Re: 777 engine imbalance (Business Week, 1/29)

From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
Date:         10 Feb 96 12:30:51 
References:   1 2 3
Next article
View raw article
  or MIME structure

>However, from the GE incidence, I would think that engine imbalance
>is a critical criteron in the blade-out and bird-strike tests.

My take on GE's problems was that the delay in certification was
because the bird-strike test took out three blades instead of just
one as required by the regulations.  Imbalance wasn't directly a
concern, though undoubtedly the "one blade" rule is based in part
on concerns over balance.

>Thus, I don't quite follow why Business Week made an issue out of
>this.  Since these tests require the engine to maintain certain level
>of thrust, the vibration that one would experience in windmilling
>cannot be any worse than that at 80 or 90% speed.

I think the point was that while the engine may well continue to
produce substantial thrust, there's apparently nothing that says the
plane must still be flyable.  The engine could be producing thrust
all the way into a crater caused by severe vibration rendering the
aircraft unflyable yet the regs apparently would still be met.

I haven't looked at the appropriate regulations myself, so this may
be entirely off base.  Perhaps someone would care to cite specific
sections of the FARs that are relevant to this discussion.

--
Karl Swartz	|Home	kls@chicago.com
		|Work	kls@slac.stanford.edu
		|WWW	http://www.chicago.com/~kls/
Moderator of sci.aeronautics.airliners -- Unix/network work pays the bills