"Bertie the Bunyip" wrote in message
...
"Rob Turk"
sednews:xmXie.4098$184.3491@amstwist00:

"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.

A fairly old idea, but it was quite successful for the Germans in WW2, the
engine giving a good SFC and allowing long range maritime patrols.
I've seen a sectioned example of this engine up close and it's fairly
complicated, not to mention absolutely huge!
http://www.billzilla.org/ideas4.htm
But it goes back even further than that, at least to 1898 when the Arrol
Johnston company made that same design into this contraption.
http://www.britishmm.co.uk/history.asp?id=65

Opposed piston (not opposed cylinder) engines of the diesel persuasion are
very close to an ideal concept. Junkers engine division JUMO used the
concept in their pre WWII 200 series. Fairbanks Morse in the US used the
concept for diesel submarines and later diesel locomotives. The Russians
used them in their tanks and the British developed the incredible three
crankshaft, 18 cylinder, 36 piston Deltec. Diesel Air Ltd. has updated the
concept in their very cool light aircraft engine.

These are all two-stroke direct injection diesels with intake and exhaust
ports at the ends of the pistons stroke. One piston uncovers the intake
ports and the opposing piston uncovers the exhaust ports so there is a
'uni-flow' scavenging effect. The cranks for the opposing pistons are out
of phase by about 20 degrees so the exhaust port opens first but closes
before the intake port does. This allows true supercharging of the
cylinder. There are neither cylinder heads nor valves to leak or cool. The
whole cylinder is bathed in coolant.

I wish all the diesel aircraft engine developers the best of luck. Their
day has come.

Bill Daniels