Pressure contour engineering for highly efficient ground effect flight

Abstract

Abstract

Introduction An ideal flight mechanism model reasonably approximates the efficiency of aerodynamic flight, similar to how ideal heat engines approximate what is possible with different engine designs. It is useful for modeling ground effect flight. The ideal model provides a benchmark against which vehicle prototype performances may be compared to rapidly assess design effectiveness; similar benchmarks have been absent to date. Methods The ideal flight mechanism model equation was derived from force and energy balances on aircraft in flight to preserve reversible losses. Data for the paper was calculated through computational fluid dynamics (CFD) to reasonable estimate aircraft performance. Results CFD performances of better performing airfoils and digital prototypes approach the lift-to-drag ratio (L/D) of the ideal mechanism model. The prominent operational parameter of the ideal equation model in ground effect flight is the ratio of the vertical perimeter area below the vehicle to the planform area. The variable is applicable for unifying two- and three-dimensional comparisons. Digital prototypes with aspect ratios less than 0.4 have lower L/D estimates than model projections, a finding identified for further study to better understand how to improve performance at low aspect ratios. Discussion Digital prototype performances were evaluated in three phases of flight: (a) takeoff, (b) cruising velocities, and (c) higher speed travel. For takeoff, hovercraft functionality may be used, but analysis indicates that wheeled suspension is more efficient. Cruising velocities operate most efficiently with ram effect lift generated in the lower cavity of the lower ground effect flight transit (GEFT) vehicle, which is capable of approaching model predictions. Vertical ducts with fans passing through the fuselage are analyzed to extend cruising travel conditions over a greater velocity range to maintain cavity pressures and sufficient lift. At higher speeds, lower lift coefficients are needed to maintain ground effect flight. Trailing-edge stagnation plates (i.e., spoilers) may be used to reduce drag under these conditions. Although jet aircraft travel at higher altitudes to reduce drag, ground effect vehicles may use stagnation plates to achieve higher flight efficiency.