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									                Civil Aero Gas Turbines: Technology & Strategy

This paper is an update of an earlier paper, “Fifty Years of Civil Aero Gas Turbines”, which was
presented as part of the celebration of Cranfield University‟s Fiftieth Anniversary. The lecture, after
briefly reviewing the early years, discusses the nature of this industry. Some of the technology drivers,
including environmental concerns, are examined to provide a background against which the
development and the future of the industry is discussed. This is followed by a brief survey of some of
the possible new civil aero gas turbine applications over the next fifty years, both the very likely and
some others. Finally, the changes that are likely to occur within the industry as a result of wider
economic and political trends are considered, as well as the implications for those working within the
industry. The development of the civil aero gas turbine has contributed in large measure to today‟s
very large civil aviation industry and is rightly seen as one of mankind‟s major engineering
achievements. A single paper cannot do justice to this industry.

1. Introduction                                           2. The Early Years
The last sixty years have seen enormous                   Civil aviation has grown because of the invention,
achievements in the field of gas turbines,                innovations and development of the gas turbine.
covering technology, design and manufacturing,            The underlying principles of the gas turbine were
which have advanced the state of the art not only         described in British Patent Number 1833 "A
for gas turbines but also for many related                Method for Rising Inflammable Air for the
industries and products. Gas turbine technology           Purposes of Producing Motion and Facilitating
continues to be at the forefront of mechanical and        Metallurgical Operations". This patent was taken
aero technologies, materials and coatings,                out by John Barber in 1791, about the time of the
production and manufacturing science. The                 French Revolution. It took some 150 years before
efforts of some of the world's most successful            the principles described by Barber were turned
corporations and most respected engineers over            into products by Frank Whittle and others,
the last six decades have placed this industry            illustrating how wide the gap often is between an
where it is rightly seen as one of mankind's major        idea and a working prototype.
engineering achievements.
                                                          Prior to Frank Whittle's work, many attempts had
Gas turbines dominate the field of both military          been made to demonstrate a gas turbine
and civil aviation, are extensively used in naval         producing positive power. Among these was the
ships, are the major prime movers for onshore             attempt of the Norwegian, Aegidius Elling (1903),
and particularly for offshore exploration and             whose machine had a rotor design similar to that
production of oil and gas. More recently, gas             of Sir Frank Whittle. The German, Stolze (1900-
turbines have become increasingly important in            1904) had a gas turbine which incorporated a
both combined heat and power and combined                 multi-stage axial compressor and a multi-stage
cycle power generation applications. Gas                  axial turbine, but the machine apparently never
turbines are able to use the widest possible              rotated without external power. The German,
range of fuels from low heating value gases to            Holzwarth (1906-1908) had a two-stage Curtis
coal, producing the lowest levels of pollutant            turbine built by the Swiss, Koerting (1903-1913).
emissions. Their range of application is too wide         The French, Armengaud and Lemale (1903-
to list here, and continues to grow.                      1905) had an internal combustion gas turbine
                                                          which had a radial compressor and a single stage
To review the last sixty years of civil aero gas          impulse turbine wheel. This project apparently did
turbines in a brief paper, is an unrealistic              result in excess power, but also included the
ambition. It is inevitable, therefore, that many          injection of steam. The project was abandoned in
important developments and advances will be               1909 when Armengaud died. The American,
missed or inadequately dealt with in this paper.          Stanford Moss (1903-1904) had a design very
However, whichever aspect of gas turbine                  similar to those of the French. This project was
technology and business is viewed, a vibrant and          also abandoned. During this period, a number of
rich contribution is uncovered. Civil aviation has        patents were registered, and a considerable
made our lives richer by creating opportunities for       experimental activity was under way. It was the
trade and access to the fruits of other cultures.

Norwegian, Elling, who is credited with having             FIGURE 2 - SIR FRANK WHITTLE BY HIS W2/700
run in 1903 the world's first gas turbine to give              ENGINE AT CRANFIELD UNIVERSITY
excess power.

          FIGURE 1 - ELLING‟S ROTOR 1903

                                                           The magnitude of his achievement can perhaps
                                                           be appreciated by recognising that the world's
                                                           three major "Prime manufacturers" of gas
These early attempts, though important in the
                                                           turbines, namely Rolls-Royce, Pratt and Whitney
subsequent successful development of the gas
                                                           and General Electric all started their gas turbine
turbine, failed to establish an industry. The gas
                                                           business based on Whittle's W2/700 gas turbine.
turbine industry today is over sixty years old and
                                                           The W2/700 was used by Rolls-Royce to launch
many see it as a "sunset industry". It will later be
                                                           the Welland, which was followed by the Derwent,
argued that the gas turbine "revolution"
                                                           Nene and Tay. Pratt and Whitney entered gas
                                                           turbines soon after the Second World War, using
                                                           the Rolls-Royce Nene to form the basis of their
The gas turbine is one of three major "prime
                                                           J42. General Electric's first gas turbine, the 1-A,
movers", the others being steam turbines and
                                                           from which the J31 was derived, was based
piston engines. Nearly all industrial activity and
                                                           directly upon Whittle's W2/700 gas turbine.
transportation relies on power from prime
                                                           Whittle's early simple engine eventually resulted
movers. The inherent high power to weight ratios
                                                           in today's large and complex industry. Indeed,
available from gas turbines ensured that gas
                                                           Whittle recalls showing Lord Hives, of Rolls-
turbines would first find their niche and then gain
                                                           Royce, his engine and stressing the simplicity of
supremacy in aerospace applications.
                                                           his engine, only to hear Lord Hives comment:
                                                           "We'll soon design the bloody simplicity out of it!"
Sir Frank Whittle, born in 1907, already as a
young man in the 1920s had the vision of aircraft
flying above the weather. This vision led him to           3. The Nature of the Industry
the jet engine, a variant of the gas turbine. Frank        The launch of a large civil gas turbine requires
Whittle took out his patent, British Patent No.            between US$ 500 million - 2500 million. The
347,206 in January 1930. Whittle's first jet engine        cumulative cash flow becomes positive typically
ran on 12th April 1937. Whittle was then just 30           between 15 and 25 years after the initial
years old. Whittle combined scientific genius with         investment. The risks are so large that many
engineering talent and great design insight.               famous engineering companies have either not
These characteristics gave him the confidence to           survived or had to become absorbed into other
persist in the face of opposition and lack of              larger surviving gas turbine companies. In the
recognition. Another of Whittle's undoubted                United Kingdom, companies such as Blackburn,
strengths was his training and education. Whittle          Napier, Bristol, Armstrong-Siddeley and De
himself says that: "I must point out that a factor         Havilland, all proud engineering names, have not
which contributed greatly to the work has been             survived as independent gas turbine companies,
the very fine training I have received in the Royal        though many of them are part of today's Rolls-
Air Force. Of my 21½ years service, I have spent           Royce. One may well ask, why do major
ten years under training, mostly engineering. In           corporations take such long-term risks and
this, I regard myself as having been very                  exposure, and why do some of the world's best
fortunate, and I hope that the outcome will do             engineers and managers put their own
something to suggest that such a degree of                 reputations, and that of their organisations, in
training should not be as exceptional in the future        potential jeopardy?
as in the present."

                                     FIGURE 3 - BUSINESS CASE - ENTRY INTO                                                                 FIGURE 4 - THE MARKET FOR POWER SYSTEMS
                                         LARGE AERO ENGINE SECTOR                                                                                  (Estimated Global Market Sizes 1991-2000 (US $Bn)
                                                                                                                                                                                                                                           Excluding Nuclear
                                         EXCLUDES:                                                                                                                                                                        550                   & Hydro
                      2000                                                                                                               1000
                                         . LEARNER                                                                                                                                                                                       250

                                                                                                                  US$Bn OVER 10 YEARS:
                                                                                                                  LOGARITHMIC SCALE
                      1500                                                                                                                            169
                                         . FACILITIES INVESTMENT                                                                                                   76

                                                                                                                                          100     C                                                                   P
                      1000               . WORKING CAPITAL                                                                                                                                                            O
                                                                                                                                                  I                                          Naval                                   A
                                                                                                                                                               M                                                      W
                                         . SALES & MARKETING SPEND                                                                                V
                                                                                                                                                                                  15         Prop‟n                   E
                                                                                                                                                  I            I                                                                     S
                       500                                                                                                                                                                                            R
                                         . PRODUCT SUPPORT ORGANISATION                                                                           L            L
                                                                                                                                          10                                                                          G
                        0                                                                                                                         A            A              H                                       E              D
                                                                           s                                                                                                  E                                       N
                                                                    t Sale                                                                        E            E                               2            2                        I
                                R&                            e Par                                                                               R            R              L                                                      S
                      -500           D      Engine Sales Spar                                                                                     O            O              O                                                      T
                                                                     AFTER 8                                                               1








