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New (2010) Stall Recovery's @ high altitudes

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New (2010) Stall Recovery's @ high altitudes

Old 27th Jul 2010, 10:07
  #81 (permalink)  
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Originally Posted by m_j
BEng Mech can do at least up to ther times 12 table
- not wot we 'aeros' used to say about them.....................I guess they use their fingers to do that?
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Old 27th Jul 2010, 16:01
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Well we did have a special course in it.

Had to learn how to deal with inches and associated constants for oil,pressure vessel and pipe work.

Learned how shite yank steel was (shocking bad for both fatigue and corrosion). Always buy from Japan cause the Brit stuff was shite as well after they shut down Ravenscraig.

All was going well until we had to convert critical crack intensity's which I think from memory are Nmm^0.75 to the yank equiv. At which point I was forced to go to the pub.
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Old 27th Jul 2010, 22:54
  #83 (permalink)  
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shouldn't there be an "area term" amongst the variables

comes in with the dimensionless coefficients

not all pilots are BSc level aeronautical engineers - some are just capable of the 3 times tables

or course - this is the reason that explanations are couched in different terms for different folks, according to their knowledge, needs and state of inebriation.

I guess they use their fingers to do that?

on occasion, depending on the quality of the grape, I have to resort to counting on my fingers and toes .. 11 is about as far as I can go.

Stick to the limits from the manufacturer - IAS/Mach/Altitude
If something untoward happens when you do 'X', undo 'X'
Learn the correct recovery actions if the problem persists.

now that's a terse set of good advice and well worth committing to memory.

inches

thanks be to tradition .. shall we confuse them all with slugs, poundals, ergs, and such like ?
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Old 28th Jul 2010, 07:19
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Currently ploughing my way through this.

God Created the Integers: The Mathematical Breakthroughs That Changed History edited by Steven Hawkins.

Keeps the grey matter stimulated.
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Old 28th Jul 2010, 10:36
  #85 (permalink)  
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Steven Hawkins

now, you're a brave man ..

When one contemplates Hawkins, what a most incredible fellow ...
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Old 28th Jul 2010, 11:16
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Its not really written by him he supply's the editing and the commentry on the particular topic under discussion and how it relates to things we use every day.

The full title is

God Created The Intergers, The mathematical breakthroughs that changed History

It starts off with Euclid 325-265BC

And finishes with Alan Turing 1912-1954

Currently working my way through Euclid Elements just now. I will admit its not everyones idea of fun. The most sobering though is that all Royal Navy midshipmen had to learn it by the time they were 14.

There is quite a bit of Mech eng interest stuff in it as well apart from goemetry with:

Newtons, Motion of Bodies
Fourier, Propagation of Heat
Cauchy, Calculus
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Old 28th Jul 2010, 11:20
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That's unfair .. now I'm going to want to go off and get a copy ...
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Old 28th Jul 2010, 12:13
  #88 (permalink)  
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While the English and their former colonists have persisted with the adaptation of a mercantile system of units to science, I am not at all in accord with the suggestion to
Originally Posted by john_tullamarine
confuse them all with slugs, poundals, ergs, and such like
because I hold it unseemly to berate the slug, poor creature. It is a necessary part of a system of consistent units.

I myself prefer the units which Mother Nature intended, in which the speed of light is 3 x 10^9, gravity is 10, the speed of sound in dry air at 15 is a third of a thousand, and, most quaintly, the Newton is about half an apple. But I do grant privileged status to the nautical mile as a minute of great-circle arc.

The point made by JT, that the essential coefficients of lift, drag, and moment are strict functions of AoA, Mach number, and Reynolds number, along with the derivation, is elegantly expressed in almost exactly those terms in Section 5.3, pp 262-8, of John D Anderson Jr., Introduction to Flight, Sixth Edition, McGraw-Hill 2008.

I tried summarising what I think are the important, sometimes revealing, points in this discussion, but it's up to about 4 pp so far, so rather than post it here I'll clean it up a little and likely post it on our blog, and publish a link here when I do.

PBL

Last edited by PBL; 28th Jul 2010 at 12:35.
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Old 28th Jul 2010, 13:02
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As a simulator instructor on the 737-300 and after reading these posts I am beginning to wonder if perhaps I am teaching an incorrect technique when discussing stick shaker recovery at high altitudes. After all, we can only use the advice given in the relevant manufacturer's FCTM and sometimes that advice is quite lacking in more detail leaving it to the reader to fill in the gaps.

