qualified your post with that comment. Have you experienced a full stall in such an aircraft? I have seen many flight test traces from airliner full stall tests and most Boeings, certainly the 747-200 and 747-400, exhibit strong nose down pitch at stall with full aft stick, from over 10 deg nose up (AOA over 20) thru zero to beyond 10 deg nose down. Not something you would do on an acceptance flight or in normal operation I entirely agree. However the test aircraft survived the buffet to fly another day. Most training, even in the simulator, is to initial buffet only, sometimes only to stick shaker activation.

First of all, you have your training slightly wrong. Training is to stick shaker, not to initial buffet. Initial buffet, is, in straight and level unaccelerated flight, many knots lower than the stick shaker activation (in reality it's AOA).

As to your comment about my qualied remarks, it's because it's true. During an aircraft's certification it's brought to a complete stall. I am sure aware any swept wing aircraft will when in a fully developed stall have very similar characteristics. I remember teaching pilots to be instructors in the T-38 and doing a full aft stick stall, the VSI was begged at 6000' fpm descending and the ailerons were totally useless, but you could still do a rudder roll. The demo was to show controlability even in that flight regeim. In a swept wing aircraft with pylon mounted engines, there is considerable side loading on the pylons during an aft stick stall and there is a maintenance check required. Again, my point was to point out it's not something airliners do on a routine basis. I have taken a 727/747/747400 to a full stall and it's not something very pleasant to ride through.

Quoting Jetlagged (Reply 12):
I think your professors need educating. Most airliners stall like any other conventional aircraft, complete with accompanying buffet.

The stick shaker ("STALL STALL" audio warning for FBW Airbus) is there to give the pilot advance warning of an impending stall. Stick shake speed is a few knots higher than stall speed itself. Buffet will inevitably also occur, it's an aerodynamic certainty.

Again, I disagree. In straight and level flight you will reach stick shaker long before you reach initial buffet. While in an accelerated stall you will probably get buffet first. Your comments about airlines stall like other conventional aircraft is true but their stall characteristiics are entirely different.
Fly fast, live slow
 
9VSIO
Posts: 653
Joined: Tue Dec 19, 2006 5:00 pm

Questions About Stalling

Tue Oct 02, 2007 10:17 pm

Do they still put stick-pushers on a/c?

Quoting PhilSquares (Reply 13):
I have taken a 727/747/747400 to a full stall and it's not something very pleasant to ride through.

Can you take me up for it?  tongue  I remember once speaking to a flight test engineer who told me he always brought along an extra set of pants for the deep stall test on a C-130.  vomit 

[Edited 2007-10-02 15:25:23]
Me: (Lining up on final) I shall now select an aiming point. || Instructor: Well, I hope it's the runway...
 
bhill
Posts: 1308
Joined: Thu Sep 13, 2001 8:28 am

Questions About Stalling

Wed Oct 03, 2007 1:41 am

Curious, "Most airline training for stall entry and recovery involves increasing angle of attack to the first indication of a stall ", I am not a pilot, but why would increasing the AOA help in a stall? I thought the the idea was to return to a laminar flow of air over the wing, not to increase the turbulent flow...no?

Thanks
Carpe Pices
 
David L
Posts: 8547
Joined: Tue May 18, 1999 2:26 am

Questions About Stalling

Wed Oct 03, 2007 2:29 am

Quoting Bhill (Reply 15):
but why would increasing the AOA help in a stall?

Just a wild guess from an armchair fan: perhaps it's not supposed to help but to cause...

Quoting Bhill (Reply 15):
stall entry

... so that stall recovery training can begin.  Smile
 
flexo
Posts: 344
Joined: Thu Mar 29, 2007 6:55 pm

Questions About Stalling

Wed Oct 03, 2007 2:39 am

What about deep stalls? I heard that T-tailed aircraft are almost impossible to recover once they enter a deep stall.
Has anyone experience there?
 
