Ampaire last week flew the second technology demonstrator of its hybrid-electric Cessna 337 Electric EEL aircraft. In October, the California-based company intends to ship the aircraft to Hawaii, where it will operate on some trial services with local carrier Mokulele Airlines.
In 2019, Ampaire flew the first demonstrator version of its converted Cessna 337 Skymaster twin. The company says that it has incorporated a number of improvements to the second demonstrator based on lessons learned from the initial test flights.
The Electric EEL is powered by a 310-hp Continental IO-550 engine installed in the tail of the aircraft and an electric propulsion unit (EPU) in the nose. For this converted Cessna 337 platform, the 200-kW electric motor has been limited to a power output of 120 kW, but Ampaire says the propulsion technology is scalable to power larger aircraft.
In the second demonstrator, the aircraft’s battery pack has been moved from inside the cabin to the underside of the fuselage and enclosed in a composite shell. This was done to provide space in the cabin for flight test engineers, equipment, and observers.
According to Ampaire, the Electric EEL will deliver a reduction in direct operating costs and carbon dioxide emissions of between 40 to 50 percent compared to existing aircraft. The state of Hawaii has set a target of using renewable energy for 100 percent of its energy needs by 2045. Ampaire has named the second demonstrator aircraft the Hawaii Bird.
Ampaire says that the latest technology demonstrator features an EPU that is lighter and has better energy efficiency with improved thermal margins due to the introduction of a liquid cooling system that has replaced the original air cooling system. The new version of the Electric EEL also features new cockpit instrumentation and new power controls for monitoring the output from both the engine and the electric motor.
Carrying five passengers, the Electric EEL is expected to be able to fly at around 138 mph for up to 1 hour and 15 minutes (plus a 30-minute reserve allowance) between recharges. On this basis, Ampaire says it will be able to operate most of Mokulele’s routes round-trip on a single charge.
The planned flight trials in Hawaii are to be conducted under an experimental aircraft certificate for "market survey" purposes. The trial operations are being partly funded by climate technology accelerator company Elemental Excelerator, which is based in Hawaii. No fare-paying passengers can be onboard, but there can be two observers on board in addition to the pilot.
“Electric aviation is the future for the commuter airline industry, and through our partnership with Ampaire, we intend to be at the forefront of that innovation,” commented Stan Little, chairman and CEO of Mokulele parent company Southern Airways. “These test flights hold the promise of expanding the inter-island service by lowering costs while reducing our environmental footprint.”
In a 35-minute first flight on September 10, test pilot Justin Gillen took the new technology demonstrator to 3,000 feet, where he made series of handling and power checks on both the engine and the electric motor. The Electric EEL will make more flight tests before relocating to Hawaii next month.
Mokulele Airlines operates services to nine destinations in the Hawaiian islands, as well as two in California.
Ampaire is not giving a firm target date for achieving type certification of the Electric EEL. The company indicated that it may chose to proceed with certification for another electric aircraft before bringing the EEL to market.
For instance, Ampaire says it is making progress with a project to retrofit a Twin Otter aircraft with an electric propulsion system. It now calls this program the Eco Otter Sx and says that it expects to have further news on this later in 2020.