All eyes on next-generation engines for cleaner, faster flight
The pressure is on engine-makers to enable the giant leap that could bring us not just a new generation of aircraft, but a whole new category.
There has long been a debate in aviation as to what comes first – the engine or the airframe? But this chicken-and-egg situation now has environmental necessity added to the mix, clearing the way for a new generation of aviation powerplant.
There is a strong wind of change blowing through the aerospace industry as environmental pressures force the industry to consider carefully the future of commercial aviation.
Criticism of emissions, along with a growing demand for flight, has led to a rapid focus on how the industry can not only meet its environmental targets but also meet the commercial demand for higher, faster and longer.
While the constant tweaking in airframe design, air traffic management and alternative fuels has led to significant enough changes to look good on paper, the pressure is on the engine-makers to get back to the drawing board and make the giant leap that could bring us not just a new generation of aircraft, but actually a whole new category of aircraft.
The partial electrification of aircraft has already made an impact. Aircraft programmes such as the Airbus A350 and Boeing 787 have increasingly used batteries to power on-board systems, but future progression to electric propulsion is increasingly being proposed.
While this is likely to first involve a hybrid option with the energy still coming from hydrocarbon fuel, the hope is it will eventually progress to a fully electric system with batteries providing sufficient energy to drive commercially viable passenger aircraft.
Urban air mobility
Sectors like the new urban air mobility depend on the development – and certification – of electric and hybrid-electric propulsion to be viable.
It wasn’t that many years ago that this was the stuff of science fiction. But today the aerospace power companies are putting their money behind the ideas to make ‘pipe dreams’ reality.
This summer Rolls-Royce bought the electric and hybrid-electric aerospace propulsion activities of Siemens in order to accelerate the delivery of its electrification strategy and boost the British company’s ambition to play a major role in the ‘third era’ of aviation.
Siemens “eAircraft business” had already worked with Rolls-Royce on the E-Fan X demonstrator project which, when flying, will demonstrate hybrid-electric propulsion at the scale required to power regional aircraft.
Rob Watson, Director – Rolls-Royce Electrical, said: “Electrification is set to have as dramatic an impact on aviation as the replacement of piston engines by gas turbines. We are at the dawn of the third era of aviation, which will bring a new class of quieter and cleaner air transport to the skies.”
“We have already made significant strides in realising our strategy of ‘championing electrification’ and this move will accelerate our ambitions in aerospace by adding vital skills and technology to our portfolio. It brings us increased scale and additional expertise as we develop a product range of hybrid power and propulsion systems.”
In an interview with FINN at the Paris Air Show in June, Paul Stein, Rolls-Royce’s chief technology officer, said electrification of flight is just one part of Rolls-Royce’s commitment to making aviation more sustainable.
“We are continuing to increase the fuel efficiency of our gas turbines, encouraging the development of environmentally friendly and sustainable aviation fuels, and pursuing the electrification of aviation. We believe that pure electric or all-electric, propulsion will power smaller aircraft in the foreseeable future, while larger aircraft will rely upon hybrid electric solutions that combine electrification with evolutions of the gas turbine.”
At Farnborough Air Show the previous year the company showcased a proposed hybrid-electric vertical take-off and landing (EVTOL) vehicle and is targeting test flights in 2021.
Airbus has had teams working on electric-powered flight demonstrators and eVTOL demonstrators, including Vahana, CityAirbus and E-Fan. According to Glenn Llewellyn, general manager, electrification at Airbus, the complex hybrid-electric aircraft demonstrator E-Fan X is the next step in Airbus’ electrification journey.
“When the demonstrator embarks on its first flight in 2021, the E-Fan X will be a giant leap towards making zero-emission flight a reality by the mid-2030s,” he said. The goal of this programme is to eventually produce single-aisle aircraft capable of carrying 100-plus passengers.
“It’s not a matter of if this will happen, it is when,” he said.
But it is not just the aerospace mega-companies that looking at differing power systems, in the USA a company called ZeroAvia has announced its advancements in developing a zero-emission, hydrogen-fuelled electric powertrain.