David L
Posts: 8547
Joined: Tue May 18, 1999 2:26 am

Questions About Stalling

Wed Oct 03, 2007 3:01 am

Quoting Flexo (Reply 17):
What about deep stalls? I heard that T-tailed aircraft are almost impossible to recover once they enter a deep stall.
Has anyone experience there?

Wasn't it precisely the deep stalls of T-tails that brought about the stick-shaker? Prototypes of the HS Trident and BAC 1-11 crashed due to to deep stalls.
 
FlightShadow
Posts: 1060
Joined: Wed Jun 15, 2005 4:43 pm

Questions About Stalling

Wed Oct 03, 2007 5:38 am

Quoting Bhill (Reply 15):
I am not a pilot, but why would increasing the AOA help in a stall?

I'm no pilot either, but I'd like to submit a guess.

Is it because increasing the AOA will help maintain altitude for a short time, allowing for the engines to spool up? As the engines start to produce increased thrust, the laminar flow over the wing increases and the AOA can be decreased again. That way, you've avoided the stall with minimal altitude loss.

Again, that's just my guess - and I'm still kinda rusty on the terminology.
"When the tide goes out, you can tell who was skinnydipping."
 
User avatar
LTU932
Posts: 13072
Joined: Fri Jan 06, 2006 12:34 am

Questions About Stalling

Wed Oct 03, 2007 5:54 am

Quoting RoseFlyer (Reply 4):
Airbus planes will increase power and lower the nose on their own if they are near a stall instead of use the stick shacker that Boeing uses. This is the difference in the philosophies of the two different companies.

What about non-FBW Airbus aircraft (the A300/A310). Do those have a stickshaker as well?
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

Questions About Stalling

Wed Oct 03, 2007 6:56 am

Quoting Flexo (Reply 17):
What about deep stalls? I heard that T-tailed aircraft are almost impossible to recover once they enter a deep stall.
Has anyone experience there?

I've never done it myself. If you stall deep enough (your AoA increases too far) the wing blankets the tail and you loose most of your pitch control authority. It should, theoretically, be recoverable but it would be harder than a recovery when you still have clean flow over the tail.

Quoting FlightShadow (Reply 19):
Quoting Bhill (Reply 15):
I am not a pilot, but why would increasing the AOA help in a stall?

I'm no pilot either, but I'd like to submit a guess.

Is it because increasing the AOA will help maintain altitude for a short time, allowing for the engines to spool up?

If you've stalled, increasing AOA will not help maintain altitude. A stalled wing looses a lot of lift...you are now much more like an anchor than a bird. Priority numero uno in a stall is to restore flow over the wings...that means get the nose down and the speed up.

Quoting FlightShadow (Reply 19):
As the engines start to produce increased thrust, the laminar flow over the wing increases and the AOA can be decreased again.

Thrust level doesn't have any direct connection to flow over the wing. Flow also doesn't have to be laminar...a turbulent flow over the wing produces lift just fine. Turbulent and separated are very different things.

Quoting LTU932 (Reply 20):
What about non-FBW Airbus aircraft (the A300/A310). Do those have a stickshaker as well?

Yes. In aircraft with direct cable connection between the tail and the yoke, turbulence from the wing as it approaches stall will hit the elevators, which you'll feel as shaking in the stick. The electronic stick shaker mimics this phenomenon in aircraft that don't have feedback to the yoke, or where it's inadequate to provide sufficient warning to the pilot.

Tom.
 
David L
Posts: 8547
Joined: Tue May 18, 1999 2:26 am

Questions About Stalling

Wed Oct 03, 2007 7:03 am

Quoting LTU932 (Reply 20):
Quoting RoseFlyer (Reply 4):
Airbus planes will increase power and lower the nose on their own if they are near a stall instead of use the stick shacker that Boeing uses. This is the difference in the philosophies of the two different companies.

What about non-FBW Airbus aircraft (the A300/A310). Do those have a stickshaker as well?

