Lighter Than Air Activities at ONERA : A Comprehensive Overview
Creators: name:  P. TAILLANDIER 
name:   D. FARCY 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: SYSTEM INTEGRATION
AERONAUTICS

description: Lighter than Air (LTA) technologies are experiencing an important revival, which can be seen by the number of LTA programs currently in development worldwide. This old-fashioned aeronautical solution truly stands for a very promising alternative from an economical point of view, thanks to its natural low energy consumption. Another great advantage of buoyancy is to offer the ability to perform low speed even stationary flights. However LTA vehicles suffer from serious disadvantages: weakness to adverse weather conditions, poor maneuverability, fragile structure and very demanding ground handling/ ground proximity operations. Two main applications are envisioned, which are heavy lift transportation, observation, surveillance. Great perspectives are anticipated with the integration of recent technological breakthroughs (in terms of structures and materials, simulation, guidance and control, hybrid/full electric propulsion). ONERA has been working on LTA subjects for the last 10 years, partnering with the main French actors of the domain. ONERA has been deeply involved in many aspects such as overall design, flight modeling, guidance/control laws, aerodynamics and more recently environmental conditions (lightning, EM Compatibility, icing, acoustics, aerology,). The purpose of this article is to provide a comprehensive review of the main results achieved by ONERA. ONERA has been involved in the flight modeling of LTA systems, using its own LTA flight simulation tool, including Guidance Navigation Control (GNC) module. This actually implies to model at proper level, besides traditional components of an aeronautical simulation, gas management systems with eventually thermal/thermodynamics aspects, ballast management, cables systems (for load transfer, tethered balloons) and mooring systems. On GNC aspects, ONERA has developed dedicated laws (up to a Critical Design Review level) to address cruise phases as well as more specific hover or station keeping using more advanced techniques. ONERA has developed hull aerodynamic models combining both experimental (wind tunnel) and numerical (CFD) approaches. ONERA led several wind tunnel campaigns within the frame of LTA programs. LTA aerodynamics are indeed very specific because it is desirable to study the full domain of aerodynamic angles. Moreover, damping coefficients and added masses shall be assessed thoroughly. An innovative approach to set up a methodology to create an aerodynamic model that takes into account local spatiotemporal variations of airspeed has been validated. All these models are compliant with flight model so that dedicated research studies in guidance and control in closed loop as well as overall performances assessment can be conducted later on. ONERA has added some research activities dealing with environmental conditions: Lightning Direct Effects, Electromagnetic compatibility, Icing, Acoustics and Meteorology. The goals are both to investigate on specific issues linked with LTA applications and to integrate the typical constraints linked with environmental conditions as soon as possible in the design process. ONERA perspectives of work on LTA subjects are actually broad in direct continuation of what has been already accomplished. The next step is the validation and the calibration of these models with flight data, hoping that full scale prototypes will fly in the near future. Some additional activities are anticipated as path planning or FDIR using IA algorithms, or Structure Health Monitoring. On all these topics, a dedicated research work will be needed as LTA applications reveal very different and traditional aeronautical engineering solutions are often not suitable.