                                                                                                                Hence, other markets such as naval propulsion,
Besides the obvious importance of gas turbines                                                                  oil and gas, and power generation are business
for military applications, the total global market                                                              streams for aero gas turbine manufacturers from
for power systems is very large indeed. For the                                                                 which they can enhance their financial
period 1991-2000, the total power systems                                                                       performance.
market (excluding nuclear, hydro, distribution and
transmission) is estimated to be US$ 814 billion.                                                               Whilst the “primes” (GE, Pratt and Whitney and
The market for power generation is beginning to                                                                 Rolls-Royce) are increasingly driven by
exceed the combined market for civil and military                                                               commercial criteria, the importance of gas turbine
aero gas turbines. However, much of the                                                                         technology is such that many governments in the
technology is generated within the aero gas                                                                     newly developed countries, and indeed, in the
turbine research environment.                                                                                   developed countries, are willing to heavily
                                                                                                                subsidise this industry. This is substantially
                                                                                                                because of the improvement in the technology
                                                                                                                and                                manufacturing
infrastructure that has followed national                                                                                                         FIGURE 5 - AIRCRAFT DEVELOPMENT
                                                                                                                                                  AIRCRAFT PRODUCTIVITY : SEAT MILES PER YEAR
investments in gas turbines. Even though the
barriers to entry into gas turbine manufacture are
high, some new companies have succeeded in                                                                                                                                                            B747-300
                                                                                                                                         160%                                                 B747-200B
breaking in the Anglo-American dominance within
                                                                                                                 % OF LOCKHEED TRISTAR

                                                                                                                                         140%                      DC-10-30
this field. Others will continue to try to enter this                                                                                                                                          B747SP
                                                                                                                                         120%                       L1011-1                                               MD-11
field for both commercial and strategic reasons.                                                                                         100%
                                                                                                                                                                                                        A300-600                  A330-300

Within civil aero gas turbines, the last 50 years                                                                                        80%                            DC-8-63
                                                                                                                                                                                                           A310-300       B767-300
has seen enormous changes. The early 1950s                                                                                               60%
                                                                                                                                                                             Super VC-10
saw the introduction of the first commercial gas                                                                                         40%
                                                                                                                                                                    DC-8-30                          1000nm MISSION
turbine powered aircraft, the Viscount, powered                                                                                                                                                      3 CLASS SEATING
                                                                                                                                         20%                 Comet 4                                 3000 HOURS PER YEAR UTILISATION
by the Dart Turboprop gas turbine, followed by                                                                                            0%

the early civil jet-powered aircraft, such as the                                                                                          1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

Comet and the Boeing 707. The early 1970s saw                                                                                                                            CERTIFICATION DATE

the introduction of the supersonic civil airliner, the
Concorde, powered by the Olympus 593 jet                                                                        The improvement in engine technology over this
engine. The Anglo-French Concorde was an                                                                        period has increased the aircraft productivity of
important example of international collaborative                                                                aeroplanes such that an aeroplane purchased in
programmes, which were to become increasingly                                                                   1950 would have a productivity of about 20% of
important for both military and civil gas turbines.                                                             that of the Tristar L1011. Large aircraft, such as
The early 1970s also saw the launch of the wide-                                                                the Boeing 747-300 and Boeing 747-400 have
bodied aircraft: the Boeing 747, the DC10, and                                                                  productivities of about 160% of that of the Tristar.
the Lockheed L1011. The Boeing 747, in                                                                          These benefits have resulted very substantially
particular, marked the start of the mass civil air                                                              because of the improvements in gas turbine
transport market, with leisure travel becoming                                                                  technology.
more important than business travel.
                                                                                                                4. Some Technology Drivers
An important measure for the success of an                                                                      Prior to a brief consideration of the changes in
aeroplane is its revenue-earning capacity or                                                                    gas turbine technology, which have delivered the
productivity, defined by the seat miles available                                                               advances in improving civil aircraft, it may be
per year.                                                                                                       useful to consider how aero gas turbines work.
                                                                                                                For this purpose, Whittle's W2/700 engine, which
                                                                                                                formed the basis of the launch of the gas turbine
                                                                                                                activity of the three Primes, is used as an

example. Incidentally, as part of        Cranfield        exhibition engine at Cranfield University since the
University's   50th    Anniversary,      Cranfield        early 1950s, and had not run for over 40 years.
University ran a Whittle W2/700 gas     turbine in
February 1996. This engine had          been an
                                                                    ROLLS ROYCE TRENT 800

The major components of the Whittle W2/700 gas
turbine consist of a compressor, a combustor, a            (The three large new competing turbofans,
turbine and a propulsion nozzle. The function of          namely, the Pratt and Whitney PW4084, the
the machine, when used as a jet engine, is to             General Electric GE90 and the Rolls-Royce Trent
increase the pressure at the exit from the turbine        800 are illustrated together on the back cover)
that drives the compressor. This increase in              The heart of the engine is the "core", where
pressure can be used either to propel the gases           further compression, after the fan, combustion
leaving the turbine through a propulsion nozzle,          and expansion takes place. The turbines within
generating thrust, or alternately, to produce shaft       the core have to produce work, not only to drive
power by the expansion of these gases past a              the compressors within the core, but also the
turbine. In Whittle's jet engine, "a power turbine"       "fan" which compresses the bypass air. The
is not included as the engine is a pure jet engine.       specific fuel consumption of an aero gas turbine
A very large proportion of the total power that a         is inversely proportional to the propulsive
gas turbine generates is required internally within       efficiency times the thermal efficiency. High
the engine to compress the air. For Whittle's gas         propulsive efficiency requires high bypass ratio,
turbine, the power required to drive the                  whilst high thermal efficiency requires a high
compressor was about 3000 hp. If the exhaust              overall    pressure    ratio,   high   component
gas power, which produced a "static thrust" of            efficiencies and high turbine entry temperature.
about 1400 lbf force, were converted to shaft
power, then the shaft power would have been               It is the energy extracted from the core that
1700 hp. This is very much less than the power            provides the power to drive the fan, and hence
required to drive the compressor.             As a        allows the realisation of a high bypass ratio
consequence, Whittle's gas turbine, and all gas           engine. The "core specific power" is crucial both
turbines, are very susceptible to small changes in        in reducing engine weight and in providing
the efficiencies of the major components such as          energy to drive the higher bypass ratio fans that
compressors and turbines, and pressure losses             lead to higher propulsive efficiency. Over the past
between intakes, diffusers, combustors and                50 years, the core specific power has risen by at
nozzles. Relatively small changes in component            least a factor of five over the early engines of
efficiency can render an engine wholly                    Whittle. Theoretically, there is a considerable
uncompetitive. If the compressor and turbine              improvement yet to come, and high temperature,
efficiencies of the Whittle gas turbine were              high performance demonstration programmes
reduced by 15%, then the Whittle gas turbine              have shown that the core power can be
would have failed to self-sustain itself, and would       increased to factors of eight to ten in relation to
of course have failed to produce any net output.          the early engines. Core power is principally a
                                                          function of turbine rotor inlet temperature. An
A modern gas turbine, as promised by Lord                 absolute limit to specific core power would be
Hives, is much more complicated.                          reached when the turbine rotor inlet temperature
                                                          reaches the limit of the maximum or
                                                          "stoichiometric" temperature that results when air
                                                          is burnt with hydrocarbon aviation fuels. This
                                                          temperature is about 2600K. In practice, it may
                                                          be necessary to limit maximum turbine rotor inlet
                                                          temperature to a value somewhere between

2000K and 2100K, because beyond these                                                                                                                                     The core thermal efficiency is defined as the
temperatures, the production of the combustion                                                                                                                            power produced by the core divided by the heat
generated pollutant, NOx rises rapidly.                                                                                                                                   added, and the propulsive efficiency is defined as
                                                                                                                                                                          the thrust times the aircraft velocity divided by
                                                                                      FIGURE 8 - CORE PERFORMANCE                                                         core power. The early turbo-jets achieved overall
                                                                   1600                                                                                                   efficiencies of about 20%. Low bypass ratio
                                                                   1400                                                                                                   engines, which became available in the early

                                                                                                 IDEAL PERFORMANCE
                                                                                                                                                                          1960s, improved propulsive efficiency, and hence
                                                          Kg / S

                                                                                                                                                                          overall efficiency, to about 25%. Current high

                                                                   1000                                                                                YEAR
                                                                                                                                                                          bypass ratio turbofans, because of both
                                         SPECIFIC CORE POWER

