From: (David T. Medin)
Organization: Rockwell Avionics - Collins, Cedar Rapids, IA
Date:         15 Jun 95 01:14:00 
References:   1 2
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In article <airliners.1995.760@ohare.Chicago.COM>, (R. Brian dosSantos) writes:
> (Thornton Shepherd) writes:
> 	>I read in Aviation Week that one of the GE90's on BA's
> 	>first 777 had experienced a "surge" ...

> The "surge" you mentioned is also called a stall.  Both the GE90 and
> the PW4084 (United's engine) surged on their first flight.  Essentially
> what happened to both engines is the following:  During climb out, at
> high angle of attack and with air entering the engine inlet at higher
> than normal incidence, the air pressure at the engine's inlet dropped
> below the pressure inside the engine's core.  The higher pressure air
> in the core escapes forward and out the engine inlet, usually with
> a loud bang and flames and smoke.  The pilot at the column of the 747
> test bed, John Cashman, which flight tested the first PW engine,
> predicted the surge at high angle of incidence.

I was watching a film on the 777 produced for the BBS (don't know when
it will or if it has aired) out at Boeing which showed the Pratt &
Whitney stall when flying on the 747 testbed at a steep angle of
attack--impressive explosions.  The engine had a series of three
stalls that more or less vindicated the position by Cashman and others
that flight testbeds were still necessary (versus total static testing
in wind tunnels, which did not find the problem with nacelle design
until much later). As I remember, it was determined that the nacelle
flexed too much relative to the blades, creating too great a gap and
thus the stall. The film included an interview with one of the chief
propulsion engineers who indicated that his initial position (for
static testing only) was wrong, as proven by the nacelle redesign
which occurred early enough in the program to avoid significant

       David Medin            Phone: (319) 395-4498
   Rockwell Collins ATD	      Internet:
     Cedar Rapids, IA