Over the duration of the SABRE project, major progress was made towards achieving the objectives of this program. The partners employed sophisticated analysis tools, which were further enhanced in this project with significant improvements to their coding and accuracy, to fully explore the design space of morphing rotors. Comprehensive analysis runs on the refined surrogate models of the different morphing concepts have shown that including detailed analysis results of the morphing concept performance into system level analysis of the power requirements and emissions of the full helicopter gives the most complete picture to date of what is achievable. Happily, our initial lower fidelity estimates which showed reductions in CO2 and NOx on the order of 5-10% have been born out by our more detailed analysis, which is currently showing 5-11% reductions, depending on the flight mode and the combination of morphing concepts used. What’s more, the depth of the technical considerations expanded significantly in the final stages of the project, with important aspects of rotor vibrations and acoustic emissions now being included. These additional analyses are important for considering the real world implications of morphing rotors, and are a key consideration before any of these technologies can be commercialised. Crucially, no show-stoppers have been identified in the acoustic and vibration analysis done to date. In fact, we have found that careful usage of the morphing devices can lead to reductions in both acoustic emissions and helicopter vibration levels.
The progress made throughout the SABRE program has also gone a long way towards advancing the maturity of the morphing technologies, supporting our second program objective. While progress on the design and experimental aspects of Work Package 2 was affected by the global pandemic, an adaptive research strategy was employed which allowed us to focus on realising the key experimental wind tunnel and whirl tower tests, while supporting this work with benchtop testing of subsystems and components along with enhanced numerical simulations. These tests showed the morphing concepts can withstand aerodynamic and centrifugal loading, with the desired levels of direct control of lift being validated in the wind tunnel.
While morphing rotor blade technologies still need further development before they are ready for industrial adoption, our work in SABRE has shown, in the most comprehensive and integrated way, that they are indeed worth pursuing, with achievable reductions in emissions that are far beyond what is achievable with traditional rotor design.
