Preliminary design of ultra-lightweight HALE configurations with high flexibility

Abstract

High Altitude Long Endurance (HALE) Unmanned Aircraft Vehicles (UAVs) are part of a new concept of "pseudo-satellites" for low-cost surveillance and communication competence. Stratospheric flight requires high aspect ratios concepts and high-lift airfoils. Moreover, new propulsion concepts must be considered in order to maintain long endurance flight. A brief study over the state on art of regulatory aspects for civilian UAVs is performed at the beginning of the work to take knowledge of the actual state in Europe and Germany. The aim of this study is to develop different HALE UAV design concepts in order to study influence on aspect ratios and different aircraft configurations, considering conventional, wingbody and canard concepts. With this, conceptual design in cruise segment is performed. Geometric and weight layout is obtained from statistical data from solar powered UAVs as well as sailplanes, characteristic by its high aspect ratio. Propulsion estimations are considered from power needed to fly, without taking into account avionics. Batteries are sized with "amper-per-hour" method, while solar panels are estimated considering the wing surface. Calculation in aerodynamics is included, as well as the study of steady flight, in which performance is realized. Lastly, a study in loads is performed through the computation of the flight envelopes. Once calculations are performed, a comparative study within the different concepts is performed with the objective of choosing one combination of airfoil, aspect ratio and concept. It will be seen that aspect ratio study leads to tendencies with no definite value, whereas wingbody concept is undoubtedly the concept with more advantages. Finally, the chosen concept is submitted to numerical calculations with Nastran with two main objectives, which are validation of the code and further load calculations.