Can airliners recover from a stall?

[allwerp]

Or is it just impossible to stall an airliner as it's got some sort of stick-pusher mechanism........:confused:

[used2flyboeing]

All airliners have gizmos to prevent stall and pitch instability that could lead to stall - Boeing uses autoslats, stick pushers, stick nudgers and engine nacelle vortex vanes/chines.

The T-tail 727 configuration has an unrecoverable deep stall characteristic hence the stick pusher or nudger. Some 767 have a stick nudger because of pitch instability - but this was removed by adding nacelle vanes. Everything else Boeing is stick shaker & autoslats .. but these arent too new - Even the Tigermoth has these really cool spring loaded autoslats for stall

Ive heard that AIRBUS has better climb performance in windshear because the computer FBW is better able to nail the stall margins to the ragged edge - then a sweating Boeing pilot with pucker factor ..

[barit1]

A lot of airliners have used nacelle strakes - the DC-10 for example. DC-8-70's likewise. They're generally used to improve deep stall characteristics.

One airline got annoyed with forgetful technicians leaving tools atop the thingies, and removed them. The manufacturer's rep got wind of this and saw to it they were reinstalled.

[Old Smokey]

allwerp,

Airliners either can (A) recover normally from a fully developed stall, or (B) have on-board systems preventing stall entry, or (C) have fitted systems or aerodynamic assistance (such as strakes) to augment normal recovery from the stall. Without falling into one of these categories, the aircraft could not gain certification.

Don't confuse this issue with the deep stall discussion on another currently running thread. Having done a fair bit of testing work in endeavouring to take this category of aircraft beyond the normal stall into the "deep stall", the object of the testing was always to ascertain that recovery was possible. It always was. Not so for the poor souls who lost their lives during BAC-111 testing, but their legacy carried on to later generations of aircraft (and at the time caused Douglas to enlarge and redesign the Stabiliser/Elevator system on the DC9).

used2flyboeing, are you sure you're not confusing the DC9 with the B727? I flew both extensively, and clearly recall the very necessary hydraulic actuation of the elevators in a forward control push, but recall no such system on the B727. Maybe C.R.A.F.T's disease is catching up with me.

Regards,

Old Smokey

[corporal klinger]

how about a spin ? any recovery possible?
may be someone tried in the sim..?

[747FOCAL]

Are we sure he is not asking if they can be intentionally held to deep stall. If that is what he is asking, the answer is yes. Hold the stick back(Boeing) and you will eventually enter deep stall regardless of the backup systems. Is it recoverable at that point? Depends on the pilot. During certification of a 727 hushkit I went through 600+ stalls as the observer. Some were so deep that the indicated air speed was less than 80 kts. During one stall, the right wing broke early and we went about 95% of the way to inverted.

If you want to get real cute, lets start talking about wind up stalls. :)

[Boeing737]

During certification of a 727 hushkit I went through 600+ stalls as the observer. Some were so deep that the indicated air speed was less than 80 kts. During one stall, the right wing broke early and we went about 95% of the way to inverted.

Jeez, that must of been some ride!Whats it like experiencing a stall in an airliner and nearly rolling completely over?i know what its like in a light aircraft (stalls that is, not inverted flight!) :}
regards
(P.s what are wind up stalls?)

[Old Smokey]

The odd-ball thing is that, having entered the deep stall (usually by 'wind-up), if the wing dropped to vertical, or you went inverted, you were 'out of the poo', because you now had normal airflow over the tail surfaces. If you mismanaged the ensuing rapid descent with increasing speed, you were back in the poo of a different type.

Normal 'full back stick' stall testing is done with idle thrust, and stabiliser trim trimmed for Vs+10, and a controlled deceleration at 1Kt/sec until stall occurs. 747FOCAL's and my definition of a 'wind up' stall may differ, but for deliberate efforts to enter the deep stall, large UP stabiliser trim was used with large thrust settings to gain high pitch attitudes just pre-stall, and then chopping the thrust and rapidly applying full UP elevator. Disneyland offers no more exciting ride.

corporal klinger, tried many fully developed spins in the simulator "just in case". Never recovered successfully from one of them.

Regards,

Old Smokey

[erikv]

All airliners that have been certified under JAR/FAR 25 (wouldn't know of a current type that isn't) can recover from a stall. On aircraft on the British register, this is even demonstrated during an air test each time the certificate of airworthiness is renewed.

It must be possible to recover (with our without assistance from devices such as a stick-pusher), but also to maintain lateral control by means of unreversed operation of the ailerons within 20 degrees of bank. Please note the difference to JAR/FAR 23 a/c where it is taught not to use ailerons in a stall and rudder is used instead.

Erik.

[Confabulous]

Remember the case of the Russian A300 that someone let his son fly? Reading the accident report, it seems that that aircraft stalled and spun. They recovered from autorotation into a dive, but too late to avoid making a crater.

Conf

[747FOCAL]

There was one flap setting (5 If memory suits me) where the Boeing test pilots did the heavy aft cg inverted thing and ended up losing nearly 20,000 ft of altitude before getting it back at around 2500 ft.

