Things With Wings

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  • The Accidental Airliner
    Posted by Bill Sweetman 3:04 PM on Aug 31, 2011

    "Our relationship with Boeing goes back more than 30 years and even we could not have predicted the phenomenal success the CFM-powered Boeing 737 program has enjoyed." Thus says CFM President and CEO Jean-Paul Ebanga on the launch by Boeing of the new 737 variant with the LEAP-1B engine.

    That's the understatement of the millennium.

    I remember the call from an Airbus contact sometime in 1980. "You won't believe this new 737 they're pushing. The engine nacelles look like hamsters."

    The hamster look - the pouchy nacelle that appeared on the first 737-300 - was part of a package of bodges and compromises that made the airplane work.

    Boeing engineer Mark Gregoire had drawn the corporate short straw a few years earlier, given the job of seeing how much more lifetime could be wrung out of the 737 and 727 lines.

    The cool kids such as Alan Mulally (who later made all the key decisions about the 787) were on the 757 and 767, which were also sucking up all Boeing's money. Boeing bosses - never happy with the fact that the 737 was the only Boeing that came second in its market segment - put Gregoire's team under strict limits, including a ban on tinkering with the wing center-section.

    This meant no changes to the landing gear, which was a problem for the groundhog-stanced 737 because there seemed no way to stick new engines, even the JT8D-200, under the wings, and without new engines the 737 was on a direct path to annihilation by the DC-9 Super 80.

    Enter CFM.
    They were motivated. The joint venture had been two weeks away from the axe not two years earlier, and was saved from the firing squad at the last minute by a DC-8 re-engining program, but there was still no new CFM-powered airplane, nearly a decade after GE and Snecma had launched the project.

    One of Gregoire's team was Walt Gillette (who was to retire as chief engineer on the 787, apprehensive about whether the company had bitten off more than it could chew). At the time, Gillette was a pioneer of newfangled computational fluid dynamics.

    CFM designed a less powerful version of the CFM56-3 engine with a smaller-diameter fan. The engine accessories were relocated to the lower sides of the fan case. Gillette used CFD to work out exactly how close the nacelle could go to the wing without all hell breaking loose, and how far the inlet lip had to be off the ground so as not to act like a vacuum cleaner.

    The answer to the latter turned out to be a ratio of the height of the inlet opening to the distance between the lower lip and the ground. A circular inlet would not work, so the Boeing team basically pulled the lower lip upwards, completing the hamster look.

    The result was good enough (and above all cheap enough) to get authorization to offer. In March 1981, Boeing got a launch order from a minor US regional carrier called Southwest Airlines.

    Since then, the 737 has been Boeing's dependable cash cow and the CFM56 has become the most successful aero-engine in history.

    The 757 is long gone. P&W abandoned its CFM56-like JT10D in favor of the 757-tailored PW2000 - and the JT10D prototype only survived because a group of engineers hid it in a potato shed, so that embarrassed corporate leaders would not scrap it.

    Tags: tw99, 737, CFM56

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