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Can airliners recover from a stall?

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Can airliners recover from a stall?

Old 9th May 2005, 14:36
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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!

Last edited by Boeing737; 9th May 2005 at 16:27.
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Old 9th May 2005, 15:01
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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.
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Old 9th May 2005, 15:44
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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
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Old 10th May 2005, 01:50
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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.

Last edited by Blip; 11th May 2005 at 00:50.
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Old 10th May 2005, 20:45
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...... 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
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Old 10th May 2005, 22:41
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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 ....
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Old 11th May 2005, 04:33
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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 ): An A-330 demonstration flight years ago at the factory in Toulouse, France was somehow allowed to enter a high rate of climb 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. . 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.

Last edited by Ignition Override; 11th May 2005 at 04:49.
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Old 15th May 2005, 04:06
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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.

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Old 15th May 2005, 12:25
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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
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Old 15th May 2005, 16:47
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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.

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Old 15th May 2005, 19:23
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Sideslip and swept wings

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.
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Old 15th May 2005, 19:42
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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.
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Old 15th May 2005, 20:21
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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!
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Old 15th May 2005, 21:14
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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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Old 15th May 2005, 23:13
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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.
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Old 16th May 2005, 05:21
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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.
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Old 16th May 2005, 08:34
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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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alf5071h is offline  
Old 16th May 2005, 09:22
  #38 (permalink)  
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Disgusted of Tunbridge
 
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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!
Rainboe is offline  
Old 16th May 2005, 16:01
  #39 (permalink)  
 
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Rainboe,

I have been on my back in a 727.

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.
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Old 18th May 2005, 06:21
  #40 (permalink)  
 
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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 , 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 ? Any assym. wing anti-ice?
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