Initial Assessment of Stability and Controllability in the Early Stage of Combat Aircraft Design

Abstract

This paper presents a methodology for the assessment of stability and controllability of combat aircraft in the early stage of aircraft design. Requirements on stability and controllability are driving factors for the design of control effectors of a combat aircraft to ensure sufficient control power throughout its intended missions. A theoretical background on stability and controllability requirements is outlined. Prerequisites such as aerodynamic data sets and a flight dynamics model are addressed. A workflow providing high-fidelityaerodynamic data by means of multi-fidelity surrogate modelling is explained. It contains the essential steps of generating such aerodynamic data sets already during conceptual and preliminary design. Based on aerodynamics, propulsion and mass properties a flight dynamics model for six degrees of freedom aircraft simulations is applied for the stability and controllability assessment. Furthermore, a software tool has been developed which calculates the available control power for comparison with the requirements. For demonstration of the methodology, a generic triple-delta combat aircraft called DLR Future Fighter Demonstrator (DLR-FFD) is introduced. It is being developed within the DLR project Diabolo and contains an initial control concept to be investigated. Additional details on the requirements defined for the DLR-FFD are given. Finally, obtained results are assessed and discussed in terms of aerodynamic characteristics and with respect to the given stability and controllability requirements. A conclusion of the analysis is drawn in terms of the investigated control effectors. The analysis revealed that both longitudinal and lateral/directional controllability requirements are not yet fully met and the aircraft design has to be reviewed.