[SystemSafety] QF 32 and the Airbus A380
michael.lemay at aero.bombardier.com
michael.lemay at aero.bombardier.com
Fri Sep 28 16:06:36 CEST 2012
I've had some experience doing loads and dynamics on transport-category
aircraft, so maybe I can provide some insight.
It's true that transport category aircraft must meet the requirements as
stated below, amongst others. In practice, this means that the lift force
you put on the wing must balance out the 'g' you're putting on the
aircraft. So, roughly speaking, a 2.5 g pitch-up maneouver needs 2.5 g of
upload on the wing. A manufacturer will produce thousands of different
load cases based on the certification requirements and derive envelopes of
maximum load with which to design the aircraft. For structure design
based on those load cases, one of the more important design parameters
turns out to be the overall bending moment induced at the wing root by the
distribution of the load along the wing. If you can reduce the worst-case
bending moment, then you can potentially save weight by reducing
structure. Conceptually, one of the ways to do this is to use flight
control surfaces such as ailerons or spoilers to redistribute load on the
wing, i.e. destroy lift outboard thus requiring additional lift inboard to
compensate (the overall load on the wing must remain the same in order to
have a balanced load case, otherwise the aircraft would accelerate in some
direction). This moves the load distribution more inboard and reduces the
overall bending moment at the wing root. However, that approach is only
valid if the wing is maneouver-critical, i.e. the worst-case design load
comes from a required maneouver. In some cases, an aircraft wing can be
gust-critical, i.e. the maximum design loads come from prescribed gust
intensities. In that case, other approaches for load reduction need to be
tried. Adding complexity to this whole thing is the fact that the
reliability of your load alleviation system needs to be taken into account
in the design. There is a FAR covering system-structure interaction (I
can't remember the number at the moment) which prescribes differing safety
factors on the design based on the reliability of the system that acts to
reduce load.
There are many papers written on this subject; unfortunately I can't
provide any citations at the moment.
Michael Lemay
Analyste / Analyst
Bureau d'enquêtes sur la sécurité aérienne / Air Safety Investigation
Office (ASIO)
Bombardier Aéronautique / Bombardier Aerospace
michael.lemay at aero.bombardier.com
(514)855-0139
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Bernd Sieker <bsieker at rvs.uni-bielefeld.de>
Sent by: systemsafety-bounces at techfak.uni-bielefeld.de
09/28/2012 09:47 AM
To
systemsafety at techfak.uni-bielefeld.de
cc
Subject
Re: [SystemSafety] QF 32 and the Airbus A380
On 26.09.12 10:37, Bernd Sieker wrote:
> 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).
Some references for that: CS 25.337 and CS 25.345, respectively.
CS 25: Certification Specifications for transport category aeroplanes,
found at
http://www.easa.europa.eu/agency-measures/docs/certification-specifications/CS-25/CS-25%20Amdt%2012.pdf
AMC 25.307 specifies that structures need be shown to support limit load
with detrimental permanent deformations, and ultimate load (usually 1.5
times limit load, CS 25.303) without failure.
AMC 25: Acceptable Means of Compliance, Book 2 of CS 25, which specifies
some acceptable means, but not the only possible ones, of showing
compliance with the specifiations in CS 25 (Book 1).
Bernd
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