A first-order potential flow panel method is used in the present work to calculate aerodynamic yaw torques and other parameters involved in the turning performance of a stratospheric lighter-than-air airship. A specific mesh is generated to model the airship geometry in order to solve the Laplace potential flow equation by a sum of source and doubled distributions on the boundary, using a mix of Neumann and Dirichlet boundary conditions. As a result, it is possible to simulate the effect of the rudder and elevons within their angular range at different flight conditions. Air flow rotation is included in the boundary conditions to simulate airship yaw rate. Thus, the result of the model includes not only yaw momentum but also its derivative with respect to yaw rate and the lateral force. They are contrasted with a series of tests carried out in a wind tunnel for a stratospheric airship model and with the literature. Despite of the simplicity of the potential method (5 s execution for a 6000-cell mesh) compared to a more complex CFD simulations, the conclusions demonstrate that the correlation between numerical and experimental data is high enough to provide valuable performance insights during the design process, showing a considerable reduction of the necessary computational resources. A 30-m ECOSAT model with proper fins can turn with a steady radius of 50 to 60 m.

The shape of a conventional airship’s envelope is usually an axisymmetric body of revolution. Previous numerical and experimental studies have indicated that at zero angle of attack, the flow over such shapes is either fully turbulent or transits from laminar to turbulent at nearly half of the envelope’s length. In most numerical investigations of such bodies, k- ɛ or k-ω-SST turbulence models are used. In recent studies, a four-equation k-ω SST-LM transition turbulence model has been proposed and shown to predict transition on a flat plate quite well. In this study, the transition of the laminar boundary layer to the turbulent boundary layer over the bodies of revolution of airship envelopes is investigated using the k – ω SST – LM transition turbulence model. The results obtained in the numerical analysis are validated with the data available in the literature. It is seen that the two-equation k-ω SST Turbulence Model is not able to capture the laminar to turbulent transition, whereas the four-equation k-ω SST-LM transition turbulence model can capture it quite well.

In this paper, we present the computational investigation on the aerodynamic characteristics of the Leading-edge protuberanced (LEP) fins subjected to Reynolds number in the range of 102 to 106 for wide range of angles of attack between 0o to 45o. The aerodynamic force coefficients like coefficient of lift (CL), coefficient of drag (CD) and surface pressure distribution with respect to chord-wise position (x/C) for the modified leading-edge protuberanced models at different Re is analyzed in detail. Assessment of aerodynamic characteristics of modified leading-edge protuberanced fins under different Reynolds number is one of the immediate issues which needs to be addressed to bring such novel design in to airships and different kinds of LTA platform.

Complex engineering projects require compartments from different engineering fields to work in close contact and exchange data from their workflows and specialized software tools regularly. Common data models are an immanent feature of systems engineering applications that can be used to reduce the number of interconnections between software modules. Using common open source data structures in airship design helps engineers evaluating and visualizing early designs using several methods. In the presented paper, we used the Extensible Markup Language (XML) data structure Common Parametric Aircraft Configuration Schema (CPACS) and associated high-level software libraries by German Aerospace Center (DLR) for a design optimization. The design optimization maximizes payload of a 15 t airship by its hull shape. Handbook methods for estimating weights and drag as well as a brute force algorithm are used in the design optimization. The result shows an explicit optimum of the design. With the experiences made, we developed an updated version of CPACS, allowing the definition of an additional vehicle category named 'dirigible'.

The transportation of heavy loads is the ultimate yet to be achieved mission for airships. Several other cargo is being transported by airships successfully. Objective of this research is focused on how load exchange with near equilibrium airships can be performed. Proposed solutions aiming at similar targets have not demonstrated successfully yet or did not meet certification requirements. We introduce a viable approach and describe the procedure, that resembles helicopter sling load operations, step-by-step. Demonstrating its viability is achieved by building a suitable airship model and performing model flight tests. The research identifies weaknesses and critical points in load exchange procedures. Setting up the flight test environment, controller and suitable airship configuration is the first step performed. Operational challenges during the flight missions result in learnings and observations of importance for performing such flight tests. Observations regarding maneuverability of the model help in improving the propulsion and controller configuration of heavy load airships.

This study aims to present a Multidisciplinary Design Optimisation (MDO) algorithm for the automatic sizing and design of an Unmanned Lighter-Than-Air (LTA) platform, given its mission requirements. The mission in question consists of a territorial mapping, made possible through the implementation of several remote sensing onboard systems. Once assigned the parameters of the mission as inputs, the algorithm, through a process of iterations, returns the optimal sizing of the airship, shows the distribution of all the systems’ masses, and chooses the preferable energy system between the two considered (fuel cells or batteries). Moreover, a sensitivity analysis on the main variables allows to examine how the variation of each of the parameters of the mission affects the distribution of the masses in the airship, and therefore how the optimal design and sizing change. Finally, further studies on the energy systems are presented, to verify the convenience of one option above the other one as a function of the distance from the mission location and the survey area.

