Preliminary Design Optimization of an Amphibious Aircraft

Abstract

An amphibious aircraft combines the speed and range benefits of a conventional aircraft with the ability to land and takeoff on open water. There are other appealing factors to operating an amphibious aircraft including convenience, the ability to operate without a hard surface runway and additional safety for overwater operations. These factors, however, all come at a cost and impact the design of the aircraft. To examine these tradeoffs, common design and optimization methods were applied to the conceptual design of an amphibious aircraft and then compared to wind tunnel results of that design. In this study, a hypothetical troop and cargo transport aircraft mission profile was selected. A sizing program was developed to create an aircraft geometry and evaluate its performance. This code was written to account for many different aircraft criteria, including tail configuration, wing and fuselage geometry, and method of water operation (floats, hydrofoil, boat hull, etc.). The sizing code was first validated on several classes of existing aircraft. It was then run in conjunction with a hybrid, particle swarm-simplex optimizer to find a configuration for the hypothetical transport aircraft with minimum overall weight. The optimized design was tested in Auburn University’s subsonic, 3 ft. x 4 ft. wind tunnel. The model was run through a battery of tests including measuring the forces and moments, and surface flow visualization. Runs were made at various angles of attack and sideslip angles. The testing included cases with several different control surface deflections. Analysis was also performed on the aircraft using Athena Vortex Lattice and Orca3D to determine stability in flight and while on water. Results of the testing were used to validate the performance parameters estimated by the design code.