Prediction of Maximum Lift Coefficient of Box-Wing Aircraft through the Combination of an Analytical Adaptation of the DATCOM Method and Vortex-Lattice Simulations

The present paper concerns the introduction of a mixed analytical-numerical method for the estimation of the maximum lift coefficient of box-wing aircraft in unflapped configuration. The analytical aspect is related to the adaptation of the method included in the United States Air Force Stability and Control Data Compendium (USAF DATCOM) by means of an approach built on the characteristics of the optimal lift distribution of the box-wing and implemented through simplifying assumptions. Since the formulation depends on parameters proper of the considered aircraft, numerical simulations are performed through a Vortex-Lattice Method to complete the input dataset. The method is first presented and then validated for the case of the 2-seater amphibious PrandtlPlane from the project “IDINTOS”, for which wind tunnel data are available. The method is then applied to two test cases for which CFD data are available: a 300 passengers mid-range PrandtlPlane, developed within the European research project “PARSIFAL”, and a regional hybrid-electric PrandtlPlane, object of study in the Italian research project “PROSIB”. Results are presented and discussed, also analyzing the links between the proposed method and relevant parameters of the box-wing design, such as taper ratios and wing loading repartition among the two wings.