Comprehensive Optimization of the Unmanned Tilt-Wing Cargo Aircraft With Distributed Propulsors

Abstract

The unmanned tilt-wing cargo aircraft using distributed propulsors is an emerging aircraft significantly different from traditional types. This paper proposes an aerodynamic, propulsion, noise, weight integrated optimization design method for this new aircraft. The method consists of several functional modules specially developed or adjusted targeting the aircraft's characteristics, such as the boundary state analysis, propeller/rotor oblique inflow analysis, waked wing analysis, propeller/rotor noise evaluation, multi-state wing mass analysis, multi-objective genetic algorithm optimization. It comprehensively considers the impact of various complex factors on the optimization results, such as the impact of distributed propulsors on the wing aerodynamics, the effect of wingtip propellers on the induced drag reduction, the coupling between wing aerodynamics and structure, the propeller/rotor aerodynamics optimization, and noise control. With the proposed method, it is possible to directly translate the top-level design requirements into the design scheme with the optimal specific system performance (such as the lowest delivery cost and highest delivery efficiency) at the very initial aircraft design stage, thereby greatly shortening the development cycle. A case study was presented. The results show that the introduction of distributed propulsors can increase the delivery efficiency by 28.2% and reduce the delivery cost by 15%; suppressing the wingtip vortices using propellers can increase the wing lift-drag ratio by 5.43%-6.65%; the slipstream generation efficiency and thrust efficiency are significantly different between different distributed propulsor schemes. To maximize the overall efficiency, it is necessary to balance between the slipstream generation efficiency and the overall thrust efficiency when optimizing the tilt-wing cargo aircraft. INDEX TERMS Convertiplane; Cargo aircraft; Unmanned aerial vehicle; Vertical takeoff and landing; Aircraft multidisciplinary optimization.

Blade Shape Optimization and Analysis of a Propeller for VTOL Based on an Inverse Method

“…The level flight mode, which includes climbing and cruising, is the main energy consumption mode for VTOL aircraft [23]. To rapidly achieve maximum energy efficiency in level flight, the inverse design method based on the Betz optimal theory was innovatively applied to the cruising stage.…”

“…An appropriate parametric method for the chord-length distribution can decrease the number of infeasible designs during the generation of the design variables. General parametric methods for the chord-length distribution of a propeller include direct interpolation [36], polynomial curve fitting [15] and Bezier curve fitting [23]. A new parametric method using a piecewise quadratic polynomial was put forward, as shown in Figure 12.…”

“…However, there are few similar works on tilt-wing or tilt-rotor aircraft, which is of importance to the safety of VTOL aircraft [22]. In addition, VTOL aircraft designed for a fast response have corresponding requirements for the maximum climb rate of vertical flight, which should also be considered in the design framework [23]. Regarding general propeller design methods, Hepperle [24] proposed an inverse design method for a minimum energy loss propeller based on the Betz theory [25] and the work of Charles [26], which were suitable for the case with a prescribed chord distribution.…”

Algorithm for Propeller Optimization Based on Differential Evolution

“…The relevance of propellers as a propulsion system has increased with the current growth in the production of unmanned aerial vehicles for various purposes around the world. The air propeller's design is an important part of aircraft design, beginning from the conceptual design stage [1]. An optimized propeller can significantly reduce emissions, improve acoustic response, and enhance performance [2].…”

“…Therefore, the use of the finite volume method is irrational because it requires large computational power. Some of the most commonly used propeller aerodynamic characteristics calculation methods currently are Blade Element Method (BEM), Blade Element Momentum Theory (BEMT), Vortex Lattice Method (VLM), and Computational Fluid Dynamics (CFD) [1,19]. For tip-loss correction, different methods are used [20], including the Goldstein function [21] and Glauert correction [22][23][24].…”