Verification and Clearance of a Flight Control System for High Altitude Long Endurance Aircraft

This paper presents a three-step clearance process for flight control software. As a novelty, grid-based non-linear closed-loop simulation testing has been added within a unit test framework as a validation step. This new feature allows developers to assess compliance with requirements quickly on a very detailed level. Within this work, the extensive testing and the validation implemented for this unit testing framework are presented. Based on high-fidelity closed-loop simulation scenarios, the unit tests, including actuator and sensor dynamics, cover all nominal flight, disturbance, and fault conditions. Furthermore, test coverage is addressed and investigated as an indicator of the test framework quality. In the second and third steps, optimization-based clearance methods and Monte-Carlo simulation techniques assess the performance of the flight control laws in the presence of a worst-case aerodynamic parameter variation. The Monte Carlo simulation validates the worst-case scenario over the entire flight envelope and for all gust disturbance scenarios considered. The presented application example is the German Aerospace Center's High Altitude Long Endurance (HALE) platform HAP-ALPHA, which is used to illustrate all steps of the presented validation and verification (V &V) framework. The design and development of the flight control software development for the HALE aircraft has been discussed in previous work and has the novelty of considering the aircraft's flexible modes for the primary flight control design. The V &V framework assures compliance with functional, performance, and software quality requirements, allowing entry into an aircraft's flight testing phase.