Critical Technology Events in

the Development of the Apache

Helicopter

Project Hindsight Revisited

Richard Chait, John Lyons, and Duncan Long 

Center for Technology and National Security Policy 

National Defense University

February 2006
 

The views expressed in this report are those of the authors and do not reflect the official 

policy or position of the National Defense University, the Department of Defense, or the 

U.S. Government. All information and sources for this paper were drawn from

unclassified materials. 

Richard Chait is a Distinguished Research Professor at the Center for Technology and 

National Security Policy (CTNSP), National Defense University. He was previously Chief 

Scientist, Army Material Command, and Director, Army Research and Laboratory

Management. Dr. Chait received his PhD in Solid State Science from Syracuse University

and a BS degree from Rensselaer Polytechnic Institute. 

John W. Lyons is a Distinguished Research Professor at CTNSP. He was previously director 

of the Army Research Laboratory and director of the National Institute of Standards and 

Technology. Dr. Lyons received his PhD from Washington University. He holds a BA from

Harvard. 

Duncan Long is a Research Associate at CTNSP. He holds a Master of International 

Affairs degree from the School of International and Public Affairs, Columbia University, 

and a BA from Stanford University.

Acknowledgments. Many people contributed to this effort. Dr. Thomas Killion, the 

current S&T executive for the Army, saw the benefit of looking back at key Army

weapons systems for insights that would be helpful in managing S&T in today’s 

environment. Former Army S&T executives George Singley and Fenner Milton gave 

freely of their time, providing both their recollections and recommendations of 

individuals to contact. On-site visits to the Aviation Advanced Technology Laboratory at 

Fort Eustis, Night Vision and Electronic Sensors Directorate at Fort Belvoir and the 

American Helicopter Society were the result of coordinating efforts by Danny Good, Jim

Ratches, and Ken Flater, respectively. Each and every person mentioned in Appendix A 

played an important role by providing valuable technical information and commentary as 

well as directing us to other contacts. Some, denoted by an asterisk, also reviewed 

sections in their area of expertise for accuracy and completeness as well as took part in 

in-depth follow-up conversations about the information and commentary that was 

provided. Full text reviews were provided by Waldo Carmona, Curt Herrick, Dick 

Ballard, Sandra Hoff, Neale Bruchman, and Larry Plaster. Al Sciarretta, working with us 

under a contractual arrangement, ably supported the effort and gave us valuable 

warfighter information based on his field experience while on active duty. 

Defense & Technology Papers are published by the National Defense University Center for Technology and 

National Security Policy, Fort Lesley J. McNair, Washington, DC. CTNSP publications are available online 

at http://www.ndu.edu/ctnsp/publications.html.

 ii 
Contents 

I. Introduction......................................................................................................1

II. Background.....................................................................................................3

Project Hindsight ............................................................................................................ 3 

The Need for the Apache ................................................................................................ 5

III. Study Methodology........................................................................................8

Scope............................................................................................................................... 8 

Approach......................................................................................................................... 8

IV. Power System..............................................................................................10

T700 Engine.................................................................................................................. 10 

Transmission................................................................................................................. 14

V. Survivability and Structural Advances .......................................................17

Vulnerability and Susceptibility Reduction.................................................................. 17 

Structural Advances...................................................................................................... 20

VI. Avionics, Fire Control, and Weapons ........................................................22

TADS/PNVS................................................................................................................. 22 

Fire Control................................................................................................................... 24 

Longbow Millimeter Wave Radar ................................................................................ 26 

Weapons Suite .............................................................................................................. 28

VII. Modeling and Simulation and Other Enabling Methodologies...............31

Co-Located Army-NASA Research Sites..................................................................... 31 

Other Collaborative Efforts........................................................................................... 32

VIII. Findings and Concluding Remarks .........................................................35

Findings......................................................................................................................... 35 

Concluding Remarks..................................................................................................... 36

Appendix A........................................................................................................37

Appendix B........................................................................................................39

 iii 
I. Introduction 

Understanding past military technological successes is crucial to defense science and 

technology investment and management. This study is the second in a series that 

examines some of the key factors that have led to meaningful technology generation and 

ultimate incorporation into the U.S. Army weapons systems we see in the field today. 

The first report covered the development of the Abrams tank.1

 Analysis of the 

development of the Javelin and Stinger missiles will follow. The results of all studies will 

be compiled in a wrap-up report that will include a look at the implications of the 

findings for today’s science and technology environment. 

We begin this paper by briefly reviewing a project that served as a source of inspiration 

for this study: Project Hindsight, a 1969 Defense Department (DOD) report.2 Hindsight

was an in-depth study sponsored by the Director of Defense Research and Engineering 

that provided some insights into the development of approximately 20 weapons systems 

across the DOD spectrum. Following the review of Hindsight, we present a short history 

of the events that led to the start of the Apache program. This is followed by a description 

of the methodology that we used to gather key data on the development of the Apache. 

The information that we have gathered is then broken out by topic area (Power System; 

Survivability and Structural Advances; Avionics, Fire Control, and Weapons; and 

Modeling and Simulation and other Enabling Methodologies) and presented in terms of 

Critical Technology Events (CTEs). CTEs are ideas, concepts, models, and analyses, 

including key technical and managerial decisions, that have had a major impact on the 

development of a specific weapons system. CTEs can occur at any point in the system’s 

life cycle, from basic research, to advanced development, to testing and evaluation, to 

product improvements. CTEs can even relate to concepts that were developed but that 

ultimately were not incorporated into the weapons system. Also, they can originate 

anywhere, from in-house laboratories, to private industry, to academia. The final portion 

of the paper presents the concluding remarks and findings based on the CTEs that 

characterize the Apache helicopter’s development. 

The CTEs are noted in the left margin throughout the report. They are summarized in 

Appendix B. CTEs are numbered only for ease of reference; there is no hierarchical or 

chronological significance to their order. 

While the link between high-tech weapons systems and battlefield success is often readily 

apparent, the geneses of and processes associated with CTEs often are not. CTEs depend 

on several important factors, including effective management, adequate funding, clear 

priorities, technical competence, and the leveraging of the resources of the private sector 

and academia. It is our hope that this retrospective look at the Apache helicopter can 

 

1

 This study, Critical Technology Events in the Development of the Abrams Tank, Defense and Technology 

Paper #22, was published in February 2006 by the Center for Technology and National Security Policy at 

National Defense University. It is available online at <http://www.ndu.edu/ctnsp/publications.html>. 2

 Office of the Director of Defense Research and Engineering, Project Hindsight: Final Report

(Washington, D.C.: Office of the DDRE, 1969). 
 

highlight the importance of these factors, and thus can be of value to current science and 

technology leadership within the Army and DOD as they wrestle with tight budgets, a 

changing workforce, and new acquisition strategies. 

 2 
 

II. Background 

In this chapter we highlight some of the objectives and findings of the first Hindsight

report of 1969. We also present a brief review of the circumstances that led to the 

creation of the Apache program. 

Project Hindsight 

This study is modeled in part on a 1969 report, Project Hindsight.

3

 In 1965, the Director 

of Defense Research and Engineering (DDR&E), Dr. Harold Brown, established a project 

to take a retrospective look at DOD investment in research and development (R&D), to 

evaluate the results, and to take stock of lessons learned. Brown’s overarching objectives 

for the study were to identify management factors that were associated with the 

utilization of the results produced by the DOD science and technology (S&T) program 

and to devise a methodology to measure the return on investment.4

 He was motivated in 

part by the House Committee on Defense Appropriations, which had questioned the 

efficiency of management and the overall payoff for the part of the Research, 

Development, Testing and Evaluation (RDT&E) program that pertained to S&T.5

 

The study was conducted by ad hoc teams of military and civilian in-house personnel. 

Some twenty weapons systems were selected for review and a set of subcommittees was 

arranged, one for each system. The systems selected for review included air-to-surface, 

ballistic, and tactical missiles; a strategic transport aircraft; a howitzer; and an antitank

projectile. Data were gathered by questionnaire and evaluated according to four criteria.6

These criteria were: 

1. The extent of dependence on recent advances in science or technology. 

2. The proportion of any new technology that resulted from DOD financing of 

science or technology. 

3. The management or environmental factors that appear to correlate with high

utilization of S&T results. 

4. A quantitative measure of the return on investment. 

The project teams made the following findings with respect to these four criteria: 7 

1. Markedly improved weapons systems result from skillfully combining a 

considerable number of scientific and technological advances (Criterion 1). 

 

3

 Ibid. 4

 Harold Brown, Letter to the Assistant Secretary of the Army (R&D), the Assistant Secretary of the Navy 

(R&D), and the Assistant Secretary of the Air Force (R&D), 6 July 1965 in Project Hindsight: Final

Report (Washington, D.C.: Office of the DDRE, 1969), 135. 5

 Ibid. 6 Office of the Director of Defense Research and Engineering, Project Hindsight: Final Report

(Washington, D.C.: Office of the DDRE, 1969), xiii. 7

 Ibid, xxi. 

 3 
 

2. More than 85 percent of the new science or technology utilized was the result of 

DOD-financed programs (Criterion 2). 

3. The utilization factor appears insensitive to environmental or management 

differences between industry, in-house laboratories, and university-associated 

science and technology centers (Criterion 3). 

4. Most utilized new technological information was generated in the process of 

solving problems identified in advanced or engineering development (Criterion 

3). 

5. Most utilized new fundamental scientific information came from organized 

research programs undertaken in response to recognized problems (Criterion 3). 

6. Technological inventiveness and the utilization rate are dependent on the 

recognition of a need, an educated talent pool, capital resources, and an adequate 

communication path to potential users (Criterion 3). 

7. Any crude approximation in measuring cost-performance will tend to be delusory 

(Criterion 4). 

With regard to finding number seven, the study failed to find a satisfactory method for 

assessing cost-benefit or cost-performance from science and technology work. To 

illustrate the difficulty that the study encountered, the report cited the example of the 

silicon-based integrated circuit. The circuit, invented during the period under review, 

revolutionized electronics and information technology and became a crucial part of 

virtually every system in the arsenal; there was no effective way to subdivide the effects 

on individual S&T programs. 

This paper will not attempt to redress this or any other shortcoming of Project Hindsight; 

Dr. Brown’s goal of quantifying the payoff of DOD investment in research and 

technology is if anything a loftier target today than it was in 1965. The fundamental 

purpose of this report, however, closely mirrors that of its predecessor: by examining the 

development of select Army systems, and in particular those signal technology events 

that propelled these systems to success, we hope to shed light on the factors that lead 

defense science and technology research to fruition. 

 

In addition to sharing a broad goal with the original Hindsight report, this paper also 

takes from it a similar unit of analysis, the CTE. Hindsight evaluations were based on a 

concept called a Research and Exploratory Development (RXD) Event. In that report, a 

RXD event has the predominant meaning of an event that “defines a scientific or 

engineering activity during a relatively brief period of time that includes the conception 

of a new idea and the initial demonstration of its feasibility.”8

 There may be one or two 

such events in the development of a component or system, or a whole string of such 

events. In the case of basic research RXD events, the report distinguishes between 

undirected (curiosity driven) and directed (problem driven) work. Lastly, the final 

fabrication of the system component or device “may or may not involve an Event 

depending on the state of the technological art at the time of fabrication.”9

 Please note 

that our signal events, CTEs, differ from Hindsight’s RXD events. Most significantly, 

 

8

 Ibid., xiv. 9

 Ibid. 

