Re: B747 technical questions

Date:         17 Aug 97 15:41:08 
From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
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>>> The JT9D was flight tested
>>> on a B-52 and the RB.211 was flight tested on the port pylon of a
>>> VC-10.  How was the CF6 flight tested?  Perhaps on a C-5A, from whose
>>> TF-39 engines the CF6 was developed?  On what, then, were the TF-39
>>> engines flight tested?

>OK, maybe I'm being the Devil's Advocate here, but Why bother ?

>>From 60 years of gas turbine flying, improved Simulated Facilities,
>improved mathematical modelling and suchlike, there is minimal info to
>be gleaned from flight testing in an unrepresentative environment.

If you're referring to the TF-39, it appeared in the 1960s.  There may
be 60 years of gas turbine flying now (actually more like 55), but much
of that experience didn't exist 30+ years ago, and the simulation
facilities were primitive compared to what exists today.  The TF-39
was the first high-bypass ratio turbofan, too, and probably 2.5 times
more powerful than any previous jet engine.

If you're talking about flight testing of engines in general, Boeing's
propulsion people and Pratt and Whitney felt that you were correct and
that flight testing the PW4084 (the first Pratt engine for the 777)
was not necessary.  It was a derivative of an existing, proven design,
and they had done extensive ground testing and simulation of it, so
they didn't expect to learn anything from flight testing.

Others in the 777 program generally accepted that position, but since
nobody had ever relied on ground test and simulation data alone, they
thought it would be wise to flight test the engine to prove that they
had in fact learned everything on the ground.  A sanity check, just
as they built a mockup of the 777's section 41 (the nose and cockpit
area) to validate the CAD tools, which were supposed to make mockups
unnecessary.

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!

--
Karl Swartz	|Home	kls@chicago.com
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