Flight Mechanical Design and Analysis of a Solar-Powered High-Altitude Platform

Abstract

The German Aerospace Center (DLR) is currently developing a high-altitude platform system in the context of the DLR-internal project HAP. The system includes the high-altitude platform itself, a flight operation concept and a ground control station. The underlying high-altitude platform is a solar-powered fixed-wing aircraft designed to be stationed in the stratosphere for several days and to carry payload for earth observation missions. The project HAP addresses the complete design process of the aircraft, from conceptual studies and detailed design up to the construction, flight test campaigns and the final operational clearance. This paper deals with the preliminary design phase of the aircraft. For this purpose, it briefly describes all disciplines involved and gives an insight into their methods used. Subsequently, it presents an assessment of the aircraft in terms of stability and control characteristics. Doing so, it first deals with a dynamic stability investigation using a non-linear 6-degrees-of-freedom flight dynamic model using a simple quasi-stationary approach to account for flexibility, in which the aerodynamic derivatives are given for different airspeed-dependent flight shapes. Based on this investigation, design changes are made. Second, it presents a control surface design choice process for the aircraft based on a defined flight mechanical requirement that is used for the design of the aircraft in lieu of those of the typical certification standards. This requirement addresses the necessary control authority to counteract the aircraft's responses due to gust encounters in order to not exceed afore-defined limits and to prevent the aircraft from entering a flight condition that it cannot be recovered from. Finally, an exemplary offset correction manoeuvre is simulated in order to demonstrate the aircraft's operability in real-flight scenarios.