 4 
 

CTEs can occur at any point in the life cycle. We leave open the possibility that CTEs 

might result from efforts that have utilized funds other than R&D. 

The Need for the Apache 

The conflict in Vietnam conclusively demonstrated the importance of helicopter-provided 

close air support. Armed helicopters could move readily within a theater of operations 

and bring significant firepower to bear to, among other things, support beleaguered 

ground units, hold enemy combatants in place for a ground attack, and secure a landing 

zone as part of a vertical envelopment operation. The attack helicopter function was 

initially performed by transport and scout helicopters, most notably the Bell UH-1 Huey 

and the OH-6A Cayuse, retrofitted with additional armament. The Army’s first purposebuilt attack helicopter, the Bell AH-1G Cobra, was deployed to Vietnam in 1967. 

While the Cobra, based on the UH-1, was a step forward in helicopter technology, the 

experience in Vietnam revealed some key deficiencies. The Cobra’s engine often could 

not provide the power to carry a full load of fuel or ammunition to the fight, and the 

aircraft proved vulnerable to ground fire.10 The latter issue was of particular importance 

to the Army because the anticipated future combat environment, on the plains of central 

Europe against an adversary with modern air defenses, promised to be even more 

hazardous to helicopters than Vietnam. 

The first attempt to build an improved, more survivable attack helicopter was 

unsuccessful. The Advanced Aerial Fire Support System program, begun in the mid1960s, produced Lockheed’s AH-56A Cheyenne. The Army tested prototypes of the 

aircraft, but ultimately rejected it. The Cheyenne was an improvement in some areas, but 

it suffered from assorted technical shortcomings. In addition, the Army had reassessed 

the threat environment and its aviation needs. The Cheyenne had been designed to engage 

ground targets while making swift passes. This was the way in which the Cobra was 

employed, but this type of operation was made significantly more dangerous by the 

proliferation of effective, man-portable, antiaircraft missiles. The North Vietnamese 

forces had some success against U.S. helicopters with the SA-7 shoulder-fired antiaircraft missile, a type of weapon the Soviet bloc would have in great supply.11 These 

losses, and subsequent experience that showed that helicopter gunships could adjust and 

sustain low-level operations,12 prompted the Army to rethink helicopter tactics and the 

capabilities that the next aircraft would need.13 

In the wake of the cancellation of the Cheyenne program, the Army refined the role that 

the Cobra’s replacement would play. Looking toward a confrontation with the Soviets, 

and measuring the increasing threat posed air defense systems and increased lethality of 

small arms weapons, it called for a stand-off tank killer, an aircraft that could be effective 

 

10 Doug Richardson, Modern Fighting Aircraft: AH-64 Apache (New York: Prentice Hall Books, 1987), 4. 11 Ibid. 12 Curt Herrick, email to authors, 5 July 2005. 13 Richardson, 4. 

 5 
 

against Warsaw Pact armor while keeping its distance from a majority of ground-fire 

threats. The basic tactical concept was for the helicopter to remain below the tree line as 

much as possible, rising only to fire antitank missiles. The Advanced Attack Helicopter 

(AAH) program requirements were defined for this mission. The new helicopter had to be 

able to operate day or night in poor weather, sustain ground fire and continue to operate, 

protect its crew in the event of a crash landing, and carry a complete complement of 

antitank weaponry. Establishing these directives necessitated close interaction between 

the developers and the user as technical capabilities were weighed against operational 

concepts to determine the limits of possible requirements. 

The AAH program issued a request for proposals to industry in late 1972. DOD picked 

two of the initial five bidders—Bell Helicopter Company and Hughes Helicopter 

Incorporated—to enter a competitive development phase in 1973. In the end, the 

Hughes14 design, designated YAH-64, won the competition. In December, 1976, Hughes 

was awarded the contract to build the new AAH. The first Apaches15 were delivered to 

the Army in 1985. 

Before describing the capabilities of the AH-64 and the most recent version, the AH-64D 

“Longbow,” a brief comparison to the AH-1G Cobra is worthwhile. The AH-64, dubbed 

the Apache, was a significant step forward from the AH-1G Cobra in every area. It was 

more survivable. The fuel tank and hydraulics were given ballistic protection. Each of the 

twin GE T700-GE701 turboshaft engines had enough power to take the aircraft home if 

the other was knocked out, a huge advantage over the single-engine Cobra.16 The 

Apache’s transmission was required to run dry for thirty minutes. Structural components, 

including the rotors, were built to sustain direct hits by small arms fire. Advanced armor 

protected the two-man crew. A lower acoustic signature and lower heat signature made 

the Apache a more elusive target than the Cobra. 

The AH-64 was also a more lethal aircraft than its predecessor. The target acquisition and 

weapon systems represented significant breakthroughs. As befitted a tank-killer, the AH64’s primary weapon was the anti-armor Hellfire missile. The laser-seeking Hellfire was 

a major upgrade over the wire-guided TOW missiles carried by later Cobra models. 

Another version of the Hellfire’s guidance system, fielded around 1997, gave the Apache 

autonomous fire-and-forget capability. This missile was guided by the Longbow 

millimeter wave radar that was introduced on the AH-64D Longbow Apache. The AH-64 

was also equipped with an innovative chain gun and could carry a range of other 

munitions, including 2.75 inch rockets. 

 

14 Hughes Helicopter was purchased by McDonnell Douglas Corporation in 1984. McDonnell Douglas 

merged with Boeing in 1997 to create the Boeing Company. 15 The helicopter was not formally named the Apache until 1981. Its first designation was AAH for 

Advanced Attack Helicopter. The Hughes design that was funded after the Army selected Hughes and Bell 

as the final two competitors for the AAH contract was called the YAH-64. To improve readability, this 

report sometimes anachronistically refers to the “Apache” and the “Apache program” in the context of pre1981 events. 16 The Marine Corps still operates a much-updated version of the Cobra. The AH-1W SuperCobra has, 

among other improvements, a second engine. 

 6 
 

The Apache’s crew controlled these weapons and piloted the aircraft with the aid of the 

Target Acquisition/Designation System (TADS) and Pilot Night Vision Sensor (PNVS). 

The sensors for these systems are mounted in a turret on the nose of the aircraft, and 

include thermal imagers, direct view optics, a television camera, a laser spot tracker, and 

a laser rangefinder. The sensor turret is slaved to the crew’s helmets, turning as they turn. 

After a review of study methodology, we describe the CTEs that led to these battlefield 

capabilities.

 

 7 
 

III. Study Methodology 

Scope 

We have chosen to focus this report on those things we deemed to be major technical 

developments. The Apache has hundreds of components that undoubtedly required some

innovation. This study intends neither to cover every CTE in the course of developing the 

helicopter nor to provide exhaustive technical detail on those CTEs that it does address. 

The intent is to concentrate on major technical developments that relate to the Apache’s

core capabilities. 

We have divided this report into four major topic areas: power system; survivability and 

structural advances; avionics, fire control, and weapons; and modeling and simulation 

and other enabling methodologies. This separation of topics comes at the acknowledged 

price of diminished discussion of integration, systems engineering achievements, and the 

teaming of in-house laboratoriess, contractors, and the program manager (PM). The 

important integration work performed by the contractor, working closely with the PM 

shop and in-house laboratories, was vital to the final product. This fact is highlighted 

again in chapter VIII of this paper and will be the subject of additional discussion in a 

summary paper after the other reports in this series have been completed. 

Approach 

This report is based primarily on interviews and correspondence with people who were 

directly involved in the development of the Apache, as well as information available in 

open source literature. Given the technical emphasis of the report, we interviewed and

corresponded mostly with technical professionals. We also sought out personnel who had 

been at the PM office and with the contractors. The objective of these communications 

was to obtain a picture of how the important critical technology events unfolded. 

The interviews covered a broad range of pertinent topics, including the historical 

background of the developments in question. The focus of discussion, though, was the 

CTEs. We asked interviewees to identify those technology events that they considered 

critical to the development of the Apache; to detail the impact of the CTEs; to indicate 

where the work in question was done; who contributed to it; who funded it; the nature of 

the funding (e.g., 6.1, 6.2, 6.3, etc.);17 the number of staff involved; and the management 

factors that contributed to success. 

 

17 DOD divides Research, Development, Test and Evaluation (RDT&E) spending into seven different

activity categories. Category 6.1 refers to the budget line item for Basic Research; 6.2 is for Applied

Research; 6.3 is for Advanced Technology Development. These three categories are referred to collectively 

as Science and Technology. 

 8 
 

Often, we first interviewed a source and then obtained further information through 

follow-on conversations and correspondence. Almost all of the discussions began with 

the interviewees providing highlights of the relevant experiences, after which we asked 

focused questions on topics not initially covered. 

It must be noted that the interviewees and correspondents were asked to relate events that 

in some cases took place decades ago. A few of these individuals are still in government 

service but most are retired or active in the private sector. Detailed information was 

sometimes unavailable. Data on funding levels, for instance, were obtainable only 

intermittently. Wherever possible, we consulted multiple individuals on the same subject 

and checked their accounts against written sources. When interviewees and 

correspondents differed on what constituted a critical technology or who had made 

essential contributions, we revisited the issue until we established the most accurate 

possible picture of events. As a result, we are confident that we have captured the most 

pertinent information related to the major technical events in the development of the 

Apache. 

 9 
 

IV. Power System 

The Apache is a substantially more powerful aircraft than the AH-1G Cobra it was 

designed to replace. We start this section with a discussion of CTEs associated with the 

Apache’s T-700 turboshaft engine, then turn to the transmission. 

T700 Engine 

The conflict in Vietnam revealed substantial shortcomings in U.S. helicopter engine 

performance. The chief problems were insufficient power, poor reliability, high 

maintenance needs, and poor specific fuel consumption.18 These deficiencies led the 

Army to develop a new engine for its next generation of helicopters. The staff at the 

Army Aviation Systems Command (AVSCOM), and especially at its Aviation Applied 

Technology Directorate (AATD) at Fort Eustis, managed the early development of the 

new engine. The AATD program, called the “1500 Demonstrator Engine Program” 

(DEMO), did work on a 1500 horsepower turboshaft engine in the late 1960s. The 

DEMO program drew on their earlier work on gas turbine engines of this size. 

