Aero Engine Development Research Articles

Resource reallocation across successive systemic innovations: How Rolls‐Royce shaped the evolution of the turbojet, turboprop, and turbofan

AbstractResearch SummaryDespite the importance of resource reallocation in shaping a variety of strategic outcomes, strategy scholars have paid only limited attention to the processes by which firms reallocate their resources across successive systemic innovations. To explore these processes, we conducted an in‐depth historical case study on Rolls‐Royce's role in three distinct systemic innovations that marked the transition from piston engines to jet engines in the civil aviation industry: the turbojet, the turboprop, and the turbofan. The analysis helps explain how and why Rolls‐Royce's central role stemmed from its ability to reallocate existing non‐scale free organizational and technical resources. A key finding of this study is the identification of the horizontal transfer of functional modules as a critical process, especially during the incipient phase of a systemic innovation. The analysis also highlights the role that specific organizational arrangements, particularly a firm's integrative capabilities, have in shaping the effectiveness with which resources are reallocated.Managerial SummaryFocusing on resource reallocation is important to understand why some firms effectively reallocate their resources through successive systemic innovations while others cannot, even if they have similar resources and face the same environmental conditions. By delving into the technological aspects of aeroengine development and exploring why Rolls‐Royce had the capabilities to successfully integrate key functional modules across various modular levels, we clarify the relationship between technology and organization that underlies resource reallocation—a topic that has received only scant attention in the strategy literature.

Rolls-Royce - 100 Years of Power

The date of December 17th 2003 is well recognised as the centenary of the first powered flight. What is less well known is that May 4th 2004 also represented another historical centenary for aerospace. On this date in 1904, the Charles Rolls and Henry Royce first met and their drive and ambition led to the formation of this world famous company. Since that day, Rolls-Royce has established itself with a reputation for excellence and innovation across a wide range of engineering products. This presentation will explore the evolution of aero-engine development at Rolls-Royce. The story starts with the highly successful Eagle and Falcon, which dominated the Allied propulsion systems of World War I. This success was followed with the Merlin, arguably the most recognised name in aerospace engines in the 1940s, before Frank Whittle’s pioneering work led to the development of the modern jet engine. Rolls-Royce is also the world leader for the unique propulsion technologies required for both supersonic and V/STOL flight and this presentation will describe design and development of these engines. The Olympus engine, which has accrued almost one million engine flying hours on Concorde and over one billion supersonic engine miles. Rolls-Royce V/STOL experience on the innovative Pegasus engine in the Harrier has also secured a position on the LiftSystemTM, the STOVL propulsion system for the Joint Strike Fighter. Today Rolls-Royce is a world leader in gas turbine technology for civil and defence aerospace, marine and energy power systems. This presentation will describe the process of developing technology once, and using it many times which has led to the development of a broad range of the latest gas turbine engines and technologies, including EJ200, F136, Adour and RTM322 for the latest military combat, trainer and helicopter aircraft. The next 100 years in gas turbine technology is certainly going to be as challenging, new and exciting as the past century. We can expect the growth of UAVs requiring More Electric, Variable Cycle and High Mach engines as well as a wealth of unique, new propulsion systems. With over 100 years success and innovation in the aerospace power business, Rolls-Royce is ideally placed to face these challenges

Challenges in Aero-Engine Joint Venture Design Development Certification and Technology Transfer Process in India

The development in the field of gas turbine engine from first generation to fifth generation is evident from the history. The ever changing requirement has driven continuous development in the area and has led the designers to struggle for best propelling machine to fly. In the global scenario it is evident that for keeping up with the pace of advancements in the gas turbine engine field, expertise is required for each subsystem/module. Major design houses of the world are now adopting an approach of developing expertise in a specialized area of aero engine development. Having developed the expertise in a specialized area, the complex aero engine can be developed through the joint venture route. In a country like India this new development philosophy through joint venture has been adopted in the recent past for many of the aero engine components. The critical issue for such a product to enter into the armed forces is certification and its associated manufacturing quality standards. This paper highlights the basic issues and challenges associated in a typical Indian Joint Venture for design development and Certification of aero engines and system. The paper also highlights the possible approach which can be adopted based on the real experience of certification process for a turbo shaft engine joint venture program recently undertaken in India between HAL and an OEM abroad.

