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AF 447 Thread No. 5

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AF 447 Thread No. 5

Old 25th Jul 2011, 23:26
  #701 (permalink)  
 
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Hi Dutch M,

Unfortunately it isn't. See my example about the landing glider, a few posts back. The airframe can't be the reference point for conservation of energy.
I didn't say use the aircraft airframe as the reference - use the moving Air Mass as your inertial reference frame.
I seem to remember a certain Mr. A. Einstein wrote a special paper about it.
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Old 25th Jul 2011, 23:36
  #702 (permalink)  
 
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Originally Posted by gums
I truly believe you could exceed the mach "protections" until reaching maybe 0.95M or so with no ill effects. I truly believe that you could fly the jet at 10 or 15 degrees AoA.
Your first sentence reminds me of D.P.Davies: "If you can choose between stalling and something else, choose something else" (IIRC). IMHO your second sentence needs to be qualified: At M.82 the airplane can be considered stalled at about 8 degrees, at M.6 (the speed at apogee, see the graph I posted recently) at about 11 degrees, whereas 15 degrees may be just flyable at Mach 0.2 - 0.3.
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Old 26th Jul 2011, 00:12
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Thanks for this update, and recent posts with sharing more info on the TAS calculations.

I have not checked, but it is probably the case, that you've calculated with an unchanged TAS at FL375 of 390knots....

Originally Posted by henra
Thanks mm43 !

That would give us a TAS of 489kts at M0,80 and 500kts at M,82.
Looking at the setting of the RTLU at the time of the beginning of UAS a Mach speed of roughly M0,80 seems likely. So we would be back somewhere around the 490kts and ~4000ft.
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Old 26th Jul 2011, 00:48
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Cool

Hi,

Gums
I refuse to believe that the Airbus is a poorly-designed jet from the aerodynamic aspect.
Domaine-de-vol-A330.pdf
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Old 26th Jul 2011, 02:09
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Yeah, 'nuts, the stall AoA for the Airbus may have something more to do with mach than I am familiar with. Most jets I flew stalled at an AoA, whether supersonic or subsonic. The supersonic regime is more complicated, but big deal. Only problems I ever saw with a subsonic design had to do with shock waves over the wings, ailerons and HS that caused neat things like control reversal and a nose down "tuck" that required you to reduce speed real quick using spoilers, speed brakes, reduced thrust, etc.

My point is that it is possible to "zoom" at a "comfortable" gee and AoA and then run outta energy and control surface authority, passing thru all the "limits" and "protections" that the system is supposed to provide. We proved the point back in the late 1970's in my little jet.

Can't get the download JC. Will try later. Is the point that the Airbus has crappy aero characteristics?

Respectfully,


P.S. I agree that avoiding a stall is a sound procedure. We can worry about pieces falling off later due to high speed or gee.
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Old 26th Jul 2011, 02:33
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Cool

Hi,

Can't get the download JC. Will try later. Is the point that the Airbus has crappy aero characteristics?
Weird ... Mediafire is reliable host and work great here ...
You can try this multi links host ... (make your choice )
Multiupload.com - upload your files to multiple file hosting sites!
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Old 26th Jul 2011, 02:54
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Originally Posted by takata
ADR fault is not self detected (there is no ADR internal failure) ; monitored channels (airspeed, Mach,...) are declared faulty by FMGCs and FCDCs, but they are still displayed.
But are not NAV ADR FAULT and faulty ADR two different species ?
  • NAV ADR FAULT is the result of an ADR internal failure or a manual switch OFF.
  • faulty ADR provides erroneous information but is not an ADR failure.