In the case of the 737-300 the FCTM states " Ground contact not a factor..at first indication of stall (buffet or stick shaker...apply maximum thrust, smoothly decrease the pitch attitude to approximately 5 degrees above the horizon and level the wings...as the engines accelerate, counteract the nose up pitch tendency with positive forward control column pressure and nose down trim..at altitudes above 20,000 ft pitch attitudes of less than 5 degrees may be necessary to achieve acceptable acceleration...accelerate to maneuvering speed and stop the rate of descent...correct back to target altitude.

From my observation in the simulator of high altitude stall recovery (above 31,000 ft for example) it is the application of maximum thrust that often causes a delay in early recovery because of the marked pitch up that occurs as high power cuts in. Unless the pilot accurately pins zero body attitude as the aircraft accelerates downhill, the aircraft tries to lift the nose and a "G" buffet returns. Perhaps the accent should be on instant lowering of the attitude to commence speed increase and only when at a appropriate speed above the initial buffet (say 30 knots?) thrust should increased? In the case above for training purposes, we close both thrust levers and maintain level flight while slowly decelerating towards the stick shaker speed.
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Old 28th Jul 2010, 13:31
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Hi Centaurus,

Post 72 from Goprdon quotes the CAA guidelines:
" The standard stall recovery technique should therefore always emphasise the requirement to reduce the angle of attack so as to ensure the prompt return of the wing to full controllability. The reduction in angle of attack (and consequential height loss) will be minimal when the approach to the stall is recognised early, and the correct recovery action is initiated without delay."

So I think it's emphasising that a reduction in angle of attack is the most important thing, secondly the application of a controllable amount of power. The problem with under slung wing engines is the pitch up couple. (TOGA power might not be controllable by the elevator at very low speeds - 737 at AMS etc.) As the speed increases - then you will be in a position to control the application of even more power.

Edit. The problem with the simulator is the lack of feeling of the "delta g" during the recovery. Most crews will trigger a secondary stall stick shake because of their over enthusiastic pitch up. In real life - they will be more aware of the "g".

Last edited by rudderrudderrat; 28th Jul 2010 at 14:30. Reason: extra text
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Old 28th Jul 2010, 14:40
  #91 (permalink)  
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The blog post is now there: Understanding Aerodynamics of Stalls

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Old 28th Jul 2010, 16:49
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Forgetting 'aerodynamics' and concentrating instead on 'stability and control', there appear to be two major contributors to recent 'underslung' accidents/incidents involving near or complete LOC following an unintentional low-speed 'event'.

1) The way that a/c flight systems are allowed to automatically continue trimming tailplanes below normal flying speeds without some form of warning to crews that this is happening

2) A failure to recognise and handle the resulting excessive pitch and low speeds following the application of recovery power.

As I and others have said over the last few years, historically initial and recurrent training has 'compartmentalised' stalling and unusual attitude recovery ie "now we will look at stalls and recoveries" and "next session we will look at nose-high low-speed recoveries". Those of us who have air-tested down to the stall know that you always STOP trimming at xkts above the stall speed so you do not get the excessive nose-up couple. We are now arriving increasingly at events where the a/c has done exactly the opposite and crews are not ready for it. With the increasing ratios of those pilots in the industry who have not got much real experience of unusual attitudes, it is apparent, to me anyway, that 'stall' recoveries MUST now lead straight into the nose-high low-speed recoveries as an exercise, meaning that I would suggest allowing trimming right down to stick shake. Recovery from these conditions is indeed simple if you are prepared for it and take the correct actions.
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Old 28th Jul 2010, 20:52
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1) The way that a/c flight systems are allowed to automatically continue trimming tailplanes below normal flying speeds without some form of warning to crews that this is happening
Except for the L1011...simply a better design, out the door with ship one.
Now, some might say...'EAL401 proved the L1011 was not up to standard'...and I would say...'IF you follow the manufactureres instructions, it was fully compliant, and still is.
IE: RTFB.
Rocket science it ain't.
Gosh, what an absolute surprise.
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Old 28th Jul 2010, 23:12
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In the case of the 737-300 ..

With the caveat that the OEM's advice for a particular aircraft is likely to be based on sensible FT work and, therefore, one should observe it .. there are a couple of considerations with engines sticking out in the front like most of today's twins -

(a) if the engine is underslung (as nearly all are) the low thrust couple doesn't help

(b) if the upset has been allowed to progress to a high alpha, there is a problem observed once power is applied. As power comes up, with the change in flow around the front of the nacelle (and through the prop disc for turboprops) there arises a significant up-force at the nacelle lip (or prop disc).

