Aurora Flight Sciences has been selected to progress into the second and third phases of the US Defense Advanced Research Projects Agency’s (DARPA’s) Control of Revolutionary Aircraft with Novel Effectors (CRANE) programme, which will see the firm develop a new, unique X-plane demonstrator that exploits innovative active flow control (AFC) technologies.
Announced by both DARPA and Aurora Flight Sciences on January 17, this move follows the successful completion of Phase 0 and Phase 1 of the CRANE programme. The former focused on the development of tools and technologies for incorporating AFC characteristics into the early stages of aircraft design, which resulted in the creation of two X-plane concepts.
Meanwhile, the latter phase saw Aurora complete the preliminary design of the selected X-plane concept and culminated with the development of an aircraft testbed that used AFC technology to generate control forces in a series of wind tunnel tests. According to Aurora, these trials provided a “rigorous foundation for developing flight control laws using AFC as a primary control effector.”
The use of AFC technologies provides opportunities to help improve fixed-wing aircraft flight control and performance. This includes the elimination of moving control surfaces – primarily on the wings and vertical stabiliser – to reduce overall drag and enhance flight control at high angles of attack, while also permitting the use of thicker wings in an aircraft’s design to improve structural efficiency and increase fuel capacity, along with the inclusion of more simplified high-lift systems.
Having now progressed to Phase 2 of the CRANE programme, Aurora – in coordination with its parent company, Boeing, and DARPA – will now focus on the detailed design and development of relevant flight software and controls for a new full-scale, uncrewed X-plane demonstrator, which will be manufactured in Phase 3 of the project – which is currently an executable option as part of this latest contract – before it is flown and assessed in a critical design review. Aurora has already launched the detailed engineering design process for this new demonstrator, which will boast a gross weight of 7,000lb (3,175kg) and a 30ft (9.1m) wingspan.
According to Aurora, the purpose-built testbed will be designed around an AFC system that supplies pressurised air to AFC effectors embedded in all of the demonstrator’s flying surfaces. “The vehicle configuration provides AFC testing for multiple wing sweeps using nozzle arrays located at the upper surface of each wing,” the firm added. It will also feature replaceable outboard wings and swappable AFC effectors, which enables the platform to trial not only Aurora’s AFC effectors, but also the AFC effectors of a variety of other designs.
If the option to progress to Phase 3 is actioned, the new uncrewed X-plane will be manufactured by the company at its facilities in Virginia, West Virginia and Mississippi. Following its construction, the aircraft will be used to validate AFC technology validation and demonstration at relevant scale and flight conditions, with the platform expected to fly at speeds of up to Mach 0.7 (864.3kph). Flight testing is expected to begin in 2025.
Commenting on the development of AFC technology in relation to the new testbed, Richard Wlezien – the CRANE program manager at DARPA – said: “Over the past several decades, the AFC community has made significant advancements that enable the integration of AFC technologies into advanced aircraft. We are confident about completing the design and flight test of a demonstration aircraft with AFC as the primary design consideration. Thanks to a variety of innovative participants, the CRANE programme has significantly advanced the state-of-the-art of multiple AFC technologies. We are uniquely positioned to build on those achievements by evaluating a wide range of relevant technologies during our planned X-plane flight tests.”
If the ongoing development and refinement of AFC technologies under DARPA’s CRANE project is successful and proves viable, it could ultimately inform and shape the design of future military aircraft. The removal of flight control-related components – such as ailerons and rudders – can offer new opportunities to shed aircraft weight and size, making them lighter and more manoeuvrable. It also has benefits for safety, reliability and maintenance, as a reduction in the number of moving parts in an aircraft would mean fewer parts are at risk of breaking. This would help increase aircraft availability and decrease the overall down-time of an aircraft going through unscheduled maintenance.
Such technology could also be incorporated into future aircraft development programmes. For instance, while the US Air Force’s (USAF’s) sixth-generation fighter – which is currently in the early stages of development as part of the wider Next-Generation Air Dominance (NGAD) family of systems – could benefit from such technology. Early concept images of the platform indicate that the sixth-generation fighter (which is being developed to replace Lockheed Martin’s F-22A Raptor fifth-generation air superiority fighter in USAF service) will be of a delta-wing design and is likely to not feature a vertical stabiliser. This could indicate that AFC technology will form the core of the platforms flight control and performance capabilities.
Such a design also brings benefits for platforms that are designed to be low observable (LO) or stealthy in the battlespace, as less moving exterior parts will result in an aircraft maintaining the same shape in any flight dynamic. This would help in ensuring that the platform’s radar cross-section (RCS) remains as low as possible and mitigate any gaps that appear in an aircraft’s exterior surfaces. While early NGAD concepts certainly suggest that AFC technology could be incorporated into it, this has yet to be confirmed, but time will tell if the programme does benefit from the work DARPA and Aurora are doing in this arena.