Le Figaro set the table to kill the pilots a second time :
Les boites noires ont révélé que c'est une erreur de pilotage qui a entraîné le décrochage de l'appareil puis sa chute en 3 minutes 30 dans l'océan. Le pilote a en effet maintenu un ordre à cabrer -c'est-à-dire a tiré le manche de l'appareil- quasiment pendant tout le temps de la chute alors qu'un ordre inverse -pousser le manche- aurait empêché l'avion de décrocher puis aurait sans doute pu permettre de récupérer l'avion durant au moins la première minute de chute.
Do not expect anything different from the BEA on Friday ...
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Old 26th Jul 2011, 04:16
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Cool

Hi,

Le Figaro set the table to kill the pilots a second time :
Not particulary the "Le Figaro" but instead the "aviation expert" of "Le Figaro" I quote Fabrice Amedeo
Note that this journalist is firstly a leasure sailor
Maybe better for him to comment BEA Mer reports ....
BEAmer : Bureau Enquêtes Accidents de mer : Rapports d'Enqutes
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Old 26th Jul 2011, 07:20
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So it looks like the report will confirm that the intial climb wasn't briefed to the Captain on his return and that the word 'stall' was not uttered, as the Chief Engineer stated some time back. I hope that the 60kt inhibit of the stall warning gets the attention it deserves.
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Old 26th Jul 2011, 08:40
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Originally Posted by CONF iture
But are not NAV ADR FAULT and faulty ADR two different species ?
- NAV ADR FAULT is the result of an ADR internal failure or a manual switch OFF.
- faulty ADR provides erroneous information but is not an ADR failure.
You are semantically right concerning internal/external faults but what matter is that those erroneous informations won't be used by the flight systems but still be displayed to the crew for information and troubleshooting. All relevant systems based on erroneous outputs would be declared inop during the fault isolation sequence (AP/FD, A/THR, PROT, RTLU, WINDSHEAR, SPD LIM, TCAS)

Concerning FMGCs and FCPCs monitoring, the effect is a rejection of the faulty sources (channel); in our case, all 3 ADRs are declared faulty by them and rejected. There is no cockpit circuit breaker at probe-pitot level and what could be displayed is a fault on ADR pannel; one may want to turn it off.

Until all ADRs are turned off, the stall warning based on Alpha is still working (if at least one AOA channel is not declared faulty), but it's computed differently as this function use a Mach correction and Mach is replaced by a default value. On the other hand, the computed stall warning based on Low Speed (VSw) is lost. Concerning Overspeed warning, it is lost as this function is based on faulty ADR channels, as well as VMax which is not displayed.

Last edited by takata; 26th Jul 2011 at 08:50.
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Old 26th Jul 2011, 10:52
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Originally Posted by Dutch M
@sensor_validation
Yeah, suppose the windspeed goes from 100 knots back to zero, does this change the Ekin of the airplane ? If not, then you will need to take the groundspeed as speed reference.
You need to keep your reference axes the same, moving at the same constant initial velocity then there is no change in Kinetic energy - but OK "v" is no longer airspeed, if windspeed changes.

The energy exchange Ekin vs Epot, is in general only valid for speeds in the direction of the change of Epot (ie Height) and not when trading speed between perpendicular axis.
WRONG. Of course you have to make assumptions about constant windspeed, thrust=drag, g constant etc but correctly applied the maths/physics works, in 3-d vector co-ordinates - until you get close to speed of light!

And back to the point, the reference points quoted for AF447 are consistent with a zoom-climb trading speed for altitude. AF447 did not get caught up in 7000ft/min updraught where an external force supplied the work done to increase the gravitational potential energy.

Note - a zoom climb was discussed on these forums as soon as the wreckage position reported, way before the BEA confirmed it - it was the most obvious way AF447 could shed horizontal speed so quickly and end up so close to its last transmitted position.

Last edited by sensor_validation; 27th Jul 2011 at 10:24. Reason: typo
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Old 26th Jul 2011, 12:01
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As Takata has pointed out that is only partly true as below a certain speed the drag will rise again due to ending up in a less good cl/cd area (higher Alpha) of the wing polar. So at the end you can probably leave excess thrust largely out of the equation.
Indeed, to confirm, the drag curve consists of profile drag + induced drag + Mach drag. The absolute value of the sum of these can indeed increase below a minimum drag speed, particularly approaching a stall, but between the normal cruise and maneouvring speed unlikely to increase much if any at all.

== DutchM ==

I really dont think you need ground speed for calculating those energy exchanges, TAS is fine surely... Unless you state you are allowing for windshear of thermal gusts , which we aren't are we, because we can't can we, because we don't know the figures do we. So we do the basic steady state air-mass TAS calculations, and bear in mind some variations may occur in practice... but if we're within the right cricketpitch, then fine.. that's what engineers do, get in the right region, check they've got the order of magnitude correct and then use some commonsense to make further deductions and corrections!

