Re: 2 vs 4 engines: R&D costs too much ?

Date:         05 Nov 99 00:04:12 
From:         "Thaddeus J. Beier" <thad@hammerhead.com>
Organization: Hammerhead Productions
References:   1 2 3
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robert wright wrote:
> >The center-line engine required for a tri-jet introduces its own share
> >of problems.  There are all the usual CG and structural issues that come
> >with any aft-mounted jet, plus concerns about safety when you put so
> >many critical systems in such a small location.  Besides the engine,
> >there are all the hydraulics for the rudder(s) and elevators.  Wing-
> >mounted engines are a lot easier to isolate.
>
>     At Boeing, when I worked on some studies for a new large aircraft to
> possibly replace the 747, we looked at twins, tris, and quads.  Trijets
> always came out worst in terms of operating economics by a long way, largely
> due to the CG issues and added weight of shielding around the engine to
> protect airplane systems in the event of a rotor burst.

I've been wondering if anybody ever considered building a three
engine airplane, with all of the engines on the wing.  Now, I
recognize that this is going to be funny looking, but work
with me for a minute.

You'd mount the single engine substantially farther out the
wing than either of the two engines on the other side, so
the thrust and weight moments could be not too far off.  You'd
probably be carrying some sideload on the tail, but you
can build an tail with some lift at zero angle of attack
that would have very little more profile drag than a
symetrical tail, although there would be some added
induced drag.

Perhaps there would be some odd responses in different
corners of the flight envelope, but modern computerized
flight controls could hide those.

You'd have a plane with more than two engines, but with
less weight and complexity than a four engine plane, and
you'd have all the engines on the wings (where they belong).
You might place the single engine on the port side, so that
there'd only be one engine on the side where jetways attach
to the airplanes.

I've been a fan of asymetrical airplanes, like Rutan's ARES
and spectacular Boomerang.  I think that they could work here,
too.

thad