Today, a new class of high-performance materials known as bio-composites is emerging, offering even more possibilities for improved environmental performance in future aerospace applications. Unlike CFRP, bio-composites are derived from natural renewable resources. They are lightweight, flexible, cost effective, and recyclable, which makes them attractive to a wide range of industrial uses.
Bio-sourced composite materials are obtained from biomass, plants, crops, micro-organisms, minerals, and bio-wastes, which are chemically or mechanically converted into bio-composites. The resulting bio-fiber is combined with a resin matrix (in the same way as CFRP composites), which then can be used alone or in complement to standard materials like carbon and/or glass fiber. In future aerospace products, bio-composites could potentially be used in primary and secondary airframe structures.
THE NEXT GENERATION
Plane and rotorcraft builders are reimagining existing aircraft forms, creating new and innovative designs that take sustainability as their guide. European manufacturer Airbus is playing a leading role in some future rotorcraft concepts.
Airbus Helicopters has been assisted in its Rapid and Cost-Effective Rotorcraft (RACER) demonstrator program by the EU-funded CA3TCH project. Using advanced simulation technology, it aims to predict the aerodynamic and aero acoustic behavior of essentially new rotorcraft configurations like the Airbus Helicopters RACER.
The futuristic-looking RACER will feature innovative environmental performance offering 15 per cent less fuel burn per nautical mile at 180kts (207mph) compared to a conventional helicopter at 130kts (150mph), as well as reduced sound pollution, a key factor being its airframe design, with its forward fuselage optimized for low drag. Its compound configuration departs from conventional helicopter design by featuring a main rotor, with wings and propellers for propulsion support instead of a conventional tail rotor.
RACER is expected to reach cruise speeds of more than 216kts (248mph). The cutting edge Safran Eco-Mode hybrid-electric system – which allows one of the two Aneto-1X engines to be switched to standby while in cruise flight – generates further fuel savings of up to 30 per cent. RACER specifically combines high speed and vertical take-off and landing (VTOL), allowing it to operate in remote areas, which could significantly extend the speed and range of HEMS and rescue services, improving chances of survival by reaching people within the first critical ‘Golden Hour’ of need.
It is hoped the RACER demonstrator proves that the compound rotorcraft configuration, which implements and combines cutting-edge technologies, will open up new mobility roles that neither conventional helicopters nor fixed-wing aircraft can presently cover in a sustainable way, for both operators and the industry.
eVTOL and Urban Air Transport
Most of the main helicopter builders are experimenting with electric/hybrid-electric propulsion and electric vertical take-off and landing (eVTOL) urban air-taxi concepts.
Balkiz Sarihan, Head of Urban Air Mobility (UAM) Strategy Execution and Partnerships at Airbus, said: “We’re testing many things like electrification and hybridization using our eVTOL platforms, which are contributing to net zero, and they have applications for our helicopters and larger commercial aircraft, too, so it’s a virtuous circle of technology investment.”
Engine builder Rolls-Royce is involved in developing a portfolio of all-electric and hybrid electric applications, in particular for the urban air mobility and regional air mobility markets. “Rolls-Royce powered electric flight is becoming a reality: e.g., the Tecnam/Wideroe regional plane will enter into service in the 2020s; Vertical Aerospace’s eVTOL is set for certification by 2024. We are continuously open to work with partners seeking to bring all-electric and hybrid-electric air vehicles to market,” a company spokesperson commented.
As part of its drive to reduce emissions in aviation over its full product range, Airbus is developing an all-electric, four-seat eVTOL lift and cruise concept featuring a wing. Called CityAirbus NextGen, it boasts a 50-mile (80km) range and a cruise speed of 65kts (75mph), which makes it ideally suited to zero-emission flight operations for a variety of applications in major cities. Its eligibility for use in medical services roles is plain to see.
“Starting out in 2014 as a strategy exercise for Airbus, we began a dedicated program of research and innovation to understand more about eVTOL technology, and along the way we coined the term ‘urban air mobility’ as it hadn’t existed before,” explained Balkiz Sarihan.
“We created Airbus Urban Mobility because the concept and its technology were not directly related to our traditional aerospace or helicopter businesses. It’s a dedicated entity, because we wanted to build it in a different way, using a different application of aircraft architecture and technology. The latter is an area that’s evolving very fast – electrification, batteries, and hydrogen power. But we believe it’s not just about a technology push – we have to create the right service to society and do so in a meaningful way,” asserted Sarihan.
“It’ll be the end of 2023 when the prototype CityAirbus NextGen flies. We’ve already completed two eVTOL technology demonstrator programs – CityAirbus and Vahana – in which we really tested the technical capabilities of both vehicles against known future uses, establishing the relative balance between hover and range capabilities, with full eVTOL being an absolute requirement. Now we really believe the technology has matured, but we are still building the market and service around it,” she said.
And so, CityAirbus NextGen was born, and the lessons learned from the Airbus double-demonstrator approach have been essential to the creation of this new generation of eVTOL vehicle.