Both of these are destabilising and reduce the longitudinal static stability. The end result is that the pilot finds him/herself in hot water.

The main emphasis for any recovery should be skewed toward reducing alpha and then, at an appropriate time for the Type, increase power.

you always STOP trimming at xkts above the stall speed

and the certification stall data (and the AFM techniques) are based on a similar approach to the matter ie, if the trim has run too far nose up then the pilot's existing problem are complicated further.

Gosh, what an absolute surprise

.. well, after all, it IS a Lockheed product .. not like those other agricultural animals.
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Old 29th Jul 2010, 10:59
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Stall testing of transport category airplanes

Originally Posted by PBL
You think people have been going out doing stalls in Airbuses to see what happens?
The aerodynamic characteristics of a modern commercial jet are determined in wind tunnels, mostly for certification purposes.
For type certification of Transport Category airplanes the 'applicant' (manufacturer) must conduct an extensive stall test programme. Details and objectives can be found in reference 1. Wind tunnel testing does not produce the evidence required for certification, but is primarily a design tool and assists in preparing the flight test crew for the more critical conditions to be tested, as explained in reference 1.
Originally Posted by PBL
So what data is it that a given manufacturer didn't have, that they would have gone back up to get because the regulators were worried again about LOC? Can anybody here say?
The major manufacturers contributing to an industry-wide effort to improve pilot training aids for upset recovery, including recovery from stalls, drew on their extensive experience. They did not have to 'go back' to get it. A detailed reply to your question 'straight from the horse's mouth' can be found in ref.2.
Originally Posted by PBL's blog
Another, Airclues, replied In the early 80s I was co-pilot on several C[ertificate] of A[irworthiness] air tests on the Boeing 747 when a full stall was completed (I believe that the UKCAA was the only authority that required this) and described his experiences. In other words, actually high-alpha-stalling large commercial aircraft, even for certification, is ancient history.
Perhaps you are confusing (type) certication with the UK CAA practice for periodic renewal (from memory: every 5 years) of the C of A of individual 'Performance Group A' aircraft on the UK Register. The UK ARB (later CAA) requires a performance flight test as a condition for renewal of the CofA. The flight test includes stalls and verification of climb performance with simulated engine failure (2nd and 4th TO climb segments). To my knowledge, the CAA is the only authority to require these tests, but possibly some former 'Commonwealth' countries follow CAA practice. The CAA requirement for CofA renewal performance testing has nothing to do with type certification testing.

Reference 1: Advisory Circular no.AC-25-7A Flight Test Guide for Certification of Transport Category Airplanes.

Reference 2: Airbus Flight Test views on Upset Recovery Training

Last edited by HazelNuts39; 31st Jul 2010 at 19:52. Reason: The CAA apparently sill requires these tests
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Old 29th Jul 2010, 12:55
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HN39,

Your reference 1 will be quite useful for those here who don't know what is taken to determine a "full stall". I point out -again - that the flight tests are only performed to determine Vs1g. That is one point - a very, very important point, but still only one - on the C_L / AoA / speed-MachNo graph collection.

Condition (i) for "fully stalled" says "pitch control reaches the aft stop and is held full aft for two seconds, or until the pitch attitude stop increasing, whichever occurs later". You can obviously do that in both Normal and Alternate Law (that is, Alternate 1) on an Airbus without actually reaching, let alone going beyond, AoA for C_L_Max (and I mean the real C_L_Max). Regs define that as "fully stalled", but it is not aerodynamically at the point of serious loss of lift, or even severe buffet.

Originally Posted by HN39
The major manufacturers contributing to an industry-wide effort to improve pilot training aids for upset recovery, including recovery from stalls, drew on their extensive experience. They did not have to 'go back' to get it.
That is what I understood also, and therefore why I was querying guiones on what he thought was done, since he was saying a lot of further testing and calibration was performed (he apparently knows some of the participants, but hasn't yet said).

Originally Posted by HN39
Perhaps you are confusing (type) certication with the UK CAA practice for periodic renewal (from memory: every 5 years) of the C of A of individual 'Performance Group A' aircraft on the UK Register
Yes, perhaps I am. Perhaps Airclues can clarify which he meant?