Subsequently, AATD was tasked to set requirements for these engines, with special 

emphasis on maintainability.19 Their approach was to estimate the outer limits of the 

existing technology and incorporate challenging goals in the request for proposals. In 

addition to addressing the problems noted above, AATD set the following specific 

requirements for the engine: 20

CTE 1 

• An inlet particle separator 

• Low maintenance/ fast overhaul; easy access to components 

• Performance targets in terms of horsepower-to-weight and specific fuel 

consumption 

• Little performance deterioration over life 

• Low acquisition cost

• A history recorder to track the health of each engine 

• Controlled development cost 

General Electric, which had provided the first-ever turboshaft engine for a rotorcraft, and 

Pratt & Whitney were the chief competitors for the contract. The work on the new engine 

was funded with 6.3 money from AATD.21 Ultimately, General Electric’s design for a 

1500-1600 horsepower engine was selected to power the Army’s new generation of 

helicopters. The Army first used the engine, dubbed the T700, in the Utility Tactical 

Transport System (UTTAS), requiring in 1971 that competitors for the UTTAS contract 

include the T700 in their designs.22 The Army strongly encouraged the competitors for 

 

18 Gene Hower, email to authors, 7 April 2005. 

19 Sandra Hoff, telephone interview with authors, 28 February 2005, and Richardson, 24. 20 Robert Turnbull, telephone interview with authors, 13 April 2005. 21 Hoff interview. 22 Richardson, 22. 

 10 
 

the AAH contract to use the T700 as well.23 The T700 family was consequently used in 

Sikorsky’s UH-60 Black Hawk (the result of the UTTAS program) and Hughes’s AH-64 

Apache. 

The Apache’s twin T700s provided substantially more power than the single Lycoming 

T53 used in the AH-1G Cobra, and were 27 percent more fuel efficient.24 This added 

efficiency meant a reduced fuel load, which enabled designers to lighten the airframe and 

choose either to realize a weight savings or carry more armaments and armor. This 

improvement in efficiency produced large savings in air frame costs.25 Each engine is 

capable of carrying the aircraft home should the other be knocked out. 

GE engineers incorporated several innovations in the T700. GE simplified the combustor 

by going to a machined-ring configuration that was made in one piece. Earlier 

combustors were made of several pieces and tended to move and slowly deteriorate, 

limiting performance and life.26 Another important aspect of the engine design is the 

scheme for removing particles from the incoming air. (Recall the disastrous attempt to 

rescue the hostages in Iran in 1980, when the intake of sand degraded helicopter engine 

performance and compromised the mission). This technology uses cyclonic effects (swirl 

vanes) in the front of the compressor together with an air pump to eject the separated 

particles. The device has been continually improved by GE over the years.27 

CTE 2 

CTE 3 

GE engineers also overcame several initial challenges. They encountered forced vibration 

of compressor blades when there was a resonant frequency common to both blades and 

housing. This problem required some redesign.28 Also, the unusually high rotational 

speed of the compressor shaft (45,000 rpm) and the power shaft (20,900 rpm, turning 

freely and concentrically within the compressor shaft) called for improvements in the 

properties and design of the disks and blades. GE learned how to manufacture these 

assemblies in one piece that they termed “blisks,” using powder metallurgy with a nickelbased alloy. This is said to be one of the first applications of powder metallurgy.29 This 

blisk design was mandatory on the first compressor stage, because a conventional 

dovetail could not hold the blade at these high rotational speeds.30 Blisks were also used 

on the rest of the compressor stages, because they improved performance and 

maintenance cost. 

CTE 4 

CTE 5 

Additional important T700 design innovations include:31 

• Minimum oil, fuel, or hydraulic lines on outside of engine 

• Special “curvic” joining the high power rotor 

• Tie rods holding the engine rotors together 

 

23 Ibid., 6. 24 Nick Kailos, email to authors, 20 May 2005. 25 Ibid. 26 Turnbull interview. 27 Ibid. 28 Ibid. 

29 Ibid. 30 Turnbull, email to authors, 5 May 2005. 31 Turnbull interview. 

 11 
 

• Spall-resistant bearing materials 

• Special compressor design for high rpm

• Run-dry oil reservoir at bearings (discussed below) 

• Special cleanliness for oil sump (clean room spec) 

• Redesign of air flows to avoid slow speed stalls 

• No lockwires to secure bolts for reduced maintenance 

While most of the work on the engine was done on contract, the Army engineers colocated at NASA Glenn in Cleveland conducted 6.1 and 6.2 work that supported the 

contractual effort and focused on the problems arising during the development of the 

Apache.32 They worked on the shape of the air foils in the turbine, on the cooling system, 

on pitting in metals, and on lubrication. They ran in-house engine tests in which they 

mapped engine temperatures, measured heat distortions and overheating, and took heat 

transfer data. They also studied contingency power, i.e., the availability of power in the 

event of an emergency, particularly the loss of one engine. More recently, they have 

studied the possible extension of the operating life of the engine and the reuse of some 

components during major overhaul. They have devised inspection protocols, including 

methods and timing of crack detection in the metals. Army engineers made the fruits of 

all this labor, including data sets from tests and experiments, available to industry.33 This 

important work laid the foundation for several engine-related technical innovations. 

One especially successful piece of Army 6.1 work at NASA Glenn was related to the 

process, now standard in the industry, for applying ceramic coatings to line the 

combustor and the blades in the hot section of the engine. Ceramic coating allows higher 

operating temperatures and hence greater efficiencies. 

CTE 6 

This engine work at NASA Glenn required 4-5 full time technologists, of whom 1-2 were 

Army employees.34 Some in-house contractor staff were also involved.35 

The Army also funded 6.1 basic research at universities on rare-earth magnets that 

enabled significant weight and size reductions for starters and generators. The engineers 

at AATD realized the significance of university findings in this area and brought them to 

the attention of GE, which first utilized them in full-scale production of helicopter 

engines in 1978.36

CTE 7 

CTE 8 Work continues today that will eventually lead to additional improvements to the T700 

series.37 A significant DOD program paralleling and reinforcing the Apache work is the 

 

32 Robert Bill, telephone interview with authors, 16 February 2005. 33 Ibid. 34 Ibid. 35 On materials research it is estimated that they devoted about 5 man years. Ibid. 36 Kailos, telephone interview with authors, 23 February 2005. 37 The latest needs statement for helicopter engines of this class is for upgrading the Black Hawk. The 

JTAGG team’s work on the development of the gas generation section for the new Black Hawk engine is

complete. However, more S&T work is needed to address integration of the power turbine, controls, 

accessories and inlet technologies. The new engine will have on the order of 3000 hp. Hoff, email to 

authors, 28 February 2005.

 12 
 

Joint Turbine Advanced Gas Generator (JTAGG) program.

38 This joint program,

managed by AATD, addresses the goals of the DOD program on Integrated High 

Performance Turbine Engine Technology. The work has been done on contract. It is a 

three-phase program with ambitious goals to produce a 120 percent increase in the ratio 

of shaft horsepower to engine weight and a decrease in specific fuel consumption of 40 

percent.39 

This new technology has already supported upgrades to the T700 leading to the T700 GE 

701C and D. The D version applies new material technologies derived from the 

Commercial CT7-8 engine experience to the power turbine section and to select other 

parts of the engine to produce a power increase to ~2000 hp and significantly improve 

predicted reliability.40 The 701D engine has completed engine airframe compatibility 

testing for retrofit to the Block I or II configuration AH-64D models as a replacement for 

the 701C engine (it maintains 701C power limits) and will be retrofitted to these aircraft 

by attrition. The 701D will be qualified in the AH-64D Block III configuration during the 

Block III System Development and Demonstration tests and will be installed on the 

production line for Block III and beyond.41 The substantial increase in power achieved 

for the 701D over the original T700-700 configuration (see figure 1 below) has come at 

the cost of minor additional engine weight. The power increase is the result of 

incremental improvements in operating temperatures, greater air flow volumes, and 

higher compressor ratios.42

 

38 Hoff, email to authors, 28 February 2005. 39 Ibid. 40 Larry Plaster, email to authors, 6 September 2005. 41 Ibid. 42 Kailos interview and Turnbull interview. 

 13 
 

Figure 1. T-700 family growth path.43

Transmission 

Work on the transmission was equally important to the Apache’s power system

development. The transmission, initially designed by Hughes,44 takes input power from

the two T700 engines, reduces the speed of rotation, and transfers the power to the main 

rotor shaft, accessory gearbox, and tail rotor assembly. Between each engine output shaft 

and the main transmission is an engine nose gearbox. Each gearbox is equipped with an 

over-running clutch. If the shaft from the transmission is running faster than the 

corresponding shaft from the turbine, the clutch disengages. When the opposite is true or 

the speeds of rotation are equal, the clutch is engaged. The turbine output shafts rotate at 

20,900 rpm. This is reduced in the gear box at the front of the engine by reduction gears 

by a factor of 2.129; the transmission and subsequent gear boxes then further reduce the 

rotational speed such that the main rotor turns at about 200-400 rpm.

45 This is a total gear

reduction of about 50:1 (compared to an automobile in which the gear reduction is only 

about 4:1). 

 

43 Figure from Hoff, email to authors, 28 February 2005. 44 Plaster, email to authors, 6 September 2005. 45 Hoff, email to authors, 18 May 2005. 

Production Engines

Development In Process 

(1,980 SHP)

T700-700 based on 1967 initiated T700-701D

1500 HP Engine Demo

(1,890 SHP)

-Increased airflow

Power -New combustor & turbine

-Improved Power Turbine

T700-401C

T700-701C* (1,698 SHP) -Increased airflow CT7-2D1 

-Improved GG turbine

-New diffuser T700-401 

T700-701*

T700-701A

CT7-2D

(1,622 SHP)

T700-700 

CT7-2A 

* Operative Engines Time

 14 
 

Special emphasis in transmission development was placed on maintainability. The unit is 

highly reliable, but in the event of a breakdown the entire transmission was designed such 

that it could be replaced in two hours.46 Among its other key features, the Army required 

that the transmission be protected against sudden loss of oil so that the Apache could 

sustain significant damage and still fly home. The resulting run-dry design enables the 

transmission to operate for up to 30 minutes after losing oil.47 This is accomplished by 

use of anti-wear additives in the lubricant that have residual lubricating effects, even 

when the fluid is drained, and by surface treatment of the metals, use of premium 

materials, and close-tolerance machining. 

CTE 9 

The transmission also required considerable work on advanced gear technology by the 

Army/NASA Glenn staff. For gears and bearings, the Army/NASA work overcame 

barriers to higher performance in terms of speed, loading, and operating temperatures. 

Work on double-vacuum melted, high hot-hardness bearing steel and on gear alloys 

“doubled the power density compared to previous engines and vastly improved 

reliability” and removed a major barrier to progress in engine and transmission 

technology.48 Results of this work are now used throughout industry.49 

CTE 10 

These transmission advances were achieved through considerable collaboration between 

the private sector, academia, and in-house laboratory engineers. The Army’s in-house 

work on transmissions was done at NASA Glenn.50 Money for work on the transmission 

came both from AATD and from mission funds from the Army Research Laboratory 

through the Army propulsion group co-located at NASA Glenn. The Defense Advanced 

Research Projects Agency (DARPA) has also supported some of this work. In the 

mission-funded area, they worked on gear-tooth profiles, spiral gears, and gear geometry. 

