First introduced in Europe in 2013, the all aluminum single seat enclosed cabin Merlin LSA has sported a variety of engines, including a Rotax 582, a specially built four stroke V-twin and even an electric motor. In fact, the Merlin airframe has served as a test bed for all kinds of propulsion and aerodynamic innovations. At AirVenture 2023, Aeromarine chief designer Chip Erwin even showcased a Merlin model with twin propellors imbedded in the wings. Erwin promises an even bigger surprise at Oshkosh later this month: a common-sense hybrid propulsion system for the Merlin.
Erwin, who has done work for the Air Force Research Lab in Dayton, Ohio, has developed a parallel hybrid drive system for light sport aircraft that utilizes an electric motor to add to thrust generated by a
piston engine during takeoff and climb, but shuts down during cruise. He points out that a major limitation of all electric aircraft is the need to lug around a heavy battery capable of providing thrust for a limited period of time. The advantage of a piston engine is that it can provide the reduced thrust necessary for cruise flight in a lightweight package, utilizing a relatively small amount of fuel.
A typical flight plan for the hybrid system would entail using the piston engine, supplemented by the parallel electric motor, to provide the combined thrust necessary for takeoff and climb. Once a cruise altitude is reached, the electric motor would be shut down and cruise would be accomplished on the piston engine alone. Erwin points out that the electric motor would be free wheeling during cruise flight (through the use of a sprag clutch) resulting in insignificant drag to the thrust produced by the piston engine.
This parallel thrust setup allows the use of a smaller, lighter and more fuel efficient piston engine, supplemented by a light weight electric motor. Since the electric motor is only used for takeoff and climb, it utilizes a fairly small battery, which is recharged by the gas motor during cruise. Formula One race cars have been utilizing this concept for the past several years, using a small but powerful electric motor to provide added torque for critical phases of each race such as the standing start and powering out of corners. The Formula One batteries for these cars are the size of a laptop battery, discharging their energy for relatively short bursts and being recharged on the straights.
The parallel hybrid system is designed to provide greater efficiencies for light sport aircraft, resulting in lighter weight and increased range. We should be able to see it all in person at Airventure, where Erwin promises an impressive display.
