Basic Design Concept on an Airship

Basic Design Concept on an Airship

Some of the earlier scientific and technical documents related to airship design can be found as technical reports from NACA and the Royal Aeronautical Society (RAeS). One of the most famous is a report by Lamb focusing on the study of inertia coefficients of an ellipsoid moving in a fluid: these coefficients were needed to keep into account added masses in airship design. The increased interest in airships of the first years of the 20th century was supported by studies on airship design focusing their attention on aerodynamics and weight which was considered at the moment the two most critical issues in the design of airships. Two reports by Tuckerman, the first dealing with the determination of forces on an airship hull and the second focusing on inertia factors show the need for a precise loads assessment in order to design a lightweight structure able to sustain the stresses due to lifting gas and dynamic pressure. The experience and knowledge in airships gained during the period 1900-1927 by pioneering designers like General Umberto Nobile in Italy, Count Zeppelin and Nikolaus Basenach in Germany, and Goodyear in the USA are reported in a book by Thomas Blakemore and Watters Pagon [4] where all the subsystems of an airship are considered one by one. The approach followed in to solve the weight estimation (which can be considered the most critical in airship design) is based upon comparison with already designed and built airships where a wide list of tables in which the characteristics of a large number of airships are listed. In the same year a book by Charles P. Burgess was edited, in which the approach to size estimation is different: this author proposes a design methodology based on preliminary design calculations, evaluation of static and dynamic bending moments, gas pressure stresses, design of cars for power systems, passengers, and flight crew, gas cells, and finally tail cones, stabilizing surfaces, and mast mooring gears. This book provides one of the first examples of a complete list of formulas to be used for the initial estimation of size and horsepower for a given performance and proposes a well coded “step by step” embodiment process to deploy the entire design process in a systematic way. A resume of the design experiences of the years up to the 1940s can be found in a technical manual in which the formulas and methodologies developed for the design are summarized in a very practical and “design oriented” way.

The Hindenburg accident and the interest towards vehicles with higher speed deadened the interest in airships, and in 1962, the US Navy program for airships stopped. The design process of airships is kept going by Kostantinov who collected the formulas and experiences in the field of airships and merged the up to date aerodynamic and structural research in a comprehensive paper. Since the 1970s, airships and blimps are designed for advertising purposes or touristic adventure trips: Goodyear in USA and Zeppelin in Germany are good examples of such activities. The increase in personal computers and the computational load available made possible the solutions of complex equations and the large number of simulations that can be ran simultaneously, compared to experimental data (as for the studies of CFD related to the German LOTTE). Also the airship design field was affected by these new capabilities: the work of Lutz et al. is one of the fist describing the optimization of the shape of an airship by means of evolutionary algorithms and stochastic methods: the airship design process can make now use of the new available computing capabilities.

Khoury and Gillet present a book in which a chapter is devoted to Design Synthesis. Airship design now focuses its attention on the integration of sub-systems and trade-off considerations. Moreover, the design process is divided in Conceptual, Preliminary and Detailed phases. Flowcharts are presented to drive and support the designer in the Conceptual Design phase, in the trade off analysis, and in the trade study process. The airship is considered as a system, and the mutual interactions between subsystems (condensed in the airship sizing matrix) is considered the key of success for a good and balanced design. Also, sensitivity analysis and parametric weight estimation (derived from the aircraft conceptual methodologies) are introduced in this comprehensive book. In the end of the 20th century, flight simulation is proposed not only for the training of pilots, but also to check the design results and to verify the behavior of the airship, even in the conceptual design phase. The availability of new film materials, efficient solar panels, and the need for high altitude observation platforms focused the attention of designers to High Altitude Platforms (HAP).

In a study by Mueller et al. the design of a HAP is presented in a parametric way: data like weight of the envelope and efficiency of solar panels are not kept fixed. The design process output is not a defined sizing, but a series of graphs which the designer can use to dimension the airship with materials available at the moment. With this method, the design can be updated if new materials or technology become available. Also, in the work of Wei et al. and Nickol et al. the attention is focused on the trade-off analysis, on the sensitivity analysis, and on how the airship would be impacted by a new technology or change in mission requirement. In the latter of these two papers, the design is based upon the proposal of several configurations, each one evaluated in the mission through a Life Cycle Cost Analysis approach where a design is considered good if it presents a cheap operational cost and a low cost for environmental impact and final dismissing.

The work of Yu and Lu presents a flowchart describing the design process for a HAP; moreover, a list of tables shows how the change of design parameters (like the purity of helium, or the sunlight hour related to the season of the year) affect the lift. The most interesting part of this study reports the effects of technology advances on airship performance parameters: by this way the designer can have an idea of how the payload can be increased with an increase in propeller weight/mass ratio and solar cells efficiency, or a decrease of envelope area weight and batteries capacity/mass ratio.

Also, Chen presents a similar work of sensitivity analysis arriving at similar results in terms of influence of weights and efficiency on the design: a design flowchart is presented here also to assure the equilibrium between lift and weight due to solar panels, structure, batteries, and propulsion systems. The multidisciplinary approach to design, which is a consequence of a concurrent engineering approach, has been applied also to airship design: the work of Ram and Pant presents the aerodynamic and structural optimization of an airship using variable thickness fabrics and a low drag shape. As the new reprint of the book Airship Technology reports, in addition to the classical interest related to materials, solar panels, and unconventional configurations, one of the challenges for the future is the design of multi gas, multi chamber airships seems to be a solution for cost reduction and lower environmental impact.