There’s a general lack of information on state of the art ultralight aircraft engines. And there’s a minefield of mis-information on what’s been happening with small two stroke engines in ultralight aircraft. Many believe that two-strokes always seize and many also believe that the only engine to use is a Rotax.
A lot of that is chewed up baloney.
I can’t clarify every issue that’s out there — and I want to establish some positive vibes for a few of the engine manufacturers that still stand strong today — and I want to precisely distill what I’ve found with the Polini Thor 250 into this small collection of words and photos.
First, the background vibes on the current crop of engines. They are good engines. Each has positives and negatives.
— Hirth is making an exceptional 50HP engine — the F23. It is what I refer to as a stump-puller. It has incredible low end torque and is ideal for ultralights with a lot of drag and a need for acceleration and power. It yanks our Belite Sealite floatplane out of the water, even in hot and high and calm conditions. It makes runway length an optional requirement. It is reliable; it is available with electric start, fuel and oil injection, and it is a great value for the money. We’ve sold a fair number of them; but it is too much engine for many of our customers. And it uses a lot of gas (think a mininum of 3.5 GPH; 4 might be more realistic.)
— 1/2VWs continue to be the ‘go-to’ engine for pilots who want four strokes. They don’t have a lot of bottom end torque, but they do have a great reputation for easy to service, reliable operation with a low fuel burn. They are heavy, and ultralight customers fight the tradeoff between weight, legal FAR part 103 operations, and the classic boxer look (which these engines share the Hirth F23). They are a great choice if you are comfortable with the weight and can stand a little longer takeoff roll.See also: