[SystemSafety] QF 32 and the Airbus A380
Les Chambers
les at chambers.com.au
Fri Sep 28 02:05:14 CEST 2012
Thanks Bernd
Very informative.
Les
-----Original Message-----
From: systemsafety-bounces at techfak.uni-bielefeld.de
[mailto:systemsafety-bounces at techfak.uni-bielefeld.de] On Behalf Of Bernd
Sieker
Sent: Wednesday, 26 September 2012 6:37 PM
To: systemsafety at techfak.uni-bielefeld.de
Subject: Re: [SystemSafety] QF 32 and the Airbus A380
On 26.09.2012 02:46, Les Chambers wrote:
> Hi All
>
> Richard De Crespigny's excellent book (QF32) on the engine explosion in
> the Qantas A380 out of Singapore is a gripping read. Richard was the
> captain and commander. The 400 passengers and crew on this aircraft owe
> him and his excellent team their lives.
>
> He provides some technical details of the A380 that are particularly
> interesting. For example, according to Richard, the A380 has 250,000
> sensors, 22 subsystems and three operating "laws". He also says that the
> airframe was designed with the avionics system in mind. That is the
> airframe is less rigid, and therefore lighter, as the flight control
> system is designed to avoid stressful in-flight situations. As a
> professional sceptic I've got to ask, "Is this true?".
Less rigid may well be right, but that only means that it flexes more,
which can help alleviate airframe stresses.
Unlike previous Airbus airliners, the manufacturer has been successfull
so far in preventing public distribution of the type's operating
manuals, but:
All transport category aircraft have to be designed for the same load
factors. These are +2.5 G and -1 G with high-lift devices retracted
("clean"), and +2.0 and 0 with flaps/slats extended (design limit load).
The airframe has to be proven physically not to break at loads below
150% of the design limit load. This is the famous "wing ultimate load
test", where the wings are bent upwards until the break. The A380 is
certified to the same standards as any other transport aircraft,
although it failed the physical test just below 150% design load
(http://www.flightglobal.com/news/articles/airbus-a380-test-wing-breaks-just
-below-ultimate-load-target-204716/).
The manufacturer strengthened the structure
(http://www.flightglobal.com/news/articles/airbus-to-reinforce-part-of-a380-
wing-after-march-static-test-rupture-206797/)
and in the end got away with it without having to re-do the destructive
test.
The "three laws" to which the author refers are the different operating
modes of the EFCS (Electrical Flight Control System), and are almost
certainly the same as in all other Airbus fly-by-wire airliners. The
first and second variety (called "normal law" and "alternate law",
respectively) limit the load on the airframe to the maximum design load
(+2.5/2.0 and -1.0/0), the third one is called "direct law" and deflects
the control surfaces directly proportional to the stick deflection, and
it is in this mode that it becomes possible to overstress the aircraft
structure.
The wing appears more "floppy" than on most other aircraft, mostly
because it is very long and has a heavy engine suspended pretty far
outboard; but that does not mean that it is any less strong than that of
other aircraft.
Other wide-body aircraft, except the 747, only have two underslung
engines and do not have as much weight outboard, so do not need to flex
as much. The old 747-1/2/3/400 wings are of a much older design and may
well be overengineered to a degree that is not necessary today to
fullfil certification criteria, and may thus be more rigid.
The B777 wing was shown to break at 154%
(http://www.youtube.com/watch?v=Ai2HmvAXcU0), which is a near-perfect
result in terms of fulfilling the specification, while not being much
heavier than necessary.
I expect the 747-8 wings to be almost as wobbly as the A380's. In fact
Boeing had flutter problems with them and was forced to introduce an
active flutter-damping system to alleviate the problem
(http://www.flightglobal.com/news/articles/faa-and-boeing-agree-on-747-8-oam
s-special-condition-354600/).
> Could anyone
> recommend some light reading on the design of the A380. The story of the
> A380 development project would also be extremely interesting.
http://www.smartcockpit.com/aircraft-ressources/A380_Briefing_For_Pilots_Par
t%202.html
... is the only substantial thing from Airbus I can find on the A380,
but it is not really about development, design and structure.
I haven't read the following, but this also sounds like something to read:
"A380 Weight Savings Using Numerical Structural Optimization" in
proceedings of 20TH AAAF Colloquium, Material for Aerospace Applications
Probably not exactly "light reading", though.
This may also give some ideas about new design methods for the A380:
http://www.altairhyperworks.co.uk/html/en-GB/Campaign/pages/papers/Aero/Pape
r6%20Airbus.pdf
And here's something a bit "lighter":
http://ultraligero.net/Cursos/diseno/Design_Of_Aircraft_Structures_Under_Spe
cial_Consideration_NDT.pdf
Cheers,
Bernd
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