As far as I'm aware, stick "shakers" and stick "pushers" are different things - a "shaker" is a warning while a "pusher" takes pre-emptive, corrective action. You can have one without the other... again, as far as I'm aware. I was also under the impression that stick pushers pre-date FBW in airliners by several years. I'm thinking early T-tail jets again - i.e. I didn't think it was a FBW v. non-FBW issue. Obviously, an expert will need to clarify.
 
User avatar
Starlionblue
Posts: 17085
Joined: Fri Feb 27, 2004 9:54 pm

Questions About Stalling

Wed Oct 03, 2007 8:10 am

Quoting LTU932 (Reply 20):
What about non-FBW Airbus aircraft (the A300/A310). Do those have a stickshaker as well?

Yes.

Quoting David L (Reply 22):
I was also under the impression that stick pushers pre-date FBW in airliners by several years.

Yes.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
BAE146QT
Posts: 981
Joined: Sun Sep 24, 2006 4:58 am

Questions About Stalling

Thu Oct 04, 2007 8:09 pm

Quoting David L (Reply 22):
As far as I'm aware, stick "shakers" and stick "pushers" are different things - a "shaker" is a warning while a "pusher" takes pre-emptive, corrective action.



Quoting David L (Reply 18):
Wasn't it precisely the deep stalls of T-tails that brought about the stick-shaker? Prototypes of the HS Trident and BAC 1-11 crashed due to to deep stalls.

Unless I am very much mistaken - and let's face it, it wouldn't be the first time - I was under the impression that the stick pusher was brought in for the reason you state (for the stick skaker) in post 18.

Assuming you have chosen to ignore the stick shaker, (or it's broken...) the aircraft noses over to avoid getting into an attitude where airflow over the high elevator is blocked by the "shadow" of the wing which, as was inadvertantly yet neatly demonstrated by Stanley Key, may well be totally unrecoverable.
Todos mis dominós son totalmente pegajosos
 
flexo
Posts: 344
Joined: Thu Mar 29, 2007 6:55 pm

Questions About Stalling

Thu Oct 04, 2007 9:16 pm

Quoting BAe146QT (Reply 24):
as was inadvertantly yet neatly demonstrated by Stanley Key, may well be totally unrecoverable.

I am sorry but I am not familiar with the example you stated, what exactly did he demonstrate and with what outcome?
 
David L
Posts: 8547
Joined: Tue May 18, 1999 2:26 am

Questions About Stalling

Thu Oct 04, 2007 10:29 pm

Quoting BAe146QT (Reply 24):
Unless I am very much mistaken - and let's face it, it wouldn't be the first time...

Ditto...

Quoting BAe146QT (Reply 24):
... I was under the impression that the stick pusher was brought in for the reason you state (for the stick skaker) in post 18.

... and diitto.  Smile

There just seemed to be some confusion between stick-shakers and stick-pushers.  Smile
 
Dufo
Posts: 796
Joined: Tue May 18, 1999 2:41 am

Questions About Stalling

Thu Oct 04, 2007 10:38 pm

Stick shaker feels pleasant but don't get in front of the yoke (how could that happen?) when the pusher kicks in Big grin
Speaking from EMB120 experience..
I seriously think I just creamed my pants without any influence from any outside variables.
 
User avatar
Jetlagged
Posts: 2562
Joined: Sun Jan 23, 2005 3:00 pm

Questions About Stalling

Thu Oct 04, 2007 11:00 pm

Quoting PhilSquares (Reply 13):
First of all, you have your training slightly wrong. Training is to stick shaker, not to initial buffet. Initial buffet, is, in straight and level unaccelerated flight, many knots lower than the stick shaker activation (in reality it's AOA).

Depends on aircraft type. For example on the A300B4 they go to buffet at one flap angle (I forget which), only to shaker at others. On a 747/744 at flap 1 the FAA certified stick shaker schedule is after initial buffet AOA. The CAA required a modified schedule so it is always before buffet (vane angle for stick shake is less at flap 0 and flap 1 than the standard FAA set-up). In reality it is based on an alpha vane schedule (not the same thing as AOA at all) but most people refer to stick shaker and buffet speeds for convenience.

