Numerical and computational (CFD–CSD) investigation of in-flight adjustable full-chord partial-span twist morphing for helicopter optimal aerodynamic performance and multi-segment operational enhancement

Abstract Rotary-wing platforms have been instrumental in the advancement of modern aviation given their unique vertical take-off and landing (VTOL) capabilities. Their applications vary in both scope and scale to include search and rescue, transport logistics, medical evacuation and surveillance and reconnaissance to name but a few. Compared to their fixed-wing counterparts however, rotary-wing platforms operate within a substantially different flow-field environment resulting in much lower aerodynamically efficient flight characteristics. One main element giving rise to these inherent characteristics is the highly transitory, dynamic, and uniquely complicated airflow environment setup on the rotating blades during normal flight regimes (hover, forward flight, etc.). Realising significant additional aerodynamic performance gains therefore can be extremely difficult to achieve, particularly given the near universal current use of a fixed, rigid, and sub-optimal/compromised rotor blade design principles for all flight segments. Such conditions represent a limited ability to integrate within a real-world operational environment any degree of reactive adaptability to changes in optimal flight requirements. This work investigates an in-flight adjustable, full-chord partial-span (FCPS) morphing rotor blade capable of changing twist during operation (rather than relying on a fixed compromise blade design) which is yet to be considered extensively within currently available literature. This CFD–CSD investigation employs CROTOR © and SimScale © for numerical and CFD analyses to define the adjustable spanwise distribution for FCPS morphing integration that achieves optimal continuous performance, while ANSYS © Modal Dynamics and MBDyn © handle the CSD. Spanwise-adjustable morphing regions are investigated from 75–95% at the tip and over 10–20% at the blade root, across a twist range of –10 to + 20°. A full-scale Sikorsky Sea King helicopter rotor-system is selected as the baseline analysis case with key performance parameter comparisons for C L /C D , FoM as well as power and thrust coefficients, all presented and evaluated. This investigation demonstrates that the FCPS twist morphing rotor concept can be tailored to multi-segment mission-specific operational requirements. For balanced performance, the 0.85 r/R configuration represents the most favourable solution, optimising the benefit-to-cost ratio between aerodynamic and operational gains and penalties in power, weight, and actuation requirements, achieving full-helicopter-level L/D gains of 7.5% in hover, 5.2% at take-off, 4.7% in low–medium cruise (µ = 0.1–0.2), 6.3% in medium–high cruise (µ = 0.2–0.31), and 1.5% in descent. These translate to a hover endurance gain of + 4.65%, hover payload increase of + 3.8%, cruise range improvement of + 9.55%, cruise payload increase of 9.38%, and a TSFC reduction of 3.8%. While additional power requirements, weight penalty, rotor tip displacement, actuation complexity, and acoustic signature increase, these remain marginal relative to the baseline and are outweighed by the advantages. Ultimately, the full-chord blade twist angle and spanwise length (at the tip, root or as a coupled arrangement) were identified as the main determinant for this enhancement highlighting the aerodynamic and operational benefits available within rotary-wing applications should this concept be practically realised.