Polymath A (mostly) technical weblog for Archivale.com

February 13, 2010

Book Review: Leichter als Luft

Filed under: Aeronautics,Engineering,Lighter than Air,Propulsion,Structures — piolenc @ 5:37 pm

Leichter als Luft

Transport- und Traegersysteme
Ballone, Luftschiffe, Plattformen

by Juergen K. Bock and Berthold Knauer

reviewed for Aerostation by F. Marc de Piolenc

Hildburghausen: Verlag Frankenschwelle KG, 2003; ISBN 3-86180-139-6, price: 39.80 Euros. 21.5 x 24 cm, 504 pages, single color, many line illustrations and halftone photographs, technical term index, symbol table, figure credits, catalog of LTA transport and lifting systems.

Summary of Contents

1. General fundamentals of lighter-than-air transport and lifting systems
2. Physical fundamentals
3. Design of airships and balloons
4. Reference information for construction
5. LTA structural mechanics
6. Flight guidance
7. Ground installations
8. Economic indicators
9. Prospects

Appendices:

A. Time chart
B. Selective type tables of operating lighter than air flight systems
C. Development concepts of recent decades
D. Systems under development or under test
E. Author index
F. Table of abbreviations
G. Symbol table
H. Illustration credits
I. List of technical terms
J. Brief [author] biographies

In LTA, which has seen only two book-length general works appear since Burgess’ Airship Design (1927), comparisons are inevitable despite a language barrier. It is therefore quite pleasing to note that the authors of this book have consciously set themselves a task that complements the work embodied in Khoury and Gillett’s Airship Technology1. While Khoury’s work is a review of the current state of the art, the present book provides

“…a scientific, technical and economic basis for a methodical, consistent procedure in developing new lighter than air flight systems as well as a catalog and appraisal of prior solutions and achievements.”

as stated in the preface by Dr.-Ing Joachim Szodruch of the DGLR. This is amplified in the authors’ Foreword:

“The observations contained herein are future-oriented and encompass without euphoria the current state of science and technology.”

This is in contrast to Khoury and Gillett’s introduction to Airship Technology, which reads in part:

“This book is intended as a technical guide to those interested in designing, building and flying the airship of today.”

The body of the book is completely consistent with its stated purpose, looking always toward the future and emphasizing how things should be done rather than how they have been done. Where examples of actual hardware and operations are needed, they are drawn from the most recent available, and meticulously documented.

Considering the authors’ long association with the LTA Technical Branch of the DGLR, it is not surprising to find that much of the material, and many of the collaborating authors listed in the Foreword, are drawn from the many Airship Colloquia held by that Branch over the years. Yet the style is seamless; there is nothing to suggest to this admittedly non-native reader where one contribution ends and another begins; style is consistent from paragraph to paragraph, and across chapter boundaries. What is more, the authors seem to have made a conscious effort to make the text accessible to non-Germans by keeping sentence structure simple and straightforward. The three-column-inch sentences, gravid with nested subordinate clauses, so beloved of the Frankfurter Allgemeine Zeitung, for example, are not to be found here, much to this reviewer’s relief.

It is compulsory to say something about the thoroughness of the book’s coverage. It is, however, difficult to formulate a “completeness” criterion for LTA, which is now more than ever an open-ended field, in which-as the authors correctly point out-the possible types are still far from exhausted, despite the antiquity of aerostatic flight. It is to the book’s credit that its presentation, too, is open-ended; that is, the authors have avoided presenting the usual narrow typology of LTA craft and their almost equally narrow applications. Instead, and in keeping with modern practice, they take a systems approach to LTA, situating it within the field of aeronautics and providing the tools that the reader needs to translate his own requirements into appropriate technology.

The only omission that might be considered significant concerns tethered aerostats: the authors appear to have neglected both tethered-body dynamics and cable dynamics in their technical and mathematical treatments. Tethered balloons as a type are mentioned, but that seems to be all the coverage that they get. Admittedly, long-tether applications have poor prospects because of potential operational and safety problems, but short-tether dynamics have caused problems in some applications that are relevant, including balloon logging, so coverage of that end of the scale would have been welcome. Tethers also play a role in some existing and proposed stratospheric balloon systems, including the exotic NASA Trajectory Control System or TCS.

