o

Supersonic

Cruise

Technology

NASA SP-472

Supersonic

Cruise

Technology

F. Edward McLean

Scientific and Technical Information Branch 1985

National Aeronautics and Space Administration

Washington, DC
Library of Congress Cataloging in Publication Data

McLean, F. Edward.

Supersonic cruise technology.

(NASA SP ; 472)

Bibliography

1. High-speed aeronautics-- Research-- United States.

I. Title. II. Series.

TL551.5.M35 1985 629.132'305 83-26912

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402

iv
Foreword

The National Aeronautics and Space Administration and its

predecessor, the National Advisory Committee for Aeronautics

(NACA), have participated since 1920 in efforts to develop the

technology required for supersonic cruise flight. Preliminary work concentrated on developing rudimentary test facilities and methods that

would permit the investigation of supersonic problems. This was accompanied by research for defining aircraft and propulsion concepts

for flight at speeds greater than the speed of sound. These early investigations contributed to the development of the joint U.S. Air

Force/Navy/Bell XS-1 airplane that was piloted on the first successful

supersonic flight by Air Force Capt. Charles E. "Chuck" Yeager in

1947o

Between 1956 and 1971, a strong research effort supported the

USAF supersonic B-70 and commercial supersonic transport concepts.

After neither of these programs resulted in a production aircraft

because of technical and political problems, NASA was given the

responsibility of establishing the technology base for a viable supersonic cruise airplane. This latter effort, known as the NASA Supersonic Cruise Research (SCR) program, was conducted from 1971 to

1981. The NASA Variable Cycle Engine (VCE) program, a propulsion offshoot of SCR, was conducted from 1976 to 1981.

The SCR program was somewhat unusual for a NASA program involving in-house and contractor participation. Several of the manufacturers provided company manpower and dollars to augment NASA
SUPERSONIC CRUISE TECHNOLOGY

funding and personnel, even though there was no contractual requirement for them to do so. Dissemination of technical information was

almost immediate to all participants because data dumps and separate

status reports were mutually transferred openly and with high frequency, and because of the day-to-day contacts by the major civilian

and military airframe and propulsion system manufacturers. The

disciplinary research/systems integration approach of the SCR and

VCE programs led to a large number of major advances in the

technology needed for supersonic flight.

This document provides a historic perspective of supersonic cruise

technology, beginning with the early NACA supersonic research and

including efforts during the B-70 and SST phase. It also records

technological progress made in the NASA SCR and VCE programs.

Since every research result could not be detailed here, only the most

critical technology issues and research findings are presented.

WILLIAM S. AIKEN, JR.

Director, Aeronautical Systems.

Division

Office of Aeronautics and Space

Technology

vi
Acknowledgments

The author wishes to express his appreciation to the following people

for their assistance in the preparation of this document: Cornelius

Driver, Domenic Maglieri, Sherwood Hoffman, Betty Pate, and

Donald Hearth of the NASA Langley Research Center; Frank

Neumann and Wilbur Middleton of the Boeing Airplane Company;

Richard FitzSimmons and Bill Rowe of the Douglas Aircraft Company; John F. McCarthy, Jr., of the NASA Lewis Research Center;

Clarence A. Syvertson of the NASA Ames Research Center; Isaac T.

Gillam IV of the NASA Dryden Flight Research Facility; and William

Pomeroy of NASA Headquarters. The author also expresses his appreciation to Donald D. Baals of the NASA Langley Research Center

for his excellent unpublished history of NACA/NASA participation in

the early supersonic technology efforts leading up to the SST effort.

vii

Contents

Chapter Page

1 INTRODUCTION .................................... 1

2 SETTING THE STAGE FOR SUPERSONIC CRUISE

TECHNOLOGY ...................................... 7

The Sound Barrier ..................................... 7

The First Supersonic Cruise Aircraft ....................... 9

The Next Logical Step .................................. 11

After the U.S. Supersonic Transport Program ............... 18

3 NACA PRELIMINARY SUPERSONIC CRUISE TECHNOLOGY (?-1956) .................................... 23

Mounting an Attack on the Sound Barrier .................. 24

Breaking the Sound Barrier .............................. 27

4 NACA/NASA SUPPORTIVE SUPERSONIC CRUISE

TECHNOLOGY (1956-1971) ..........................

The U.S. Air Force B-70 Bomber Program .................

The U.S. Supersonic Transport Program ...................

35

35

39

ix
SUPERSONICCRUISETECHNOLOGY

Chapter Page

5 FOREIGN SUPERSONIC TRANSPORT PROGRAMS ......................................... 55

The Soviet TU- 144 ................................ 55

The British/French Concorde ........................ 58

6 LESSONS LEARNED IN PRE-1972 SUPERSONIC

CRUISE EXPERIENCE ........................... 65

The Military/Commercial Difference ................. 65

A Successful SST Will Permit Little Room for Design

Compromise .................................... 68

The Value of Focused Technology Efforts .............. 70

U.S. Technology Subsidization ...................... 72

Evolution of an Acceptable SST Will Be Difficult ........ 73

Perceptions of a "Rampant" Technology ............... 75

Summary of Lessons Learned ........................ 76

7 SUPERSONIC CRUISE PROBLEMS AND POTENTIAL ............................................ "79

Technical Problems ................................ 80

Environmental Problems ............................ 86

Supersonic Cruise Potential ......................... 92

PURSUING THE PROBLEMS AND POTENTIAL

OF SUPERSONIC CRUISE FLIGHT: THE NASA

SCR AND VCE PROGRAMS ...................... 101

Objectives and Rationale of the NASA SCR Program .... 102

Organization and Elements of the NASA SCR Program .. 104

Alterations to SCR Program Structure ................ 108

Dissemination of SCR Technical Information .......... 112

Scope of NASA SCR Program ....................... 114
SUPERSONIC CRUISE TECHNOLOGY

Chapter Page

9 PROGRESS IN SUPERSONIC CRUISE TECHNOLOGY SINCE 1972 ............................ 115

Progress in Environmental Issues ..................... 116

Progress in Aerodynamics ........................... 123

Progress in Structures and Materials .................. 126

Progress in Propulsion .............................. 134

Progress in Configuration Concepts/Integration ......... 142

Summary of Progress ............................... 156

10 SUPERSONIC CRUISE TECHNOLOGY BEFORE

(1971) AND AFTER (1982) THE NASA SCR AND VCE

PROGRAMS .................................... 157

Comparisons ..................................... 158

Possible Ramifications of SCR and VCE Technology .... 165

11 FUTURE DIRECTIONS OF SUPERSONIC CRUISE

RESEARCH ..................................... 171

REFERENCES ................................... 175

SELECTED ADDITIONAL READING ............. 183

xi

CHAPTER 1

Introduction

The National Advisory Committee for Aeronautics (NACA) was

established by the United States Congress in 1915 as the aeronautical

research arm of the U.S. Government. NACA's principal goal was to

establish and maintain a preeminence for America in the field of

aeronautics, an assignment that NACA performed with distinction until 1958. At that time a new agency, the National Aeronautics and

Space Administration (NASA), was formed by Congress to absorb and

continue the aeronautical duties of NACA and to take on the additional

responsibility of conducting a program for the exploration of outer

space. One of NASA's chartered goals is "the preservation of the role of

the United States as a leader in aeronautical and space science and

technology and in the application thereof to the conduct of peaceful activities within and outside the atmosphere." L *

For more than 60 years, first NACA and then NASA has

endeavored to live up to its assigned goals. Working independently or

in concert with the military services and other organizations, scientists

and technicians at NACA/NASA have solved or assisted in the solutions of the most complex problems associated with flight. The solutions of these problems have led to dramatic extensions of the boundaries of manned and unmanned flight in the atmosphere and in outer

space. In addition, while solving the problems, NACA/NASA has

* Superscript numbers refer to references, which are listed at the end of this document.
SUPERSONIC CRUISE TECHNOLOGY

developed and acquired unique experimental facilities for use in the investigation of almost every facet of flight.

A substantial portion of the aeronautical research effort at

NACA/NASA has been devoted to the consideration of problems

associated with manned flight at supersonic speeds up to four times the

speed of sound. The purpose of this research was to develop a

technology base that would permit the military services and the

aerospace industry of the United States to take full advantage of the

recognized potentials of high-speed flight-more rapid response, improved offensive capability, increased survivability for military aircraft, reduced trip times, improved comfort, and increased productivity for commercial air transports.

The NACA/NASA program to provide a continuously viable supersonic technology base has evolved in three fairly distinct phases. First,

there was a preliminary supersonic technology effort that began in the

mid-1930s during the NACA era and lasted almost until NACA was

f Preliminary Rezearch_

!

\

Supportive Research

U.S. SST Program >

_-70 Bomber Program >

I Sound Barrier [

Broken by XS-11

I

I

I

I

I

I I I I

1_5 19_ 1_5 1_0

I

I

I

l II

I II

I II

I II

I |

1965 1970

Year

Technology Focused

<.As, vcE>

f

% NASA SCR

I I I

1975 1980 1985

Phases of NACA/NASA researchon supersonic cruise lechnolagy.
INTRODUCTION

absorbed by NASA in 1958. In this period, NACA developed experimental methods and facilities for the study of supersonic problems

and contributed to the technology base used to prove the feasibility of

manned supersonic flight. Later, this technology was part of the data

base used in developing a number of military airplanes such as the

century-series fighters, the B-58 supersonic dash bomber, and the

SR-71 supersonic reconnaissance airplane, which is still operational.

Although these airplanes demonstrated many of the potential advantages of supersonic flight, they all had limited payload capability or

relatively short nonstop flight distances unless refueled in the air.

After the feasibility of supersonic flight was established, NASA

raised its research sights to consider the difficult technical problems

posed by the concept of supersonic cruise flight (i.e., sustained,

unrefueled supersonic flight of a large-payload airplane over transcontinental and intercontinental distances). This second phase of the

NACA/NASA supersonic technology effort began shortly before the

formation of NASA in 1958 and lasted until 1971. During this period,

NASA's principal task in supersonic technology was to conduct specific

research in support of America's efforts tO develop a supersonic cruise

bomber (the B-70) and a commercial supersonic transport (the U.S.

SST). Initiated in I957, the B-70 was essentially canceled 2 years later

when the decision was made to depend on intercontinental ballistic

missiles (ICBMs) for America's strategic defense. The program for

developing a U.S. SST began in 1963 and ended in 1971 in a sea of

controversy involving a m_lange of technical, environmental, political,

and social issues.

Many people assumed that the cancellation of the U.S. B-70 and

SST programs, along with the limited success of foreign SST efforts,

provided positive proof that the promised advantages of supersonic

cruise flight do not exist. Others believed that the advantages existed

but that ways for using them had not been found. This latter belief led

to the third phase of the NACA/NASA supersonic technology effort- a

focused research program for solving the remaining technical problems

that have inhibited the general acceptability and applicability of the

concept of supersonic cruise flight. This program, which became

3
SUPERSONIC CRUISE TECHNOLOGY

known as the NASA Supersonic Cruise Research (SCR) program with

a supersonic propulsion offshoot called the NASA Variable Cycle

Engine (VCE) program, spanned the period between 1971 and 1981.

During this period, NASA conducted a broad attack on the problems

of supersonic cruise flight with the support of the U.S. aerospace industry.

In each of three phases of supersonic cruise technology effort,

NACA/NASA made vital contributions to the supersonic "state of the

art." The early NACA preliminary research contributed substantially

to the present understanding of high-speed flight and helped to open

the door to the Moon and the planets. Although not assigned a

decision-making role in America's aborted attempts to develop the

B-70 and SST, NACA/NASA provided supporting research and concepts that were very important to these programs. More recently, the

NASA SCR and VCE programs have made outstanding progress in

identifying solutions to the major problems associated with supersonic

cruise flight. In fact, these latter programs have brought the technology

base for an environmentally acceptable and economically competitive

supersonic cruise transport very near at hand.

Notwithstanding these important contributions, the NACA/NASA

supersonic cruise technology program has not measured up to the success normally expected of a NACA or NASA program. There is currently no large-payload, long-range supersonic cruise aircraft in the air

with an American label, and there seems to be little prospect for one in

the future. With the cessation of the NASA SCR and VCE programs

in 1981, no focused United States efforts remain for providing the

technology for supersonic cruise aircraft. In spite of NACA and

NASA's outstanding contributions to the understanding of supersonic

cruise flight, the future of this concept is uncertain at best.

This rather bleak prognosis for the concept of supersonic cruise flight

has tended to dim the lustre of early NACA research in this area. The

spirited controversies that swirled around the B-70 bomber and U.S.

SST programs, and eventually led to their cancellation, have obscured

the NACA/NASA contributions to supersonic technology during these

two programs. And the continuing SST controversy has perhaps
INTRODUCTION

depreciated the outstanding progress in supersonic cruise technolog-y

that has resulted from the recent NASA SCR and VCE programs.

The purposes of this document are to provide a brief perspective of

the early NACA supersonic research, to revizw the NACA/NASA

supersonic technology efforts during the B-70 and SST programs, to

discuss the factors and events that led to the formulation of the NASA

SCR and VCE programs, and to record the supersonic cruise

technology progress that has been made in these latter programs. No

attempt is made to provide a detailed history of supersonic cruise

technology or to single out every research result. Rather, consideration

is given to the most critical technology issues and research findings.

The character of NASA's research on supersonic cruise flight has

been influenced by the arguments for and against the concept, and by

the ebb and flow of the nation's commitment to supersonic cruise

development. Chapter 2 considers these arguments and commitments

and essentially "sets the stage" for supersonic cruise technology efforts.

The remaining chapters examine the results and ramifications of these

technology efforts.

CHAPTER 2

Setting the Stage for Supersonic

Cruise Technology

After his first successful flight in a powered heavier-than-air vehicle

in 1903, man continued to search for ways to fly faster and faster_ This

quest for speed was motivated by several factors. The early daredevil

pilots sought, perhaps, a few days in the record book, the cheers of the

crowd, or tl.e satisfaction of flying faster than anyone else. The military

services wanted faster airplanes to gain a tactical edge over the real and

potential enemies in the sky. The airline operators looked for faster,

larger .transport airplanes to attract more passengers and to satisfy

steadily increasing passenger demand. Test pilots and aeronautical

scientists were driven to investigate the unknowns of faster speeds to

extend the usable boundaries of flight for both civilian and military

airplanes. Spurred by these and other motivating forces, the quest for

speed led to more sophisticated airplanes, to more powerful engines,

and, by 1946, to flight speeds that approached the mythical speed barrier- Mach 1, the speed of sound.

THE SOUND BARRIER

By 1946, there was general, but not universal, public opinion that

the speed of sound in air-- 760 miles per hour at sea level and 660 miles

per hour at an altitude of 36000 feet--represented an impenetrable

barrier through which no airplane could fly. 2 A number of airplanes

and pilots had been lost during flights at velocities near the speed of

sound, and others had experienced strong buffeting and loss of control.
SUPERSONIC CRUISE TECHNOLOGY

Speed

(mph)

50O0

400O

3000

2000

1000 Speed of Sound 7

i • i I • l I

1900 1910 1920 1930 1940

Year

I

1950

O • •

A

1960 1970

Year Pilot

Speed

(mph) Year

1903 Orville Wright

1922 William Mitchell

1932 James Dootittle

1947 Charles Yeager

1948 Richard Johnson

1951 William Bridgeman

1953 Frank Everest, Jr.

1953 Scott Crossfield

1953 Charles Yeager

America's quest for speed.

7

223

294

700

671

1238

755

1291

1600

Pilot

1956 Frank Everest, Jr.

1956 Milburn Apt

1957 Adrian Drew

1958 Walter Irwin

1959 Joseph Rogers

1960 Joseph Walker

1961 Robert White

1961 Joseph Walker

1967 Peter Knight

Speed

(mph)

1900

2250

1208

1404

1526

2196

3603

3645

4564

8
SETTING THE STAGE

Great Britain had abandoned all efforts to develop manned research

airplanes for flying through the sound barrier, citing as a reason,

among others, that "We have not the heart to ask pilots to fly the highspeed models, so we will make them radio-controlled." 3 In the United

States, however, a research effort was under way on the rocketpowered Bell X-I, which would lead to the first successful flight of a

manned aircraft through the so-called "sound barrier" on October 14,

1947, by U.S. Air Force Capt. Charles Yeager.

The first flight at supersonic speeds was a pivotal event in aviation

history. Man soon found that he could design and construct airplanes

that passed smoothly through the once formidable "sound barrier" and

onward to speeds that pushed him to the outer fringes of the atmosphere and into space. In the early 1950s, supersonic flight of

military "century series" fighter planes became commonplace, and the

U.S. Air Force developed the B-58 bomber, which had a supersonic

"dash" capability of Mach 2-- twice the speed of sound. First flown in

1956, this airplane signaled the approach of the era of supersonic cruise

flight.

The years leading to the first supersonic flight wer.e exciting years in

the progress of aviation technology in the United States. Technology

advances in the speed and versatility of aircraft were supported not

only by the government, but by wealthy patrons, organizations, and

individual entrepreneurs lured by the prospects of worldwide fame and

cash prizes offered in national and international competitions. As aircraft entered the supersonic speed regime, however, the escalating

costs of further increases in speed appeared to place future high-speed

technology strictly in the province of the U.S. Government.

THE FIRST SUPERSONIC CRUISE AIRCRAFT

The first successful flight at supersonic speeds, along with subsequent experience gained in fighters and the B-58 program, led the

U.S. Air Force to consider the development of a large-payload, longrange supersonic cruise aircraft. On December 23, 1957, the North

9
SUPERSONIC CRUISE TECHNOLOGY

First "reaF supersomc crutse alrcraft-the U.S. Air Force North American B-70

bomber.

U.S. Air Force Lockheed YF-12--companion to the SR-71 that had supersonic cruise

capability but without appreciable payload.

10
SETTING THE STAGE

American Aviation Company (now Rockwell International) was placed

under contract to design and produce the B-70 supersonic bomber, an

airplane that was to have intercontinental range capability at a sustained supersonic cruise speed of Mach 3--three times the speed of

sound. At the announcement of the B-70 contract award, factories

across the country began to hum in a massive project that would soon

involve 8000 contractors spread throughout the nation. 4 However, this

flurry of activity was to subside rather rapidly since, only 2 years after

the B-70 contract was issued, the Eisenhower administration essentially canceled the program with the justitication that "the age of

manned bombers was doomed by intercontinental ballistic missiles." 5

Many members of the U.S. Congress were not happy with the

cancellation of the B-70 bomber program, and the battle between the

Congress and the White House lasted through the remainder of the

Eisenhower administration and into the administration of President

John F. Kennedy. During attempts to keep the B-70 program alive,

the Preparedness Investigating Subcommittee of the powerful Senate

Committee on Armed Services recomrfiended in a report dated July 8,

1960, that "unless an operational supersonic bomber is developed now'

there will be no replacement for the B-52 at the time at which it enters

its period of obsolescence (mid- 1960s)." 6 It was 22 years later, in 1982,

that the Reagan administration selected the Rockwell B-1 bomber as a

replacement [br the B-52.

All efforts to restore production funding for the supersonic B-70

bomber were unsuccessful, and the program was limited to the construction of two prototype aircraft. In 1964, the U.S. Air Force announced the secret development of a high-ahitude reconnaissance

airplane, the SR-71, which had a supersonic cruise speed of' Mach 3.

Although this airplane is still in operation, production was limited, and

the B-70 bomber program represented the last major interest of the

U.S. military services in long-range supersonic cruise flight.

THE NEXT LOGICAL STEP

Although the July 1960 report of the Preparedness Investigating

Subcommittee did not succeed in its primary goal of securing produc11
SUPERSONIC CRUISE TECHNOLOGY

tion funding for the B-70, the report left a ray of hope for the supersonic cruise aircraft concept with these words:

It is generally believed by air transportation authorities that a Mach 3 cruise

transport represents the next log,cal step [author's italics] beyond the present

family of jet transports. For both economic and prestige reasons, other nations, including the Soviet Union, will be interested in taking this step ahead

of the United States. The impact of a supersonic transport on world traveling

habits and on the entire field of transportation is expected to be far greater

than the impact that accompanied introduction of current jet transports. Our

leadership in commercial aviation will almost certainly be lost unless the Nation continues the development of Mach 3 technology and applies it as

promptly as possible to air transport adaptations. ?

NASA had expressed a view similar to that of the subcommittee in a

report dated June 1960, which stated: "The successful development of a

supersonic transport is of vital importance to the national prestige as

well as the commercial stature of the United States." B Six months

later, the Federal Aviation Agency recommended "that the Executive

and Legislative branches of our government give prompt and careful

attention to the immediate establishment of a national program for the

development of a commercial supersonic transport aircraft." 9 The

pressures for a U.S. supersonic cruise airplane program appeared to be

mounting, with or without the B-70.

Was the development of a commercial supersonic cruise transport the

next logical step in the evolution of the air transportation system? It certainly appeared to be in light of the situation that existed in the early

1960s. Among the factors that tended to favor this step were:

• The introduction of American-buih subsonic jet transports in 1958

and 1959 had revolutionized the world's air transportation industry. The added speed and comfort of these jet airplanes over

the existing propeller-driven transports led to a rapid increase in

airline passenger demand and much improved airline productivity. Due to the popularity of its new subsonic jet transports, the

American aircraft industry captured a dominant share" of the

world transport market, and the export sales of subsonic jet

12
SETTING THE STAGE

transport aircraft became an increasingly important positive factor

in the American foreign balance of trade.

• The development of a commercial supersonic transport (SST) for

airline service in the early 1970s would be properly timed to

replace the subsonic jet transports that were just going into

service.

• Programs for developing a supersonic cruise transport had been

announced by the Soviet Union (TU-144) and bv a consortium of

the British and French governments (Concorde). Both of' these

programs were to receive government funding support and,

without a competing American aircraft, could threaten United

States domination of the world's air transport market.

• Although the production program for the supersonic B-70 had

been canceled, two of the advanced airplanes were to be constructed. It appeared probable that research results and design information obtained on these two large B-70 airplanes would be

applicable to an SST and would therefore effectively reduce the

development cost of such an aircraft.

• The American X-I airplane was the first manned vehicle to tly at

supersonic speeds. Since that flight, the military services and

NASA had conducted many supersonic wind tunnel and flight

tests. By 1963, manned American winged vehicles had flown to

altitudes of 354 200 feet (67 miles) and at speeds of 4100 miles per

hour (six times the speed of sound). These altitude and speed

marks were recorded by an experimental aircraft, the X-15, and

were not directly indicative of America's ability to develop an

SST. However, the achievements of this experimental aircraft did

indicate the advanced level of the nation's high-speed aircraft

technology.

• The U.S. Congress had provided the military services and NASA

with funding for acquiring unique research facilities that could be

used in investigating nearly every aspect of supersonic cruise

flight. In NASA alone, the research facilities for transonic and

supersonic investigations represented an investment of over $180

13
SUPERSONIC CRUISE TECHNOLOGY

million. _'' _ By the early 1960s, these research facilities had been

widely used in the supersonic B-70 bomber program and in the investigations of potential SST configurations.

• Both NASA and the American aircraft industry had a large

number of experienced research engineers and scientists who had

been involved in supersonic research and flight investigations.

These factors, along with others that were present in the early 1960s,

indicated the readiness of the United States to pursue the development

of an SST and take what appeared to be the next logical step in the

evolution of air transportation. However, negative factors were also

present at this time, and many questioned the wisdom of taking the

step. Among these negative factors were:

• By 1963, America had placed manned spacecraft into Earth orbit

and was well into a massive program for landing a manned

spacecraft on the Moon by the end of the decade. The development of a commercial SST would also be a big federal undertaking, and it was questionable whether two programs of such

technical magnitude could be successfully managed and funded at

the same time. The two programs would also tend to compete for

support and interest.

• Historically, military airplane development had served as a

pacesetter for technical developments that were subsequently used

by the commercial sector. Because the military services had not

fully developed a supersonic cruise aircraft, any such venture

would have to be justified by the commercial application alone.

Without military participation, the cost of development for commercial application would be much higher.

• Even with military support, the cost of supersonic cruise aircraft

development would be beyond the means of the U.S. airplane industry, and hence, government financial support would surely be

required. Never before had the government provided direct financial support in the development of a commercial airplane.

14
SETTING THE STAGE

• The airlines had just invested heavily in the new subsonic jet

transports and were less than enthusiastic about another new

airplane, even a decade in the future.

• A number of major technical problems, such as engine noise,

sonic boom, off-design performance, and operating flexibility,

were still to be solved before an SST would be economically viable

and environmentally acceptable. Although it was generally believed that these problems could be solved, they represented a

substantial technical risk.

These and other issues relating to the advisability of an American

program for developing a commercial SST were debated both inside

and outside the government during the early 1960s. The U.S. Congress provided funding for preliminary SST research in fiscal year

1961, and announcements of the Russian and British/French SST programs came in 1962 and 1963, respectively.

The announcement of an American SST program came on June 5,

1963, when the late President John F. Kennedy, speaking at Air Force

Academy graduation exercises, told. the assembled group:

As a testament to our strong faith in the future of airpower, and the manned

airplane, I'm announcing today that the United States will commit itself to an

important new program in civilian aviation .... It is my judgment that the

government should immediately commence a new program in partnership

with private industry to develop at the earliest practical date the prototype of a

commercially successful supersonic transport superior to that being built in

any country in the world .... This commitment, I believe, is essential to a

strong and forward-looking nation and indicates the future of the manned aircraft as we move into the missile age as well .... t2

With this recommendation by President Kennedy and approval by the

U.S. Congress, it appeared that the United States was finally ready to

take the next logical step in the evolution of air transportation--the

development of a commercial supersonic cruise transport. The Federal

Aviation Agency (FAA), which had been assigned management

responsibility for the new program, followed up quickly after receiving

the go-ahead from Congress. The FAA presented a Development Plan

15
SUPERSONIC CRUISE TECHNOLOGY

on June 19, 1963,13 and issued a "Request For Proposals" on August

15, 1963.

The FAA plan for commercial SST development called for two or

three phases. Phase I was an initial design competition between all interested airframe and engine manufacturers. If a clearly superior "winning combination" resulted from this competition, these contractors

would be awarded contracts for the development program by May 1,

1964. If there was not a clear winner, a phase II competition would be

interjected between the two leading airframe and engine manufacturers from phase I. The final selection of the airframe/engine combination to go into the development phase would then be made early in

1965.14 As a matter of fact, the phase II "winning combination" was not

selected until December 31, 1966, almost 2 years behind schedule.

The winning design in the FAA SST competition was the Boeing

Commercial Airplane Company concept, the B-2707-200. The proposed airplane was to cruise at a supersonic speed of Mach 2.7 (nearly

1800 miles per hour) and was estimated to weigh 675 000 pounds. The

airplane made use of the then controversial variable-sweep or swingwing concept now incorporated on the F-111 and F-14 airplanes. In

this concept, the wing can be swept during flight from a forward position for low-speed flight conditions to a rear position for supersonic

cruise flight. Boeing saw this complex arrangement as the best means

of achieving low noise at takeoff and landing and good flight efficiencies

at all parts of the flight spectrum. The B-2707-200 was to be powered

by four General Electric Company GE-4 turbojet engines that used

afterburners (i.e., additional fuel was burned in a duct at the rear of the

engine to provide increased power at takeoff and during acceleration).

On April 29, 1967, the FAA awarded contracts to Boeing and General

Electric to proceed with prototype development of the B-2707-200

airplane. 15

After working on the design problems involved in the complicated

variable-wing-sweep mechanism for about 1 year, Boeing concluded

that the concept could not be integrated into a viable supersonic

transport within the contract weight limitations. 16 Consequently, in

April 1968, Boeing asked for and received the FAA's permission to

16
SETTING THE STAGE

" F

Lockheed 1.-2000 concept in competition with Boeing in U.S. SST competition.

BoeingGeneral Electric 2707-200 concept that won the U.S. SST competition.

17
SUPERSONIC CRUISE TECHNOLOGY

change to a simpler fixed-wing concept. This concept, a double-delta

wing configuration labeled the B-2707-300 (Dash-300), was now to

become the American entry in the SST sweepstakes. At the time of

Boeing's decision to switch to the Dash-300, the other two entries in the

SST race, the Soviet TU-144 and the British/French Concorde, were

nearing flight status. The TU-144 made its maiden flight on December

31, 1968,17 and the Concorde took to the air on March 2, 1969.18

The American program for developing an SST was a more demanding technical challenge than those for the TU-144 and the Concorde.

The U.S. decision to leapfrog the foreign supersonic versions by going

to a larger size and higher speed brought forth temperature, materials,

and potential operating problems not experienced by the foreign

designers. Delays by the FAA in selecting an airplane for development

and by Boeing in generating an acceptable design were perhaps inevitable. These delays, along with increasing public concern over environmental issues, allowed opponents of the SST effort to mass forces.

With each passing year, in spite of strong White House support, votes

appropriating SST funding got closer and closer in the U.S. Congress.

Finally, on March 24, 1971, the U.S. Senate voted 51 to 46 to cancel

the SST development program. 19 On May 12, 1971, the House of

Representatives made a last-ditch move to continue the program at

least to the end of June 1971. The Senate refused to go along with the

House, and the American SST program finally died on the night of

May 19-20, 1971. 20

AFTER THE U.S. SUPERSONIC TRANSPORT PROGRAM

By the time Congress terminated the SST program, over $1 billion had

been spent on it, but the social costs of the termination were also high.

Seven thousand Boeing workers and 6000 General Electric workers

were laid off immediately. Seattle, Washington, with a 15 percent

unemployment rate, became a mini disaster.area. 21 There was also the

question: What would happen to America's future interest in highspeed research and flight? The wide-body subsonic jet transports had

been put into airline service in 1969 and would serve air

18
SETTING THE STAGE

transportation's productivity needs for the near term. But could an industry that had increased its productivity by 500 percent in the past 15

years while doubling its average speed continue to grow if the speed remained static? What would happen to the American airplane industry

if improved, economically viable versions of the British/French Concorde and/or the Russian TU-144 were developed?

Following the cancellation of the American SST program, the Nixon

administration and some members of Congress were concerned about

these questions. The military services had shown no further interest in

long-range supersonic cruise flight after the B-70 bomber program.

Now, without the focus of the national SST program, there would likely be little emphasis on supersonic cruise research by the airframe

manufacturers, the propulsion industry, or NASA.