In this contribution we propose two novel concepts of an adaptive ultra-light high-altitude aerostats. Both proposed concepts enable changes of aerostat volume and shape during the flight, which results in the possibility of vertical motion control. The first proposed construction is telescopic aerostat with multi-segmented construction and controllable segments’ couplings. In turn, the second construction is based on a self-deployable tensegrity structure equipped with prestressed and tensioned elements of controllable lengths. Basic advantages and features of the proposed design are shown using dedicated numerical examples.

Helium filled aerostats can be lifted by the traditional hot-air balloon (SKYLAB), in the compact form, and then, after reaching some starting level , helium can be pumped into the aerostat (using storage tank with a compressed gas), starting its autonomous mission. Optimal design process of aerostats dedicated to perform determined mission (between the altitudes and ) will be discussed with preliminary experimental verification process, based on scaling procedure of aerostat mini-model, so-called CANDY, and fly-tests on SKYLAB will be proposed.

Titanium dioxide has sustained a vital role over the past few years as the most widely used material among various commercial inorganic UV absorbers due to its chemical stability, low cost, and good UV protection. TiO2 and numerous organic UV absorbers have been explored to be incorporated in TPU (Thermo-Plastic Polyurethane) based films for coated and laminated textiles useful for aerostats and airships as LTA (Lighter than Air) hull material. TPU films based on TiO2 were prepared using commercially available UV additives (Hindered Amine Light Stabilizer, benzotriazole-based UV absorber, and Antioxidant) at various concentrations. Prepared films were optimized to achieve the best possible combination of all UV enhancing materials and assessed for artificial weathering tests. UV-VIS spectrum and infrared spectrum were obtained. Characterization of material and another testing such as Tensile testing, Yellowness index, UPF, and gas barrier properties of prepared TPU/TiO2 films were determined after every 100 hours. TPU/TiO2 films that incorporate UV absorbers and other additives accomplished the requirement for improved resistance against UV and photooxidation.

The aim of the present study was to develop a continuous laminated material system that could be very lightweight, having very high strength, extremely low helium permeability. In this paper, a multilayered laminated structure has been designed, prepared, characterized, and developed using high-performance fabric including para-aramid (Kevlar) fabric as a strength layer due to high strength-to-weight ratio and excellent mechanical properties in order to achieve a lower aerial density material with the help of PU based adhesive and different polymeric films including PVF film as a weather resistance layer and BOPET film as a gas barrier layer. The artificial weathering of all the prepared specimens was carried out in a from 100 h to 400 h machine in order to decide the approximate durability of the laminated samples. The prepared unexposed and exposed laminates were subjected to various mechanical and physicochemical characterizations such as tensile testing, cut slit tearing testing, t-peel testing, helium gas permeability testing, and UV protection factor testing. It has been investigated that the helium gas permeability of Kevlar-based laminate (K5 laminate) was 0.04 L/m2/day which is extremely low and there was no significant change in tensile properties from fabric to laminate, even after 400 h of UV exposure. The tearing strength of laminates was significantly enhanced than that of fabric due to the greater flexibility of PU adhesive. Therefore, using this type of multilayered laminated fabric would be the potential, effective and new alternative for the envelope of high-altitude airship applications.

The high interlaminar strength in the multilayered structure is one of the crucial parameters of lighter than air (LTA) envelope material. In this work, different Polyurethane (PU) based adhesives were functionalized and their synergistic effect of adhesion with fabric has been studied. Three types of PU based adhesives were used which were based on two-component systems that was further functionalized with carbon black and UV-additives and the peel strength was determined. PU based adhesives were applied on a substrate and laminates were prepared and the gram per square meter (gsm) of the adhesives was optimized. The Tensile strength, UV resistance property of the functionalized adhesives were improved and the UPF of the adhesives film was measured. Thermal properties and stability of the functionalized adhesives films were analyzed through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The crosslinking and the interaction between the carbon black and PU based thermoset adhesives was analyzed through Fourier transform infrared spectroscopy (FTIR). Also, the prepared adhesive films were exposed to artificial weathering for 200 hr. Functionalized PU adhesives films shows excellent weather resistance behavior as compared to neat adhesive films due to better UV resistance property of carbon black.

This study investigates the influence of the artificially accelerated weathering test on the degradation behaviour of thermoplastic polyurethane (TPU) films. Accelerated artificial weathering test parameters were specially designed to simulate outdoor natural exposure parameters with higher UV radiation exposure. Artificial weathering tests were carried out in a laboratory weatherometer and changes in mechanical properties, chemical structure and morphology were studied. In this study, two types of polyether based aromatic and aliphatic TPU films were exposed for 500 h. The result shows that exposure to UV radiation affects the key properties like breaking strength, helium gas barrier and surface properties of TPU films. The mechanical strength reduces as the irradiance time is increased. The SEM and AFM analysis reveal that the film surface that was exposed to irradiance become rough and cracks on the surface were observed. The FTIR analyses of the exposed film prove that chemical structure changes due to the formation of the polyurea group. It was found that aromatic TPU gets crosslinked after 300 h exposure, however, in aliphatic TPU long molecular chains break into shorter chains, the number of chain scission increases with increasing exposure time.