This, however, is the only flaw in an otherwise comprehensive LTA design/analysis toolkit.

One especially notable and praiseworthy inclusion is subchapter 1.4 regarding regulation and certification. This topic, though a concomitant of any aeronautical project, is one that most techically oriented authors would prefer to avoid or to give only summary treatment, but Bock and Knauer dive into it fearlessly, setting forth in considerable detail, and with the help of flowcharts, German, Dutch, British and American certification categories and procedures, with reference to the governing documents. Not surprisingly, there is more detail about the German process, with which both authors have considerable experience. They also review the history and evolution of the European Joint Airworthiness Regulations (JAR), which are keyed to—-and sometimes based on—-corresponding Parts of the US Federal Aeronautical Regulations (FAR).

They do not flinch even from discussing certification costs and fees. Although they admit that the general policy of regulatory authorities is to require payments to government from the applicant that offset the costs incurred in administering and examining a certification application, they conclude that, compared with the cost of development of an airship, the regulatory fees charged are of only minor importance. It is not clear whether they consider here the costs incurred by idling the works while some bureaucrat makes up his mind! Perhaps it hasn’t happened to them…

Typography, binding and book design

The basic layout is in two columns, with generous leading and gutters, making the somewhat smaller than usual typeface easy to follow and to read. Equations are set in a slightly larger, bolder font and occupy the full width of the page, avoiding a common legibility problem with two-column layouts. There are no drop-outs to be found anywhere. The eggshell-white paper is thin enough to keep the book’s 500-plus pages within a thickness of less than an inch (2.5 cm), yet the paper is completely opaque, without bleedthrough and with perfect reproduction of fine-screen halftones. A color section is mentioned in the table of contents, but all pages in the review copy are single-color. The cover is paper, rather than cloth covered, printed front, spine and back in white on a dark blue background (reproduced in reverse for this review). This type of cover is less durable than the traditional cloth, but is in widespread use for textbooks and technical works despite this.

Second (English) Edition

Work is now in progress on a second edition, which will be published in English by Atlantis Productions. Note that this will not simply be a translation of the first, German edition but a new work, composed ab initio and including whatever revisions might seem appropriate considering response to the first edition. Both of the authors have a very strong command of English, so there is no reason to fear the damage that some excellent German technical works have suffered at the hands of translators (Eck’s treatise on Fans comes to mind).

A “must have” in either language.

1 While a more thorough and detailed comparison of the two books would have been desirable, it is unfortunately not possible, as Aerostation never received a review copy of Airship Technology. Such comparisons as can be made here are based on brief access to that book during a consulting stint.

This review originally appeared in Aerostation, Volume 27, No. 3, Fall 2004

February 7, 2010

Safety and Risk

Filed under: Engineering,Structures — piolenc @ 5:55 pm

This is taken from chapter notes for a book project about ropeways (aerial tramways) for use in mountainous areas of the Third World.

Safety and Risk

Inasmuch as an unreasonable standard of safety can kill a meritorious ropeway project, it is worth devoting the necessary space to a discussion of the related—but very different—concepts of risk and safety.

Risk is quantifiable, provided that the necessary data are available. It is simply the probability that a certain type of loss, or a certain level of loss, will occur over a certain span of operating time or output. Actuaries compile these figures and use them to compute, among other things, the premiums to be charged for insurance against the loss whose probability they have computed.

Safety, however, is not the inverse of risk. Risk, as we have seen, is quantifiable and objective, while safety ultimately rests on a value judgment—a subjective appraisal that will differ from place to place and from individual to individual. Typically, a standard of safety is expressed in terms of a maximum risk level deemed acceptable by the individual or organization concerned, and is determined by comparison to available alternatives.