Just had a friend go up in a learjet test flight where they entered stall and it would not push over and they fell for like 20 seconds with it kicking and bucking all over the place. Full redline power is the only thing that saved them.

For those of you that have been in actual stalls, question for you.... Granted its more pronounced in tail mounted engines, but what do the noises your hearing from the aircraft sound like to you?

:)

[john_tullamarine]

A note of caution for those who might be tempted to generalise or extrapolate from the particular to the general and play test pilots with their light aircraft ...

Be aware that stall definitions and test protocols have varied over the years. In particular, some aircraft were tested only to the point of stall and to pull such animals into the stall might well involve some excitement ... like being upsidedown and/or spinning.

Be very wary of using rudder to do things in the stall.

[747FOCAL]

john_tullamarine is right. Playing around with stalls is not for the amatuer pilot. I have never flown them accept in the sim. The only way I will go up and do anything like that is if the pilots flying have been doing it for years. There are only a few places on the planet you can find them boys and at $1000 USD per flight hour I think maybe Disneyland would be a better choice.

:cool:

[fireflybob]

Notwitstanding that some T tail types may not recover due to deep stall, perhaps we ought to add that other types will recover providing there is sufficient height to recover before hitting the ground!

[AfricanSkies]

"what do the noises your hearing from the aircraft sound like to you?"
-----------

At somewhere less than 80kts on a T-tail at FL290 it goes really quiet and its as if she's relaxing, a few joints creaking...

[barit1]

BAD things can happen (http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001208X07150&key=1)

[4seater]

The initial stall characteristic in the Robin 2160 (although not a jet aircraft) is a very fast roll rate during the initial 3 to 4 spins (incipent stage), once you have developed into a stable spin the prop stops spinning and the only sound is the wind moving over the aircraft.

The recovery technique that I have been taught is the Beggs procedure 1) Throttle to iddle 2) identify direction of the spin 3) Take your hands off the stick, place on top of dash 4) Full opposite rudder until spinning stops 5) allow the speed to increase until the prop start starts spinning again 6) pull up out of the dive.

[Old Smokey]

barit1 describes a horrifying, but completely avoidable situation. As tha accident report indicates, the flight crew had received no training in recovery from the fully developed stall. Not their fault, and not the fault of probably most airline pilots who have never seen the stall characteristics of their aircraft.

The standard training syllabi indicate training for recovery from the stall warning only. In one sense that's a good thing, the aircraft is still fully controllable, and the onset of the stall warning is the appropriate time to IMMEDIATELY initiate stall recovery actions, there's no question about that. On the other hand, with high fidelity simulators available, I have always campaigned for additional simulator training demonstrating the fully developed (full back stick) stall, and have always given that exercise to my trainees as a bit of 'bonus' training. Control and recovery procedures differ considerably from their earlier full stall training on prop aircraft, and the application of the intuitive responses learned at this phase could be disastrous. Sadly, this seems to have been the case for the ill-fated DC8 crew, who might have benefited from such training.

I have done a lot of fully developed stalls during flight testing, but, with trainees in the aircraft whilst awaiting simulator certification, also did a lot of recoveries from the stall warning, NEVER to the fully developed stall. On one occasion, the student got such a fright as the overly assertive stall warning triggered, that he applied full BACK stick, precipitating the full stall. On that day, my own full stall exposure paid big dividends. It can, and does, happen.

Hopefully, one day, pilots will receive simulator training in recognition of and recovery from the full stall. Until that day, the title of this forum should perhaps have been amended from "Can airliners recover from a stall?" to "Can airline pilots recover from a stall?"

Regards,

Old Smokey

[Boeing737]

There was one flap setting (5 If memory suits me) where the Boeing test pilots did the heavy aft cg inverted thing and ended up losing nearly 20,000 ft of altitude before getting it back at around 2500 ft.
Just had a friend go up in a learjet test flight where they entered stall and it would not push over and they fell for like 20 seconds with it kicking and bucking all over the place. Full redline power is the only thing that saved them.
i think thats enough to frighten the **** out of anybody! :sad: :yuk: :)
how far do you reckon they will go with stall testing on the a380?surely they will only be incipient stalls. :}

[Old Smokey]

how far do you reckon they will go with stall testing on the a380?
All the way, certification requires it. And, as a special bonus, the Australian CAAS will want a little bit more because QANTAS have ordered the A380, just as they did for the TAA A300 so many years back.

Mind you, all the way might be a great big nothing, minimum 'Z' speed and all that.

Regards,

Old Smokey

[Boeing737]

And, as a special bonus, the Australian CAAS will want a little bit more because QANTAS have ordered the A380, just as they did for the TAA A300 so many years back
why so?whats with the TAA A300?

Thanks for that smokey!

[747FOCAL]

AfricanSkies,

If you are in a powered stall it certainly won't be quiet, at least at the back of the plane. Powered stalls sound like a pack of gorillas rapidly pounding their fists on the fuselage. It's the engines compressor stalling and shooting flames out the front.
:E

[Old Smokey]

Boeing737,

It's over 20 years ago, testing my memory a bit, but the Australian Authority (CASA's predecessor) were not satisfied that Airbus had adequately demonstrated the stall, and required further tests. No stall to their satisfaction could be demonstrated, simply a minimum achievable speed, the 'Z' speed, with incomplete airflow separation.

