Rotorcraft, “fast” rotorcraft, and 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. A helicopter is a type of rotorcraft, but not all rotorcraft are helicopters.
In Clean Sky 2, two very different types of rotorcraft are planned - a tiltrotor and a compound rotor:
A tiltrotor is an aircraft which 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. But 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 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 service 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 LifeRCraft Compound Rotorcraft demonstrator. Additionally, the Programme interfaces with other Clean Sky 2 Programme areas –– where there are mutual interests and opportunities, and synergy can be extracted from sharing research activity across the Programme to mutual benefit.
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.
Concerning 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 LifeRCraft, 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.
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 current Tiltrotors’ state-of-the-art. The project will also facilitate the development of substantial R&T activities to increase the knowledge base, as the Tiltrotor platform has not yet been certified for civil aircraft use.
The NextGenCTR demonstrator will also be used to generate a research and innovation volume of 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 has been 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 trajectories optimisation (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 which focus on drag reduction of the prop-rotor and airframe fuselage and wing will be necessary (due to a new generation of prop-rotor, modified fuselage-wing architecture). The key enabling feature of a Tiltrotor, namely the tilting mechanism enabling vertical take-off and landing, will be completely redesigned 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.
A new prop-rotor will require substantial research (aero-acoustics, by modelling/by tests) to reduce noise emissions (to be validated at near full scale). In Clean Sky 1, noise reduction is mainly addressed through trajectories optimisation (this will in any event continue 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 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 can be extracted is not available. 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 in the period 2005-2012). 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 LifeRCraft 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 substantiate the potential to combine in an advanced rotorcraft payload/range/speed capacity 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 attributes 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 concerned FRC Leader under private funding is clearly poised to bring game-changing mission capability 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 on one side through participation in Clean Sky projects and other research activities at EU or local level
- New rotor blade concepts aimed at improved lifting efficiency and minimizing noise
- Airframe drag reduction through shape modifications and interference suppression
- Engine intake loss reduction and muffling
- Innovative electrical systems e.g. brushless generators, high voltage network, efficient energy storage and conversion, electrical actuation
- Eco-Design approach, substituting harmful materials, and green production techniques
- Fly-neighbourly demonstration of new flight guidance functions and approach
This LifeRCraft project essentially consists of the following main activities and deliveries:
- Airframe structure and landing system: Advanced composite or hybrid metallic/composite construction, featuring low weight and aerodynamic efficiency
- Lifting rotor and propellers: Low drag hub, pylon and nacelles, 3D-optimized blade design
- Drive train and power plant: New drive train architecture and engine installation optimised for the LifeRCraft configuration
- On board energy, cabin and mission systems: Implementation of the more electrical rotorcraft concept to minimise power off-takes from the engines and drive system
- Flight control, guidance and navigation: Smart flight control exploiting additional control degrees of freedom inherent to LifeRCraft configuration for best fuel economy and quieter flight
LifeRCraft 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, AgustaWestland (now Finmeccanica - Europe) 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 the recent wind-tunnel testing earlier this year of Clean Sky 2's LifeRCraft Demonstrator, manufactured by Airbus Helicopters. Testing proved the compound aerodynamic configuration is viable in terms of efficiency, sustainability and performance, and it will undergo a more extensive design review before the end of 2016. The idea is to offer a rotorcraft that brings a hitherto unavailable combination of payload, speed and range. And 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 very diversified in itself) there are many applications of rotorcraft across civil transport such as passenger transport, search and rescue, medevac, policing, 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.
Building on the Clean Sky 1 technical accomplishments that feed in to the even more extensive ambitions of Clean Sky 2's NextGenCTR and LifeRCraft, 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 Airbus H160 which will imminently reach the market already are poised to act as flagships for European design and technologies 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 / mobility capabilities and open exciting new markets