Eurocopter might exhibit a hybrid helicopter, using both piston engines and electric motors like a hybrid car, by Heli-Expo 2020. Parent company EADS last year unveiled a helicopter concept that could burn 50 percent less fuel than its traditional equivalent. EADS Innovation Works is devising a way to combine diesel engines, generators, batteries and electric motors. According to Peter Jänker, research team leader for electric power and responsible for the project, those technologies might be mature in four to nine years.
The concept is part of EADS’s eCO2avia effort for greener aircraft. Jänker’s team, with input from Eurocopter, has worked on a three-metric ton- class (6,600 pounds) helicopter. “The hybrid concept would be suitable for small or large airframes,” he said. The hybrid helicopter researchers envision diesel engines that feed batteries through electric generators. In turn, electric motors drive the rotors.
EADS engineers currently working to improve physical models are “intensively running computer simulations,” Jänker said, adding that the results confirm the imminence of a serial hybrid helicopter.
Meanwhile, researchers are considering the relative merits of two versus three engines. While two engines can be enough for redundancy, there are additional benefits to having three he said. “On a twin, each engine must be able to provide maximum power. On a three-engine helicopter, two of engines may combine to deliver maximum power,” Jänker said. Thus, he said, designers can avoid oversizing the engine.
The key challenge the project poses is weight. “For the engines, we are aiming for a power density of two kilowatts per kilogram. Right now we are at 1.6,” Jänker said. Weight can be pared through elimination of the main gearbox, which will be unnecessary with a direct electric drive. In addition, the tail rotor’s electric drive allows designers to get rid of the tail rotor shaft. Battery technology is also expected to improve over the years and thus provide lighter electric power storage. Jänker hopes they will achieve “reduced fuel consumption at competitive weight.”
The helicopter’s fuel savings will come from several features. First, diesel engines could burn 30 percent less fuel than today’s turboshafts. Second, changes to aerodynamics and systems are expected to yield additional fuel savings. For example, replacing mechanical linkages with electric connections allows the main rotor and its electrical drive to be tilted forward during cruise flight avoiding the drag resulting from a nose-down attitude.
In addition, the tail rotor has no mechanical linkage to the main rotor and its power source and thus can be disengaged at higher speeds, when the rudder provides enough yaw control. The resulting decrease in fuel burn will also help reduce weight. “For a 600-plus-kilometer range [320 nm], we think a hybrid helicopter would consume 660 pounds of fuel, versus 1,230 pounds with today’s technology,” Jänker said.
The developers also hope the hybrid concept will reduce the helicopter’s noise footprint. Takeoffs and landings should be possible on electric power alone, reducing the perceived noise.
The next steps for the project are maturing electric motors and testing low-weight combustion engines, said Jänker. EADS is considering opposed-piston, opposed-cylinder engines. He did suggest that certification could be challenging because a large electric system would be replacing mechanical dynamics, however, Jänker insisted that redundancies, with three engines and two segregated batteries–which can enable the pilot to fly for a few minutes with all engines out–will help demonstrate a high level of safety.