I stand correction in detail, but that's the basic history.

Regards,

Old Smokey

[Blip]

Old Smokey.

I am very interested to know more about deep stall recovery of a conventional jet (such as the B737) with a swept back wing, wing mounted engines and conventional tail.

My guess would have been to initially apply up to full forward control column in an effort to reduce the AoA of the wings and holding that full forward position (or at least reducing only to the point of pulling zero G's) until such time that the airspeed is sufficient for the wings to pull the positive G's required to recover from the dive without stalling a second time.

No doubt there would be high rates of descent involved. At low levels, this would be a major problem. I wonder how low is too low.

I'm guessing there is initially a chance that the tailplane might stall. After-all it is at a high angle of attack too and you have, by pushing the control collumn forward, put it's co-efficient of lift at a maximum.

Approach-to-stall recovery calls for the application of maximum thrust. I'm not sure if that the pitch-up moment is desireable during a deep stall.

Is it possible do describe a generic deep stall recovery technique for the type of jet aircraft described above and perhaps outline the different considerations between approach-to-stall and deep stall?

Thankyou.:)

[Mad (Flt) Scientist]

...... with high fidelity simulators available, I have always campaigned for additional simulator training demonstrating the fully developed (full back stick) stall,

.....

Hopefully, one day, pilots will receive simulator training in recognition of and recovery from the full stall.

I'm sure OS knows this already, but it has to be pointed out nonetheless. No commercial simulator is validated for such a region of the flight envelope - there are maybe a couple of stall test points mandated by the standard simulator qualification requirements, and those are simple straight stalls...nothing dynamic, nothing fancy.

It would be quite an expansion of the simulator flight model development to allow other than generic training for the stall and post-stall regime. You're looking at adding details like sensitivity to entry rate for the dynamic cases, all kinds of things that are simply glossed over for a training sim.

And that's assuming the data even exists; I don't fancy trying to explain to the test team why I need rudder doublets post-shaker onset in order to model the directional characteristics of the plane for the sim....

apologies for the threadjack

[john_tullamarine]

Following on from MFS ..

(a) sims are computers and should work well in the validated model regions, especially if the operator spends a bit of time keeping them tweaked well .... but, necessarily, they are a bit of a guess outside.

For most considerations, there is a value to be had from whatever generic training may be available in non-validated regions but that relies on whether, and to what degree, the box presents a quasi-realistic story to the pilot.

We need to be aware that sometimes the sim can present quite false information which may be of counterproductive training value which ought to be avoided.

As a for instance, some years ago I was involved with a 732 sim which had to have a rudder model update per FAA direction as the unit was used by US AOC holder crews.

Due to everyone else's taking bigger steps backward than I was capable of (had nothing to do with the time it was to be programmed, I guess ) ... I ended up playing driver for the before and after testing which the sim OEM folk wanted done ..

Looking at things like crossover speeds, and other low speed bits and pieces such as VMC and general yaw/roll responses, the "before" model was extremely unconvincing and of no training value, the "after" pretty interesting to say the least and, I concluded, of considerable use for extra exposure training for crews ... chalk and cheese.

Gut feel is that stall exposure in the typical sim is of questionable, and perhaps, counterproductive, value ..

(b) ... as opposed to a good dose of UA exposure training which, in my limited view, is real good value for familiarisation with the instrument panel pictures, even when one discounts the body sense limitations. For this reason, I have opted for doing the exercise off motion so that we don't cause the jacks too much angst ...

It really doesn't take long for the typical pilot to get the hang of getting the bird back under control in the UA scenario.

If I recall back to my initial flying training days (Victa 115) ... at the end of the PPL training, I had a bunch of hours to burn off (RAAF ATC flying scholarship for those old enough to remember them .. not too sure whether I should have given those hours back .. aahh ... no way, José) and one exercise we did was circuits and aeros under the hood .. probably 10 hours or so in total.

Confusing for the first bit but, after a couple of hours, limited panel basic aeros were pretty straight forward. (I can still remember, very vividly, the first blind landing .. waiting for the ground to catch up with the altimeter ... good value stuff, I thought).

(c) one needs to keep in mind that the design standards have varied and developed over the years and some aircraft were never certificated to be pulled into the stall regime .. ie one does it in the real world at one's interest.

For instance, the Mojave folk at NTPS tell the tale of a USAF trainee who did this on, as I recall, a B58 ... found himself, shortly thereafter, in an inverted spin .... point of the tale is that, prior to doing anything "unusual" one ought to do some homework in the TCDS and related Standards to get a handle on what might have been applied to, and looked at during, the original certification ....

[Ignition Override]

Old Smokey: the DC-9 uses the left hydraulic system, after pushing far full forward on the yoke, to actuate the elevator control tabs up, that is, to the full nose down position. With loss of the left hyd. system, the elev. accumulator should give one or (is it?) two actuations.

The US FAA (regulators) never required aircraft builders to install an accurate angle-of-attack system. The present windshear warning system only reacts to a dangerous microburst (heavy downdraft due to masses of cool air). It can even give a very brief false warning during normal gusty winds. A stall warning can even go off for a split second with almost no turbulence during on-speed flap or slat retraction (with wings level).

