Oshkosh and the Body Hybrid-Electric

Cessna’s 337 Skymaster was a unique, iconic, and controversial aircraft. “Mixmaster” pilots used to call it—sometimes affectionately, sometimes not—on account of its unconventional, centerline-thrust, engine configuration which featured a standard, nose-mounted, puller [tractor] propeller, and a not so standard, tail-mounted, pusher propeller.

Cessna produced the last Skymaster in 1982, and with the departure of the last 337 from Cessna Aircraft Field, the Skymaster’s flight into the annals of obscure aviation oddities seemed assured.

Comes now Ampaire, the Hawthorne, California aerospace concern, and its Electric EEL technology demonstrator—a Cessna 337 Skymaster retrofitted with a forward electric-motor. Incidentally, EEL is a mirror-image homage to the aircraft’s original 337 designation. On 21 July 2022, Ampaire test pilot Elliot Seguin departed California’s Mojave Airport in the Electric EEL and flew 1,135-miles to Hays, Kansas, and in so doing accomplished the longest-ever flight of a hybrid-electric aircraft. The following day, Mister Seguin urged the Electric EEL another 660-miles to Wittman Regional Airport in Oshkosh, Wisconsin, where the aircraft currently occupies a place of honor at EAA’s AirVenture event—the beating heart of experimental aviation.

Along the 1.880-mile, record-setting flight the EEL realized a fuel-savings of up to forty-percent over a standard Skymaster—a small fortune at 2022 fuel prices.

The EEL’s parallel hybrid thrust scheme comprises a single, reciprocating engine and an independent electric drivetrain. The forward Continental IO-360 piston engine with which Cessna endowed the original Skymaster is replaced with an electric motor powered by a battery in a parallel hybrid configuration. The 337’s centerline thrust eliminates the engine-out yaw characteristic of conventional twin-engine airplanes—a useful attribute in an airplane designed to test engine technology.

Ampaire senior vice president Dr. Susan Ying said of the record flight: “By the time the EEL returns to California it will have flown more miles than any hybrid-electric aircraft, over 15,000, including airline demonstration flights in Hawaii and the UK. It is flying with great reliability and demonstrating the workhorse nature of hybrid-electric aircraft.”

Dr. Ying adds: “We are taking the technology and expertise developed with the electrical EEL and applying it to our first commercial product, the hybrid-electric nine-seat Eco Caravan regional aircraft, which will make its first flight later this year. That aircraft will demonstrate fuel savings up to seventy-percent and emissions reductions up to 100 percent when using sustainable aviation fuel.”

Dr. Ying’s assertions are borne out by promising initial sales of the Eco Caravan—a Cessna 208B Grand Caravan retrofitted with a hybrid-electric drivetrain. What’s more, Ampaire is diligently working toward attaining FAA supplemental type-certification of its Eco Otter, a hybrid-electric iteration of de Havilland’s famously robust DHC-6 Twin Otter—by 2024

FMI: www.ampaire.com