Re: Wing vs. tail-mounted engines?

Date:         04 Apr 2001 16:41:09 
From:         jthorn@galileo.thp.univie.ac.at (Jonathan Thornburg)
Organization: Universitaet Wien (Vienna, Austria) / Institut fuer Theoretische Physik
References:   1 2 3 4
Followups:    1 2 3
Next article
View raw article
  or MIME structure

In article <airliners.2001.58@ditka.Chicago.COM>, Wolfgang Keller
<w_keller@gmx.de> writes:
>What are the actual design tradeoffs today and how did the situation
>evolve over the past decades to favor wing-mounted engines that much?

In article <airliners.2001.79@ditka.Chicago.COM>,
JohnMcGrew <johnmcgrew@aol.com> wrote:
>Weight:  Putting engines in the back requires extra load carrying structure,
>both for the thrust and the weight of the engine itself.  On the other hand,
>little extra structure is required for the wing mounted engine since there's
>structure already there; the wing is mostly structure.  Advantage: Wing Mount.
[[...]]
>However, most rear engine configurations necessitate a T-Tail configuration for
>the horizontal stabilizer, which requires extra weight for structure at the top
>of the vertical stabilizer, as opposed to conventional horizontal stabilizers
>attached to existing structure at the end of the fuselage.
[[...]]
>Maintenance:  Most maintenance on wing-mounted engines can be performed at
>ground level without lifts or scaffolding.  Significant appeal to maintenance
>staffs.  Advantage: Wing.

These are the big reasons in practice, especially the lower weight
(--> lower drag at the same lift/drag ratio --> lower fuel burn).

>Aerodynamics:  Rear-mount allows for a cleaner wing design, and less conflicts
>with airflow and mechanics for slats and flaps.  Advantage: Rear.

With modern design techniques (computer + wind-tunnel) the aerodynamic
difficulties of wing-mount (podded) engines can be dealt with without
serious difficulty.

The industry doesn't care much about it, but safety is another big
advantage of wing-mounted engines:  What kills people in a jet crash
is often not the crash itself, but the ensuing fire.  Tail-mounted
engines mean fuel pipes running from the wing (where the fuel tanks are)
aft through the fuselage to the engines, i.e. you've got fuel right
in the fuselage with the passengers.  In contrast, wing-mounted engines
allow all the fuel to be kept in the wings, some distance away from the
passengers.  (Some designs do put fuel tanks in the wing center sections
anyway.)

--
-- Jonathan Thornburg <jthorn@thp.univie.ac.at>
   http://www.thp.univie.ac.at/~jthorn/home.html
   Universitaet Wien (Vienna, Austria) / Institut fuer Theoretische Physik
   Q: Only 6 countries have the death penalty for children.  Which are they?
   A: Congo, Iran, Nigeria, (Pakistan[*]), Saudi Arabia, United States, Yemen
      [*] Pakistan reportedly ended it in July 2000. -- Amnesty International
                         http://www.web.amnesty.org/ai.nsf/index/AMR511392000