They also published data sets for use by industry.51 

Recent work at Army/NASA Glenn and in industry on face-gear drives will be put in 

service in the latest Block III Apache upgrade. This technology, developed over 10 years 

of work at NASA Glenn and industry, splits the engine input torque evenly between 

upper and lower face gears (which are smaller and lighter than conventional main-drive 

sun gear designs), eliminating one planetary gear stage and allowing more power 

throughput with no increase in transmission size or weight.52 

 

46 Herrick. 47 Turnbull interview. 48 Bill, email to authors, 22 February 2005. A comprehensive report on this work by Army/NASA Glenn

engineers is: Erwin Zaretsky, ed., Tribology for Aerospace Applications (Park Ridge, Illinois: The Society 

of Tribologists and Lubrication Engineers, 1997). 49 Bill email. 50 Bill interview. 51 Ibid. 52 F.L.Litvin et al, “Face Gear Drives, Design, Analysis, and Testing for Helicopter Transmission 

Applications,” Propulsion Directorate, U.S. Army Aviation Systems Command and NASA Lewis Research 

Center, NASA Glenn Technical Reports No. E-7743, 1992; Boeing News Release “New Apache 

Transmission Technology Offers More Power and Capability,” February 22, 2005; D.G. Lewicki et al, 

“Evaluation of Carburized and Ground Face Gears,” U.S. Army Research Laboratory and NASA Glenn 

Research Center, NASA Glenn Technical Research Report No. E-11700, 1999; F.L.Litvin et al, “Handbook

 15 
 

One of the key technology breakthroughs needed to successfully produce the split-torque 

face gear design was development of a grinding machine capable of economically 

producing the face gears with their complex gear-tooth profiles in production quantities.53

The manufacturing technology was developed via a partnership between Boeing and 

Northstar Aerospace of Canada in which Northstar provided much of the gear 

manufacturing technical expertise and the funding required to develop the advancedtechnology gear-grinding machine.54

In addition to development of the face-gear technology, the new Apache main 

transmission scheduled to be fielded with the AH-64D Block III upgrade includes several 

other significant rotorcraft transmission technology achievements developed by both 

government and industry research. The end result of the combined efforts of NASA 

Glenn, AATD, Boeing, Northstar Aerospace and Penn State University is a new Apache 

main transmission design that is the same size as the old design but is capable of 25% 

more power throughput and has more than twice the endurance life of the current 

design.55

 on Face Gear Drives With a Spur Involute Pinion,” University of Illinois at Chicago and the Boeing 

Company, NASA Glenn Technical Report No. E-12127. 53 Plaster, email to authors, 6 September 2005. 54 Ibid. 55 Ibid. 

 16 
 

V. Survivability and Structural Advances 

Some of the most important innovations on the Apache had to do with keeping the crew 

safe. Crew safety was a fundamental requirement of the AAH program. The helicopter 

had to be able to withstand hits from heavy machine guns, and its crew must have a 95 

percent chance of surviving a crash at a vertical speed of 42 feet per second.56 In this 

chapter we first present CTEs associated with two categories of survivability: 

vulnerability (reducing the likelihood of a kill if hit) and susceptibility (reducing the 

likelihood of being hit in the first place). This is followed by a discussion of important 

structural advances. 

Vulnerability and Susceptibility Reduction

The Apache benefited from a range of noteworthy advances designed to protect the crew 

and the aircraft from hostile fire. Important strides were made in ballistic protection. In 

the mid-to-late 1970s, using about $200,000 per year of 6.2 funds, the Army Materials 

Laboratory at Watertown developed the concept of using a transparent laminate armor 

material to separate front and rear cockpits.57 The material, a glass/polycarbonate 

laminate, was patented by Army researchers and used above the seat line. With this 

shielding system in place, the likelihood that both the Apache pilot and gunner would be 

injured by a single hit was significantly reduced. 

CTE 11 

The development of ceramic composite materials by industry58 and the Army laboratory 

at Watertown59 led to additional ballistic protection for Apache crew members. Seats that 

provided ballistic protection had their origin in the mid-1960s, when work at Watertown 

showed that ceramic materials, with their high hardness and stiffness, were effective 

against small arms ammunition of the type encountered in Vietnam. Boron carbide was 

demonstrated to be the most effective ceramic material; when coupled with glassreinforced composite back-up material, it was able to defeat small arms threats. 

Following the Vietnam War, the use of Kevlar was proposed by Watertown as a material

for the rear of the boron carbide armor.60 This combination provided even better weight 

efficiency and was chosen for use in the Apache for the helicopter crew seats.61 

CTE 12 

Another flight-safety effort addressed the hazards presented by communication and 

power lines. These wires are a particular threat during nighttime or adverse-weather 

 

56 Richardson, 5. 57 Gordon Parsons, telephone interview with authors, 3 March 2005. 58 William Perciballi, interview with authors, Phoenix, AZ, 11 December 2005. 

59 Deborah E. Gray, The U.S. Army Laboratories at Watertown, Massachusetts Contributions to Science 

and Technology: A History (Watertown, MA: Army Research Laboratory Materials Directorate, August 

1995) 39. 60 Ibid., 40. 61 Ibid. 

 17 
 

daytime operations, especially in confined areas and during nap-of-the-earth (NOE)62

flying. Analysis of Army accidents showed that over 16 percent of Army aviation 

fatalities and over 8 percent of materiel losses in peacetime operation between January 

1974 and January 1980 were due to in-flight wire strikes.63 In the late 1970s, separate 

U.S. and Canadian programs addressed the issue and developed systems for wire strike 

protection. The U.S. design, developed by AATD, was very basic: a cutter/deflector 

system consisting of an upper and lower cutter that would sever steel, copper and 

aluminum wires. The Canadian design was similar and a cooperative effort ensued. To

evaluate the design, a unique qualification test procedure was developed by AATD and 

full-scale qualification tests of Army helicopters were successfully conducted by AATD 

at NASA’s Langley Research Center.64 As a result, the system was retrofitted to the 

Apaches in the mid-1980s and built into all Army helicopters except the CH-47. Current 

research in avoiding wire strikes focuses on avoidance.65 

CTE 13 

Recognizing that despite the above advances, hostile fire, wires, or other factors would 

occasionally bring down the aircraft, the Army placed great emphasis on protecting the 

Apache’s crew during a hard landing. This emphasis was especially prudent considering 

that the Army required the AAH to execute NOE operations; low-speed, ground-hugging 

flying, sometimes at night, increases the probability of having an accident or being hit by 

ground fire. The Apache benefited from work at AATD towards the goal of having a 

crashworthy rotary-wing aircraft. A helicopter crash research program involving subject 

matter experts from private-sector safety groups was initiated in the late 1950s and 

continued into the 1980s. The program was funded by 6.2 and 6.3 monies. The funding 

levels were modest at first but ramped to about $1 million per year.66 Other Services also

contributed to the effort as part of the Joint Logistics Commanders Aircraft Survivability 

Group’s activities.67

CTE 14 

In this pre-Apache effort, data were gathered from full-scale crash tests and actual 

helicopter crash investigations. These data showed the presence of several deficiencies.68

Among them were loss of occupiable volume due to structural collapse, inward buckling 

of frames, seat tear-out due to floor breakup, and penetration into occupied areas by 

landing gear and the main rotor gearbox. The landing gear was designed in accordance 

with conventional practice at that time for hard landings with some reserve. Crash energy 

attenuation was not a consideration, thus excessively high acceleration forces were 

allowed to be transferred to the occupants. 

 

62 Flight at varying airspeeds as close to the earth’s surface as vegetation, obstacles and ambient light will 

permit, while generally following the contours of the earth. 63 LeRoy T. Burrows, “Wire Strike Protection for Helicopters,” U.S. Army Aviation Digest, September 

1980, 36. 64 Ibid., 38. 65 Neale Bruchman, email to authors, 17 January 2006. 66 LeRoy Burrows, telephone interview with authors, 2 March 2005. 67 Herrick. 68 C. Hudson Carper and LeRoy T. Burrows, “Evolving Crashworthiness Design Criteria,” Energy

Absorption of Aircraft Structures as an Aspect of Crashworthiness Conference Proceedings (Neuilly Sur 

Seine, France: Advisory Group for Aerospace Research and Development, May 1988), 2.

 18 
 

As the data were evaluated, the emphasis of the Army program shifted from crash 

prevention to improving occupant survival and reducing materiel losses. This emphasis 

led to the first ever crash-survival design guide for light fixed- and rotary-wing aircraft.69

It was published in the late 1960s and revised in the 1970s and 1980s. The design guide 

was subsequently converted into a military standard, Mil-Std 1290, which governed the 

design of both the Apache and Black Hawk helicopters and created a systems approach to 

design for crashworthiness. It called for the following important areas to be addressed: a 

structure of sufficient strength and stiffness to prevent aircraft plowing in soft soil; proper

retention strength for high mass items to preclude break-away and to maintain a 

survivable occupant volume; use of crushable structures and load-limiting designs for 

landing gear and aircrew seats to reduce occupant acceleration; restraint systems and 

padding to prevent injury from flailing; and post-crash hazard reduction—protection from

flammable fluids and emergency egress provisions for the occupants under all 

conditions.70 As a result of this significant step forward, the Apache crew has a 95 

percent chance of surviving a crash with no spinal or thermal injury when the helicopter 

approaches the ground at rates of up to 42 feet per second.71 

CTE 15 

The Army’s development of sound design criteria for crashworthy fuel systems has 

produced the largest payoff in the endeavor to improve rotorcraft crash safety.72 Before 

this work, 41 percent of fatalities from otherwise survivable crashes were attributed to 

post-crash fuel fires.73 This number has been reduced to zero percent for aircraft equipped 

with internal and external crashworthy fuel systems.74 Changes were made in both fuel 

system materials and design. Self-sealing and tear-resistant polymers enhanced protection 

of the fuel tank. Changes were also made in the breakaway, self-sealing valves, fuel lines, 

filling system, and vents. The work was a contractual effort funded by AATD. In 1968 

the Army Chief of Staff approved use of the fire-resistant system in the first helicopter—

the UH-1—and the fleet in Vietnam was retrofitted. This level of fire safety was then

specified in Mil Std 1290 and in the design guide and incorporated in the subsequent 

requests for proposals for the Apache and Blackhawk.75

CTE 16 

In addition to these ballistics and crashworthiness improvements, the Apache 

incorporated several advances designed to prevent the aircraft from being targeted at all. 

There was a major effort through the Army’s S&T program and Aircraft Survivability 

Equipment program to develop a suite of active and passive defenses. In-house 

laboratories such as AATD and CECOM, working closely with industry, provided 

CTE 17 

 

69 LeRoy T. Burrows and Kent F. Smith, “Crashworthy Helicopters Save Lives and Equipment,” Army

Research, Development and Acquisition Bulletin, July-August 1989, 6. 70 Ibid. 71 Burrows interview. This holds true only with the reasonable roll/yaw/pitch envelop that is cited in MilStd 1290. 72 Burrows, email to authors, 6 May 2005. 73 Burrows interview. 74 Ibid. 75 It is important to note that much of the fire safety technology specified in Mil Std 1290 and included in

the Crash Safety Design Guide was derived from the automobile racing industry, which had been forced to

incorporate crashworthy fire safety features into racing cars due to the extreme flammability of the high

octane fuels used for Indy Car racing. Plaster, email to authors, 6 September 2005. 

