The Performance Assessment of a Small Lighter-Than-Air Vehicle for Earth Science Remote Sensing Missions

This summer, a lighter-than-air (LTA) drone was tested in Alaska to measure glacier bedrock fracture density and orientation. Five flights were made in low wind conditions, and the directional stability of the airship made it too challenging to control in flight to realistically acquire useful image sets. The directional stability of the airship, when compared to an actively stabilized consumer-grade quadcopter was inferior. Flight logs and GPS data from the GPS on the LTA drone were analyzed and a quantitative assessment of the observed instability was made. The yaw axis and pitch were analyzed, and the yaw axis instability was greater than the pitch axis instability. The source of this instability included the excessive sensitivity of the yaw thruster, and the inherent yaw instability of the blimp shape. An attempt was made to reduce the yaw instability by reducing the yaw motor size. The observed instability may have also resulted from external sources like wind gusts and the glacier microclimate. The analysis informed modifications of the LTA drone to make it more stable for glacier research, which were implemented and tested. The thrust output of the tail motor was reduced by 59%. This change was associated with a reduction in median heading variability of 47% between test flights before and after modification. The reduction was proven statistically significant at a 99% confidence interval. Also, recommendations for further modifications include the implementation of autonomous flight control and envelope optimization

Modélisation et Commande d’un Dirigeable Propulsé par la Force de Flottabilité

A new concept of airship without thrust, elevator or rudder is considered in this thesis. It is actuatedby a moving mass and a mass-adjustable internal air bladder. This results into the motion ofthe center of gravity and the change of the net lift. The development of this concept of airship ismotivated by energy saving. An eight degrees-of-freedom complete nonlinear mathematical model ofthis airship is derived through the Newton-Euler approach. The interconnection between the airship’srigid body and the moveable mass is clearly presented. The dynamics in the longitudinal plane is analyzedand controlled through a LQR method, an input-output feedback linearization, and the maximalfeedback linearization with internal stability. Thanks to maximal feedback linearization, an efficientnonlinear control is derived. In this process, modelling, analysis, and control are solved for specialcases of the airship, which become gradually closer to the most general model. The most constrainedspecial case reduces to a two degree-of-freedom system. It is shown that the basic properties of thistwo DOF mechanical system remain instrumental for the analysis and synthesis of advanced airshipmodels. These properties are far from being obvious from the most complex model. Through a singularperturbation approach, the superposition of the two control actions in the longitudinal plane andin the lateral plane is shown to achieve the control of the dynamics in three dimension.Un nouveau concept de dirigeable est considéré dans cette thèse. Une commande non linéaire est mise en oeuvre, fondée sur la linéarisation maximale de la dynamique

Aeronautical Engineering: A special bibliography with indexes, supplement 69

This bibliography lists 305 reports, articles, and other documents introduced into the NASA scientific and technical information system in March 1976

Proceedings of the Interagency Workshop on Lighter than Air Vehicles

Papers presented at the workshop are reported. Topics discussed include: economic and market analysis, technical and design considerations, manufacturing and operations, design concepts, airship applications, and unmanned and tethered systems

Aeronautical Engineering: A continuing bibliography with indexes (supplement 166)

This bibliography lists 558 reports, articles and other documents introduced into the NASA scientific and technical information system in September 1983

Robust Controller Design for an Autonomous Underwater Vehicle

Worldwide there has been a surge of interest in Autonomous Underwater Vehicles (AUV). The ability to operate without human intervention is what makes this technology so appealing. On the other hand, the absence of the human narrows the AUV operation to its control system, computing, and sensing capabilities. Therefore, devising a robust control is mandatory to allow the feasibility of the AUV. Motivated by this fact, this thesis aims to present, discuss and evaluate two linear control solutions being proposed for an AUV developed by a consortium led by CEiiA. To allow the controller design, the dynamic model of this vehicle and respective considerations are firstly addressed. Since the purpose is to enable the vehicle’s operation, devising suitable guidance laws becomes essential. A simple waypoint following and station keeping algorithm, and a path following algorithms are presented. To devise the controllers, a linear version of the dynamic model is derived considering a single operational point. Then, through the decoupling of the linear system into three lightly interactive subsystems, four Proportional Integral Derivative controllers (PIDs) are devised for each Degree Of Freedom (DOF) of the vehicle. A Linear Quadratic Regulator (LQR) design, based on the decoupling of the linear model into longitudinal and lateral subsystems is also devised. To allocate the controller output throughout the actuators, a control allocation law is devised, which improves maneuverability of the vehicle. The results present a solid performance for both control methods, however, in this work, LQR proved to be slightly faster than PID.É visível, a nível mundial, um aumento considerável do interesse em Veículos Autónomos Subaquáticos (Autonomous Underwater Vehicles - AUV). O que torna esta tecnologia tão atraente é a capacidade de operar sem intervenção humana. Contudo, a ausência do ser humano restringe a operação do AUV ao seu sistema de controlo, computação e capacidades de detecção. Desta forma, conceber um controlo robusto é obrigatório para viabilizar o AUV. Motivado por este facto, esta tese tem como objetivo apresentar, discutir e avaliar duas soluções de controlo linear, a propor a um AUV desenvolvido por um consórcio liderado pelo CEiiA. Para que o projeto do controlador seja possível, o modelo dinâmico deste veículo e respectivas considerações são primeiramente abordados. Com a finalidade de possibilitar a operação do veículo, torna-se essencial a elaboração de leis de guidance adequadas. Para este efeito são apresentados algorítmos de Waypoint following e Station keeping, e de path following. Para a projeção dos controladores é derivada uma versão linear do modelo dinâmico, considerando um único ponto operacional. Através da separação do modelo linear em três subsistemas são criados quatro controladores Proporcional Integral Derivativo (PID) para cada grau de liberdade (Degree Of Freedom - DOF) do veículo. É também projetado um Regulador Linear Quadrático (LQR), baseado na separação do modelo linear em dois subsistemas, longitudinal e lateral. É ainda apresentada uma lei de alocação de controlo para distribuir o sinal de saída dos controladores pelos diferentes atuadores. Esta provou melhorar a manobrabilidade do veículo. Os resultados finais apresentam um desempenho sólido para ambos os métodos de controlo. No entanto, neste trabalho, o LQR provou ser mais rápido do que o PID