                                                                    800           WHITTLE (1937)                                                 STOICHIOMETRIC
                                                                                                                                                      LIMIT               improvements in core thermal efficiency and
                                                                    600                                                              NOx LIMIT
                                                                                                                                                                          propulsive efficiency, achieve overall efficiencies
                                                                    400                                                                                                   of 35%. Ultra high bypass ratio engines such as
                                                                    200                                                                                                   the advanced ducted propulsor and prop fan may
                                                                                                                                                                          be able to achieve even higher overall
                                                                      800      1000     1200     1400   1600     1800        2000      2200     2400      2600
                                                                                        TURBINE ROTOR INLET TEMPERATURE - K
                                                                                                                                                                          efficiencies, in the region of 50% perhaps
                                                                                                                                                                          sometime during the next twenty-five years. It
The increase in core specific output has been                                                                                                                             needs to be noted, however, that as bypass
                                                                                                                                                                          ratios are increased, the engine drag and weight
hard won by very large investments in high
                                                                                                                                                                          increase. These increases can offset much of the
temperature technology, covering both the
                                                                                                                                                                          potential improvement offered by improvements
materials capability and turbine vane and blade
                                                                                                                                                                          in propulsive efficiency.
cooling. From the early engines, which had a
turbine entry temperature at take-off of about
                                                                                                                                                                                                                                       FIGURE 10 - OVERALL EFFICIENCY
1000K, we have today's advanced turbofans                                                                                                                                                                                                                            THRUST * AIRCRAFT VELOCITY
operating with take-off turbine entry temperatures                                                                                                                                                                                 OVERALL EFFICIENCY o =
                                                                                                                                                                                  CORE THERMAL EFFICIENCY t = HEAT ADDED

                                                                                                                                                                                                                                                                                  HEAT ADDED

of about 1700K.                                                                                                                                                                                                                                                                                                YEAR
                                                                                                                                                                                                                             0.7                0.1         0.2      0.3      0.4        0.5         0.6
                                                                    FIGURE 9 - HIGH TEMPERATURE TECHNOLOGY                                                                                                                   0.6                                           HIGH BPR
                                                                   2300        UNCOOLED                 COOLED                                                                                                               0.5

                                                                               TURBINE                  TURBINE                               DEMONSTRATION                                                                                                                          ADVANCED DUCTED
                                                                               BLADES                   BLADES                                CAPABILITY                                                                     0.4                                                     PROPULSOR
                                                                                                                                                                                                                                                            TURBOJET        LOW BPR
                                                                   1900                                                                        CERAMICS
                                                                                       CURRENT                                                                                                                               0.2
                                                                   1700                PRACTICE
                                                                                                                                                                                                                                       SUBSONIC FLIGHT
                                                                   1500                                                                                                                                                       0
                                                                             WROUGHT ALLOYS
                                                                                                                                                                                                                                   0     0.1   0.2    0.3     0.4    0.5    0.6    0.7   0.8   0.9         1
                                                                   1300                                                                          CS CAST ALLOYS
                                                                                                                                                                                                                            PROPULSIVE EFFICIENCY p =                              * AIRCRAFT VELOCITY
                                                                                                                                           DS CAST ALLOYS                                                                                                           CORE POWER
                                                                   1100                                  CONVENTIONALLY
                                                                                                         CAST ALLOYS
                                                                      1940       1950          1960     1970          1980          1990       2000            2010
                                                                                                                                                                          Substantial improvements have also been
                                                                                                               YEAR                                                       achieved in component efficiencies, sometimes
                                                                                                                                                                          expressed as "polytropic efficiencies". The
Demonstration engines have been run at                                                                                                                                    thermal efficiencies of current engines in service
temperatures in excess of 2100K. Material                                                                                                                                 are approximately 45% based on polytropic
capability improvement alone accounts for some                                                                                                                            efficiencies of 88% at cruise conditions. From
300K in approximately fifty years, averaging                                                                                                                              now and during the early part of the next century,
about a modest 6K per year, in spite of very large                                                                                                                        it is likely that engines will enter service with
investment. In the early sixties, cooled blade                                                                                                                            thermal efficiencies approaching 50%, based on
technology was introduced which has allowed an                                                                                                                            polytropic efficiencies of 92% and increases in
increase of a further 400K, averaging about 12K                                                                                                                           cycle pressure ratio and turbine entry
per year. The increase in core specific power                                                                                                                             temperature. During the second quarter of the
benefits the economics of the aircraft first by                                                                                                                           21st century, thermal efficiencies of 55% may be
reducing the weight of the engine, and then by                                                                                                                            realised. This implies component polytropic
increasing the propulsive efficiency of the power                                                                                                                         efficiencies of 94% and cruise turbine entry
plant because of the possibilities of increasing                                                                                                                          temperatures between 1600K and 1800K.
bypass ratio.

The overall efficiency of a gas turbine propulsion
unit is defined as the useful thrust work divided
by the heat input. The useful thrust work equals
the product of the thrust and aircraft velocity. The
overall efficiency is the product of the core
thermal efficiency and the propulsive efficiency.

                                                      FIGURE 11 - EFFECT OF COMPONENT                                                            prediction methods associated                                  with      the
                                                     EFFICIENCY ON THERMAL EFFICIENCY                                                            mechanical integrity of the blade.
                                                65                                                                TURBINE
                                                                                                             ENTRY TEMPERATURE
                                                                                                                                                            FIGURE 13 - COMPONENT EFFICIENCY LOSS
                                                                                                                          1800 K                          DISTRIBUTION AND RESEARCH ACTIVITY - FANS
                     THERMAL EFFICIENCY %

                                                                                                                          1600 K
                                                                          SECOND QUATER
                                                                          21ST CENTURY                                    1600 K                                    CAUSE OF LOSS      RESEARCH ACTIVITY        AVE LOSS REDUCED:

                                                55              POLY 94%                                                                               TIP
                                                                                                                                                                                                                FROM%      TO%

                                                        10% SFC                                                          1400 K                                    SECONDARY LOSS     CONTROLLED CLEARANCE     0.75       0.5
                                                                                                                                                                                       TIP GEOMETRY
                                                        POLY 92%              EARLY 21ST
                                                50                                               13.7%                    1600 K
                                                                               CENTURY                                                                              SHOCK LOSS         OBLIQUE SHOCKS           4.0        3.5

                                                        ENGINES                                                                                                     CLAPPER LOSS       REMOVE: WIDE CHORD       1.5        0
                                                45      SERVICE                                                                                                     PROFILE LOSS       IMPROVED DIFFUSION       2.5        2.0
                                                                    TYPICAL                                               1400 K
                                                                                                           TAKE-OFF                                                 BLADE BOUNDARY     IMPROVED DIFFUSION       0.75       0.5
                                                      POLY 88%                                                                                         ROOT 100%   LAYER SEPARATION

                                                40                                                                                                                                     PLUS SUPERCRITICAL
                                                 600       650     700        750          800       850       900        950        1000                                              OUTLET GUIDE VANE        2.5        1.5
                                                                                                                                                 CLAPPERED RADIAL EFFICIENCY
                                                               COMPRESSOR DELIVERY TEMPERATURE - K                                                 BLADE                                                        12.0       8.0

                                                                                                                                                                                       POLYTROPIC EFFICIENCY%   88.0       92.0

Over the last fifty years, the cumulative effect of
component, cycle and propulsive efficiencies has                                                                                                 The redesign, by Rolls-Royce, of the RB211
been an improvement of about 50%, averaging                                                                                                      "clappered" blade by a wide chord blade with
approximately 1% per year. The improvement in                                                                                                    improved boundary layer separation control and
component, cycle and propulsive efficiency taken                                                                                                 an improved outlet guide vane reduced the
over the whole period is approximately equal.                                                                                                    estimated component loss from 12% to 8%,
However, the introduction of high bypass ratio                                                                                                   improving the fan blade polytropic efficiency from
turbofans 1970s saw a dramatic improvement in                                                                                                    88% to 92%. This design had to be backed up by
propulsive efficiency.                                                                                                                           advances in manufacturing technology such that
                                                                                                                                                 the skin of the hollow titanium blade could be
FIGURE 12 - CIVIL AERO GAS TURBINE CRUISE SFC TRENDS                                                                                             supported off a super-plastically formed rib. The
                                                STRAIGHT LOW
                                                                MEDIUM HIGH
                                                         BYPASS BYPASS BYPASS
                                                                                                                                                 resulting     design    proved    superior    both
                                                                                                                                                 aerodynamically and in terms of its ability to
                                     10                                                             COMPONEN                                     resist bird-strike. The change to the wide chord
                                                                                                                   T EFFICIEN
                                                                                                                                                 blade resulted in very substantial improvements

                                                                                                                                                 first to Rolls-Royce's RB211 family of engines,
                                     30                                                                          E     EFFIC
                                                                                                                                                 and subsequently to other engines. This is a
                                                                                                                                                 good example of an innovative design and
                                     40                                                                   PRO
                                                                                                                 IVE E
                                                                                                                      FFIC                       sustained investment in appropriate technologies,
                                                                                                                                                 resulting in a competitive advantage.
                                     60          BYPASS RATIO
                                                                                                                                                 The temperatures and forces associated with gas




