Date: 16 Oct 97 00:44:11
From: Iain Stuart <big-iain@big-iain.demon.co.uk>
Organization: What ?
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In article <airliners.1997.2452@ohare.Chicago.COM>, H Andrew Chuang
<Chuanga@cris.com> writes
>In article <airliners.1997.2418@ohare.Chicago.COM>,
>Malcolm Weir <malc@mci2000.com> wrote:
>>The point was, while all in-flight shutdowns are serious, possibly the most
>>serious type of event involves fan blade failures...
> All engines
>do have to go through a fan-blade-failure test just like they have to
>go through birdstrike tests (but not a rotor-disk-failure test). In
>most cases, a fan-blade failure should not cause a catastrophic failure
>of the engine.
Let's get technical. FAN BLADE FAILURE
All engine marks need to show that a single blade release will be
contained. This needs to be shown for any stage of compressor / turbine,
and for failure at the worst possible position on the blade (ie not just
the tip being released). Damage to other blades must also not cause
hazardous effects.
This can be demonstrated by full running engine test, and suitable rig
test, or by analysis. The cost of the engine test is massive, and thus
rarely done. The analysis method is cheaper, but usually requires
reading across data from engine tests. (NB I believe that the GE90
engine test involved blade failure at the "most likely" failure position
(not the worst), and the FAA agreed !)
However, multiple blade release or disc burst are not required to be
contained. (Think about the energies involved...it's not practical.) The
risk of such failures must be shown to be acceptable low, and this is
why discs have declared service lives and inspection schedules. This
does rely on the professionalism of the engine operator, and several
failures I know of cannot be blamed on the engine design.
Now....BIRD INGESTION etc.
Similar rules cover bird ingestion, hail ingestion etc. There are bird
ingestion rules for small birds, medium birds and large birds, and the
numbers to be swallowed vary with engine size. Again, compliance can be
demonstrated by engine test and/or analysis. The current requirements
are that bird ingestion causes no hazardous effects, and that the engine
continues producing at least 75% thrust for 15 minutes without throttle
tweak.
And, yes... the widechord fan blades do CF out the debris / nuggets away
from the core, and the core suffers less damage. Ask the airlines,
they'll confirm this.
-----------
Iain Stuart
They're my opinions !
