Influence of Mach Numbers and Telescoping Positions on Aerodynamic Performance of Variable Diameter-and-Speed Tilt-Rotors

Influence of Mach numbers and telescoping positions (TP) on the aerodynamic-enhancement mechanism of Variable Diameter-and-Speed Tilt-Rotors (VDSTR) was investigated by utilizing Blade Element and Momentum Theory (BEMT), with the original metal-blade tilt-rotors of XV-15 employed as the benchmark. First, by fixing the operational tip Mach numbers while allowing free cooperation of variable diameter and speed, the mechanism was analyzed, and the effects of air compressibility and telescoping position on the mechanism were further scrutinized. Then, advantages over single-variable techniques were highlighted by comparing hover and high-speed forward flight performance. The results highlight distinct aerodynamic improvement mechanisms for VDSTR in different flight states. The reduction of induced power compensates for increased profile drag power, a fundamental mechanism enhancing VDSTR in hover. The mechanism relies on blade contraction in high-speed forward flight, effectively reducing profile drag power. Moreover, compared to the original XV-15 blade, VDSTR enhances forward flight efficiency by 6.93% under specified load and Figure of Merit (FM*) by 4.07% under the designed load, resulting in a power reduction of 51.5 kW and 24.9 kW, respectively, and outperforming single-variable methods. Outward TP movement consistently negatively affects efficiency gain in both states. Optimal TP for promoting aerodynamic-enhancement under both flight states is identified between the root and middle sections of the original blade.