The horizontally opposed piston engine integrates
well with modern single-engine aircraft. There is little
to no additional drag penalty because the engine fits
within the width of the side-by-side seating arrangement
of virtually all post-World War II light aircraft designs.
It allows a high thrust line with good over-the-nose
visibility. Compared with a radial engine with the same
number of cylinders, an opposed engine would be
heavier; however, because of balance considerations,
for the same smoothness of operation, a radial engine
requires more smaller cylinders than an opposed engine
does. Therefore, in practice, opposed engines in this
size class are short and compact with little to no weight
penalty in comparison to radial engines. Finally, since a
small number of cylinders are lined up on each side of
the engine, air cooling is not a major problem. For these
reasons, the air-cooled, horizontally opposed engine has
virtually displaced all other piston engine configurations
in the light aircraft arena.
