I've not really paid that much attention to engines until building the engine for my WNW Pup - 72nd scale engines being too small to really see the detail. I noticed that there's only one pushrod (and, I assume one valve) per cylinder. I presume this is the 'monosoupape' engine?
I've looked these engines up in Janes Fighting Aricraft of World War One but, apart from photos and specs. it doesn't say a great deal.
What I'm wondering is were they two-strokes, or were they four-strokes and is there some other internal method of opening whichever valve isn't served by the pushrod?