Stick shaker speed and initial buffet speed might not be that far apart, depends on the aircraft and configuration. For example, from a flight test of a 747-400D (FAA stall warning computer), flap 1 stick shaker activates at 1 knot less than the initial buffet speed. For Flap 30 at a similar weight, buffet starts some 20 knots less than stick shaker so in this case a considerable spread.

Quoting PhilSquares (Reply 13):
As to your comment about my qualified remarks, it's because it's true.

Well we'll have to agree to disagree on that. My information comes from objective full stall flight test results which bear out what I said. Your information comes from subjective experience, presumably from the days when they used to stall these aircraft on air tests.

BTW, I never said a full stall in an airliner would be comfortable, the buffet (even in a simulator) is impressive. Nevertheless a pitch down g break is common, especially on Boeings.

I stand by my comment that Pilotboi's professors are wrong to generalise about airliner stall characteristics in that way. There is no great difference except in degree.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
IFACN
Topic Author
Posts: 149
Joined: Sun Nov 20, 2005 7:14 am

Questions About Stalling

Fri Oct 05, 2007 10:03 am

Quoting Pilotboi (Reply 2):
while stalling, an airline will not do this. In fact, an airline won't even 'correct itself' like a C172. If you've ever tried it - you can stall a C172, and simply let go...and it will correct itself

Did it with my instructor. He called it "pilotless stalling"  Smile Stall it, don't touch the commands, don't apply any power and it recovers (loosing about 500ft). Of course it must be perfectly trimmed...

Quoting PhilSquares (Reply 13):
I have taken a 727/747/747400 to a full stall and it's not something very pleasant to ride through.

I suppose so... The first time I brought our CAP-10 to a full stall and recovered, it scared the hell out of me; I can't imagine what's the feeling in a bigger plane.

Thanks a lot for your discussion!

A.
 
ex52tech
Posts: 553
Joined: Wed Dec 06, 2006 2:28 pm

RE: Questions About Stalling

Sat Oct 06, 2007 9:41 pm

Quoting Starlionblue (Reply 7):
No. The causes of the Mulhouse crash don't have a lot to do with stall characteristics, although the behavior during the final stages of flight is strongly influenced by the stall protection on the aircraft. The stall protection on the aircraft prevented a stall. And so the plane crashed wings level. The crash itself was unavoidable more or less from the time the pilots started the flypast.

When I went to Airbus school we discussed that crash at length. The pilot wasted precious seconds waiting for the auto throttles to bring the power back up on the engines to prevent the stall, but they were to low and the airplane thought it was landing, so the pilot had to add power himself, a little to late. The stall protection built into the flight control computers did keep the wings level throughout the crash, which the investigators felt was the reason for so few fatalities.

It's impressive how it works, but he was just to low for it to kick up the power. We got that straight from an Airbus instructor. The accident investigators felt that if that airplane hadn't been equipped with that system it would have dropped a wing and cartwheeled in.

Loose nut behind the wheel, or side stick in this case, was the cause.
"Saddest thing I ever witnessed....an airplane being scrapped"
 
User avatar
Starlionblue
Posts: 17085
Joined: Fri Feb 27, 2004 9:54 pm

RE: Questions About Stalling

Sun Oct 07, 2007 12:44 am

Quoting Ex52tech (Reply 30):
The pilot wasted precious seconds waiting for the auto throttles to bring the power back up on the engines to prevent the stall, but they were to low and the airplane thought it was landing, so the pilot had to add power himself, a little to late. T

Indeed.

