Fast Rotorcraft IADP
Rotorcraft and “fast” rotorcraft - what are the key challenges?
Rotorcraft (sometimes referred to as rotary wing aircraft) are aircraft that use lift generated by rotors - these are assemblies comprising several rotor blades that revolve around a mast. Rotorcraft generally have one or more rotors to provide lift throughout the entire flight, and while a helicopter is a type of rotorcraft, not all rotorcraft are helicopters.
In Clean Sky 2, two very different types of rotorcraft are planned - a tiltrotor and a compound rotorcraft:
A tiltrotor is an aircraft that generates both lift and propulsion using rotors that are mounted on swivelling engine pods or nacelles, usually mounted on a fixed wing – or are comprised of tilting rotors driven through gearboxes delivering the torque which comes from fixed engines. A tiltrotor can also have rotors that are mounted on fully tilting wings.
A compound rotorcraft is an aircraft that combines a rotor with a supplementary form of propulsion - usually additional thrust engines or propellers.
The challenge in rotorcraft design is always to improve payload-lifting capability, reduce fuel burn and increase the vehicle's range – the traditional objectives in aeronautical design. In Clean Sky 2, the two demonstrator aircraft planned have a very specific and novel feature: by combining forward “pull” or thrust with the vertical lift capability, both aircraft models will “bridge the gap” between traditional helicopters and fixed-wing aircraft. This means that due to their speed and range these novel vehicles will approach the mission capability of fixed-wing aircraft, yet also be able to take off and land vertically, and, importantly, “hover” in a fixed position over the ground when needed.
Also in Clean Sky 2, particular emphasis is placed on emissions and noise – for it is the noise nuisance level and the unique issue of taking off and landing in direct proximity to communities - especially restricted in urban areas - that can make rotorcraft unneighbourly.
Part of the challenge in tackling this noise issue is the fact that rotorcraft often operate in an unusual spectrum of different environments. A case in point is emergency services or medical evacuation helicopters that have to fly in and out of urban and densely populated areas, often following unique flight paths and landing into - and taking off from - the location needing the aircraft’s capability of “airlifting” (e.g. evacuating or rescuing) people.
The Fast Rotorcraft IADP consists of two concurrent concepts: the Tiltrotor demonstrator and the RACER Compound Rotorcraft demonstrator. Additionally, the Programme interfaces with other Clean Sky 2 Programme areas –– where there are mutual interests and opportunities, and synergies can be leveraged by sharing research activity across the Programme, benefitting the broader ambitions of Clean Sky 2.
Examples in the technical area relate to the development of airframe, engine and system technologies covered in the respective Clean Sky 2 ITDs. But equally, these joint activities cover the methodology for technology evaluation of fast rotorcraft demonstrations and the Eco-Design concept implementation, along with the programme management activities for the Fast Rotorcraft IADP.
In respect of the methodology for technology evaluation, the activities will allow defining objectives and criteria adapted to the fast rotorcraft missions in line with the general TE approach for Clean Sky 2.
In addition, the tools used in Clean Sky 1 GRC1-GRC7 projects will be adapted and further developed in order to enable the assessment of conceptual rotorcraft models corresponding to the new configurations to be demonstrated in Clean Sky 2.
In respect of Eco-Design concept implementation, the activities will allow coordinating approaches and work plans in the two demonstration projects regarding the greening of rotorcraft production processes, ensuring complementarity of case studies. The general Life Cycle Assessment approach will be coordinated with the participants of the Eco-Design TA.
What is particularly significant here is that these two demonstrator fast rotorcraft in the Clean Sky 2 programme not only introduce new technologies – these aircraft are also pioneers of a new segment within the rotorcraft category, bringing completely new capabilities. For example, the high speed of the RACER, in a medevac situation, would enable the rotorcraft to reach offshore oil or wind-farm platforms within the "golden hour" - the critical first 60 minutes following a medical emergency event when paramedic access to those in need can make all the difference to patient recovery. In addition, tiltrotors will enable communities with limited ground infrastructure to fly “faster and further”, supporting future European mobility objectives - of ultimately being able to travel between any two points in the EU within four hours.
The Next-Generation Civil Tiltrotor demonstrator (NextGenCTR):
NextGenCTR will be dedicated to the design, construction and flying of an innovative Civil Tiltrotor technology demonstrator, the configuration of which will go beyond current architectures for this type of aircraft. NextGenCTR’s demonstration activities will aim to validate its architecture, technologies/systems and operational concepts.
