Rajkumar S. Pant

A METHODOLOGY FOR DETERMINATION OF BASELINE SPECIFICATIONS OF A NON -RIGID AIRSHIP

This paper presents a methodology for arriving at the baseline specifications of a non -rigid airship of conventional configuration, given the performance and operational requirements. Specifi cally, the methodology calcula tes the envelope volume required to carry a use r- specified payload, and also arri ves at the mass breakdown, a nd per forman ce estimates . Alternatively, the payload that can be carried by an airship of specified envelope volume can also be estimated. Sensitivity of parameters such as pressure altitude, ambient temperature, cruising speed, Helium purity level, engine power, env elope length to diameter ratio etc. on the payload available or envelope volume requi red can also be determined . T he baseline specifications of two airships for transportation of goods and passengers under hot and hi gh conditions obtained using this method ology are presented . Results of sensitivity analysis for one airship are also discussed. 1 NOMENCLATURE

Multidisciplinary Shape Optimization of Aerostat Envelopes

an = coefficient for parabolic rear shape a1, a2, b1, b2, c1, c2, d1, d2 = coefficients of cubic splines that parameterize the center portion of the envelope CD = drag coefficient d = envelope diameter l = envelope length n = load per unit length along meridians, i.e., in warp direction n’ = load per unit length along latitude circles, i.e., in weft direction pR = internal overpressure in the aerostat envelope R = radius of curvature of spherical front portion of envelope R1, R2 = radii of curvature and transverse curvature of an inflated structure XD = design vector for shape optimization

Dynamic Stability Analysis of a Tethered Aerostat

incorporates the concepts of apparent mass, dynamic tether and allows 6 degrees of freedom for the motion of the aerostat. Estimation of aerodynamic coefficients is based on empirical relations and curves available in literature. Weight and buoyancy are calculated based on geometry of the aerostat. Appropriate values for operational altitude and desired angle of attack of the aerostat are assumed. Moment balance about confluence point gives the optimal location of the confluence point. Equations of motion for the aerostat and dynamic tether are simulated and appropriate boundary conditions are applied. Force balance gives the tether tension force and its orientation at the confluencepoint.Basedonthetethertensionanditsorientationattheconfluencepoint,thetetherprofileisestimated bybreakingupthetetherintoseveralelasticsegments,eachinequilibrium.Onceequilibriumisestablished,thewind isperturbed andthe response of the aerostat issimulated. Thepaper reportsthe results of simulation carriedout for the TCOM 365Y aerostat and the aerostat response to various ambient velocity profiles. I. Introduction T ETHERED aerostats fall under the category of lighter-than-air systems.Agashavinglowerdensitycomparedwithambientair (usually hydrogen or helium) is enclosed in an envelope and the difference in their densities gives rise to buoyancy. In an aerostat, buoyancy is the major source of lift, whereas in heavier-than-air systems (e.g., fixed-wing aircraft or rotorcraft), aerodynamic lift produced due to relative motion between the ambient air and the vehicle is the major source of lift. The various components of a typical aerostat system are outlined in Fig. 1. The hull or envelope is a bag containing the lifting gas. Fins are attachedattherearendofthehullandprovidestabilitytotheaerostat; they are usually in the form inflated structures, filled with lifting gas orair.Thepayload,whichisusuallyasurveillancecameraoraradar, is mounted one the envelope. A series of ropes called confluence lines connect the hull to a single point called confluence point, to which the main tether is attached. Aerostats can remain stationary for long duration in reasonable weather, which makes them a very good choice for surveillance, advertising, and raising antennae for wireless communication, to name a few. In real life, aerostats have to operate in highly varying weather conditions and winds. Aerostat failures have occurred because of abrupt changes in the wind, which result in shock loads. Estimation of these shock loads is an important requirement in aerostat design, and it can be accomplished by modelling the dynamics of an aerostat and predicting its response to sharply fluctuating winds. This paper starts with a brief history on the development of modeling and simulation of aerostats. The next section deals with equilibrium analysis of tethered aerostats, in which the angle of

A generic methodology for determination of drag coefficient of an aerostat envelope using CFD

Aerostat envelopes are generally bodies of revolution with length to diameter ratio ranging from 3 to 5. Drag coefficient for this class of bodies can be obtained using empirical formulae or co-relations based on experimental studies. However such formulae are valid for specific class of envelope shapes only and result in errors of around 30% compared to the values determined by numerical methods. The motivation for the present study arose from the need for a simple but generic methodology to estimate coefficient of drag as a function of envelope geometry, thus eliminating the need for running numerically expensive CFD codes each time the shape is altered during an optimisation exercise. In a previous study, the envelop shape was parameterized in terms of six geometric coefficients, and a shape generation algorithm was developed to generate various possible shapes satisfying manufacturing and few geometric design constraints. An empirical co-relation for envelope drag coefficient was developed, but it was not amenable to coupling with an MDO process, since it required detailed geometric data about the envelope shape, especially the coordinates of several points at the nose and trailing edge, and the grid density in these regions. In the present study, around 600 feasible shapes satisfying the user-specified volume and length constraints were generated using the shape generation algorithm. The flow patterns over these shapes were studied using FLUENT CFD Package and a better corelation was obtained by fitting a quadratic response surface using Design-Expert package. The current methodology uses only the values of six design variables to determine the drag coefficient, thus making it easy to integrate with a multi-disciplinary optimization algorithm for determining optimum envelope shape.

