Folding-wing Unmanned Aerial Vehicles (UAVs) have become a key platform in modern aerial applications, owing to their superior portability and rapid deployment capabilities. While the tandem-wing configuration offers a compact solution for strict folding constraints, the resulting high wing loading necessitates a maximized lift coefficient (C_L) to ensure efficient low-speed loitering. This study presents an aerodynamic optimization framework aiming to maximize the C_L of a folding tandem-wing UAV. A combined optimization strategy integrating Optimal Latin Hypercube Sampling (OLHS), orthogonal polynomial surrogate models, and the Multi-Island Genetic Algorithm (MIGA) is established. With aft wing parameters determined, global sensitivity analysis identifies the fore wing span as the dominant factor, contributing 47.40% to lift performance. Crucially, although vertical separation contributes only 6.53% to C_L and sweep angle just −1.22% to drag coefficient, their strong interaction effects with wing span confirm their non-negligible role. Finally, the flow field characteristics at the wing root of the optimized configuration undergo significant changes, resulting in a 4.28% increase in the C_L. This work validates the important role of parameter interaction effects in aerodynamic optimization and provides a theoretical basis for the design of geometrically constrained aerial vehicles requiring high lift coefficients.

Although electric vertical takeoff and landing (eVTOL) aircraft are considered a viable solution for urban air mobility, rotor–airframe aerodynamic interference remains a critical challenge as it affects hover and cruise performance. This study investigates the aerodynamic interaction mechanisms of tiltrotor and tiltwing eVTOL configurations across cruise and hover flight modes using a computational framework coupling steady Reynolds-averaged Navier–Stokes equations with the virtual blade model. During cruise, rotor slipstream improves aerodynamic efficiency by increasing the effective angle of attack and accelerating the upper-surface airflow on the wing, yielding a 28.18% increase in the lift coefficient at an angle of attack of 3°. During hover, the horizontal wing in the tiltrotor configuration acts as an aerodynamic obstruction, inducing a partial ground effect that reduces local induced velocity and generates an asymmetric high-thrust region. Meanwhile, the impinging downwash causes a fountain effect, producing a download force equivalent to 14.69% of rotor thrust. A parametric analysis of five tiltwing schemes revealed tilting the 0.3R-0.9R wing segment as the critical design intervention because it alleviates downwash blockage, suppresses the fountain effect, and reduces download forces by 81.79%. Although the relief of the partial ground effect marginally reduces rotor thrust by 5.34%, it improves the net hover aerodynamic efficiency. This study reveals mechanisms of rotor wake enhancement and download interference in eVTOL multimode flight, which indicates that suppressing fountain effects is a key factor for improving hover efficiency.

Small-scale rotor design must balance hover efficiency and acoustic performance; however, costly aeroacoustic evaluations make multi-objective optimization computationally demanding. This study develops a surrogate-assisted framework using eight radial basis-function variables to parameterize spanwise chord and twist variations. Aerodynamic loads are evaluated with a reformulated vortex-particle method, while acoustic models estimate tonal and broadband noise. Baseline validation results in a 3.1% thrust coefficient error and captures the principal acoustic directivity trend. Gradient-boosted regression trees guide adaptive sampling, with candidate designs required to retain at least 95% of the baseline thrust coefficient. A total of 304 direct evaluations identify a 16-design thrust-feasible Pareto front. At 5400 RPM, the maximum-FM design improves FM by 11.31% while reducing OASPL by 1.06 dB, whereas the minimum-noise design reduces OASPL by 2.97 dB while increasing FM by 3.00%. Thrust-matched reassessment confirms that these performance benefits are maintained with lower shaft-power requirements. The improvements are primarily the result of the selective spanwise redistribution of thrust and torque rather than uniform unloading; the minimum-noise design shifts loading inboard and weakens the outer-span wake, whereas the maximum-FM design increases thrust while limiting torque growth and produces stronger downstream momentum transfer.