Preliminary Engine Sizing for a Tactical Unmanned Aerial Vehicle

Abstract

An aircraft engine represents a concentration of weight, inertia, and gyroscopic forces that require accurate estimation, selection and integration for a safe and efficient flight operation.  This is more critical in tactical unmanned aerial vehicles and very small aircraft due to the severe effects of aerodynamic forces on their weight class.  Therefore, this article describes engine sizing for a Medium Altitude, Long Endurance (MALE) Unmanned Aerial Vehicle (UAV) using the matching plot technique. A conceptual framework of a conceptual UAV was modeled in an open Vehicle Sketch Pad (VSP) and the wetted area of major airframe components was measured. The consideration for drag estimation based on the wetted area includes the fuselage, wing, vertical/horizontal tail and landing gear. Each of these components was separately assessed for its contribution to the overall drag estimate and consequently aircraft performance. Thus, the Matching plot technique based on the aircraft performance was used in sizing the engine. This technique employs the use of flight mechanics theories to evaluate aircraft performance requirements which includes stall speed (Vs), maximum speed (Vmax), takeoff run distance (STO), maximum rate of climb (ROCmax), and service ceiling (hc).  The variation of power loading (W/P) with respect to wing loading (W/S), for all the parameters was plotted on a single grid. The acceptable regions and design points were determined based on the desired performance criteria.  This solution helps in ensuring that large power output is obtained per unit engine size and weight.  It also ensures a balanced distribution of aerodynamic forces.