===========
Possibly worth consideration (as airline pilots seem increasingly unfamiliar these days with hand-flying through heavy thermal activity, wicked windshear or terrible turbulence - ?)

Flying in a +ve going thermal, with increasing x and z wind-vector components, glider pilots can find that stick back for extended periods is quite OK, with an almost unstallable feel to the aircraft (for reasons possibly explained some while ago)
Conversely, when this 'free energy' phase is exited, you are effectively in heavy adverse windshear, known to some as 'going over the falls' for obvious reasons! It's a horrible feeling, as if your very lifeblood was being drained... and if you don't respond, it may well be. (I've heard hang-gliders say they've had to hand-stand on the bar to prevent -ve 'g' tuck during some exits from the back-side of thermals.
Now, I'm definitely not comparing a 300 kt IAS airliner with an 80 lb hang-glider, even though the latter does have a sensible AR (8 to 10), span as big as a Spitfire and several hundred square feet of wing.

Only by strong pitch stability or quick and considerable ND inputs, is a very quiet & lonely sensation avoided, with a subsequent stall or wing drop...

So, it is interesting that a strong right wing drop seems to have had to be countered early on in this series of events, around when the climb started (strong and persistent wing drop, is frequently one wing entering quite different air than another). Then after quite safely holding NU (and a high angle of attack) for some time, we have the new THS* position... and a quite telling one I'm sure the report will atest to.

It is this * that our (hypothetical) glider pilots wouldn't have had to deal with... just a firm but controlled ND to accelerate back down through dirty colder slow air (!)

Last edited by HarryMann; 26th Jul 2011 at 12:51.
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Old 26th Jul 2011, 14:27
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Originally Posted by sensor_validation
Post #710

Originally Posted by Dutch M
The energy exchange Ekin vs Epot, is in general only valid for speeds in the direction of the change of Epot (ie Height) and not when trading speed between perpendicular axis.
WRONG. Of course you have to make assumptions about constant windspeed, thrust=drag, g constant etc but correctly applied the maths/physics works, in 3-d vector co-ordinates - until you get close to speed of light!
The way I read Dutch M's reference to Ek and Ep exchange, is that the Ek - or speed vector - need to have a vertical component (direction of height), for the energy conservation exchange to take place. Which is CORRECT.

With no vertical component, there is no height gained/lost, and no potential energy change, or exchange. An object that goes horizontally, from zero speed, all the way to a certain speed, will not get potential energy regardless of how slow, or fast.
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Old 26th Jul 2011, 14:40
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Hi gums;

IIRC, Tubby Linton provided a set of AoA graphs two or three threads ago, (now ancient history, at this pace!), repeated below, which show quite clearly, the effects of Mach, and of slats/flaps at lower speeds.

I had a long and very productive discussion with HN39 in the third thread earlier this year on "stall AoA". Davies discusses AoA's of 15deg and very early (Private Licence time in the '60's), I was left with the impression that "the" stall angle for transport aircraft was "15deg" (or so), altitude and Mach not considered; of course, this is not so but I never encountered a correction to that impression in my career...high altitude stalls were simply never done and never discussed, I think, with legitimate reason given limited sim time and expanding items to cover over the decades.

One can see the effects of extended slats and flaps and the AoA's are in accord with Davies' "approach case". IIRC he doesn't discuss high altitude stall in detail, even in his section on "jet upset". With increased Mach, I learned that the stall AoA reduces substantially - in the neighbourhood 4deg, not 15!, etc, as can be calculated from the tables below which are employed by the A330 FWC [Flight Warning Computer] to trigger the Stall Warning in other than Normal Law. In Normal Law, the Stall Warning will trigger, but only at an AoA > 23deg, as described in the chart.

HN39, it was indeed Davies who said, "...choose any other alternative...", etc.