Some major US airlines each have dozens of 'mainline' (aircraft with 100 seats or more) planes which have no stickpushers. Pilots claim that an inexperienced pilot can fly a newer Airbus with no chance of stalling, overspeeding or overstressing the plane. They and the aviation magazine pilot evaluations, published in "Aviation Week & ST" etc, claim that computers prevent this. This might also be the case with the new Embraer jets.

As for puzzling automation (to me :uhoh: ): An A-330 demonstration flight years ago at the factory in Toulouse, France was somehow allowed to enter a high rate of climb :confused: with one throttle at idle and stalled and/or "VMC-rolled" and soon crashed. Two helpless Italian pilots were a captive audience on the jumpseats.:ugh: :yuk:. One day when I am willing to give up lots of seniority in order to fly the Airbus, I will look forward to finding out what mode or combination of "FLCH" or "VNAV/ VS" type modes can result in this. I don't remember the 757 having this capability, whether with both engines at takeoff power or just one. In the simulators with an engine failure at V1, we hand flew the plane at V2 to about 1,000', from what I remember.

[AirRabbit]

Folks – please don’t assume that because you can “recover” from a fully developed stall in a simulator, that you’ll be able to do the same thing in the airplane. Taking a simulator into a fully developed stall, either for pilot experience or testing of the simulator, rapidly approaches being an exercise in irrelevance. Simulators are wonderfully good training, testing, and checking tools that, when used correctly, will allow a pilot to develop a set of skills that he/she will be able to use in the airplane without modification. But this wonderful tool is merely that, a tool. And, as most tools, it has limitations. The aerodynamic program used in modern simulators is modified with data that is collected during flight-testing of the airplane. For the curious, look at the requirements for the necessary flight tests for airplane certification. You will see that the maximum parameters are something like 25 – 28 degrees positive pitch (maybe as high as 30), 10 – 15 degrees negative pitch (maybe as low as 20), 45 – 50 degrees of bank (maybe up to 60), and very, very small amounts of sideslip – maybe up to 5 degrees – and that is with almost zero angle of attack. With this programming, the simulator will perform and handle (assuming its been programmed and tested correctly) very closely to that of the aircraft. However, take that simulator outside of those parameters, and all bets are off. No one, not even the airplane manufacturer’s engineering folks, are in a position to know, or guess, as to what the airplane will do.

The things I’ve read in this string are mostly correct – and I certainly agree with the statements that “playing around with stalls is not for the amateur pilot.” Well, in a transport category airplane, this activity isn’t for the very experienced pilot either, unless that pilot is specifically trained for and is specifically intending to do very specific things; is specifically prepared to do such things in the airplane; has the monitoring, and even emergency safety equipment installed and checked; etc. I also agree with those here who have cautioned against the cavalier use of the rudder. Nothing wrong with keeping the airplane in coordinated flight – but using the rudder to do something else – particularly something the rudder wasn’t intended to do – is probably foolhardy. Remember, airplanes are generally fool proof – but very few are idiot proof.

AirRabbit

[Old Smokey]

Mad (Flt) Scientist, John_T, AirRabbit,

I read loud and clear where you’re coming from, I entirely agree that unless the simulator has been programmed for, and validated by flight testing for a particular flight regime, it is indeed negative value to provide training in such an area. I agree, too, with AirRabbit that the Roll / Pitch response available from the simulator may not extend to the degree required to accurately accommodate a particular aircraft’s response/s at and beyond the stall.

My (work induced) late response to reactions to my proposal that pilot training in the simulator should be extended to the fully developed stall is fortuitious in that AirRabbit has reduced my typing load in providing the key to what I was trying to say, i.e. It would be quite an expansion of the simulator flight model development to allow other than generic training for the stall and post-stall regime
Generic training was the point that I was trying to make. Pitch / Roll rates etc. need not be accurately representative of that which might be encountered in an actual stall, as an example, it matters little if a ‘wing drop’ is at 90°/sec or 180°/sec, provided that the response was appropriate, i.e. a wing drop is precipitated by certain action (or inaction).

My concern is that fully developed stalls do occur, they carry a very high fatality rate, and pilots have no training in the disciplines to be used in recovery from the fully developed stall. To refer to my earlier quote -
Control and recovery procedures differ considerably from their earlier full stall training on prop aircraft, and the application of the intuitive responses learned at this phase could be disastrous

In comparing a pilot’s intuitive response learned on straight wing propeller aircraft, there are some VERY significant differences –

(1) Approach to stall – On the prop aircraft, it’s control wing drop with rudder, don’t even breathe on the roll control. Fatal for the swept wing jet, where it’s RAPIDLY correct wing drop with roll control, don’t even breathe on the rudder. During deliberate stall tests on jets, it’s a case of feet OFF the rudders, engine synch ON, Yaw Damper OFF – all to avoid any yaw moment.