Optimization of aero-engine combustion chambers with the assistance of Hierarchical-Kriging surrogate model based on POD downscaling method

In view of the long calculation cycle, high processing test and cost of the traditional aero-engine combustion chamber design process, which restricts the engine optimization design cycle, this paper innovatively proposes a surrogate model for the performance of aero-engine combustion chambers based on the POD-Hierarchical-Kriging method. Through experiments, the predicted results of the POD-Hierarchical-Kriging model are compared and analyzed with the calculated results of the one-dimensional program, and the root mean square error of the predicted values of combustion efficiency and total pressure loss is 0.0064% and 0.1995%, respectively. The accuracy of the POD-Hierarchical-Kriging model is compared with the cubic polynomial model, the basic Kriging model and the Hierarchical-Kriging model. It verifies the feasibility and accuracy of the POD-Hierarchical-Kriging model for the prediction of performance of aero-engine combustion chambers. The global sensitivity analysis method is applied to obtain the influence effect of design variables on the performance. Then, a multi-objective optimization method based on the NSGA-II algorithm is studied, and finally the optimal set of Pareto solutions is obtained and analyzed, which can be used to guide the optimal design of aero-engine combustion chambers and accelerate the progress of aero-engine development.

Preface

The purpose of the three-day 2022 International Conference on Aerospace and Control Engineering (ICoACE 2022), held via virtual form on December 23rd-25th, 2022 in Guangzhou, China, was to create a timely forum for multi-disciplinary discussions related to the recent developments on control engineering triggered by aerospace.As usual, the program of the meeting consisted of keynote speeches, oral presentations, the former including speeches delivered by six sophisticated professors from different areas. The speakers covered three main topics: i) Several Key Issues for High-Fidelity Simulation Requirement of Modern Aeroengine; ii) Aircraft Power Supply System Development: From Multi-Electric Aircraft to Electric Propulsion Aircraft; iii) Based on IoTs Parking Navigation With Continuous Information Potential Field Research. Among them, the first report mainly introduced the current situation of high fidelity simulation technology of aeroengine, the application of high fidelity simulation technology in Aeroengine development process, and the future demand of the digital twin applied in the aeroengine high fidelity simulation technology.In the framework of experimental and theoretical approaches, the conference gathered together 100 delegates from all over the world and addressed a number of highly relevant aspects of aerospace and control engineering. Covering Materials Surface Physics, Electric Automation, Distributed Control System, Physics of Gases, Plasma Physics, the selected contributions of this Special Issue provide guidance for future interdisciplinary developments. In this way, the multi-scale aspects of material-based aerospace, mechanics and control engineering should be considered.We received various manuscripts of invited papers and contributions presented at the Seminar. All of these have been peer reviewed and are collected in this volume. We would like to thank all the anonymous colleagues who have acted as referees to assess the suitability of the various articles for publication in the Journal of Physics: Conference Series. We are confident that the high quality of both invited and contributed papers contained in these Proceedings will be appreciated by the aerospace community.We would like to express our thanks to all the authors for their time and genuine efforts, and to the reviewers for their fruitful comments during the preparation of this volume. We also acknowledge the support provided in various ways by Nanchang Institute of Technology who acted as host to the Conference.The Committee of ICoACE 2022List of Committee member is available in this Pdf.

Large-Scale Simulation of Full Three-Dimensional Flow and Combustion of an Aero-Turbofan Engine on Sunway TaihuLight Supercomputer

Computational fluid dynamics- (CFD-) based component-level numerical simulation technology has been widely used in the design of aeroengines. However, due to the strong coupling effects between components, the numerical simulation of the whole engine considering the full three-dimensional flow and multi-component chemical reaction is still very difficult at present. Aimed at this problem, an efficient implicit solver, 'sprayDyMFoam' for an unstructured mesh, is developed in this paper based on the Sunway TaihuLight supercomputer. This sprayDyMFoam solver improves the PIMPLE algorithm in the solution of aerodynamic force and adjusts the existing droplet atomization model in the solution of the combustion process so as to meet the matching situation between components and the combustion chamber in the solution process. Meanwhile, the parallel communication mechanism of AMI boundary processing is optimized based on the hardware environment of the Sunway supercomputer. The sprayDyMFoam solver is used to simulate a typical double-rotor turbofan engine: the calculation capacity and efficiency meet the use requirements, and the obtained compressor performance can form a good match with the test. The research proposed in this paper has strong application value in high-confidence computing, complex phenomenon capturing, and time and cost reduction for aeroengine development.