                                      1955              1965        1975            1985           1995        2005         2015
                                                                                                                                                 turbine related machinery are very high indeed.
                                                                                                                                                 As an example, a single high pressure turbine
Cycle efficiency has improved steadily over the                                                                                                  blade has a centrifugal force equivalent to the
years, as improved blade and disc materials                                                                                                      weight of a heavy truck, and produces the power
became available, along with the application of                                                                                                  output ten times higher than a family car. If
blade cooling technology allowing designs of                                                                                                     released at the root whilst moving vertically
higher pressure ratio and higher turbine entry                                                                                                   upwards, and if no restraining forces were placed
temperatures to be realised. Whilst component                                                                                                    in the path of the released blade, the energy
efficiencies saw some improvement in the early                                                                                                   contained within the blade would propel it some
years, much of the improvement in component                                                                                                      10 kilometres high. The local gas temperature
efficiencies came after the late 1970s, when large                                                                                               about this blade, which carries these high loads
powerful computers and very advanced test                                                                                                        and produces this large power output, can be as
facilities allowed the aerodynamics of these                                                                                                     much as 200K higher than the melting point of
components to be explored in detail.                                                                                                             the high temperature alloy used to manufacture
                                                                                                                                                 the blade.
An example of improvements in component
efficiencies is the "wide chord" fan blade. The
realisation of the wide chord fan blade required
improvements in aerodynamic design techniques
based on the detailed understanding of the flow
about the blade, an innovative mechanical
design, research into the manufacturing
techniques necessary to manufacture a hollow
wide chord fan blade, and improvements in the

    FIGURE 14 - HIGH PRESSURE TURBINE BLADE                                                  FIGURE 15 - AIRPORT NOISE TRENDS

                                                                                                                                                                                         PUBLISHED UK NOISE AND


                                                                                 NOISE AND                                                                                               NUMBER INDEX CONTOUR

                                                                                 MOVEMENT                                                                                                AREAS (35, 45 & 55 NNI) FOR

                                                                                 INTEGRATED                                                                                              HEATHROW SUMMER OPERATIONS

                                                                                 EXPOSURE                           ADVENT OF
                         • CENTRIFUGAL FORCE EQUIVALENT                          INDICATORS                        HIGH BY PASS
                           TO WEIGHT OF HEAVY TRUCK


                                                              LEVEL (DB)

                         • POWER OUTPUT 10 TIMES                                                                              RECESSION

                           HIGHER THAN FAMILY CAR                           -6

                                                                                                                                 WORLD FLEET

                         • LOCAL GAS TEMPERATURE

                                                                                                           OF JET                 TURBOFAN                                                          NO LOW BYPASS
                                                                            -8                             FLEET
                           200oK HIGHER THAN ALLOY                                                                                                                                                 ENGINES IN FLEET

                                                                                          EL F
                           MELTING POINT

                                                                           -10                  NO
It is the very large investment in research and                            -12
                                                                             1940     1950            1960             1970     1980                                                   1990      2000      2010    2020   2030
development undertaken over many years that
has delivered today's high efficiency, high bypass            5.2 Combustion Generated Pollutants
turbofans and today's cost efficient aircraft. In
spite of the pressures to reduce weight and                   Concern for the environment, in recent years, has
improve efficiency by the use of very high                    begun to focus much more on combustion
pressures, stress levels and temperatures, the                generated pollutants. Current legislation is
civil aero gas turbine industry has had an                    concerned with the landing and take-off cycle
excellent record in terms of safety. Additionally,            which includes taxi in and out (26 minutes) at
engine lives have increased substantially, and                very low power, final approach (4 minutes) at low
"in-flight shutdown rates" have been reduced                  power, take-off (0.7 minutes) at maximum power,
progressively.                                                and climb (2.2 minutes) at high power.

                                                                                             FIGURE 16 - AIRPORT ENVIRONMENT
5. Environmental Concerns                                                                     IMPROVEMENT - BELOW 3000 FEET

                                                                                                                                                                                              REDUCTION OF POLLUTANTS
5.1 Noise                                                                           TYPICAL OPERATION

                                                                                                                                  GRAMS OF EMISSIONS PER PASSENGER (LTO CYCLE)
                                                                                                              TIME IN
                                                                                                                                                                                 200     1970 - 1973
                                                                                                      SETTING MODE                                                                       1979 - 1983
During the 1960s, the level of noise around                                                           (%)     (MINS)                                                                     1985 - 1988
airports became progressively less acceptable.                               TAXI (IN & OUT)                   7        26
                                                                             FINAL APPROACH                30           4
Much of the world's fleet was based on pure jet                              TAKE-OFF                     100           0.7                                                      120
aircraft, and jet noise increases very rapidly as                            CLIMB                         85           2.2

the exhaust gas jet velocity is increased. Airport                         LOWER POWER SETTINGS - UNBURNT FUEL

noise is sometimes expressed as an integrated                              AND CARBON MONOXIDE PREDOMINATE.
exposure indicator based on noise and                                      HIGH POWER SETTINGS - SMOKE AND
                                                                           OXIDES OF NITROGEN PREDOMINATE.
movement, and noise and index number contours                                                                                                                                      0
                                                                                                                                                                                                         CARBON     NOx
are used to estimate airport noise exposure. In                                                                                                                                       HYDROCARBONS

the early 1970s, the advent of the high bypass
ratio turbofan substantially reduced the noise                Smoke (soot) as a pollutant for civil aero gas
from the fleet such that by the mid-eighties, the             turbines has very nearly been eliminated
world fleet comprised approximately 50% high                  because of improvements in fuel air preparation.
bypass turbofans. Many of the earlier low bypass
ratio engines are being progressively replaced by             Unburnt hydrocarbons and carbon monoxide are
modern high bypass ratio turbofans, and this will             pollutants that are produced at low power. There
further reduce noise levels from aero gas                     have already been substantial reductions in the
turbines. By the time the 600 - 800 seater aircraft           level of unburnt hydrocarbons and carbon
come into service in the first quarter of the next            monoxide as measured by the landing and take-
century, it is likely that aircraft noise will begin to       off cycle defined by the International Civil
approach, or even exceed engine noise, a                      Aviation Organisation (ICAO).
concept that would have seemed strange in the
1970s and 1980s.                                              Oxides of nitrogen are produced at high power
                                                              settings. As engine technology has improved,
                                                              both the pressure ratio and turbine entry
                                                              temperature have been progressively increased.
                                                              Consequently, it appears that the reduction in
                                                              oxides of nitrogen has been modest when
                                                              compared with earlier engines. However, the
                                                              application of a constant level of combustor
                                                              technology would have resulted in a substantial
                                                              increase in the level of NOx produced.

                                                              Current legislation as formulated by ICAO does
                                                              not define any limits for cruise NOx. Whilst there

is no evidence that civil subsonic aircraft are                         and latitude and pressure (or altitude). This
likely to damage the ozone layer, the possibility                       integrated approach allows "scenario studies" to
needs to be explored. The level of oxides of                            be undertaken to identify appropriate engine
nitrogen released by civil aircraft are very small                      configurations and cycles, including the effect of
when compared to the oxides of nitrogen                                 engine degradation, on cruise NOx emissions.
produced by industry, power generation and
ground transport. However, NOx generated by                                 FIGURE 19 - LATITUDE-LONGITUDE NOx DISTRIBUTION
aero engines is released at high altitude, and in
that important regard differs from NOx produced
at ground level, at least as far as considerations
regarding the ozone layer are concerned.


                                                                           London-Tokyo / 12 km     Parts per trillion by volume (pptv)

                                                                        Engines that are optimised for take-off NOx, the
                                                                        only circumstance currently covered by ICAO
                                                                        legislation, are not necessarily the best in terms
                                                                        of cruise NOx. It is very likely that the cruise NOx
                                                                        will prove to be the more important parameter,
                                                                        particularly for aircraft flying very long ranges. As
                                                                        the aircraft flies, the fuel already burnt makes the
One of the studies under way at Cranfield                               aircraft lighter, and the most efficient way to fly
University seeks to quantify the amount of NOx                          the aircraft is to fly it at progressively higher
generated by an aircraft flying a particular route,                     altitudes as more fuel has been burnt. Therefore,
and how this NOx mixes within the earth's                               very long range aircraft, for example, flying from
atmosphere. This "systems approach" includes a                          Tokyo to London, often fly at relatively high
model of an aircraft, a model of an appropriate                         altitudes towards the end of their flight, precisely
aero gas turbine, the combustor technology                              when they are near the North Pole where the
employed, and the aircraft flight management.                           ozone layer is closest to the earth's surface.
The systems approach integrates all the above
issues in a computer simulation of the aircraft,                                 FIGURE 20 - ZONAL MEAN NOx DISTRIBUTION

engine, combustor and the flight route. The
computer programme is initially being used to
study flights of a Boeing 747-400 for long ranges
such as London to Tokyo. The NOx generated
during the flight is distributed along an emissions
track between London and Tokyo.

             FIGURE 18 - LONDON-TOKYO : DAILY
                  CRUISE NOx EMISSIONS

                                                                             London-Tokyo          Parts per trillion by volume (pptv)

                                                                        Such studies will contribute to our understanding
                                                                        of the interplay between the various technologies
                                                                        and help with the formulation of appropriate
                                                                        legislation. In particular, such studies need to be
                                                                        undertaken prior to the design definition and
                                                                        launch of the next generation of the civil
                                                                        supersonic transport, as this aircraft is likely to fly
     10.3 flights per day (1992 scheduled traffic with B747-400s)       substantially within the earth's ozone layer.

