Rotorcraft Fuselage Sizing Methods in the Open-Source Framework PANDORA

Abstract

Rural depopulation resulting in altered hospital coverage, new challenges for medical evacuation during military operations, and increased off-shore activities of energy suppliers, lead to changed requirements of helicopter emergency medical services (HEMS). Recently, interest has significantly increased to overcome the traditional physical limitation of flight speed by providing helicopters with auxiliary propulsive devices, so-called compound rotorcraft. In order to assess these novel rotorcraft concepts, an integrated, multidisciplinary, and automated design procedure has been established at the German Aerospace Center (DLR) using the data model CPACS (Common Parametric Aircraft Configuration Schema). The design processes of rotary- and fixed-wing aircraft highly resemble each other: In the first stage of a typical aircraft design process, the conceptual stage, basic characteristics are established that typically consist of e.g. outer dimensions (i.e. its aerodynamic shape), flight performance, mass breakdown, etc. At this stage of the design process mostly fast, analytical, and statistical methods are applied featuring many simplifications. In the subsequent preliminary design phase the detail level increases. The continuously growing computational power has enabled design engineers to integrate higher fidelity methods at this design stage. At the DLR Institute of Structures and Design, tools have been developed in the last couple of years that use finite element (FE) methods to size aeronautical fuselage structures according to static load cases to allow a more precise prediction of the structural mass, and thus in turn to a different maximum take-off mass which is considered as a major design parameter. Although based on the same framework approach, these FE based tools developed for preliminary sizing of rotary- and fixed-wing fuselages diverged over the years due to different project requirements, such as specific modeling aspects, different syntax for the involved FE solvers, or different design emphases. These issues resulted in different tools to generate FE meshes and to conduct analyses with some inconsistencies between the individual tools. In order to unify the tools, the development of the software framework PANDORA (Parametric Numerical Design and Optimization Routines for Aircraft) has been started at DLR in 2016 from scratch using the Python programming language. The key idea behind PANDORA is to generate one common software framework to model, analyze, and size both fixed- and rotary-wing fuselage structures. Particular focus in the development of PANDORA lies in the use of dedicated open-source packages and the interchangeability of different commercial and open-source FE solvers. This paper first shows the approach of the PANDORA toolbox for fixed-wing aircraft. Then, the process of adapting respectively integrating specific modeling and analysis methods for rotorcraft fuselages into the new framework is shown. Concluding this article an outlook of new enhancements into PANDORA is given highlighting its benefits in the context of preliminary structural analysis of novel rotorcraft concepts.