S2 Stream Surface Approximation Approach for Quasi Three-Dimensional Turbine Time-Marching Design Method

A fast and reliable turbine design method is necessary in aeroengine development practice. As Q3D time-marching method iteration process can be time consuming and unstable, a novel S2 stream surface approximation approach coupled with flow tangential condition is proposed to reduce the computation requirement. The surface approximation uses a quadratic function of axial coordinate x to formulate distribution of circumferential coordinate θ . The flow tangential condition inherently represents inviscid blade force effect, and the formulation of inviscid blade force is not needed. A corresponding personal Q3D turbine computer code was developed, which was suitable for both design and analysis applications. The Q3D design method solves Euler’s equation through third-order Godunov’s scheme with TVD property in finite volume method. Semi-implicit Crank-Nicolson’s temporal scheme is implemented. Profile, secondary, and tip clearance energy loss models are added to predict viscous losses. Blade row exit swirl is required as the convergence target for Q3D design. A two-stage turbine and a single-stage high-pressure turbine were designed and analyzed by the Q3D method. Viscous 3D CFD was utilized to check design performances. The results showed that the Q3D method could finish a design case within 1 min. At design point, Q3D mass flow rate error was no more than 1.25%, expansion ratio error was no less than -0.022, and isentropic efficiency error was no more than 0.37 percentage points. The Q3D design method is fast and accurate. The stream surface approximation approach is suitable for Q3D design and analysis.

IVOC/SVOC and size distribution characteristics of particulate matter emissions from a modern aero-engine combustor in different operational modes

The particulate matter (PM) of Intermediate-Volatile Organic Compounds (IVOC) / Semi-Volatile Organic Compound (SVOC) from aircraft engine emissions, despite being significant precursors of secondary organic aerosols deteriorating air quality in the vicinity of airports, have not been fully investigated at molecular level. In this study, the particulate IVOC/SVOC emissions from a rig test on a Technology of Low Emission Stirred Swirl aero-engine combustor, being operated with dual diffusion and premixed-dominant combustion modes, have been characterized via a two-dimensional gas chromatography-time of flight mass spectrometer (GC × GC-ToFMS). The IVOC/SVOC compounds, including 25n-alkanes, 15 cyclic alkanes and 13 polycyclic aromatic hydrocarbons were analyzed in this study. We found that including the premixed-dominant combustion mode at climb/takeoff conditions reduced the particulate IVOC/SVOC emissions significantly by nearly 80%, compared to using the diffusion combustion mode alone at idle/approach condition. Meanwhile, the measurements on organic PM obtained from a scanning mobility particle sizer spectrometer with a catalytic stripper demonstrated a consistent trend with the the IVOC/SVOC emissions, which were also suppressed by over 85% at climb/takeoff compared to idle/approach. The inter-relationship between the size-resolved organic PM and the speciated IVOC/SVOC emissions has been further explored, showing that the nucleation mode PM is dominated in organic PM by over 50%, in which IVOCs/SVOCs may be a significant contributor. This study expands the understanding of aviation-emitted organic particles, and suggests a path for future aero-engine development to mitigate the IVOC/SVOC emissions particularly at low power conditions. However, compared to the real aero-engine emissions, the results from rig combustor tests should be interpreted with great care, since there are still some work to be done to establish the quantitative relationship between emissions from rig combustors andthose from real engines.

Design methodology of a highly loaded tandem rotor and its performance analysis under clean and distorted inflows

Compact and efficient compressor design is one of the key challenges in aero-engine development. The flow through a compressor is exposed to adverse pressure gradients, which limits the maximum allowable flow turning in a compressor blade. Tandem blading is an interesting concept to achieve a higher total pressure rise by augmenting the flow turning angle. Variation in axial overlap and percentage pitch of the forward and aft blade elements largely influences the behavior of the tandem configuration. In the present study, the genetic algorithm is used to optimize the axial overlap and the percentage pitch for the tandem rotor. Results indicate that a lower axial overlap and higher percentage pitch results in optimum performance. The paper presents the parametric study of four tandem configurations with different axial overlaps and percentage pitches. A detailed experimental analysis of the four different tandem configurations is included in this paper. The behavior of the tandem rotor is examined under the clean and radially distorted inflow. Further, a comparison is drawn with a conventional single rotor in terms of aerodynamic parameters such as total pressure rise, axial velocity, and stall margin. The experimental analysis is supplemented by some interesting computational results, which are included to provide some insight into the complex flow field of the tandem rotor. Tandem rotor design is observed to have a higher sensitivity to radial tip inflow distortion. The upstream shift of the aft rotor blade adversely affects the total pressure rise and stall margin of the tandem rotor.