Early in 1972, to fill this void in supersonic cruise research, the

Nixon administration instructed NASA to formulate a focused supersonic technology program. The goal of this program was to provide

answers to the environmental, performance, and cost problems of an

SST and to establish a state of "technology readiness" within 3 to 4

years. The administration provided $11.7 million for this program in

fiscal year 1973, and President Nixon requested $46 million in the

fiscal year 1974 budget32 Opponents of the SST saw this program as a

move to "restart the SST" and cut the funding back to $10.1 million for

fiscal year 1974, but at least the program was under way.

The supersonic technology program that evolved from the concerns

of the White House and some members of Congress was first called the

NASA Advanced Supersonic Technology (AST) program and has

subsequently been known as the NASA Supersonic Cruise Aircraft

Research (SCAR) program and the NASA Supersonic Cruise

Research (SCR) program. This program, hereafter referred to as the

SCR program, operated continuously as a focused technology, program

in the NASA budget from fiscal year 1973 to fiscal year 1981 at a funding level of $8 million to $11.7 million per year. In fiscal year 1975, the

SCR program identified a new propulsion concept, the "variable cycle

19
SUPERSONIC CRUISE TECHNOLOGY

engine," which showed promise of solving the noise and off-design

operating problems of an SST. The variable cycle engine (VCE) study

was broken out as a separate focused program under the management

of the NASA Lewis Research Center. The VCE program operated

from fiscal year 1976 to fiscal year 1981 at funding levels ranging from

$0.5 million in the initial year to approximately $6.0 million in the

peak years, FY 1979 and FY 1981.

As focused efforts within NASA, the SCR and VCE programs took a

fresh look at all of the problems exposed in the U.S. and foreign SST

programs-excessive noise, marginal range/payload capability, high

cost, poor economics, etc. The major airframe manufacturers, Boeing,

Douglas Aircraft Company, Lockheed-California Company, and

Rockwell International, and the major propulsion system companies,

General Electric and Pratt and Whitney Aircraft Company, were

called into a partnership of research and technology. Some of these

companies added their own funds to those of the government to stretch

the research capability of the programs, 2s and the results of in-house

company-funded research were published and reported along with

those of the government-funded technology effort. This provided for an

almost unprecedented instantaneous exchange of technical information

between companies competing in both military and civilian projects

and led to very little duplication of effort.

A recent report summarizes the NASA SCR and VCE program

results as follows:

Dramatic progress has been made in the major technical discipline areas,

making it possible to show large gains in range/payload capability for supersonic transport type airplanes. At the same time, stringent environmental

noise and pollution restraints can be met. Even if the supersonic airplanes

should cost twice as much per pound as their subsonic competition, the supersonic vehicles may nearly equal subsonic tourist ticket prices while reducing

trip time to less than half its present value. Two very recent developments, as

yet unproven, one structural, one aerodynamic, could provide the performance improvement margin necessary to end the subsonic jet dominance of the

long-haul over-water passenger market. Advanced SSTs could displace subsonic jets on these routes just like the subsonic jets displaced the propeller

airplanes. 2+

20
SETTING THE STAGE

Unfortunately, this report goes on to say that "funding limitations

have forced cancellation of the focused government/industry

approach .... ,, 25

Now that we have "set the stage" for the various phases of the

NACA/NASA research and technology effort on supersonic cruise

flight, let us turn back to the beginning and consider some of the details

of this effort.

21

CHAPTER 3

NACA Preliminary Supersonic Cruise

Technology (?-1956)

No "red letter" date marks NASA's entry into the field of supersonic

cruise research. In the late 1930s and early 1940s, NACA engineers

and scientists were conducting preliminary studies of airplane and

engine combinations that might possibly fly at velocities greater than

the speed of sound. However, these studies were limited by the uncertainties that existed in the aerodynamic characteristics of airplanes that

were considered for such flight. At that time, wind tunnels were of the

closed-throat type, and as the speed of the airflow approached that of

sound, the tunnels "choked." Shock waves forming off the test model

and its supports would reflect off the tunnel walls, inhibiting accurate

measurements of flow characteristics and behavior around the model.

This condition persisted from about Mach 0.7 to about Mach 1.3, the

very area in which the scientists were interested, the transonic region

between subsonic and supersonic flight. _6 Without some better

research data in the transonic region, the accomplishment of transonic

or supersonic cruise flight seemed hopeless.

With the entry of the United States into World War II in December

1941, the means for removing the uncertainties of transonic and supersonic flight became critically important. Greater high-speed capability

was incorporated in each new American fighter and attack airplane,

and these airplanes were getting into difficulties because of local

regions of transonic and supersonic flow, even though their forward

speeds were still subsonic. "Army Air Forces and Navy combat

squadrons suddenly found that their aircraft faced a new and frighten23
SUPERSONIC CRUISE TECHNOLOGY

ingly mysterious danger aside from the enemy. An epidemic of tail

failures during dives appeared in three production high-speed aircraft,

the Republic P-47 Thunderbolt, the Curtis SB2C Helldiver, and the

Bell P-39 Airacobra." 27 Although NACA was able to recommend

suitable fixes for these three aircraft, the aerodynamic uncertainties of

flight at velocities near the speed of sound remained. The turbojet

engine, introduced in an experimental aircraft in Britain in 1941,

promised further increases in speed if the aerodynamic uncertainties

could be resolved. By 1943, "... the only remaining barrier to highspeed flight--including flight faster than the speed of sound- appeared

to be a knowledge barrier, where aerodynamicists could not predict

with certainty what occurred in the turbulent speeds of transonic flight.

The immediate problem facing aerodynamicists was how to arrive at

accurate research tools and methods to derive needed data and strip the

mystery from compressibility and transonic aerodynamics." 28

MOUNTING AN ATTACK ON THE SOUND BARRIER

In the early 1940s, with no immediate prospects for solving the wind

tunnel blockage problems at velocities near the speed of sound, NACA

engineers developed several stopgap methods for obtaining transonic

aerodynamic data. One of the methods involved the dropping of

weighted bodies from high altitudes. "The bodies would then attain

velocities equal to or faster than that of sound. Radar and visual tracking from the ground could determine the speed and path of the falling

body." 29 Another method, developed by Robert Gilruth of the NACA

Langley Laboratory, involved placing small models in the local transonic and supersonic flow fields that were known to exist over the wing

of a North American P-51 "Mustang" during high-speed dives.3° These

methods-together with the later NACA rocket-propelled model work

under Gilruth-provided vital data on drag variation through the

speed of sound. 3j However, there was rising sentiment that a research

airplane was the best way to secure the transonic data necessary, for

breaking the "sound barrier" and proceeding into the supersonic speed

regime.

24
NACA PRELIMINARY TECHNOLOGY

As early as 1939, Ezra Kotcher, a senior instructor at the Army Air

Corps Engineering School at Wright Field, advocated comprehensive

flight research programs for correlating wind tunnel data with full-scale

performance. 32 In 1944, over 4 years after Kotcher's recommendation,

and after a name change from Army Air Corps to Army Air Force in

1941, Air Force Headquarters authorized a study into the possible

development of an experimental article for investigating aerodynamic

phenomena in the 600- to 650-mph range. 33Kotcher went on to make a

comparative investigation of the merits of rocket and turbojet propulsion for the transonic research aircraft in early 1944. The study showed

that, from every standpoint, rocket power appeared to be better for

transonic research aircraft because high speeds could be attained, making dives to high Mach numbers unnecessary. 34

At NACA, John Stack and Eastman Jacobs were the chief proponents of a transonic research aircraft. Stack had proposed the idea in

1941 and had set up a team consisting of himself, Milton Davidson,

Harold Turner, and Walter Williams to study possible research configurations. Jacobs had earlier set up a group that also included Davidson and Turner, along with Macon C. Ellis, Jr., and Clinton E.

Brown. The Jacobs group was particularly interested in an aircraft

with a "Campini" engine that promised ample thrust for flying at transonic speeds if aerodynamic problems could be solved. 35

Capt. Walter S. DieM, USN, the Navy Bureau of Aeronautics

representative on the National Advisory Committee for Aeronautics,

felt as early as 1942 that the research airplane appeared to be the only

way to convince people that the "sonic barrier" was just a steep hill. 36

On September 22, 1944, 1st Lt. Abraham Hyatt, a Marine Corps

engineer attached to the Bureau of Aeronautics, proposed the development of a turbojet-propelled high-speed research airplane for acquiring

knowledge on transonic drag, flight loads, and stability and control, as

well as data on engine thrust and duct inlet design. 37

With the transonic problems of high-speed military airplanes becoming more serious by the day, representatives of the Army Air Force,

25
SUPERSONIC CRUISE TECHNOLOGY

U.S. Navy, and NACA met at the NACA Langley Laboratory on

March 15, 1944. Two meetings that day tied together the separate interests in the possible development of a transonic research aircraft.38

The parties present had different ideas as to what the research aircraft

should be and what it should try to accomplish, but there was general

agreement that some type of transonic aircraft was urgently needed.

The NACA representatives suggested a joint effort for constructing a

turbojet-powered research airplane, 39 and NACA followed up on July

10, 1944, by submitting a turbojet research airplane design proposal to

the Army Air Force. The Air Force rejected the NACA design as being

too conservative because its studies had shown that the turbojet engine

would not give the aircraft good high-speed capabilities. *° The NACA

design was more in line with the research aircraft requirements that

were recommended by the Navy's Lt. Abraham Hyatt a few months

later.

As the end of 1944 approached, both the Army Air Force and the

Navy had program s under way for developing their own separate transonic research air_raft. Both services relied on the advice of NACA in

establishing and guiding their programs. The Navy chose to develop a

turbojet research airplane, which became the Douglas D-558. The

Army Air Force chose to develop the more radical rocket-propelled

design--the Bell XS-l-rejecting NACA's recommendation of airbreathing engines. 4_ Note that neither the XS-1 nor the D-558

resulted from extensive design competitions for finding the best transonic research airplane. Ezra Kotcher had some difficulty interesting

Army Air Force contractors in developing this "one of a kind" airplane,

and was rejected several times before Bell agreed to develop the XS-1.

Similarly, the Navy went to Douglas, a principal Navy airplane builder

at the time, and requested that the company work on the design that

was to become the D-558. Careful attention by the Army Air Force,

the Navy, and NACA kept the two separate research airplane programs from being duplicative. Although different in organizational

structure and function, the three groulSs worked together in a common

mission to solve the problems associated with transonic flight.

26
NACA PRELIMINARY TECHNOLOGY

BREAKING THE SOUND BARRIER

As dawn approached on October 14, 1947, the Muroc Dry Lake in

Southern C_lifornia became a beehive of activity. The focus of attention was the Bell Aircraft Corporation's XS-1, America's first transonic

research aircraft. This was the day that the XS-1, piloted by Capt.

Charles E. Yeager of the newly named U.S. Air Force, would attempt

to fly through the mysterious "sound barrier." The assembled

engineers, technicians, and pilots anticipated success because the aircraft had nearly reached supersonic speeds on its previous flight 4 days

earlier.

Poised and ready for its most important mission, the XS-1 was the

result of almost 3 years of intensive effort by the Bell Aircraft Corporation, Reaction Motors, Inc., the Air Force, and NACA. Only 1 year

First supersonicairplane-the U.S. Air Force Bdl XS-1 experimental airplane.

27
SUPERSONIC CRUISE TECHNOLOGY

after Ezra Kotcher secured a commitment from Bell to design and construct three transonic research airplanes, Bell completed the first

XS-1. Less than 16 months after construction, the XS-1 had successfully completed its first powered flight with the new Reaction

Motors rocket engine. Six months later, the XS-1 was ready to go

supersonic.

NACA engineers and aerodynamicists participated with the Bell

Aircraft Corporation and the Air Force in many elements of the XS-1

design and flight-test program. Floyd Thompson, Assistant Chief of

Research at the NACA Langley Laboratory, decided to use a "thin"

wing based on transonic wingflow test results obtained by NACA's

Robert Gilruth. 4_John Stack recommended that the horizontal tail be

made relatively thinner than the wing to ensure that the airplane could

be controlled even if critical conditions occurred over the wing. 43 Stack,

Gilruth, and others further suggested that the horizontal tail be "allmoving" to ensure adequate control during transonic flight and that the

horizontal tail be placed as high as possible on the vertical fin to position it above the wing wake. 44 NACA engineers set the ultimate design

load factor 45 and recommended the research instrumentation that

would go on the airplane. 46 Walter Williams, a NACA Langley

engineer who had been on John Stack's transonic design team, was

project engineer for the NACA group that was responsible for the flight

tests, data gathering, and data dissemination.

Although the XS-1 had flown successfully during the contractor program and the early Air Force flights, some people believed that the

airplane would disintegrate because of compressibility effects at sonic

speeds. However, after his epoch-maklng flight of October 14, 1947,

here is what Capt. Yeager had to say about it:

_Ariththe stabilizer set at 2° the speed was allowed to increase to approximately .98 to .99 Mach number where elevator and rudder effectiveness were

regained and the airplane seemed to smooth out to normal flying

characteristics. This development lent added confidence and the airplane was

allowed to continue to accelerate until an indication of 1.02 on the cockpit

Mach meter was obtained. At this indication the meter momentarily stopped

28
NACA PRELIMINARY TECHNOLOGY

and then jumped to 1.06 and this hesitation was assumed to be caused by the

effect of shock waves on the static source. 47

Yeager had attained an airspeed of 700 mph, Mach 1.06, at an

altitude of approximately 43 000 feet. He had become the first pilot to

successfully exceed the speed of sound. There had been no violent buffeting or wrenching of the airplane, and Yeager did not note anything

spectacular about broaching the "sound barrier." _8

Yeager's flight laid to rest the myth of the "sound barrier" and opened

the door to the possibilities of supersonic flight. Data obtained by

NASA pilots on the XS-1 and the Navy's D-558 transonic research aircraft provided a rich trove of transonic and supersonic flight information. During the period September 25, 1947, to November 6, 1958,

NASA pilots made 358 research flights in various versions of these two

aircraft.

Navy transonic research airplane-the Douglas Aircraft Company D-558.

29
SUPERSONIC CRUISE TECHNOLOGY

Another important aspect of the XS-1 and D-558 programs was the

impetus they provided to the development of better ground-based

research facilities and testing methods. The requirements for the best

possible data in the development of these two aircraft led directly to

several important innovations in wind tunnel testing. In 1945, NACA

Langley engineers, adopting Gilruth's wing-flow techniques,

developed the "transonic bump" method for wind tunnel testing. With

the use of a carefully designed "bump," a region of transonic flow could

be generated in the tunnel even though the main flow remained subsonic. Langley engineers also developed an entirely new method of

testing high-speed models using special sting supports with internal

balances. Using small models and the nonchoking sting support

system, Langley wind tunnel engineers could test the XS-1 and D-558

almost up to the speed of sound. 49

Perhaps the most important ground-test development spawned by

the XS-1 and D-558 programs was the "slotted wall" transonic wind

tunnel. In 1946, Ray Wright at NACA Langley suggested the use of

slots in wind tunnel walls to more nearly duplicate free-air conditions.

Making use of this concept, John Stack and his associates cleveloped a

"slotted wall" transonic wind tunnel that was essentially free of the

"choking" experienced in existing solid-wall tunnels. With this tunnel it

was possible, for the first time, to increase tunnel airspeed continuously

through Mach 1 by merely increasing fan speed. For this important

development in aviation research, John Stack and his associates at

Langley received the prestigious Collier Trophy in 1951.50

The American quest to break the "sound barrier" also led to several

revolutionary aerodynamic discoveries that have had a lasting effect on

the design of high-speed aircraft. Two of the most important of these

discoveries were the swept wing and the "area rule," both of which were

made at the NACA Langley Laboratory.

Before 1945, military and civilian airplanes made use of straight

wings that were essentially perpendicular to the direction of flight-an

adequate wing orientation for speeds up to 300 to 400 mph. As airplane

3O
NACA PRELIMINARY TECHNOLOGY

velocities approached the speed of sound, however, the straight wing

gave rise to large increases in the drag or resistance of the airplane. In

1944, Robert T. Jones of NACA Langley noted that these drag increases could be substantially reduced by sweeping the wings back

from the direction of flight. Jones had developed his wing-sweep theory

independently and without knowledge of the pioneering wing-sweep effort of German scientist Adolph Busemann in 1935. The discoveries of

these two scientists changed the shape of high-speed airplanes, and

essentially all such aircraft now employ swept-back wings.

The discovery of the "area rule" was almost directly due to the

development of the "slotted wall" transonic wind tunnel and the

capability it provided to test models near Mach 1. In 1951, while conducting such tests, NACA Langley engineer Richard Whitcomb and

his team observed the expected shock disturbances from the nose of a

model, but also found additional disturbances emanating from the

trailing edges of the wings. Whitcomb believed that these latter disturbances were leading to high drag and that they were caused by irregularities in the cross-sectional area distribution at the wing/fuselage

juncture. He theorized that drag could be substantially .reduced if the

total combined cross-sectional area of the wing, fuselage, and tail were

adjusted to approach that of an ideal streamlined body. Thus, the

fuselage should be constricted where the wings were attached and expanded at their trailing edges. Subsequent wind tunnel tests proved

Whitcomb's concepts, and the transonic "area rule," with its attendant

"coke bottle" fuselage shape, was born. 5_ The "area rule," which

resulted in a Collier Trophy for Whitcomb, was later expanded to

supersonic speeds by Boeing and NASA engineers and is a major tool

in the design of high-performance supersonic airplanes.

Thus, the necessary first step in the evolution of supersonic cruise

flight--"breaking the sound barrier"--had been successfully taken. As

NACA engineers and scientists participated in this effort, they produced breakthroughs that would have far-reaching effects on the shape

of future civilian and military aircraft. However, NACA was aware

that short-duration supersonic flights of small experimental airplanes

31
SUPERSONIC CRUISE TECHNOLOGY

did not ensure the ready development of long-range supersonic aircraft. Much work was yet to be done.

During the latter part of the 1940s and the first half of the 1950s,

NACA prepared for the new era of supersonic flight. With the support

of the U.S. Congress, a wind tunnel construction program was initiated at all three of NACA's ground test centers. As a result of the

Unitary Plan Act, passed by Congress on October 27, 1949, a large

transonic/supersonic wind tunnel complex was built at NACA Ames,

Moffett Field, California; a new supersonic tunnel was constructed at

NACA Langley, Hampton, Virginia; and a large supersonic tunnel,

dedicated to propulsion system integration, was established at NACA

Lewis, Cleveland, Ohio. In addition, the Unitary Plan Act authorized

a new Air Force aeronautical test center at Tullahoma, Tennessee,

now known as the Arnold Engineering Development Center (AEDC).

Under the Unitary Plan, NACA was to concentrate on industrial

development work (i.e., commercial aircraft), and the Air Force

AEDC was to focus on military development testing. 52

In addition to acquiring these facilities with increased research

capability, NACA made other preparations for the approaching era of

supersonic cruise flight. At the Ames and Langley aeronautical

centers, scientists began to collect data on a myriad of aeronautical

configurations that appeared to be suitable for supersonic cruise flight.

These two NACA groups also began the development and validation of

analytical methods that could be used in supersonic design and

analysis. The Lewis propulsion center initiated a massive effort for

developing turbojet engine technology for supersonic airplanes. The effort covered the aerodynamic design of all components of the engine,

inlet, and nozzle and the development of new high-temperature

materials and cooling techniques for turbine blades and considered the

most suitable design characteristics of a turbojet engine. Meanwhile, at

the NACA Flight Research Center at Edwards, California, engineers

and pilots continued to collect valuable transonic and supersonic data

on a bevy of high-speed research airplanes such a_ ihe X-2, X-4, X-5,

D-558-II, and XF-92. Also under way at NACA was an advanced

32
NACA PRELIMINARY TECHNOLOGY

structures research program in which new materials, such as titanium,

and the "super alloys" were being investigated at the temperature levels

to be expected during supersonic flight.

The preparations for the development of long-range supersonic

airplanes were being made. The question now was: When would the

development begin?

33

CHAPTER 4

NACA/NASA Supportive Supersonic

Cruise Technology (1956-1971)

As NACA prepared for the approaching era of supersonic cruise

flight, the military services followed up quickly on the knowledge

gained in the X-1 and D-558 programs. By 1953, the first American

supersonic fighter, the North American F-100, had been developed,

and it was soon followed by the Mach 2 fighter, the Lockheed F-104.

In 1956, the Convair B-58, a medium range bomber also having Mach

2 "dash" capability, was brought into the Air Force inventory.

All of these aircraft performed well in the transonic and supersonic

speed regimes, but they all had rather short supersonic range and duration of flight. Even though a number of aircraft were now capable of

flying at supersonic speeds, the total flight experience at supersonic

speeds was still very small. For example, during its first 10 000 hours of

flight time, the B-58 bomber logged only 500 hours at speeds above

Mach 1.5.53

This early flight experience with supersonic aircraft gave little indication that a vehicle could be developed that would be capable of sustained long-range supersonic flight. At this point, it appeared that the

advent of the concept of supersonic cruise flight would hinge on some

substantial breakthrough in aerodynamic, structural, or propulsive

efficiency.

THE U.S. AIR FORCE B-70 BOMBER PROGRAM

In late 1951, Gen. Curtis LeMay, Commander of the U.S. Air

Force's Strategic Air Command, began looking around for a B-47

35
SUPERSONIC CRUISE TECHNOLOGY

bomber replacement. A "split mission" aircraft was envisioned--one

that would cruise subsonically to the enemy early-warning line (EWL)

and then "dash" supersonically to the target. On October 14, 1954,

after several years of study and consideration, the Air Staff published a

general operating requirement (GOR) for a supersonic strategic

bomber for the 1965-1975 time period. 54 This GOR initiated the

preliminary studies that would lead to the Air Force supersonic B-70

bomber program.

Four companies responded to the Air Staff GOR and undertook

preliminary design studies for such an aircraft: General Electric for

propulsion, IBM for homing and navigation devices, and Boeing and

North American for design integration and the manufacture of the entire weapon system. 55

At the time of these preliminary B-70 studies, the Air Force perhaps

expected little more than a larger version of the B-58. There was little

to indicate that more than supersonic "dash" capability could be

achieved, and "the only recourse available to the design engineer was

the so-called brute-force concept- tremendous fuel capacity and an optimized aerodynamic shape for the target sprint." 56

General LeMay is said to have groaned when he saw the resultant

1955 B-70 design; the concept called for jettisonable wing-tip tanks

that weighed 191 000 pounds and were about the size of a B-47. Grossing out at more than 750 000 pounds, the design featured a huge

canard arrowhead control surface that cut the pilot's forward vision by

50 percent. 57

Shortly after Air Force rejection of this preliminary concept, a

NACA aerodynamic "breakthrough" was revealed that had dramatic

implications on the B-70 program and on future supersonic design

philosophy. This breakthrough was the product of A. J. Eggers and

C. A. Syvertson of the NACA Ames Research Center. 58 Their

research indicated that a substantial quantity of favorable "compression

lift" could be created on the under surface of a wing at supersonic

speeds by the proper placement of a body or "splitter" beneath the wing

surface. A supersonic airplane that employed this concept could effectively ride its own shock wave. The "compression lift" concept was

36
NACA/NASA SUPPORTIVE TECHNOLOGY

tested at the NACA Ames, Lewis, and Langley centers. Dr. Hugh

Dryden, the NACA Director, had this to say about the compression lift

concept in 1958 testimony to the U.S. Congress:

A year or so ago, the Air Force was reconciled to the idea that the best it could

obtain in the way of performance from a new large bomber would be what the

engineers call high subsonic cruise plus supersonic dash similar to the B-58.

About a year ago a strange and wonderful thing happened. It was as if the

pieces of a jigsaw puzzle began falling into place. Almost simultaneously

research programs that had been under way at NACA labs in Virginia

[Langley], California [Ames], and Ohio [Lewis] began paying off.

The result--this is oversimplification, but it is not overstatement-was that

the companies [i.e., North American and Boeing] and the Air Force suddenly

realized it would not be much harder to design a long-range bomber that

could fly its whole mission supersonic than to design one that would fly subsonic all the way with only a small fraction of the flight supersonic. Not only

that, but the top speed of the prospective bomber was raised to Mach 3, about

2000 miles an hour. 59

The aerodynamic promise of Eggers and Syvertson's compression lift

concept encouraged the Air Force to proceed with the B-70 bomber

program. A North American configuration, which made use of this

concept, was selected as the winning entry in the B-70 competition.

The company was awarded a design and production contract on

December 23, 1957. The production contract was not to remain in effeet very long, however° On December 3, 1959, a teletype from the

Pentagon informed North American that "THE B-70 IS BEING

REDIRECTED AS FOLLOWS: (A) CEASE ALL STUDY,

DESIGN, DEVELOPMENT AND FABRICATION AND TEST

WORK TOWARDS THE B-70 WEAPON SYSTEM IN WING

STRENGTH IN ACCORDANCE WITH THE MASTER PHASING SCHEDULE; (B) PROCEED WITH DESIGN, DEVELOPMENT, FABRICATION AND TEST WORK AND PRODUCE

ONE XB-70 FOR THE EARLIEST POSSIBLE FLIGHT DATE

CONSISTENT WITH TENTATIVE FUNDING CEILINGS .... - 60

37
SUPERSONIC CRUISE TECHNOLOGY

North American B-70 bomber program spurred supersonic cruise research.

This Pentagon directive was eventually amended to permit the construction of two. B-70 aircraft, but it effectively signaled the end of the

U.S. military's interest in long-range supersonic cruise aircraft. The intercontinental ballistic missile (ICBM) had replaced the manned

bomber as America's major strategic weapon system.

The first of the two B-70 prototypes authorized by the Pentagon

made its initial flight on April 21, 1964. It attained the design cruise

speed of Mach 3 (2000 mph) in May 1965. The second aircraft made its

first flight on July 17, 1965. This latter aircraft had been heavily instrumented by NASA for research experiments when it was lost in a

tragic midair collision with an F104 on June 8, 1966. The two B-70

prototypes flew a combined total of about 100 missions.

The B-70 bomber was a remarkable airplane for its time period.

Designed before the development of high-speed computers and

automated aerodynamic and structural design methods, the B-70 provided a mass of useful data on aerodynamics and sonic boom. NACA

provided one of the principal design features of the airplane (i.e., compression lift). Although it was never conclusively proven whether the

38
NACA/NASA SUPPORTIVE TECHNOLOGY

B-70 obtained the full predicted benefits of compression lift during

flight, the principle of compression lift or "favorable lift interference"

was incorporated in later aerodynamic design methods.

THE U.S. SUPERSONIC TRANSPORT PROGRAM

There was a feeling in some quarters that the cancellation of the Air

Force B-70 bomber program would be a mortal blow to the concept of

supersonic cruise flight, at least in America. The B-70 was expected

not only to establish the feasibility of such flight, but also to serve as a

proving ground for a future commercial supersonic transport. A wing

of long-range B-70 bombers could rapidly obtain the 20 000 or so

hours of supersonic flight experience that were desired prior to commercial development. Moreover, later models of the B-70 could try out

new technology for later application on the commercial transport

airplane.

Many were happy to see the demise of the B-70 production program

and were even more pleased that this demise might inhibit or deter the

development of a commercial SST. Concerns were rising about the effect of a fleet of SSTs on the environment, and the questions about

pollution, safety, radiation, noise, etc., were beginning to dim some of

the ardor for the apparently insatiable quest for higher speed. One of

the most disturbing phenomenon associated with supersonic flight was

the sonic boom--a startling thunderclap that is produced by a vehicle

moving at supersonic velocity through the atmosphere.

NASA, by 1960 heavily involved in the national space program,

looked on the challenge of supersonic cruise flight as well within its

chartered responsibility for preserving the leadership of the United

States in aeronautical science and technology. While recognizing the

difficult problems that had to be solved before commercial supersonic

flight, NASA saw such flight as a rational and necessary evolution in

commercial transportation. Accordingly, NASA began to build rapidly

on its base of supersonic technology with the firm belief that this

39
SUPERSONIC CRUISE TECHNOLOGY

technology would be useful to the United States. This belief was

strongly shared by others both within and without the government.

In the early 1950s, NACA had initiated concerted efforts to improve

the technology of supersonic cruise flight. Now, in the latter half of the

decade, the newly formed NASA was stepping up the research and

technology efforts. Fundamental programs were under way in all

design and operational areas associated with supersonic cruise flight.

At each of the NASA aeronautical centers, engineers were seeking

ways to provide the levels of aerodynamic, propulsive, and structural

efficiencies that would be required of a viable commercial SST. A

variety of aerodynamic and propulsive concepts that had the potential

for meeting the required efficiency levels were exhaustively tested in

the NASA low-speed and new supersonic Unitary Plan wind tunnels.

Programs for studying the air traffic control and other operational

problems were initiated in cooperation with the FAA. In 1960, NASA

formed a Supersonic Transport Research Committee to coordinate and

guide this mushrooming supersonic technology effort.

In mid-1960, the NASA Langley Research Center summarized the

effects of supersonic research of the 1950s on the technical status of the

supersonic transport. John Stack, who had been heavily involved in

NACA's earlier transonic research, said in his introduction to this

technical summary:

The prospects tor commercial flight at supersonic speeds herald a new era in

the transportation field, The successful development of a supersonic transport

is of vital importance to the national prestige as well as the commercial stature

of the United States. If the United States is to achieve a supersonic air

transport capability at the earliest practical date, a vigorous effort is demanded on all fronts. 6_

Stack went on to comment about the potential SST configurations that

had evolved from NASA studies: "While many of these configurations

have serious limitations for commercial operation, reasonably clear

definitions of the problem areas have been achieved and possible new

approaches are under study." 62

4O
NACA/NASA SUPPORTIVE TECHNOLOGY

Therefore, in 1960, NASA believed that the development of a commercial SST was of vital importance to the United States and that

supersonic research had come a long way toward providing the

technology for a viable SST, but that much research effort was still required before the goal could be reached. NASA was busily conducting

this research.

In 1961, the preliminary groundwork for establishing a U.S. SST

program moved forward. Representatives of NASA, the Federal Aviation Agency, and the Department of Defense met to consider the

responsibilities of each agency in the event that such a program would

be approved by the U.S. Congress. Out of this meeting came a joint

report which indicated that "A vigorous [SST] effort must be started

immediately in order to have an operational aircraft in the 1970 time

period." 63 The report suggested the following agency roles in such an

effort:

• Federal Aviation Agency--Leadership and fiscal support

• Department of Defense--Administrative and technical support by

the U.S. Air Force

• National Aeronautics and S]_ace Administration--Basic research

and technical support.

Secretary of Defense Robert S. McNamara, NASA Administrator

James E. Webb, and FAA Administrator N. E. Halaby signed this

joint agency report. The three agencies established an SST Steering

Group, consisting of the Administrator, FAA, Chairman (Halaby); the

Assistant Secretary of the Air Force for Research and Development

(Joseph S. Imirie); and the Director of Aeronautical Research, NASA

(Stack). The Steering Group was to coordinate joint effbrts on SST

problems.

Shortly after this joint agency report was signed, an FAA request for

$12 million in fiscal year 1962 SST funding came before the U.S.

Senate. This funding was to provide for FAA-managed research that

would augment the supersonic effort at NASA. On July 31, 1961, a

motion was made in the Senate to strike the SST funding from the FAA

41
SUPERSONIC CRUISE TECHNOLOGY

budget. The first SST funding measure barely survived when the "motion to strike" the funding failed to pass on a 35 to 35 tie vote. 64 An SST

funding level of $11 million was subsequently approved by Congress,

and the FAA research program was under way.

FAA received an additional $20 million in fiscal year 1963 to continue the preliminary. SST research program. NASA assisted FAA in

monitoring the research contracts and grants that evolved from this

program.

Meanwhile, NASA engineers were homing in on some aerodynamic

configurations that showed very good potential for meeting the requirements of a commercial SST. From approximately 20 concepts,

four aircraft arrangements had emerged as likely SST candidates after

a series of analyses, wind tunnel tests, and refinement. In the latter half

of 1962, NASA prepared to submit these four concepts to an SST

feasibility study by the American airplane industry.

NASA SUPERSONIC COMMERCIAL AIR TRANSPORT (SCAT)

FEASIBILITY STUDIES

The NASA/Industry SCAT Feasibility Studies were initiated in

January 1963, making use of $1 million of NASA funds. The major

purposes of the studies were to bring the NASA SST effort into focus

and to establish the technological state of the art for guidance of a possible national SST program. NASA would also receive the unique expertise of industry in the evaluation of the four candidate SST concepts

and in the identification of areas requiring further research attention.

The four NASA configurations submitted for industry feasibility

studies bore the designations SCAT-4, SCAT-15, and SCAT-16

(generated at the Langley Research Center), and SCAT-17, which

was developed at the Ames Research Center. All three of the Langley

designs incorporated highly swept arrow wings. The SCAT-4 wing

was fixed, the SCAT-15 made use of auxiliary variable-sweep panels

to improve low-speed performance, and the SCAT-16 was a classical

variable-sweep wing design. The Ames SCAT-17 configuration was

characterized as a fixed-delta-wing airplane with a small auxiliary wing

or canard near the nose.

42
NACA/NASA SUPPORTIVE TECHNOLOGY

NASA supersonic transport feasibility concept-- the highly swept fixed arrow-wing concept

SCA T-4.

NASA SST feasibility concept-the variable-sweep SCA T-15 with blended body and interlocking wings (forerunner of the fixed-wing SCA T-15F.)

43
SUPERSONIC CRUISE TECHNOLOGY

NASA SSTJeasibility concept- the SCA T-16 with highly swept arrow wing in aft posilion.

NASA SCA T-16 with wings in swept-forward position.

44
NACA/NASA SUPPORTIVE TECHNOLOGY

NASA SST feasibilit.y concept-- thefixed delta-wing SCA T-17 with forward canard and

aytt_it.

The Boeing Airplane Company and Lockheed California Company

were selected to assess the feasibility of the four SCAT designs on a

3200-nautical-mile SST mission with 125 passengers at a cruise Mach

number of 3, as well as the feasibility of one of the designs as an

aluminum Mach 2 transport. In addition, they were to evaluate several

engine types and levels of propulsion technology. In flying the mission,

the sonic boom levels could be no more than 2 pounds per square foot

(psf) in climb and no more than 1.5 psf while at cruise conditions. The

engine noise would be comparable to present-day subsonic jet aircraft.

The results of the NASA SCAT Feasibility Studies were reported on

September 17-19, 1963, at a Langley Research Center conference. 65

The studies indicated the following:

• Either a Mach 3 variable-sweep transport, patterned after the

SCAT-16, or a fixed-wing transport, tbllowing the lines of the

SCAT-17, could make the New York/Paris mission with 125

passengers.

• If the SCAT is to be a competitive transport, an advance in the

propulsion state of the art would be required.

45
SUPERSONIC CRUISE TECHNOLOGY

• A Mach 2 aluminum SCAT could not make the mission within

the sonic boom constraints used in the study.

• Titanium was preferred over stainless steel as the basic material

for a Mach 3 SCAT.

• For the transport to have satisfactory, characteristics, research in

several areas would be urgently needed. The aircraft needs to

have better aerodynamic performance than that used in the

studies, and configurations need to be devised that can obtain the

high aerodynamic performance while still maintaining low structural weight. Research and development work in the engine field

is required. Research is needed in stability and control to improve

flying qualities of the aircraft. Considerable work is needed to

establish confidence in the use of titanium. Research is needed to

determine if the sonic boom can be reduced. Research is needed to

determine the public acceptance of sonic boom so that boom

restrictions can be set at the highest possible level.

In essence, on the basis of then-current status of technology in

almost all areas of research, the NASA SCAT Feasibility Studies of

1963 indicated that a commercial supersonic transport was not feasible.

However, 1 month later, on August 15, 1963, FAA circulated to industry the "Request for Proposals for the Development of a Commercial Supersonic Transport." The United States SST program was

under way.

FAA SST EVALUATIONS

While the NASA SCAT Feasibility Studies were in progress, President Kennedy and the U.S. Congress took the actions that launched

the American commercial SST program. With the release of the FAA's

request for proposals, NASA's role changed from one of having its own

concepts evaluated by the airplane industry to one of evaluating the

SST concepts of the airplane industry.

The FAA allowed the interested airplane and propulsion companies

about 4 months to develop and submit proposals for the SST development program. During this time, NASA participated with the FAA in

46
NACA/NASA SU PPORTIVE TECH NOLOGY

setting up evaluation criteria and organizing the SST Evaluation

Team. The FAA development plan called for one evaluation during

January 1964, which was to be followed by:

• Selection of the winning airframe/propulsion combination by May

1964

• A 1-year detailed design effort ending in May 1965

• First flight of a United States SST in the fall of 1968

• SST entry into passenger service in the summer of 1970 66

As it turned out, four FAA SST evaluations were held before the

selection of the "winning combination" on December 31, 1966. The

evaluation process extended from January 1964 to October 1966-a

period of 33 months. During this time, NASA provided totals ranging

from 41 Evaluation Team members in the first evaluation to 74

members in the last evaluation in September 1966. Approximately

one-third of the evaluators were from NASA, and about two-thirds of

NASA's representation were from the Langley Research Center.

Langley engineers also provided a large part of the analytical tools that

were used in the evaluation process and, during the last three evaluations, conducted extensive wind tunnel tests on models provided by the

contractors. In the final evaluation, Ames Research Center conducted

low-speed wind tunnel tests of contractor models.

Three airframe companies--Boeing, Lockheed, and North

American--and three engine companies--General Electric, Pratt and

Whitney, and Curtis Wright--submitted proposals for evaluation in

January 1964. The first FAA/SST evaluation found that none of the

airframe/engine combinations met the basic criteria of range (4000

statute miles), passengers (125 to 160), or sonic boom (2.0 psf during

climb, 1.5 psf during cruise). The principal problem areas appeared to

be cruise aerodynamic performance and sonic boom.

From this first evaluation, Boeing, Lockheed, General Electric, and

Pratt and Whitney proposals were judged to have the most potential,

and they were continued in a competition that was to last nearly 3

years. In none of the subsequent FAA evaluations, including the final

47
SUPERSONIC CRUISE TECHNOLOGY

one in late 1966, did any of the airframe/engine combinations

simultaneously meet all of the evaluation criteria. Throughout the

selection process, Boeing steadfastly stuck to the variable-sweep concept with its uncertain weight penalty and promised advantages in mission versatility and cruise performance. Lockheed just as firmly stayed

with their relatively uncomplicated fixed double-delta-wing design,

which offered simplicity at the expense of possible growth potential.

Because each concept had possible advantages and potential disadvantages, the selection of the Boeing/General Electric (B-2707-200/GE-4)

combination on December 31, 1966, was less than a clear-cut decision.

The difficulty of this decision was borne out in April 1968 when Boeing dropped the variable-sweep B-2707-200 and changed to the

B-2707-300, a fixed double-delta-wing design not unlike the Lockheed

configuration. After Boeing had worked the Dash-300 for most of 1968,

the FAA called for a validation team to review the design. The United

States Supersonic Transport Integrated Configuration Validation

Group met on-site at Boeing in December 1968 and January 1969 to

review the Dash-300 design. This validation, unlike the previous

rigorous FAA evaluations, represented little more than an audit of

Boeing substantiating information.

This "validation" exercise was the last formal contact between the

NASA evaluators and the FAA SST program before the cancellation of

the program in May 1971. Individual contacts of NASA engineers with

the Boeing SST team continued until the program was terminated.

The cancellation of the U.S. SST program was a severe blow to

those who had devoted a large part of their careers to research on

supersonic cruise flight. The aura of negativism and controversy that

surrounded the program in its last phases tended to depreciate the real

accomplishments that had been made by both NASA and the SST contractors. Some of these accomplishments are summarized herein.

IMPROVEMENTS IN SUPERSONIC DESIGN AND ANALYSIS METHODS

At the beginning of U.S. interest in supersonic cruise flight, the

aeronautical literature contained theories for optimum supersonic area

distributions, optimum supersonic wings, and optimum supersonic lift

48
NACA/NASA SUPPORTIVE TECHNOLOGY

Boeing B2707-300 with four GE-4 engines- theproposed U.S. SST at the time program was canceled.

distributions. 67,_ The problem was that no means were available for

designing these optimum aerodynamic features into a complicated

supersonic aircraft. There were also no "real flow" constraints on the

first-order theories and no means for handling the design effects of

"favorable lift" interference.

Immediately preceding and during the course of the U.S. SST program, NASA and industry engineers adapted the principal elements of

these basic theories into high-speed digital computer programs. "Real

flow" constraints and "favorable lift" interference were incorporated,

and each element of the theory was validated with carefully controlled

wind tunnel tests. These programs can be used to design, analyze, and

optimize the aerodynamic characteristics of complex, arbitrary supersonic configurations with a high degree of accuracy.

The design and analysis methods developed during this program

were the standards for supersonic evaluation of the proposal SST configurations, and they are widely used today in the design of supersonic

military airplanes.

49
SUPERSONIC CRUISE TECHNOLOGY

IMPROVEMENTS IN SONIC BOOM TECHNOLOGY

Prior to NASA's emphasis on supersonic cruise technology, little was

known about sonic booms except that they were generated by airplanes

flying at supersonic speeds. The principal airplane factors that caused

them and the manner in which they were propagated were still

mysteries.

Using the asymptotic pressure-field theory developed for supersonic

projectiles 69 and the lift-area equivalency principles of the supersonic

area rule, TM NASA Langley developed and validated a "far field" sonic

boom estimation procedure for use in the FAA SST evaluations. It was

later discovered at Langley that the SST, because of its relatively large

size, would generate "near field" sonic booms with somewhat lower

levels than those predicted by the "far field" method. The discovery of

this "near field" application to the SST opened up a new field of

research in sonic boom minimization. This application was immediately incorporated into the methodology for sonic boom prediction and

has been the subject of many research papers.

Until this point, the sonic boom disturbance was assumed to be

propagated through a mean uniform atmosphere that accounted for

differences between the atmospheric pressures between the airplane

and the ground. In 1969, this approximation was greatly ir'nproved

with the development of a method for propagating the sonic boom

through a stratified atmosphere. 71

In addition to these developments in sonic boom methodology,

NASA engineers participated in the measurement of sonic booms from

essentially every supersonic airplane, participated in all of the FAA

sonic boom acceptability programs, gathered a bulk of data on the effect of atmospheric disturbances, and conducted studies on the possible

damages that might be caused by sonic booms Thus, in the period

1959-1969, NASA brought the status of knowledge on sonic booms to a

very high level.

IMPROVEMENTS IN SUPERSONIC CRUISE AERODYNAMIC EFFICIENCY

The lift/drag ratio is used by aerodynamicists as a measure of the

aerodynamic efficiency of a given configuration. At the beginning of

5O
NACA/NASA SUPPORTIVE TECHNOLOGY

the U.S. SST program, lift/drag ratios of 7.0 to 7.5 were typical of aircraft designed for supersonic cruise flight in the range from Mach 2 to

Mach 3.

As one means of validating the supersonic design methodology that

had recently been developed, in 1964 Langley engineers designed an

SST configuration that demonstrated a lift/drag ratio of 9.3 at Mach

2.6. This level was 25 to 30 percent above the previous state of the art.

The design, called the SCAT-15F, was a fixed-wing version of the

variable-sweep SCAT-15 that was considered in the earlier SCAT

Feasibility Studies. The SCAT-15F incorporated the principles of

wing design, wing/fuselage integration, engine placement, and

favorable lift interference that were validated in the process of developing the supersonic design methods.

The SCAT-15F was considered by both Lockheed and Boeing during 1965 and was studied again by Boeing in 1968 as a backup to the

Dash-300. The concept was also the subject of a 1966 NASA study on

the feasibility of a low sonic boom domestic transport requested by the

FAA.

Although neither contractor adopted the SCAT-15F as a primary

SST concept in spite of its superior supersonic cruise efficiency, many

of the design features of the aircraft were incorporated in the contractor

designs.

IMPROVEMENTS IN PROPULSION TECHNOLOGY

By the end of the U.S. SST program, turbojet and turbofan engines

producing 50 000 to 60 000 pounds of thrust appeared feasible compared to about 30 000 pounds at the start of the program. On October

28, 1966, the GE-4 engine produced 52 600 pounds of thrust on the

test stand, and on December 11, 1966, the other SST engine, the Pratt

and Whitney JTF 17, produced 57 000 pounds of thrust--a Free World

record at that time. 72

Much of the improvement in supersonic engine capability was attributable to the high-temperature turbine and advanced materials

51
SUPERSONIC CRUISE TECHNOLOGY

NASA SCA T-15F fixed-wing conceptthat advanced state-ojf-the-artlevelsof supersonic

cruiseaerodynamics.

programs of the NASA Lewis Research Center. This same technology

has also brought improvements in present-day subsonic turbojet and

turbofan engines.

Kelly Johnson, the noted Lockheed designer of the U-2, SR-71, and

other advanced airplanes, once said, "At supersonic flight speeds

around Mach 3, our current and proposed jet engines produce only

about 25 percent of the thrust propelling the aircraft. The inlet duct

pressure distribution provides about 50 to 60 percent of the thrust and

the exhaust ejector the rest." 73

The importance of the propulsion system inlet was not overlooked in

NASA's effort in support of the SST program. The NASA Ames

Research Center became the hub of the SST inlet program and provided much of the technology that would go into the Boeing transport.

Engineers at Ames conducted detailed large-scale tests of axisymmetric

52
NACNNASA SUPPORTIVE TECHNOLOGY

and two-dimensional inlets in the Ames facilities and developed a

number of innovations to improve inlet performance.

IMPROVEMENTS IN STRUCTURES AND MATERIALS TECHNOLOGY

The U.S. decision to develop a Mach 2.7 transport led to the requirement for a new structural material. Aluminum, the material most

generally used in airplane construction, would not survive in the 500°F

temperature environment experienced at that speed. Although

stainless steel had been used in the construction of the B-70 supersonic

bomber, the scant design information available indicated that titanium

would be a better high-temperature material. A large part of NASA's

effort in support of the SST was devoted to expanding the status of

knowledge on titanium. At both the Langley and Lewis Research

Centers, exhaustive research programs were conducted to determine

the design variables, material properties, and fabrication problems of

titanium. Now, because of these technology efforts and other studies

carried out by the aerospace industry, titanium has replaced aluminum

in some areas of current subsonic airplan&, even where temperature is

not a problem.

As in the aerodynamics area, the design methodology in structures

was vastly improved because of the SST program. The more complex

structural design problems associated with the SST -- compared to subsonic aircraft-led to the requirement for advanced methods for design

and analysis. As a result of efforts by both NASA and industry,

sophisticated and accurate computerized structural design and analysis

methods were developed. Adaptations of these SST methods are currently used in the design of advanced subsonic aircraft and are being

applied to automotive and other vehicle designs. TM

OTHER TECHNOLOGY ADVANCES DERIVED FROM THE

U.S. SST PROGRAM

The concepts of relaxed static stability and variable camber flaps on

the wing leading edge were developed and evaluated in the U.S. SST

program and have since been applied to the F-16 fighter. Various

53
SUPERSONIC CRUISE TECHNOLOGY

elements of the Boeing 747 jumbojet are direct descendants of development work on the SST. Digital displays and advanced navigation

systems developed for the SST are now being used in the advanced

subsonic jet transport--the Boeing 767. 75

Stratospheric emission impact is another important technology area

that was spurred by the SST program. Although particulate emission is

not a problem unique to the SST, unknowns about the problem contributed to program cancellation. The SST program, in turn, perhaps

led to the U.S. Congressional mandate to sort out the unknowns about

atmospheric pollution. From this mandate grew the Department of

Transportation's Climatic Impact Assessment Program (CIAP) and

the High Altitude Pollution Program (HAPP). In addition to the contributions of its own atmospheric analysis and monitoring efforts,

NASA was a prominent participant in the interagency activities arising

from CIAP and HAPP. As indicated later, these programs led to a

much better understanding of atmospheric pollution phenomena.

The cancellation of the U.S. SST program perhaps kept these important technology advances from being a complete victory for those

who had worked on them. Would the same "hollow" victory be the fate

of participants in the foreign SST programs?

54
CHAPTER 5

Foreign Supersonic Transport

Programs

Supersonic transport programs by the Soviet Union and a consortium of the British and French governments perhaps precipitated

America's entry into the SST race. Problems experienced in these

foreign programs might also have influenced America's decision to step

out of the race, at least for the present. Whateverthe case, the cancellation of the U.S. effort in 1971 left the supersonic market to the Soviet

TU-144 and the British/French Concorde. Since these foreign programs have probably directly or indirectly influenced the NASA supersonic technology effort, it might be well to take a brief look at them

before proceeding.

THE SOVIET TU-144

The first flight of a prospective commercial SST was made by the

Soviet Union's TU-144 on December 31, 1968. Design development of"

this airplane was initiated in 1962, and the formal development project

was started in 1964. The airplane was designed to cruise at Mach 2.2

(approximately 1350 miles per hour) and to carry 140 passengers a

distance of 4000 statute miles. The TU-144 employs a highly swept

ogee-deita wing, and the production version of the airplane makes use

of small retractable canard surfaces near the nose to control approach

speed. In the original version, four Kuznetsov NK-144 turbofan

engines in the 38 000-pound thrust class were clustered close together

along the wing centerline in twin-ducted nacelles that stretched over

the full length of the wing. 76 Andrei Tupolev, the well-known Soviet

55
SUPERSONIC CRUISE TECHNOLOGY

Soviet TU-144 supersonic transport airplane.

Soviet TU-144 (courtesyof Aviation Week and Space Technology, McGraw-Hill, Inc.).

designer responsible for the TU-144, revealed in June 1966 that he had

borrowed the B-70's " 'compression lift' design to let the wing ride on

top of the shock wave induced by the engine intake splitter .... ,, 77

This technological advancement (discussed in Chapter 3) had been

discovered by NACA's Eggers and Syvertson.

Although most elements in the development of the TU-144 have

been clothed in secrecy, many problems were obvious in the early

prototypes. Cruise-drag was a problem because of the poorly

sculptured wing design and engine placement. The four engines were

56
FOREIGN PROGRAMS

clustered in a split nacelle directly under the fuselage. This arrangement necessitated that the landing gear and carriage be placed in the

outer wing. Consequently, a large proportion of the outer wing was

unavailable for fuel. 78

Based on engine technology available at the time, the turbofan appeared to be a poor choice of power plant for the TU-144. The average

jet velocity of a turbofan engine is less than that of a turbojet of comparable technology. Consequently, to provide thrust equal to a turbojet, the comparable turbofan must be larger in diameter, or additional

fuel must be burned in the fan duct. Eastern European sources indicated that the TU-144 used "30-40 percent of available reheat" at

Mach 1.9, a situation that could cause severe fuel consumption rates

and drastically reduce range. 79

Because of the rather crude status of the first TU-144 prototype, it

can be conjectured that this airplane was constructed to "scoop" the

Concorde, which it did, and to provide data for incorporation into later

prototypes. There were three such prototypes in the program leading

up to the production aircraft. 8°

The "production" version of the TU-144 showed many refinements

over the earlier prototypes. The wing was more elegantly tailored, and

the engines were moved from the clustered arrangement under the

fuselage to two twin nacelles outboard on the wing. The landing gear

was stowed in more favorable locations within the engine nacelles, permitting a 40 000-pound increase in fuel capacity. The basic engines

were not uprated, but larger burners were incorporated to increase

thrust. The production version of the TU-144 first flew in mid-1972. 8_

The TU-144 was involved in a tragic accident at the Paris Air Show

in 1973. While making low-speed runs, the aircraft went out of control

and crashed, killing the crew and a number of spectators. Although no

official report as to the cause of the crash has been given, it is believed

that the breakup in flight was due to structural overload, s2

The current status of the TU-144 program is difficult to ascertain.

Rumors are that the aircraft was used in passenger service for a short

57
SUPERSONIC CRUISE TECHNOLOGY

time and in freight service for a while and is now grounded. Other

rumors say that an advanced version of the TU-144 is under development. Aleksei I. Smenkov, Soviet first deputy minister of civil aviation,

said after the tragic 1973 Paris accident, "We know there are plans for a

larger airplane. Of course, our industry will not stop with this model.

But so far, we have been talking about real airplanes, airplanes we

know." 83 A lot has happened since Smenkov made this statement, but

none of it has been particularly good for the concept of supersonic

cruise flight. About the only thing that can be said with certainty is

that, in building and flying three prototype and five or so production

SSTs, the Soviet Union has amassed a great deal of experience in commercial supersonic cruise flight.

THE BRITISH/FRENCH CONCORDE

In spite of being cast as a transportation "heavy" by critics around the

world, the British/French Concorde ranks as one of the foremost

technical achievements that -has ever been made. The two nations that

developed this aircraft not only spoke different languages, but also used

different measurement systems. Yet, out of this unusual alliance came

the first and, so far, only commercial supersonic transport in regular

passenger service. Like it or not, the Concorde is a remarkable

airplane. It reduced the trip times between continents to one-half of

those of the best of the subsonic jet transports, an accomplishment that

would have been cheered in bygone years. The Concorde is perhaps

the world's most tested transport airplane and, in its operations to date,

has experienced no major accidents and has had no passenger fatalities.

The Concorde was probably born out of the desire of the British and

French aircraft industries to break the virtual monopoly that the

American airplane industry was building in the commercial subsonic

jet transport market. The British had missed the chance to corner this

market when early problems beset the De Havilland Comet, the first

commercial jet transport. The British Overseas Airways Corporation

(BOAC) had introduced the DH Comet I turbojet transport into

58
FOREIGN PROGRAMS

passenger service on May 5, 1952, some 6 years before America's first

turbojet transport, the Boeing 707. In its second year of operation,

however, two Comets mysteriously exploded in flight, killing 55 people, and the Comets were withdrawn from service in April 1954.

"The British Concorde SST at Dulles Airport in Washington, D. C. (courtesy of BOAC).

British Concorde (courtesy of BOA C).

59
SUPERSONIC CRUISE TECHNOLOGY

French Concorde(courtesy of BOA C).

Subsequently, exhaustive tests indicated that metal fatigue had caused

the Comet disasters. By the time the problem was fixed and the Comet

returned to service on October 4, 1958, however, the American turbojet aircraft had just about cornered the market. 8_

Th_ problems with the Comet prompted the British Ministry of

Aviation to set up the Supersonic Transport Aircraft Committee

(STAC) to consider the pros and cons of a British supersonic transport

program. The first meeting of STAC on November 5, 1956, was really

the beginning of the British SST effort. At this meeting, interest

centered on a slender delta wing configuration for long-range Mach 2

flight and an M-wing concept with waisted fuselage for short-range

operation at Mach 1.2. B5

The STAC considered all the problems associated with supersonic

flight from the sonic boom to ozone, radiation, and airport noise.

When Sir Morien Morgan submitted his STAC report to the controller

of aircraft at the Ministry of Supply on March 9, 1959, no less than 500

separate studies were attached. The principal recommendations of the

report were that the British government should embark as soon as

possible on a program for two airliners -- a 3450-mile, 150-passenger

airplane with a cruise speed of not less than 1200 mph (Mach 1.8) and

a second airplane capable of carrying 100 passengers over a stage

6O
FOREIGN PROGRAMS

length of 1500 miles with a cruise speed of about 800 mph (Mach

1.2). 86 The report went on to say:

Since this country's future will depend on the quality of itstechnological products and since its scientific manpower and resources are less than those of the

U.S.A. and U.S.S.R., it is important that a reasonable proportion of such

resources are deployed on products which maintain our technical reputation

at a high level. A successful supersonic aircraft would not only be a commercial venture of high promise but would also be of immense value to this country as an indication of our technical skillY

Duncan Sandys, the British minister of aviation, strongly backed the

STAC report with the statement, "If we are not in the supersonic aircraft business, then it's really only a matter of time before the whole

British aircraft industry packs it in. It's obviously the thing of the

future. It may pay. It may not pay, but we cannot afford to stay out. If

we miss this generation of aircraft we shall never catch up. We will end

up building executive aircraft." s8

Sandys' recommendation that the British government proceed with.

the supersonic transport effort was taken, and preliminary design

studies were begun. The long-range Mach 1.8 contract was given to

the Bristol Aircraft Company and the medium-range Mach 1.2 study

to Hawker Siddeley Canada, Incorporated.

In the meantime, the Sud Aviation Company in France had independently decided on a slender delta-wing approach to their new

Super-Caravelle, the same general approach favored in the British

long-range Mach 1.8 study. Sud Aviation and Bristol designers were

on common ground.

After about 2 years of discussions and exchanges of information, the

British and French designers came into general agreement on the

characteristics an SST should have and on how they would proceed on

a joint program. The Supersonic Aircraft Agreement, signed on

November 29, 1962, committed both nations to the development of an

SST. The agreement contained no break clause--neither country.

could withdraw from the program without the approval of the other.

61
SUPERSONIC CRUISE TECHNOLOGY

The absence of this escape clause probably ensured the survival of the

Concorde. 89

The aircraft that evolved from discussions between the British and

French designers was essentially an all-aluminum design with a thin

ogee-delta wing. It was to be powered by four Bristol/Siddeley

(BS-593) Olympus engines in the 35 000-pound thrust category. These

straight turbojets were equipped with afterburners for use in takeoff

and acceleration to cruise flight conditions. Originally, the aircraft was

to carry 128 passengers a distance of 4000 statute miles at a cruise

speed of 1450 mph (Mach 2.2). During the course of development,

however, the cruise speed was reduced to 1350 mph (Mach 2.05), and

the passenger load was reduced to the order of 90 to 100 on transatlantic missions.

Although a number of technical problems were encountered during

the development of the Concorde, perhaps the most critical problems

were in the political arena. Less than 2 years after the project was

launched, the United States announced their program for building a

larger, faster SST. BOAC, apparently doubtful that the smaller, more

conservative Concorde would have adequate range for the transatlantic

operation, placed an order for six U.S. SSTs. 9° Caught by this announcement and the escalating cost of the Concorde -- the projected

cost had risen to twice the original estimate--the British government

opted to get out of the program in late 1964.

The British appeal to France to break the SST agreement was refused, and the French let it be known that there was a binding agreement between the two countries "to develop and produce jointly a civil

supersonic transport aircraft." It was clear that the French could well

take their grievance to the International Court of Justice at The Hague

and could probably win. 91

The British government did not want to face the embarassment of an

international lawsuit while they were trying to get into the European

Common Market. Consequently, they assured the French that they

would honor the treaty. In reflecting on the decision later, Prime

Minister Harold Wilson wrote:

62
FOREIGN PROGRAMS

Had we unilaterally denounced the treaty, we were told, we could have been

taken to the International Court, where there would have been little doubt

that it would have found against us. This would have meant that the French

could then have gone ahead with the project no matter what the cost, giving

us no benefit from the research or the ultimate product. But the court would

almost certainly have ruled that we should be responsible for half the cost. At

that time, half the cost was estimated--greatly underestimated as it turns

out--at 190 million pounds. This we should have had to pay with nothing to

show for it .... 92

The Concorde project survived through several changes in government; it survived the removal of Charles DeGaulle as French president; it survived several strikes in both countries; it survived technical

difficulties that required a redesign of the wing and engine exhaust

system; and it survived the escalating costs that were to rise from a

1965 estimate of $400 million to a 1977 total cost of about $4 billion, 93

ten times the original estimate.

The first flight of the Concorde was originally scheduled for 1967,

and it was to enter passenger service in the middle of 1971. As it turned

out, the first test flight did not occur until March 1969, and passenger

service did not begin until 1976, with flights from Paris to Rio de

Janeiro (via Dakar) by Air France and from London to Bahrain by

British Airways. Service from Paris and London to Washington, D.C.,

began on May 24, 1977. The combined level of service for the two

airlines was about 110 flights per month for the first year of operation

and rose to about 140 flights per month after the inauguration of flights

to New York in December of 1977. 94 In 1982, the level of service was

reduced because of a worldwide recession and the escalating price of jet

fuel.

The Concorde has been described as a "supersonic bust" 95 and as an

aircraft with "disastrous economics." 96 In some respects, these descriptions are accurate. The shortcomings of the Concorde are attributable,

in part, to the limited passenger load and to the conservative approach

followed in the design. For the first really operable supersonic

transport, this design approach was probably in order. The balance of'

the shortcomings are in the minds of those who are not ready for the

63
SUPERSONIC CRUISE TECHNOLOGY

supersonic transport. An airplane can hardly be a success if its

operators have to fight endless legal and political battles to secure landing rights in American airports that have previously been open or if

they must fight a mob that is resisting the plane's approach by lying

down on the runway.

The fact remains that, in its first 3 years of operation, the Concorde

carried 400 000 passengers over 25 million miles and accumulated

nearly 30 000 flying hours. 97 In the next 3 years, these numbers trebled

as the Concordes accumulated nearly 100 000 hours of passenger service. This record was achieved without a serious accident and with very

low utilization because of limited landing rights.

Although many feel that the Concorde program proved to be

economically disastrous, 9s the technical achievement of the Concorde

is best summarized by the words of Goeffrey Knight:

Technically, Concorde's is a triumphant story. Apart from the American

space programme, I can think of no other aircraft project involving high

technology that has come through with such success. We are probing the frontiers of knowledge all the time, and advanced the state of our art at every

stage. 99

The American SST program was canceled after 8 years without the

construction or flight of a prototype. The Soviet Union's SST program

is essentially at "parade rest" after the construction and flight of eight to

ten aircraft. Sixteen Concordes were built by the British and French

before the assembly lines were closed. Only the state-owned airlines of

the participating countries purchased the Concorde, and it is the only

SST currently in regular passenger service. How long it can maintain

this service is yet to be determined.

Why have these three advanced aircraft programs, launched with

such high expectations and with the support of their respective governments, failed to really open up the era of supersonic cruise flight? Are

there some lessons to be learned from the essential failure of these programs?

64
CHAPTER 6

Lessons Learned in Pre-1972

Supersonic Cruise Experience

Over the past 35 years, four of the world's most advanced

technological nations-Great Britain, France, the Soviet Union, and

the United States--have mounted concerted efforts to develop longrange supersonic airplanes. It was once anticipated that these efforts

would lead to the wide use of supersonic transport airplanes by the

early 1970s. In reality, only the British/French Concorde has achieved

a modicum of success, and this success has been tempered by the fact

that only a few of these airplanes were built and that no replacement

aircraft or advanced supersonic transport is under serious consideration. Although the Concorde is an outstanding technical achievement,

its current limited-passenger service certainly does not represent the

anticipated coming of the era of supersonic commercial air transportation.

In spite of large expenditures of time and money, the efforts to

develop an environmentally acceptable, economically competitive

supersonic transport have not been successful. Even with this lack of

success, however, perhaps some important lessons can be learned from

the efforts. Some of these "lessons learned" are now discussed, not

necessarily in order of importance.

THE MILITARY/COMMERCIAL DIFFERENCE

Each of the efforts to develop a successful SST took considerably

longer than expected--even the American effort that did not result in a

65
SUPERSONIC CRUISE TECHNOLOGY

flight vehicle. Also, each of the programs led to substantially higher expenditures than were estimated at the outset. A contributing factor in

the underestimation of the time and costs of commercial SST development was the overly optimistic projection of the value of supersonic

military flight experience. All of the nations involved in attempts to

develop a commercial SST had constructed and flown experimental

and military supersonic airplanes. This flight experience had, in fact,

provided the data that suggested the feasibility of supersonic commercial flight. And, of course, the engineers involved in the development of

SSTs were aware of differences between military and commercial

supersonic flight. It is doubtful, however, that the magnitude of these

differences was fully understood at the beginning of the SST development.

Clarence L. (Kelly) Johnson, leader of Lockheed's well known

"Skunk Works" airplane design team was said to have made the following remark, "Give me a big enough engine and rll design you an ironing board that'll fly." 100 This statement, whether actually made or not,

leans toward a representation of the design philosophy followed in

many of the early military supersonic airplanes. Most of these

airplanes were designed for maneuverability, high rates of climb, and

short-range flight at supersonic speeds. The engines were sized to provide performance rather than efficiency, and little attention was given

to noise or other environmental factors. Extended ranges were made

possible by aerial refueling or flight at subsonic speeds, recourses that

would not be desirable in a commercial SST from safety and economic

considerations.

The nearest military prototype for a commercial SST was the

American B-70 bomber. In the design of this airplane, efforts were

made to achieve the high levels of supersonic cruise efficiency demanded of a commercial SST. However, no attempt was made to meet environmental constraints or economic requirements. The B-70 did not

have to operate in the strict environment of a commercial airport, did

not have to meet the reserve fuel requirements of an SST, and was not

designed for the 50 000 hours of life expected of a commercial

transport. In addition, the B-70 operation was not threatened by sonic

66
LESSONS LEARNED IN PRE-1972 EXPERIENCE

boom restrictions. Thus, the critical elements in SST design--

economics, airport performance, reserve fuel requirements, airplane

life, and sonic boom--were not controlling elements in the design of

the B-70, nor have they been in any other military design.

With the cancellation of the B-70 program, there was no longer any

supersonic military airplane that even remotely resembled the design

and operating requirements of an SST. The bulk of the supersonic

military, airplanes spend only a few minutes of each mission at the searing temperatures experienced at high-speed flight conditions. On the

other hand, the SST would be bathed in temperatures of one to two

times the boiling point of water for nearly 3 hours on an intercontinental flight. At Mach 2.7 cruise conditions, for example, the nose of the

proposed Boeing SST would have been 6 inches longer than when it

was sitting on the ground. This heat-expansion problem, not present in

most military airplanes, forced Boeing to consider abandoning the

traditional primary cable control system in favor of a triply redundant

electrical command or fly-by-wire system with cable backup. L°_

The pilot and crew of supersonic military airplanes are provided

with pressure suits for protection against sudden decompression at high

altitudes. Such protection would not be practical nor acceptable for 200

to 300 passengers on an SST flight. Accordingly, the SST structure has

to provide a fail-safe protection against rapid decompression, an event

that would bring quick death to the passengers from ebullism--boiled

blood-at an altitude of 60 000 feet. At this altitude, there would not

be time to reach for the oxygen mask._°2

In the development of commercial subsonic transports, the step from

military to commercial application was small. In some cases, particularly in the era of propeller-driven airplanes, the transition was

essentially direct. Approximately 25 000 hours of subsonic jet bomber

cruise experience preceded the first American commercial subsonic jet

transport design--the Boeing 707. _03 This has not been the case in the

supersonic speed regime. The military design criteria for aerodynamic

performance, structures, and operations have been so different from

the criteria required for an acceptable SST that little technology

transfer has been possible, except in the propulsion area.

67
SUPERSONIC CRUISE TECHNOLOGY

A SUCCESSFUL SST WILL PERMIT LITTLE ROOM

FOR DESIGN COMPROMISE

Past experience indicates that there will be little room for design

compromises in the development of a successful SST. To meet the

stringent environmental constraints of noise, sonic boom, and pollution in a safe, economically competitive SST will require the best possible combination of aerodynamic, structural, and propulsion

technologies. Isolated advances in the disciplinary technologies are

meaningless unless they can be integrated into a congruent airplane

that meets all mission requirements.

Technology integration is important in the development of aircraft

for any flight speed. Disciplinary technology advances are not

automatically applicable to any airplane until a careful integration

study is made, particularly in the case of supersonic airplane design.

The performance of all elements of the design are interrelated, and

these interrelationships are as important in the overall design as the

basic elements. For example, the placement of engines on a supersonic

airplane not only affects the performance of the engines, but also affects

the aerodynamic and structural design and performance of the

airplane. Similarly, the structural design influences aerodynamic performance, and aerodynamic characteristics and flight speed are critical

in the structural design and material selection. The miscalculation or

simplification of any of these mutual interactions can lead to a failure to

meet the overall airplane requirements.

Commenting about the British/French and American SST design

approaches, Dr. A. E. Russell of the Bristol Aircraft Company remarked, "The Mach 2 solution offers close competition on similar

financial arrangements [to the subsonics] while the Mach 3 hotrod

needs a very indulgent backer and an uninhibited operator .... ,, 10_ In

their decision to develop an aluminum Mach 2 SST with a simplified

ogee-delta wing, the British and French perhaps knowingly compromised aerodynamic potential in return for a measure of confidence

in structural design and projected costs. In spite of this conservative approach, however, the Concorde development did not go as planned.

68
LESSONS LEARNED IN PRE-!972 EXPERIENCE

Entry into flight service took 50 percent longer than anticipated, and

the project ran up costs 10 times the original estimate. Without

depreciating the technical achievement embodied in the Concorde, the

limited range/payload capability and marginal aerodynamic potential

were factors that led to the lukewarm acceptance of the airplane by the

world's airline operators.

In further commenting about the American effort to develop an SST

somewhat faster than the Concorde, Dr. Russell said, "The advocates

of Mach 3 airliners seem to be confronted by a formidable array of selfinflicted difficulty!" 105 Although the final choice of cruise speed for the

proposed American SST was only Mach 2.7, the U.S. design was at

the opposite extreme from the Concorde in that no element of the

design could be considered conservative. The higher temperatures at

Mach 2.7 made it necessary to switch from aluminum--a material that

had been used on nearly all the previous transport airplanes. The complicated variable-sweep feature of the proposed American SST was

chosen in a conscious effort to achieve flexibility of operation and optimum aerodynamic performance, but this feature also posed structural

design and weight problems of uncertain magnitude. The Boeing

Airplane Company made a concentrated effort over 2 years to reap the

potential aerodynamic advantages of variable sweep. As Fortune

magazine reported:

Boeing Co.'s attempt to build a supersonic airliner has turned out to be the

most bafflingly complicated job of research and development in the histo_ of

American industry--and it may end up the costliest. The undertaking has

come to demand engineering resources, human and inanimate, second only

to those going into the national effbrt to put a man on the moon. During the

five years that Boeing has been engaged in this task on a significant scale - the

last two at maximum effort--the company has run up 30,000 hours of

research on eight different wind tunnels scattered across the nation, 80,000

hours of analysis on computers that include the largest in existence and a total

of 8 1⁄2 million engineering man-hours altogether--all this to the end of reducing the Boeing vision of the SST engineering drawings from which the shop

can begin to fabricate a prototype._°6

In spite of this effort, the potential aerodynamic advantages of variable

sweep could not be reconciled with the structural and weight uncertainties, and the concept was dropped from SST consideration.

69
SUPERSONIC CRUISE TECHNOLOGY

It should be pointed out that there is nothing wrong with the ogeedelta-wing concept of the Concorde or the variable-sweep feature proposed on the Boeing B-2707 SST. The delta wing has been successfully

used on supersonic military airplaines such as the F-102, F-15, and

B-58 and on several foreign military aircraft. Similarly, the variablesweep wing idea is used in the United States on the F-111, F-14, and

B-1 airplanes and in the Soviet Union on several military airplanes.

However, none of these aircraft are required to meet the operating and

economic requirements of the SST. Successful application of a disciplinary concept to one mission did not guarantee its useful application to an SST mission.

The lesson--the importance of technology integration--learned in

past SST experience was a principal element in the NASA SCR program that will be discussed later.

U.S. Air Force B-I variable-sweep bomber made by Rockwell International.

THE VALUE OF FOCUSED TECHNOLOGY EFFORTS

We sometimes like to believe that most of America's advances in the

science of high-speed flight have resulted from "basic disciplinary research" conducted in a laboratory atmosphere by dedicated scientists

working at the outer fringes of the state of the art. As a matter of fact,

this is not the case. American "advanced fundamental basic aeronautical research" provided a totally inadequate foundation for the era of

7O
LESSONS LEARNED IN PRE-1972 EXPERIENCE

transonic and supersonic flight that exploded upon us in the 1940s.

Aeronautical testing methods in the transonic and supersonic speed

regimes were crude and inadequate; there were no reliable methods for

transonic and supersonic design and analysis; and U.S. technology of

turbojet engines was essentially a "buy in" from our British allies. In

March 1941, because of reports of German research into reaction

powerplants, the Army requested that NACA study jet propulsion.

The Army Air Corps chief, General Henry H. "Hap" Arnold,

journeyed to Great Britain, where he was surprised to learn that the

British were preparing to flight-test a turbojet engine, the Whittle

W-1. He subsequently arranged for the development of the Whittle

engine in this country by the General Electric Company. 107

While moving rather slowly in the basic research mode, U.S.

technology of high-speed flight made rapid advances under the focus

and urgency of America's efforts to "break the sound barrier" and later

under the focus of efforts to develop a commercial SST. Within a

relatively short time, U.S. engineers and scientists had solved testing

problems at transonic speeds, developed methods for use in the design

and analysis of high-speed airplanes, improved the facilities for testing

at supersonic speeds, developed a fairly complete understanding of

sonic boom, and launched a comprehensive technology program for

improving the performance of jet engines.

Note also that America's basic space technology was unsuccessful in

developing and launching a Vanguard satellite in 1957 during the International Geophysical Year program. Under the leadership of a

former German scientist, Dr. Wernher yon Braun, and using German

technology (Jupiter C modified intermediate range ballistic missile),

America's first space satellite, the Explorer, was successfully launched

in 1958. After that, with the focus of a national space program, U.S.

engineers made rapid and remarkable strides in space technology.

As a result of recognition of the importance and value of focused

technology efforts, this approach was followed in the NASA Supersonic

Cruise Research (SCR) and Variable Cycle Engine (VCE) programs

to be discussed later.

71
SUPERSONIC CRUISE TECHNOLOGY

U.S. TECHNOLOGY SUBSIDIZATION

A recent report by the Office of Technology Assessment of the U.S.

Congress indicated that "One of the most important lessons learned

[from the U.S. SST program] is that a genuine and important national

interest will have to be clearly identified before any future hightechnology large-scale commercial undertaking can expect to receive

significant Government support in the future." ,08 Although this statement is probably true, it serves to point up anomalies in the subsidization policies of the U.S. government.

One of the fastest growing commercial enterprises in America is the

satellite communications industry. This industry has directly benefited

from the NASA satellite program and the millions of dollars expended

on it. The electric power companies have directly benefited from the

billions of dollars that the U.S. government has spent in developing

nuclear energy. The U.S. railroads, unable to make it on their own, as

well as the mass transit systems and the interstate highway network,

have received billions of dollars in government subsidies over the past

few years. For years, the U.S. government has provided millions of

dollars in subsidies to the maritime interests in this country, with the

stipulation that the ships built can be used by the U.S. military in the

event of war. Billions of dollars are also spent by the U.S. government

each year to purchase surplus commodities from the agricultural community, and additional millions are spent in storage costs for these

farm products. In addition, the NASA space shuttle, which is under

development by the government at a projected cost approaching $10

billion, is expected to have many commercial uses.

In spite of these obvious subsidies of" many commercial ventures, the

U.S. government has been reluctant to directly participate in the

development of high-technology commercial airplanes. In fact, in the

1940s, the U.S. Congress refused to approve funds for constructing a

subsonic jet transport to meet the challenge of the British Comet. 109 If

the Comet had not developed problems, this decision could have cost

the U.S. aircraft industry the tremendous business it now has in subsonic jet transports. The airplane industry is currently one of the

72
LESSONS LEARNED IN PRE-1972 EXPERIENCE

largest employers in the nation and has had a long-term positive effect

on America's balance of trade. The air transportation industry, user of

airplane industry products, has been a powerful factor in America's rise

to economic and technological preeminence. It is difficult to understand the political aversion to direct support of these industries.

Although this aversion was temporarily put aside by President Kennedy and the Congress in 1963 in their support of the U.S. SST program, the uncertainty of government support was one of the factors

that was to plague the effort from start to finish.

Government funding was only one of the uncertainties that led to the

cancellation of the U.S. SST program. There were worries about environmental impact and passenger safety. There were questions about

radiation and air-traffic control. The airlines did not know if the SST

would be economically viable or if they could afford such airplanes.

The airplane manufacturers had committed heavily to the development

of "wide-body" subsonic jet transports and were concerned that the

SST would reduce the subsonic market.

In view of these uncertainties, it was difficult to determine if the

development of a commercial SST was of genuine and vital importance

to the interests of the United States. It was purely a matter of semantics

that the subsidization of an SST was different from that of a commercial railroad, a commercial satellite communications company, or a

commercial power company. However, Congress certainly could not

be expected to continue funding the SST when the people who would

build and use it were negative or ambivalent. 110

EVOLUTION OF AN ACCEPTABLE SST WILL BE DIFFICULT

In the advancement of a technology, it is not generally anticipated

that the prototype of an innovation or improvement in the state of the

art will provide the ultimate answer in terms of performance. This

ultimate answer will come after evolutionary refinements and improvements in the finished product. However, the prototype is expected to demonstrate performance and provide a firm basis for future

73
SUPERSONIC CRUISE TECHNOLOGY

improvements in both performance and costs. This process has been

followed in the development of the air transportation industry. The

Boeing 707 and the Douglas DC-8, prototypes of the highly efficient

subsonic jet transport fleet, represented a revolutionary step in air

transportation. From these original prototypes, more efficient, more

productive, more comfortable, and safer subsonic jet transports have

evolved.

The experiences of the Concorde and the U.S. SST programs indicate that the evolution of an acceptable SST will be difficult. The

Concorde represents a technological triumph for its British and French

developers. However, in the eyes of its potential customers--the

airlines--the Concorde did not represent a suitable prototype for

development into a family of advanced SSTs. Consequently, the Concorde has not been allowed the evolutionary cycles that were so important in the development of subsonic transport technology. In the case of

the U.S. SST, enough uncertainty existed about the acceptability of

the design to preclude further funding of the project.

Almost no one will deny that "the SST presents the greatest

challenge in aviation history .... -1,, Consequently, perhaps too

much was expected of both the Concorde and the American SST program. Both programs were conducted during a period of social unrest

and upheaval, and both efforts sought to bring about a quantum jump

in the technology of air transportation. Both efforts anticipated that the

unacceptable prototypes would evolve into acceptable SSTs through

future advances in technology. Because of the nebulous nature of these

projected technology advances and the mounting costs of the projects,

however, the evolutionary phases did not come to pass.

In any future eftort to introduce the SST into the air transportation

system, it appears that the prototype SST must be acceptable in nearly

every respect. "There will be no room for unsuspected bugs in the

SST." There will also be no margin for error, and this is the greatest

challenge of all, for no commercial airliner ever built has been completely free from design bugs. _a2 The available technology must be

more than adequate to sustain the program, and answers to all the

74
LESSONS LEARNED IN PRE-1972 EXPERIENCE

uncertainties must be in hand. It is unlikely that an acceptable SST will

be permitted the luxury of evolving from an unsatisfactory prototype

base.

PERCEPTIONS OF A "RAMPANT" TECHNOLOGY

It is quite possible that the Concorde and the American SST would

be in wide use today had it not been for a rising sentiment that

technology had "gone wild." Citizens of the highly developed nations

were becoming more and more concerned about noise, pollution of

rivers and the atmosphere, and what they perceived to be a misuse of

our natural resources. Unchecked technological growth was seen to

have been responsible for slums, pollution, and even the Vietnam

War. _13 The SST became a symbol of technical arrogance and an object on which anti-technology sentiment could be focused.

Many people who had gratefully acknowledged and taken advantage

of great advances in air transportation felt that these advances had

gone far enough. The horror stories about SST noise, sonic boom, fuel

use, and atmospheric pollution were enough to convince large

segments of the population that the SST was a harbinger of

catastrophe. Anti-SST groups, which began to form in the United

States and Europe, initiated concerted efforts to stop the Concorde and

the U.S. SST programs.

The organized efforts against the SST were perhaps the first

evidence of a powerful new area of politics-- the politics of technology.

Fundamental to the new politics was the choice that industrial society

made about what priority it allocated to technical growth and what

priority it gave to the environment. At stake were such important ['actors as the public's right to question governmental decisions in areas

that might affect drastically the quality of life for everyone. _4

The politics of technology, which surfaced while the American SST

was under development and at about the time the Concorde [light tests

began, became a factor in these and other technology programs. Ettorts

to develop nuclear energy, to make use of oil shale and coal deposits, to

75
SUPERSONIC CRUISE TECHNOLOGY

construct oil and gas pipelines, and to search for new mineral deposits

came into the sphere of the new political force.

The opponents of the SST had legitimate questions and concerns

about what the operation of such a vehicle would do to the environment. They also had legitimate questions as to why the SST was being

developed and why the governments were paying for it. Untortunately,

SST proponents waited too long to face up to these questions. In the

meantime, the anti-SST forces were providing their own answers,

which in many cases are now recognized as exaggerations or half

truths. Consequently, the SST was unable to assume its legitimate role

as the next revolution in the air transportation industry. Rather, it

became billed as a development program for the benefit of "jet-set

playboys and their ladies" 115 and one of the most resented

technological programs of all time.

It cannot be stated with certainty that the "politics of technology" led

to the cancellation of the U.S. SST program or that it has been a factor

in the reluctant acceptance of the Concorde. However, it is almost

assuredly true that any future.SST effort in this country will be subject

to this new political force.

SUMMARY OF LESSONS LEARNED

In summary, some of the lessons learned from the pre-1972 supersonic cruise experience are as follows:

• Major differences exist between the technologies required for a

supersonic military aircraft and an acceptable SST. Aeronautical

technology, that is applicable to supersonic military aircrati may be

totally useless tor a commercial SST.

• A successful SST will require the best possible combination of

disciplinary technologies. An exciting technical innovation in one

discipline is unusable if it cannot be successfully integrated with

the other disciplines.

• Focused technology, efforts will bring about a more rapid improvement in the aeronautical state of the art than will basic generalized

research.

76
LESSONS LEARNED IN PRE-1972 EXPERIENCE

• U.S. subsidization policies are rife with anomalies. A stronger

case must be made for the SST or any other high-technology item

before much government support can be expected.

• A future evolution of an acceptable SST is not likely. The

technology tor a satisfactory prototype must be in hand, and

answers to the uncertainties must be available.

• The politics of technology will be a powerful factor in anv future

high-technology effort.

These "lessons learned" had an impact on the tormulation of the

NASA post-1972 program in supersonic technology. But, why was

there a post-1972 NASA supersonic technology program? What were

the problems to be worked on? After the SST program was canceled, is

there still some promise in the concept of supersonic cruise tlight?

77

CHAPTER 7

Supersonic Cruise Problems

and Potential

Senator William Proxmire, an astute politician and outspoken critic

of U.S. government funding of the SST, said in 1970 that "it seems utter folly to continue with the production of this plane (the SST) until we

have developed the technology necessary to make supersonic flight

compatible with respect for our environment." !t6 At the same time,

Representative Henry Reuss said, "Considering increased airport

noise, sonic booms, air pollution, and potentially harmful weather

changes, the SST, for which the American public is being compelled to

pay, is an environmental outrage." 117 On the other hand, Representative John McFall commented that, "It seems to me that the SST has

become a symbol of the need to improve our environment, and in a

sense it is a false symbol because the SST is really not that important to

the environment, but it has become sort of a rallying point for those

who want to improve the environment." 118

The environmental argument certainly was a factor in the cancellation of the U.S. SST program and the negative acceptance of the Concorde. The deeper underlying reason for the failure of the SST,

however, was the fact that the level of aeronautic technology available

in the 1960s was not adequate to sustain the development of an

economical SST. It was expected that, when the SST was under way,

solutions could be found to the critical technical problems. In the end,

the SST would meet everyone's concept of what it should be.

The expectations of the SST proponents and developers were neither

unreasonable nor unusual. Many high-technology programs had

79
SUPERSONIC CRUISE TECHNOLOGY

begun with less than all the technical answers to become successful additions to the state of the art. However, the lengthy, expensive, and

sometimes fitful efforts to develop supersonic technology during the

course of the Concorde and American programs provided arguments

for SST opponents and detractors. These efforts also served to alienate

the interest of SST supporters, the people, the governments, and even

the developers. What are some of these critical technical problems of

supersonic cruise airplanes?

TECHNICAL PROBLEMS

AERODYNAMIC PROBLEMS

The level of aerodynamic efficiency (lift/drag ratio) at supersonic

cruise speeds is a critical factor in the performance of a supersonic

cruise airplane. All other things being equal, the higher the supersonic

lift/drag ratio, the greater the range potential for a given fuel supply or

the lesser the fuel requirement for a given range. If no other factors

were involved, the design with the highest value of supersonic lift/drag

ratio would lead to the most efficient supersonic cruise airplane. According to all available aerodynamic theories and tests, a supersonic

design utlizing a highly swept arrow-head wing would provide the

highest attainable levels of supersonic lift/drag ratio.

As a matter of fact, the supersonic cruise lift/drag is not the only

critical aerodynamic factor in the design of a supersonic cruise

airplane, particularly a commercial SST. An SST is also expected, and

required, to operate efficiently at subsonic speeds. The reserve fuel requirements- the fuel required for flight to an alternate destination and

holding for landing clearance--are based mainly on subsonic lift/drag

ratio. The noise characteristics of the airplane are also related to lowspeed aerodynamic performance. For these low-speed flight conditions,

theory and experience suggest that a moderately swept-wing design

provides the highest levels of aerodynamic efficiency. Highly swept

wings were seen to provide relatively poor aerodynamic performance in

this low-speed regime.

8O
PROBLEMS AND POTENTIAL

As a possible means of resolving the conflicting wing-sweep requirements in the subsonic and supersonic flight modes of a supersonic

airplane, NASA proposed the use of variable sweep--a concept that involves altering wing sweep during flight to the most optimum position.

This concept has been successfully adapted in the design of military aircraft, in which range/payload performance and efficiency are not

critical design factors. However, during the SST program, it proved to

be unfeasible because of weight and integration problems. Both the

Concorde and the American SST developers finally chose a swept-delta

or deha-ogee wing design that was a compromise between subsonic and

supersonic lift/drag ratios. Although understandable, this compromise

was a limiting factor on the growth potential, range/payload characteristics, and economic feasibility of the two airplanes. Technology,

was not available to permit the achievement of the necessary, optimum

or near-optimum aerodynamic efficiency at supersonic cruise conditions while simultaneously meeting the other design and operating reAerodyna m ic

Efficiency

(lift/drag)

The SCR Aerodynamic "Problem"

High wing =weep il GOOD at supersonic speeds, BAD subsonicallyit's just the opposite for low wing sweep.

\ '

I

Subsonic <_ Supersonic

_1 1 I J J

Mach Number

Supersonic cruise aircraft aerodynamic "problem. "

81
SUPERSONIC CRUISE TECHNOLOGY

quirements. The development of this high lift/drag (arrow-wing)

technology, could dramatically improve SST performance.

PROPULSION SYSTEM PROBLEMS

In developing a propulsion system for supersonic cruise airplanes,

the engine designer runs into the same incompatible flight conditions

faced by the aerodynamicist. At supersonic speeds, engine thrust or

power is provided most efficiently by moving a relatively small volume

of air at high velocities, a characteristic of the straight turbojet engine.

At subsonic speeds, however, it is more efficient, and quieter, to move

a larger volume of air at fairly low velocities, a feature of the turbofan

engine. For application to an SST, a turbojet engine sized to give optimum performance at supersonic speeds does not provide adequate

thrust at takeoff and during climb conditions. The turbojet also requires more fuel for subsonic overland operations and for alternate

Problem 1 .: The turbojet engine is more

efficient than high-bypass turbofan at

supersonic cruise conditions, but highbypass turbofan is more efficient for

subsonic operations.

Specific

Fuel

Consumption

Supersonic /

Crui_

,f ,,

Turtp, jet Turbofan

Q,

\

Subsonic

Cruise (M = 0.9)

Jet

Noise

Problem 2.: High jet-velocity turbojet

engine is desirable for supersonic cruise

but is noisy around the airport. The

inverted velocity profile (IVP) coannular

nozzle illustrated in inset is a characteristic of VCEs and gives inherent noise

relief.

Turbojet [_

Bypass Ratio c::C>

Supersonic cruise aircraft propulsion "problem."

Jet Velocity

82
PROBLEMS AND POTENTIAL

field and "hold" reserves than the turbofan. On the other hand, a turbofan engine would be quieter than a turbojet engine, but would require more fuel for the critical supersonic cruise condition. The turbofan engine also requires a larger diameter, with increased drag, than

the turbojet to provide the same thrust level.

Turbojet engines were selected for both the Concorde and the U.S.

SST because of their more efficient performance at the critical supersonic cruise conditions. Afterburners were incorporated to augment the

basic engine thrust for takeoff, climb, and acceleration to cruise speed

and altitude. The afterburner essentially increased the basic jet exit

velocity and, hence, thrust by burning fuel in a duct at the rear of the

engine. The afterburner proved to be a noisy way to produce thrust

and made it unlikely that either the Concorde or the U.S. SST could

meet the new Federal Aviation Regulation (FAR), part 36, noise rule

enacted by the FAA in 1969. In the latter stages of the American program, an oversized nonafterburning turbojet engine was considered in

an effort to meet this new noise rule. The weight and size of the engine

had a catastrophic effect on the American design. In the belief that the

FAR 36 noise rule would not be applied to an airplane already under

development, the Concorde retained the afterburning turbojet engine.

The afterburning turbojet engine has been the major powerplant for

supersonic military airplanes for which engine noise and subsonic flight

efficiency are not primary design parameters. Large turbofan engines

are now used almost exclusively on subsonic jet transports because of

their superior noise characteristics and subsonic fuel efficiency.

Because a commercial SST must operate efficiently at both subsonic

and supersonic speeds, it could use an engine that incorporates the best

features of the turbojet and turbofan engines. This technology was not

available during the SST program, and the turbojet engine with afterburner was selected as the best compromise.

Other technical problems in the propulsion discipline impacted the

development of an SST. For example, the inlet is as critical to engine

performance as the engine itself. Unless the inlet can deliver air to the

engine in an efficient manner, the engine cannot perform efficiently on

83
SUPERSONIC CRUISE TECHNOLOGY

an overall basis. The nozzle, or engine exit, also contributes importantly to propulsion system performance and noise. Both the inlet and nozzle, as well as the engine itself, require a high degree of control for

maximum performance. Although considerable work was done on inlet

and nozzle configurations during the SST program, further intense eftort was required, particularly with a new engine cycle. Questions also

remained about engine emissions and pollution, particularly on afterburning engines. This problem became a critical issue in the latter

stages of the U.S, SST program, when fear was expressed that nitric

oxide (NOx) emissions from SST engines would seriously deplete the

protective ozone layer in the atmosphere and lead to a substantial increase in skin cancer. The technology was not available to allay these

fears or to effectively reduce the emission levels.

STRUCTURES AND MATERIALS PROBLEMS

Structures and materials technology for building supersonic airplanes was certainly available in the 1960s. A number of supersonic

military airplanes were already in service, and an advanced titanium

supersonic reconnaissance airplane, the SR-71, was under development. As the SST program proceeded, it became readily apparent that

the structural design of an SST presents different challenges than the

design of a military airplane and has more impact on the acceptability

of performance. Structural materials are also used differently on an

SST than on a military aircraft.

The structure ofa milita_ airplane is usually rigid because of the requirements of maneuverability. The weight, safety, and cost of the

structure are important, but have no direct bearing on whether the aircraft is considered satisfactory for its design mission. On the other

hand, the structure of an SST is generally quite flexible because it has

no harsh maneuver requirement and because the structure is usually

lightly loaded. The weight, safety, and cost of the structure are extremely important factors in the acceptability and economic performance of an SST.