Bell Nexus 4EX
Bell’s Nexus 4EX e-VTOL four-duct tilt rotor (with echoes of the company’s V-22 Osprey VTOL tiltrotor) has been conceived as a solution to delivery and commuter challenges, carrying goods, people, and data to serve business or city-wide demands. “The Bell Nexus 4EX can operate as an electric-only vehicle or a hybrid-electric configured vehicle. With a hybrid platform, the Nexus 4EX promises an extended reach to travel farther or to more remote locations, based on your mobility needs,” said the manufacturer.
French engine maker Safran, which is building the hybrid-electric engine for the Nexus eVTOL vehicle, is also exploring uses for its electric and hybrid-electric engines on traditional helicopters.
The UK-based aerospace, and technology company Vertical Aerospace has partnered with Leonardo Helicopters for the design, testing, and manufacture of Vertical’s VX4 eVTOL vehicle. With capacity for a pilot and four passengers, the four tilt-rotor VX4 is projected to be capable of speeds up to 174kts (200mph), with a range of over 100 miles and zero operating emissions. Vertical is already considering medevac and HEMS roles for the VX4. The company has what it believes is the largest conditional pre-order book (by value) in the eVTOL industry, with up to 1,350 aircraft worth US$5.4 billion from the likes of American Airlines, Avolon and Bristow.
The ‘perfect flight’
While the aerospace industry works hard to develop new engine technologies, sustainable aviation fuels, and design more energy-efficient aircraft, some plane makers and operators have been working on ways to fly more efficiently.
Express air freight carrier DHL has been identifying ways to reduce its carbon footprint by ‘smarter’ operating. By utilizing the latest technology, optimizing its route network, and choosing efficient carriers, DHL has found ways to save jet fuel and reduce its carbon footprint.
In July 2020, DHL partnered with its operating airline, European Air Transport GmbH, to plan the ‘perfect flight’. This ground-breaking demonstration flight was made from Leipzig, Germany, to New York-John F. Kennedy (JFK) International Airport, to test the effects of operating under optimal flight conditions. With air traffic considerably reduced due to Covid-19, the carrier planned and scheduled the most eco-friendly North Atlantic crossing possible, with all air traffic control sectors along the route supporting their efforts. DHL described how they achieved the ‘perfect flight’:
“To prepare for the flight, we identified more than 50 steps to minimize fuel consumption. These included washing the engine pre-flight to improve aerodynamics, optimizing the route using a state-of-the-art flight planning system, calculating the optimal take-off trajectory (unrestricted climb to cruising altitude), and determining the best possible descent procedure to JFK (constant angle with minimum engine power. A total of 13 agencies, such as the German Air Traffic Control, National Air Traffic Services UK (NATS), and the US Federal Aviation Administration, took part in the flight planning and operation.
“The results speak for themselves. Loaded with its standard payload (approx. 60 tons of freight), the Airbus A330-200F consumed 1,000kg less fuel, which reduced the flight’s CO2 emissions by 3,150kg. NATS reported that the flight through UK airspace scored 0.013 on its 3Di index, which they use to calculate each flight’s environmental efficiency. With zero being perfect, that’s about as close as you can get.”
Energy efficient flights
Launched in February 2021, Airbus is leading ALBATROSS – a large-scale initiative of major European aviation stakeholder groups to demonstrate the feasibility of implementing energy efficient flights in the short term. These are being made through a series of gate-to-gate live demonstration flights across Europe, combining several R&D technical and operational innovations.
Airbus commented: “ALBATROSS follows a holistic approach by covering all flight phases, directly involving all relevant stakeholder groups (such as airlines, Air Navigation Service Provider, network managers, airports, and industry) and addressing both operational and technological aspects of aviation and Air Traffic Management (ATM). Many solutions will be put into practice during the flight demonstrations, from new precision approach procedures to continuous climb and descent, a more dynamic management of necessary airspace constraints, sustainable taxiing, and sustainable aviation fuel (SAF) usage.
“Thanks to the transmission of four-dimensional trajectory data, ATM will be able to optimize and better predict an aircraft’s trajectory, thereby enabling it to immediately and concretely reduce a flight’s environmental footprint.”
These live trials began in September 2021 and will ultimately involve around 1,000 demonstration flights, showcasing real-life operating solutions and possibilities for making the ‘perfect flight’ with the potential to save fuel and reduce CO2 emissions. The first results are expected during 2022.
Smarter helicopter ops
Helicopter operations contribute a small percentage to greenhouse gas emissions – actually, less than one per cent of the aviation industry’s CO2 emissions – but they can be a significant source of local air pollution around airports and in urban areas. Research by the UK’s Cranfield University School of Engineering in 2011 into the environmental impact of the operation of conventional helicopters at mission level concluded that smarter use of rotorcraft by focusing on mission profile management can have positive effects on fuel burn and reduced emissions.
The future could be green
Developments in the fields of electric propulsion, small core gas turbines, smart design and composite materials have created a virtuous circle, which link to efficiency challenges related to aerodynamics, propulsion, and weight. Together and individually, they can improve overall performance and reduce fuel burn in fixed- and rotary-wing aircraft, leading to reduced carbon emissions, which in turn reduces running costs for the operators. Thus, if new aircraft that incorporate these features appeal to their users, then manufacturers will want to build them, improving balance sheets all round. This is good for the climate, good for sustainability and good for business – a win-win.