Demonstration activities will show significant improvement with respect to the current state-of-the-art Tiltrotors. The project will also facilitate the development of substantial R&T activities to increase the knowledge base, building on the upcoming Leonardo Tiltrotor platform civil certification, which combine the benefits of a helicopter with the speed and capabilities of fixed-wing aircraft into a single vehicle.
The NextGenCTR demonstrator will also be used to generate a body of research and innovation activities above a certain critical mass (not available today for Tiltrotors within the EU), comparable to that of well-proven conventional helicopter platforms.
NextGenCTR will continue and further develop what was initiated in Clean Sky 1, and launch new activities specific to Clean Sky 2 and the NextGenCTR project. In the area of CO2 emissions reduction, NextGenCTR will continue and develop engine installation and flight trajectory optimisations (this is currently carried out using analytical models and with scaled model tests, whereas Clean Sky 2 will validate it at near full scale).
Specific new activities in Clean Sky 2 will focus on a revised wing to reduce drag, with tilting flaps to minimise rotor downwash impingement in hover mode, as well as a new tail configuration to provide enhanced aerodynamic efficiency.
The key enabling feature of a Tiltrotor - the tilting mechanism enabling vertical take-off and landing - will be completely redesigned, incorporating a fixed engine installation with a split gearbox to provide the proprotor tilting mechanism, based on new capabilities in aerodynamic and structural analysis, design, and next-generation manufacturing and assembly principles. This will also allow important operational cost reduction to address the competitiveness of the architecture and solutions adopted.
In Clean Sky 1, noise reduction was mainly addressed through trajectory optimisation (this is continuing in Clean Sky 2, and will be linked to SESAR concepts where necessary). Clean Sky 2 transversal subjects will cover new materials (e.g. thermoplastics, surface treatments, less hydraulics and more electrical systems) validating them at full scale and in real operational conditions, and sustain the development of the Technology Evaluator for the case of the Tiltrotor.
Parameters need to be defined to show how Clean Sky 2 achieves progress in line with a specific Tiltrotor roadmap (a direct comparison with conventional helicopter architecture would be inappropriate as the two configurations must be regarded as substantially different types of rotary-wing platforms).
Today, certified tiltrotors are not available in the civil sector (while only one product is available in the military). Hence, a database from which baseline information for the current state-of-the-art might be extracted, does not exist. Therefore, ‘key performance parameters’ (KPP) will be introduced to show NextGenCTR’s progress with respect to reference data taken as baseline (mainly referring to technologies which have been tested or conceptually designed between 2005 and 2012). Objectives will be defined considering tiltrotor specifics and in line with the main pillars of Horizon 2020 (towards Smart, Green and Integrated Transport), and Clean Sky 2 (which addresses environmental compatibility - Greening Objectives – competitiveness, Industrial Leadership, and mobility).
Attention to the project’s impact on the EU Economy and job creation will also be considered, looking at potential revenues, workforce productivity, rate of new employment (in particular of higher educated personnel) and R&D expenditure.
The Compound Rotorcraft demonstrator:
The RACER project aims to demonstrate that the compound rotorcraft configuration - implementing and combining cutting-edge technologies from the Clean Sky 1 Programme - opens up new mobility roles that neither conventional helicopters nor fixed wing aircraft can currently cover in a sustainable way, for both the operators and the industry.
The project will ultimately confirm the potential to combine payload/range/speed capacity in an advanced rotorcraft with agility in vertical flight. This will also include the capability to land on unprepared surfaces with nearby obstacles, and to load and unload rescue personnel and victims while hovering.
Other target capabilities of the demonstrator are that it will have a long range, high cruise speed, low fuel consumption and gas emission, low community noise impact, and be productive for operators. As the current world helicopter speed record-holder, this architecture developed within Europe by the FRC Leader under private funding is clearly poised to bring game-changing mission capabilities to the market once matured and validated.