As you say, he was too low in any case. I guess my point is that any protection systems became academic once the aircraft had been flown into a low energy, low altitude, low speed situation. Barring RATO pods, there wasn't much that could be done. Turbofans don't spool up that fast. That's why commercial aircraft are landed with quite a bit of power on in case that power is needed for a go around. In the Mulhouse case, the engines were practically idling at low altitude. BIG mistake.

As for "thought it was landing", I always find that phrase a bit weird. A go around can be performed from the runway if necessary so the aircraft itself does not hinder throttle up. However at that altitude I believe the flight computers didn't feel the need to add power ("we're landing"). Thus as you say it was up to the pilot to tell the aircraft what to do.

Quoting Ex52tech (Reply 30):
The accident investigators felt that if that airplane hadn't been equipped with that system it would have dropped a wing and cartwheeled in.

Indeed.

Quoting Ex52tech (Reply 30):
Loose nut behind the wheel, or side stick in this case, was the cause.

The pilot's main error was an inflated idea about the aircraft capabilities. I guess he drank the Cool-Aid and subconsciously told himself that the protection systems would fix most problems he created. Thus he broke the cardinal rule of "using his superior flying skills to stay out of situations where he might have to use them". And with passengers aboard!

Add to that the absence of a briefing, flying below legal airshow altitude, and a last minute (when in sight of the field) change of runway, and this was literally an accident waiting to happen.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Viscount724
Posts: 18974
Joined: Thu Oct 12, 2006 7:32 pm

RE: Questions About Stalling

Sun Oct 07, 2007 1:14 am

Quoting David L (Reply 18):
Quoting Flexo (Reply 17):
What about deep stalls? I heard that T-tailed aircraft are almost impossible to recover once they enter a deep stall.
Has anyone experience there?

Wasn't it precisely the deep stalls of T-tails that brought about the stick-shaker? Prototypes of the HS Trident and BAC 1-11 crashed due to to deep stalls.

Some deep stall and stick-shaker/pusher history here.
http://oea.larc.nasa.gov/PAIS/Concept2Reality/deep_stall.html

The complete NASA document has good summaries of quite a few other aerodynamic subjects (e.g. stalls, windshear, lightning protection, winglets etc.)
http://oea.larc.nasa.gov/PAIS/Concept2Reality/
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Questions About Stalling

Sun Oct 07, 2007 5:09 am

Quoting Jetlagged (Reply 28):
Well we'll have to agree to disagree on that. My information comes from objective full stall flight test results which bear out what I said. Your information comes from subjective experience, presumably from the days when they used to stall these aircraft on air tests

Sorry not true, since my background it in flight test both in the military and commercial side. I was involved in the 744 certification and have done numerous acceptance flights. On a new aircraft acceptance flight one thing that is tested is the initial buffett and where it is first observed. In addition, the stick shaker calibration is also verified in all flap configurations.

It's just a little more than "subjective experience".

[Edited 2007-10-06 22:13:04]
Fly fast, live slow
 
ex52tech
Posts: 553
Joined: Wed Dec 06, 2006 2:28 pm

RE: Questions About Stalling

Sun Oct 07, 2007 8:38 am

Quoting Starlionblue (Reply 31):
However at that altitude I believe the flight computers didn't feel the need to add power ("we're landing").

Yeah, that is what I meant. The "old / bold pilot" saying plays in here. I would have been impressive if he had pulled it off.

[Edited 2007-10-07 01:42:57]
"Saddest thing I ever witnessed....an airplane being scrapped"
 
David L
Posts: 8547
Joined: Tue May 18, 1999 2:26 am

RE: Questions About Stalling

Sun Oct 07, 2007 10:19 am

Quoting Ex52tech (Reply 30):

It's amazing how differently that story is related by those who know what they're talking about compared to those who've only seen the video on YouTube.  Smile

Quoting Viscount724 (Reply 32):
Some deep stall and stick-shaker/pusher history here.
http://oea.larc.nasa.gov/PAIS/Concep....html

Thanks for that.
 
