Re: 727 engine config (was Re: Searching for info on a 20 year old crash)

From:         rdd@cactus.org (Robert Dorsett)
Organization: Capital Area Central Texas UNIX Society, Austin, Tx
Date:         20 Nov 93 00:41:09 PST
References:   1 2
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In article <airliners.1993.746@ohare.Chicago.COM> you write:
>The 727 is Boeing's only trijet, and is the only trijet I know of with
>all three engines at the tail. 

Others include the Trident, Tu-154, and more...

>Anybody know why Boeing gave up on trijets
>after the 727, and why nobody else has built a trijet with three engines
>at the back?

Having all the engines up at the back does provide something of a challenge
for maintenance.  It's much easier to maintain engines slung under the wings.
For quite some time, Boeing was going to sling two under the wings (in a 
configuration which looked quite similar to the L-1011), but decided on 
a rear-mounted configuration for clearance and foreign object damage 
considerations.  This was apparently a very intense issue within Boeing.

The 727 trijet configuration was a result of:

1.  A compromise between the launch customers of EAL and UAL.  EAL wanted
two engines for economy, United wanted four for safety.  Boeing talked them 
into three.

2.  The IFR dispatch restrictions at the time heavily favored a three-
engined airplane (as opposed to a twin); the ability to take off in marginal
conditions was quite a bit better.  Boeing wished to use this to differentiate
the airplane against the twins and quad turboprops it was competing against.

By the mid-late 60's, the second requirement had disappeared, and the 
economics and safety (reflected by improvements in engines, namely the
JT8D, which the 727 pioneered) of twins became so good that airplanes such 
as the 737 and DC-9 began to appear.


> Finally, (shades of the ETOPS discussion) does anyone know of
>any incident involving a 727 which did not result in a crash, but would have
>if the 727 was a twin?

If you're referring to a *727*, the question is impossible to answer.  Thrust
limitations of engines produced in the 1960s would not have permitted the 
airplane to be certified with two engines.  I believe the first twin  
anywhere near the 727's operating weights was the 757, which utilizes
a different type of engine and engine technology.



---
Robert Dorsett
rdd@cactus.org
...cs.utexas.edu!cactus.org!rdd