(2) Stall encounter – For the prop aircraft, elevator effectiveness is usually not a problem. It may be for some T-tailed types, but power application is usually sufficient to restore airflow over the tail surfaces. For the T-tailed jet the elevator can become almost useless, particularly if it is a control tab system such as the DC9 (You get one guaranteed shot from the accumulator Ignition Override, no-one was brave enough to see if a second one was available). Any forces applied causing further pitch up (e.g. tip stall, thrust application from underslung engines) may not be manageable with elevator control alone. Here, the correct use of stabilizer trim is essential, as the much larger stabilizer can be one’s worst enemy or best friend. It’s essential to cease trimming during deceleration at about Vref, such that positive back elevator is required to induce the stall. A stabilizer trimmed ‘to the stall’ will not be ‘lift producing’ if the elevators are relaxed, whereas if trimmed to Vref, it is immediately lift producing upon elevator relaxation, and a good degree of ‘self recovery’ from the stall is possible merely by just ‘letting go’. In the unfortunate event of going beyond the full stall to the deep stall, running stabilizer trim forward may be your only saviour.

(3) Stall Recovery – On the prop aircraft, it’s simultaneously apply maximum Power and forward elevator. A smooth pitch up can be commenced almost immediately due to the slipstream effect of instantly recovering a large portion of the wing from the stall. On the jet aircraft, it’s a case of apply forward elevator, and only when the aircraft has responded with a pitch down, apply full Thrust. The delay between the two actions is essential for several reasons, one importantly being that asymmetric spool-up right at the stall is disastrous. For the rear engined aircraft, compressor stall is highly likely until the wing is first unstalled, aside from engine damage, the ensuing thrust asymmetry is unacceptable. For the wing mounted underslung engined aircraft, a thrust induced pitch-up at the stall is asking for very big trouble, and again thrust must be delayed until the wing is unstalled and a reasonably normal elevator authority is returned. Pitch up after the initial stall recovery must be MUCH slower than for the prop aircraft. Even at full thrust, there is no significant increase in air flow over the wing, and it’s necessary to wait until the speed has increased before gently pitching up. The intuitive ‘prop aircraft’ pitch up inevitably leads to a secondary stall, something I’ve observed with countless trainees during recovery from THE STALL WARNING, without ever venturing to the fully stalled condition in the first place.

All of the above is why I’m a strong advocate of teaching fully developed stall training in the simulator. I have done full stall evaluation on 3 aircraft types, all of them T-tailed, and for the reason that the regulatory authority required to be fully satisfied that ‘deep stall’ provision had been adequately made. This was particularly so for 2 of these types where wind tunnel evaluation indicated a significant ‘deep stall’ potential in their original configuration, and the effectiveness of preventative systems (in these cases, strakes) proven. Deep stalls were repeatedly attempted, but in all cases the prevention / recovery systems were fully effective. The simulator was being developed in parallel with the flight testing, and much of the stall responses immediately passed on to the simulator engineers who reproduced it quite well. Much of it was subjective, but with particular emphasis on the yaw/roll relationship approaching the stall, well incorporated. The latter merely required crossover response data with appropriate ‘break point’ insertion into the code. The generic responses are programmable, and, in my view, important to demonstrate in these areas –

(1) The danger of any yaw input approaching the stall,
(2) The effectiveness and ESSENTIAL use of roll control down to the stall,
(3) The ineffectiveness of the elevator at the stall,
(4) The essential need to NOT trim the stabilizer to the stall, and it’s effectiveness for deep stall recovery if used appropriately,
(5) Thrust must not be increased until initial stall recovery is accomplished (Compresser stall, pitch up etc.)
(6) The need to exercise much slower pitch up following stall recovery to prevent secondary stall.

I consider these criteria essential to incorporate due to the significant differences to that which the pilot was taught during earlier ‘prop’ training. Again, I say that most of the very occasional catastrophies following a full stall on Transport aircraft are preventable WITH TRAINING. The techniques taught on propeller aircraft, and for recovery from the stick shaker on transport aircraft are inappropriate if the full stall is encountered.

I have deliberately NOT mentioned the aircraft types involved here, lest someone might try it, and it should be stressed that individual aircraft types will vary considerably, as does the same aircraft in different circumstances. Even the generic comments which I’ve made here are for T-tailed aircraft, I’ve not done any of this work on conventional aircraft. When I was press-ganged into doing this work, it was not until after hundreds of hours of observation of wind tunnel test results, and many flights with test pilots that I went ‘solo’ in any of this work. I will add my name to the list of those giving caution here, until you have been exposed to a lengthy preparation process, and accompanied by a test pilot for training purposes, and you are in a very controlled environment, and you are flight testing in an already proven corner of the envelope, DON’T_EVEN_THINK_ABOUT_IT!