User avatar
Starlionblue
Posts: 17085
Joined: Fri Feb 27, 2004 9:54 pm

RE: Questions About Stalling

Sun Oct 07, 2007 11:33 am

Quoting Ex52tech (Reply 34):
I would have been impressive if he had pulled it off.

Indeed (again). But the accident was a blessing in disguise in many ways. It made it perfectly clear to any pilot transitioning to a FBW Airbus product the dangers inherent in piloting this kind of aircraft. Not saying it is more dangerous than a "traditional" aircraft, just that the dangers are very different from those involved in piloting in other aircraft. The fact that it was all captured on tape reinforces the lesson. It's one thing to see the charred wreckage: quite another to actually see the crash on crisp footage with sound.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
Jetlagged
Posts: 2562
Joined: Sun Jan 23, 2005 3:00 pm

RE: Questions About Stalling

Sun Oct 07, 2007 5:32 pm

Quoting PhilSquares (Reply 33):
It's just a little more than "subjective experience".

Apologies, I had no idea you were involved in test flying. But I still have the objective evidence in front of me......
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
BAE146QT
Posts: 981
Joined: Sun Sep 24, 2006 4:58 am

RE: Questions About Stalling

Tue Oct 09, 2007 8:48 am

Quoting Flexo:
I am sorry but I am not familiar with the example you stated, what exactly did he demonstrate and with what outcome?

He demonstrated that if you ignore repeated warnings from the stick pusher and allow a Trident to get into a deep stall, you'll likely auger in. The result was that a hundred-odd people died.

To be fair, the crash was far more complex than that and reads like a human-factors horror story.

Long story short, he apparently suffered a heart attack while climbing out of Heathrow. There was no CVR so we'll never be 100% sure who did what in the cockpit, but it seems in his pain-addled state, he accidentally retracted the droops. The two other pilots in the cockpit with him either didn't notice, or didn't dare correct the mistake (he had seniority, they were very young, CRM was still several years in the future...), even though the aircraft was quite clearly telling them that they had better take action.

After multiple stalls and stick pusher activations, (which don't appear to have been acted upon), the aircraft entered a deep stall.

Whether the deep stall was totally unrecoverable, or whether there just wasn't altitude to do so amounts to the same thing. The aircraft went in tail-first.
Todos mis dominós son totalmente pegajosos
 
User avatar
Starlionblue
Posts: 17085
Joined: Fri Feb 27, 2004 9:54 pm

RE: Questions About Stalling

Tue Oct 09, 2007 3:06 pm

Quoting BAe146QT (Reply 30):
The two other pilots in the cockpit with him either didn't notice, or didn't dare correct the mistake (he had seniority, they were very young, CRM was still several years in the future...), even though the aircraft was quite clearly telling them that they had better take action.

IIRC he was also well known as being a hard-ass who didn't take kindly to juniors disputing his authority in any way.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
BAE146QT
Posts: 981
Joined: Sun Sep 24, 2006 4:58 am

RE: Questions About Stalling

Tue Oct 09, 2007 5:09 pm

Quoting Starlionblue (Reply 31):
IIRC he was also well known as being a hard-ass who didn't take kindly to juniors disputing his authority in any way.

Yessir, I believe that has been said of him. In fairness though, (obviously I never met him), it would probably be kinder to say that he was a product of his time.

His reportedly unprofessional behaviour in the terminal that afternoon was a response to his fellow airmen's threatened union action which, in turn, he viewed as unprofessional. It was this shouting match which may have precipitated that last heart attack, (it was non-fatal - he died of blunt force trauma apparently). He literally blew a gasket.

The above might be off-topic and I apologise to IFACN for derailing his thread, but it brings up this point;

The man was so feared, that he seems to have caused the two young, qualified pilots in the cockpit with him (Google says they were 22 and 24) to not react in time to what their aircraft was telling them. To what their aircraft must have been screaming at them. I'd love to hear an explicit description (I'm looking at you, SlamClick and PhilSquares!), of what a stall feels like in an airliner.