Because of the flexible nature of SST structure, the relationship between structural and aerodynamic design is very important. The differ84
PROBLEMS AND POTENTIAL

ing aerodynamic forces during the takeoff, subsonic cruise, climb and

acceleration, and supersonic phases of flight alter the shape of the flexible structure. The shape of the structure in turn influences the

aerodynamic forces An accurate assessment of these mutual interactions is necessary for achieving an optimum overall design.

During the course of the SST program, supersonic structural design

methods were available. These methods were cumbersome and time

consuming, however. It was not unusual to make a configuration

change that was expected to improve performance, only to find that an

adverse weight increase due to the configuration change had canceled

the anticipated improvement.

Another structures problem exposed by the SST effort was the

absence of well-defined, low-cost fabrication for supersonic highstrength aluminum and titanium structures. The mounting costs of the

development phases of the Concorde and the U.S. SST were

significantly affected by fabrication cost, and the projected production

costs made the SST a questionable economic venture.

The U.S. decision to develop a Mach 2.7 SST posed a materials

problem that was not present in the Concorde program. At the higher

temperatures experienced at Mach 2.7 flight conditions, the available

technology for necessary nonmetallic materials such as fuel-tank

sealants was inadequate. This problem had not been resolved at the

time the American SST program was canceled.

TECHNOLOGY INTEGRATION PROBLEMS

The pre-1972 supersonic cruise experience indicated the overwhelming importance of technology integration in developing a successtul

SST. Perhaps no other high-technology program besides the SST has

been considered unsuccessful when its pertbrmance goals have been

met. The Concorde essentially met its design expectations in aerodynamic performance, structural weight, propulsion system efficiency,

safety, noise, sonic boom, etc. However, many consider the airplane to

be a failure because the levels of technology, although successfully

85
SUPERSONIC CRUISE TECHNOLOGY

employed, were not adequate to make the Concorde an economical

transportation system.

The American SST program was unsuccessful because the advanced

levels of technology employed were never integrated into a coherent

airplane. The complicated variable-sweep and highly swept arrowwing concepts offered dazzling advantages in aerodynamic performance, but the structural design methods and materials were not

available to make them work within acceptable weight limitations. The

relatively simple structural concepts of the delta wing offered fantastic

weight advantages, but had insufficient aerodynamic potential to

promise more than a marginal SST. Propulsion systems that offered

optimum performance at supersonic speeds were not very good at subsonic speeds, and vice versa.

The experiences of both SST programs indicate that the development of a successful supersonic transport will depend more on the advancement of the state of the art of integrated technology than on the

advancements in the separate disciplinary technologies. In the least,

the disciplinary technologies must be developed within the focus of the

integrated airplane and mission requirements.

ENVIRONMENTAL PROBLEMS

The pre-1972 supersonic cruise experience exposed a number of environmental problems that were either critical to the acceptability of

the SST or unanswered by its proponents. The major environmental

issues associated with the SST were:

• Engine noise

• Sonic boom

• Engine emissions

• Radiation exposure.

Although only two of these issues--engine noise and sonic

boom--proved to be significant, all of the environmental questions

merit consideration and will be factors in any future SST effort. Some

86
PROBLEMS AND POTENTIAL

people consider the anxiety and uncertainty caused by these environmental issues to be the factors that finally led to the cancellation of

the American SST effort.

ENGINE NOISE

Any piece of machinery that produces work, power, or any other

useful product creates noise. The SST engines would certainly be no

exception. Each of the four Concorde engines produce on the order of

35 000 to 40 000 pounds of thrust at takeoff, and the four engines on

the U.S. SST would have produced about 60 000 pounds of thrust

each. Both the British/French and U.S. engines made use of afterburners, and both engines were developed before the promulgation of

the FAR 36 noise rules in 1969. Neither engine could meet the noise

rules, but it was generally believed that the noise rules would be waived

since both SST programs had been initiated before the rules were

adopted.

In the early 1970s, the support for the American SST was waning,

and the Concorde was undergoing flight tests. At this time, public sentiment, driven by widely held perceptions that all jet aircraft are noisy,

began to swing heavily against the noise that was to come from the

SST. In an effort to win support for the flagging American effort, a

belated attempt was made to bring the proposed U.S. SST within the

1969 noise rules. To do this would require the development of a new

engine, a further delay in the program, and substantially more money.

This gambit did not work, and the Concorde developers were left to

fight the SST noise battles.

By the time the U.S. SST program was canceled in 1971, it was too

late for the Concorde to meet the new noise rules. The airplane was

under construction, and it proposed to fly in the face of the rising

public clamor over SST noise. The Concorde developers maintained

that the Concorde noise would be no worse than that of the early subsonic jet transports, which were still in use throughout the United

States, Europe, and the rest of the world. Although the Concorde

essentially produced the same levels of noise as the early transports, the

87
SUPERSONIC CRUISE TECHNOLOGY

stance of the Concorde developers led to a showdown with the

American public in 1977 when the Concorde sought landing rights in

the United States. After a great furor, the Concorde was granted a

16-month trial period to operate into and out of the Dulles Airport in

Washington, D.C., and, later, to John F. Kennedy Airport in New

York City. Since the hectic public demonstrations died down after the

first few Concorde flights, little has been said about Concorde noise.

Because of its unique operating capabilities to climb and turn away

from the heavily populated regions, the Concorde has added very little

to the noise exposure of the citizens of Washington, D.C., or New York

City.

Even though the SST has not been the noise "monster" that many

people expected it to be, noise is one of the major technical problems to

be solved before any future generation of SSTs will be acceptable. An

aircraft engine, or any other machine, cannot be expected to produce

60 000 to 70 000 pounds of useful force without producing noise.

However, it is possible to reduce the noise levels substantially below

those of the first generation SST without compromising the ability to

meet other SST requirements.

A NEW SOUND BARRIER--THE SONIC BOOM

When Chuck Yeager broke the so-called "sound barrier" with his

flight in 1947, he introduced the world to an even more intractable barrier to acceptable supersonic flight--the sonic boom. This nerveshattering disturbance created a ground swell of resentment toward

supersonic flight and represents one of the most difficult aeronautical

problems to be faced by the technical community.

The sonic boom is essentially a direct result of supersonic flight.

Disturbances in air can travel only at the speed of sound and, hence,

cannot move ahead of an aircraft that is traveling at supersonic speeds.

Consequently, a sharp pressure pulse forms and is swept behind the

airplane to form a conical surface in which the pressure and

temperature are locally higher than in the surrounding air. This conical surface follows the supersonic aircraft along its flight path. When a

point on this conical surface passes over" an observer on the ground,

88
PROBLEMS AND POTENTIAL

The sonic boom pressure disturbance, Ap, is a constant companion of

an airplane in supersonic flight and was one of the major environmental

concerns of the SST program. The furor caused by this phenomenon

led to the pe$1mge of an operating rule that forbade commercial supersonic flights over the continental limits of the United States. As indicated

by the inset sketch, the large size of the SST permits it to retain the

"near-field" characteristics at the ground. For many flight conditions,

the SST sonic boom levels can be reduced by shaping the airplane.

_P L "'_Near Field

Sonic boom disturbance.

there is a rapid increase in pressure, which the observer perceives as a

boom. 119 The level of sonic boom expected of SSTs was 2 to 3 psf,

which represents a rather miniscule change in the ambient pressure at

sea level of 2116 psf. The abrupt nature of the pressure disturbance

startles the observer, and this is the factor that makes the sonic boom

such an environmental nuisance. The sonic boom levels created by an

SST are not expected to cause any appreciable property damage. 12o

In the early phases of the U.S. SST program, the permissable sonic

boom levels for an SST were set at 2 psf in the climb and acceleration

phase of flight and 1.5 psf at supersonic cruise conditions. These

restrictions severely affected the ability of the SST evaluation airplanes

to make a reasonable range/payload mission. Consequently, the sonic

boom restrictions were relaxed to a level of 2.5 psf during climb and acceleration and 1.7 psf at cruise. The public fears over sonic boom continued, however, and some people expected the SST program to be

89
SUPERSONIC CRUISE TECHNOLOGY

canceled because of sonic boom considerations alone. To allay these

fears, and perhaps to save the program, Congress passed a law in 1971

prohibiting supersonic flights of civil aircraft over the continental

United States. This law, which is still in effect, made the potential

American SST a strictly over-water airplane with a more restricted

market.

The sonic boom is an irreversible fact of supersonic flight.'2_ Means

have been found to reduce the levels of sonic boom caused by a large

supersonic aircraft and to alter the shape of the disturbance. 1_2

However, no realistic ways have been discovered to eliminate the

disturbance completely. This problem remains a challenging technical

goal.

ENGINE EMISSIONS

In the early 1970s, shortly before the SST program was canceled,

there was concern that the engine emissions from a fleet of supersonic

transports would have a drastic adverse effect on the chemistry of the

upper atmosphere. The greatest of these fears was that the nitrous

oxide emissions would deplete the ozone in the atmosphere, reduce the

shielding from the Sun's ultraviolet rays, and thus cause an increase in

the incidence of skin cancer. This concern, originally directed at the

anticipated supersonic aircraft, spread to the potential impact of the

growing fleet of subsonic aircraft. _23

As mentioned in Chapter 4, these concerns led the U.S. Congress to

instruct the Department of Transportation (DOT) to conduct a scientific study that would provide information for assessing the potential

ozone-depletion effects. This major study, the Climatic Impact Assessment Program (CIAP), drew on nine other Federal departments and

agencies, seven foreign agencies, and the individual talents of 1000 investigators. The results of this study were not conclusive because of the

simplified atmospheric models that were available. Indications were,

however, that the first generation of SSTs would cause climatic effects

that are much smaller than those minimally detectable. The report

went on to say that if high-flying aircraft (including subsonic aircraft)

9O
PROBLEMS AND POTENTIAL

increase greatly in number beyond the year 1980, improvements over

1974 propulsion technology will be necessary to ensure that emissions

do not significantly disturb the stratospheric environment. TM

A subsequent High Altitude Pollution Program (HAPP), conducted

by the FAA, indicated that the earlier DOT CIAP study had substantially exaggerated the extent to which future aircraft will reduce the

ozone layer. Present understanding of the phenomena indicates much

smaller impacts and perhaps no net impact at all.t_5 Encouraging as

these results may be, the question of atmospheric pollution by air

transport engines will continue to be raised. The technical challenge is

to continue to search for and find means for reducing the levels of

undesirable engine emissions.

RADIATION EXPOSURE

Because supersonic transports will cruise at higher altitudes than

previou_ commercial aircraft, there will be less atmosphere to filter out

radiation from outer space. This opens the possibility that the crew of

an SST might undergo excessive radiation exposure. It may be rationalized that the SST crew will be exposed to more intense radiation

over shorter periods because of the higher speed and reduced trip time

for a given flight. This factor would tend to compensate and equalize

the total radiation exposure of supersonic and subsonic crews. The best

evidence to date is that such radiation exposure will not exceed permitted occupational levels. 126

OTHER SUPERSONIC CRUISE PROBLEMS

Several other problems were evidenced by the prior supersonic

cruise experience, such as fuel usage, cost, economics, and air-traffic

control. These factors are almost directly related to the status of

technology and the severity of the environmental restraints. These

issues will have to be considered in any future supersonic transport

program.

91
SUPERSONIC CRUISE TECHNOLOGY

SUPERSONIC CRUISE POTENTIAL

As technical problems and environmental issues eroded support for

the U.S. SST program in the early 1970s, the real reasons and potential for supersonic cruise flight were obscured in the conflict that eventually led to program cancellation. Many of the arguments that had

been used to sustain the program either were proven false or were

much less important than had previously been claimed. Other supportive arguments were difficult for the average person to understand and,

hence, were not helpful in bringing public support to the program.

Among the arguments used to support the development of a U.S.

SST were:

• National prestige/foreign competition

• Technological fallout

• Employment

• Balance of trade

• Increased airline productivity.

NATIONAL PRESTIGE/FOREIGN COMPETITION

Both the NASA and FAA recommendations for a national SST program cited prestige and the threat of foreign competition as major

reasons for initiating such a program. At the time these arguments

were used, they were probably valid. If either or both of the foreign

SST efforts were to result in a viable supersonic transport, it was in the

interest of the United States to do likewise. However, it is almost axiomatic that prestige and foreign competition are not normally sufficient motivation for a commercial venture. This sort of venture is

usually made to capture and sustain a market for the product and to

make a profit. Certainly, the British/French consortium and the Soviet

Union introduced their programs in an effort to recapture some of the

air transportation market that they had lost to the United States.

92
PROBLEMS AND POTENTIAL

When it began to appear that neither the British/French nor the

Soviet SST programs would be economically successful, the arguments

about national prestige and foreign competition were no longer able to

generate support for the U.S. SST program. Even so, the answers to

this argument are probably not all in as yet. By carrying their respective SST programs to flight hardware, the foreign nations have gained

a mass of supersonic experience that is not available to the United

States.

TECHNOLOGICAL FALLOUT

A major argument of SST proponents was that an American SST effort would provide a technological fallout that would be valuable to the

aircraft industry in general and to other industrial and military applications. L27This had certainly been the case in other high-technology ventures.

As mentioned in previous chapters, the focus of the SST program

provided major improvements in the state of the art in supersonic

design and analysis, sonic boom, supersonic propulsion, structures and

materials, advanced navigation systems, etc. Completion of the SST

program to prototype flights would probably have brought further

technological gainsi However, if the major goal-a viable SST-is not

attained, the technology fallout would probably not be worth the expense of the program. A costly program cannot be sustained on the

basis of technology fallout alone.

EMPLOYMENT

Proponents of the SST cited the favorable effect on employment as a

principal reason for continuing the SST program. It was claimed that

the U.S. SST program would provide a direct labor force of 50 000

highly skilled jobs with potential application throughout the United

States. Taking into account the multiplier factor, the SST program

could have more reasonably affected 150 000 jobs. 128

Although everyone was in favor of employment, it was easy to say

that these workers could be applied to programs of more value than

that of the SST. On a few occasions, the United States has instituted

93
f

SUPERSONIC CRUISE TECHNOLOGY

programs for the major purpose of providing employment. One of

these was the Work Projects Administration (WPA) during the depression of the early 1930s. The U.S. government has also awarded hightechnology programs to companies in regions of high unemployment.

However, no expensive high-technology effort has been either started

or maintained on the basis of the employment it would provide.

BALANCE OF TRADE

The U.S. balance-of-trade argument for the SST was one of the

most difficult arguments for the public to understand. Figures were

quoted on U.S. balance of trade both with and without an American

SST, with and without an advanced Concorde, with and without a successful Soviet TU-144, and nearly every combination in between. The

impacts ranged from a positive U.S. trade balance of $16.6 billion if

the United States would compete with an advanced Concorde to a

negative U.S. trade balance of $18.7 billion if we would not compete

with the Concorde, a total swing of $35.3 billion. 129

These balance-of-trade figures became moot when the Concorde

program proved to be less than successful, and no plans for the

development of an advanced Concorde became apparent. Many people assumed, with relief, that the relative economic failure of the Concorde would remove the need for any further consideration of the influence of the SST on U.S. trade balance. This assumption represented

a subtle change in the U.S. reaction to foreign competition. When the

British Comet subsonic jet program faltered in the 1950s, the American

aircraft industry moved in with subsonic jet transports, which subsequently captured the largest part of the subsonic jet transport market.

FGreign sales of these early jet transports and derivatives have consistently provided the most favorable positive effect on the U.S.

balance of trade. On the other hand, when the Concorde program

faltered, many in the United States dropped the SST and went on to

other pursuits. It is difficult to assess what would have happened if the

U.S. airplane industry would have been ready to move in with a

superior SST.

94
PROBLEMS AND POTENTIAL

It is also difficult to make a meaningful balance-of-trade argument

based on assumptions of any number of predicted events happening,

estimating a number of future markets for airplanes of unknown

characteristics, etc. One thing is certain, however. The U.S. airplane

industry is one of our greatest assets and has been one of the major

positive factors in the foreign balance of trade. It is to the advantage of

the U.S. government and the American people that this industry remain competitive.

INCREASED AIRLINE PRODUCTIVITY

A recent report published by the Office of Technology Assessment

(OTA) of the U.S. Congress stated as one of its findings that "The most

compelling argument for an advanced supersonic transport is improved productivity-seat-miles generated by an aircraft per unit

time." 130 Other than the SST advantages of improved comfort and

reduced trip time, the OTA statement might be carried further to say

that there is no real reason for an advanced SST unless it provides increased productivity within desired economic and environmental constraints. This

is the true goal of supersonic cruise flight and the challenge of supersonic technology.

Over the past 50 years, the demand for commercial air transportation has increased at a phenomenal rate. In the United States alone,

the demand grew from 93 million revenue-passenger-miles (rpm) in

1930 to nearly 163 billion rpm in 1975. This represents a remarkable

1750-fold increase in air traffic during the period. Perhaps the most

astonishing aspect of the air transportation growth picture is that only a

4.5-fold increase in the number of transport airplanes has been required to meet this 1750-fold increase in air travel demand. Until now,

the U.S. airplane and propulsion companies, unfettered by the size,

speed, and utilization limitations that have led to the decline of the

ship, train, and motorbus as principal intercity carriers, have met this

increasing travel demand by providing successive generations of more

productive air transports. The continuous evolution of these advanced,

95
SUPERSONIC CRUISE TECHNOLOGY

1O0 -

80

60

U.S. Intercity

Traffic (percent)

40

20

Train

_1 I I I

Air

Motorbus

1950 1955 1960 1965 1970 1975

Year

As a result oJ productivity and comfort, the airplane is taking over the transportation

market (source: Air-CAB Bureau of Accounts and Statistics," TrainMotorbusInterstate Commerce Commission).

more productive air transports has successfully prevented air transportation from entering the period of stagnation and decline experienced

by other commercial transportation systems.

Productivity has become a widely used yardstick for measuring progress. The Gross National Product (GNP), as well as the rate of growth

of the GNP, of the United States, for example, is closely followed by

economists. The continuous aim of the U.S. industry is to increase the

amount of a given product that is created per unit cost. There is no particular gain to the industry, or the count_, if twice the manpower,

twice the time, or twice the cost is required to generate twice the

product.

The product of any transportation system is revenue-passengermiles, and the major measurement of the progress of the,system is the

96
PROBLEMS AND POTENTIAL

improvement in product per unit of time or per unit of equipment. For

an individual transportation unit or for the entire transportation fleet,

the product can be written:

PRODUCT (rpm) -- Revenue Passengers x Speed (mph) x Hours

The first two terms on the right-hand side of this equation (revenue

passenger miles per hour) is considered to be the productivity of the

given unit or fleet.

In the foregoing equation, the Revenue Passengers term is related to the

size of the transportation unit or fleet, since the larger the unit or fleet

the greater the number of revenue passengers that can be transported.

The Speed term is simply the velocity at which the revenue passengers

are transported, and the Hours term is the number of hours that the

unit or fleet is operated during the period that the PRODUCT is to be

measured. The fleet total hours can be increased by improving the

utilization of a given unit or by providing more units. Thus, we can say

that the principal elements of the PRODUCT of a transportation

system are size, speed, and utilization hours.

In the past, the U.S. aircraft industry has met the need for improvements in fleet product or productivity by making simultaneous

increases in size, speed, and utilization hours with each successive

generation of transport aircraft. Of course, the fleet productivity did

not immediately reach the productivity levels of the new aircraft

generation because older aircraft remained in the fleet. Gradually,

however, the impact of the new aircraft was felt, and the average fleet

productivity improved. During the 25-year period 1951-1975, this improvement in average fleet productivity led to the emergence of the

airline as the major intercity passenger vehicle in the United States

with over 80 percent of the traffic. During this same 25-year period, the

Civil Aeronautics Board statistics were of sufficient detail to determine

the relative contributions of increased size, speed, and hours to the

tremendous increases in U.S. airline product. Each element made an

important contribution.

It should be recognized that improved airplane productivity,

whether achieved through increased size, speed, or utilization, will per97
SUPERSONIC CRUISE TECHNOLOGY

Productivity

180

160

140 --

120 --

B

60 --

40 --

20 --

0 -- [

1950

Revenue 100

Passenger Mile

rpm's/Year

(billions)

8O

Productivity

Jet A/C

Introduced

Wide-Body A/C

Introduced

Increased

Hours

t JO--

/ II

I Increased

I II Sizl

?

Increased

Speed

an mnlm am n n n u m un n nn numm nn n

L I I I I I I

1954 1958 1962 1966 1970 1974 1978

Year

The elements of the airplane's increase in productivity-- increased speed, size, and hours

(source." CAB Bureau of Accounts and Statistics).

mit a reduced number of aircraft to carry a given passenger traffic. The

high productivity of an advanced SST, for example, could limit production to 200 to 400 aircraft and would, of course, affect initial cost

and break-even point of the Return on Investment. However, reduced

number of aircraft to do a given job is one of the principal aspects of increased productivity in the air transport business.

98

/
PROBLEMS AND POTENTIAL

If past trends continue, the demand for air travel will increase

significantly in the future. To meet this demand, it will be necessary to

increase the size, speed, or number of air transports or to improve the

use of the airplanes that are currently in the airline fleet. The option of

increased size offers some room for improvement, but an airplane can

get too big to be effective on anything but a specific route. Similarly,

small improvements can be made in aircraft utilization, but there is a

limit to the number of hours in a day that passengers want to depart

from or arrive at an airport. Therefore, the only options for meeting

further increases in air travel demand are to increase the number of air

transports in the fleet and/or to increase the speed. Increasing the

number of air transports in the fleet will meet passenger demand but

will soon result in congestion in the terminal or congestion in the air. It

Advanced SST

1790 mph, 300 seats

Boeing 747 Jumbojet

545 mph, 400 seats I

British/French I

117,720

Concorde

1360 mph, 110 seats I

U.S. Dome=tic

Airline Fleet

81,600

I

[

289,980

I

30,024

Load Factor = 0.54

I I I 1

0 50 100 150 200

Cruise Productivity (1000 rpm/hour)

I

25O

Productivity levels of aircraft (plus for SST).

I

3OO

99
SUPERSONIC CRUISE TECHNOLOGY

will not increase fleet productivity. Consequently, the only real hope

for meeting the increased demand for air transportation in the future is

to again remove the barriers to increased speed that Capt. Chuck

Yeager removed some 35 years ago.

The goal and promise of supersonic cruise technology is to again

open the air transportation industry to the advantages of increased

speed--not speed for speed's sake, not speed for the jet-setter's sake,

but speed for the reason that it is a necessary ingredient of productivity.

Because speed serves productivity only when it can be bought within

desirable economic and environmental guidelines, this was the goal

and challenge of the supersonic cruise technology effort conducted

under the NASA Supersonic Cruise Research (SCR) and Variable

Cycle Engine (VCE) programs.

100
CHAPTER 8

Pursuing the Problems and Potential

of Supersonic Cruise Flight: The NASA

SCR and VCE Programs

As indicated in the previous chapter, a number of difficult technical

and environmental problems are associated with commercial supersonic cruise flight. Most of these problems were not satisfactorily

resolved during the U.S. SST program. Although an American SST

could have been developed with the supersonic technology available at

the time, such an SST would not have measured up to the standards of

performance and environmental acceptability that the people and the

government of the United States demanded. Such an SST would also

have been a marginal investment for its airline customers.

Contrary to some views, the cancellation of the U.S. SST program

did not establish the insolubility of the problems of commercial supersonic cruise flight or alter the fact that increased speed is an important

element of improved productivity, but is a desirable characteristic to be

sought and achieved. Consequently, the demise of the SST did not lead

to the discontinuation of supersonic cruise technology efforts within the

United States. A number of members of the U.S. Congress were concerned about the possible competitive threat of SST efforts in England,

France, and the Soviet Union and were in favor of further supersonic

technology efforts. The U.S. aeronautical research agency, NASA,

viewed the supersonic cruise problems as challenging and difficult, but

amenable to solution through a focused research effort.

In early 1972, the Nixon administration directed NASA to formulate

a supersonic research program that would provide the technology' _br a

i01
SUPERSONIC CRUISE TECHNOLOGY

viable commercial supersonic transport. This new program was

developed in early 1972 and was originally called the NASA Advanced

Supersonic Technology (AST) program. It was to build on the

knowledge gained during the U.S. SST program and was to bring a

state of supersonic cruise "technology readiness" within 4 years.

However, because the opponents of any future American SST program

quickly read into the acronym, AST, a program for developing an advanced supersonic transport, the designation was changed to Supersonic Cruise Aircraft Research (SCAR) in 1974. The pace and funding

of the program was also cut back so that no "technology readiness" date

could be specified. Even with the sharp cutback in anticipated funding,

the word "Aircraft" in the title SCAR still gave rise to the spectre of

NASA developing an SST. Consequently, the title of the program was

changed to Supersonic Cruise Research (SCR) in 1979. This latter

designation (SCR) will be used in the balance of this document.

OBJECTIVES AND RATIONALE OF THE NASA SCR PROGRAM

The official objectives of the NASA SCR program were as follows:

The Supersonic Cruise Research Program has been undertaken to provide a

sound data base to support rational decisions in consideration of future civil

and milita_ ' supersonic cruise aircraft.

The objectives are to define the potential benefits and trade-offs of advancements in aerodynamic efficiency, structures and materials, propulsion

systems, and stability and control methods applied to promising advanced

supersonic aircraft concepts that also meet environmental requirements. Integration of the technical disciplines will be undertaken, needed analytical

tools developed, and wind tunnel and laboratory investigations will be conducted in a closely coordinated eflbrt to provide an advanced technology base.

As this statement shows, the principal objective of the NASA SCR program was to conduct or support disciplinary research on the problems

of supersonic flight and to provide advancements in the state of

technology. However, in line with one of the lessons learned in the

102
NACA SCR AND VCE PROGRAMS

prior SST effort (see Chapter 6), the disciplinary research was to be

conducted and assessed, when possible, on the basis of its impact on an

integrated supersonic airplane system. This would preclude the expenditure of large amounts on research solutions that had no real application to a practical airplane.

The basic approach of the SCR program, then, was to search for the

solution to supersonic problems through disciplinary research. Most of

these problems were well known (see Chapter 7), but no satisfactory

solution had been found. When the new SCR research suggested a

potential solution to a supersonic problem, the applicability of the suggested solution was assessed by determining if it could be integrated into a practical commercial supersonic airplane and mission. If the

potential solution withstood the test of the integration exercise, attempts would be made to further validate the solution with wind tunnel

tests or hardware construction and tests. If the potential solution could

not be integrated, it was discarded, and the disciplinary research teams

sought another solution to the problem.

The integrated technology approach of the NASA SCR program was

one of its most important aspects. This approach helped to point out

the most fertile areas for research and permitted progress to be

measured in a quantitative manner.

An important decision in the formulation of the SCR was to conduct

the program in a focused manner. SCR was a "line item" in the NASA

budget, and this factor promoted an interest and impetus within the

aerospace community that a NASA in-house generic research program

probably would not have provided. It was perhaps this display of interest by the U.S. government and NASA that prompted some aerospace companies to augment the SCR program with company funding

and manpower.

The SCR program was set up to involve all of the NASA

aeronautical centers. As the program progressed, it also involved many

of the aerospace companies, research organizations, and universities.

It was believed that solutions to the supersonic problems could be

103
SUPERSONICCRUISETECHNOLOGY

[1 ̧

Studies

t

Research

In Critical

Problem Areas

Integrated Technology

Advances

That Effect Aircraft,

Safety, Cost, and

Performance

I[ Operational Demonstration 1

J of Technical Solutions J

JWhen Deemed to be in the J

J Public Interest J

SCR operating plan.

found if there was wide enough participation by those who had experience in the field. Before the SCR program came to an end in 1981,

more than 100 separate organizations had been involved in some

aspect of the effort. TM

ORGANIZATION AND ELEMENTS OF THE

NASA SCR PROGRAM

The NASA SCR program was conducted under the overall direction

of the Office of Aeronautics and Space Technology at NASA Headquarters. Day-to-day operation of the program was the responsibility of

the SCR Program Office established at the NASA Langley Research

Center. Although the program office had a leader for each major

disciplinary, research area, the effort required for solving the supersonic

cruise problems was in the hands of the research organizations within

NASA. The important technology integration function was under the

leadership of" the SCR Program Office.

104
NACA SCR AND VCE PROGRAMS

At the outset, the major elements of the SCR program were as mentioned earlier in the objectives statement. The disciplinary research

elements were Aerodynamic Performance, Propulsion, Structures and A,laterials, Stability and Control, and Stratospheric Em,'ssions Impact. Mzssion

Performance Integration, or Systems Integration Studies, was the other major

element written into the original SCR Program Plan. Brief descriptions

of these elements follow.

AERODYNAMIC PERFORMANCE

This research element was responsible for developing and testing advanced aerodynamic concepts that could be applied to the commercial

supersonic transport mission. The element also was responsible for

developing and validating advanced analytical techniques for use in

___ Miuion

Performance

Integratlon

] ]

Structures

Propulsion and

Materials

Nolle

Reduction

t Reduction Pollution ]

t Dynamics

and

Control

Experimental]

Sn_na I

, st._ I

Unique I

Components I

I

AirframePropulsion

Syltem

Interactions

i Variable

Cycle

En_linel Structural Concepts

_ Delign Data

and Tools

i

Materials

Applications

Fuel Tank

Sealants

J

Aerodynamic

Performance

" Concept I

DevelopmentJ

t Theory ]

Development I

Sonic

Boom

!

Stability

and

Control

Design Data and Tools

Pilot/

Aircraft

Interface

Stabilization I

and Control I

Systems j

q Dev(Hopment Base I

I I

I

I

I

i

I

I

I

I I

[ Flight I

] Research ]

IExperlmentsj

Elements of NASA SCR program.

105
SUPERSONIC CRUISE TECHNOLOGY

aerodynamic design and analysis, and for conducting studies to improve the understanding of sonic boom phenomena. Subelements of

this research area were Concept Development, Theory Development,

and Sonic Boom. Research under the discipline was conducted or

monitored mainly by personnel of the Aerodynamic Directorates at the

NASA Ames and Langley Research Centers.

PR()PUI.SI()N

The major goal of this SCR research element was to develop a propulsion system that would efficiently meet the conllicting requirements

of subsonic and supersonic operation. Solutions were also needed for

the noise and pollution problems that became critical issues in the latter

stages of the U.S. SST program. Subelements of the Propulsion program were Engine Studies, Noise Reduction, Pollution Reduction,

Dynamics and Control, and Unique Components. This research was

conducted or monitored by personnel at the NASA Lewis Research

Center.