The average number of flights per day are used
to establish the level of NOx emitted per day. The
atmospheric model then calculates the mixing of
the NOx, both in terms of latitude and longitude,

                          FIGURE 21 - ULTRA LOW NOx TECHNOLOGY                                                                        The growth of the air travel business has been
                         DEMONSTRATED AT CRANFIELD UNIVERSITY                                                                         dramatic. Since 1946 the airline industry has
                                      FOR ROLLS ROYCE
                 100                                                                                                                  averaged a compound annual growth rate of
                          CONVENTIONAL TECHNOLOGY
                                                                                                                                      10.4% per annum. Over the last twenty-five years
                                                                                                                                      the industry has grown at 6.6% per annum. This
                                                                                                                                      growth in world air travel is driven by two factors,
                                                                                                                                      the growth of the world economy (i.e.
   EXIT NOx/E1

                                                                                                                                      affordability), and the costs of travel.
                                              ULTRA LOW NOx

                   1                                                                                                                                                 FIGURE 23 - THE AIRLINE INDUSTRY GROWTH
                                                                                                                                                                          DRIVERS - GROWTH IN WEALTH
                                                                                                                                                                             AND THE COST OF TRAVEL

                 0.1                                                                                                                                                 60                                                                                                 100000

                                                                                                                                       AVERAGE FARES (US CENTS PER
                                                                                                                                                                                                             History          Forecast
                   1850           1900        1950          2000      2050        2100          2150      2200                                                                   OECD GDP

                                                                                                                                          RPM, 1996 ECONOMICS)
                                         PRIMARY ZONE FLAME TEMPERATURE, K                                                                                           50          PER HEAD

                                                                                                                                                                                                                                                                                 REAL GDP PER HEAD
Over the last fifteen years, the gas turbine

                                                                                                                                                                     30                          WORLD GDP                                                              1000
industry has made a very large investment in                                                                                                                                                      PER HEAD
                                                                                                                                                                                                                              CHINA GDP
developing the technology necessary to reduce                                                                                                                        20                                                       PER HEAD
combustion generated pollutant emissions. All                                                                                                                        10
                                                                                                                                                                               THE REDUCTION OF
the engine manufacturers have developed their                                                                                                                        0
                                                                                                                                                                             AIRLINE YIELDS (FARES)













combustors to meet the increasingly tighter
emissions legislation, and are working on
technologies to meet future changes in the                                                                                            The growth of people‟s wealth has been a
emissions legislation that will come into force in                                                                                    significant impetus to airline growth. As
the year 2008.                                                                                                                        economies recovered after the Second World
                                                                                                                                      War and world trade was freed up, the demand
The next challenge in terms of atmospheric                                                                                            for fast, safe and economic travel created a
pollution is global warming. This issue is likely to                                                                                  demand for air transport. In the last twenty years,
impact on airframe and engine design and is                                                                                           prices have reduced to such an extent that a
addressed later in the paper.                                                                                                         large industry has built up around the leisure air
                                                                                                                                      travel sector. Some observers suggest that the
6. The Development and Future of the Civil                                                                                            industry is maturing. It is true that overall growth
Aero Gas Turbine Industry                                                                                                             rates are slowing down. However, in 1990, on
                                                                                                                                      average a UK or USA citizen took at least one air
The world airline industry is a business which                                                                                        trip per year. For countries like Brazil, Mexico and
accounts for between 0.5-1% of the Western                                                                                            Indonesia, one person in ten took a trip. For
world‟s GDP. The supporting civil aero engine                                                                                         China and India, the ratio is one person in
industry has sales today of well over $15 billion                                                                                     seventy-five. Clearly, there is much growth
per annum. The four aero engines that power the                                                                                       potential for this industry from the demand side of
Boeing 747 „Jumbo Jet‟ are priced at some $7                                                                                          the equation.
million each and represent about 20% of the
aircraft purchase price. This is a cyclic capital                                                                                     That the real cost of travel has reduced is
industry, and its fortunes relate to the growth in                                                                                    illustrated by the change of airline yields. „Yield‟
the world economy.                                                                                                                    as used by the airline industry is defined as the
                                                                                                                                      revenue generated per passenger mile, or unit
                              FIGURE 22 - WORLD REVENUE PASSENGERS                                                                    fares. In 1946, it would have cost £4000 for a
                                 KILOMETERS (RPKs) VERSUS WORLD                                                                       return flight across the Atlantic in 1996
                                         ECONOMIC GROWTH                                                                              economics, today it can be done at 5% of the
                                                                             WORLD RPKs
                                                                                                              8                       cost. The early yield reductions were principally a
                                                                             WORLD GDP (Right Scale)          7
                                                                                                                                      result of improvements in technology in both the
                                                                                                                                      airframe and engine. Aircraft have also become
                                                                                                                                      much more productive through a combination of

                                                                                                                   GDP % CHANGE

                 10                                                                                           4

                                                                                                                                      larger capacity and range capability brought
                  5                                                                                           2
                                                                                                                                      about by advances in technology discussed
                                                                                                              1                       earlier, mainly improvements in overall efficiency,
                  0                                                                                           0                       in specific power and cost of ownership.

                       1969    1971   1973   1975    1977   1979   1981   1983   1985    1987   1989   1991
                                                                                                              -2                      More recently, the airlines have utilised
                                                                                                                                      information technology to develop sophisticated
                                                                                                                                      customer reservation systems and so-called
                                                                                                                                      „yield management systems‟. The end result is
                                                                                                                                      that on average, aircraft now fly fuller and the

economic benefits can be shared with the fare-                                       FIGURE 24 - THE LEVEL OF COMPETITION AND
                                                                                       NUMBER OF ENGINES PER AIRCRAFT TYPE
paying customer. Industry forecasters predict that
yields will reduce at 1% per annum for the next
twenty years. This impacts the engine                                                2                     THE AVERAGE             History                                4
                                                                                                            NUMBER OF              Forecast
manufacturers in two ways. Firstly, the engine

                                                             ENGINES PER AIRCRAFT

                                                               No OF COMPETING
                                                                                                           PER AIRCRAFT
needs to be designed to burn less fuel and cost

                                                                                                                                                                              No OF ENGINES
                                                                                                                                                                              PER AIRCRAFT
less to maintain. Secondly, the price for the
                                                                                    1.5                                                                                   3
powerplant will be expected to decrease. If the
engine manufacturers cannot deliver these
essentials, then the forecast of five to six per cent                                                   THE AVERAGE NUMBER
                                                                                                        OF COMPETING ENGINES
per annum annual growth rate for the airline                                         1
                                                                                                            PER AIRCRAFT
industry will be jeopardised.











One of the greatest drivers of technological
                                                             The downside to this state of affairs is that there
innovation is competition. Incidentally, even
                                                             may be too much competition in the engine
though the civil aero gas turbine industry can
                                                             sector. There are recent examples of engines
rightly be thought of as a mature industry, this
                                                             being given „free‟ to airlines by certain engine
does not result in identical designs, as is readily          manufacturers. It is difficult to see how profits can
apparent if the engines of the three Primes (GE,
                                                             be made in the long term if this sales tactic
PW and RR) for the Boeing 777 are compared in
                                                             continues even with the large aftermarket
even the most cursory way. The civil aero engine
                                                             business generated by jet engines. The problem
sector is intensely competitive. One of the
                                                             is compounded by the trend to two powerplants
reasons for this is the structure of the market.
                                                             per airframe, even on large aircraft. Engine unit
The three Prime manufacturers have to sell their             volumes will grow slower as a result.
products to the three aircraft manufacturers in the
first instance. Increasingly over the years, aircraft
                                                             In the longer term, economic realities will catch
have been made available with a choice of
                                                             up with the engine industry. An outcome may be
engine manufacturer. Where the market size is
                                                             that at best there will be two engine
big enough, all three engine manufacturers will              manufacturers per aircraft type. This does not
have an engine available. The aircraft                       mean that only two manufacturers will survive.
manufacturers and the airlines have benefited
                                                             Partnerships are likely to develop whereby two
from this competition. The airlines have low
                                                             Primes will collaborate in certain sectors. An
prices for their powerplants and this feeds
                                                             example of this is the International Aero Engines
through to reduce fares. As a result the overall
                                                             collaboration between Rolls-Royce and Pratt and
industry grows which benefits the airframers. An             Whitney (with other partners) to produce a
example of this is the competition between the
                                                             25,000 lb. thrust engine for the 150 seater aircraft
Airbus A340 and the Boeing 777. The Boeing
                                                             sector. In May 1996, an announcement was
777 is available with a choice of three engines,
                                                             made by GE and Pratt and Whitney that they had
and intense competition between the engine
                                                             agreed to the joint development of turbofan
manufacturers has driven prices down. This
                                                             engine for the Boeing 747x. This partnership is
helped Boeing win several competitions over the              now offering an engine for the Airbus A380 in
Airbus A340, which has only one engine supplier
                                                             competition with the Rolls-Royce Trent 900
(CFM 56-5). However, the next growth version of
the Boeing 777 is offered with only one engine
                                                             A lot of interest in the aero engine industry is
(GE 90).
                                                             focused on the headline grabbing original
                                                             equipment sales successes of the major engine
Competition is so intense that GE‟s recent                   manufacturers. However, the improvements in
purchase of Honeywell, which would markedly
                                                             the in-service operations of engines are having a
increase GE‟s scope of supply to civil aviation,
                                                             fundamental impact on the industry. Firstly,
has raised concerns among competitors and the
                                                             engines are getting more reliable. This is
European Commission.
                                                             measured by „in-flight shut down rates‟. The very
                                                             high reliability of current engines is the reason for
                                                             the move to two powerplants per aircraft, even for
                                                             extended range operations over water.