For example, suppose that we are offered a ride on a single span, single car, to-and-fro ropeway with an open car that carries the rider over a deep gorge swept by high, cold winds. Such a ropeway, if installed in a developed country, would likely carry only goods if it were allowed to exist at all; there would likely be other, more comfortable and less risky alternatives available for carrying passengers, and the rickety mechanism would be condemned out of hand as “unsafe.” Transplant the same rig to a remote corner of Nepal or Bhutan, where the only alternative is a five-hour walk on a narrow, icy windswept path with a vertical cliff face on one side and a sheer drop on the other, and it will be praised as the acme of safety and comfort! The risk is the same in both hypothetical cases, but the “safety” value judgment is very different.

None of this causes a problem, so long as the individuals and groups directly concerned are free to choose the risk levels that they will accept. Unfortunately, we live in an age where government has arrogated itself the authority to make these decisions for us, even in countries generally considered “free.” The result is that government workers with secure, high-paying jobs, living and working in relatively low-risk environments, are making risk-acceptance decisions for people in very different circumstances. In most cases the bureaucrats mean well, but have little knowledge of conditions in the areas affected by their decisions and do not understand the adverse consequences of risk-averse regulation.

Tragically, one consistent consequence of applying arbitrary “safety” standards is higher risk. This paradoxical result arises as follows.

1. A novel, previously unapproved transport method is proposed, usually to supplant or supplement an existing transport medium. For our example, let the new method be a ropeway across a gorge, and the existing one a footpath and ford.

2. The new method is not part of the traditional infrastructure, so it must be studied and approved by competent authority. Said authority imposes safety requirements that it deems reasonable, including the provision of safety interlocks to prevent the ropeway from operating unless the car’s loading gate is latched, high factors of safety for the cables, redundant brake mechanisms and so forth.

3. The proponents of the ropeway find that they cannot afford to build to the standards imposed. In some cases, they may find that supporting infrastructure (e.g. electrical power), costing many times the price of the ropeway itself, will have to be provided to meet the requirements.

4. Result: the existing method remains the only one available, even though it is far more risky than even a very crude ropeway. Inevitably, some people will die in falls or by drowning who would have survived if the ropeway had been available, and they will die because because someone living far, far away had the power to deprive them of a less risky alternative…in the name of safety.

December 22, 2009

Early "Seabasing" Concepts – Still Relevant

Filed under: Aeronautics,Engineering,Floating Structures,Materials,Structures — piolenc @ 6:25 pm

Recently, thanks to the efforts of a friend in the States, a report collection that was formerly available only on 35mm microfilm has been scanned into PDF files. While entering the 400 or so reports into my catalog I came across a 1934 critique, by Charles P. Burgess of the US Navy’s Bureau of Aeronautics, of a proposal by Edward R. Armstrong for a chain of floating airstrips called “seadromes.” These were to consist of an overhead deck and a submerged ballast tank, connected by a double row of vertical cylinders. If that sounds familiar, it should – it’s more or less the standard configuration for modern Very Large Floating Structures (VLFS), including the US Navy’s proposed SeaBase platforms. That was a bit of a surprise to me, because none of the articles on VLFS or sea basing that I’ve seen has acknowledged Armstrong’s much earlier work, which began during WW1 and continued until his death in 1955.

But it gets more interesting, because Burgess’ critique and alternative are just as applicable to the modern proposals as they were to Armstrong’s. Noting that a small waterplane area is the ultimate reason for the stability under wave action of Armstrong’s seadromes, Burgess proposed a more shiplike unitary hull with an anvil-shaped cross section – swollen at the bottom to accomodate ballast, spreading at the top into a wide flight deck – giving a small and very fine waterplane area and much lower resistance to forward movement than the multiple prisms of Armstrong’s concept. In the process, he created a configuration now known by the acronym SWASH – Small Waterplane Area Single Hull – about thirty years before its time. Burgess seems to have been more conscious than Armstrong of the difficulties of deep-ocean anchorage; his concept emphasizes powered station-keeping, which is facilitated by the hydrodynamically favorable hull. Burgess also anticipates modern seabasing proposals, emphasizing the value of a shiplike configuration in getting out of harm’s way if the area starts to “heat up.” I’ve uploaded Burgess’ report to the Files area of the Nation-Builders group on Yahoogroups (file name is BA157.pdf).