Fly Safe, fly in the KNOWN area,

Old Smokey

[AirRabbit]

The only additional comment I might offer in addition to all the preceding comments (in respectful opposition to the advocacy of training fully developed stalls in a simulator), is that as the stall is approached, even with very careful, flight idle power, one knot per second deceleration, in calm air, with pitch trim stopped a relatively safe point, one very, very important aspect is the side slip. A VERY minor difference in this single parameter will more than likely to provide a rather dramatic difference in handling characteristics as the stall is approached and entered. However, given the tolerances for matching flight test data, the simulator, once programmed, will do it exactly the same way, every time – and the pilot at the controls of the simulator can be relatively wide of the mark with all the above parameters, and get essentially the same response. This is likely to cause an incorrect understanding of what to expect if similar circumstances are encountered in flight. Of course, the regulator can demand a narrowing of the tolerances allowed – but the cost of such narrowing goes up at least exponentially. And, even if this cost were justified, the tolerances were narrowed to almost zero, and the simulator was programmed to respond exactly as programmed, the only time the simulator would respond like the airplane (and it would respond more like the airplane than before) would be when ALL of the parameters of the flight test airplane were met (to within those now tightened tolerances) in the simulator. Just a bit off in any of the parameters and the simulator will do one of two things: revert back to the generic programming (not validated with flight test data) or get “stumped” and not know what to do – sort of like “division by zero.” Neither result is appropriate and the training presented to the pilot would be, at best, inaccurate. Simulation is a formidable and powerful training tool. It took the simulation industry decades to get the aviation world to recognize and trust the simulator. Well, that effort has succeeded and may have succeeded to an over zealous level. Whatever is learned in a simulator is likely to be transferred to the aircraft – even if what is learned is not correct.

Two “war stories” to drive this point a bit:

1. In the early operation of the MD-11, a flight crew was enroute from DFW to MIA. Over TPA the crew experienced an engine fire warning on the number 3 engine. All attempts to determine if the warning was real or false resulted in the belief that it was a real, honest-to-goodness engine fire. The crew, having declared an emergency and initiated a descent for landing at TPA, attempted to extinguish the fire. They attempted to discharge all the extinguishers they could, but the extinguishers “malfunctioned.” After landing and evacuation, the officials determined that there was no fire, merely a false warning, but, and this a BIG but, when they attempted to discharge the extinguishers, they worked perfectly. The reason? The flight crew (both pilots) attempted to exercise the procedures learned in their simulator. But the simulator was not checked in this area and the force required to discharge the bottles in the simulator was about one-fifth of what was actually required. The crew gave up, believing that they had done all they could. The significance of the story is that even when two different pilots believe they are in immediate danger, what they learned in a simulator takes over. Unfortunately, there are a disturbingly large number of similar situations where inappropriate simulator training led an unsuspecting crew to the brink of danger.

2. A flight crew was attempting to slow, descend, and prepare to enter holding at 15,000 feet. The autopilot was engaged but the autothrottles were not. As one would expect with modern, FMS equipped aircraft, the altitude and holding fix were achieved at the same time. The crew was engrossed in the typical “prepare for arrival” stuff. The autopilot leveled the descent and initiated a right bank to enter holding. As you would expect, without a corresponding increase in power at that time, the airspeed decayed quickly. It was a smooth holding pattern entry. However, as the aircraft was rolling toward the maximum commanded bank angle, the stick shaker activated. The captain took immediate control, grabbed the yoke, disengaged the autopilot, and “feeling” just like the stall entry he had just completed earlier in that week in simulator training, he did as his instructor had encouraged him. He advanced the throttles and used right rudder to help bring the nose down to allow more easy acceleration out of the impending stall. Unfortunately, the rudder was a bit much, and the airplane continued to bank, very quickly, and exceeded 110 degrees of right bank. Several passengers were injured and at least one flight attendant was taken to the hospital with a broken arm (or clavicle?). Why?? The simulator was an older machine and one of the characteristics was when you exceeded a preset angle of bank, the program stopped. You could take your hands and feet off the controls and it would stay at that pitch/bank attitude (“division by zero”). The instruction was to “pressure the down rudder to gradually bring the nose down to the horizon while adding power, accelerate and roll to wings level.” This is what the crew was attempting to do. But it didn’t work. Very powerful training tools, those simulators!

The application here is that if we “teach” something, virtually anything, in the now revered, simulator, when the flight crew sees, hears, or feels something similar in the airplane, they are likely to DO what they did in the simulator. My respectful opposition to Old Smokey’s position is minor, but, I believe, significant. I believe we should show pilots what UAs look like, both outside the window AND on the gauges. From this information a lot of very valuable discussion can, and should, take place. But I’d prefer to stop short of “teaching” in a simulator, the techniques to use in an airplane in such instances. I would MUCH rather use the simulator to teach the characteristics of the airplane at airspeeds down around the stick shaker. We do it in small airplanes, why not larger ones? “Slow flight.” I’d like to see pilots learn to recognize what his/her airplane feels like at these low airspeeds; see how much control deflection is necessary to achieve turns. See how much rudder displacement it takes to stay coordinated. See how much power it takes to climb at that airspeed. I’d like to see a combination of all of the above – in the simulator.

My apologies for getting long-winded here – but this is a serious issue that deserves a lot of discussion. And I would welcome that.

AirRabbit
:D

[barit1]

While a student pilot, I had the opportunity to get a bit of dual in a Ryan PT-22 (civil designation ST3KR). It had a very slight sweepback - no more than 5 degrees - to compensate for a lighter engine than earlier models.

Because it had a good reputation for aerobatics, I wanted to do some slow flight and stalls for familiarization. We did a few straight-ahead stalls, power on and off, and it seemed straightforward enough, good buffet warning, easy recovery.

