Re: Wing vs. tail-mounted engines?

Date:         04 Apr 2001 16:41:23 
From: (Don Stokes)
Organization: Daedalus Consulting
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JohnMcGrew <> wrote:
>Noise:  Clearly, advantage rear, except perhaps for those sitting in the back.
>Advantage: Rear Mount.

I don't think it's quite that clear-cut.  Vibration from rear-mounted
engines is transmitted directly into the rear of the cabin, rather than
into the wing and wing root, and the wing itself protects the cabin from
exhaust noise (at least on most designs -- the 737-100/200 have exhausts
behind the wing, but modern designs are well underneath).  Intake noise
is also closer to the cabin in tail-mounted designs.

The wing probably directs more noise groundward from the exhaust.

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

But at the expense of putting the engines in a messy place.  Wing
mounted designs put the intakes in more or less clear air, whereas tail
mounted have aerodynamic effects from the wing and fuselage to contend
with.  I believe this is why you don't see high bypass engines mounted
on the sides of the tail on any aircraft -- the big fans tend to be more
touchy about screwball intake flow than their lower bypass brethren.
(This doesn't seem to have stopped the DC-10 and L-1011 from having top
mounted intakes.)

-- don