A good article on Armstrong and his platform proposals:
http://www.americanheritage.com/articles/magazine/it/2001/1/2001_1_32_print.shtml

The back-issue archive at Popular Science magazine’s http://www.popsci.com also has many articles and news items about Armstrong’s work.

The main difference between Armstrong’s proposal (and Burgess’ counterproposal) and what is mooted now is the current emphasis on modularity. Both Armstrong and Burgess proposed unitary platforms, while nowadays the ability to assemble large units from small, identical components is highly prized – one VLFS concept even involves dynamic assembly and disassembly in situ to suit changing conditions! Armstrong’s configuration is implicitly modular – it consists largely of identical units repeating at equal intervals – which explains its prevalence in modern proposals. Burgess the naval architect, on the other hand, gives his SWASH a beautiful continuously-curved waterline in plan, so his hull could only be built as a single unit. It turns out, though, that minor changes would make Burgess’ configuration “modularizable,” and at the same time cheapen its construction considerably, without compromising its main advantages.

The main change is redesigning the load waterline to consist of a long parallel section, tapered abruptly and symmetrically at both ends. This allows the hull to consist of a variable number of identical “center” units capped with identical “end” units at bow and stern. The end units would have identical propulsion units built in, each capable of giving the whole shebang steerage way and not much more. You end up with the SWASH equivalent of a double-ended ferry, but with only enough installed power for station-keeping. Substituting waterjets with orientable nozzles for conventional screw propellers would allow even very large assemblies to be maneuvered without tugboats. The center units, containing no machinery, could be manufactured in very summary facilities much less well-equipped than standard shipyards. It might be advantageous to make the end units in regular shipbuilders’ yards.

Taking the whole idea one step further, the individual units could be built with double hulls, providing enough reserve flotation to allow them to float, albeit with little reserve buoyancy and with decks awash, even when fully flooded. This would allow them to be assembled into complete vessels or platforms on the water. End units would even be navigable under their own power when unmated and fully flooded – the machinery spaces, located in the ballast tank area, would be sealed and connected with the deck by a narrow trunk like the conning tower of an old-style submarine. This in turn would allow end units and center units to be assembled in separate areas, the end units, mated in pairs, being driven under their own power to where their center units awaited them. The mating operation itself could be carried out in open water, with the end units connecting, independently, with center units one by one until they had enough between them; then the two half-vessels would maneuver to join up.

When newly assembled, the new platform would look like a monitor without the gun-turret, deck flush with the water, but with the hull complete it would gradually be pumped dry inside, ready for fitting-out. It might even be possible to equip the propulsion units to serve as high volume, low pressure pumps, at least in the initial stages of pumping-out.

Materials and manufacturing technology are pretty much ad lib. – steel or aluminum, riveted or welded are feasible, but my favorite is of course ferrocement, which if properly executed can be longer-lived than any other material. Joining method for mating the sections is also up in the air. If the sections are made of steel and they were intended to remain assembled, welding would be the obvious method of choice; bolts are the obvious reversible method, but they are very expensive and would have to be fitted, in our hypothetical open-water assembly method, by divers working underwater and in very poor visibility. One technique that appeals to me is adapted from a system developed for assembling buildings from prefabricated panels in earthquake-prone areas, namely lacing the structure together with steel cables. For permanent assembly, the cables can be grouted into their channels; otherwise they can be secured with cable thimbles at their ends. Post-tensioning would then be possible, which would relieve bending loads on very long assemblies.

Armstrong’s patents:
Canada:
253,140
628,310

US:
1,378,394
1,511,153
1,892,125
2,248,051
2,399,611
2,963,868

France:
532,360
572,543

Burgess’ critique: US Navy Bureau of Aeronautics, Lighter than Air Section, Design Memorandum No. 157, February 1934, “A Proposal for a Single Hulled Seadrome,” by C. P. Burgess. Available from the Files section of the Nation-Builders group on Yahoogroups (see link above).

Powered by WordPress