Re: B747 technical questions

Date:         27 Aug 97 03:57:52 
From:         stephen@genesis1.physics.YALE.EDU (Stephen B. Selipsky)
Organization: Yale University, Department of Computer Science, New Haven, CT
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In article <airliners.1997.1793@ohare.Chicago.COM> kls@ohare.Chicago.COM (Karl
Swartz) writes:

> On one of the first test flights (on the first 747), the PW4084 had a
> compressor stall.  This turned out to be due to insufficient rigidity
> in the fan housing.  At takeoff power, under high angle-of-attack, and
> with a cross-wind, the fan housing ovalised too much and impacted the
> fan blades.  It's a good thing they did go ahead with flight testing!

   On the "21st Century Jet" PBS program on the 777 project, the P&W
representative claimed that they had previously scheduled a "high
angle-of-attack, cross-wind" ground test that would "definitely" have
picked up the stall problem, but the flight test result happened to
have come in earlier.  Hard for an outsider to know the "damage control"
to "reality" ratio there...
   I gathered from the program that a compressor stall is simply flow
separation from the compressor blades, no different from a wing stall;
does it necessarily also involve or cause mechanical conflicts as
described above?  Or (hazy memory here) did the ovalizing cause too
much of an air gap between blades and housing, thus somehow inducing
the airflow separation?
Stephen B. Selipsky   
Yale University Physics Dept.   Phone: 203/432-6923
P.O. Box 208120                 Fax:   203/432-6175
New Haven, CT  06520-8120       Home:  203/782-2065