Airbus Helicopters is preparing the ground for the future introduction of so-called “eco-mode” operations on twin-engined rotorcraft, a series of patent filings reveal.
Covering critical aspects of such flights – particularly safety – the patent applications appear to be an important step towards any roll-out of the concept.
Eco-mode, which sees one of a pair of engines shut down during cruise as a fuel-saving measure, will make its debut on the Racer high-speed demonstrator next year.
Nonetheless, the airframer and propulsion supplier Safran Helicopter Engines both view the technology – a form of hybridisation – as a relatively straightforward means of improving the fuel-economy and environmental performance of conventional twin-engined helicopters.
Airbus Helicopters says the idled engine can be started within 5-7s in an emergency thanks to a high-power battery, but its patent filings show an extra layer of protection is contemplated.
Although monitoring of the operational engine will detect any sign of failure, the manufacturer sees a risk that if the idled powerplant cannot be restarted quickly enough, the helicopter could end up in a “critical and non-recoverable low-rotor-speed state”.
Additionally, it warns, “the situation becomes even more severe” if the autopilot is engaged, the rotor interia is low and the pilot “less attentive”, noting that the in-built delay in switching between automated and manual control inputs presents a further risk.
Developed by the airframer’s German unit, the solution would “enable a safe and reliable continuation of a given flight mission at a pre-failure cruising altitude” or along a specific route, it says.
Should a failure of the operational engine be detected, the system would automatically begin the autorotation of the main rotor by “adjusting at least the main rotor actuators”.
If performed autonomously, this would ensure “accurate power loss and engine-failure handling” is “guaranteed, thus increasing flight safety and reducing crew workload significantly.”
Additionally, the automated entry into and stabilisation of the autorotation would prevent “any critical and non-recoverable low main rotor speeds and excessive sink rates” from developing, it says.
The patent also foresees the system automatically optimising the speed of the helicopter and the main rotor to reduce the power demand as the idled engine restarts and to minimise height loss.
“Finally, automated recovery of an initial pre-failure cruise altitude and/or flight route ensures safe continuation of the flight in an One Engine Inoperative (OEI) condition with an optimised speed.”
Airbus Helicopters says the automated protections will be part of a dedicated single-engine operation (SEO) mode autopilot function.
If the pilot is manually flying the aircraft, “the SEO mode autopilot function does not engage automatically” in normal circumstances, it says.
But “if the pilot response to the engine failure is insufficient” and certain key parameters are approaching “critical” levels, the “SEO mode autopilot function preferably engages automatically”.
Meanwhile, the airframer’s French unit has filed a pair of patent applications detailing additional functionality around eco-mode operations.
One prevents a pilot from entering or exiting SEO unless all the required conditions are met, while another implements an optimised route-selection function – picking the most economical altitude and flightpath depending on the operating mode selected.