A large scale airworthy demonstrator embodying the new European compound rotorcraft architecture will be designed, integrated and flight tested. This demonstrator will achieve Technology Readiness Level 6 at whole aircraft level in 2020. The project is based on:
- identified mobility requirements and environmental protection objectives
- lessons learnt from earlier experimentation with the X3 low scale exploratory aircraft
- technology progress achieved for rotorcraft subsystems through participation in Clean Sky projects and other research activities at EU or local level
The individual technologies from Clean Sky 1 (Green Rotorcraft ITD, Smart Green Operations ITD, Eco-Design ITD) that will be further matured and integrated into the RACER demonstration during Clan Sky 2 include:
- New rotor blade concepts aimed at improved lifting efficiency and minimising noise
- Airframe drag reduction through shape modifications and interference suppression
- Engine intake loss reduction and muffling
- Innovative electrical systems including brushless generators, high voltage network, efficient energy storage and conversion, and electrical actuation
- Eco-Design approach, substituting harmful materials, and green production techniques
- Fly-neighbourly demonstration of new flight guidance functions and approach
The RACER project consists of the following main activities and deliveries:
- Airframe structure and landing system including an advanced composite or hybrid metallic/composite construction, featuring low weight and aerodynamic efficiency
- Lifting rotor and propellers incorporating a low drag hub, pylon and nacelles, and 3D-optimised blade design
- Drive train and power plant, including new drive train architecture and an engine installation optimised for the RACER configuration
- On board energy, cabin and mission systems, that will include implementation of a more electrical rotorcraft concept to minimise power off-takes from the engines and drive system
- Flight control, guidance and navigation, using a smart flight control exploiting additional control degrees of freedom inherent to the RACER configuration for best fuel economy and quieter flight
RACER Demonstrator overall design, integration and testing
All coordination and cross cutting activities relevant to the whole vehicle will deliver a full range of ground and flight test results and a final conclusion.
The rotorcraft market is markedly different from the fixed wing aircraft market. Acquisition of new rotorcraft is slowly recovering after the global economic downturn of 2008, but growth is nothing like that of the medium and large fixed wing aircraft markets.
Another differentiator is the geographic distribution of operators and manufacturers:
There are more civil rotorcraft operated in the US than in all the European nations put together: North America operates 35% of the global fleet (12,054 aircraft), followed by Europe (27% = 9,378 aircraft), Asia-Pacific (18% = 6,085 aircraft), Latin America (13% = 4,416 aircraft), Africa (5% = 1808 aircraft), and the Middle East (2% = 546 aircraft) (source: Flightglobal’s Fleets Analyzer database - September 2015).
But, contrast that with who actually manufactures these aircraft and the picture becomes more nuanced. Airbus (Europe) has 34% of the market, Leonardo Helicopters has 20%, Bell (USA) has 19%, Robinson (USA) 12%, and Sikorsky (USA) 5%.
Europe's share of manufacturing in Rotorcraft appears to be growing, and technology is a key driver underpinning this trend.
A specific example of Clean Sky 2's relevance in all this was wind-tunnel testing of Clean Sky 2's RACER Demonstrator, manufactured by Airbus Helicopters. Testing proved the compound aerodynamic configuration is viable in terms of efficiency, sustainability and performance. The idea is to offer a rotorcraft that brings a new combination of payload, speed and range, similar to the path traced by tiltrotors that will be further enhanced by the NGCTR in the near future. This is just the beginning of Clean Sky 2's rotorcraft efforts.
Tomorrow’s challenge, today’s call to action
The rotorcraft segment of the aircraft manufacturing sector is resilient due to its diversity. Outside of military rotorcraft (which is much more diversified) there are many applications of rotorcraft across civil transport such as passenger transport, search and rescue, medevac, policing, and surveying. They perform missions which no other aircraft type can accomplish – landing on unprepared territory, landing in urbanised locales, travelling to and from oil rigs in the sea, mountain rescue – operating in all types of hostile environments and weather conditions.
Building on the Clean Sky 1 technical accomplishments that feed in to the even more extensive ambitions of Clean Sky 2's NextGenCTR and RACER, our demonstrator programmes tackle a multitude of bold, interconnected technology challenges, and will integrate the progress made into a new class of air vehicle: Fast Rotorcraft that bridge the current gap between traditional helicopters and faster, longer range fixed wing aircraft. This will firmly establish European aeronautics at the forefront of the civil rotorcraft segment of the market.
European products such as the Leonardo AW169 and Airbus H160, the latter at the threshold of service entry readiness, are already poised to act as flagships for European design and technology endeavours and bring wider acceptance of features such as composite airframe – relatively new in helicopter construction on this scale. Europe's strong technological capabilities will translate into rotorcraft with improved specifications and performance, lower running costs and flights that produce less noise and reduced emissions. And the unique and game-changing features of the Fast Rotorcraft concepts being matured and validated in Clean Sky 2 will provide new transport and mobility capabilities and open exciting new markets.