Abstract
The paper presents the derivation of a new equivalent skin friction coefficient for estimating the parasitic drag of short-to-medium range fixed-wing unmanned aircraft. The new coefficient is derived from an aerodynamic analysis of ten different unmanned aircraft used for surveillance, reconnaissance, and search and rescue missions. The aircraft is simulated using a validated unsteady Reynolds-averaged Navier Stokes approach. The UAV’s parasitic drag is significantly influenced by the presence of miscellaneous components like fixed landing gears or electro-optical sensor turrets. These components are responsible for almost half of an unmanned aircraft’s total parasitic drag. The new equivalent skin friction coefficient accounts for these effects and is significantly higher compared to other aircraft categories. It is used to initially size an unmanned aircraft for a typical reconnaissance mission. The improved parasitic drag estimation yields a much heavier unmanned aircraft when compared to the sizing results using available drag data of manned aircraft.
Highlights
Conceptual aircraft design is a multidisciplinary optimization problem
These UAVs have take-off masses from 15 kg up to about 700 kg, and they are often used for reconnaissance, surveillance, and search and rescue missions
They are sometimes termed shortrange (SR) to medium-range (MR) UAVs, and referred to as “tactical UAVs” [4]. They are named SMR UAVs in this publication. These UAVs are larger than micro and small UAVs, where aerodynamic aspects are of minor importance, but they are significantly smaller than Medium-Altitude or High-Altitude Long Endurance (MALE/HALE) UAVs, where manned aircraft drag estimations might be used [5]
Summary
Conceptual aircraft design is a multidisciplinary optimization problem. The design routine is divided into several sub-models that are responsible for estimating the new aircraft’s properties, including weight, propulsion, cost, or aerodynamics. They are named SMR UAVs (short-to-medium range) in this publication These UAVs are larger than micro and small UAVs, where aerodynamic aspects are of minor importance, but they are significantly smaller than Medium-Altitude or High-Altitude Long Endurance (MALE/HALE) UAVs, where manned aircraft drag estimations might be used [5]. In such SMR UAVs can be seen as the lightest UAV class for which aerodynamic aspects are critical, and their sizes and shapes dictate different aerodynamic behaviour compared to heavier aircraft.
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