Then my instructor (Prof. Irwin Treager, who wrote that terrific turbine engines text) asked me to try one with just a bit of cross-control. The approach to the stall was normal, but it didn't just break - it suddenly snaprolled 360 degrees before I had a chance to respond!

Treager had taught a very good lesson that day - even a little sideslip paired with a little sweepback can get ugly in a hurry.

Moth and Harvard pilots can probably confirm this.

[speed freek]

Shooting off at a slight tangent, I know that the software protects Airbus from stalling, however lets just say, and we're being very theoretical here, that the software fails, and a complacent crew don't realise they're approaching a stall. ie. No stall buffet felt because of lack of feel, and faith in the system that'll 'save the day'. My question is, is there a stall warning fitted to the aircraft? ie. A warning tone like on the light aircraft.

[FlapsOne]

speed freek

Yes there is a stall warning 'fitted' if you have sufficient failures to end up in the unlikely position that could stall an Airbus.

Ign Override

A little mis-leading to quote the 1994 330 crash in TLS.

It was a test flight where a very unlikely set of circumstances, and an error, combined to produce a tragic accident.

You will be along time searching for the Auto Flight software that is designed to do that!

[alf5071h]

I don’t see that any one has answered Blip’s question directly; so here is an attempt.
First few if any civil aircraft will ever enter a deep stall; those ‘T’ tail types that may be susceptible will be fully protected (normally a stick push system). I suspect that your question relates to a ‘fully developed’ stall.

The theory of stall recovery requires a reduction of AOA by pitching down or increasing speed, or both; or if in an accelerated stall by reducing ‘g’.

The practice of stall recovery is to follow the advice in the manufacturers manuals as each aircraft type will have it’s own peculiarities.

Stall recovery does not normally require violent manoeuvres (zero ‘g’ push / then pulling lots of ‘g’). A fully developed stall may require more nose down attitude, but the certification requirements require civil aircraft to have a nose drop at the stall anyway. Similarly these aircraft should not suffer from rapid roll off or yaw excursions, although over swing from a wing drop recovery at 60 deg could exceed 90 deg (cert testing requires a demonstration that the aircraft can be controlled within these limits by use of aerodynamic controls – thus the lateral controls will have some effectiveness. With a roll-off and nose low attitude the speed should be increasing (a stalled wing does not mean no lift, just insufficient to maintain level or sensible pitch controlled flight). Also it would be unusual for a low thrust line to produce a significant nose up pitch, although the effect of this pitch can be felt as a change of trim. The longer the time that the aircraft is in the stall the more altitude that will be lost. The recovery time (altitude lost) depends primarily on using the approved technique; all of the above aspects depend on the aircraft type.

Tail plane stall is normally associated with ice contamination; don’t forget that the ‘lift’ force on the tail acts in the opposite sense to the wing. The general recovery technique for a tail stall (identified by rapid stick forward movement and pitch-over) is to pull back hard and reduce flap angle, totally different to recovering from a wing stall. However, always follow the manufacturer’s advice. I do not know of any jet aircraft that is declared as being susceptible to a tail stall.
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Unless specifically authorized everything else is forbidden.

[Rainboe]

I believe tailplanes are less susceptible to stalling for these reasons- they have less sweepback to delay stalling until after the wing has stalled, and their cross section shape is less prone to stalling than the wing root area. Should the tailplane start stalling, it will lose its downforce hence reducing angle of attack and mitigating the wing stall. In real life, it is the wing root area where the stall commences, and I think remains unless you really blow it- the wing tips and tailplane remain unstalled. In a Trident type T tail superstall, the whole shooting match is stalled and permanently unrecoverable.
I had the deep misfortune to be copilot on VC10 stall approach tests. I found 95 knots in a VC10 deeply unfunny and swore they would never get me up again on those.

[747FOCAL]

Rainboe,

Not to flame you or anything, but the stall starts at the wingtip. Not the root.

Tailplanes have less sweep back? the 727 has a lot of sweep to say that.

But then again, what do I know. :E

[alf5071h]

747FOCAL “…the stall starts at the wingtip. Not the root.”

OK in theory for a swept wing, but in practice most swept wing aircraft have small (or not so small) tweaks or fixes to ensure that the wing root stalls before the tip. E.g. wing fence, VGs, notches, LE kinks, and LE stall breakers.

A wing tip stall may give a strong pitch up and / or reduce the lateral control effectiveness, both unacceptable features for the certification of a civil aircraft. JAR/FAR 25.201, 203.

I do not know what specific aerodynamic fixes the 727 had, but those aircraft registered in the UK had a stick pusher fitted.

Rainboe, don’t forget that the tail plane is also affected by wing downwash, even to some extent, those aircraft with ‘T’ tails.
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Unless specifically authorized everything else is forbidden.

[Rainboe]

Focal- incorrect. The root area has greater angle of attack as well as other aerodynamic refinements to prevent the tips stalling before the roots. Should one tip stall first, you would find yourself on your back as well as other complications to sort out!

[747FOCAL]

Rainboe,

I have been on my back in a 727. :E

I agree with what Alf said. I just did not say it all that well with the amount of lager I had in me at the time.