In this paper, the aerodynamic model parameters (stability derivatives) of the aerostat is investigated based on a CFD based approach. The stability derivatives due to the translational motion of the aerostat are considered for the analysis in this paper. The extraction of the stability derivatives involves the simulation of the oscillations of the aerostat along the vertical direction (heave motion) and axial direction (surge motion). A forced sinusoidal oscillation is used for the simulation of the aerostat, and one stable period of oscillation is taken for the derivatives extraction. Four different aerostats are considered for the current study with four different angles of attack. Zhiyuan aerostat, HAA aerostat, NPL aerostat and GNVR aerostat are the aerostats considered for this study. The stability derivative results obtained for the four aerostats are analysed and compared with respect to their geometrical features. The dynamic stability derivatives of the Zhiyuan aerostat suggests its superiority among the four aerostats considered.

Dynamic instabilities often impair the operations of a tethered aerostat (such as supporting antennas and/or aerial platform), especially during the strong wind conditions. Effect of various geometrical parameters on longitudinal stability boundaries of an aerostat tethered in a steady wind is presented in this paper. The mathematical modeling used for stability analysis of the tethered aerostat includes buoyancy forces, apparent mass terms and static forces resulting from the tether cable. The effect of variation of geometrical parameters on longitudinal stability boundaries of the tethered aerostat has been presented graphically. The presented analysis and a judicious/ feasible choice of various geometrical parameters of the tethered aerostat can be utilized to design a new aerostat that can remain stable for wide range of wind speeds.

This paper presents the design of adaptive fault-tolerant control for a stratospheric airship model with actuator faults. First, linear airship dynamics is derived from the nonlinear airship model. Derivation of post-fault airship model including various actuator faults and external disturbances followed by controller stability analysis of adaptive fault-tolerant control is presented. Simulation results are presented for actuator efficiency loss and actuator bias fault, and compared with reference state trajectories. Results show efficacy of the proposed adaptive controller in following the reference trajectory with desired transient characteristics in the presence of actuator faults. 

This paper describes design and development of an integrated Guidance, Navigation, and Control (GNC) algorithm for smooth navigation of an airship following a series of planar waypoints for surveillance applications. The guidance algorithm employed in this study is a look ahead based steering guidance law which provides the required guidance command to the controller for executing the target mission. The command signal generated by guidance law is based on the airship current location relative to the next target waypoint. Two different control architectures are used in the GNC algorithm in order to execute the guidance command and carry out the path following mission. A Proportional-Integral–Derivative (PID) law based outer loop kinematic controller is designed to control airship attitude/orientation and a Linear Quadratic Regulator (LQR) based inner loop optimal controller is designed to control the airship’s speed and angular rates. Performance and robustness of developed GNC scheme are evaluated in MATLAB® based simulation environment for two different flight scenario. Results show that an optimal path following trajectory is obtained with minimum deviation from the given target waypoints.

Stabilizing the remotely operated hybrid VTOL tilt rotor unmanned aerial vehicle that has an envelope of gas particularly installed to provide hydrostatic buoyancy force to generate lift, with a payload bay equipped with sensors and electronic components attached to the envelope and having a pair of wings extended on both the sides of the bay to generate lift through motion as well act as a stabilizing surface, and the thrusters pivoted at wing tip would be tilted with powerful servo motors to provide vertical takeoff and landing capabilities. This manuscript deals with stabilizing the undamped forces and moments using automatic control system. Mathematical modeling of equations would be framed based on the obtained kinematics of flight that would be converted to autopilot codes in MATLAB. The MATLAB results further determines the stability of the designed tilt rotor Plimp Unmanned Aerial Vehicle.

Maneuver design is a vital prerequisite for autonomy in aerospace guidance and control. It ensures system safety by analyzing the feasibility of the proposed maneuvers. This paper demonstrates a holistic approach to maneuver design by emphasizing its feasibility with consideration on the complete dynam-ics of the system and its constraints. Computational bifurcation analysis is em-ployed to generate a sequence of trim solutions based on specified state and con-trol constraints that define a stipulated maneuver. Implementing this approach on a stratospheric airship model helps attempt a few of its challenging and interest-ing facets like autonomous hovering, ascending, and descending by gauging its performance and formulating realistic maneuvers pertaining to the imposed lim-itations on the lateral excursion, control and state constraints. The effectiveness of the proposed maneuvers is then evaluated using numerical simulations with computed control schedules in an open-loop.