Thermodynamic analysis of nutating disc engine topping cycles for aero-engine applications

Within the next thirty years the evolutionary approach to aero engine development will struggle to keep abreast with increasingly stringent environmental targets. Therefore radical approaches to aero-engine development in terms of energy savings need to be considered. One particular concept involves the inclusion of a pressure-rise combustion system, within the architecture of an aero-engine, to provide additional shaft power. The nutating disc engine concept is a strong contender due to its power density. The feasibility of the nutating disc engine has been previously investigated for unmanned vehicle applications. However, this paper investigates the performance benefits of incorporating a nutating disc core in a larger geared open rotor engine for a potential entry in to service in 2050. In addition, a methodology is presented to estimate the size and weight of the nutating disc core. This methodology is pivotal in determining the overall performance of the novel aero-engine cycle. The outcome of this study predicts a potential 9.4% fuel burn benefit, over a state of the art geared open rotor in the year 2050. In addition, the sensitivity of the nutating disc design variables highlights the possible fuel burn benefits compared against a comparable year-2000 aircraft mission.

CFM56: A Study Case of Aero-engine

CFM56 series engine is an amazing example in the civil aviation engine history. CFM international is composed of French SNECMA and American GE Corp joint venture, and the cooperation of two companies is also called a model of international cooperation. In this paper, CFM56 series engine's development history is studied, and the successful experiences and lessons of the CFM international company in aero engine development project is demonstrated. Engine has high technical difficulty, long development cycle, and high business risk significantly. CFM56 engine’s successful experience has made an excellent example for the development of China’s aero engine group and C919 in the international aviation market.

Enhanced Computational Fluid Dynamics Modeling and Laser Doppler Anemometer Measurements for the Air-Flow in an Aero-engine Front Bearing Chamber—Part I

Modern aero-engine development requires also a gradual increase in the overall effectiveness of lubrication systems. This particularly applies to bearing chambers where a complex two-phase flow is formed by the interaction of the sealing air and the lubrication oil. It is important to increase the level of understanding of the flow field inside the bearing chamber and to develop engineering tools in order to optimize its design and improve its performance. To achieve this, an experimental and a computational study of the whole front bearing chamber were carried out for a range of shaft rotational speeds and sealing air mass flow. The experimental measurements of the air velocity inside the chamber were carried out using a laser Doppler anemometer (LDA) in two-phase air/oil-flow conditions. The experimental facility is a 1:1 scale model of the front bearing chamber of an aero-engine. Computational 3D modeling of the bearing chamber was performed. The bearing gap and the presence of lubrication oil were modeled as an anisotropic porous medium with functions relating the pressure loss of the air coming through the gap and the tangential component of velocity of the air exiting the gap of the ball bearing with the air-flow rate through the gap and the rotational speed of the shaft. The methodology to obtain the above mentioned functions and the results of the detailed study are given (Aidarinis, J., and Goulas, A., 2014, “Enhanced CFD Modeling and LDA Measurements for the Air-Flow in an Aero Engine Front Bearing Chamber: Part II,” ASME Paper No. GT2014-26062). The enhanced computational model of the chamber implementing the law of pressure drop of the “lubricated” bearing and the function of modeling the tangential velocity of the air exiting the bearing was used to calculate the flow field for the full range of the measurements. A limiting curve dividing the operational map of the bearing chamber into two areas was predicted. Large vortical and swirling structures dominate the flow and they vary in size according to the position of the operation point relative to the limiting curve. Operation above the limiting curve leads to flow classified as type I with air going through the ball bearing while for operation below the limiting curve line the flow is classified as type II, there is no air-flow through the bearing gap.

