Hot or cold
Rotax engines ended the three-handed dance
These horizontally opposed, direct-drive behemoths need 1.5 to 2 cubic inches displacement per horsepower.
Rotax engines are much more modern, if the 1970s could be considered modern. That’s when the company came on the scene with its two-stroke ultralight and glider engines. Today it offers four-stroke varieties up to around 141 horsepower. The popular 912 ULS puts out 100 horsepower on only 82.6 cubic inches, and a sister turbocharged version puts out 141 horsepower on the same displacement.
The Rotax design is different from a Lycoming or Continental in a few fundamental ways. It’s both air- and liquid-cooled, meaning there’s at least one radiator. Thus, the concepts of overheating, shock cooling, and watching the cylinder head temperatures like a vulture are all gone, replaced by a car-like set-it-and-forget-it mentality. The cylinders are horizontally opposed and can be fed via a carburetor or fuel injection. But they fire at a much higher rpm than most pilots are accustomed to. As a result, there’s a reduction gearbox so the propeller spins more in the traditional range.
Most important, Rotax engines feature dual electronic ignition. Gone are the days of tractor magnetos, and all the associated cold starts and hot starts. Rotax engines fire whether hot or cold with the same procedures, which doesn’t include a three-handed dance.
