Re: Are Two Engine 757 & 767 Jets Dangerous?

Date:         12 Dec 96 03:49:25 
From: (Michael Hore)
Organization: Kralizec Dialup Unix Sydney, +61-2-837-1183 V.32bis
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kls@ohare.Chicago.COM (Karl Swartz) writes:

>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.

If I remember the _Flight International_ article I quoted before (I
don't have it to hand just now), the Airbus fellow they interviewed
claimed that they originally started with two separate airframe
designs, but as they went along the designs evolved towards each other
to the point where it made more sense to combine them.  So I guess
the degree to which the A330 and A340 are "optimized" for the two
markets is in the eye of the beholder.  (I'm actually agreeing with
you here, BTW).

>Most or all of those contributors have some association with Boeing,
>and thus no doubt will be written off by the Airbus fans.

Probably true.  (I've got no axe to grind either way, BTW, though
I wouldn't mind if Qantas bought 777s and Ansett A330s - it would
make life around here more interesting  :-)

>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.

That's a good point - but is the adverse yaw from a failed outboard
engine on a 4-engined a/c much less than on a twin (assuming placement
equivalent to the inboard engines of the quad)?  I guess in the
former case you have the option of reducing thrust on the other
outboard engine, and still have enough thrust left to stay in the

>I'm pretty sure the A330's engines are attached at the same point as
>the A340's inboard engines.

Correct.  And I understand they did a *lot* of computer work on the
airflow between the engines and the fuselage.

>If so, the A340 is carrying around more
>rudder than it needs

Anyone who really knows, care to comment?  I'd be interested,
for one.

Cheers,  Mike.

Mike Hore