STRUCTURES AND MATERIALS

Major goals of the Structures and Materials research element were

to develop structural concepts and materials that would efficiently

withstand the constantly variable load and temperature environment

that is experienced during a supersonic flight. The developed concepts

and materials would also have to be relatively low-cost if a commercial

supersonic transport was to be economically viable. To meet these

goals, improved analytical methods for structural design and analysis

would be required, as well as improved nonmetallic materials such as

fuel-tank sealants and windshields. Subelements of the Structures and

Materials program were Structural Concepts, Design Data and Tools,

Material Applications, and Fuel-Tank Sealants. Research in this element was under the direction of personnel from the Structures Directorate of the Langley Research Center with participation by engineers

and scientists at the Dryden Flight Research and Ames Research

Centers.

106
NACA SCR AND VCE PROGRAMS

STABILITY AND CONTROL

The research responsibility of this SCR element was to develop

methods for accurately determining the stability characteristics and

control requirements for large, flexible supersonic cruise aircraft and to

determine the requirements and problems associated with stability

augmentation systems and active control systems. Sube]ements of this

research were Design Data and Tools, Pilot/Aircraft Interface, and

Stabilization and Control Systems. Research was directed mainly by

the NASA Ames and Dryden Flight Research Centers, with some participation by the Langley Research Center in the Active Control area.

STRATOSPHERIC EMISSIONS IMPACT

The critical research goal of this SCR element was to answer questions that arose during the SST program concerning the pollution of

the upper atmosphere by high-flying aircraft. Major questions involved

the jet-wake chemistry and how the jet wake propagated and

dissipated. There were also questions about the level of stratospheric

pollution due to natural causes alone. This research area was critical to

the future of supersonic cruise aircraft, but was not a problem unique

to such aircraft. The NASA Office of Space Science had been the principal NASA group involved in the problem of stratospheric pollution,

and after October 1, 1976, NASA research in this area was funded and

managed by that group. All of NASA's aeronautical centers participated in some facet of the investigation of upper atmospheric pollution.

MISSION PERFORMANCE INTEGRATION

The important function of this element of the SCR program was to

assess the impact of disciplinary technology advances on the integrated

performance of various supersonic cruise aircraft concepts. With this

element, it was possible to measure the progress of the technology effect

and determine if the technology for an economically viable, environmentally acceptable commercial supersonic transport had been

identified. The SCR program was fortunate to get talented, experienced systems integration teams from the Boeing Commercial Airplane

107
SUPERSONIC CRUISE TECHNOLOGY

Company, the Lockheed-California Company, and the Douglas Aircraft Company of McDonnell Douglas. An excellent in-house team

was also assembled through a NASA nonpersonal services contract

with Ling-Temco-Vought. The SCR program was also fortunate to

secure experienced propulsion system design groups from the General

Electric Company and Pratt and Whitney Aircraft Company.

It might appear that the SCR program was somewhat frivolous for

bearing the expense of four systems integration teams and two propulsion design teams. Actually, however, this was a major strength of' the

program. First, the three major U.S. airplane companies with capability to develop a supersonic cruise aircraft were in the program. (The

fourth company, Rockwell International, was brought in later with a

propulsion-integration contract.) Second, the two propulsion companies with the capability to build an American supersonic engine were

in the program. Third, all of the integration teams had different ideas

as to what a commercial supersonic cruise aircraft should look like,

what altitude and speed it should fly at, what it should be made of, and

how many passengers it should carry. This variation of reference

airplane permitted the disciplinary technology to be assessed over a

wide range of applications and conditions. Finally, all of the industry

teams contributed important disciplinary technology advances during

the course of the SCR program in addition to performing their integration functions.

In addition to the foregoing technical factors, the inclusion of the

major aerospace companies added an important competitive tone to the

program. As a result of this competitive atmosphere, company

managements assigned some of their best engineers to the program and

supported in-house supersonic cruise research with company funding.

ALTERATIONS TO SCR PROGRAM STRUCTURE

During the course of the SCR program, some additions, subtractions, and alterations were made to the program structure. Although

the Stratospheric Emissions Impact research that had been supported

by SCR funds was returned to the NASA Office of Space Science in

108
NACA SCR AND VCE PROGRAMS

ill lj

g

109
SUPERSONIC CRUISE TECHNOLOGY

1976, the SCR program kept abreast of efforts in the field. Added to

the SCR program were the important elements of Flight Experiments

and Airframe/Propulsion System Integration. Broken away from SCR,

but still closely associated with the effort, was the important VCE

program.

FLIGHT EXPERIMENTS

The U.S. Air Force provided NASA with a high-altitude supersonic

YF- 12 airplane prior to the beginning of the SCR program. Although

the airplane did not meet the requirements of a commercial supersonic

airplane, it had been useful in supersonic experiments conducted by

the Dryden Flight Research Center. It became a useful adjunct to the

SCR program, being used to flight-test advanced structural panels, to

validate methods for aeroelastic analysis, and to investigate the problems associated with airframe/propulsion system interactions at supersonic speeds. The YF-12 was also quite useful in the study of control

system problems and in the development of control system concepts.

Personnel at the NASA Dryden Flight Research Center supervised the

flight tests and experiments involving the YF-12.

AIRFRAME/PROPULSION SYSTEM INTEGRATION

In 1977, after the SCR program had identified a technology base

that could lead to a viable SST, it became apparent that a more detailed look should be taken at the important interfaces between the

airplane and its propulsion system (i.e., the engine inlets and nozzles).

Accordingly, the Lewis Research Center, the SCR Program Office,

and the mission integration contractors developed a research program

|br studying these interfaces. Personnel from the Lewis Research

Center monitored this effort, which was initiated in 1977.

VARIABLE CYCLE ENGINE PROGRAM

During the first 3 years of the SCR program, the propulsion system

contractors, General Electric and Pratt and Whitney, identified

engines that showed promise of efficiently meeting the subsonic/supersonic requirements of an SST mission. The two engines accomplished

the conflicting requirements of subsonic/supersonic flight with variable

110
NACA SCR AND VCE PROGRAMS

/

USAF Lockheed YF-12 served very useful junction with flight tests for SCR and VCE

programs.

iii
SUPERSONIC CRUISE TECHNOLOGY

features that permitted the engine to change operating characteristics

during flight. To focus effort on these two promising "variable cycle"

engines, a separate Variable Cycle Engine program was established in

1976. Although the VCE program became a separate "line item" in the

NASA budget, it was closely associated with the SCR program. A program office at the NASA Lewis Research Center was formed to

manage this effort.

DISSEMINATION OF SCR TECHNICAL INFORMATION

In many respects, SCR technical information was disseminated in

the same manner as that of other NASA programs. Nearly 1000

reports and presentations resulted either directly or indirectly from

research supported by the SCR program. 132. 133 In addition, formal annual reviews of the disciplinary research and mission integration results

and two major NASA conferences* were held in 1976 and 1979. These

conferences were well attended by members of the aerospace, military,

and academic communities.

Certain elements of NASA SCR technology and data were controlled through the use of the heading "For U.S. Government Agencies

and their Contractors Only." A unique feature of the SCR program,

however, was the rapid and almost simultaneous dissemination of this

technology and data to most of the major military and civilian airplane

and propulsion manufacturers. This rapid dissemination was possible

because four major airplane and two major propulsion manufacturers

were involved in the SCR program. Boeing, Lockheed, and Douglas

were prime mission integration contractors, and Rockwell was involved in a propulsion integration contract. General Electric and Pratt

and Whitney provided propulsion data to all of the airplane contractors. Each of these contractors presented their disciplinary research and

mission integration results at the annual SCR reviews. Except for the

first few years, when neither propulsion contractor wanted the other

*The SCAR Conference (NASA CP-001, 1976) and Supersonic Cruise Research '79

(NASA CP-2108, 1980).

112
NACA SCR AND VCE PROGRAMS

present at his review, the annual meetings were open to representatives

from all companies. During the course of the SCR program, Boeing,

Lockheed, and Douglas conducted a considerable amount of SCRrelated technology effort with their "in-house" funding and manpower.

All of the companies reported the results of these proprieta_ data at

meetings attended by the other contractors.

An unusual spirit of cooperation existed among the contractor teams

even though each was competing for a larger share of the SCR funding.

For example, Rockwell, which had bid unsuccessfully to become an

SCR mission integration contractor, provided a meeting place for the

three winning teams to review their progress. On another occasion,

Douglas provided the SCR office with some valuable proprietary noise

suppressor data for use in a program for supporting the Federal Aviation Agency in setting noise rules for supersonic aircraft.

Equivalent

Full-Time

Manpower

,2o 100

8O

6O

4O

2O

Total SCR Industry Manpower

Industry-Supported SCR Menpower

SCR Government-Supported Industry Manpower

[ l I I I I I

1974 1975 1976 1977 1978 1979 1980 1981

Fiscal Year

Major airplane contractors supported SCR and VCE with "in-house"fundin¢ and manpol.lJdr.

113
SUPERSONICCRUISETECHNOLOGY

SCOPE OF NASA SCR PROGRAM

Some opponents of the SST saw the SCR program as a surreptitious

attempt to resurrect the SST that had just been canceled by the U.S.

Congress. This feeling became even more prevalent when the program

brought the major airframe and propulsion manufacturers into the

systems integration function. Further misunderstanding resulted from

the use of reference supersonic transport airplanes and missions for

measuring the progress of the technology.

These concerns, though probably natural, were completely unfounded. The SCR program was no more than an effort by NASA to

meet its chartered commitment to provide technology that would ensure American supremacy in civilian and military aircraft. The $300

million NASA supersonic technology effort proposed in response to the

Nixon administration directive was by no means an SST development

program. Rather, it was a minimum 4-year proposed program for providing the technology base for possible future use in the development of

an SST. The decision to involve all of the major airframe and propulsion compahies was made essentially to get as much help and as many

ideas as possible for solving the very difficult supersonic Problems. The

use of practical supersonic cruise aircraft for assessing technology was

dictated by experience, which had shown that an advancement in one

supersonic discipline means little unless it can be integrated with the

other supersonic requirements.

The cutback of anticipated SCR funding in the second year and the

eventual support level of around $10 million per year made it impossible to set or shoot for any "technology readiness" date. However, this

cutback in funding support did not alter the supersonic cruise aircraft

problems or change the SCR objective of finding solutions to these

problems. The scope of the program had always been to establish a

technology base that could be used to develop a viable SST whether it

was a 4-year program or an indefinite one. The next two chapters

describe some of the efforts of the SCR program to establish this

technology base.

114
CHAPTER 9

Progress in Supersonic Cruise

Technology Since 1972

In the years since 1972, the U.S. Congress has supported a number

of research programs on supersonic cruise technology. In addition to

the NASA SCR and VCE programs, there were the Department of

Transportation (DOT) SST Follow-On Program, the Climatic Impact

Assessment Program (CIAP), the High Altitude Pollution Program

(HAPP), and the NASA Emissions Reduction Research and

Technology Program. The DOT SST Follow-On Program supported

the continuation or completion of research on several technology items

associated with the then-canceled SST. Some of this research found important application to later military and commercial airplanes, and

some of the technology elements became the basis for other NASA and

industry programs. TM Results from the CIAP and HAPP efforts provided a substantially improved understanding of atmospheric pollution, and the NASA Emissions Reduction Program provided means for

reducing the pollution from jet engines. 135

The DOT SST Follow-On, CIAP, HAPP, and NASA Emissions

Reduction efforts were directed either to the solution of a specific

supersonic cruise problem or to the accumulation of data that would

shed light on the magnitude of the problem. All of the programs contributed greatly to the supersonic technology, but none had the overall

responsibility for developing the base for a viable supersonic cruise aircraft. This responsibility was given to the NASA SCR program when it

was established in 1972. The SCR effort was to assimilate the results of

the other supersonic programs with whatever new research was

115
SUPERSONIC CRUISE TECHNOLOGY

necessary for developing the desired supersonic technology. The VCE

offshoot program bore the same responsibility in the propulsion area.

Supersonic technology efforts in the United States after 1972 involved several hundred individual, but coordinated, research efforts.

The SCR and VCE programs alone had more than 100 research areas,

many of which involved subareas and phases. Some of these research

areas were not expected to provide far-reaching technology advances,

but were needed to furnish data banks that could be used to make a

dramatic breakthrough. In other research areas, such as engine noise,

any advance would be dramatic because of the "front line" importance

of the research area. Although this chapter and the next deal mainly

with progress in these "front line" issues, they also mention the important "data gathering" efforts, when appropriate. Liberal excerpts are

taken from Driver's excellent paper entitled Progress in Supersonic Cruise

TechnologT. 13_ This chapter examines progress in environmental issues,

aerodynamics, structures and materials, propulsion, and configuration

concepts/integration.

PROGRESS IN ENVIRONMENTAL ISSUES

Environmental issues such as noise, sonic boom, and pollution had a

lot to do with the cancellation of the U.S. SST program and with the

failure of supersonic cruise aircraft to assume a prominent role in air

transportation. These issues could also be responsible for a reticence to

consider the SST as a future transportation system. Certainly, any

future SST program would have to answer the environmental questions before any action could be taken. Although progress has been

made on many of the environmental issues, some questions remain.

UPPER ATMOSPHERIC POLLUTION

As indicated in Chapter 7, the SST brought fears of ozone depletion

in the upper atmosphere and of an increase in the incidence of skin

cancer on the Earth. The CIAP study showed these concerns to be

overstated, and the later HAPP program indicated a possible increase

116
PROGRESS IN TECHNOLOGY SINCE 1972

in ozone rather than a depletion, ts; Nevertheless, there is still a lack of

complete understanding of the chemistry of the upper atmosphere and

the effect of jet-engine emissions on it. Consequently, programs for

reducing emissions are still needed.

Among the programs that attempted to provide the technology for

reduced engine emissions were the NASA Emissions Reduction

Research and Technology program and elements of the SCR Propulsion and VCE programs. These programs identified concepts that

could reduce nitrous oxide (NO) emissions to less than one-third the

levels of first-generation SSTs and provide for substantial reductions in

carbon monoxide (CO) and unburned hydrocarbons (THC). 13a

Although further study of the chemistry of the upper atmosphere could

indicate that these concepts (complicated advanced burners) might be

unnecessary, their validation for subsonic or supersonic use is

desirable.

SONIC BOOM

As indicated in Chapter 7, the sonic boom is a direct result of supersonic flight, and no means is available for eliminating this accompaniment of such speeds. As mentioned in Chapter 4, NASA has conducted

and supported a massive program for improving the understanding of

sonic boom and for reducing its impact by design. None of these programs have given a reliable hint, however, that this disturbance can be

completely abolished. Consequently, the major goal of the SCR program was to establish a level of public acceptability of the sonic boom to

guide research on design methods for reducing the disturbance. Plans

for this program were put in limbo when the anticipated funding tbr the

SCR effort was reduced from more than $40 million in the second year

to approximately $10 million. Because a rule was in effect that prohibited supersonic overland flights of commercial supersonic aircraft, it

was difficult to justify a large sonic boom effort in light of the cut in the

overall program.

It is quite possible that a level of sonic boom can be found that is acceptable to most of the public and that such a level could be achieved

through the design methods developed by NASA and others. From the

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SUPERSONIC CRUISE TECHNOLOGY

standpoint of the SCR program, it was decided that the most feasible

way to accomplish this goal was to develop the technology for an

outstanding overwater SST, provide the technology that would permit

the flexibility of efficient subsonic overland flight, and then use this

vehicle to explore the sonic boom acceptability question. Although this

did not represent a direct frontal attack on sonic boom, it appeared to

make best use of the funding at hand.

ENGINE NOISE

Engine noise, a necessary environmental issue with all modes of

engine-powered airplane flight, was a particular problem with the

SST. Although many of the subsonic jets were as noisy, they appeared

to be much more necessary than supersonic transports. Much progress

was being made on subsonic jet transport noise, and nothing less could

be tolerated for an SST. Consequently, engine noise was a primary

research element of the NASA SCR program and, later, the NASA

VCE program.

During the course of the SCR and VCE programs, some exciting

technologies were discovered that showed promise for dramatically

reducing the projected noise of supersonic cruise aircraft. The first of

these technology advances was the inherent coannular noise reduction

of the variable cycle engines under consideration in the SCR propulsion program at the NASA Lewis Research Center. These engines

utilized an "inverted jet" velocity profile (i.e., a high-velocity outer jet

stream exhausted through a high-radius-ratio annulus and a lower

velocity jet stream exhausted through an inner nozzle). This system

was the opposite of the normal turbofan engine, which has an inner

high-velocity stream and an outer low-velocity stream. The inverted

velocity profile (IVP) coannular nozzles were extensively tested and

validated in a series of model-scale tests, tests on a complete running

engine, and free-jet tests to check the effects of forward velocity. 139

These tests verify a significant noise reduction (approximately 7

EPNdB) relative to a fully mixed conical nozzle at the same specific

thrust and mixed-pressure ratio, t4°

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PROGRESS IN TECHNOLOGY SINCE 1972

Coannular noise tests in Boeing anechoic facility (courtesy of Boeing).

The second important engine noise development in the SCR program was the mechanical suppressor technology validation by the

Douglas Aircraft Company. This effort, perhaps the most complete

one under the partial aegis of the SCR program, involved: (1) smallscale suppressor development tests by Douglas at a Douglas facility; (2)

spin tests of the suppressor on Roll Royce's rotating-arm rig in

England; (3) flight tests of the mechanical suppressor nozzles on a Rolls

Royce Viper 601 engine installed on a Hawker Siddeley HS-125 aircraft modified to accept the engine/nozzle/suppressor/treated-ejector

combination; and finally (4) tests of the engine, nacelle, and nozzles on

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SUPERSONIC CRUISE TECHNOLOGY

i

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a simulated fuselage in the NASA Ames Research Center 40- by

80-foot wind tunnel. The combination of tests indicated that the

Douglas muhitube/lobe retractable suppressor with acoustically treated

translating ejector would provide 12 to 16 EPNdB noise redu':,ticn

relative to a conic nozzle at equal thrust and a thrust loss of 4.5 percent

relative to a conic nozzle at takeoff. 1_1,_42This suppressor performance

is much better than that of previous suppressors, and the results provide real hope that the mechanical suppressor can be a powerful noisereduction device on future supersonic airplanes. It remains to be seen

whether suppressors of this type can be integrated on the engine and if'

they can withstand the operating pressures and temperatures at takeoff

conditions.

A third important noise technology development of the SCR program was the concept of acoustic shielding. Two methods of noise

shielding were considered. First, the Lockheed Company placed the

engines in an over/under arrangement on the wing and used the wing

and fuselage to shield some of the noise from the ground. This approach promised a noise reduction of 3 to 5 EPNdB compared to that of

placing all engines under the wing in the conventional manner. J43 The

other approach to noise shielding made use of a thermal acoustic shield

(i.e., a high-temperature low-velocity gas stream, partially surrounding a high-velocity central jet exhaust). This concept was borne out in

theoretical predictions and experimental tests conducted by NASA, the

Boeing Company, and the General Electric Company. Although this

noise reduction concept is still being investigated, the effect is believed

to be associated with the reflection and refraction properties of the

high-temperature acoustic shield._**

The use of "minimum noise" flight profiles during terminal area

operations was the fourth noise reduction concept to show promise in

the SCR program. This approach essentially makes use of advanced

operating procedures such as thrust modulation during ground roll and

takeoff, engine cutback at optimum "noise" altitude, thrust cutback to

optimum "noise" level, and configuration changes during takeoff other

than raising the landing gear. Making use of these procedures during

takeoff and using decelerated approaches and increased glide slopes

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SUPERSONIC CRUISE TECHNOLOGY

Increased Glide Slope

Decelerating Approach Thrust During Ground Roll

(ground attenuation)

Inlet

Choking

/

Optimum Center of Gravity /

__1 Two-Position Landing Gear

Advanced operatingproceduresfor noise reduction.

Auto

Throttle

_- Auto

Flaps

Acceleration/Altitude

(optimization and trades)

during landing operations can lead to substantial decreases in engine

noise exposure. 145 Unfortunately, current Federal Air Regulations

(FAR) do not permit these advanced procedures. Several elements of

the SCR and supporting programs could make it possible to certify

these procedures in the future. The YF-12 flight research program included an effort to develop a cooperative airplane/engine control

system that would permit the fine degree of control required of the advanced operating procedures. 146 In addition, the SCR stability and

control element supported visual piloted simulator studies of the use of

these procedures on an advanced supersonic transport. It was determined that the advanced operating procedures did not compromise

flight safety. 147

The substantial noise reduction potential of the methods identified in

the NASA SCR and VCE programs give rise to some optimism about

the potential noise characteristics of future supersonic cruise aircraft.

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PROGRESS IN TECHNOLOGY SINCE 1972

Although probably not any of these separate methods will provide the

desired noise levels, a combination of methods appears to be possible.

The basic underlying principles of most of these noise reduction

methods have been validated in some form of experimental program,

in sharp contrast to the noise technology situation that existed at the

close of the SST program in 1971. At that time, the only readily

available noise reduction technology was a vastly oversized propulsion

system that had an extremely deleterious effect on the entire airplane

concept.

PROGRESS IN AERODYNAMICS

As indicated in Chapter 4, the status of the aerodynamic technology

for supersonic cruise vehicles had been brought to a high level by the

close of the SST program in 1971. Not only had accurate supersonic

design and analysis methods been developed, but an advanced arrowwing configuration, the NASA SCAT-15F, had been introduced. The

supersonic cruise aerodynamic efficiency (lift/drag) of the SCAT-15F

was 25 percent greater than the previous state of the art. In spite of this

advanced level of aerodynamic technology, however, the supersonic

and supporting aerodynamic activity was near its peak during the SCR

program. It was found that improvements to the design and analysis

methods could still be made,14s and it was also indicated that entirely

new methods might be needed to predict detailed aerodynamic

parameters, such as pressure distributions, at critical structural and

control design conditions. 149 Meanwhile, the highly efficient supersonic arrow-wing concept stood unused because of questionable subsonic aerodynamic characteristics, which also gave rise to relatively

poor noise characteristics.

Although some effort was spent on improving supersonic

aerodynamic efficiency during the NASA SCR program, LS°, Ls_ the

principal thrust of the aerodynamic program was to find potential solutions to the low-speed aerodynamic problems of the highly swept

arrow-wing concept. This thrust was doubly important because

Lockheed and Douglas had reference configurations that employed this

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SUPERSONIC CRUISE TECHNOLOGY

SCR program also considered improvements in high-speed aerodynamics. SCR/

McDonnell-Douglas model tested at NASA Ames and Langley Unitary wind tunnels.

concept, and .at one point, Boeing proposed an arrow-wing supersonic

technology demonstrator airplane.

For investigating how to improve the low-speed performance of

highly swept arrow-wing concepts, the SCR program supported a

massive model construction program that included large models of a

blended concept, the NASA reference SCAT-15F derivative, the

McDonnell-Douglas Mach 2.2 concept, and a number of generic

arrow-wing models. The experimental programs for testing this myriad

of models were conducted mainly by personnel in the NASA Langley

Research Center 30- bv 60-foot tunnel, the 7- by 10-foot tunnels, and

the VSTOL tunnel. Man}, technicians and engineers were involved,

and nearly every conceivable test variable was considered. As a result

of" this concerted effort, the low-speed aerodynamic efficiencies of

arrow-wing concepts were improved, _$2 solutions for some of the

stability and control problems were found, _53 and a substantial arrowwing low-speed data base was established. _5_, _55

124
PROGRESS IN TECHNOLOGY SINCE 1972

I

__. !_'-__o _ '"- ®E

" }o 8-"

•- _,_ ._-..,, _

f..} • • • "I" • _ • •

..,j

co:

w.

125
SUPERSONIC CRUISE TECHNOLOGY

SCR aerodynamic test program- low-speed tests of McDonnell-Douglas arrow-wing concept in Langley Research Center 30- by 60-foot full-scale wind tunnel.

Not only did the low-speed performance of arrow wings improve

during the SCR program, but the low-speed and high-speed performance of the Boeing-300 delta-wing concept improved 16 percent as

well. 156The combined improvements in aerodynamic analysis methods

and aerodynamic efficiencies, accomplished during the SCR program,

essentially brought this research discipline into a state of"technology

readiness" for the development of viable supersonic cruise aircraft.

PROGRESS IN STRUCTURES AND MATERIALS

As indicated in Chapter 7, the structures and materials technology

for building a supersonic cruise aircraft was available in the 1950s. The

technology for building an acceptable supersonic transport was not

available, however, and much of the technological shortfall was in the

126
PROGRESS IN TECHNOLOGY SINCE 1972

._ _

_.{ _

._ _-_

• _

•_ _

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SUPERSONIC CRUISE TECHNOLOGY

Another of SCR's test efforts to improve low-speed aerodynamics oj highly swept arrow

wings- blended model in Langley full-scale wind tunnel.

SCR variable-sweep model in 30- by 60-foot wind tunnel.

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PROGRESS IN TECHNOLOGY SINCE 1972

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SUPERSONIC CRUISE TECHNOLOGY

structures and materials discipline. Mentioned particularly were the

inability to rapidly and accurately assess the effect of design changes on

the complex flexible structure of a supersonic transport and the absence

of adequate low-cost structural concepts and fabrication techniques.

Another critical need, which was not mentioned, was for a fuel-tank

sealant material that would retain its integrity in supersonic flight applications.

The structures and materials effort that evolved out of SCR support

concentrated on these problems, but it also provided important data

bases on supersonic loads and landing loads. An in-depth summary of

this program is presented by Richard Heldenfels of the Langley

Research Center in Supersonic Cruise Research '79. 157

The NASA effort to improve methods for structural design and

analysis has spanned the area from attempts to improve inputs, such as

unsteady aerodynamics, 158 to research for improving the massive combination of programs that provide the design and analysis capability. 159

This effort has been successful as "advances continue to be made in the

structural analysis and design area with the result that computational

procedures are available now to design quickly a vehicle structure that

meets the requirements for strength, divergence, and flutter with active

controls included. This can be done accurately and early erlough in the

design process to avoid costly changes during detail design." 160

Research efforts to develop low-weight, low-cost structural concepts

and low-cost fabrication techniques also covered a wide range of activity, from the time/temperature/stress analysis of composite materials at

supersonic flight conditions, 161 to the fabrication of relatively large

superplastically formed titanium panels. 162 This latter fabrication process, the superplastic forming and concurrent diffusion bonding

(SPF/DB) of titanium, appears to offer much promise for weight and

cost reductions on future supersonic aircraft.

The SPF/DB process, which was being investigated by Rockwell International during the B-1 bomber program, essentially involves the

heating of a sheet or sheets of titanium in a mold until the titanium

reaches a malleable temperature. A gas is then injected into the mold,

and the titanium is either blown into a shape prescribed by the mold or

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PROGRESS IN TECHNOLOGY SINCE 1972

Advanced structural methodspermit the useof many structural elements and degreesof freedom for more accurateanalysis,

Roll Spot Weld Pattern

Before Superplastlc Forming

Welded

Gas Pressure _ - _

Gas

Pressure --_'_

Partially Formed

Complete Sandwich

Suprrplo.zticforming and concurrentdiffusion bonding(SPF/DB) of titanium- an exciting process that permits complex structural elements to be blown into shape•

131
SUPERSONIC CRUISE TECHNOLOGY

SPF/DB structural panel fabricated by McDonnell-Douglas (courtesy of Douglas

Aircraft).

Array of complex structural elements formed by Rockwell International with the SPF/DB

process (courtesy of Rockwell International).

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PROGRESS IN TECHNOLOGY SINCE 1972

More Rockwell International SPF/DB samples (courtesy of Rockwell International).

bonded to another titanium sheet with a bond of parent-metal strength.

There seems to be no limit to the structural elements that can be

formed by this process, and no fasteners are required within the structural element. An analysis of the use of this process in the design of a

supersonic transport wing showed significant advantages over the

aluminum brazed titanium honeycomb that was used in the Boeing

U.S. SST design.163

The Douglas Aircraft Division of McDonnell-Douglas has made further studies on the SPF/DB process. In this SCR-supported effort, four

flat titanium sheets are placed in a mold, heated to plastic-metal

temperatures, blown into shape, and diffusion-bonded together. Sandwich cover panels for the wing of a reference airplane configuration

made in this manner, combined with similar methods for the wing internal structure, have reduced wing weight by about 7 percent. In addition, a change in the fuselage structure from titanium skin stringer to

a titanium SPF/DB sandwich construction reduced the fuselage weight

by about 22 percent, _64

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SUPERSONICCRUISETECHNOLOGY

Still another fallout of the SCR program is a technique that makes

use of fibers to reinforce the basic titanium structure. This process

promises further dramatic gains in structural efficiency and further cost

reductions.a6_, _66

The final major problem area in the structures and materials

research discipline was the need for a suitable fuel tank sealant for

high-speed, high-temperature operation. This was a problem in the

SST program and was the subject of study in the DOT SST Follow-On

Program. During the SCR program, this research area, directed by the

NASA Ames Research Center, produced elastomers based on a

polymeric heterocyclic fluoroether that could prove to be a satisfactory

fuel tank sealant for supersonic airplanes. This material has shown excellent thermal stability and low-temperature flexibility. It retains the

stable characteristics in the presence of jet fuel and resists oxidation at

high temperatures. 167

In summarizing the technology effort in the SCR structures and

materials effort through 1979, it has been indicated that "This

technology can be used to design safe and durable structures of reduced

weight and cost to improve the performance and economics of future

supersonic cruise aircraft. "_68 This statement was amplified in a Boeing

report which stated that the "Results of this work have been very encouraging and, in particular, have made it possible to define configurations of high aerodynamic potential. These configurations have been

considered practical only because of the design refinements possible by

the successful development of structural technologies .... 169

PROGRESS IN PROPULSION

Engine noise and pollution are serious propulsion problems and

were considered as such in the SCR program, If these two issues are

considered in the environmental impact area, as has been done in this

document, the main remaining and still critical issues confronting the

SCR propulsion discipline were the development of propulsion systems

that could efficiently meet the contradictory operating requirements of

subsonic and supersonic speeds, and then to develop the component

134
PROGRESS IN TECHNOLOGY SINCE 1972

Concept

• Combination of Advenced Titanium

and High Strength Fibers

Joined by

-- Diffusion bondlng

-- Brazing

Into a Unitized, Load Carrying

Structure

Applications

• Stiffness Critical Structure

• Compression Buckling

• High Axial Loads

Fibers -_ Titanium

Bond_.____ ._/._1 /Matrix Benefits

_6__8_ (Ref. Titanium Plate)

_tanl.m (_

Exciting new structural process makes use of titanium rein)forcedwith fibers.

• Up to 65% Reduction in Weight

• Up to 24% Savings in Cost

SCR structures effort includes aeroelastic tests of Boeing SCA T-15F arrow-wing model

(courtesy of Boeing).

