Fareastdriver (#10729),
"...Two reasons for spinners come to my mind. One is to streamline the nacelle and the second is to stop the engine being overcooled. My little experience on American radials; CH57 Mojave; which had little aerodynamic cooling, showed that on the whole the gills were only fully opened in the hover ..."
I can see the sense of that in a helicopter. And even in fixed wing, in India, with twin-row US radials, we always took-off with cowl gills full open. As for spinners, I always thought that they were only cosmetic. The old "Battle", which was really a handsome aircraft, would have looked more complete with a spinner. But I can't see how a spinner would increase the cooling much.
But having the two-postion (Valiant), or constant-speed mechanism (Harvard) in full view from the side after start-up, enabled many a stude to understand how a "Wasp's" worked better than any lecture. (What was it btw ?)
Our Hamilton Standard props on the VV had a simple "dome" front, much neater, and didn't need a Spinner.
Danny.