Re: Wing vs. tail-mounted engines?

Date:         27 Mar 2001 16:05:14 
From:         "ME Incorporated" <whyyou@boddah.me>
Organization: World Trade Network, Inc. (WT.net)
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"Wolfgang Keller" <w_keller@gmx.de> wrote in message

> What are the actual design tradeoffs today and how did the situation
> evolve over the past decades to favor wing-mounted engines that much? What
> would be the impact of, for example, drastically increased fuel prices
> and/or significantly more strict noise regulations (=> engines with bypass
> ratio >>10)?

I'm no expert, but the biggest concern is saleablity.

In other words, if all things are equal, what's the x factor in selling an
Airbus or a Boeing (or a McDonnell Douglas, before the merger...)

The DC10 was orignally thought of as a twin engine.  Then a four engine.
The three engine was perfect, given it's requirement.  But how to mount it?
And of course, Lockheed got into it too, and designed the Tristar.  While
they both have tail mounted engines, they did their differently.

DC10 way up on a "banjo" fitting, the largest forged piece at the time, and
the L10 in the fuselage using a duct.

In BOTH cases, it was a harder sell than a twin or four engine, because of
the mainenance of the third, tail mounted engine.

In a 717/DC9/MD80 or a 727, this was a little be easier, because they
weren't as high off the ground.  But in a DC10, well, this was a BIG deal.

And so, with more powerful engines, and the complaints/requests of big
clients such as American, United, etc, these tail mounted engines are
becoming a non desired design.  Hence, the design of the 777.  Very much an
airplane designed by and with the airlines, and not just the plane makers
designing around a spec.  You can bet that Boeing wanted more engines, and
maybe in the tail, but because of that maintenance thing, two is cheaper,
and wing mounted cheaper still.

Anyway.  It's economics.  The airlines would rather have simpler maintenance
requirements than the DC10/747s require, which translates into less money
spent.  Bean counting anyone?  8^)  Two underwings are simpler than 4, and
way simpler than any tail buried DC10.

BTW, from an engineering standpoint, the wing is easier to build/design when
hanging engines off of it, instead of "clean" like the 727.

At least, that's what I've read/heard/figured out.  I'm sure someone's gonna
boot me in the head now...  Go on then!  8^)