Maybe it’s all the rituals before you start one, and the smoky, off-beat rumble that follows. Possibly because it makes the aeroplane look so completely different, spelling “aviation” and “vintage” in letters writ large. No doubt about it, radial engines are compelling, but it’s still hard to say exactly why. During the early years of aviation, putting the cylinders in a ring offered plenty of advantages. It was a good way to increase the number within a depth – the crankcase need only be one cylinder deep. And more cylinders equalled increased power, although nine seems to be the limit – you can only divide 360 degrees so many times and still leave room to fit the barrels. Cooling was easy, the cylinders were all presented equally to the breeze, which is always a bonus when trying to extract more from them.
Radials are exclusive now because they’re extinct from the mainstream, and any practical advantages of the layout have been rendered irrelevant by more modern technology – well, post-WWII, at any rate. And the status quo wasn’t likely to change because, until recently, there weren’t any new radials. Only in the last decade-and-a-half have two new radial designs appeared, each in the 100-140hp division – the Rotec, developed by two Australian aeromodelling brothers, and the Verner, a Czech company which had previously made twin-cylinder engines for ultralights.
It’s likely that the business case was to supply the nostalgia market – install one on a Kitfox and it invests that thirties look without doing anything else – but we should perhaps investigate further.