Modelling-ABC by Wilfried Eck
Combustion engines with cylinders arranged to form a star. Some had more than one row.
In model kits cylinders lack detail. One has to live with it for it's simply impossible to reproduce the fine cooling ribs accurately. As most WW I rotary engines were of cylindrical shape a more convincing representation can be achieved by sanding the cooling ribs off and winding very fine copper wire around (secured with CA glue). Another point are electrical (ignition-) cords leading from the crankcase to the individual cylinders. Here also fine wire painted the actual colour (mostly black or red brown) gives better results.
Cylinders in shiny chrome silver may be appropriate for a Harley or Kawasaki motorbike, but not for WW II engines. Actually they were of a light middle gray colour (with a slight brown tint). WW I engines were of very dark colour, nearly black, but with shiny ribs. Crank cases (gear boxes) also appeared in variations of gray, only some pre WW II engines showing dull silver. So do not paint all engines alike.
Try to have a look at the real thing by consulting photos.
Common name for cast plastic parts of non polystyrene material. Sometimes indispensable and sometimes pure waste of money. In between come these parts which are useful, but could be made by the modeler himself, saving money for more important things.
The worst thing I saw were flaps for a P-51. Simple wedges with many small holes. Rivets the real one had indeed, but flush with the surface (so nearly invisible). Making a simple wedge could be made easily by any self respecting modeler.
Then there are "the one and only correct control surfaces for a ...", but the fabric covering sagging considerably. - Is to say one mistake was substituted by another (the required parts could be easily made, see page "fabric covering"). This list could be continued for some length.
So have a close look at the parts deemed necessary.
But it isn't all bad: The Czech firm CMR produces kits not available in polystyrene form in outstanding quality (see CMR webpage).