Fourth Airborne Geoscience Workshop

The focus of the workshop was on how the airborne community can assist in achieving the goals of the Global Change Research Program. The many activities that employ airborne platforms and sensors were discussed: platforms and instrument development; airborne oceanography; lidar research; SAR measurements; Doppler radar; laser measurements; cloud physics; airborne experiments; airborne microwave measurements; and airborne data collection

Alocação de controle desacoplada rápida em sistemas de controle superatuados

Over-actuated systems usually require nonlinear control allocation methods to map Virtual Control Actions (VCAs) into Real Control Actions (RCAs). This process requires computational efforts sometimes not available on embedded robotic platforms. It is in this context that this work presents the design of an Quadrotor Tilt-Rotor (QTR) through a new concept of control allocation with uncoupled RCAs, where the initial nonlinear system is divided into partially dependent linear subsystems with fast and robust convergence. For this purpose, the RCAs are divided into smaller sets, used sequentially to linearize and solve the system. The reduction of the initial nonlinear control effectiveness matrix is improved by selecting each subset in a different arrangement of VCAs. However, the choice of this arrangement may lead to absence, partial or full superposition of VCAs in the subsystems. The technique was validated through mathematical tutorial cases, QTR simulation tests and open field flight and gyroscopic test bench experimental tests. Finally, the control allocation technique proved to be reliable, robust, efficient and applicable in the QTR when there is full superposition of VCAs between the subsystems.Sistemas superatuados geralmente requerem métodos de alocação de controle não lineares para mapear as Ações de Controle Virtuais (ACVs) em Ações de ControleReais (ACRs). Esse processo exige esforços computacionais que, as vezes, são limitados em plataformas robóticas embarcadas. E neste contexto que este trabalho apresenta o projeto de um Veículo Aéreo Não-Tripulado (VANT) do tipo Quadrotor Tilt-Rotor (QTR) superatuado, utilizando de um novo conceito de alocação de controle com ACRs desacopladas, onde o sistema não-linear inicial é dividido em subsistemas lineares parcialmente dependentes. Para esse propósito, as ACRs são divididas em conjuntos menores, usados sequencialmente para linearizar e resolver o sistema. Para melhorar a redução da matriz de eficácia de controle não-linear inicial, é possível selecionar para cada subconjunto um arranjo diferente de ACVs. Contudo, a escolha deste arranjo pode gerar ausência, parcial ou completa superposição das ACVs nos subsistemas. A validação da técnica foi realizada através de exemplos matemáticos tutoriais, testes de simulação e experimentais do QTR em uma bancada giroscópica e em campo aberto. Por fim, a técnica de alocação de controle se mostrou confiável, robusta, eficiente e aplicável no QTR quando se tem superposição completa das ACVs entre os subsistemas

Design and Analysis of Air-Stiffened Vacuum Lighter-Than-Air Structures

Lighter-than-air (LTA) systems have been developed for numerous applications and have taken several forms. Airships, aerostats, blimps, and balloons are all part of this family of systems, which uses Archimedes principle to achieve neutral and positive buoyancy in air by replacing an air volume with LTA gases. These lifting gases stiffen the otherwise compliant envelope structures, allowing them to sustain the pressure difference brought by the displaced air. The compliance of these structures is a byproduct of the weight requirement, materials and geometrical arrangement of which these structures are built from, typically resulting in dimensionalities that exhibit low or virtually non-existent in-plane bending stiffness. The former has constrained the development of LTA structures that utilize an internal partial vacuum, rather than a lifting gas, to achieve positive buoyancy, where the structure would be subjected to a pressure differential near atmospheric pressure. Given the above limitation, this research presents the development trajectory and structural characterization of air stiffened designs, which utilize air to shape and serve as the core of a set of enclosing envelopes. The development trajectory established a simulation framework that enables the structural characterization of air-stiffened designs under a variety of geometric and loading conditions. Such framework allowed for the development of finite element solutions that included geometric, fluid-structure and contact nonlinearities, with capacity for further generalization. Given the developed framework, the structural characterization of the Helical Sphere and Icoron air-stiffened designs demonstrated a reduction of material modulus and strength requirements compared to membrane-over-frame designs, and showed the capability of air-stiffened designs to be tailored for specific material strength limits

Aeronautical Engineering: A continuing bibliography, 1982 cumulative index

This bibliography is a cumulative index to the abstracts contained in NASA SP-7037 (145) through NASA SP-7037 (156) of Aeronautical Engineering: A Continuing Bibliography. NASA SP-7037 and its supplements have been compiled through the cooperative efforts of the American Institute of Aeronautics and Astronautics (AIAA) and the National Aeronautics and Space Administration (NASA). This cumulative index includes subject, personal author, corporate source, contract, and report number indexes