Airbus Helicopters is contemplating a future hybrid-electric powertrain that combines multiple functions within one system, a recent patent application discloses.
The airframer is already testing a variety of hybrid-electric solutions on its platforms – for example, to provide emergency back-up power for single-engined helicopters, or to enable fuel saving through so-called ‘eco-mode’ operation of twin-engined types.
However, the invention covered by the patent application, published on 24 January but filed last year, seeks to bring seven different functions together.
These comprise two different start-up processes – a regular engine start and a rapid reactivation of an engine idled in flight for eco-mode fuel saving; two emergency power modes in case of an engine failure or rotor speed drop; electrical generation to recharge the batteries; ventilation of the combustion chamber without the engine running; and a seventh, neutral mode.
One emergency power mode would be triggered if an engine fails and the turbine of the other is operating above a certain threshold.
The other boost function, meanwhile, would be activated in a similar engine-out situation, but one in which the turbine of the other engine is rotating below a set limit. In that case, the electrical power would be used to avoid any drop in rotor speed while the turbine spools up.
According to the patent filing, the system would consist of twin turbine engines, an electric motor – coupled to just one turbine – an electrical power source and control system.
That automated control system would enable the rapid switching of modes, going from restart, to neutral and then to power boost within the same flight phase, the application discloses.
Meanwhile, Airbus Helicopters’ German operation is considering the complexities of storing hydrogen or batteries aboard a rotorcraft.
It notes that while conventional fuel is stored in deformable bladders in the subfloor area of the cabin with no effect on energy-dissipating structural deformation in a crash, the rigid nature of batteries or hydrogen tanks would pose a safety hazard for occupants. Additional safety risks posed by the two alternative power sources are also a consideration, it notes.
Instead, Airbus Helicopters proposes “external energy source storage containers” located in a “lower area” of the rotorcraft, protected by a “crashable structure” formed by the fuselage and fuselage outer shell.
In addition to offering protection to occupants, such a design would pose fewer integration challenges, and also allow modular energy sources – batteries or hydrogen fuel containers – to be easily exchanged.
