Re: SURGE ON GE90 ENGINE

From:         bds4798@aw101.iasl.ca.boeing.com (R. Brian dosSantos)
Organization: none
Date:         06 Jun 95 10:11:05 
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tshepherd@med-med1.bu.edu (Thornton Shepherd) writes:

	>I read in Aviation Week that one of the GE90's on BA's
	>first 777 had experienced a "surge".  Can anyone tell
	>us what a surge is and why it's of concern?  Will this
	>problem delay the delivery of the BA aircraft?

My knowledge is based on discussions of these events with others much
more knowledgeable than I am and from casual reading...so easy on the
flames.  I welcome corrections.

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.  As I am writing this
I am reading the June 2nd edition of Boeing News (insiders call it
the Boring Snooze).  The headline title is _777 ETOPS...Here Now_.
So to answer your question about delay of certification...I don't think
a surge will delay certification--unless the cause is identified as
something more dramatic than what caused the surge on the PW.

---
R. Brian dos Santos
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(The Boeing Company's opinions are its own and not mine)