 19 
 

advances in the following areas: engine exhaust IR suppressor design; the ALQ-144 IR 

countermeasure system, a device designed to jam incoming heat-seeking missiles; lowsignature paint and windshield concepts; and radar and laser warning systems.76 

Structural Advances 

During the Apache development, the idea of using integral armor for structural loadcarrying purposes as well as for ballistic protection was advanced by Hughes Helicopter 

during discussions with Army materials scientists.77 Hughes utilized this innovative 

approach to realize significant weight savings. For example, the company made extensive 

use of electro-slag, high-strength steel for integral armor application in such components 

as hydraulic actuators, rotor pitch links, bearing sleeves, and crank assemblies.78

Fabrication from steel that exhibited high hardness and strength as well as high toughness 

enables the components to sustain ballistic impact and continue to function. 

CTE 18 

Among the next major structural challenges for ongoing Apache development work was 

the design of an all-composite rotor blade for the aircraft. Materials scientists and aircraft

engineers have been working on incorporating composite materials, which have high 

strength to weight ratios, into helicopter rotors for many years. Fiberglass composite 

materials had been under consideration for rotor blade applications since the late 1940s, 

when fiberglass rotor-blade prototypes were tested in the private sector under Air Force 

contract.79 In the late 1960s, AATD explored the use of fiber composite materials, and 

the processing methods thereof, for structural components, including the main rotor 

blade.80 Also in the 1960s, Hughes fabricated a unidirectional fiberglass composite 

prototype blade for the Cobra helicopter.81 The exceptionally low service life of metal 

rotor blades in Vietnam (as low as 25 flight hours) due to fatigue and ballistic and foreign 

object damage again spurred interest in composite materials in the early 1970s.82

Continued interest led Kaman Aircraft in the mid-1970s to design and manufacture the 

world’s first production all-composite rotor blade for the AH-1G Cobra.83 

CTE 19 

These and other efforts in this area have paved the way for the eventual addition of an allcomposite rotor blade to the Apache. When the Apache was first fielded, composite 

materials were not yet available that could meet the AAH program ballistic requirement 

at an acceptable weight: the rotor had to be ballistically tolerant to damage from a 23mm 

high explosive incendiary (HEI) round. To meet this requirement, the Apache main rotor 

blade initially was manufactured from metal using four, interlocked, metal spar 

CTE 20 

 

76 Raymond Wall, email to authors, 20 January 2006. 77 Dino Papetti, telephone interview with authors, 23 February 2005. 78 Gray, 67. 79 Richard M. Carlson, “Composite Structures,” American Helicopter Society Magazine, May 1994, 32. 80 Ward Figge, telephone interview with authors, 16 February 2005. 81 Ibid. 82 Figge, email to authors, 16 May 2005. 83 Kaman Corporation, “Kaman History.” Available online at: 

<http://www.kaman.com/history/kamanhist_main.html>, accessed 9 August 2005. 

 20 
 

structures.84 This unique structural design provided a very lightweight blade structure that 

could meet the stringent ballistic requirement. Research done after initial fielding of the 

Apache by AATD, combined with experience gained by Boeing in developing composite 

blades for the CH-47, the commercial model MD-900, and the Comanche (the planned 

armed reconnaissance helicopter that the DOD canceled in 2004), resulted in new 

materials and analytical tools for blade spar sizing. This allowed the design of a new 

single spar, all-composite main rotor blade for the Apache, which is planned for fielding 

in 2008.85 The design process for the composite spar was noteworthy. The design was 

generated and refined using a series of prototype blade sections subjected to 23mm HEI 

live-fire testing.86 Refinements in the design after each test resulted in a final design that 

exceeded the capability of the original metal blade design to continue operations after 

damage from a 23mm HEI round. 

It should be noted that the use of composites for rotor blades and other helicopter 

applications was supported by important research on the materials’ failure modes. Since 

the 1970s, a group of Army researchers co-located at the NASA Langley Research Center 

has been among the leaders in quantifying the delamination process in composite 

materials. As a result of this effort, crack energy release rates at the delamination front 

have been documented. In the 1990s, this work led to accepted test methods and 

guidelines for determination of delamination, which is highly important to the ability to 

predict failure in composite materials.87 

CTE 21 

 

84 Plaster, email to authors, 6 September 2005. 85 Ibid. 86 Ibid. 87 T.K. O’Brien, email to authors, 2 March 2005. 

 21 
 

VI. Avionics, Fire Control, and Weapons 

In this section we cover the CTEs that have been instrumental in giving the Apache the 

capability to operate day or night under adverse weather conditions, to find, track, and 

destroy enemy targets. These capabilities, combined with those discussed above, make 

the Apache the world’s most advanced attack helicopter. 

TADS/PNVS 

The Target Acquisition and Designation Sight and the Pilot Night Vision Sensor 

(TADS/PNVS) are key to the Apache’s ability to operate at all times, especially in all 

conditions, to find, track, and fire upon targets. Designed by Martin Marietta, 

TADS/PNVS is an integrated system that pulled together for the first time thermal 

imaging devices, laser range finders and laser designators.88 The TADS is used by the 

gunner/co-pilot for target search, detection, designation, and tracking. It has a Forward 

Looking Infra-Red (FLIR) sensor for night operations; a TV camera with both narrow

and wide views for day operations; direct view optics; a laser spot tracker; and a laser 

rangefinder.89 The PNVS has a FLIR sensor that gives the pilot the wide-angle view that 

is needed to fly and maneuver at night as well as to locate targets. The sensors for both 

units are located in a rotating turret mounted on the Apache’s nose. 

CTE 22 

Critical to the TADS/PNVS is the FLIR sensor. The significant strides that the Army

laboratories made in FLIR technology while working on the Abrams tank90 and other 

weapons systems also benefited the Apache. Among these advances were a common 

module approach to FLIR production and a minimum resolvable temperature (MRT) 

determination as a way to measure FLIR performance. Also, it should be noted that for 

the Apache, with the work on the MRT as a foundation, the U.S. Army Night Vision 

Laboratory (NVL) produced a mathematical model that could be used to evaluate the 

performance of IR devices.91 The model predicts the performance in terms of the 

probability of recognition and detection. As a result of the success of the model, the 

Army required that it be used to evaluate the performances of IR devices that were 

included in proposals submitted to the government during the Apache development, as 

well as subsequent Army weapons acquisitions that required thermal imaging. 

CTE 23 

 

88 Richardson, 26. 

89 CTEs related to the laser rangefinder have already been detailed in our earlier paper on the Abrams tank.

CTEs include the early work on the ruby laser rangefinder, the improvements that came with development

of the Nd:YAG laser that provides the wave length required for target designation for semi-active seekers,

and work to improve eye safety characteristics. 

90 Some CTEs associated with FLIR development that apply to the Apache have already been detailed in

our earlier paper on the Abrams tank. 

91 James A. Ratches et al., Night Vision Laboratory Static Performance Model for Thermal Viewing 

Systems (Fort Belvoir, VA: U.S. Army Electronics Command, April 1975). 

 22 
 

The Apache required significantly longer operational target engagement ranges than 

existing systems; it demanded a FLIR with more than twice the resolution of the one used 

by the Abrams.

92 The Apache initially had a non-standard high line rate imaging system

that was enabled by significant improvements in detector and optics quality sponsored by 

NVL and Frankford Arsenal.93 

CTE 24 

In-house engineers at NVL also played a major role in the development of PNVS for

night piloting and NOE flying.94 Field exercises demonstrated the ability to fly below the 

tree tops at night with thermal imaging. The different trade-offs in FLIR system design 

compared to those for targeting systems were pursued to optimize sensor design for 

piloting parameters, such as field-of-view and sensitivity sufficient for background 

discrimination. 

CTE 25 

One of the most important features that contributes to the battlefield effectiveness of the 

Apache and enhances the capability of TADS/PNVS is the use of the Integrated Helmet 

and Display Sight System, better known as IHADSS, which slaves the helmet to the 

sensor turret so that the pilot views the terrain and target area through the PNVS. 

Similarly, TADS is slaved to the co-pilot/gunner’s helmet, as is the chain gun. Both crew 

members’ helmets are fitted with a monocle-like heads-up display that gives piloting and 

target information. 

CTE 26 

The initial head mounted sight, which evolved into the IHADDS, had its beginning at 

Frankford Arsenal in the mid-1960s.95 The Cobra incorporated a mechanical linkage for 

the pilot and co-pilot gunner stations for directing fire with the 20MM turreted Gatling 

gun. It was realized, though, that this mechanical linkage could be improved upon with 

an infrared, acoustic, or magnetic-based sensor linkage system.96 Industry noted the idea 

and began to provide internal funding to conduct needed R&D.97 They worked closely 

with engineers at Frankford Arsenal, who had the necessary in-house talent to move the 

idea forward. At Frankford, a group of about 10 engineers with backgrounds in areas 

such as optical design, mechanical design, testing, and systems analysis supported the 

project over a period of approximately 5 years.98 During this time period, the technology 

was continuously transitioned to industry. As a result, the Apache IHADSS makes use of 

infrared linkages.99 

With IHADSS, symbols representing such important information as aircraft heading, air 

speed, altitude, and target cueing is superimposed on displays that fit in front of the 

pilot’s and gunner’s right eyes. The crew thus see the data in addition to the scene being 

viewed. This enables the crew to fly and fight without having to look at the panelmounted displays in the cockpit. This capability is especially important with NOE flying. 

CTE 27 

 

92 Joseph Lehman, email to authors, 11 May 2005. 93 Ibid. 

94 James Ratches, email to authors, 4 May 2005. 95 Donald Furmanski and Lehman, telephone interview with authors, 1 April 2005. 96 Lehman email. 97 Furmanski and Lehman interview. 

98 Ibid. 99 Ernest Burcher, email to authors, 18 May 2005.

 23 
 

The Army laboratory co-located with NASA Ames played a key role in optimizing 

symbology for the Apache.100 Being co-located at the NASA Ames Research Center, 

where they had access to a flight simulator, engineers at the aerodynamics laboratory 

were able to define protocols that were used for the evaluation of the proposed symbols. 

Design standards were established and transitioned to industry to ensure that the proposed 

symbols and the pilot’s feel for the motion of the helicopter were matched.101 Additional 

enabling methodologies involving leveraged capabilities at NASA Research Centers are 

discussed in chapter VII. 

CTE 28 

Fire Control 

The Apache’s fire control system integrates the data needed to ensure that the aircraft’s 

crew can accurately fire on the targets they identify using TADS/PNVS and other 

sensors. The heart of the fire control system is the helicopter’s on-board fire control 

computer. Important work on fire control for Army rotorcraft was done at BRL during 

the 1970s and early 1980s. BRL research provided a general 6-degree of freedom (6-

DOF) model for ballistic weapons, namely gun ammunition and rockets, which could

compensate for helicopter downwash, projectile drag, aircraft motion, atmospheric 

conditions, etc.102 This model was integrated with Apache’s on-board fire control 

computer; combined with target motion data from the TADS, it provided significantly 

increased engagement accuracy. 

CTE 29 

Another challenge was the software control and integration of multiple complex target

acquisition systems. This capability to manage these systems evolved from fundamental 

work done at Frankford Arsenal in the mid-1970s in software algorithms.