Aircraft configuration and flight profile optimization using simulated annealing

Abstract This paper discusses the application of simulated annealing in the conceptual design and optimization of twin-turboprop Commuter & Regional aircraft to obtain the optimum configuration and flight profile of such aircraft for operation over a given stage length. Generalized cost of travel incurred by a passenger for air travel between two cities is considered as the objective function to be minimized. Generalized cost is assumed to consist of four cost terms, viz., access cost, flight cost, time cost and airport cost. A computational methodology was developed for the estimation of these cost terms for short-haul air travel, as a function of 17 design variables and nine constraints. A simulated annealing optimization method was coupled to this methodology and a case study for short-haul business travel in India was carried out. A modified optimization strategy was adopted to reduce the overall computation time required. The results obtained in this case study are discussed in the paper.

Design and Fabrication of an Aerostat for Wireless Communication in Remote Areas

** † ‡ § This paper provides details of an endeavour to study the efficacy of aerostats as a platform for cost-effective wireless communication as an alternative to fixed tower networks, to fill the digital devoid of the communication in sharing the knowledge and information from urban societies to sparsely populated rural areas in India. The main design intent was to develop a platform to hold wireless communication equipment at an altitude of 100-250 m AGL, so that last-mile wireless connectivity could be established over a radius of around 10 km from the aerostat launch site. The paper provides details of a methodology for design and performance analysis of the aerostat, and examining the sensitivity of various operational parameters. The methodology is a systematic collation of various design approaches and concepts, which were examined during the ongoing design and field trial exercises related to remotely controlled airships and aerostats at the Lighter-Than-Air Systems Laboratory of the institute. The various design decisions were driven by the availability of local materials for different components. The paper describes the design process followed, and fabrication techniques employed for developing experimental aerostat prototypes.

A Methodology for Conceptual Design and Optimization of a High Altitude Airship

This paper describes the methodology for conceptual design of a high altitude airship (HAA), which has to be posed in an optimization framework. The paper starts with the review of projects, studies, programs related to design and development of stratospheric airship carried word-wide and highlights the global developement in this field. Critical issues affecting the stratospheric airship design are discussed in brief. The details of methodology for initial sizing of solar powered stratospheric airship is presented and the need of coupling this methodology with the other optimization methodologies are discussed. Given the basic operating and performance parameters, the methodology sizes the airship, and arrives at the mass breakdown of system. The final developed methodology would be coupled with the optimization algorithm to obtain an optimal solution for some user-defined objective function.

Application of Lighter-Than-Air Platforms for Power Beaming, Generation and Communications

Retail power beaming using millimeter waves offers a rapid way to bring electric power to areas such as rural India where the terrestrial wired grid lags the demand for communications, connectivity and other services. Synergy between infrastructure development for communications and for power allows local, regional and global power exchange. This helps to bring renewable power generation devices of all scales into a seamless grid including space-based, stratospheric, low-altitude, and surface infrastructure. This paper presents a conceptual study of how lighter-than-air platforms (LTA) including uninhabited, remoted controlled or autonomous aerostats and airships, may be used for the above purpose. The paper highlights the synergistic application of LTA systems to the delivery of power, generation of a small amount of power, and provision of low-cost communications systems in remote areas. Significant experience has already been accumulated in using LTA systems in India for various purposes. Wind patterns drive the optimum altitude for a self-propelled LTA above 21,000 m, suitable for large stratospheric platforms. Altitudes above 4000 m would enable a tethered LTA to convey millimeter wave power through a wave guide integrated into the tether, tunneling through the high-loss regions of the atmosphere. The millimeter wave power beaming application requires demonstration of the projected antenna mass and other parameters. Tethered aerostats, autonomous powered airships and very high altitude platforms all offer excellent opportunities. Initial sizing explorations show feasible solution spaces.

Remotely Controlled Airship for Aerial Surveillance: From Concept to Reality in under a month

A remotely controlled airship was designed, fabricated and demonstrated within a tight timespan of under a month after receiving the go-ahead. The main design requirement for this airship was to be able to operate from the Helipad located at an altitude of 6572 feet AMSL under ISA+20 deg. C. The images of the terrain below were recorded during the flight, and transmitted in real-time to a ground based system using an onboard telemetry system. The paper describes the methodology followed for sizing of the envelope and key components of the airship, and the procedure followed for in-house fabrication and testing. The major issues that cropped up during the operation of the airship in harsh weather conditions of rain and mild snow, as well as in night time are also highlighted. The demonstration established the efficacy of remotely controlled airships for aerial photography and data collection by snow scientists.

Generation of Optimized Routes and Schedules for Surface Movement of Aircraft on Taxiways

Due to growing congestion at major airports, many conflicts occur during the motion of aircraft on taxiways, leading to delays. This study aims to devise a strategy to arrive at optimized routes and schedules for surface movement of aircraft on taxiways, which can facilitate the airport surface movement controllers in optimal sequencing of arrivals and departures at a busy airport. Shortest routes for operation on a network of runways and taxiways are obtained using Dijkstra’s algorithm. A modified Time Dependent Shortest Route algorithm using mixed-integer programming is used for generating conflict free trajectories with minimum total overall delay for a group of aircraft operating on predetermined routes, in a given time window. The algorithm was run for a hypothetical test case on CSIA, Mumbai to illustrate its efficacy.