                                        FIGURE 25 - THE RELIABILITY OF ENGINES                                                                                                              FIGURE 26 - THE MANAGEMENT OF RISK
                                          AND THE INCREASING „TIME ON WING‟
                                                                                                                                                                                           “COMMON CORE”, DEMONSTRATORS, CFD
    AVERAGE TIME BETWEEN ENGINE                                                                                                                                                            SPECIALIST SECOND TIER COMPANIES
                                      40000                                                                                   1

                                                                                                                                             (EVENTS/THOUSAND FLYING HOURS)
      OVERHAUL (FLYING HOURS) 1                                           HISTORY         FORECAST
                                                     IFSD Rate

                                                                                                                                                IN FLIGHT SHUT DOWN RATES
                                      30000                                                                                                                                                REVENUE SHARING PARTNERSHIPS
                                  CURRENT                                                                                                                                                        - FUNDING
                                  RECORD                                                                                      0.01                                                               - MARKET
                                      20000                                                                                                                                                      - TECHNOLOGY
                                                                                                                                                                                           LONG TERM DEALS
                                      10000                    TBO                                                                                                                               - LOCK IN THE AFTERMARKET BUSINESS WITH
                                                                                                                                                                                                   THE OE SALE

                                         0                                                                                    0.00001










                                                                                                                                                                                           POLITICAL POSITIONING
                                                                                                                                                                                   The issue that dominates business plans is the
                                                                                                                                                                                   large research and development costs for
Another issue of more long term consequence is
                                                                                                                                                                                   producing new engines. The new engine
the expected trend in engine „life on wing‟. This is
                                                                                                                                                                                   produced by General Electric for the Boeing 777
the average time an engine will stay on an
                                                                                                                                                                                   cost over $2 billion. Even for an organisation as
aircraft before being removed for a service. When
                                                                                                                                                                                   big as GE, this is a large exposure. Companies
an engine is removed, it is usually stripped down
                                                                                                                                                                                   have therefore endeavoured to spread this
and worn parts are replaced. This provides the
                                                                                                                                                                                   exposure by sharing engine programmes with
basis for the engine manufacturers‟ aftermarket,
                                                                                                                                                                                   other companies. By reducing the bill for each
a high profit margin business which is forecast to
                                                                                                                                                                                   programme, the Primes can participate in more
grow with the total engine fleet. However, with
                                                                                                                                                                                   sectors and therefore spread the risk of a
the steadily improving life of aero engines, it
                                                                                                                                                                                   technical or market failure. However, one has to
could be that an engine will not require a major
                                                                                                                                                                                   observe that this strategy has not, so far at least,
service for the duration of the aircraft‟s twenty-
                                                                                                                                                                                   made partner companies very rich. The major
five year life. Consider that in fifty years time, the
                                                                                                                                                                                   European collaborators, state owned SNECMA of
oldest engine in use will not have entered service
                                                                                                                                                                                   France and MTU of Germany (part of Daimler-
until twenty-five years from now. The result could
                                                                                                                                                                                   Benz Aerospace) are both in financial difficulties
be the partial or complete loss of the engine
                                                                                                                                                                                   and both have rather impatient owners. One of
manufacturers‟ aftermarket business. Companies
                                                                                                                                                                                   the problems for these companies is that they do
would have to make compensating higher profits
                                                                                                                                                                                   not have a large spare parts base unlike the
on the original equipment sale. More
                                                                                                                                                                                   Primes who have been in the industry since its
interestingly, the loss of the aftermarket revenues
                                                                                                                                                                                   inception in the 1940‟s.
based on decades of Prime incumbency
eliminates a major market entry barrier. Perhaps
                                                                                                                                                                                   Recently, engine companies have been signing
this is when a new wave of companies will gain
                                                                                                                                                                                   long term aftermarket agreements with airline
entry into the business.
                                                                                                                                                                                   customers. Instead of the airline repairing and
                                                                                                                                                                                   overhauling an engine, the manufacturer does it.
The risks are high in the aero engine business.
                                                                                                                                                                                   The engine company becomes more of a service
Technical,     commercial      and    geo-political
                                                                                                                                                                                   provider than a supplier of spare parts. The
considerations all impact the industry. Technical
                                                                                                                                                                                   manufacturer charges the airline for his
risks have progressively been reduced by the use
                                                                                                                                                                                   powerplant usage (i.e. usually by flying hour).
of "common cores", “demonstrators”, “technology
                                                                                                                                                                                   This has the advantage for the airline that their
on the shelf”, validated design methods and data
                                                                                                                                                                                   cash flows are much more predictable with this
bases, computational fluid mechanics and finite
                                                                                                                                                                                   type of deal. This also applies to the engine
element computer techniques along with
                                                                                                                                                                                   manufacturer.    This means that the engine
improvements in quality assurance. Players,
                                                                                                                                                                                   manufacturer has secured more of the revenues
smaller than the Primes, may choose to reduce
                                                                                                                                                                                   associated with the product. The next step may
risk by becoming “specialist companies”, such as
                                                                                                                                                                                   be that the supply of the powerplant itself is
Fiat in gearboxes, IHI in shafts and perhaps MTU
                                                                                                                                                                                   wrapped into such deals. The engine
in Low Pressure Turbines.
                                                                                                                                                                                   manufacturer becomes very similar to a utility - a
                                                                                                                                                                                   provider of power. However, this has the problem
                                                                                                                                                                                   that the engine manufacturer has to carry a large
                                                                                                                                                                                   financing burden to fund the supply of the engine.
                                                                                                                                                                                   Perhaps financing intermediaries will enter this
                                                                                                                                                                                   field, as has been the case within the aircraft
                                                                                                                                                                                   supply sector.

                                                                                                                                                                                   Political realities mean that the engine companies
                                                                                                                                                                                   have had to place work into countries where they
                                                                                                                                                                                   wish to sell jet engines. There was a trend in the

1980‟s to sign up partners to a engine
programme who could secure enough political
influence to ensure an airline order from the
partner‟s home country. This strategy has had a
rather patchy track record recently as the Primes
attempt to neutralise a competitor‟s position with
an alliance of their own. A good example of this is
in Japan where the indigenous manufacturers
have multi-relationships with the three Primes. An
additional issue is that home governments
appear to have less control over the buying
decisions of their domestic airlines. This appears
to be the case as a country matures
economically. The movement by governments to
privatise their airlines has exacerbated the                Very recently, Boeing have announced their
situation. Offset and countertrade will continue to         intent to proceed with their “Sonic Airliner” and
be used tactically but the trend is away from               implied that they will not launch a direct
choosing partners solely for industrial positioning         competitor to the Airbus A380. This, industry, so
reasons.                                                    often referred to as a mature or “plateaued out”
                                                            industry, continues to have the capacity to
7. Application and Design Changes Over The                  surprise even informed observers.
Next Fifty Years:
                                                            FIGURE 28 – BOEING SONIC CRUISER
"Nothing is certain, not even that" (Albert
It is perhaps unwise to speculate too far into the
future, but the level of investment that is required
in this industry ensures that the next two or three
developments are identifiable a decade or two
prior to their launch.

The growth in passenger traffic on some long-
range routes, particularly associated with flights
to Asia Pacific from Europe and the United
States, has identified the need for a very large
passenger aircraft. These aircraft, anticipated to
carry between 500 and 800 passengers over a
range of 8000 nautical miles, have been studied
for some years. There was considerable
uncertainty as to whether the Airbus A3XX would
attract sufficient orders for it to be launched. The
number of firm and “options” sales of the A380
(the launch version of the project A3XX) has no
doubt pleased Airbus. Boeing had for sometime               Somewhere towards the end of the first quarter of
maintained that a growth version of their 747               the next century may see the launch of a civil
would satisfy market needs. The engines                     supersonic transport. The engine used for this
required to power the A380, whilst new, are                 "Concorde replacement" aircraft will nearly
either derivative engines or within established             certainly be a variable cycle engine to give low
technology and engine architecture, and as such             noise at take-off combined with high cruise
do not pose a significant risk to the launch of this        specific thrust. The take-off mode would have a
aircraft.                                                   high bypass ratio to reduce jet velocity and hence
                                                            noise, with the engine reverting back to a cycle
FIGURE 27 – AIRBUS A380 “SUPER JUMBO”                       not dissimilar to that of Concorde‟s Olympus 593
                                                            engine for supersonic cruise. Ultra-low NOx
                                                            combustor technology will be an essential
                                                            requirement for this development.