Anyway, it's amazing how we, as a species, can subsume our survival instinct over something so intangible and transient as "seniority". What was going through their minds as the altimeter unwound?
Todos mis dominós son totalmente pegajosos
 
David L
Posts: 8547
Joined: Tue May 18, 1999 2:26 am

RE: Questions About Stalling

Tue Oct 09, 2007 5:35 pm

Quoting BAe146QT (Reply 40):
I'd love to hear an explicit description (I'm looking at you, SlamClick and PhilSquares!), of what a stall feels like in an airliner.

 checkmark  That would be interesting. I'm guessing, among other things, a feeling that the bottom has fallen out of your world... and vice versa.
 
BAE146QT
Posts: 981
Joined: Sun Sep 24, 2006 4:58 am

RE: Questions About Stalling

Tue Oct 09, 2007 6:00 pm

Quoting David L (Reply 41):
and vice versa.

"So imagine you've had a murgh phall from the worst curry house you can think of. Now imagine you've drunk a pint of saltwater afterwards..."

Mate - the first time my instructor cut the mixture and the Big Fan stopped spinning, I felt like that.

We did this over his house in Colchester. He told me that it was a signal for his wife to wave at the plane.

I'm not sure he wasn't drunk*

I am sure that it focussed my mind.





* Kidding. Best teacher I have ever had. If you recognise yourself from that story, I want to tell you that you took my fear of aircraft away from me that day. And instilled respect.
Todos mis dominós son totalmente pegajosos
 
User avatar
Starlionblue
Posts: 17085
Joined: Fri Feb 27, 2004 9:54 pm

RE: Questions About Stalling

Tue Oct 09, 2007 10:51 pm

Quoting BAe146QT (Reply 40):
Anyway, it's amazing how we, as a species, can subsume our survival instinct over something so intangible and transient as "seniority". What was going through their minds as the altimeter unwound?

Many accounts of combat show this phenomenon, especially before the 20th century. Imagine marching slowly forward in a packed formation towards an arrowstorm or massed gunfire, while your comrades are dying around you in droves. What led people to do this? Fear of their superiors, but mostly the fear of losing face before their fellow soldiers. As it is often put, the objective is to make the soldiers more afraid of seeming like cowards than of death.

I could recommend all sorts of good Military SciFi books where this is well described.  Wink
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
IFACN
Topic Author
Posts: 149
Joined: Sun Nov 20, 2005 7:14 am

RE: Questions About Stalling

Wed Oct 10, 2007 7:58 am

Quoting BAe146QT (Reply 40):
The above might be off-topic and I apologise to IFACN for derailing his thread, but it brings up this point;

No apologies needed, all of the above discussion is really interesting to me, expecially the human factor considerations.

A.
 
IFACN
Topic Author
Posts: 149
Joined: Sun Nov 20, 2005 7:14 am

RE: Questions About Stalling

Wed Oct 10, 2007 9:34 am

Speaking of T-tail: I've recently seen some ultralight aircraft (don't ask me make or models) equipped with T-tails and wondered how they'll behave in a deep stall situation.

Remember that my experience about stalls doesn't go beyond stalling a C172 or a CAP-10...

A.
 
BAE146QT
Posts: 981
Joined: Sun Sep 24, 2006 4:58 am

RE: Questions About Stalling

Wed Oct 10, 2007 8:17 pm

Quoting IFACN:
expecially the human factor considerations.

It's funny, because those are the aspects of flying that tend to least interest hobbyists or people with a casual interest in aviation. Ironic when you consider that that's precisely the area where - according to consensus in a thread here a few months ago - aviation has improved more than anywhere else over the last 30 years.