135
SUPERSONIC CRUISE TECHNOLOGY

.c

C

<

"0

C

136
PROGRESS IN TECHNOLOGY SINCE 1972

technology that would make these engines possible. Since the noise and

pollution progress has already been discussed, only progress in the latter areas will be discussed here.

PROPULSION STUDIES

The SCR approach to the supersonic transport propulsion problem

was to take a fresh look at all the propulsion cycles that would have any

chance of meeting the demanding supersonic mission. These early

studies were conducted by the NASA Lewis Research Center with the

assistance of the propulsion system manufacturers, Pratt and Whitney

and General Electric, 17° and making use of the SCR mission integration contractors, Boeing, Douglas, and Lockheed.

On the basis of these preliminary SCR studies, it was soon apparent

that a successful SST would require an engine cycle that would approach the performance of the turbojet engine at supersonic speeds and

the turbofan engine at subsonic speeds. Subsequently, such engines

were identified, and the evolution of the Variable Cycle Engine proLow-Noise Variable Coannular

Inlet Compressor Nozzle/Reverser

Variable Turbine System

Fan Low-Emissions

Duct Burner

Lo¥

Primary Burner

Flow diagram of Pratt and Whitney variable-streamcontrolengine (VSCE) in SCR/VCE

program (courtesy of Pratt and Whitney).

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SUPERSONICCRUISETECHNOLOGY

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PROGRESS IN TECHNOLOGY SINCE 1972

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SUPERSONIC CRUISE TECHNOLOGY

gram had begun. Through the process of evaluation by the mission integration teams on a realistic supersonic cruise aircraft mission and on

a series of realistic supersonic airplane configurations, the technical

shortcomings of the engine cycles could be identified and progressive

alterations could be made. Through this refinement process, by 1976,

each propulsion contractor had identified a "variable cycle engine" that

showed promise. At this stage, the NASA VCE program was formed to

develop and conduct programs for validating the critical features of

these two engines. This VCE effort continued to be closely tied to the

SCR program, and the propulsion companies were under contract not

only to the VCE program but also to the SCR mission integration contractors. This situation led to rapid dissemination of technical information between the two programs and among the airframe and propulsion

contractors.

VARIABLE CYCLE ENGINE

The most important propulsion development in the SCR program

was, of course, the "variable cycle engine" concept and the apparent inherent noise advantage of the dual coannular exhaust discussed in the

previous section on "Progress in Environmental Issues." The details of

the VCEs that evolved from the SCR program and were followed in the

VCE program are not important to this discussion, but only the overall

function of the engine. A good description of this function is provided

by Sigalla:

The need for variable-cycle engines in relation to the problem of designing a

successful SST had been recognized for a long time. But it was only as a result

of the SCR program that coordinated research by airplane manufacturers,

engine manutacturers, and NASA technologists led to the mechanical and

thermodynamic definition of such engines by Pratt & Whitney Aircraft and

General Electric. It should be noted that a variable-cycle engine is not defined

by any specific mechanical scheme. Rather, it is defined by its ability to meet

a set of requirements aimed at eliminating the poor subsonic and transonic

performance of supersonic engines designed for higher Mach numbers

without affecting adversely the supersonic cruise performance of those

engines. Such requirements are high supersonic cruise performance with low

specific fuel consumption and high specific thrust (comparable to a dry turbojet cycle), and subsonic cruise range factor almost equal to a supersonic cruise

140
PROGRESS IN TECHNOLOGY SINCE 1972

range factor with the goal that subsonic fuel consumption be at least halfway

between those of a turbojet and a bypass ratio 5 turbofan. Currently defined

study variable-cycle engines meet these requirements._TJ

A statement of the important advances in propulsion technology attributable to the SCR and VCE programs was recently made by

Driver:

Of particular interest has been the evolution of airflow management to reduce

off-design penalties. This gain has been made possible, in part, by the advent

of digital controls. This technique has also resulted in the term variable-cycle

engine, which implies operation at cruise like a turbojet, and operation at offdesign conditions similar to a turbofan. Advanced subsonic engines now

operate with 6 or 7 internal control variables, whereas these advanced supersonic engines will have more than twice as many control variables--partially

as a result of variable inlets and nozzles. The control of off-design performance has made important reductions in the fuel reserve requirement, paying

important dividends in additional payload range. It should be recognized that

both G.E. and Pratt & Whitney have actually run the critical engine features

on a test stand and verified the design features studied in the SCR/VCE program. In the G.E. case, the variable-cycle engine features have been incorporated in a J-101 engine and the performance gains verified on the test stand

with a running engine. 172

Thus, the SCR/VCE program identified two advanced engines that

showed promise of efficiently meeting the supersonic aircraft requirements, pointed out several methods that could be used to reduce

the engine noise and emissions to acceptable levels, and provided some

preliminary validation tests to determine whether all of the elements

could be put together in a unit. Much additional effort would have to

be spent to make these concepts into real supersonic cruise aircraft

engines, but the elements of the technology had been identified.

It should be noted that "variable cycle engines" identified in the

NASA SCR and VCE programs do not represent significant advances

in propulsion cycle efficiencies over previous supersonic turbofan or

turbojet engines. The advantage of these engines is the element of airflow control that provides for a better overall performance on the

supersonic cruise mission than either a turbofan or a turbojet engine

would provide. In addition, these engines would deliver the improved

overall performance with less weight, less fuel, and reduced noise.

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SUPERSONIC CRUISE TECHNOLOGY

PROGRESS IN CONFIGURATION CONCEPTS/INTEGRATION

As indicated in Chapter 7, one of the major technical problems of the

past SST program was the integration of a myriad of disciplinary concepts into an acceptable SST. In many instances, the aerodynamicist

was looking for solutions to aerodynamic problems, the structures

engineer was after a solution to structures problems, the propulsion

engineer was working on propulsion problems, etc. Actually, all of

these disciplinary personnel should have been working on airplane

problems because, if the disciplinary solution could not become an integrated solution to the airplane problem, it was really not a solution.

Because of this overriding importance of integrated technology in the

complicated SST mission, the NASA SCR program made mission performance integration the central element of the program. (See Chapter

8.) The three industry teams (Boeing, Douglas, and Lockheed) and

one NASA in-house team not only assessed the applicability of

disciplinary concepts, but also introduced disciplinary concepts and integrated concepts.

It is very clear that the progress on the VCE was attributable mainly

to the day-to-day interplay between the mission integration or systems

studies teams and the propulsion manufacturers. The integration team

could rapidly point out where the propulsion system had a shortcoming

in thrust or performance, and the propulsion manufacturer could make

modifications to overcome this shortcoming. Many iterations were

made on the VCEs before they measured up to the SST mission.

From the standpoint of technology growth, it was fortunate that each

of the mission integration teams had a different overall configuration

concept on which to assess the technology advances. Douglas opted for

a highly swept arrow-wing concept similar to the NASA SCAT-15F,

but designed for a lower cruise Mach number (2.2 compared to 2.7 for

the SCAT-15F). With the lower design Mach number and the noise

suppressor technology developed in a joint Douglas/NASA effort,

Douglas hoped that the SST mission could be accomplished with a

straight turbojet engine or a very low bypass turbofan. Lockheed also

chose an arrow-wing configuration, but placed two of the four engines

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PROGRESS IN TECHNOLOGY SINCE 1972

McDonnell-Douglas reference concept for technology assessment.

Lockheed reference airplane for SCR technology assessment. Note overunder engine locations on wing.

Boeing technology assessment concept for SCR-the improved blended-wing version of

Dash 300 SST.

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SUPERSONIC CRUISE TECHNOLOGY

unconventionally above the wing for noise shielding purposes. Cruise

Mach numbers between 2 and 2.55 were considered. Boeing made use

of an updated blended version of the delta-wing 2707-300 airplane that

was under study as the U.S. SST candidate. Because of this choice,

both Boeing and the SCR program had the benefit of a storehouse of

information that had been built on this concept. Boeing considered

cruise Mach numbers between 2.2 and 2.7. The final reference configuration was the NASA in-house concept that made use of an updated highly swept SCAT-15F configuration that was proposed to

cruise at Mach 2.7. The NASA in-house mission integration team used

the modified SCAT-15F as an evaluation concept, and the NASA

Lewis Research Center used it in their engine cycle studies early in the

SCR program. A large data base was also available on this configuration because of its study by Boeing, Lockheed, and Rockwell International during the U.S. SST program.

Several important disciplinary technology advances were spurred by

the mission integration teams. Among these were the Douglas suppressor effort and the Lockheed noise-shielding concepts discussed in

the engine noise section, the family concept of SST.design introduced

by Boeing, and the twin-fuselage idea suggested late in the SCR program.

Supersonic technology demonstrator airplane proposed by Boeing (courtesy of Boeing).

144
PROGRESS IN TECHNOLOGY SINCE 1972

Douglas noise-suppressor models (courtesy of McDonnell-Douglas).

DOUGLAS NOISE SUPPRESSOR CONCEPT

Douglas chose to take a "near term" rcfcrcncc airplanc concept with a

Mach 2.2 cruisc speed and a relativclysimple mini-bypass engine. If

thisairplane was to have a chancc to make a good supersonic cruiseaircraft, even with advanced aerodynamic and structures technology,

some sort of noise suppressor would be required. Consequently,

Douglas dcsigned and staticallytested a number of small suppressor

models. One of thcsc models, a muhitubc/lobe concept, showed excellent staticnoise reduction capability. However, many mechanical

noise supprcssors have demonstratcd significantlevelsof noise reductionsat staticconditions, but have losteffectivenessat forward velocity.

In addition, any significantnoise reduction was accompanied by a

grcat loss of thrust,t73 a very undesirable characteristic.For the

Douglas suppressor to be different,itwould have to be proven before

any real technology advance could be presumed. And, as mcntioned

earlierin thischapter, thc Douglas suppressor proved to be different

aftera conccntratcd seriesof wind tunnel, spin rig,and flighttestsinvolving Rolls Royce, the Douglas Company, the NASA SCR Office,

145
SUPERSONIC CRUISE TECHNOLOGY

Most promising Douglas suppressor validated in wind tunnelflight test programs

(courtesy of McDonnell-Douglas).

British Aerospace, and the NASA Ames Research Center. The fact

that the Douglas suppressor passed the tests 174 was important because

the other noise reduction techniques (i.e., coannular effects, noise

shielding, and advanced operating procedures) could not in themselves

bring the engine noise to desirable levels.

NOISE SHIELDING

The placement of two of the engines above the wing so that the wing

and fuselage could be used as a noise shield was an idea proposed by

Lockheed early in the SCR program. As pointed out earlier in this

chapter, this placement provided a substantial noise reduction of 3 to 5

EPNdB. However, the technology areas that this opened for further

study and data accumulation were just as important. The airflow patterns and pressures on the upper surface of a highly swept wing are

quite different than those on the lower surface where the engines had

146
PROGRESS IN TECHNOLOGY SINCE 1972

been placed in the past. The technical questions about whether the

aerodynamic design and analysis programs would handle this unconventional case and how this engine placement would affect inlet

design and operation, etc., had to be answered. This engine placement

would also probably make more of the wing trailing edge available for

controls, and this factor had to be considered. Thus, the desirable goal

of noise reduction led to disciplinary problems in aerodynamics and

design integration. _75

AIRPLANE FAMILY CONCEPT

One of the major strengths of the American airplane industry has

been the development of families of subsonic jet transports from a given

basic design by fuselage "stretching" or small evolutionary changes.

These airplane "families" have met the operating requirements of a

variety of airlines and route structures, and this approach has led to

large savings in costs to the manufacturers and airlines. A big weakness

of both the Concorde and U.S. SST programs was that each was essentially based on a "one airplane" effort. Because of the more critical

dependence of airplane resistance (drag) on airplane shape (area

distribution) in the supersonic flight regime, the practice of fuselage

stretching or lengthening did not appear to be feasible. In addition, it

was far too costly to develop and certify differently sized airplanes and

engines to meet the specific requirements of each of the airlines. As a

result of these factors, a "one-sized" Concorde was proposed to cap" are

the North Atlantic passenger traffic from the 120- to 140-passenger

Boeing 707 and Douglas DC-8 subsonic transports that were then

available. By the time the Concorde was in service, however, the competition on the North Atlantic had grown to include the 250- to

450-passenger "jumbo" jet aircraft, the Boeing 747, the Douglas

DC-10, and the Lockheed L-1011. The Concorde could not compete

with the productivity of these large aircraft even with a 2.5-times cruise

speed capability. A larger Concorde would have preserved the productivity advantages of the SST.

A breakthrough in the supersonic "airplane family" idea was turned

in by the Boeing mission integration team during the SCR program.

147
SUPERSONIC CRUISE TECHNOLOGY

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SUPERSONIC CRUISE TECHNOLOGY

As a means of increasing the marginal cruise efficiency of their deltawing reference airplane, the Boeing team considered the use of

wing/body blending to improve cruise aerodynamics. ,76 Blending provided a 16 percent increase in cruise lift/drag, 177 and the study indicated that a supersonic family of airplanes might be possible with the

use of lateral fuselage "stretch" rather than the longitudinal stretch that

had been employed in creating a subsonic "family." Preliminary results

showed that the lateral stretch provided large changes in passenger

capacity with relatively small changes in construction and performance

when compared to the original design. Before this approach could be

adopted, however, aerodynamic and structural validation would have

to be accomplished and emergency egress and safety problems would

have to be considered. The "proof of concept" studies were completed

with the use of Boeing "in-house" and SCR-supported manpower with

the result indicating the "lateral-stretch" concept to be feasible for either

blended or conventional wing/body structures. The results also suggest

that future supersonic airplanes can and should be designed as

members of a family. 178

The Boeing study of the "family" concept indicated that, by means of

fairly simple body inserts, supersonic transports can be evolved with

payload variations from 230 to 330 passengers and ranges from 3200 to

5200 nautical miles with essentially the same levels of aerodynamic efficiency. This important technology will allow the designer to match

various airline payload range requirements while keeping the expensive parts of the airplane unchanged. 179

LARGE-PAYLOAD SST CONCEPTS

Toward the end of the SCR program, Boeing conducted a study on

large-payload supersonic cruise airplanes that could compete with

future large double-decked subsonic airplanes. One of these was a large

supersonic transport with two decks that could fly from New York to

Paris with 500 passengers. Another concept that Boeing considered

made use of twin fuselages separated by the engine package. Initial

evaluation of this concept indicated the surprising result that perhaps a

60 percent increase in volume could be obtained at no cost in

150
PROGRESS IN TECHNOLOGY SINCE 1972

151
SUPERSONICCRUISETECHNOLOGY

/

/

152
PROGRESS IN TECHNOLOGY SINCE 1972

2_

153
SUPERSONIC CRUISE TECHNOLOGY

Large-payload, high-productivity concept proposed by Boeing-double-deck passenger

facilities (courtesy of Boeing).

aerodynamic efficiency. _8° These preliminary results, although exciting in their meaning to supersonic flight efficiency and productivity,

were not validated to the same depth as other elements of the SCR program because of the termination of the program.

OTHER TECHNICAL INNOVATIONS

A number of other important concepts were studied during the SCR

program and were brought to a greater state of technology readiness.

Among these were the use of active controls to suppress undesirable

aeroelastic deflections or vibrations without resorting to heavier, more

costly structural elements, 181and the use of active-control landing gear

to reduce the forces on the wing during landing impact. 182Both of these

concepts promised reductions in weight or improvements in fatigue

life. Another important concept developed by Boeing was a leadingedge flap that could control the vortex on the leading edge of highly

154
PROGRESS IN TECHNOLOGY SINCE 1972

_z

_.s

I

155
SUPERSONIC CRUISE TECHNOLOGY

/

/

A rtist's concept o[ twin-fuselage SS7_

swept arrow wings and prevent flow separation.Z83 This flap development was one of the principal elements leading to an improvement in

the low-speed lift/drag of arrow wings, one of the primary goals of the

SCR aerodynamic performance discipline.

SUMMARY OF PROGRESS

During the course of the NASA SCR and VCE programs

(1972-1981), substantial technical progress was made in all elements of

technolo_' relating to supersonic cruise flight, with the possible exception of sonic boom. (As mentioned earlier, the SCR program did not

have sufficient funding to determine the level of acceptability of sonic

boom, and an operating rule was in effect that forbade the supersonic

overland flight of commercial aircraft.) The science of technology integration was also advanced, and a number of new concepts were identified that could lead to acceptable, competitive supersonic transport

aircraft. In the next chapter an attempt is made to quantify the SCR

and VCE progress and to discuss the possible ramifications of this

progress.

156
CHAPTER 10

Supersonic Cruise Technology Before

(1971) and After (1982) the NASA

SCR and VCE Programs

Although much supersonic technology progress was made before

and.during the SST program (see Chapters 3 and 4), the cancellation

of that program in 1971 raised many questions about the status of

technology. The combined improvements and advances of several

decades of research were not sufficient to ensure a viable supersonic

transport. Both the Concorde and the proposed U.S. SST were

marginal from the standpoint of aerodynamic, propulsive, and structural efficiencies, and both were projected to have critical environmental problems in the areas of engine noise, pollution, and sonic boom.

No technology for solving these problems appeared to be on the

horizon, and as a result, the U.S. SST program was canceled and the

Concorde production program was severely curtailed.

Over the decade since the cancellation of the U.S. SST program, the

NASA SCR and VCE programs have had the responsibility of filling

this supersonic technology void and providing the base for a viable

supersonic transport. Some of the progress from this technology effort

was described in the previous chapter. This chapter will present quantitative comparisons of the technology progress and will discuss some of

the possible ramifications of the results.

157
SUPERSONIC CRUISE TECHNOLOGY

COMPARISONS

EMISSIONS

Most of the progress on engine emissions was made outside the SCR

and VCE programs, but it was still principally motivated by the questions that had arisen about the supersonic transport. The NASA Lewis

Research Center effort on burner technology provided practical

burners for SCR application that had nitrous oxide emission indices of

about one-half of those that existed at the end of the U.S. SST program. Conceptual burners were considered that can lead to emission

indices less than 20 percent of conventional burners.

NASA participated in studies for improving the understanding ot the

effect of engine emissions on the depletion of the protective ozone layer

in the atmosphere. Although this influence was largely unknown at the

close of the SST program, the DOT CIAP and the HAPP programs

have done much to answer the questions. Where the earlier CIAP and

National Academy of Sciences studies showed a substantial, but noncritical, depletion of ozone due to engine emissions, later HAPP studies

have shown that this effect might actually lead to a small increase in

ozone. This represents a rather dramatic reversal in tl-ie technical

understanding of the atmosphere, but it does not alter the fact that this

question should be a continuous subject of study.

ENGINE NOISE

As mentioned earlier, the only noise reduction technology available

at the end of the U.S. SST program was the use of large oversized

engines that resulted in extremely large performance losses by the proposed SST. These performance losses would prohibit the SST from

making a minimal North Atlantic mission. The SCR and VCE programs substantially improved this technical situation by identifying

and partially validating four methods of noise reduction: mechanical

suppression, noise shielding, coannular effects, and advanced

operating procedures. It is estimated that a combination of these effects

could be used on a current SST design to reduce the noise 10 to 12

158
BEFORE/AFTER SCR AND VCE PROGRAMS

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SUPERSONIC CRUISE TECHNOLOGY

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BEFORE/AFTER SCR AND VCE PROGRAMS

decibels (dB) below the levels expected of the U.S. SST concept.

Another 10-dB reduction would likely result from a continuing focused

research program on supersonic cruise aircraft over the next 8 to 10

years.

These identified noise reductions are quite dramatic and indicate

that the noise exposure levels for supersonic cruise vehicles can be comparable to their equivalent subsonic counterparts. _s4

AERODYNAMICS

At the close of the U.S. SST program in 1971, the cruise aerodynamic efficiency of the proposed airplane concept was marginal, and

no means were readily available for improving this efficiency. Concepts

such as the highly swept arrow wing provided the desirable cruise efficiency, but were aerodynamically deficient at low speeds. This

technical quandry has been somewhat alleviated by aerodynamic

research conducted by NASA and SCR contractors. Through the use

of wing/body blending, along with a slight strake extension, the cruise

aerodynamic efficiency of the delta-like SST configuration has been

improved by about 16 percent to come within 10 percent of the highly

swept arrow wing and 33 percent better than the Concorde. In addition, the SCR aerodynamics program identified flap arrangements that

produce a 16 percent improvement in the low-speed lift/drag of the arrow wing compared with 1971 levels when plain flaps were used. These

aerodynamic improvements have very favorable connotations for both

concepts.

STRUCTURES AND MATERIALS

As the U.S. SST program drew to a close in 1971, the proposed

airplane had an aeroelastic problem of serious magnitude, and this

problem was further compounded by a late decision to consider oversized engines for reducing noise. The proposed titanium structure was

acceptable, but the fabrication costs were expected to be high. Along

with improved methods for designing and assessing aeroelastic

characteristics, the NASA SCR program has provided some structural

161
SUPERSONIC CRUISE TECHNOLOGY

Relative

Noise

Levels,

(EPNdB)

Supersonic

_ (_71 U.S. SST

Subsonic _L_-=_ COncOrde

_ _ _,-Present Design

_ _ _ Advanced

_" Design

10dB _..,.__ (.._) _ ..,.,....

_ I

1960 1970 1980 1990

Year

Then and now noise status.

LID

Takeoff

Climb

(250 kn)

12

10

8

6

4

-- _ Delta

Wing _

n Plain No

Flap Flaps

1971 1971

Arrow Wing

I f

Plain

Flap

I

1971

_ Potential

I I I

Variable Vortex

Camber Flap

1 I

1979 1980

Then and now comparison of low-speed aerodynamic efficiency.

162
Aerodynamic

Cruise

Efficiency

Ratio

BEFORE/AFTER SCR AND VCE PROGRAMS

1.5

1.0

0.5

1.14

1.00/!_"" "" "" $ +

s

s

1.45

1.33 .-- ... -.- _ -- "-*

Concorde 1971 1977 Arrow

SST SST Wing

Then and now comparison of supersonic cruise efficiency.

concepts and fabrication processes that offer drastic reductions in the

weight and/or cost of supersonic structures. The superplastic forming

and concurrent diffusion bonding (SPF/DB) .of titanium, first proposed

by Rockwell International and then brought to a high state of

technology readiness by Douglas, offers a 25 percent reduction in

weight and a 33 percent reduction in cost when compared to conventional titanium plate. Further improvements developed by Douglas inelude the use of fiber-reinforced advanced titanium (FRAT) to provide

additional reductions in weight at some cost penalty. Weight reduction

is one of the most powerful means for improving the performance of an

airplane.

PROPULSION

The General Electric GE-4 afterburning turbojet engine that was

proposed for the U.S. SST was perhaps the best compromise that

technology could provide in 1971. It provided reasonably good supersonic performance and, with the use of afterburners, provided adequate thrust for takeoff and acceleration to cruise speed. Because it was

basically a turbojet engine, however, its performance at subsonic

163
1.0 --

0.8 --

0.6-

Relative

Weight

end Cost

Index

0.4 -

SUPERSONIC CRUISE TECHNOLOGY

0.2 -

o I

_ Weight

F'] Cost

O.75

I

I0.67

I

0.48

).76

m

0.84

0,35

Conventional SPF/DB 15% Fret 35% Fret

Titanium Trull Core SPF/DB SPF/DB

Plate Truss Core Truss Core

Concept Conflguretionl

Ben_'ts from SCR advanced structures and materials program.

speeds was only nominal. In addition, the use of the afterburner for

takeoff and climb implied noise levels that were well above the

108-EPNdB level established by the FAR 36 noise rule placed in effect

in 1969. The proposal to use an oversized GE-4 to reduce noise not

only created drastic problems in airplane integration, but would also

have led to performance degradations in the propulsion system.

Perhaps the most spectacular development of the SCR and VCE

programs was the replacement of the uncertain 1971 propulsion

technology with the "variable cycle engine" and the component

technologies for reduced noise and emissions. When compared to the

1971 GE-4, the VCE provides a 10 percent reduction in supersonic

cruise specific-fuel-consumption (sfc), a similar reduction in transonic

sfc, and a remarkable 24 percent reduction in the sfc at important subsonic speeds. Furthermore, the VCE provides this improved perform164
BEFORE/AFTER SCR AND VCE PROGRAMS

ance with a weight that is only 75 percent of that of the GE-4. This

represents a tremendous gain in propulsion technology, and

remember, many elements of the VCE were validated during the SCR

and VCE programs.

MISSION INTEGRATION

It is difficult to quantify the technology improvements in mission integration or the impact of the SCR concepts on technology for supersonic cruise flight. It is certain, however, that these systems integration

studies were responsible for many of the disciplinary technology advances, and concepts such as the "supersonic airplane family" offered

solutions to long-time questions.

POSSIBLE RAMIFICATIONS OF SCR AND VCE TECHNOLOGY

With no current effort in the United States involving the area of

supersonic cruise flight, there are no realistic projections for the use of

Rdctiv_ 0.8

Specific Fuel

Consumption

0.7

1 °0 B

0.9-

0.6-

0.5

Superlonlc

=_P_\ Tranlonlc

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Reletive

Weight

1971

GE4 _ 1.00

VCE _ 0.75

Improvements in propulsion as a result of SCR/VCE programs.

165
SUPERSONIC CRUISE TECHNOLOGY

166
BEFORE/AFTER SCR AND VCE PROGRAMS

SCR or VCE technology other than the isolated elements that will find

their way onto subsonic transports or on short-range supersonic

military aircraft. There is no military interest in supersonic cruise flight

in the true sense, and there appears to be little interest in this concept of

flight within the U.S. Government or the airplane industry. There are

sporadic bursts of activity on the possibility of using SCR and VCE

technology to develop a supersonic business jet transport,_a5 but there

is no way to assess the sincerity of these efforts. Certainly a large

amount of money would be required to develop such an airplane, and

it would almost assuredly have to come from private sources.

Although there are no present potential applications of the SCR and

VCE technology efforts, there are still possibilities for the development

of an outstanding supersonic transport. As mentioned earlier in this

chapter, the noise and emissions would be greatly reduced from prior

SST levels, and the technology advances in structures, aerodynamics,

and propulsion would lead to great improvements in range/payload

capability, fuel use, cost, and economics.

RANGE/PAYLOAD CAPABILITY

If we forget for a minute that the 1971 SST had perhaps unacceptable noise characteristics, it was to transport 280 passengers a distance

of 3600 nautical miles. With the use of SCR and VCE "airplane family"

technology, approximately 385 passengers could be transported the

3600-nautical-mile distance, a payload improvement of 37.5 percent.

Or, the 280-passenger payload of the 1971 SST could be transported a

distance of 4950 nautical miles with SCR and VCE technology, a

range improvement of 37.5 percent. In providing this 37.5 percent improvement in range/payload capability, the SCR/VCE technology

SST would burn only about one-half as much fuel per seat-mile as the

1971 SST.

ECONOMICS/PRODUCTIVITY

One means of measuring the economics of supersonic transports is to

determine the ticket surcharge that the supersonic passenger would

167
SUPERSONIC CRUISE TECHNOLOGY

Passengers

400

300

200-

1O0 -

O_l

0

1971 SST

I I

10(30 2000 3000

Still Air Range (n.rni.)

SCR/VCE SST Airplanenology

Concorde

_ e°_ _" e

4000 5000 6000

Rangepayload capability then (1971) and now (1982).

IOO0

Fuel per

Seat (Ib)

5OO

Concorde

0 3000 n. mi. Trip

U.S. SST Canceled

707-320

l-_C-10-30 SCR Studies

747 Stretch

747 Stretch, New Wing -_'_IJ All New

0 I- L t t J

1960 1970 1980 1990 2000

First Flight

Fuel-use trends as a result oJ SCR/VCE programs.

168
BEFORE/AFTERSCR AND VCE PROGRAMS

have to pay for the airline to make a return on investment equal to the

subsonic transport. For the 1971 SST, the required surcharge was

about 50 percent above the subsonic tourist rate. The SCR and VCE

technology would provide the basi* to drive this surcharge to nearly

zero. 186 The major reason for this, of course, is the fact that the SCR

and VCE programs have been able to restore speed to the productivity

equation at very little increase in total operating costs.

OTHER POSSIBLE RAMIFICATIONS

The NASA SCR and VCE technology could lead to supersonic

military-troop and equipment-moving transports that would give real

meaning to the term "rapid deployment forces." There is also some

possible application of the technology to the development of a supersonic missile carrier. 107

Now that the NASA SCR and VCE programs have identified solutions to some of the major problems of supersonic cruise flight, what is

the future course of the effort? The final chapter addresses this

question.

m

O Concorde 1981 Fuel Price

150-

Percent Economies of Scale

Surcharge \\ and High-Leverage

Over \\ Technology Advances

Sublonic 100-

Tourist

U.S. SST - W_

50 - Canceled Advanced SST

Equel RO, __"_-_-._k

0 1 1

1960 1980 200O

First Flight

Required ticket surcharge for supersonic travel.

169
Relative

Total

Operating 2

Cost/

Seat-Mile

n

1!-

0

1930

SUPERSONIC CRUISE TECHNOLOGY

\ %

\ %

\ • %

\ % Supersonic Aircraft

\

%.

...... ASUBT

Subsonic Aircraft

I I I I I I I I

1950 1970 1990 2010

Year of Introduction into Commercial Service

Projected operating cost of supersonic transport approaches that of advanced subsonics.

1 500 - Multibody O---_---

Productivity,

Seats X AST f_ Iii]

Cruise Speed_1000 Seat- Subs°_)eCkD°Ub'_ I"il]

Mile/Hour / Speed

500 - / and

jt Capecity

__C] 747 SR H

Ca_:crity 7_>-_CTConcorde _

Propeller Aircraft _ __" - "_ee"_--

0 - C.._.dC_j_._ Jet bnglne _j=

I I I J Swept Wing 1 _1 I

1920 1930 1940 1950 1960 1970 1980 Future

Introductory Year

Productivity history and projectionfor the long-rangeairline market.