103 Keeping 

FLIRs, lasers, radars, rockets, missiles, and cannons precisely aimed with proper timing 

so that no firing errors occurred was a daunting task. The answer was fast computer 

programming using innovative algorithms coupled with equally innovative boresighting 

aids and procedures.104 Exploiting Frankford Arsenal’s experience developing the fire 

control system computers/microprocessors, engineers there were able to develop the first 

helicopter system controller. 

CTE 30 

In today’s Apache, the multiple microprocessors and disciplined software management, 

together with a multiplexed digital databus (the standard for which was developed by 

IEEE and detailed in Mil-Std 1553), provide the interconnections for the avionics suite, 

including the TADS/PNVS system, IHADSS, and the navigation system. The Mil-Std 

1553 databus concept was a key technology required to enable the high degree of 

integration used by the Apache’s onboard processing and sensor systems to display 

relevant piloting and targeting information to the crew. The 1553 databus technology was 

CTE 31 

 

100 Andy Kerr, telephone interview with authors, 9 March 2005. 101 Ibid. 102 Burcher email. 103 Lehman email. 104 The Apache was the first Army system platform requiring millions of lines of computer code. Lehman 

email. 

 24 
 

derived primarily from work done on the Air Force’s B-1 bomber program, which was 

essentially the first practical application of the high-speed databus concept.105 

The digital architecture also enabled integration of other key elements of the fire control 

system for the Apache Longbow: the mast mounted millimeter wave (MMW) fire control 

radar (discussed in the following section) and the integral radar frequency interferometer 

(RFI). Industry led development of the RFI.106 The system, which is integrated with the 

Longbow MMW, passively detects and analyzes radar emissions from potential 

targets.107 The fire control system combines information from the fire control radar and 

the RFI to rapidly provide a clear picture of the battlefield. 

CTE 32 

Another key improvement to the Apache’s fire control relates to communication among 

aircraft. Initially known as the Automated Target Handover System, the Improved Data 

Modem (IDM) permits the Apache to digitally communicate crucial threat, targeting, and 

other operational information with other aircraft and with ground units so that the force 

has a unified picture of the battlefield. This could be considered one of the first elements 

of network-centric warfare for Army aviation.108 Industry was heavily involved with 

development of the IDM, as was the Army’s in-house avionics program. 

CTE 33 

AATD Aviation Weaponization Group: It should be noted that as many 

ideas, such as the mast mounted sight, millimeter wave radar, and ever more 

powerful microprocessors, began to emerge, the Army aviation leadership 

wanted to establish an organization that would be in position to waste little 

time in applying the technology to aviation-specific needs.a

 As a result, an 

Army aviation weaponization group was created at AATD in the late 1970searly 1980s. This was a key management decision; the new organization 

played a major role in recognizing and bringing forward worthwhile ideas 

(CTEs), such as developing and integrating the Longbow MMW radar 

system, coordinating with other laboratories (both in-house and out-ofhouse), and managing the efforts with industry. 

a. Kailos interview. 

 

105 Plaster, email to authors, 6 September 2005. 106 Brad Rounding, telephone interview with authors, 3 August 2005. 107 Plaster, email to authors, 23 January 2006. 108 Burcher email. 

 25 
 

Longbow Millimeter Wave Radar 

The AH-64D version of the Apache incorporated upgrades in several areas, but the most 

notable of these was the Longbow MMW fire control radar.109 The radar, mounted on the 

Apache’s mast, supplemented the FLIR with a second, completely independent target 

acquisition sensor. The Longbow enabled the Apache to carry a second type of Hellfire 

(discussed below). This new missile was guided by radar rather than semi-active laser.

This greatly enhanced the Apache’s lethality in adverse atmospheric conditions, because 

infrared sensor and laser-guided weapons can have difficulty coping with smoke, dust,

fog, and precipitation. This fire control radar is normally used independent of TADS for 

rapid automatic detection of targets within a 34-square mile area, and the classification 

and display of the 16 highest priority targets.110 The Army is converting about 590 of 

more than 800 AH-64As to the D configuration.111 

The use of MMW radar for military purposes has been the subject of research since the 

1950s. Its application as an all-weather sensor for helicopter applications gained attention 

in mid-1960s. Two programs were important to advancing MMW radar applications to 

armed helicopters.112 The first was the Frankford Arsenal/Emerson Electric Moving 

Target Radar System Program. The system, based on Ka-band radar technology, was first 

tested on a UH-1 Huey helicopter and demonstrated a capability to significantly enhance 

the ability of the crew to detect moving targets in vegetation as well as in the open. It was 

married to the FLIR system on the Cobra Helicopter and deployed to Vietnam, where it 

was evaluated by the Army Concept Team in 1970.113 The radar increased the range at 

which the crew could detect targets by 1000 meters beyond what could be detected by the 

FLIR alone.114 

CTE 34 

The second helicopter radar system of note in the mid-60s was the Texas Instruments 

Rotor Blade Radar System.115 The TI system used a transmitter in the leading edge of the 

UH-1 Huey rotor blades and a receiver on the nose of the helicopter to detect targets. 

This system never left the R&D stage, but served as exploratory technology that helped 

to lead to the successful Longbow radar discussed below.116

In the 1980s, Martin Marietta defined the advantages of using a higher frequency MMW

radar to detect, classify, and recognize the target and transfer the information for use by a 

 

109 The Longbow Fire Control Radar also has a Terrain Profiling Mode (TPM), which is supposed to 

provide obstacle detection and adverse weather piloting aids to the Longbow Apache crew; however, the 

pilots do not often use this feature. Burcher email. 110Jane’s Avionics, “AN/APG-78 Longbow Radar.” Available online at: <http://www4.janes.com>, 

accessed 4 August 2005. 111 Jane’s All the World’s Aircraft, “Boeing AH-64 Apache.” Available online at: 

<http://www4.janes.com>, accessed 4 August 2005. 112 Lehman email. 113 Ibid. 114 Ibid. 115 Ibid. 116 Ibid. 

 26 
 

radar seeker missile weapon system.

117 Briefings were given to the Army leadership on 

this concept. In the early 1980s, the effort gained high-level support within the Army, 

which instituted a program to field such a system. This program (which is classified, thus 

limiting information on the R&D effort) yielded the Longbow. The Longbow is produced 

by a joint venture between Lockheed Martin (which subsumed Martin Marietta) and 

Northrop Grumman (which bought Westinghouse Electric Corporation, a partner with 

Martin Marietta in Longbow development). 

CTE 35 

Important to the MMW radar was the very fast analog circuitry provided by gallium

arsenide (GaAs) semiconductors. In the 1980s, a DOD program administered through 

DARPA established the industrial base to supply GaAs to the military.118 This program, 

known as the MIMIC (microwave monolithic integrated circuits) program, provided the 

basis for product, process, and applications technologies. The program was funded at 

nearly $1 billion over 6 years from 1987 to 1993.119 Program management was shared 

among the services, with the Army’s Electronics Technology and Development 

Laboratory (ETDL) overseeing about one-third of the effort. The bulk of the funds went 

for contract studies ranging from basic research to technology demonstrations. Included 

here was funding (about $20 million) for work at the ETDL on qualification of GaAs 

material for integrated circuit chips, associated reliability testing, and technology 

demonstrations. The work included coordinated efforts in the private sector and 

universities. The work on technology demonstrations included the development of a 

power amplifier for the Longbow MMW radar.120 

CTE 36 

Further MIMIC benefits: It is interesting to note that another fielded result 

of the MIMIC program was a multiple option fuse for a chip programmable 

in the field.b

 Shortly after the MIMIC program was completed a small New 

Jersey company began to offer such chips for the direct (satellite) television

business. Now the GaAs chips are used as amplifiers in cell phones—an 

enormous market facilitated by this DOD MIMIC program.

c

 

b. Vladimir Gelnovatch, email to authors, 6 September 2005. 

c. Ibid. 

Another key innovation associated with the Longbow radar is its location on the mast. 

This idea had its origin in the late 1960s to late 1970s. The Army leadership was 

concerned with the low operational life of the light observation helicopters in Vietnam, 

which were projected to last only 17 flight-hours in a mid-intensity conflict 

environment.121 It was obvious that the observation helicopters had to be hidden or 

masked from view to survive. The solution came from the Helicopter Fire Control Branch 

at Frankford Arsenal: a mast-mounted sight that would allow the helicopter to remain 

CTE 37 

 

117 Maurice Yeager, telephone interview with authors, 16 March 2005. 118 Vladimir Gelnovatch, email to authors, 6 September 2005. 119 Ibid. 120 Ibid. 121 Lehman email. 

 27 
 

concealed.122 In less than three months and with a small amount of in-house money, the 

concept of a mast mounted sensor was demonstrated. Results were briefed to the Army

leadership and quickly led to a major program involving key players from industry, 

including Honeywell, Rockwell International, and Martin Marietta. The OH-58 Kiowa 

Warrior observation helicopter was one of the first systems to employ a mast-mounted 

FLIR sight. Eventually, as the Apache Longbow evolved, the mast was chosen as the site 

for the MMW radar. Besides reducing the helicopter’s susceptibility to enemy detection 

by allowing the sensor to see over terrain while the airframe remained concealed, there 

were two additional benefits: the mast was located at the aircraft’s center of gravity, and 

installing the sight on the mast conserved space that was in short supply elsewhere on the 

aircraft.123 

Army-NASA tests: Important aerodynamic studies conducted at the ArmyNASA site were also key to the location of the Longbow radar. Researchers 

were able to show the aerodynamic effect of the sight’s location and 

configuration and ensure that its addition would not compromise the 

aircraft’s airworthiness.d

 Similar research, including NASA wind-tunnel 

tests,e

 detailed the rotor-fuselage interaction and aided in designing the 

horizontal stabilizer (discussed also in “Co-Located Army-NASA Research 

Sites”).f

d. T.A. Ghee and H.L. Kelley, “Flow Visualization of Mast-Mounted-Sight/Main Rotor 

Aerodynamic Interactions,” AIAA-93-3517-CP. 

e. J.C. Wilson and R.E. Mineck, “Wind-Tunnel Investigation of Helicopter rotor Wake

Effects on Three Helicopter Fuselage Models,” NASA TM X-3185, 1975. 

f. R.W. Prouty “Development of the Empennage Configuration of the YAH-64 Advanced

Attack Helicopter,” USA AVRADCOM-TR, 82, D-22, February 1983.

CTE 38 

Weapons Suite 

Once the target has been identified, whether by the Longbow or by other means, the 

gunner has at his disposal several effective options. The Apache carries rockets and 

missiles on four articulated external pylons, two on each wing-like structure extending

from the sides of the main fuselage. The aircraft can carry up to 16 Hellfire missiles or 76 

2.75-Inch Folding Fin Aerial Rockets or a combination of missiles and rockets. It also has 

a turreted 30mm cannon under the nose linked to a load of 1200 rounds. 