                                                                 ADVANCED STUDY ENGINE



      • CIVIL SST EXPERIENCE                                  APPROX 10% BETTER FUEL CONSUMPTION
                                                               THAN BEST CONVENTIONAL TURBOFAN
                                                              IMPROVED PROPULSIVE EFFICIENCY HAS
                                                              TO „PAY‟ FOR INCREASED INSTALLATION
If the new very large passenger aircraft were                DRAG AND WEIGHT AND COST OF GEARBOX
unable to support more than one or two engine
manufacturers, the civil supersonic passenger              We may eventually see an "all-electric gas
aircraft market will be such that there is probably        turbine". The power produced by the turbines in
going to be room for only one aircraft and engine.         this engine would drive electric generators. The
This will require collaboration on an international        electric generator would, via electric motors, drive
basis possibly involving all the current major             the engine's fan and the intermediate and high
airframe and engine companies along with a                 pressure compressors, at their desired speeds
number of emerging players. This aircraft and              and in their appropriate locations. The engine
engine will provide technology and manufacturing           rotors would be supported by electro-magnetic
experience at the forefront when it is launched,           bearings, removing the need for oil systems. It
and Europe's experience with the Concorde                  would be possible to maintain the balance of the
places it in a position to obtain an appropriate           various rotors by measuring any out of balance
share in this milestone project.                           forces and compensating these with varying
                                                           electro-magnetic fields applied to the electro-
Ultra-high bypass ratio engines or alternatively           magnetic bearings. All engine and aircraft
propfans have been studied for some time. It is            systems would be electrical, leading to
clear that such engines could improve the fuel             simplification and weight reduction. It would be
consumption over the best conventional turbofan            possible for engines to "share" components such
technology by about 10%. Concerns remain                   that a loss in turbine output in one engine could
about the additional installation nacelle and              be compensated by sharing the turbine output
interference drag penalties, and the weight of the         from other engines within the aircraft. Such
low pressure system, namely the turbines, to               designs would also allow, if necessary, the
drive the large low speed fan, the weight of the           separation of the gas generator from the fan.
fan, and the size and performance of the                   Finally, if in the future, the industry were to move
reduction gear. Fuel prices to date, and forecast          towards wholly laminar flow aircraft (involving
fuel prices, are low and have reduced the market           boundary layer suction), then a distributed
case for this development.                                 electrical gas turbine would give the flexibility
                                                           necessary to contemplate such a design. The
                                                           likely benefits from the combination of a very low
                                                           drag aircraft and an all-electric gas turbine could
                                                           be very substantial indeed.

                                                                      As the rotor blades experience both the high
                                           • NO RADIAL DRIVE
                                           • NO ACCESSORY
                                                                      temperature gases of the high pressure turbine,
                                           • NO OIL SYSTEM
                                                                      and the low temperature gases of the low
                                           • INTERMITTENT             pressure turbine, they operate at an equilibrium
                                             LOADS FLEXIBILITY
                                           • FEWER FLUIDS             temperature defined by these two temperatures,
                                           • REDUCED PARTS
                                             INVENTORY                the velocities within the rotor, and the relative
                                           • FAULT DIAGNOSIS
                                                                      time spent within each of the two partial
                                                                      admission stages. This would allow the selection
                                    E.M. BEARINGS:
                                                                      of a combustor exit temperature such that the
                                    LIFE, ROTOR DYNAMICS              turbine rotor did not require any cooling, even
      • HANDLING AND SFC BENEFITS                                     though the high pressure stage operated at
      • “SHARED” COMPONENTS                                           relatively high turbine entry temperatures. Whilst
        INCLUDING LAMINAR INTAKE AND FUSELAGE                         the efficiency of the double-pass turbine would be
                                                                      lower than that of conventional turbines, the lift
8. Design Curiosities                                                 fan would be used only for the short time period
                                                                      required for vertical take-off and landing.
Two unusual personal design offerings are
included in this lecture. They are the "lift fan                      8.2 The "Two Combustor Variable Cycle Aero
driven by a single rotor double-pass turbine" and                     Gas Turbine".
the "two combustor variable cycle aero gas
turbine". It continues to be important to explore                     As aero gas turbine designers seek solutions
new design concepts, particularly within                              where the duty of the gas turbine is very different
universities who wish to have an interest in the                      during different parts of the operating regime,
whole product and not solely in individual                            variable cycle aero gas turbines either offer
component technologies.                                               substantial advantages over fixed geometry
                                                                      machines, or provide the only possible solution.
8.1 The Lift Fan Single Rotor Double-Pass                             The introduction of variable geometry within the
Turbine                                                               hot section of the gas turbine to achieve variable
                                                                      cycle operation is viewed with trepidation
The concept is directed towards a very high                           because of lifing, weight and cost implications.
thrust to weight ratio lift fan. If realised, the lift fan
could be buried within a wing because it has an                       An alternative approach would be to have a
unusually short length. The relatively few parts                      second combustor following the high pressure
associated with this lift fan engine should result in                 turbine, which would now sit between the first
a low cost solution.                                                  combustor and the second combustor. This
                                                                      design would allow the variation of the volume
The unusual aspect of this proposal is that the lift                  flow to the high pressure turbine and the
fan is driven by a double-pass tip turbine. The                       intermediate (or low pressure) turbine by varying
double-pass tip turbine is designed such that the                     the exit temperatures from each of the two
static pressure at the inlet and exit is essentially                  combustors. Hence, a variable geometry engine
the same, for both the stages. This allows two                        could be achieved without introducing any
partial admission turbines to be designed sharing                     mechanical features within the hot section to vary
the same circumference. The "high pressure                            the engine cycle. This concept has the added
turbine" is formed by the first sector of the whole                   advantage that by burning within two combustors,
turbine, the "low pressure turbine" being formed                      the maximum temperatures reached would be
by the remainder of the circumference.                                lower than a conventional single combustor
                                                                      design, and would hence result in lower levels of
           FIGURE 31 - SINGLE ROTOR DOUBLE                            oxides of nitrogen. This conceptual design needs
                                                                      further study.
    BLEED FROM                              LOW PRESSURE
  “PARENT” ENGINE                              INLET                              FIGURE 32 - DOUBLE COMBUSTOR
                                                                                    VARIABLE CYCLE TURBOFAN

                                            HIGH PRESSURE

      PARTIAL                                 TIP DRIVEN
     ADMISSION                                    FAN

                                                                                        HIGH PRESSURE    INTERMEDIATE / LOW
                                                                                         COMBUSTOR      PRESSURE COMBUSTOR
   LOW PRESSURE                             LOW PRESSURE                               CONTROLS HIGH       FOR CONTROL OF
   TURBINE STAGE                              EXHAUST                                  PRESSURE SPOOL    INTERMEDIATE / LOW
                                                                                                           PRESSURE SPOOL

9. Implications of Global Warming                                                                                              hence emissions, compared with conventional
In the longer term, civil aviation will have to face                                                                           airframes for the same duty. Studies of such
up to the vexed question of global warming. In                                                                                 airframes show suggest that deep integration of
this context, the pollutants are not only the oxides                                                                           the engine and airframe as the most
of nitrogen, but also carbon dioxide and water                                                                                 advantageous way forward.
vapour. As discussed earlier there have been
substantial reductions in the level of oxides of                                                                               Advances in conventional aero engine cycles are
nitrogen produce and further advances can be                                                                                   always being explored. Recently, GE indicated
anticipated. Improvements in engine and airframe                                                                               an interest in increasing engine pressure ratios
design have reduced carbon dioxide and water                                                                                   from the current level of about 45 to 60. Such
vapour emissions per passenger mile. However,                                                                                  large increases pose a number of complex
the historical and predicted growth of civil                                                                                   challenges to the engine designer. It has been
aviation does mean that this is a complex and                                                                                  argued that further increases in engine pressure
difficult question.                                                                                                            ratio will increase the problem of hot section
                                                                                                                               cooling to such an extent that the returns in
The Intergovernmental Committee has recently                                                                                   performance enhancement will be modest.
reported the issue of global warming on Climate
Change in their reports on “Emissions Scenarios”                                                                               Changes in airframe design and environmental
and the impact of aviation on the atmosphere.                                                                                  pressures may create an opportunity for novel
Whilst significant uncertainties remain, the                                                                                   engine cycles, such as the “double pass tip
conclusion that this problem needs to be                                                                                       turbine” discussed earlier or an all electric
addressed is not in doubt.                                                                                                     solution and even “fuel cells” in the long term.

