Stealth Pilot
:

On Mon, 09 May 2005 01:54:33 -0500, Chris W wrote:

As most of you probably know the opposing cylinders on most engines are
slightly offset to allow for the piston connecting rods to attach to the
crank at different spots. I know of a few model airplane engines, where
instead of having the cylinders offset and having the connecting rods on
different sections of the crank, the connecting rods interlock and are
on the same section of the crank. I have been told that the engines
that are built like this run very smooth with almost no vibration.
Obviously they have an odd firing pattern, but I guess having the 2
cylinders perfect in line makes it so well balanced. These are all 2
cylinder engines, on a 4 cylinder engine with a spark every 180 degrees,
it seems like it would be even smoother. My question is why don't they
make any engines for real airplanes like that? The 180 - 540 degree
firing sequence probably isn't as big a deal for the high rpm of model
airplanes as it would be for the low rpm of typical GA planes, so it
would probably only be suitable for engines with a multiple of 4
cylinders. It seems like it would be easier to make too, simpler crank
shaft, perfectly symmetrical crank case. The only more complicated part
would be the connecting rods. Just curious.

what you are trying to describe is called DESAXING after a french guy
with the surname desaxe.
the change in alignment is really not that much.
it does work.

Umm, don't thnk that's what he's talking about. A few early radials used
desaxe cyliners, but that's a cylinder that's been offset form the
centerline of the crank to take advantage of a straighter conrod during the
power stroke. prolly worked OK, bu ti think they only use it in two strokes
nowadays if at all.
What th ewirter seems to be describing is an arrangement where two opposing
pistons share a crankpin. I've seen twins like this and they vibrate like
hell. A boxer (whihc most all flat opposed engines are) is a much smoother
arrangement.


Bertie