Airbus Helicopters is flying an H120 powered by a diesel engine in place of its usual Turbomeca Arrius 2F turboshaft. The main benefit of the effort, part of Europe’s Clean Sky joint technology initiative, is expected to be significantly lower fuel consumption.
The 30-minute first flight on November 6 started with a hover and various low-speed maneuvers, before the helicopter transitioned to 60 knots. The engine is a 4.6-liter V8, featuring high-pressure (1,800 bar) common-rail direct injection and one turbocharger per cylinder bank. The cylinders have a 90-degree V. To reduce weight, designers looked to racecar design for inspiration, evident in the construction of the cylinder heads (aluminum) and connecting rods (titanium). The high-compression engine, as Airbus Helicopters prefers to call it, runs on kerosene/jet-A.
The Fadec’s performance has been particularly satisfactory, according to Tomasz Krysinski, Airbus Helicopters’ head of research and innovation. When the pilot increases the collective pitch, the Fadec injects more fuel into the combustor for more power. “As a result, the rotor’s speed changes by a maximum of three rpm, less than one percent of the nominal 406 rpm,” Krysinski told AIN.
Fuel burn has already proved to be much lower than with the Arrius 2F, 143 pph versus 220 pph in hover, a reduction of 35 percent. The companies involved in the project expect specific fuel consumption to be cut by half at economy cruise speed. “It is interesting for those cycles that include a long portion of relatively slow forward flight, like the police do,” Krysinski suggested.
Aerial work operations could also benefit from the piston engine. Unlike a turboshaft, a turbocharged piston engine retains its power at altitude and in hot temperature. In the mountains, this can be felt from around 3,500 feet, according to project manager Alexandre Gierczynski.
The engine produces 442 hp compared with the Arrius 2F’s 504 shp. However, “we use the same power for takeoff and the high-compression piston engine will be better in hot-and-high conditions,” Gierczynski said.
Other objectives include a 30-percent improvement in direct operating cost and a 2,000-hour TBO. Asked about emissions other than CO2, Krysinski said there is no standard for comparing turboshafts and piston engines. “Burning less fuel cuts pollutant emissions,” Krysinski noted. There is no plan on the diesel engine for a NOx-reduction device or a particulate filter, like those now mandatory on cars. One reason is weight: after further development, the flight-tested piston engine will tip the scales at 530 pounds–twice the weight of a turboshaft of equivalent power.
In addition to Airbus Helicopters, the project involves Teos Powertrain Engineering and Austro Engine. The former company, which has experience in car racing, designed and manufactured the prototype engine. The latter firm, a specialist in diesel engines for fixed-wing aircraft, has been in charge of the Fadec, the fuel system and obtaining a permit to fly.
Iron-bird tests started in February 2014 and the first ground runs took place one year later. The project dates back to 2009, when a first attempt failed for lack of funding. The companies aim to bring the engine to technology readiness level six, suitable for program launch.