"Matt Whiting" wrote in message
...
Sport Pilot wrote:
Most flat fours are not a boxer, and many twins are not. A boxer
engine will weigh and cost more. It's not really needed on a flat four
anyway, as on a non boxer the pistons on the front and rear pair will
be going opposite directions


True, but this doesn introduce a "rocking couple" vibration mode. There's
no free lunch WRT to engine design. :-)

Although some configurations come close (I-6, V-8, etc.)


Matt

A very interesting design is the Diesel Air engine (www.dair.co.uk). They
have two pistons per cylinder, moving in opposite directions. The ignition
happens in the center of the cylinder, which is also the center of the
engine. All forces that can cause vibration are supposed to cancel eachother
out, so there's a minimum of vibration. The engine has two cranks which are
mechanically coupled on the outside to bundle the power to the prop.
Pictures are on their site.

Rob