Investigation of partial span full chord twist morphing as a means for rotary-wing aerodynamic performance enhancement

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. 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 the ability of a novel full-chord, partial-span(FCPS) blade-twist morphing concept to improve this metric yet to be considered extensively within currently available literature. Overall, the work leverages the software package, CROTOR _© to identify the optimal spanwise distribution with which to integrate this morphing functionality for best performance. Spanwise positions ranging from 0.75r/R - where r/R is the ratio of spanwise blade position to length - to 0.95r/R at the rotor blade’s tip and from 0.10r/R to 0.20r/R at the rotor blade’s root are evaluated over a twist range of − 10° to + 20° with the overall cost/benefit analysis considered. A full-scale Sikorsky Sea King helicopter rotor system is selected as the baseline analysis case with key performance parameter comparisons for lift coefficient, lift-to-drag ratio, Figure of Merit (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 mission-specific operational requirements. For a balanced performance(enhancing efficiency without incurring significant power penalties or secondary losses), the 0.85r/R configuration constitutes the most favourable solution achieving C _L /C _D gains of 20.3%(hover), 14%(take-off), and 12.2%(cruise) accompanied by FoM increases of 3.8%(hover) and 1.3%(take-off), and a propulsive efficiency(ηₚ) rise of 2.73%. These correspond to 3.8% endurance, 2.5% payload, and 15.3% range improvements. The implications of linear and non-linear FCPS morphing are also considered. Ultimately, the full-chord blade twist angle(both root and tip) was identified as the main determinant for this enhancement highlighting the potential benefits available within rotary-wing applications if such a concept can be practically realised.