Re: Are Two Engine 757 & 767 Jets Dangerous?

Date:         08 Dec 96 04:12:36 
From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
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>So it appears to me that the A340 would always have had 4 engines, regardless
>of what engines might have been available.  It's part of Airbus' philosophy
>of meeting 2 markets (medium range / long thin) with 2 designs optimized
>for each.

Unfortunately, Airbus did not produce "2 designs optimized for each"
market, they produced one design in two substantial variants, one or
both of which are necessarily a compromise.  Several contributors to
sci.aeronautics.airliners have noted that you can't design one wing
that's optimial for both a two- and four-engined aircraft.

Most or all of those contributors have some association with Boeing,
and thus no doubt will be written off by the Airbus fans.  Try, then,
the more obvious need for more rudder authority on a twin to
compensate for an engine out than on a four-engined airliner.  Even
on designs with less drastic differences in terms of engine count and
placement exhibit this -- the DC-10's wing engines are closer to the
fuselage (which results in more drag) than those on an L-1011, because
the placement of the #2 engine results in a smaller rudder and thus
less rudder authority to counter asymmetric thrust.

I'm pretty sure the A330's engines are attached at the same point as
the A340's inboard engines.  If so, the A340 is carrying around more
rudder than it needs.  Alternately, if the A330's engines are closer
to the fuselage to allow use of a tail and rudder that are adequate
for the A340, then drag is greater than would be the case for an un-
compromised design.

--
Karl Swartz	|Home	kls@chicago.com
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Moderator of sci.aeronautics.airliners -- Unix/network work pays the bills