Today's conventional helicopters are powered by thermal engines that convert fossil fuels into energy. Long considered ideal for air travel because of their ability to generate large quantities of power with a limited mass of fuel, fossil fuels are likewise notorious for producing emissions such as nitrogen oxide and carbon dioxide (CO2).
The aviation industry contributes around 2,5 percent of global CO2 emissions. Important efforts have already been made to limit fuel consumption in aviation, but clearly much more needs to be done – and helicopters are at the forefront of this effort. Thanks to their small size and low power needs compared with most fixed wing aircraft, helicopters are the ideal testbed for new technologies, and lessons learned can be extended to larger applications.
The solutions being tested today are many: from decreasing the emissions output of conventional thermal engines, to going for the holy grail of fully electric flight – and everything in between.
Airbus Helicopters’ long-term innovation roadmap involves exploring all options, brick by brick, and making incremental improvements towards an emissions-lighter future. Here’s a look at what’s happening now.
Becoming less conventional
“Our engineers have come a long way in making traditional technologies greener, working on a wide range of research projects that in some cases are already reducing emissions,” says Tomasz Krysinski, head of research and innovation at Airbus Helicopters. “The recently certified H160 is the cleaner and quieter helicopter in its class, paving the way for a reduced environmental footprint in helicopter operations”.
Integrating Airbus Helicopters’ latest technological innovations, the next generation medium twin H160 benefits from a 15% reduction in fuel burn, thanks to its Arrano engine by Safran Helicopter Engines, and a 50% reduction in exterior sound levels, thanks to its Blue Edge main rotor blades.
Krysinski cites other projects underway that aim to reduce fuel consumption through a combination of improved aerodynamics, weight reduction, and more efficient thermodynamic cycles, in hopes of one day integrating such improvements on other Airbus helicopter products.
According to Krysinski, the ultimate step is to go to another sort of energy, which could be hydrogen or fuel cells. This technology has made significant advances, particularly in the fixed wing segment, but the power requirements for a helicopter remain a challenge. That being said, Krysinski expects hydrogen technologies could be mature enough to fly on a helicopter demonstrator as early as 2029.
There is also the electrically-powered “eco-mode”, which enables the pausing and restarting of a gas turbine in flight on twin-engine helicopters. Developed with Safran Helicopter Engines, and first tested on the Bluecopter demonstrator (an H135 testbed), this technology will generate fuel savings while increasing the range of helicopters. The “eco-mode” will be tested next on the Racer high-speed demonstrator currently being developed in the frame of the Clean Sky 2 European research programme, and which aims to reach a 220kt cruise speed while cutting CO2, NOx and noise emissions by 20%, when compared to current helicopters.
A fully electric future
At the opposite end of the spectrum is the fully electrically powered helicopter. Dogging this ambition is the challenge of how to store electric energy efficiently, from the perspective of both mass and volume, using today’s technology. (In the simplest terms, a large quantity of batteries is required to equal the performance of fuel. This means that the battery in an electric car - let alone a helicopter - can represent approximately a third of its empty weight)
But Airbus Helicopters is optimistic, especially as electric energy storage technology is improving.
“Despite the engineering challenges in front of us, we see real possibilities in electrification,” says Luca Cossetti, Innovative Power Solutions at Airbus Helicopters. “Once the technologies are ready (e.g., batteries), the challenge will be to integrate them into an overall aircraft design and to devise or adapt systems which allow safe, efficient, emission-free flight.”
The company has already made concrete progress in building a fully electrically powered demonstrator, known as CityAirbus. The eight-rotor aircraft plays a key role in the path towards zero-emission helicopters.
With its first untethered flight in December 2019, CityAirbus is already enabling the development of key technological bricks for autonomy and electrification that will contribute to the development of urban air mobility and traditional helicopters alike.
The middle ground: hybridisation
Another option is to combine the best of both worlds. This is known as hybrid-electric propulsion, which marries a conventional thermal engine with an electric-propulsion system.
“Hybridisation enables us to optimise,” says Cossetti, whose team is developing a hybrid-propulsion solution for air vehicles. “You could use the thermal engine in certain phases of flight, thereby optimising its efficiency and consumption for that specific situation, and compensate with electrical power when the power demand is higher, such as during take-off and landing for a rotorcraft.”
Hybridisation could also lead to gains in flight safety. As early as 2011, Airbus Helicopters successfully flight-tested a single-engine helicopter with an electric motor connected to the main gearbox. The research intention was to see if, in the event of an engine failure, the back-up electric motor could maintain the rotor revolutions for an additional 30 seconds, giving the the pilot more time to react and perform an autorotation manoeuvre to the ground.
Since that first foray, battery technology has advanced significantly, with “one kilogram of batteries now providing twice as much energy as before,” according to Krysinski.
Ten years later, the ambition of the project is still very much alive. Airbus Helicopters is now modifying a single-engine H130 testbed helicopter with a 120-kW electric motor connected to the main gearbox, which will provide an emergency electric backup system (EBS) in the event of an engine failure.
“We’re now closer than ever to getting workable hybrid technology which has similarities to the way hybrid cars work,” Cossetti adds. Rotorcraft approaches would be similar to automotive in the way that systems manage the timing and blending of thermal and electrical power generation. “We’re planning to optimise the use of thermal and electric power to improve the overall safety, efficiency and decrease environmental impact (consumption and noise).”