Theoretical model proposal on direct calculation of wetted area and maximum lift-to-drag ratio

Abstract

Purpose As measuring flight performance by experimental methods requires a lot of effort and cost, theoretical models can bring new perspectives to aircraft design. This paper aims to propose a model on the direct calculation of wetted area and L/D-max. Design/methodology/approach Model is based on idea that the wetted area is proportional to aircraft gross weight to the power of 2/3 (W-g(2/3)). Aerodynamic underpinning of this method is based on the square-cube law and the claim that parasitic drag is related to the S-wet/S-wing. The equation proposed by Raymer was used to find the L/D-max estimate based on the calculated wetted area. The accuracy of the theoretical approach was measured by comparing the L/D-max values found in the reference literature and the L/D-max values predicted by the theoretical approach. Findings Proposed theoretical L/D-max estimate matches with the actual L/D-max data in different types of aircraft. Among the conventional tube-wing design, only the sailplanes have a very low S-wet/S-wing. The S-wet/S-wing of flying wings, blended wing bodies (BWBs) and large delta wings are lower than conventional tube-wing design. Lower relative wetted area (S-wet/S-wing) is the key design criterion in high L/D-max targeted designs. Originality/value The proposed model could be used in wing sizing according to the targeted L/D-max value in aircraft design. The approach can be used to estimate the effect of varying gross weight on L/D-max. In addition, the model contributes to the L/D-max estimation of unusual designs, such as variable-sweep wing, large delta wings, flying wings and BWBs. This study is valuable in that it reveals that L/D-max value can be predicted only with aspect ratio, gross weight (W-g) and wing area (S-wing) data.