Hybrid cars have almost as much potential in the air as they do on the ground. Ampaire claims that the first-generation hybrid system used in its ElectricEel demonstrator can reduce fuel consumption by 50% to 70% and has just set a world record for endurance in the air.
This isn't as intuitive as in a car, where a hybrid system's ability to harvest braking energy during traffic stops/starts can have a huge impact on overall fuel consumption. When an electric aircraft is cruising, the engine will run at a constant speed.
But Ampaire said that with a hybrid system, a smaller, more efficient and less powerful internal combustion engine can be used, and the electric booster only needs to be turned on during takeoff, landing or rapid acceleration. If the electric and combustion engine powertrains have separate propellers, an airborne version of regenerative braking can also be run to recover some energy during deceleration.
This is the case with the Electric Eel demonstrator, which uses a Cessna 337 Skymaster twin-tail donor aircraft that can use either pushrod propellers or traditional nose propellers. The two power systems are completely independent and run in parallel.
Ampaire said that in the next generation of ElectricEel, it plans to use a parallel series layout, in which a combined hybrid engine system will power the rear propeller, while also powering the electric motor of the nose propeller. This not only allows for the regenerative air braking mentioned above, but also allows the gasoline engine to charge the battery during flight. Current Eel aircraft need to be recharged in a hangar between flights, but next-generation aircraft will have greater flexibility and can run on fuel alone where charging facilities are not available.
The aircraft currently has some impressive achievements in its demonstration phase, burning significantly less fuel than a standard Cessna aircraft and requiring an estimated 25%-50% less maintenance. Now it has set what the company believes is an endurance record for a hybrid aircraft, with a flight that lasted "a full 12 hours," with more than two hours of spare fuel and batteries unused.
On this flight, the Electric Eel traveled 1,375 miles (2,213 kilometers), a simple circle over Camarillo Airport in California, and may not be the most exciting mission in the world. But both range and endurance greatly exceed the 5 hours and 745 miles (1,200 kilometers) listed on the Cessna Skymaster standard push/pull aircraft specification sheet.
Range and endurance remain huge challenges for all-electric aircraft - so hybrid propulsion may serve as a transitional measure to significantly reduce fuel consumption and emissions as the global industry moves towards decarbonization.
Please watch the "Electric Eel" fly over the beautiful coast of Hawaii: