Re: Convair 990 + misc.

From:         drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Organization: Boeing Commercial Airplane Group
Date:         01 Apr 94 13:11:23 PST
References:   1
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In article <airliners.1994.1089@orchard.chicago.com>,
Tobias Henry Lutterodt  <luterodt@phoenix.Princeton.EDU> wrote:
>I'd like to clear up this question:  Is it true that before, Boeing 
>designed engine mounts to give when an engine seized and let the 
>engines fly while now (post-Amsterdam) they are trying to keep the
>engines attached to the plane if at all possible?  Terry?

I am not clear on exactly how the strut design criteria have changed in the
last couple of months (I could ask my strut stress animal, I guess :-)).
I can say a little bit about past criteria and how we got there.
There are at least two very critical design cases.  One is where the engine
seizes, phi dot = 0, omega dot approaches infinity :-).  Given the enormous
amount of rotational energy stored in the rotating parts of a turbine
engine that would have to be reacted out through the strut, wing, and
fuselage, it is more economical (lighter by tons) to design the
engine/strut to depart the airplane in a controlled manner.  The other
major case that comes to mind is a gear up landing.  The engines hang down
and collect up obscene amounts of concrete during such operations.  If this
were all that happened, it wouldn't be too bad.  It is when the engines hit
an obstruction (like an embankment) and are torn off of the wing that
things become exciting.  We want the engine to depart safely, which means
without rupturing the fuel tanks in the wings.  The single most critical
condition of a safe evacuation is the lack of jet fuel mingling with hot
engine parts at the crash site.

This is all very clear, yet we are finding that the structural solutions to
those problems are vulnerable to corrosion and poor maintenance practices.
There may not be a graceful fix for this exposure (this is not my
specialty) and I have heard noises suggesting we design to keep the engine
on the airplane even if it seizes.  I have not heard anyone address the
crash separation issues - but as I say, this isn't my area and I only know
what I read in AvWeek.  :-)

If this isn't confusing enough, let me know and I'll see if I can murk it
up a bit.  :-)

Terry

-- 
Terry
drinkard@bcstec.ca.boeing.com
"Anyone who thinks they can hold the company responsible for what I say has
more lawyers than sense."