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-   -   Habsheim (https://www.pprune.org/tech-log/528034-habsheim.html)

CONF iture 21st Apr 2014 14:49


Originally Posted by HN39
How does that differ from the definition of Vs1g?

Quite different as Vs1g is the stall speed at 1g.
If Airbus wanted no safety margin they would have set alpha max to alpha stall at 1g and modified their graph accordingly.

http://i45.servimg.com/u/f45/11/75/17/84/hud_0210.png

HazelNuts39 21st Apr 2014 15:40


Originally Posted by CONF iture
Quite different as Vs1g is the stall speed at 1g.

So how would you demonstrate it in normal law in a certification flight test?

P.S.

The diagram you posted is a schematic illustration that alpha-max is just shy of alpha-CLmax. Alpha-CLmax would define Vs1g for a conventional airplane, but not for a FBW airplane with a flight control system that is designed to prevent achieving and exceeding alpha-CLmax. The difference between alphamax and alpha-CLmax (the safety margin) is the performance penalty that must be paid for having a 'hard' stall protection, and Airbus has never made a secret of that fact.

Conventional aircraft having a stickpusher pay a similar price in performance if the pusher is set to fire before alpha-CLmax.

CONF iture 22nd Apr 2014 00:55


Originally Posted by HN39
The diagram you posted is a schematic illustration that alpha-max is just shy of alpha-CLmax.

Therefore Valphamax is not Vs1g.


Alpha-CLmax would define Vs1g for a conventional airplane, but not for a FBW airplane with a flight control system that is designed to prevent achieving and exceeding alpha-CLmax.
Actually the FCS is designed to achieve alpha max without exceeding it.
Nevertheless temporary overshoot could happen due to turbulence but without significant effect.
Also Gordon Corps demonstrated how temporary overshoots seem to actually take place and so without negative effect.

The diagram I posted is from the Airbus documentation and is applicable to their FBW airplanes.


So how would you demonstrate it in normal law in a certification flight test?
This is a question Airbus and/or the airworthiness authorities could answer.

roulishollandais 22nd Apr 2014 01:45


a 'hard' stall protection
...like AF447 ?
Didn't we agree we must no more say the mantra "Airbus cannot stall" ?

HazelNuts39 22nd Apr 2014 15:27


Originally Posted by CONF iture
This is a question Airbus and/or the airworthiness authorities could answer.

Indeed ...

DozyWannabe 22nd Apr 2014 18:15


Originally Posted by CONF iture (Post 8444781)
Also Gordon Corps demonstrated how temporary overshoots seem to actually take place and so without negative effect.

That's based on your assumption that he was in CONF FULL, which is not explicitly confirmed in the video or elsewhere.


Actually the FCS is designed to achieve alpha max without exceeding it.
But it makes no promises about the rate at which it is achieved.

@roulis : That's not what's being said - the aircraft is protected from stall provided that the required features are operational. Without that, it definitely can stall - no-one on this thread has argued otherwise.

gums 22nd Apr 2014 22:00

@ Doze


@roulis : That's not what's being said - the aircraft is protected from stall provided that the required features are operational. Without that, it definitely can stall - no-one on this thread has argued otherwise.
The AF447 was not in the "primary" control laws. And seems that the crew at Habsheim did something to avoid the "primary" laws for their slow, high AoA pass.

It appears that the Habsheim problem was not a flight control computer problem, and the jet did everything it was supposed to do. The AF447 accident showed that the jet can get into a stall if you "do it right". And we learned that in the Viper, after being assured you could not stall the jet. NOT! With a high pitch attitude you could run outta smash and overshoot the progrmmed "protections". Unlike the 'bus, we actually got into a "deep stall".

My feeling is we should let this thread go. It seems obvious that the crew screwed up and crashed a perfectly good jet into the trees.

CONF iture 23rd Apr 2014 02:22


Originally Posted by Dozy
That's based on your assumption that he was in CONF FULL, which is not explicitly confirmed in the video or elsewhere.

Has been already addressed here.
You have been unable to counter my argumentation.


But it makes no promises about the rate at which it is achieved.
Actually it is fast enough that the FTCM states :
"This immediately provides maximum lift"

DozyWannabe 23rd Apr 2014 03:06


Originally Posted by CONF iture (Post 8446286)
Has been already addressed here.
You have been unable to counter my argumentation.

Yes - your inference and assumption that because he specifies 15 degrees, therefore it must be CONF FULL. What I said was that the actual config is not explicitly confirmed in the video or elsewhere - you may be right, but there's no definitive way to tell.


Actually it is fast enough that the FTCM states :
"This immediately provides maximum lift"
Which FCTM, which page? Can you provide more context? HAP mode is described in the FCTM I posted at the beginning of the thread as providing maximum aerodynamic lift, but the word "immediately" is not used.

CONF iture 23rd Apr 2014 13:06


Originally Posted by Dozy
Yes - your inference and assumption that because he specifies 15 degrees, therefore it must be CONF FULL. What I said was that the actual config is not explicitly confirmed in the video or elsewhere - you may be right, but there's no definitive way to tell.

Your lack of argumentation proves my point.
Thank you


Which FCTM, which page? Can you provide more context? HAP mode is described in the FCTM I posted at the beginning of the thread as providing maximum aerodynamic lift, but the word "immediately" is not used.
FCTM A320 OP-020. P 12/16

In case of GPWS/SHEAR:
Set the thrust levers to TOGA
Pull the sidestick to full aft (For shear, fly the SRS, until full aft sidestick).
Initially maintain the wings level
This immediately provides maximum lift/maximum thrust/minimum drag. Therefore, CFIT escape maneuvers will be much more efficient.

DozyWannabe 23rd Apr 2014 17:57


Originally Posted by CONF iture (Post 8446902)
Your lack of argumentation proves my point.
Thank you

Er, no it doesn't. It just means that I don't have any way to confirm whether your supposition is in fact correct, and frankly, neither do you.

Given that this thread started largely as a result of your requests, I have to say that regardless of what you think of me or my input, there are a significant number of qualified and knowledgeable people who have taken the time to sift through the data and attempt to provide answers to your technical questions - and I'm frankly staggered at your dismissive attitude towards them if the results don't fit your preconceived notions of what happened.


FCTM A320 OP-020. P 12/16
Got it - and you're playing fast-and-loose with context again.

You're quoting from the "Operational Recommendations" section, which includes the warning:


The PF must not deliberately fly the aircraft in alpha protection, except for brief periods, when maximum maneuvering speed is required.
Not only does the nature of the Habsheim flight fall outside the parameters of normal ops, thus rendering this particular section (which goes on to assume an airspeed of Vapp) somewhat irrelevant - but Asseline's handling of the aircraft after crossing the threshold completely contravenes that warning.

As HN39 has pointed out, in such circumstances "maximum lift" may not initially be a great deal.

CONF iture 24th Apr 2014 23:33

If CONF 3 was the setting for the video demo, why alpha max was at 15 when it was at 17.5 for Habsheim ... ?
What about simply answering the question Dozy ...

DozyWannabe 25th Apr 2014 14:54

Hi CONF,

Look - all I am saying is that in the video, the configuration is not explicitly specified. Nothing more, nothing less.

steamchicken 30th Apr 2014 19:49


12h30'20'' - CDB: (...) on fait un passage cent pieds, train sorti et l, tu me laisses faire. Je t'amne en alpha max, je dbraye l'alpha floor et ce moment l, si je te dis que c'est dur, tu m'aides et tu tiens les gaz vario zro. (...)
"plus kk que moi, tu meurs. autant, c'est plutot les passagers"


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