Due to the high aspect ratio and low induced drag of aircraft with strut-braced wings, they are being extensively studied due to their fuel-saving potential. This thesis aims to expand the fundamental knowledge in the design of aircraft with Strut Braced Wings (SBW) by achieving the following objectives.

The objectives of this thesis are twofold, with their primary focus on evaluating the effect of changing the typical design variables for an SBW, such as the wing span, root chord, spanwise strut attachment location, wing taper ratio, wing sweep and engine location on the aerodynamics, weights and performance of an SBW. The first objective was to evaluate the significance of including the propeller slipstream effects in the preliminary stage design optimisation of a low-speed, short-range SBW. This aligned with the hypothesis that the performance of an SBW could be enhanced by using swirl recovery. The second objective of this thesis was to investigate the sensitivity of various design variables to the aircraft’s fuel burn and other performance metrics at the optimum SBW design.

A Design of Experiments (DOE) approach was used to explore the design space involving the typical influential SBW design parameters. The geometry and mesh files were created using OpenVSP for every DOE point. This was followed by the aerodynamic analysis in a panel method-based software called Flightstream, which could capture the relevant aerodynamic flow phenomena with reasonable accuracy. The aerodynamic analysis was performed twice- first without considering slipstream effects and second by simulating them. Regression-based analytical equations, particularly designed for the weight estimation of the wing and strut, were used from the literature. Empirical equations from FLOPS were used for the rest of the aircraft components. The performance of the SBW was calculated iteratively using the Breguet range equation along with a few modifications. All the SBW designs were constrained by a maximum wing loading criterion.

From two sets of the DOE results (with and without propeller effects), it was observed that the two optimum SBW designs were identical in terms of external geometry and performance. A deeper investigation revealed that the variation in the spanwise engine positioning (to maximise the swirl recovery) resulted in a marginal change of the induced drag (less than two drag counts). It was concluded that the propeller slipstream effects could be excluded from the preliminary stage, design optimisation of a propeller-powered, short-range SBW to reduce computational expense. However, the results should be treated with a pinch of salt due to the limitations of panel methods. Moreover, the SBW was optimised only for cruise, not for other flight phases such as take-off and climb, which may benefit from swirl recovery.

Finally, a sensitivity analysis was performed to evaluate the trends in the performance metrics, such as fuel burn, lift-to-drag ratio, wing loading and maximum take-off weight when subjected to variations in the design variables at the optimum. The impact of the fuel burn was quantified, while the other performance metrics were qualitatively answered. The research findings revealed that certain design variables had a greater influence on fuel burn than others when varied by ±10% w.r.t their optimum value...