I don't take any ghoulish pleasure in it, but I find the various CVR transcripts fascinating. Behaviour of an aircrarft in a crash can tell you much about what happened, but only the people themselves can tell you their motivations, state of mind or distractions.
Todos mis dominós son totalmente pegajosos
 
redflyer
Posts: 3882
Joined: Thu Feb 24, 2005 3:30 am

RE: Questions About Stalling

Thu Oct 11, 2007 3:10 am

Quoting PhilSquares (Reply 9):
during the acceptance flights the stick shaker c/b is pulled (both systems). Next you go into the performance data with the gross weight and altitude. You then come up with an initial buffett speed. The tolerance is 1/-0 KIAS. A stalled aircraft if you let go of the controls will do exactly as a 172 will do, it's trimmed for that speed and it will seek it. Now in a fully developed aft stick stall, you're correct. But Airliners don't do those kind of stalls because of the damage that would be caused by the violend airframe buffetting!

Fascinating post, PhilSquares. I gotta ask: what was the minimum altitude for performing stalls on a beast like the 744? Also, was anyone else on board during the stall tests? I would've loved to ride in the very nose of a 747 during a climbing stall with flaps retracted (high AOA) and feel the floor underneath drop!

Quoting Tdscanuck (Reply 21):
If you stall deep enough (your AoA increases too far) the wing blankets the tail and you loose most of your pitch control authority.

That was one reason (of several) the Piper Tomahawk never became very popular with flight schools back in the 70's when it was manufactured. It also picked up the name Piper TRAUMAhawk for that very reason. I never understood why Piper gave their "trainer" airplane a T-tail.

Quoting BAe146QT (Reply 40):

A truly excellent post! You really put that incident into perspective.

Quoting BAe146QT (Reply 40):
What was going through their minds as the altimeter unwound?

I would venture to guess what goes through most pilot's minds when the instruments tell them something is happening that they THINK should not or could not possibly be happening -- they spend precious time analyzing the situation without doing the obvious.
My other home is in the sky inside my Piper Cherokee 180.
 
BAE146QT
Posts: 981
Joined: Sun Sep 24, 2006 4:58 am

RE: Questions About Stalling

Thu Oct 11, 2007 4:46 am

Quoting RedFlyer (Reply 47):
A truly excellent post! You really put that incident into perspective.

Many thanks, Red. Nice of you to say so.

Quoting RedFlyer (Reply 47):
I would venture to guess what goes through most pilot's minds when the instruments tell them something is happening that they THINK should not or could not possibly be happening -- they spend precious time analyzing the situation without doing the obvious.

The trouble is that taking an action without assessing a situation can make it worse, though how much worse your situation can get when you're stalled in an airliner at a few thousand feet probably doesn't require much debate.

I'm not a psychologist, (and I don't play one on TV) but think you could view the phases of the thought process as something like this;

1) Disbelief -----> 2) Acceptance/Comprehension -----> 3) Analysis/Planning ------> 4) Action

In the case of Papa India's flight crew, I doubt that they reached the planning stage. They may well not have known that those high-lift devices had been retracted and, if that was the case, then I reckon you're right - they sat there wondering what was happening to them.

Mind you, I've now been at work for 21hours straight, so there is a chance I'm rambling.
Todos mis dominós son totalmente pegajosos
 
IFACN
Topic Author
Posts: 149
Joined: Sun Nov 20, 2005 7:14 am

RE: Questions About Stalling

Thu Oct 11, 2007 4:30 pm

Quoting BAe146QT (Reply 46):
Quoting IFACN:
expecially the human factor considerations.

It's funny, because those are the aspects of flying that tend to least interest hobbyists or people with a casual interest in aviation. Ironic when you consider that that's precisely the area where - according to consensus in a thread here a few months ago - aviation has improved more than anywhere else over the last 30 years.

I'm always interested in understanding the man-machine interaction and how the 4M (mission, meteo, man, machine) are the key points to a safe flight. Mostly because, after a good classroom training and 35 hrs in the cockpit of a C172, I now understand how important are one's "human performances and limitations", even if I'm going to fly only a traffic pattern.

A.

Who is online

Users browsing this forum: Bambel, Yahoo [Bot] and 12 guests