Ricky wrote in news:8e1e5bc2-64ba-4c74-921c-
:


Bertie!

(Or anyone who may want to speculate)

I'm in the last stages of A&P training (already a "P") but I can't
figure out if a big bird would be substantial enough to break
conpressor blades, or interior compressor or turbine blades for that
matter.
I'm guessing the first stage blades would turn the bird into soup. I
also know that first (and second & sometimes later stage) blades are
usually made of much harder material to absorb fod.
I'm also aware that sometimes an abrasive grit is used in turbine &
compressor washes so the blades are understandably very, very tough,
especially with the extreme temps of interior turbine blades.
So, after watching the 757 bird ingestion my college-A&P mind is
trying to figure out exactly what happened, why the turbofan spit fire
and such.
I asked an instructor today & he said the first stage blades likely
will break with a large bird and, of course, cause chaos the rest of
the way through the engine. He also said that small birds can pass
through without even being noticed.
So I'm guessing that exactly what happened is likely up to a wide
range of speculation until you could get into the engine and see but
I'm still curious of ya'll's speculation, too (ya'll's; that's Texan!)

Yes, he's right. Small ones often go right through. If they go through
the core, you can smell them, in fact. You usually get a small
"whumpfh" as they go through.
I know of a large flock of starlings that stopped a JT8 instantly and
broke it;'s mounts.
A large-ish bird will definitely wreck blades. Probably the first
compressor stages will go and the debris from those will take out th
erest of the compresser and the turbine. I've seen an engine you could
see right through with only shards of the blades left on the spools like
an eaten cob of corn. Actually I've seen a few of these, all JT8s.
I'd say that 757's engine was in the same shape after eating that heron.
the fire spitting is due to an uneven flow through the engine. Since th
ecompresser section was screwed, it would be providing air to the burner
cans erratically and instead of a nice smooth fow, you get a series of
pulses. We usually call them compresser stalls.
The grit they clean the engines with is usually something like walnut
shells, AFAIK, but I'm not an engineer! Your insturctor would know
infinitely more about this stuff than I do.

Bertie