Weight & Balance Estimation with Automated Structural Analysis for Subscale Flight Models

Abstract

Unconventional aircraft designs have the potential to lower the impact of aviation on emissions and climate as compared to conventional aircraft designs. However, the flight dynamics behaviour of such unconventional configurations must be carefully evaluated by studying Stability and Control (S&C) characteristics to design safe aircraft and mitigate risks in flight. Various methods, that are a combination of numerical and experimental methods, have been used in the literature to predict the Stability and Control (S&C) characteristics. Sub-scale Flight Testing (SFT) is one such method that can predict aircraft flight behaviour, especially in the case of unconventional designs for which legacy information is unavailable and wind tunnel tests can partially predict aircraft dynamics. In order to successfully use SFT, the Sub-scale Model (SM) used in SFT must be carefully designed such that the results of SFT can be scaled-up to predict full-scale flight behavior. Furthermore, the SM should be able to complete the required SFT mission safely (the model is trimmable, statically stable and dynamically stable throughout the flight envelope). Finally, the SM must be designed with a short leadtime, as the time available for SFT in the overall design cycle is limited. Thus, the design of sub-scale models is a multidisciplinary task. In this thesis, an appropriate methodology is identified and developed to design the structural components of SM, position Commercial Off-The-Shelf (COTS) components and estimate the mass, inertia and the associated Center of Gravity (CG) of the SM. These are important inputs to determine the flight dynamics behaviour of the SM. Secondly, the structural analysis capabilities are automated to ensure that the structure does not fail in flight under critical load conditions. To shorten the design lead-time, methodologies developed in this thesis are formalized using a Knowledge Based Engineering (KBE) system. This KBE application automates the estimation of the weight & balance of a SM, which includes software modules for structure generation, flight equipment selection and positioning and the automated pre/post-processing task for Finite-Element (FE) analysis. Such a KBE application enables structural studies for different SM scale sizes, design variables such as rib pitch or frame pitch, and load cases. This KBE application to estimate the weight & balance properties of the SM can be coupled with other disciplines such as aerodynamic analysis, flight dynamics toolbox, etc. as part of a Multidisciplinary Design Analysis and Optimization (MDAO) workflow to quickly design sub-scale models that can be used to predict full-scale flight behaviour. 
Three different case studies are performed to demonstrate the effectiveness ofthe methodology and the KBE application. Each case study predicts the different aircraft configuration namely, a conventional Citation II and two unconventional models being the Prandtl-Plane and the Flying V. The methodologies can therefore be used for future SFT activities and can help in successfully comparing the subscale aircraft model behavior to the full-scale aircraft behavior, thereby making Subscale Flight Testing a step closer to reality.