The Apache was designed primarily as an antitank weapon system, and its main 

armament for that mission is the Hellfire (HELicopter Launched FIRE-and-forget) 

missile.124 The Hellfire is a 7-inch diameter guided missile carrying a large shaped-

 

122 Ibid. 123 Ibid. 124 This discussion of Hellfire missiles is brief. We will release another report in this series that deals 

exclusively with the development of two other Army missile systems, the Javelin and the Stinger. 

 28 
 

charge warhead for the penetration of tank armor. Each of the four weapons pylons can 

carry up to four Hellfire missiles. 

The Hellfire, designed and initially built by Rockwell International Corporation, was the 

culmination of many years work to replace TOW (Tube-launched, Optically-tracked, 

Wire-guided) missiles as the main antitank weapon available for helicopter use. The 

major shortcoming of the TOW was that the helicopter needed to remain exposed while 

the missile homed in on its target. Further, its limited range brought the helicopter closer 

to the threat. The Hellfire flies faster and farther than its TOW predecessors, enabling

greater standoff firing distances. The Hellfire with which the Apache was initially 

equipped was guided by a semi-active laser (SAL) seeker. The missile homes on a laser 

spot that can be projected either from the Apache or other aircraft or ground observers. It 

has lock-on-before-launch and lock-on-after-launch capability. If the target has been 

designated by another source, the Apache can return to cover immediately after the 

missile has left the launch rail. There have been three models of SAL-guided Hellfires. 

The Hellfire’s SAL seeker was designed independently from the rest of the missile. The 

laser system had its origin in the mid- to late-1960s. At that time there was exploratory 

research interest at Redstone Arsenal in the development of a laser-based, semi-active 

system.

125 Also important was a systems study at Hughes Helicopter and Martin Marietta 

for a SAL missile. The study concluded that such a concept was within the state of the 

art.126 In the early 1970s, Martin Marietta, with DARPA funds, carried the concept 

further and conducted a field demonstration that showed a successful hit of a ground 

target by a SAL-guided rocket.127 Martin Marietta won a multi-service laser seeker 

design contract known as Low Cost Alternate Laser. It was initially an alternate seeker 

for the Hellfire, but Martin Marietta was eventually made an equal partner on the Hellfire 

contract, and its seeker was added to the Rockwell airframe.

128 

CTE 39 

As described earlier in the chapter, the AH-64D Longbow Apache is equipped with a 

MMW radar. A new type of radar-guided Hellfire was designed for use with the 

Longbow. This missile (considered to be a second generation weapon, with the first 

generation encompassing the three SAL models) provided the Army with its first 

helicopter all weather attack system. It also provided a true autonomous fire-and-forget 

capability. The Longbow Hellfire can lock on to the target before launch or it can be 

inertially guided to the target area based on a position derived from the mast mounted 

acquisition radar and then acquire the target with its own radar. 

CTE 40 

Though less advanced and individually less lethal than the Hellfire, rockets add important 

capability to the Apache. The 2.75 inch rockets, for use primarily against personnel and 

 

125 U.S. Missile Command, “Hellfire.” Available online at: 

<http://www.redstone.army.mil/history/systems/HELLFIRE.html>, accessed 5 August 2005. 126 Ibid. 127 Kailos interview and Yeager interview. 128 Rockwell has become part of Boeing and Martin Marietta is now part of Lockheed Martin. Today, SAL

Hellfire missiles are manufactured by Hellfire Limited Liability Company, a Boeing/Lockheed Martin joint 

venture. The Longbow Hellfire is made by Longbow Limited Liability Company, a joint venture between

Lockheed Martin and Northrop Grumman. 

 29 
 

soft-skinned vehicles, are fired from re-usable pod launchers suspended from two winglike extensions attached to the main helicopter body. The Apache can carry up to four 

pods of 7 or 19 rockets each for a maximum of 76. The unguided rockets are used 

primarily for area saturation.129 Though the 2.75 inch rocket is a relatively simple 

weapon, engineers have made progressive improvements, equipping it with a more 

powerful motor and alternative payloads, including flechettes, multi-purpose 

submunitions, flares, and smoke.130 

Below the nose of the Apache is a rapid-fire, turreted 30mm chain gun. The chain gun 

gets its name from the electrically driven chain that feeds ammunition into the breach. 

This simple innovation, similar in principle to a basic drive belt, solved the difficult 

problem of machine-gun jamming. A conventional machine gun relies on energy from 

the exploding cartridge of the first round to advance the ammunition belt to the next 

round. If one round fails to fire, the gun jams, and there is no easy way to clear a jam

from a gun mounted on the underbelly of an aircraft in flight. Engineers at Hughes 

Helicopter came up with a new single-barreled chain gun design for the Apache that 

could fire 11 rounds per second, was highly reliable, resistant to dirt and wear, and could 

continue to fire when rounds failed.131 Hughes initially developed the design for a 20mm 

weapon, but adapted it for the Apache when the Army made a 30mm cannon a 

requirement for the AAH. 

CTE 41 

 

129 Richardson, 38. 130 Ibid. 131 Ibid., 40.

 30 
VII. Modeling and Simulation and Other Enabling 

Methodologies 

In addition to the work on specific systems and components described above, the Army 

supported more broadly applicable research to improve helicopter technology that 

continues to benefit the Apache program. Much of this work was in computer modeling. 

The Army also conceived of new ways to collaborate with academia and industry in this 

and other important areas. 

Co-Located Army-NASA Research Sites 

The development of very powerful computers has transformed many branches of science 

and engineering. Computer models replace, to a considerable degree, expensive and timeconsuming physical experimentation. A great many experiments can be conducted on the 

computer in less than the time it would take for one physical experiment. In many 

instances, experiments are carried out only to validate the computer models. 

Much of the modeling work related to helicopter development has stemmed from colocation of Army engineers and scientists at NASA research facilities.132 These sites are 

at NASA Langley, NASA Glenn, and NASA Ames. This 6.1 and early 6.2 work, which 

made use of NASA staff and experimental facilities, enabled verification of the 

predictions made by the computer-based models. The experimental work also provided 

data sets for use by industry. The use of NASA facilities was especially significant 

because the Army did not, and still does not, have its own, very expensive experimental 

facilities, such as special purpose, carefully calibrated wind tunnels. 

Some computer-based models and techniques that resulted from this highly leveraged 

Army-NASA effort have been utilized throughout the aeronautical and space scientific 

community. Examples include:133 

• Development of new computer modeling techniques in computational fluid 

dynamics (CFD) and finite element (FE) structural analysis 

• Research into the physics and mechanics of helicopters, including computer 

modeling of the aerodynamics of airfoils for engine turbines and helicopter rotors 

• Comprehensive structural mechanics using the NASTRAN FE computer program 

• Studies of the vibrational behavior of the rotor-structure interactions, the loading 

on the rotors, and the flight behavior of the system 

• Use of CFD to design the airfoils in the gas turbine engine 

• Research to better understand dynamic stall effects 

• Vibration analysis by FE analysis 

 

132 Bill interview; Wolf Elber, telephone interview with authors, 17 February 2005; Kerr, telephone 

interview with authors, 23 February 2005. 

133 Ibid. 
 

• Development and application of a comprehensive aircraft model for rotorcraft 

aeromechanics using CFD coupled with Computational Structural Mechanics 

Many of the above technologies were relevant to the development of the Apache. For 

instance, interaction between the rotor and the airframe of the AH-64, particularly in the 

tail, caused serious, potentially catastrophic vibrations. Applying advanced structural 

dynamics analysis and comprehensive aeromechanics analysis, researchers worked with 

industry in a major configuration redesign of the tail, relocating the horizontal stabilizer 

and converting it to a movable stabilator.134 They then verified the work in the wind 

tunnel. It is interesting to note that this particular issue received the close attention of the 

Apache PM, who made the necessary resources available and was involved with making 

the key decisions necessary to keep the program on track.135 

CTE 42 

In a related effort, researchers generated a “comprehensive and definitive” data set called 

Design Analysis Methods for Vibrations (DAMVIBS), which was generated through 

experimental work at NASA structural dynamics test labs and other experimental rigs.136

The research included the design of special instrumentation to obtain information that 

was used to update structural dynamics modeling capability for dynamics and loads 

estimation and control. 

Significant advances in rotorcraft computer codes used to simulate complex helicopter 

aerodynamics and helicopter flight control laws resulted in development of an 

Engineering Design Simulator (EDS) for Apache at Boeing Mesa. The EDS had 

operational fidelity that was accurate enough for it to be certified by the Army test 

community for use as an A-Model to D-Model transition trainer.137 The EDS was also 

used by the Army to complete Limited User Test tasks required to obtain the full 

Airworthiness Release in lieu of expensive aircraft flight testing. This significantly 

reduced the time required to complete qualification and testing of the AH-64D model, 

and put this weapon system in the hands of the user much sooner than would have 

otherwise been possible. 

CTE 43 

Other Collaborative Efforts 

In 1994, the Army established the National Rotorcraft Technology Center (NRTC) at the 

Army’s unit at NASA Ames to enhance collaboration between the military, academia, 

and industry. Although the NRTC was established too late (1994) to impact the earlier 

development of the Apache, it represents an enhanced effort to produce technology for 

use in upgrades of the Apache and for future Army helicopters. It does this by formally 

involving both universities and industry. The NRTC facilitates communication and 

technology planning among the participants. It also funds and manages Rotorcraft 

Centers of Excellence (CoEs) at three universities: the University of Maryland, Penn 

State University, and Georgia Tech. The NRTC convenes the Rotorcraft Industry 

 

134 Elber interview. 135 Herrick. 136 Kerr, telephone interview with authors, 4 March 2005. 137 Plaster, email to authors, 6 September 2005. 

 32 
 

Technology Association to provide industry input into the planning and prioritization of 

the research program at NRTC. The three university Rotorcraft CoEs receive $2.4 million 

annually, divided roughly equally.138 This is Army 6.1 funding for basic research. In 

addition, the centers receive funding from NASA, other government agencies, industry, 

and the universities themselves that total about $12 million annually for all three CoEs.

139

This funding, combined with the 6.1 funding for the three Army units co-located at 

NASA facilities, supports most of the basic research done on helicopters in the Army.

140 

The funding for the Rotorcraft CoEs is largely for costs associated with engineering 

students and their projects—there are about 100 graduate students and three times as 

many undergraduates. The university programs at the CoEs emphasize aeroflight 

dynamics, computational modeling, power trains, smart composites, design optimization, 

and technology for unmanned aero vehicles. The centers produce well-trained graduate 

engineers at the BS, MS, and PhD levels, approximately 75 percent of whom go into 

industry.141 Their presence in the helicopter industry strengthens the technology base and 

improves technology transfer. 

It should be noted that the CoEs have developed experimental facilities, some of which 

are unique. More will become unique if NASA closes its facilities. (Additional 

commentary on this is provided in the findings and concluding remarks). These include 

test rigs for rotor blades and hubs, wind tunnels, blade whirl towers, and large-scale 

vacuum chambers. 

