Re: GE90 comments

From: (Andrew Chuang)
Organization: International Internet Association.
Date:         22 Nov 94 12:10:42 
References:   1
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Robert Ashcroft (rna@leland.Stanford.EDU) wrote:

: A Pratt and Whitney employee sent me the following to be posted:

: I'm responding by e-mail since my access to the Net is at the moment
: read-only.  Perhaps if you find my comments of interest, you'll post them.
: GE actually has two separate sets of problems with the GE-90.  The one you
: spoke of involves their petition to change the rules with respect to 
: certification requirements.  One requirement is to explosively fail a fan
: blade while the engine is operating at max power.  The traditional way to do 
: this is to blow the blade root apart.  P&W has done this and Rolls Royce
: expects to soon, if they haven't already.  GE wants to fail the blade 
: further away from the center of the engine.  Much less mass, so less
: energy released.  Speculation is that they gotta have the waiver, 
: because they know they cannot pass the old test.
: In addition, they are way behind in their experimental test plan, because
: parts in their test engines keep failing.  The most recent major failure
: was in the lenticular seal between (I think) th\e high and low turbines.
: I must declare an interest:  I'm a 20 year employee of P&W, and I am
: truly outraged at what GE is trying to do with the FAA on this fan 
: containment test.

I had a follow-up of Mr. Ashcroft's previous post.  It must be lost
somewhere in the cyberspace.  There should be some clarifications of the
above comments by a P&W employee.  Note, I'm not trying to defend for GE
nor FAA.

The GE90 fan blades are distinctively different from P&W's and R-R's.  The
former are made of carbon composite while the latter two are made of
hollowed titanium.  GE's argument was based on some probability analyses
which FAA agreed.  FAA actually solicited opinions from both P&W and R-R.
The implication of the rule change is that GE will be able to certify the
engine with less material on the casing, hence make the engine weigh less.
Since GE90 is the biggest engine of the three, it needs to cut down its
weight to be competitive.  Whether GE and FAA are compromising on safty,
I don't have the expertise to make the call.

I would like to point out in one of the letters to the editors of AvWeek or 
Flight Int'l, a composite "expert" speculated that GE analyses were flawed.
I'm not going into the details, if you are interested, read AvWeek.  

         |  H Andrew Chuang  |