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Old 29th Jul 2010, 14:09
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Originally Posted by PBL
You can obviously do that in both Normal and Alternate Law (that is, Alternate 1) on an Airbus without actually reaching, let alone going beyond, AoA for C_L_Max (and I mean the real C_L_Max).
I didn't think the discussion was limited to Airbus A320/330/340/350/380. Can you really authoritatively state that Airbus never stalled any of those airplanes beyond the g-break? Bear in mind that certification is not limited to normal configurations and conditions but also considers icing, system failures and their consequences and probabilities (ref. FAR 25.1309 etc), turning flight stalls, accelerated stalls, low and high altitudes ... What about other manufacturers?

Anyway, I have considerable difficulty in accepting your statement that "In other words, actually high-alpha-stalling large commercial aircraft, even for certification, is ancient history." From my perspective, it doesn't do justice to the rigidity, thoroughness and expense in money and manpower of the type certification process of large airplanes.

regards,
HN39
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Old 29th Jul 2010, 16:08
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Originally Posted by HazelNuts39 View Post
I didn't think the discussion was limited to Airbus A320/330/340/350/380. Can you really authoritatively state that Airbus never stalled any of those airplanes beyond the g-break? Bear in mind that certification is not limited to normal configurations and conditions but also considers icing, system failures and their consequences and probabilities (ref. FAR 25.1309 etc), turning flight stalls, accelerated stalls, low and high altitudes ... What about other manufacturers?
In most cases, the full suite of certification test for stalling are not required for failure conditions and the like, since it is assumed that either (a) a procedure will be applied which will reduce the probability of a full stall sufficiently or (b) the probability of the failure itself, in combination with the stalling probability, is so low as to be acceptable.

The most obvious example is failure of a stall protection system - obviously, if the aircraft needs such a system in order to be compliant with the basic requirements, it will never be able to meet those same requirements with that system failed. And it is in general not required to do so; the criteria for "Continued Safe Flight and Landing" - the condition to be demonstrated subsequent to the failure - are less stringent that the full certification requirements.
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Old 29th Jul 2010, 17:44
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Originally Posted by HN39
I didn't think the discussion was limited to Airbus A320/330/340/350/380. Can you really authoritatively state that Airbus never stalled any of those airplanes beyond the g-break?
I don't work for Airbus, and their flight test program is likely proprietary information, so I am not in a position to state authoritatively anything about it at all.

Originally Posted by HN39
Anyway, I have considerable difficulty in accepting your statement that "In other words, actually high-alpha-stalling large commercial aircraft, even for certification, is ancient history." From my perspective, it doesn't do justice to the rigidity, thoroughness and expense in money and manpower of the type certification process of large airplanes.
Opinions may differ and yours is a reasonable point of view (with which I do not necessarily agree). But I am wondering whether I overstated the case and am inquiring. The wording of statements causes some problems here, as I pointed out in my blog note. Here is a further example: BOAC made a valid point that if you are "fully stalled" you don't want to try lifting wings with aileron. But he meant something different from CS 25, for which an Airbus holding Alpha_Max (less than C_L_Max) for two seconds counts as "fully stalled". I prefer (what I take to be) BOAC's meaning, but you can't argue with regs; if they say "chicken and onion pie" means the left windshield pane, then the left windshield pane it is, and we have to find another word for our lunch.

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Old 29th Jul 2010, 20:02
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Your reference 1 will be quite useful for those here who don't know what is taken to determine a "full stall".

One of the problems with these sorts of discussions for the newchums is that there is a very important caveat which MUST be considered - the Design Standards (which include stall protocols) are living animals. Over the years the Standards evolve and what was the rule yesterday can change quite significantly today.

Hence, for all Type specific discussions going beyond a bit of a yarn on PPRuNe, one MUST

(a) check the TCDS for the relevant frozen Design Standard revision(s) applicable to the particular certification

(b) refer to that/those (generally now superseded) documents rather than the current words

For US flight test interpretation, we need to look at the relevant revision either of 25-7 or 23-8.

Most importantly - if one tries to run a stall iaw the "wrong" Standard revision, one can be in for a short sharp wakeup call when the bird does something totally unexpected.

For instance, I can recall a very experienced TP relating a tale about a particular popular light cabin class twin. The original stall protocols went to the initial stall with a prompt recovery. During a training period with a TP student, the student thought it might be a good idea to hold the aircraft into the stall .. whereupon they found themselves promptly in an inverted spin .. there are many traps for young players if folk fancy themselves as putative TPs without having put in the hard yards with the TP training and post grad exposure/experience.
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