Re: Photo of Pan Am 747 W/5 engines

From:         Michael.F.Lechnar@boeing.com
Organization: e
Date:         21 Oct 96 02:29:20 
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Followups:    1
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In article <airliners.1996.2103@ohare.Chicago.COM> john1082@aol.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."