Experimental investigation on forced response of mistuned bladed disc rotor in an aero-engine

An experimental investigation on forced response of a first stage compressor mistuned bladed disc rotor is performed in an operational aero-engine. It is desired to evaluate the maximum blade amplitude response of the bladed disc for the existing blade mistuning pattern depending on blade mode, exciting engine order, and aerodynamic influences. Finite element analysis on a single cantilever blade is performed and the possible resonances are estimated. Bench tests on a stand-alone blade are conducted to verify the finite element predictions. Experiments are conducted on a full-scale core engine using blade tip timing system. Blade tip timing system utilizes noncontacting sensors installed on the engine casing which provides vibration responses of all the blades in a rotor. The vibration responses obtained from blade tip timing system is validated using simultaneously measured strains from a few blade-mounted strain gages. A good correlation is observed between the predicted and measured blade responses. The effect of blade mistuning on the amplitude resonant response of the bladed disc is explored experimentally. It is observed that the maximum amplitude response of the blades due to forced resonant excitation is far below the fatigue limits for the prevailing blade mistuning pattern. The present exercise of quantifying the blade resonant responses through efficient implementation of the blade tip timing system is crucial to understand and thus avoid high-cycle fatigue, which is one of the most serious problems in aero-engine development.

Model validation for structural dynamics in the aero-engine design process

A model validation technique in structural dynamics and its application in aero-engine development is introduced. The concept and the approaches of model validation based on reference data supplied from experimental tests or from supermodel simulation are discussed in detail. An aero-engine component is used as an example to demonstrate the validation using the experimental test and supermodel information, respectively. A satisfactory agreement with both approaches is achieved, and finally, a strategy of model validation for the whole engine model is introduced.

2020 vision: the prospects for large civil aircraft propulsion

AbstractThis paper will examine the prospects for propulsion systems for large civil transport aircraft over the next two decades, to the year 2020. This period is likely to see the market drivers for future propulsion system development change from the more traditional ones of fuel consumption and weight, to also include those that affect the impact of civil aviation on the environment, and the continuing pressure to reduce the cost of ownership of civil engines, namely, product unit cost, maintenance costs and reliability. Fifty years of civil aero-engine development are reviewed and trends showing the likely limits to the main engine performance parameters are provided. The paper concludes with consideration of a number of new civil aircraft and engine concepts that may emerge in the next 20 years

Metal matrix composites for aeroengines

Metal matrix composites (MMCs) will play a significant role in the future of gas turbine aeroengine development. This paper outlines the benefits and some of the potential applications for Al and Ti MMCs and discusses issues involved in the introduction of this relatively new class of composite materials into engine components. The potential for cost savings and performance improvements which may be achieved by the introduction of silicon carbide particulate reinforced Al alloys (Al–SiCp MMC)are discussed, where the properties of the composite can be tailored to meet the requirements of a specific application. Some of the processing implications for Ti matrix composites (Ti MMCs) are explained for a range of component applications. Illustrations are given of how the manufacturing process can be controlled for a complex component. Finally, the influence of raw material, manufacturing, and component costs on the successful introduction of MMCs into aeroengines is discussed.

Viscous Three-Dimensional Simulation of Transonic Compressor Stage on Parallel Hardware

The continued thrust toward more efe cient, economic, and lower-emission turbomachinery along with the reduced lead time available for design iterations and the high cost associated with extensive rig and engine tests keepspushing forwardthestateoftheart incomputationale uid dynamics. Thepaperstartsoffwitha discussion of the aeroengine development processand its timescales. The place and importanceof Navier -Stokesmethods in the development process are addressed, and the three-dimensional viscous codeemployed for aerodynamic design and analysisofturbomachinery atMotoren-und Turbinen-UnionMisintroduced. Abrieftreatmentofthecode is followed by a discussion of its implementation on parallel hardware architectures to reduce turnaround times for incorporation as an integral part of the design process; excellent performance on symmetric multiprocessing- parallelarchitecturesisdemonstrated.Thee rstthree-dimensionalviscoussimulationsandthee rstdetailedanalysis of thesingle-stagetransonic compressorrig attheTechnical University of Darmstadt, a research rig representative of modern high pressure compressor front stages, are presented. Computed results are compared to experimental data in terms of radial distributions derived from traverse data, in terms of rotor Mach number e elds derived from L2F data on S1 and S2 planes, and in terms of performance parameters critical to designers. The excellent agreementbetweensimulationsandexperimentsdemonstratesthecode' spredictivecapabilityforturbomachinery design. With qualitative and quantitativeagreement demonstrated, e owdetailsover the outer 40% span and in the tip region of the rotor are examined, based solely on computational results. Three-dimensional simulations with and without tip clearance are compared to two-and-one-half-dimensional simulations to separate the ine uence of tip leakage on the rotor blade Mach number e elds from other three-dimensional effects. The complex e ow near the tip, involving an interaction of casing boundary layer, blade boundary layer, shock systems, and tip, leakage e ow, is analyzed to further the understanding of highly loaded transonic compressors and to identify potential for performance improvements. The analysis explains the e ow features found in this research rig and identie es the mechanisms contributing to the rather high loss and blockage near the casing.