It aims to deliver the same performance as a conventional aircraft engine, and much lower operating costs and said it will start supplying its platform to commercial operators and aircraft manufacturers in 2022, initially targeting up to 500-mile regional flights in 10 to 20-seat fixed-wing aircraft.
Val Miftakhov, ZeroAvia founder and CEO said: “Using hydrogen produced from local renewable energy is the most practical way to enable zero-emission aircraft of commercially meaningful size on traditional 300 to 500-mile regional missions. It will also be more economical than conventional turbine engines, or even the battery-based systems, on the total cost basis. We calculate the total costs of operating a ZeroAvia aircraft to be close to half of what it costs to fly a conventional turbine aircraft, due to lower fuel input costs, higher powertrain efficiency, and reduced maintenance costs.”
Earlier this year the FAA issued an experimental R&D Certificate to ZeroAvia’s platform on a Piper aircraft. At a two-tonne take-off weight and six seats in a business-class arrangement, it is said to currently be the world’s largest zero-emission aircraft flying without any fossil fuel
It is initially targeting 500-mile flights to serve the short-haul and commuter air travel markets, which make up nearly half the commercial flights worldwide and could achieve similar per-seat economics as today’s large regional jets, allowing economical use of smaller local airports for point-to-point travel with virtually no security lines or delays, Miftakhov said.
Also in the US, a company called Ampaire has developed an aircraft, based on the six-seat Cessna 337 Skymaster, retrofitted with Ampaire's proprietary electric propulsion system and powered by a lightweight battery system.
The battery-powered electric motor replaces a combustion engine of the aircraft's original two-engine configuration, and the resulting system is a ‘parallel hybrid’, meaning the internal combustion engine and electric motor work in concert to optimise power output as the plane carried out its first test flights.
But while work is carried out on the new electric aircraft proposals, developing greater efficiencies on existing programmes to meet new challenges are underway. Both Paris and Farnborough airshows saw growing excitement in the world of supersonic civil aircraft. But it is a simple fact that supersonic passenger aircraft won’t be going anywhere without supersonic engines.
Another of the aerospace giants, GE, announced last year it is developing an engine called Affinity for the Boeing-backed Aerion supersonic business jet. The Affinity engine is a twin-shaft, twin-fan turbofan which will be used on the 12-passenger AS2 business jet. Aerion plans to be flight testing a prototype of the AS2, which is designed to fly at a cruising speed of Mach 1.4, in 2023.
Aerion believes its supersonic technology will be rolled out across the wider civil aviation market over time. “Our mission is to enhance global mobility with supersonic speed, starting with business aviation, and following with successively faster and larger designs for business and commercial aviation,” said Aerion CEO Tom Vice. “GE Aviation is making this new efficient, sustainable supersonic era possible through its pioneering work on the Affinity engine.”
Going even faster Reaction Engines say that interest in hypersonic air systems is growing worldwide.
The UK firm has been developing its hypersonic Sabre engine for a reusable spacecraft but now Rolls-Royce and BAE Systems are working with Reaction to conduct a two-year study into hypersonic propulsion systems for the UK Ministry of Defence, with the technology demonstration linked to its Project Tempest future combat air system activity.
“SABRE’s unique feature is a pre-cooler which reduces the temperature of the incoming compressed air,” explained Forces.com. “This means the engine does not need to cope with extreme temperatures which require special materials. At high altitudes, it is a rocket, but, at lower altitudes, it works like a jet engine - sucking in and compressing air.”
This could see the eventual development of a fifth-generation fighter with a Mach 5 capability.
Once the powerplant works than the door is open to a new generation of aircraft. Until then, congratulations to CFM who have clocked up a billion hours on the CFM 56 engine.
Describing it as a “mindblowing milestone”, CEO Gaël Méheust told FINN: “We just passed one billion flight hours with the CFM56 engine. It’s sometimes hard to understand what one billion flight hours is, but if you convert it into years it represents 15,000 years, so it is a huge milestone we are celebrating. We are thanking our customers because they are the ones who flew our engines carrying 35 billion people - which is five times the population of earth.”
And that is quite some feat.