                                                                                                                               Aircraft designed to burn hydrogen or methane
                                   FIGURE 33 - AVIATION’S IMPACT ON THE GLOBAL
                                                       ATMOSPHERE                                                              are also possibilities. “Cryoplane” is a current EU
                                      Air Traffic Global Warming Accumulated to 1992                                           multi-national project study looking at both novel
                                                  From NOx                                                                     airframes and engines.
        Radiative Forcing (W/m²)


                                                                                                                                       FIGURE 36 - HYDROGEN FUELLED “CRYOPLANE”
                                                        CH4                                 Aerosols
                                           CO2    O3           H2O   Contrails   Indirect               Soot      Total
                                                                                  Cirrus               Aerosols



                                        Estimates of the globally and annually averaged instantaneous
                                      radiative forcing from aircraft due to changes of greenhouse gases,
                                                  aerosols, and contrails accumulated to 1992.

A number of policy options arise from the from
the      “Kyoto   Accord”.     However,  recent
announcements from the US Administration
illustrate how complex this debate will become
with this important global problem.

                                                 FIGURE 34 - POLICY OPTIONS
                                                                                                                               10. Concluding Remarks
                                                       THE KYOTO PROTOCOL                                                      The wider economic and political trends will
   • Environmental agreement signed by governments in 1997 to                                                                  continue to influence the airlines and
     address global warming                                                                                                    manufacturers. Historically, we have seen the
   • Overall 5% cut required from 2008-2012 greenhouse gases                                                                   primacy of the nation state. There were „flag‟
     relative to 1990 levels
                                                                                                                               carriers and national champion manufacturers.
   • Control of aviation emissions delegated to ICAO                                                                           The trend to a more liberal world trading regime
   • CAEP WG 5 looking at a range of market-based options                                                                      has inevitably had an impact on the industry.
   • European Commission has indicated interest in such instruments                                                            Some observers say we will see large regional
     to meet its specific Kyoto targets
                                                                                                                               power blocs, others foresee nations fragmenting
                                                                                                                               into local ethnic or religious areas.

                                                                                                                               Within the airline industry, we have seen cross
The technological options include developments                                                                                 border alliances and even ownership of foreign
in airframes, engines and change of fuel used.                                                                                 carriers. The major engine companies, until
                                                                                                                               recently, have not made significant strategic
“Blended Wing” body airframes offer substantial                                                                                moves outside their home countries. Essentially,
(about 30 percent) reduction in fuel burn, and                                                                                 the securing of partners at an engine programme

level was enough for national positioning                                         environment. This is an important issue since the
reasons.     More    recently,     the  engine                                    industry‟s know-how is highly biased towards
manufacturers have been more ambitious. Pratt                                     „learning-by-doing‟ rather than fundamental
and Whitney were at one time considering an                                       breakthroughs in technology, as in the
equity exchange with MTU. General Electric has                                    pharmaceutical industry.
said it would consider purchasing a stake in
SNECMA if the company is ever privatised.                                         As „learning-by-doing‟ becomes increasing more
However, it is Rolls-Royce that has made the                                      difficult in tomorrow‟s new global environment,
most significant strategic initiatives with its                                   the importance of replacing this with the very best
German joint-venture company with BMW AG,                                         education, which encompasses all aspects of the
and the recent acquisition of the US based                                        relevant gas turbine technologies, including
Allison Engine Company.                                                           design, will prove a challenge. Sir Frank Whittle's
                                                                                  observations about the contribution of his own
All the three Primes would argue that they                                        education and training, will be ever more relevant
consider such strategic actions make financial                                    in the future. Those engineers aspiring to be the
sense but there are likely to be three other                                      future leaders within this industry will require an
imperatives. Firstly, Primes fear that the world                                  understanding of the competitive business issues
may consolidate into protectionist regional power                                 and be able to work with international teams
blocs. To produce business cases with adequate                                    dispersed sometimes over many countries.
rates of return, engine programmes have to be
sold on a global scale. Therefore, a presence in                                   The capability to deliver to agreed, and ever
each region is important to minimise the risk of                                  tighter, timescales will be a necessary discipline.
exclusion     from     key markets.     Secondly,                                 The time to launch a new aero-gas turbine has
government support for engine technology                                          been historically longer than that required to
development is not global but national. Primes                                    launch a new aircraft. In order to reduce their
wish to secure as much state aid for their                                        risk, aero-engine manufacturers have been
programmes as possible. This can only be                                          reorganising the period from a commitment to an
guaranteed by ownership of the indigenous                                         engine, to certification, to bring this time in line
manufacturer. Finally, a stake in the home                                        with the time required for the launch of an
manufacturer may open lobbying opportunities to                                   aircraft. The ability to manage the process in the
secure sales from the country‟s airlines. The                                     shortest possible time-scale will prove to be of
effect of relationships at the engine programme                                   very significant commercial advantage. The
level can often be weakened by indigenous                                         timely completion of the various phases towards
manufacturers allying with competitors in another                                 certification create the opportunity to review the
thrust sector. To overcome this, the Primes could                                 implications of the design on the product life-
opt for control of the company.                                                   cycle costs and competitiveness, reducing much
                                                                                  of the risk.
                                                                                     FIGURE 34 - SUCCEEDING IN THE 21ST CENTURY
                    History             Today                Future
                  Nation State     Regionalism                                     • GLOBAL VALUE ADDED COLLABORATIONS
   Unit                                                  Fragmentation
                                                                                   • TIME SCALES MANAGEMENT TO INCLUDE LIFE
                  Flag Carrier,    Global, Regional     Global, Regional,
                                                             Niche                   CYCLE RISK MANAGEMENT
   Airline          Domestic
  Industry                                                                         • GLOBAL SOURCING BY PRIMES : RESEARCH TO MANUFACTURE
                  Technology      Business Orientated   Service Orientated
                                                                                   • SUCCESSFUL SUPPLIERS : WORLD CLASS “SYSTEMS” NICHE PLAYERS
  Engine                          Free World Market      Global Market             • EDUCATION FOR COMPETENCE, CONFIDENCE AND CREATIVITY

    Firm         Home Country     Global Positioning    Optimisation of
  Strategy         Dynamics                             Global Structure          The ability to create collaborations that tap into
                                                                                  the knowledge of customers, suppliers and
                                                                                  others on a global basis will be one of the skills to
In the long term, one could imagine the Primes                                    cultivate. The organisation and participation in
becoming more and more fragmented. The                                            networks that tap new knowledge to create value,
corporate „brain‟ may reside in the current home                                  and international relationships that add to this
country. However, research and development                                        value, will be among the new competencies that
could be done in another country and                                              engineers on the way to the top will need to
manufacturing in yet another. The company                                         acquire.
would optimise its operation using the criteria of a
country‟s competitive advantage i.e. funding                                      Engineers aspiring to manage this industry will
availability, factor conditions and market                                        need personal qualities such as integrity and
potential. The downside to this vision is that                                    openness, co-operation and team spirit,
corporate „experience‟ is likely to be lost as                                    commitment and ability to work under pressure.
programmes are shunted to the best economic

As the risks associated with the technology used           Nonetheless some references         are   included
are reduced, the ability to innovate conceptually,         together with related literature.
in design, product life-cycle and business
definition will become more important. Such skills
and attitudes are anchored in the confidence,
which experience and education have to provide.
                                                           References and Related Literature
There will be very few universities with either the
background, or perhaps the interest to invest in           Airbus Industrie. “Market Perspectives for Civil
such a difficult and specialised task of educating         Jet Aircraft”. February 1993.
people at this level. Such programmes will thrive
when supported by world-class organisations,               J. W. Allen, F. W. Armstrong and R. M. Denning.
who see the investment in their future technology          “Evolution of Aviation and Propulsion Systems:
leaders as crucial to their success, and a "shared         the Next 50 Years”. Proc of the IMech E Journal
learning environment" as part of that investment.          of Aerospace Vol209 G1 1995.

The primes will source their research, design,             F. W. Armstrong. “The Aero-Engine and its
development and manufacture on a global basis              prospects - 50 Years After Griffith”. Lecture to
from those who have earned the reputation of               the RAeS 18th November 1976.
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consequences for suppliers and others who                  Government Policy - The Airlines‟ View of the
relate to this industry. Those organisations that          Future”. Financial Times Conferences - World
do not have the culture to be world class, or are          Aerospace and Air Transport, September 1994.
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Brief CV

Professor Riti Singh, CEng FIMechE FRAeS
FIDGTE, Professor of Gas Turbine Engineering

Professor Riti Singh is the Executive Head of
Department      of   Power    Engineering     and
Propulsion, and the Deputy Head of the School of
Engineering, Cranfield University. He has wide
interests in gas turbine technology, ranging from
strategy and life cycle costs, design and
application, combustion, cycle simulation and

Professor Singh has over 30 years' experience in
gas turbine research, design and development in
industry, and more recently in post-graduate
education and research. He has held senior
appointments in Rolls-Royce plc in the UK, ASEA
Brown Boveri in Sweden, and was Chief
Engineer at Kongsberg Gas Turbines, Norway.

Over the past fifteen years, Professor Singh has
acted as a Consultant in over twenty countries for
over fourty organisations.


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