From: Michael.F.Lechnar@boeing.com Organization: e Date: 21 Oct 96 02:29:20 References: 1 Followups: 1
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In article <airliners.1996.2103@ohare.Chicago.COM> email@example.com (John1082) writes: >Several jets had the ability to ferry an engine to an out of the way spot. >The early 747 could do it and I believe the L1011 could as well. There >could be others. > >This would likely have been a built in option when the plane was built, >with the hard points built into the wing from the beginning. > >But what a fuel guzzler if used. For what it's worth, a good generalized number for the fuel penalty for carrying a spare engine is 15%. There are also speed restrictions. For the -200 with RR engines, the limit is Mach .82/320 KIAS. Spare engine carriage was developed due to the lack of 747 main deck freighters during the early days. No narrow body freighter could accomodate a built-up big fan engine. The combination of more wide body freighters and an increase in engine reliability has made spare engine carriage a rare event. In fact, for the 747-400, only the RB211 engine model is certified to carry a spare engine. The others have the capability, but since no customer wanted to use it, performance flight testing for certification was not done. Mike Lechnar Aircraft Performance Engineer "If I was speaking for Boeing, I wouldn't be doing it here."