$24,900 Diesel Announced by Superior, Legend Cub

Bosch fuel injection is used on the new Superior Gemini diesel. What look like cam covers are actually crankshaft covers in this opposed-cylinder engine.
Bosch fuel injection is used on the new Superior Gemini diesel. What look like cam covers are actually crankshaft covers in this opposed-cylinder engine.

General aviation engines too stagnant for you? Superior Air Parts has an affordable cure coming in their just announced Gemini diesel at $24,900. First application is on the Super Legend Cub as we learned in a joint announcement from Superior and Legend Cub this morning at AirVenture.

No clone this, the new Gemini - it is a water cooled, two-crankshaft, opposed piston 3-cylinder 2-stroke. That means three cylinder bores, each with two pistons reciprocating towards each other. The dual crankshafts live at the outer ends of the engine where the valves and rocker arms normally found in typical horizontally-opposed aircraft engines.

As a 2-stroke diesel the Gemini uses a small rootes-type blower to scavenge (not supercharge) the cylinders. The compact alternator and large muffler are also visible.
As a 2-stroke diesel the Gemini uses a small rootes-type blower to scavenge (not supercharge) the cylinders. The compact alternator and large muffler are also visible.

The two crankshafts are mated through a geartrain terminating at the prop shaft in the engine’s center. This allows thrust-making 4000 engine and 2500 propeller rpm. With the engine mounted in a flat configuration Superior says the packaging and weight are favorable to the timeless Continental O-200 so the Gemini should easily package under numerous existing cowlings.[sc:ad180]

Superior has worked with Weslake, an English consultancy, on the Gemini. Advantages to the design are remarkably tight packaging, a very rigid block, short, lightweight and stiff crankshafts and reported notably smooth running. Gear noise is said to be minimal, with the engine essentially silent behind the usual propeller noise.

Looking rather involved is a Gemini cylinder. Intake and exhaust ports are shared through the cylinder walls by two opposing pistons. Hardly a new concept, Jumo used this exact layout very successfully during WWII.
Looking rather involved is a Gemini cylinder. Intake and exhaust ports are shared through the cylinder walls by two opposing pistons. Hardly a new concept, Jumo used this exact layout very successfully during WWII.

Superior is debuting the Gemini in naturally-aspirated, 100 hp form via the Super Legend Cub with a series of follow-on turbocharged engines following. First of these is rated at 125 hp and future engines will add cylinders (remember, two pistons per cylinder in 3-, 4- and 5-cylinder form) to reach 550 hp.

Superior says the engine will be built in their Coppell, Texas facility with parts sourced from best-case suppliers (German forgings, U.S. machining).

There is still a long way to go before the Gemini is a proven quantity but the program is well underway with dyno mules already running. Expect the bare Super Legend Cub airframe wearing the mock-up Gemini engine at Air Venture to be flying at Sun-and-Fun next spring.

Check out this video by Paul Berorelli from our sister publication AVweb:

httpv://www.youtube.com/watch?v=lZQVnKurel8

Tom Wilson

Tom Wilson is a professional magazine writer and nurtures an ongoing affair with all things internal combustion. His writing is most often found in automotive magazines, but aviation is his first love. Working as a line boy, he learned to fly while in high school, but still hasn’t mastered the art of keeping a paper chart in an open cockpit.

One Reply to “$24,900 Diesel Announced by Superior, Legend Cub”

  1. Looking forward to this technology maturing. Eagerly watching Superior's development of this engine.

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