Mass storage system reduces aero engine development time

Mass storage system reduces aero engine development time

Two-Stroke or Turbine? The Aeronautical Research Committee and British Aero Engine Development in World War II

Pendant la seconde guerre mondiale, les chercheurs britanniques ont developpe un projet de recherche en aeronautique afin d'elaborer un systeme de defense permettant la localisation et l'interception des bombes grâce a des avions et de leur systeme de radar

Two-stroke or Turbine? The Aeronautical Research Committee and British Aero Engine Development in World War II

Two-stroke or Turbine? The Aeronautical Research Committee and British Aero Engine Development in World War II ANDREW NAHUM All the ascendancy of the Hurricanes and Spit­ fires would have been fruitless but for this sys­ tem . . . which had been devised and built before the war. ... It had been shaped and refined in constant action, and all was now fused together into a most elaborate instrument of war, the like of which ex­ isted nowhere in the world. [Winston Churchill, The Second World War]1 During the 1930s, the growing apprehension in Britain about air attack began to provoke a shift in strategic thinking away from a purely retaliatory posture, which relied on a bomber force to counter the threat of bombers, toward a mixed strategy in which defensive interceptor fighters were to have a vital role. This new per­ ception stimulated an intensive program of research and develop­ ment in radar, in the control of fighters from the ground, and in aero engines. A connection between radar developments and a shift Mr. Nahum is senior curator of the National Aeronautical Collection at the Science Museum, London. He gratefully acknowledges the support of the museum in the conduct of this research, and thanks his colleagues Timothy Boon, Sir Neil Cossons, Dr. Robert Bud, and Dr. Alan Morton for many helpful comments. John Bagley, the author’s predecessor as curator of the aeronautical collection, provided a unique insight into the organization of government science from his time at the Royal Aircraft Establishment (RAE), Farnborough, and gave immense encourage­ ment for the undertaking of this work. Dr. David Edgerton at the Imperial College was generous with his comments. Finally, the author is grateful to the editor and referees of Technology and Culture for invaluable suggestions. ’Winston Churchill, The Second World War, vol. 2 (London, 1949), pp. 293-94. This is taken from a description of Churchill’s visit to the fighter control center at Northolt on September 15, 1940, the turning point ofthe Battle ofBritain. It conveys his instinctive appreciation of the way in which the functional integration of the British air defense system had created a pivotal strategic asset.© 1997 by the Society for the History of Technology. All rights reserved. 0040-165X/97/3802-0002$01.00 312 British Aero Engine Development 313 in policy in the mid-1930s to support jet engine development has previously been surmised.2 This study goes farther and establishes a direct linkage between early secret knowledge of radar and a wide range of British high-power aero engine work. The relationship between these programs casts light on contem­ porary planning for air defense and reveals a remarkably holistic approach to the pressing problem ofbomber interception. This gave rise to an integrated defense system which was, at that time, uniquely powerful and on which national survival in the Battle of Britain was to be critically dependent. There is a conventional stereotype of British defense science in this period. A lone inventor or “boffin,” committed, passionate, dis­ organized, inspirational, is pitted against the rigidity of officialdom (which is ultimately overcome). It is a scenario that has done great service to motion picture makers, for example in The Dam Busters, where the eccentric genius Barnes Wallis eventually sells his idea for a bouncing bomb to skeptical officials and Royal Air Force (RAF) officers.3 A more purposeful and technocratic vision of British defense re­ search can be found in the official histories of World War II or in a work such as Margaret Gowing’s Britain and Atomic Energy. More recently, there hasbeen an even stronger claim to characterize Britain as a “militant and industrial nation” with the contention that “the English state chose the aeroplane as its key strategic technology.”4 The account here differs from these models. It does not seek to locate the roots of British air defense uniquely in government or “the state,” nor in the insights of exceptionally inventive engineers. Rather, it portrays these roots as diffused to a remarkable extent through a both formal and informal network ofindividuals who, for the most part, were already in a social and professional relationship reaching back to World War I. Some were indeed government...