A twin-engine Cessna 337 Skymaster with its engines arranged in a unique push-pull configuration has been retrofitted by Ampaire as its Electric EEL, with an electric motor replacing the forward piston engine. (Photo: Ampaire)
Electric propulsion systems developer Ampaire last week achieved its longest flight with the Cessna 337 Skymaster that it has converted to hybrid-electric power. On October 8, the six-seat, Electric EEL aircraft took off from the Los Angeles-area Camarillo Airport and made a 341-mile flight to Hayward Executive Airport in the San Francisco area in 2 hours and 35 minutes. Ampaire, claims this was the longest flight to date for what it defines as a “commercially relevant” aircraft using electric propulsion.
The Electric EEL is powered by a 310-hp Continental IO-550 engine installed in the tail of the aircraft and a 130-kW electric motor in the nose. According to Ampaire, the piston engine powered all taxiing, and then a combination of it and the electric motor were used for takeoff and climb. The cruise phase was mainly powered by the piston, while the motor was put in low power mode, before being switched to idle during descent and landing.
The company did not answer questions from AIN about how much fuel was consumed during the flight or provide any details about payload weight. The batteries for the electric motor are attached to the underside of the fuselage in a composite nacelle.
The flight was piloted by test pilot Justin Gillen and flight-test engineer Russell Newman, the flight averaged 135 mph as it traversed California’s Central Valley at an altitude of 8,500 feet. “The mission was a quite normal cross-country flight that we could imagine electrified aircraft making every day just a few years from now,” said Gillen. Normally the Cessna 337 can cruise at up to 190 mph and Ampaire said its pilots had opted to make “conservative” use of the electric motor “to optimize for a specific battery state of charge upon landing.”
The demonstration took place little more than a year after the first EEL made its first flight, and just four weeks after this aircraft, the second in the program, took to the skies. Known as the Hawai’i Bird, this airframe will now be partially disassembled at Hayward and shipped to Hawaii to take part later this year in a series of proving flights with Mokulele Airlines on its short-haul routes. That test program will be partially funded by Elemental Accelerator, a green-technology financial support platform.
“The trial flights with Mokulele will not only demonstrate the capabilities of the EEL but will help to define the infrastructure required for wide adoption of electric aviation by airlines and airports,” said Ampaire general manager Doug Shane, adding “the ability to put innovative electric technologies into the air rapidly to assess and refine them is central to Ampaire’s strategy to introduce low-emissions aircraft for regional airlines and charter operators within just a few years.”
According to the company, the EEL can cut fuel use and emissions in half on shorter routes where its electric powerplant can run at higher power settings and generate similar reductions of up to 30 percent on longer regional routes such as Camarillo to Hayward.
The Electric EEL program is viewed as just a stepping stone toward a larger goal, said company CEO Kevin Noertker. “Our next step will likely be a 19-seat hybrid-electric retrofit program that will lower emissions and operating costs, benefitting regional carriers, their passengers, and their communities,” he explained. “Ampaire, with funding from NASA and others, is in the midst of design studies for such an aircraft based on the de Havilland [now Viking Air] Twin Otter aircraft. That hybrid-electric aircraft will be called the Eco Otter SX.”