PJ2



Last edited by PJ2; 26th Jul 2011 at 14:53.
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Old 26th Jul 2011, 14:54
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Hi airtren,

With no vertical component, there is no height gained/lost, and no potential energy change, or exchange.
We are not considering ballistics.
Aeroplanes convert P.E. to K.E. on every descent by simply using the wings.
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Old 26th Jul 2011, 15:03
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I think PF's initial ss back is starting to gel into the 'climb command', once again. Nothing about BEA suggests that is so.

As to Harry Mann's 'wing drop', as far as it may be the result of airmass flow, it may well indicate a very robust 'up elevator'.

Between the first NU and the second STALL WRN. , only Nose Down inputs are mentioned.

Roll excursions are mentioned. The a/c is climbing rapidly, rolling, and losing energy.

At the 'top' of climb, the AoA decreases, (6?), and there are STALL wrns.


Harry. Climbing, unstable in Roll (with corrections), and losing energy, would not the a/c STALL with increasing loss of altitude due loss of energy, regardless of pitch commands? as the a/c loses energy in climb, the AoA is affected as much by arrival at apogee as Pitch, perhaps more?

In a serious updraft, the correct input, (perhaps other than none!) might be Nose Down? Hold Altitude? Lose as little as possible?

BEA report seems to suggest that PF was not reacting to the climb. Too many here seem to assume the PF was "along for the ride".

Again, I think the source of the STALL was timed to the loss of the autopilot and autothrust. If in an uncommanded climb, of course the PF would not advance the Throttles. He would input ND, and BEA have not said he did not.

With the loss of 'g' at the top, TOGA and "back pressure" relief would be correct? Especially if associated with STALL WARN?
 
Old 26th Jul 2011, 15:06
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Hi ruderruderrat,
Originally Posted by rudderrudderrat
Hi airtren,

Originally Posted by airtren
With no vertical component, there is no height gained/lost, and no potential energy change, or exchange.
We are not considering ballistics.
Aeroplanes convert P.E. to K.E. on every descent by simply using the wings.
An airplane descent implies a speed spacial vector that has a vertical component (vertical speed component), and so the Ep to Ek conversion takes place. And that is true in general with any descent, involving airplanes and wings or not.

If the airplane flies flat, horizontally, the vertical speed component is NULL, and there is no Ep change/exchange. An Ep to/from Ek conversion starts as soon as there is a non-NULL vertical speed component (up, or down) of the speed vector.
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Old 26th Jul 2011, 15:09
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If unaccelerated?
 
Old 26th Jul 2011, 15:27
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Originally Posted by bearfoil
If unaccelerated?
The aerodynamic braking during airplane controlled descent consumes the gain of Kinetic Energy, resulted from the Ep to Ek conversion, resulted from the loss of height/elevation. Slowing down for landing, means decreasing the Ek. What is left of the Ek, at touch down, is consumed (converted into other forms of energy) further through aerodynamic and mechanical braking.

The Ep to Ek conversion takes place regardless of controlled descent, or free fall. The difference is that in a free fall the Ek gain (or most of it, to be accurate) is not consumed/converted until the very end of the descent.

The airplane case is not different than a car descending a hill, from the generic Ep to Ek conversion perspective.

A car's free hill descent, will mean gain of speed - Ek not consumed. A controlled descent at constant speed, or decreased speed, requires different degrees of braking. The braking is consuming the Ek gain through friction, converting into Thermal Energy - brakes are quite hot at the bottom of the hill.
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Old 26th Jul 2011, 15:59
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At the 'top' of climb, the AoA decreases, (6?), and there are STALL wrns.
Stall warnings started 15 seconds before the top of the climb, at 0210:51, when Alpha reached 6° (BEA).
0210:05 = 0210:05 => 275 kt; FL350; Alpha was about 3° (estim.)
0210:16 < 0210:50 => 215 kt; FL375; Alpha was about 4° (BEA)
0210:51 = 0210:51 => Stall Warnings; Alpha was about 6° (BEA)
0211:06 ~ 0211:06 => 185 kt; FL380; Alpha was about 16° (BEA)
During those 15 seconds at the beginning of the stall warning sequence (stall warning only stopped 35+ seconds later, after 0211:40)... the AOA increased by 10°.

Last edited by takata; 26th Jul 2011 at 16:16. Reason: correction FL375
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