In addition, the focused research at the CoEs has led to some significant accomplishments 

in a number of areas applicable to current as well as next generation helicopters:142

• Development of analytical and design tools—CFD and FE —and the application 

of these tools to rotorcraft problems 

• Advanced composite rotor blade technology 

• Viscoelastic dampers for the rotors 

• Vibration prediction and active control 

• Simulation of maneuvering wakes 

• Modeling and simulation of steady and transient noise generation in terms of 

enemy detection 

The CoE activities are important to the following characteristics that future aircraft may 

possess:143

• Heavy lift capability 

• More powerful engines 

• More fuel efficient engines

144

 

138 Inderjit Chopra, interview with authors, College Park, MD, 5 April 2005. 139 Ibid. 140 Ibid. 141 Ibid. 142 Ibid. 143 Ibid., except where noted. 144 Plaster, email to authors, 6 September 2005. 

 33 
 

• No swashplates 

• Wide application of advanced composite materials 

• Fly-by-wire and integrated electro-optical systems 

• Automatic rotor speed control via increased use of smart sensors, structures, and 

actuators (to increase both range and endurance) 

• Compound helicopter capability 

A more recent collaborative effort that will have a far-reaching impact on many future 

DOD systems is the effort known as the Rotorcraft Pilot Associate (RPA) program,

developed and tested by Boeing and AATD.145 The RPA program developed very robust 

Cognitive Decision Aiding System (CDAS) software intended to reduce the workload of

the Apache’s crew in the highly complex, low altitude combat environment. The RPA 

program demonstrated in both a high fidelity aircraft simulator and in a specially 

modified test Apache that models based on human behaviors could be used to make 

decisions for routine flight and navigation tasks on behalf of the crew, freeing them to 

concentrate on the battle at hand. RPA technology has also been applied to UAV control 

and to the Future Combat System Warfighter Machine Interface.146 The Apache Block III 

configuration will incorporate eight of the approximately 20 cognitive decision aiding 

behaviors demonstrated during the RPA technology demonstration program.147

CTE 44 

 

145 Ibid. 146 Ibid. 147 Ibid. 

 34 
VIII. Findings and Concluding Remarks 

Findings 

1. We have identified 44 Critical Technology Events in the development of the Apache 

helicopter. 

• Power System CTEs 

o T700 Engine: 8 

o Transmission: 2 

• Survivability and Structural Advances CTEs 

o Vulnerability and Susceptibility Reduction: 7 

o Structural Advances: 4 

• Avionics, Fire Control and Weapons CTEs 

o TADS/PNVS: 7 

o Fire Control System: 5 

o Longbow Millimeter Wave Fire Control Radar: 4 

o [Sidebar:1] 

o Weapons Suite: 3 

• Modeling and Simulation and Other Enabling Methodologies CTEs 

o Co-Located Army-NASA Research Sites: 2 

o Other Collaborative Efforts: 1 

2. Success in meeting user needs was due to many factors. Among the most important 

was the expertise of the Army in-house scientists and engineers. In-house laboratories 

were deeply involved in CTEs that pertained to requirements that were vital to the 

development of the Apache. For example, the laboratories devoted a great deal of 

attention to crashworthiness, ballistic protection, thermal imaging, and the fire control 

system. The competence and dedication of the industrial partners was also crucial to the 

program’s success. Industry’s creative work on the T700 series of helicopter engines is an 

example. 

3. The Army experiences with helicopters in Vietnam had a strong influence on the 

Apache program. Needs identified by the user included better crew protection and crashworthiness, more payload, improved fuel economy, and more capable weapons systems. 

These needs drove specifications for a new, more powerful engine, many innovations in 

protecting the crew and reducing fatalities from crash, fire, and enemy munitions, and 

improved targeting and fire control systems. 

4. The Army funded most of the technical work on the Apache. Before the Apache 

program was begun, the Army specified and funded a competition for the design of a 

new, more powerful helicopter engine and for targeting and fire control systems. 

However, industry originated and provided some financial support for early work on 
 

some components, e.g., the Hellfire missile and the mast-mounted millimeter-wave radar 

concept. 

5. Integration of the many systems and components was critical for success. The Apache 

is a complex weapons system containing many different subsystems and components. 

These were integrated under the supervision and strong leadership of the Program

Manager’s office, which championed the program throughout the development cycle and 

ensured effective teaming among all government and industry contributors. 

6. Basic and early applied research were done at co-located Army-NASA research sites.

Since 1968, the Army and NASA have collaborated at NASA Langley, NASA Glenn, 

and NASA Ames. This arrangement greatly facilitated work on structures, propulsion, 

and modeling and simulation. NASA’s specialized experimental facilities were used to 

validate models and test out new concepts, e.g., in large, special purpose wind tunnels. 

Concluding Remarks 

These findings and conclusions apply to the Apache helicopter and may not apply to 

other Army weapons systems. While the analysis in this report has suggested to us some 

general recommendations that likely would apply to other Army weapons systems, we

will reserve judgment until we have completed our series of papers. Also left until we 

complete the series of reports will be any comments related to current matters of interest, 

such as acquisition strategies and technical personnel skill mix. 

We would like to re-emphasize that this study has not set out to capture every technical 

innovation in the development of the Apache. Nor have we striven to present the CTEs in 

exhaustive technical detail. We are confident, however, that we have captured most of the 

major technical events pertaining to the helicopter and that these events support the above 

conclusions. 

 36 
 

Appendix A 

Individuals Contacted for the Apache project 

Key 

Civil 

Service 

Employee 

 CSE Academia ACD Active 

Military 

 AM

Government

Retired 

 GR Military Retired MR Industry 

Retired 

IR

Consultant CST Private Sector Employee PSE Contractor CTR

* denotes that the individual reviewed some or all of the draft document for completeness and 

accuracy. 

Last Name First 

Name 

Apache-era Organization Current Status 

*Ballard Richard HQ, Department of the Army

(CSE) 

GR, CST 

Bill Robert Army laboratory co-located at 

NASA Glenn (CSE) 

GR 

*Burcher Ernest Aviation Applied Technology 

Directorate (CSE) 

CSE

*Burrows LeRoy Aviation Applied Technology 

Directorate (CSE) 

GR

Buser Rudy Night Vision Laboratory 

(CSE) 

GR

*Carmona Waldo Aviation Applied Technology 

Directorate (AM) 

MR, PSE 

Chopra Inderjit University of Maryland (ACD) ACD 

*Del Coco Gene Frankford Arsenal (CSE) GR 

*Elber Wolf Army laboratory co-located at 

NASA Langley (CSE) 

CSE

*Figge Ward Aviation Applied Technology 

Directorate (CSE) 

GR

*Furmanski Donald Frankford Arsenal (CSE) GR

Gelnovatch Vladimir Electronic Technology and 

Device Laboratory (CSE) 

CSE

Giordano Robert Communications-Electronics

Command (CSE) 

GR, CST 

Good Danny Aviation Applied Technology 

Directorate (CSE) 

GR, CTR 

*Herrick Curt Apache PM Office (AM) CST 

*Hoff Sandra Aviation Applied Technology 

Directorate (CSE) 

CSE

Hower Gene General Electric (PSE) PSE 

 37 
 

*Kailos Nick Aviation Applied Technology 

Directorate (CSE) 

GR, CST 

Keesee Robin Human Engineering

Laboratory (CSE) 

CSE

*Kerr Andrew Army laboratory co-located at 

NASA Ames (CSE) 

CSE

*Lehman Joseph Frankford Arsenal (CSE) GR

*Meitner Peter Army laboratory co-located at 

NASA Glenn (CSE) 

CSE

*O'Brien T.K. Army laboratory co-located at 

NASA Ames (CSE) 

CSE

*Papetti Dino Materials Technology

Laboratory (CSE) 

GR

Parsons Gordon Materials Technology

Laboratory (CSE) 

GR

Plaster Larry Bell Helicopter/McDonnell

Douglas (PSE) 

PSE

Perciballi William Materials Technology

Laboratory (CSE) 

PSE

*Ratches James Night Vision Laboratory 

(CSE) 

CSE

Rounding Bradley Officer, US Army (AM) PSE 

*Sciarretta Al Officer, US Army (AM) MR, CST 

*Sibert George Officer, US Army (AM) MR 

Singley George Aviation Applied Technology 

Directorate/Army Aviation 

Systems Command HQ (CSE) 

GR, PSE 

*Turnbull Robert General Electric (PSE) PSE 

Wade Jack Survivability and Lethality 

Analysis Directorate (CSE) 

GR

Wall Raymond Aviation Applied Technology 

Directorate (CSE) 

CSE

*Yeager Maurice Martin Marietta (PSE) CST

 38 
Appendix B 

Critical Technology Event List 

Number CTE Report Section 

1 AATD sets engine requirements T700 Engine 

2 Simplified combustor design T700 Engine 

3 Particle separator design T700 Engine 

4 Re-design to reduce vibration of compressor 

blades 

T700 Engine 

5 Blisks T700 Engine 

6 Ceramic coating T700 Engine 

7 Rare earth magnets T700 Engine 

8 Incremental T700 improvements T700 Engine 

9 Run-dry transmission Transmission 

10 Gear technology advances Transmission 

11 Transparent armor to separate cockpits Vulnerability and Susceptibility 

Reduction 

12 Improved armor for seats Vulnerability and Susceptibility 

Reduction 

13 Wire-strike protection Vulnerability and Susceptibility 

Reduction 

14 Priority placed on crashworthiness Vulnerability and Susceptibility 

Reduction 

15 Crash survival design guide Vulnerability and Susceptibility 

Reduction 

16 Crashworthy fuel system Vulnerability and Susceptibility 

Reduction 

17 Active and passive susceptibility measures Vulnerability and Susceptibility 

Reduction 

18 Load-bearing armor Structural Advances 

19 Composite materials for the rotor Structural Advances 

20 Composite rotor blade for Apache Structural Advances 

21 Analysis of delamination process in 

composite materials 

Structural Advances 

22 TADS/PNVS TADS/PNVS 

23 FLIR performance model TADS/PNVS 

24 High-resolution FLIR for TADS TADS/PNVS 

25 Pilotage-optimized FLIR for PNVS TADS/PNVS 

26 Head mounted site for IHADSS TADS/PNVS 
 

27 Symbology for IHADSS TADS/PNVS

28 Protocols and design standards for IHADSS 

symbology 

TADS/PNVS

29 Model for rotorcraft ballistic fire control Fire Control 

30 Software integration Fire Control 

31 1553 databus Fire Control 

32 Radio frequency interferometer Fire Control 

33 Improved Data Modem Fire Control 

34 Early rotorcraft targeting radars Longbow Millimeter Wave 

Radar 

35 Longbow MMW radar Longbow Millimeter Wave 

Radar 

36 MIMIC Longbow Millimeter Wave 

Radar 

37 Mast-mount for Longbow Longbow Millimeter Wave 

Radar 

38 Aerodynamic studies for mast-mounted 

Longbow 

[Sidebar]

39 SAL seeker for Hellfire Weapons Suite 

40 Longbow Hellfire Weapons Suite 

41 30mm chain gun Weapons Suite 

42 Modeling to prevent structural failure due 

vibration 

Co-Located Army-NASA 

Research Sites 

43 Engineering design simulator Co-Located Army-NASA 

Research Sites 

44 Rotorcraft Pilot Associate program Other Collaborative Efforts 

 40