170
CHAPTER II

Future Directions of Supersonic

Cruise Research

During the past decade, the NASA SCR and VCE programs have

identified technology that will meet many of the needs of future supersonic cruise aircraft. At a cost of about 7.5 cents per year for each

American, these programs have identified and validated many

elements of an important new engine concept--the variable cycle

engine; identified and partially validated four promising means of

noise reduction; built and tested a wide variety of wind tunnel models

to establish a comprehensive aerodynamic data base; promoted and

spread the technology of superplastic forming and bonding of titanium

from which grew the FRAT effort; answered the age-old problem of

SST sizing with the SST airplane family concept; developed two largepayload, high-productivity concepts that can compete with almost any

future airplane and may, because of their size, have sonic boom advantages; and promoted many improvements to the analytic methods for

structural design and analysis. Quite important also, the SCR and

VCE programs have kept a cadre of skilled, dedicated supersonic

specialists alive in the airplane industry. These teams, along with

NASA and other SCR and VCE contractors, were to continue to

validate the elements of supersonic cruise technology that had been

identified and coritinue highly focused programs for identifying even

more advanced technology. There were still "bugs" in the SPF/DB and

FRAT structural forming processes, and there were some areas of

uncertainty in almost every disciplinary field, as well as in the area of

concept integration. There were also fertile fields like sonic boom and

171
SUPERSONICCRUISE TECHNOLOGY

laminar flow at supersonic speeds that had to be reopened because of

the high potential payoff. And, of course, the focused nature of the program would bring further "breakthroughs" that could not be anticipated.

When this document was proposed in early 1981, the final chapter

was to outline the future course and milestones of the SCR and VCE

programs. Work had been initiated on the critical inlet configurations

that were to "feed" air to the variable cycle engines. In addition, wind

tunnel models were planned for determining the aerodynamic

characteristics of the large-payload twin-fuselage concept that was

under consideration, and the focused SCR and VCE programs were to

move forward in other areas. However, as a result of budget problems

in fiscal year 1982, NASA canceled the focused SCR and VCE programs. With the Soviet SST program in a stagnant state and no further

Concordes in sight, there appeared to be no clear and immediate need

for SCR technology and there was no clear expression of commercial

interest in the VCE program.

The cancellation of the NASA SCR and VCE programs has led to

the breakup of the industry teams that participated in the supersonic

cruise effort and has left the future status of supersonic cruise

technology in doubt. The NASA Lewis Research Center will probably

test the inlet hardware that has been prepared, and NASA will continue an effort in supersonic technology. However, this effort will not

provide a unified research attack on problems unique to supersonic aircraft and will not generate the interest and support of industry that a

focused program would.

172
FUTURE DIRECTIONS OF RESEARCH

_ _ u |

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SUPERSONIC CRUISE TECHNOLOGY

Important SCR/VCE inlet tests will be continued (courtesy of Boang).

Douglas inlet hardware for tests at NASA Lewis Research Center (courtesy of McDonnellDouglas).

174
References

1. National Aeronautics and Space Act of 1958, Public Law 85-568, 85th Congress,

H.R. 12575, July 29, 1958, p. 1.

2. Hallion, R., Supersonic Flight, The Macmillan Company, New York, 1972, p. 2.

3. Ibid, p. 1.

4. Dwiggins, D., The SST: Here It Comes Ready or Not, Doubleday & Company, Inc.,

Garden City, New York, 1968, p. 110.

5. Ibid., p. 110.

6. Ibid., p. 111.

7. Ibid., p. 111-112.

8. The Supersonic Transport-A Technical Surnmao_, NASA TM D-423, June, 1960,

p.l.

9. Comme*cial Supersonic Transport Aircraft Report, DOD/NASA/FAA, Washington, D.C., December 1960, p. 2.

10. Baals, D. D., and Corliss, W. R., Wind Tunnels of NASA, NASA SP-440, 1981.

11. Technical Facilities Catalog, NASA NHB 8800.5A (I), October 1974.

12. Dwiggins, D., op. cir., pp. 4-5.

13. Supersonic Transport Development Program, FAA, Washington, D.C., June

19, 1963.

14. Dwiggins, D., op. cir., p. 131.

15. Ibid., illustration 33.

16. Costello, J., and Hughes, T., The Concorde Conspiracy, Charles Scribner's Sons,

New York, 1976, pp. 147-151.

17. Ibid., illustration opposite p. 154.

18. Knight, G., Concorde: The Inside Stoop, Stein and Day, New York, 1976, p. 64.

19. Costello, J., and Hughes, T., op. tit., p. 188.

20. Ibid., p. 189.

21. Ibid., p. 189.

22. Ibid., p. 225.

23. Driver, C., Progress in Supersonic Cruise Technology, AIAA Paper 81-1687,

August 1981, p. 1.

24. Ibid., p. 5.

175
SUPERSONIC CRUISE TECHNOLOGY

25. Ibid., p. 5.

26. Hallion, R., 0p. cir., p. 13.

27. Ibid., pp. 17-18.

28. Ibid., p. 18+

29. Ibid., p. 21.

30. Ibid., p. 22+

31. Ibid., p. 22.

32. Ibid., p. 12.

33. Ibid., pp. 19-20.

34. Ibid., pp. 20-21.

35. Ibid., pp. 16-17.

36. Ibid., pp. 22-23.

37. Ibid., pp. 24-25.

38. Ibid., p. 23.

39. Ibid., p. 23.

40. Ibid., p. 24.

41. Ibid., pp. 26-27.

42. Ibid., p. 39.

43. Ibid., p. 42.

44. Ibid., p. 43.

45+ Ibid., p. 36.

46. Ibid., p. 42.

47. Ibid., p. 109.

48. Ibid., p. 109.

49. Ibid., p. 45.

50. Baals, D. D., and Corliss, W. R., op. cir., pp. 61-62.

51. Ibid., pp. 62-63.

52. Ibid., pp. 65-66.

53. Dwiggins, D., op. tit., p. 34.

54. Ibid., p. 109.

55. Ibid., p. 109.

56. Ibid., pp+ 109-110.

57. Ibid., p. 110.

58. Eggers, A. J., and Syvertson, C+ A., Aircraft Configurations Developing High

Lift-Drag Ratios at High Supersonic Speeds, NACA RM-A55105, 1955.

59. Dwiggins, D., 0p. tit., p. 108.

60. Ibid., pp. 110-111.

61. The Supersonic Transport--A Technical Summary, op. cit., p. 1.

62. Ibid., p. 1.

63. Commercial Supersonic Transport Aircraft Report, DOD/NASA/FAA, Washington, D.C., June 1961, p. ii.

64. Dwiggins, D., op. cir., p. 119.

176
REFERENCES

65. Proc. NASA Conference on Supersonic-Transport Feasibility Studies and Supporting Research, NASA T_| X-905, 1963.

66. Supersonic Transport Development Program, op. cit., p. 56.

67. Hayes, W. D., Linearized Supersonic Flow, North American Aviation, Inc., Report AL-222, June 18, 1947.

68. Jones, R. T., Estimated Lift-Drag Ratios at Supersonic Speed, NACA TN 1350,

July 1947.

69. Whitman, G. B., The Flow Pattern of a Supersonic Projectile, Cornmun Pure

Appl. Math., Vol. V, No. 3, Aug. 1952, pp. 301-348.

70. Hayes, W. D., op. cir.

71. Hayes, W. D., Haefeli, R. C., and Kulsrud, H. E., Sonic Boom Propagation in

a Stratified Atmosphere, with Computer Program, NASA CR-1299, 1969.

72. Dwiggins, D., op. cit., p. 189.

73. Ibid., p. 188.

74. Office of Technology Assessment, Impact of Advanced Air Transport Technology, Part 1: Advanced High-Speed Aircraft, OTA-T-112, April 1980, p. 31.

75. Ibid., p. 31.

76. Dwiggins, D., op. tit., p. 213.

77. Ibid., p. 213.

78. Anon., TU-144: 1965-1978, Flight International, Sept. 30, 1978, p. 1230.

79. Ibid., pp. 1229-1230.

80. Ibid., p. 1230.

81. Ibid., p. 1230.

82. Ibzd., p. 1230.

83. Anon., Aviation Daily, Vol. 207, No. 36, June 20, 1973, p. 281.

84. Dwiggins, D., op. cir., pp. 199-200.

85. Costello, J., and Hughes, T., op. cir., p. 25.

86. Ibid., pp. 26-27.

87. Ibid., pp. 27-28.

88. Ibid., p. 39.

89. Ibid., pp. 51-52.

90. Dwiggins, D., op. tit., p. 202.

91. Ibid., pp. 203-204.

92. Costello, J., and Hughes, T., op. cit., p. 97.

93. Office of Technology Assessment, op. cir., p. 27.

94. 1bid., pp. 27-28.

95. Gillman, P., Supersonic Bust: The Story of the Concorde, Atlantic, Vol. 239,

Jan. 1977, pp. 72-81.

96. Melville, F., The Concorde's Disastrous Economics, Fortune, Jan. 30, 1978, p. 67.

97. Leyman, C. S., Concorde with the Airlines, Supersonic Cruise Research '79, NASA

CP-2108, Part 2, 1980, pp. 714-757.

98. Office of Technology Assessment, op. cit., p. 28.

177
SUPERSONIC CRUISE TECHNOLOGY

99. Knight, G., op. tit., p. 167.

100. Dwiggins, D., op. cit., p. 148.

101. Ibid., p. 224.

102. Ibid., p. 26.

103. Ibid., p. 34.

104. Ibid., p. 33.

105. Ibid., p. 33.

106. Costello, ,]., and Hughes, T., op. cir., p. 144.

107. Hallion, R., op. cir., pp. 15-16.

108. Office of Technology Assessment, op. cir., p. 31.

109. Lynch, D. M., Barriers to Innovation in Transportation." A Case Study of the SST,

Massachusetts Institute of Technology, 1975, p. 83.

110. Ibid., p. 89.

111. Dwiggins, D., op. tit., p. xv.

112. Ibid., p. xv.

113. Lynch, D. M., op. cir., p. 86.

114. Costello, J., and Hughes, T., op. cir., p. 278.

115. Dwiggins, D., op. cir., p. 163.

116. Lynch, D. M., op. cir., p. 75.

117. Ibid., p. 75-76.

118. Ibid., p. 76.

119. Carlson, H. W., and McLean, F. E., The Sonic Boom, International Science and

Technology, July 1966, p. 70.

120. Office of Technology Assessment, op. tit., p. 88.

121. Lynch, D. M., op. cir., p. 51.

122. McLean, F. E., Some Nonasymtotic Effects on the Sonic Boom of Large Airplanes, NASA TN D-2877, June 1965.

123. Office of Technology Assessment, op. cit., p. 89.

124. Grobecker, A. J., Coroniti, S. C., and Cannon, R. H., Jr., The Effects of Stratospheric Pollution by Aircraft, DOT-TST-75-50, December 1974.

125. Broderick, A. J., Stratospheric Effects from Aviation, AIAA Paper 77-799, July

1977.

126. Office of Technology Assessment, op. cit., p. 90.

127. Lynch, D. M., op. cir., p. 60.

128. Magruder, W. M., The SSTand the National Interest (SST White Paper), Department of Transportation, Feb. 1971.

129. Ibid., figure G-10-300-7/10/70.

130. Office of Technology Assessment, op. cir., p. 3.

131. Hoffman, S., and Varholic, M. C., Contracts, Grants and Funding Summary of

Supersonic Cruise Research and Variable-Cycle Engine Technology Programs,

1972-1982, NASA TM-85650, 1983.

178
REFERENCES

132. Hoffman, S., Bibliography of Supersonic Cruise Aircraft Research (SCAR) Program from 1972 to Mid-1977, NASA RP-1003, 1977.

133. Hoffman, S., Bibliography of Supersonic Cruise Research (SCR) Program from

1977 to Mid-1980, NASA RP-1063, 1980.

134. Sigalla, A., Overview of Boeing Supersonic Transport Efforts--1971-1979,

Supersonic Cruise Research 79, NASA CP-2108, Part 2, 1980, pp. 826-827.

135. Duerr, R. A., and Diehl, L. A., Advanced Technology for Controlling Pollutant

Emissions from Supersonic Cruise Aircraft, Supersonic Cruise Research 79, NASA

CP-2108, Part 1, pp. 535-549.

136. Driver, C., op. cir.

137. Sundararaman, N., Environmental Effects of Aircraft at Cruise: An Update,

Supersonic Cruise Research 79, NASA CP-2108, Part 1, 1980, p. 523.

138. Duerr, R. A., and Diehl, L. A., op. cir.

139. Driver, C., op. cir., p. 3.

140. Ibid., p. 3_

141. Ibid., p. 3.

142. FitzSimmons, R. D., McKinnon, R. A., and Johnson, E. S., Flight and Tunnel

Test Results of the MDC Mechanical Jet Noise Suppressor Nozzle, Supersonic

Cruise Research 79, NASA CP-2108, Part 1, 1980, p. 453.

143. Wright, B. R., Sedgwick, T. A., and Uric, D. M., An Advanced Concept that

Promises Ecological and Economic Viability, Pr0¢. SCAR Conference, NASA

CP-001, Part 2, 1976, p. 946.

144. Driver, C., op. cir., p. 3.

145. Driver, C., and Maglieri, D. J., Some Unique Characteristics of Supersonic

Cruise Vehicles and Their Effect on Airport Community Noise, AIAA Paper

80-0859, May 1980.

146. Albers, J. A., and Olinger, F. V., YF-12 Propulsion Research Program and Results, Proc. SCAR Conference, NASA CP-001, Part 1, 1976, pp. 417-456.

147. Grantham, W. D., and Smith, P. M., Development of SCR Aircraft Takeoff and

Landing Procedures for Community Noise Abatement and Their Impact on

Flight Safety, Supersonic Cruise Research '79, NASA CP-2108, Part 1, 1980, pp.

299-333.

148. Carlson, H. W., and Mack, R. J., Estimation of Leading-Edge Thrust for

Supersonic Wings of Arbitrary Planform, NASA TP-1270, 1978.

149. Manro, M. E., Bobbitt, P.J., and Kulfan, R. M., The Prediction of Pressure

Distributions on an Arrow-Wing Configuration Including the Effect of Camber,

Twist, and a Wing Fin, Supersonic Cruise Research '79, NASA CP-2108, Part 1,

1980, p. 72.

150. Robins, A. W., Carlson, H. W., and Mack, R. J., Supersonic Wings with Significant Leading-Edge Thrust at Cruise, Supersonic Cruise Research '79, NASA

CP-2108, Part 1, 1980, pp. 229-246,

179
SUPERSONIC CRUISE TECHNOLOGY

151. Roensch+ R. L., and Page, G. S., Analytic Development ofan Improved Supersonic Cruise Aircraft Based on Wind Tunnel Data, Supersonic Cruise Research '79,

NASA CP-2108, Part 1, 1980, pp. 205-227.

152. Bower, R. E., Introductory Remarks, Supersonic Cruise Research 79, NASA

CP-2108, Part 1, 1980, pp. 9-12.

153. Coe, P. L., Jr., Thomas, J. L., Huffman, J. K., Weston, R. P., Schoonover,

W. E., Jr., and Gentry, G. L., Jr., Overview of the Langley Subsonic Research

Effort on SCR Configurations, Supersonic Cruise Research 79, NASA CP-2108,

Part 1, 1980, pp. 13-33.

154. Coe, P. L., Jr., Smith, P. M., and Parlett, L. P., Low-Speed Wind Tunnel Investigation of an Advanced Supersonic Cruise Arrow-Wing Configuration,

NASA TM-74043, 1977.

155. Coe, P. L., Jr., Huffman, ,J. K., and Fenbert,.J.W., Leading-Edge Deflection

Optimization tor a Highly Swept Arrow Wing Configuration, NASA TP-1777,

1980.

156. Sigalla, A., op. cir., p. 831.

157. Heldenfels, R. R., Introductory Remarks, Supersonic Cruise Research '79, NASA

CP-2108, Part 2, 1980, pp. 553-561.

158. Morino, L., and Tseng, K., Steady, Oscillator' and Unsteady, Subsonic and

Supersonic Aerodynamics (SOUSSA) for Complex Aircraft Configurations,

AGARD CP-227, 1978, pp. 3-1-3-14.

159. Stroud, W. J., and Sobieszczanski, J., Advanced Structural Sizing Methodology,

Proc. NASA CTOL Transport Technology Conference, Hampton, Virginia, Feb.

28-March 3, 1978, NASA CP-2036, Part I, pp. 311-330.

160. Heldenfels, R. R., op. cir., p. 553.

161. Haskins, J. F., Kerr,J. R., and Stein, B. A., Time-Temperature-Stress Capabilities of Composites for Supersonic Cruise Aircraft Applications, Proc. SCAR Conference, NASA CP-001, Part 2, 1976, pp. 799-828.

162. Fischler, J. E., Opportunities for Structural Improvements for an Advanced

Supersonic Transport Vehicle, Supersonic Cruise Research '79, NASA CP-2108,

Part 2, 1980, pp. 589-616.

163. Ascani, L. A., and Pulley, J. K., New Advancements in Titanium Technology

and Their Cost and Weight Benefits, Proc. SCAR Conference, NASA CP-001, Part

2, 1976, pp. 757-782.

164. Driver, C., op. cir., p. 2.

165. Ibid., p. 2.

166. Bales, T. T., Hoffman, E. L., Payne, L., and Reardon, L. F., Fabrication

Development and Evaluation of Advanced Titanium and Composite Structural

Panels, NASA TP-1616, 1980.

167. Heldenfels, R. R., op. cit+, p. 555.

168. Ibid., p. 555.

169. Sigalla, A., op. cir., p. 824.

180
REFERENCES

170. Stewart, W. L., Introduction, Proc. SCAR Conference, NASA CP-001, Part 1,

1976, p. 338.

171. Sigalla, A., op. tit., p. 823.

172. Driver, C., op. cit., p. 2.

173. Ibid., p. 3.

174. FitzSimmons, R. D., McKinnon, R. A., and Johnson, E. S., Flight and Wind

Tunnel Test ResuLts of a Mechanical Jet Noise Suppressor Nozzle, AIAA Paper

80-0165, 1980.

175. Wright, B. R+, Sedgwick, T. A., and Uric, D. M., op. cir., pp. 939-984.

176. Neumann, F. D., Toward a Second Generation Fuel Efficient Supersonic Cruise

Aircraft: Design Characteristics and Feasibility, Proc. SCAR Conjerence, NASA

CP-001, Part 2, 1976, pp. 849-866.

177. Sigalla, A., op. cir., p. 831.

178. Neumann, F. D., and Whitten, J. W., A Family of Supersonic AirplanesTechnical and Economic Feasibility, Supersonic Cruise Research 79, NASA CP-2108,

Part 2, 1980, pp. 833-854.

179. Driver, C., op. cir., p, 4.

180. Ibid., p. 4.

181. Doggett, R. V., Jr., and Townsend, J. L., Flutter Suppression by Active Control

and Its Benefits, Proe. SCAR Conference, NASA CP-001, Part 1, 1976,

pp. 303-333.

182. Goetz, R. C., Loads Technology for Supersonic Cruise Aircraft, Proc. SCAR Conference, NASA CP-001, Part 2, 1976, pp. 692-693.

183. Runyan, L. J., Middleton, W. D., and Paulson, J. A., Wind Tunnel Test Results of a New Leading Edge Flap Design for Highly Swept Wings--A Vortex

Flap, Supersonic Cruise Research '79, NASA CP-2108, Part 1, 1980, pp. 131-147.

184. Driver, C., and Maglieri, D. J., op. tit.

185. Kelly, R., Supersonic Cruise Vehicle Research/Business Jet, Supersonic Cru+se Research '79, NASA CP-2108, Part 2, 1980, pp. 935-949.

186. Driver, C., op. cit., p. 4.

187. Ibid., p. 5.

181

Selected Additional Reading

AERODYNAMICS

Brown, C. E., and McLean, F. E., The Problem of Obtaining High Lift-Drag Ratio at

Supersonic Speeds, Jour, Aero. Sci., Vol. 26, No. 5, May 1959.

Brown C. E., McLean, F. E., and Klunker, E. B., Theoretical and Experimental

Studies of Cambered and Twisted Wings Optimized for Flight at Supersonic

Speeds, Proc. of Second International Congress of the Aeronautical Sciences, Vol. 3,

Sept. 1960, pp. 4.15-431.

Carlson, H. W., A Modification to Linearized Theory for Prediction of Pressure Loading_ on Lifting Surfaces at High Supersonic Mach Numbers and Large Angles of

Attack, NASA TP-1406, 1979.

Carlson, H. W., and Middleton, W. D., A Numerical Method for the Design of

Camber Surfaces of Supersonic Wings with Arbitrary Planform, NASA TN

D-2341, 1964.

Dollyhigh, S. M., Theoretical Evaluation of High Speed Aerodynamics for Arrow

Wing Configurations, NASA TP-1358, 1979.

Jones, R. T., Wing Plan Forms for High-Speed Flight, NACA TN-1033,

March 1946.

Kulfan, R. M., and Sigalla, A., Real Flow Limitations in Supersonic Airplane Design,

AIAA Paper 78-147, .]an. 1978.

McLemore, H. C., and Parlett, L. P., Low Speed Wind Tunnel Tests of a 1/10 Scale

Model of a Blended-Arrow Supersonic Cruise Aircraft, NASA TN D-8410, 1977.

"An essentially complete listing of formal reports, contractor reports, articles, meeting

papers, and company reports related to and sponsored by the NASA SCR and VCE

programs can be found in NASA RP-1003 (1977) and NASA RP-1063 (1980), by

Sherwood Hoffman.

183
SUPERSONIC CRUISE TECHNOLOGY

Sears, W. R., Aerodynamics, Noise, and the Sonic Boom, AIAAJour., Vol. 7, No. 4,

April 1969.

Shrout, B. L., and Fournier, R. H., Aerodynamic Characteristics of a Supersonic

Cruise Airplane Configuration at Mach Numbers of 2.30, 2.96, and 3.30, NASA

TM-78792, 1979.

ENVIRONMENT (NOISE, SONIC BOOM, AND POLLUTION)

Carlson, H. W., Barger, R. L., and Mack, R. J., Application of Sonic-Boom

Minimization Concepts in Supersonic Transport Design, NASA TN D-7218,

June 1973.

Diehl, L. A., Reck, G. M., Marek, C. J., and Szaniszlo, A. J., Stratospheric Cruise

Emission Reduction Program, NASA CP-2021, 1977, pp. 357-391.

Goodykoontz, J., Effect of a Semi-Annular Thermal Acoustic Shield on Jet Exhaust

Noise, NASA TM-81615, 1980.

Goodykoontz, J., and Von Glahn, U., Noise Suppression Due to Annulus Shaping of

an Inverted-Velocity-Profile Coaxial Nozzle, NASA TM-81460, 1980.

Knott, P. R., Brausch,J. F., Bhutiani, P. K., Majjigi, R. K., and Doyle, V. L., VCE

• Early Acoustic Test Results of General Electric's High Radius Ratio Coannular

Plug Nozzle, Supersonic Cruise Research 79, NASA CP-2108, Part 1, 1980,

pp. 417-452.

Maglieri, D.J., Carlson, H. W., and Hubbard, H. H., Status of Knowledge on Sonic

Booms, NASA TM-80113, 1979.

McLean, F. E., Carlson, H. W., and Hunton, L. W., Sonic Boom Characteristics of

Proposed Supersonic and Hypersonic Airplanes, NASA TN D-3587, Sept. 1966.

NASA Conferences on Sonic Boom Research, NASA SP-147, April 12, 1967; NASA SP-180,

May 9-10, 1968; and NASA SP-255, Oct. 29-30, 1971.

Poppoff, I. G., Whitten, R. C., Turco, R. P., and Capone, L. A., An Assessment of

the Effect of Supersonic Aircraft Operations on the Stratospheric Ozone Content,

NASA RP-1026, 1978.

Proc. of Sonic Boom Symposium, Jour. Acoust Soc. America, Vol. 39, No. 5, Part 2,

May 1966.

Proc. of Sonic Boom Symposium, ,]our. Acoust. Soc. America, Vol. 51, No. 2, Part 3,

Feb. 1972.

Turco, R. P., Toon, O. B., Pollack, J. B., Whitten, R. C., Poppoff, I. G., and

Hamill, P., Stratospheric Aerosol Modification by Supersonic Transport and

Space Shuttle Operations-Climate Implications,,]0ur. Appl. Meteorol., Vol. 19,

No. 1, Jan. 1980, pp. 78-89.

184
SELECTED ADDITIONAL READING

PROPULSION

Calder, P. H., and Gupta, P. C., Engine Options for Supersonic Cruise Aircraft,

AIAA Paper 78-1054, July 1978.

Cole, G. L., Atmospheric Effects on Inlets for Supersonic Cruise Aircraft, NASA TM

X-73647, 1977.

Fishbach, L. H., Stitt, L. E., Stone,J. R., and Whitlow,J. B.,Jr., NASA Research in

Supersonic Propulsion: A Decade of Progress, NASA TM-82862, 1982.

Franciscus, L. C., The Turbine Bypass Engine--A New Supersonic Cruise Research

Propulsion Concept, A1AA Paper 81-1596, 1981.

Howlett, R. A., and Smith, M. G., Jr., Advanced Supersonic Transport Propulsion

Systems, SAE Paper 771010, Nov. 1977.

Johnson, H. W., and Conrad, E. W., NASA Engine Systems Technology Programs:

An Overview, AIAA Paper 79-928, July 1978.

Krebs, J. N., and Allan, R. D., Supersonic Propulsion-- 1970 to 1977, AIAA Paper

77-832, July 1977.

Westmoreland, J. S., and Packman, A. B., A Successful Step Toward an Advanced

Supersonic Transport Engine--Acoustic and Emissions Results from the Pratt

and Whitney Aircraft Variable Cycle Engine Program, AIAA Paper 81-1593, July

1981.

STABILITY AND CONTROL

Averett, B. T., Simulator Investigation of Arrow-Wing Low-Speed Handling

Qualities, Supersonic Cruise Research '79, NASA CP-2108, Part 1, 1980, pp.

285-298.

Berry, D. T., A Summary of YF-12 Handling Qualities, NASA CP-2054, Vol. II,

1978, pp. 31-57.

Chalk, Charles R., Flying Qualities Design Criteria Applicable to Supersonic Cruise

Aircraft, Supersonic Cruise Research '79, CP-2108, Part 1, 1980, pp. 251-267.

Gilyard, G. B., and Burken, J. J., Development and Flight Test Results of an Autothrottle Control System at Mach 3 Cruise, NASA TP-1621, 1980.

McGehee, J. R., and Dreher, R. C., Experimental Investigation of Active Loads Control for Aircraft Landing Gear, NASA TP-2042, Aug. 1982.

Rezek, T. W., Pilot Workload Measurement and Experience on Supersonic Cruise

Aircraft, NASA CP-2054, Vol. I, 1978.

185
SUPERSONIC CRUISE TECHNOLOGY

STRUCTURES AND MATERIALS

Adelman, H. M., Sawyer, P. L., and Shore, C. P., Optimum Design of Structures at

Elevated Temperatures, AIAAJour., Vol. 17, No. 6, June 1979, pp. 622-629.

Bales, T. T., SPF/DB Titanium Technology, NASA CP-2160, 1980.

Boeing Commercial Airplane Co., Study of Advanced Composite Structural Design

Concepts for an Arrow Wing Supersonic Cruise Configuration, NASA

CR-145192, 1978.

Del Mundo, A. R., McQuilkin, F. T., and Rivas, R. R., SPF/DB Primary Structure

for Supersonic Aircraft (T-38 Horizontal Stabilizer), NASA CR-163114, 1981.

Greene, W. H., and Sobieski, J. S., Minimum Mass Sizing of a Large Low-Aspect

Ratio Airframe for Flutter-Free Performance, NASA TM-81818, 1980.

Guess, M. K., Kaneko, R. S., and Wald, G. G., Advanced Materials and Fabrication

Processes for Supersonic Cruise Aircraft, Supersonic Cruise Research 79, NASA

CP-2108, Part 2, 1980, pp. 687-712.

Haftka, R. T., and Shore, C. P., Approximate Methods for Combined Thermal/

Structural Design, NASA TP-1428, 1979.

Payne, L., Fabrication and Evaluation of Advanced Titanium Structural Panels for

Supersonic Cruise Aircraft, NASA CR-2744, 1977.

SYSTEMS INTEGRATION/CONCEPTS

Brown, R., Integration of a Variable Cycle Engine Concept in a Supersonic Cruise

Aircraft, AIAA Paper 78-1049, July 1978.

Chacksfield, J. E., Arrow Wing- Its Potentialities and Drawbacks with Regard to InFlight Aerodynamic Research, Aircraft Eng., Vol. 49, No. 8, Aug. 1977, pp. 4-8.

Driver, C., Advanced Supersonic Technology and Its Implications for the Future,

AIAA Paper 79-0694, March 1979.

FitzSimmons, R. D., The Advanced Supersonic Transport: What It Is and How It

Compares, Acta Astronaut., Vol. 4, No. 1-2, Jam-Feb. 1977, pp. 131-143.

FitzSimmons, R. D., Technology Readiness for an SST, AIAA Paper 78-356,

Feb. 1978.

FitzSimmons, R. D., Rowe, W. T., and Johnson, E. S., Advanced Supersonic Transport Engine Integration Studies for Near-Term Technology Readiness Date,

AIAA Paper 78-1052, July 1978.

Goodmanson, L. T., and Sigalla, The Next SST-What Will It Be?, AIAA Paper

77-797, July 1977.

Horwitch, M., Clipped Wings-The American SST Conflict, The MIT Press,

Cambridge, Mass., 1982.

Maglieri, D. J., and Dollyhigh, S. M., We Have Just Begun to Create Efficient Transport Aircraft, Astronaut. Aeron., Feb. 1982, pp. 26-38.

186
SELECTED ADDITIONAL READING

Radkey, R. L., Welge, H. R., and Roensch, R. L., Aerodynamic Design of a Mach

2.2 Supersonic Cruise Aircraft, Jour. Aircraft, Vol. 15, No. 6, June 1978,

pp. 351-357.

Rowe, W. T., Technology Development Status at McDonnell Douglas, Supersonic

Cruise Research 79, CP-2108, Part 2, 1980, pp. 873-888.

187

About the Author

F. Edward McLean went to work at NACA as an aerospace

technologist in 1948, only 8 months after Charles E. Yeager's historic

supersonic flight. McLean was involved in supersonic research from

that time until his retirement in 1978. His major contributions were in

the areas of supersonic airplane design and sonic boom. He was a

technical advisor in the Federal Aviation Administration's SST evaluations and was NASA representative to the U.S. Air Force during the

development of the F-15 fighter aircraft. McLean was an original

member of the SCR Program Office at the NASA Langley Research

Center, and was head of the office from 1974 until his retirement.

Among his many honors were the NASA Special Service Award for Exceptional Service in 1967 for his application of"near-field" technology

to the reduction of sonic boom and the NASA Exceptional Service

Medal in 1978 for his conduct of the NASA SCR program.

189