[Ignition Override]

You folks not only understand various aspects of stalls quite well, but really know how to explain it ;)! True about the 330 disaster at Toulouse. Maybe "Aviation Week & ST" explained it well, but I probably misunderstood :=.

747 FOCAL-just one problem setting up an approach to stall in the real plane (twin turbofan from VR-62, but near Saginaw, MI [MBS]), is that when pulling both throttles back to where the bleeds are barely closed, about 52-55& N1, it is easy for one throttle to be set just a bit below what you want, and one engine can accelerate faster, even when they are not intermixed :rolleyes: , as is so often the case these days with one clever airline which rents the engines.

What was it like in the 727 ( I never flew it)? How slow were you-then how fast when you recovered :ooh:? Any assym. wing anti-ice?

[Old Smokey]

Ignition Override,

You have correctly addressed a significant problem encountered in tests to the fully developed stall, that is, that (1) any assymetric thrust or slip is to be avoided at all cost, and (2) assymetric engine spool-up during recovery is to be avoided. Your quote -
when pulling both throttles back to where the bleeds are barely closed, about 52-55& N1, it is easy for one throttle to be set just a bit below what you want, and one engine can accelerate faster
If I may refer back to my earlier post, I think that these two items were covered -
During deliberate stall tests on jets, it’s a case of feet OFF the rudders, engine synch ON, Yaw Damper OFF – all to avoid any yaw moment.
All of that in the interests of avoiding assymetric thrust during the stall, PARTICULARLY the Engine Synch to ON. On aircraft without Engine synch, it was necessary to judiciously maintain the engine parameters equal, and
apply forward elevator, and only when the aircraft has responded with a pitch down, apply full Thrust.
During the recovery it is essential to FIRST unstall the aircraft before applying thrust. In so doing, the wings are at an AoA somewhat below the stall, and small thrust assymetry can be tolerated. Preventing engine stall is a secondary but important consideration.

Like 747FOCAL, I have seen the world upside down from B727, DC9 and other cockpits, I don't ever want to see it that way again. Even the best stall warning system does not 'know' the wing condition, and the worst I've seen was a test on a 'dog' aircraft with paint overspray on the upper wing surface, the full stall ocurred about 20 Kt above schedule, and before the stall warning activated. I think that this instance alone stands to justify such stall training as is possible for flight crews.

Regards,

Old Smokey

[barit1]

Forgive me for being a decade or two behind the times, but the last synchronizer I can recall working on was a turboprop. What turbofan aircraft/engine configuration(s) offers or requires a synchronizer? What flight modes is it used in? Is it strictly used to avoid assymetric thrust, or to tune out noisy heterodyne beats?

[psy clops]

I'm sorry to step back down the thread here, but a question please to clear something up for my simple brain! I fly a variable geometry swept wing military jet (not a Flogger), and was a bit confused about Old Smokey's Approach to stall ...where it’s RAPIDLY correct wing drop with roll control
Now I can understand that thinking with my toy as we have no ailerons and the spoilers should do the trick on the other wing I guess; then again the downwash on the taileron will be a nightmare - I hate knock-on effects:confused:. Nevertheless, I always thought that as soon as unintentional wing drop occurred , the AoA on that side wing increases. Is it not true that dropping an aileron (increasing your effective camber (cue FMS)) will further increase your AoA of the downgoing wing. Which I always thought was detrimental for lift?

Just for information, when we get towards the stall, wings level unloading seems to do the trick. Actually did the 'trial' once when a little disorientated during a fight, and can confirm that technique does work to below HUD reading speed (50 kts). Avoided use of the rudder then too. Probably best to avoid that regime with passengers however!

Finally, we have a hopeless, no visual simulator where I am at the moment, but I still think that there is benefit from going through the procedures required approaching the stall. Notwithstanding the valid comments about realism and simulator performance envelope, if nothing else, one can practice the cadence of the recovery. I really can't see there being too many negatives in that - and at least if you have to do it for real, it won't be for the first (and consequently perhaps last) time.

Looking forward to the help!

Psy

[Few Cloudy]

Psy-Clops and Old Smokey,

You both address the sensitive matter of controling bank during stall.

It is so, that down moving aileron increases the angle of attack on that wing, thereby possibly exceeding stall aoa and aggravating the roll tendency. For this reason military training taught keeping the wings level by secondary effect of rudder.

Although not at all a fan of rudder in flight on large aircraft (done to death on other threads) I have used this technique on air tests of the MD-80 series. If used sensitively it worked well. MDC once had a DC-9 invert on them during such a test, because one wing leading edge had been cleaned and the other one was covered in a layer of crushed flies.

By the way, we went to full stall (but not to stick pusher, which was some percent beyond the stall) on these flights.

FC.

[Old Smokey]

A quick reply - In transit.

What the last 2 respondants say is perfectly correct for an aircraft which only has aileron for roll control. For aircraft using aileron and roll spoilers, the spoiler is far more effective in roll control. Near the stall the spoiler dumps the lift on the rising wing more effectively than does the aileron, and, as a bonus, produces a little yaw in the direction desired.

Regards,

Old Smokey