Subsonic versus Supersonic Business Jets - Full Concept Comparison considering Technical, Environmental and Economic Aspects

I Table of Contents

II Abbreviationsi

III Figures

IV Tables

1 Introduction

2 History of Supersonic Travelling

3 Motivation
3.1 Mobility, Range and Travelling Time
3.2 Prestige
3.3 Efficient use of free Airspace at high Altitudes
3.4 Platform for new Technologies
3.5 To Generate Profit
3.6 Supersonic Cargo Transport
3.7 Supersonic Non-Civil Applications

4 Technical Aspects
4.1 Basics of Supersonic Flights
4.1.1 Definitions for Mach Number and Speed of Sound
4.1.2 Subsonic, Transonic and Supersonic Speed
4.1.3 Sonic Boom
4.1.4 Supersonic Cruise Efficiency
4.1.5 Aircraft Range Considerations
4.2 Design and Manufacturer Organisations
4.2.1 Aerion Corporation
4.2.2 Dassault Aviation SA
4.2.3 Gulfstream Aerospace Corporation (GAC)
4.2.4 Mitsubishi Heavy Industries (MHI)
4.2.5 Raytheon Aircraft Company
4.2.6 Sukhoi-Gulfstream
4.2.7 Supersonic Aerospace International (SAI)
4.2.8 Tupolev PSC
4.3 Research Projects
4.3.1 Environmentally High Speed Aircraft (HiSAC)
4.3.2 Japan Aerospace Exploration Agency (JAXA)
4.3.3 National Aeronautics and Space Administration (NASA)
4.3.4 Supersonic Cruise Industry Alliance (SCIA)
4.4 Safety Considerations
4.4.1 Atmospheric radiation at high altitudes
4.5 Summary Specifications for Supersonic Business Jet Concepts

5 Environmental Aspects
5.1 Aircraft noise
5.1.1 Engine noise
5.1.2 Aerodynamic noise
5.1.3 Noise from aircraft systems
5.1.4 Effects of aircraft noise
5.2 Exhaust Emissions
5.3 Fuel Consumption (non-renewable resource)

6 Economic Aspects
6.1 Aviation Outlook
6.1.1 Business Aviation Outlook – General
6.1.2 Business Aviation Outlook – “High-End” Segment
6.2 Supersonic Business Jet - Market Analyse
6.2.1 Customer Groups for a small SSBJ
6.2.2 Approach I – Estimation based on the Subsonic Business Jet High-End Market
6.2.3 Approach II – Use and Correlation of Existing Market Studies conducted for SSBJ
6.3 Product Life Cycle
6.4 Acquisition (Programme) Costs
6.4.1 Research, Development, Test and Evaluation Costs (RDTE)
6.4.2 Procurement and Production Costs
6.5 Programme Cost Estimation based on RAND DAPCA IV model
6.6 Cost-Volume-Profit Analysis
6.7 Programme Financing
6.8 Ownership Costs
6.8.1 Direct Operational Costs (DOC)
6.8.2 Crew Cost
6.8.3 Fuel/Oil/Additives Cost
6.8.4 Maintenance Cost
6.8.5 Landing fees (Noise, Emissions)
6.8.6 Indirect Operational Costs (IOC)
6.8.7 Total Operational Costs (TOC)
6.9 Aircraft Utilisation
6.10 Disposal Costs
6.11 Marketing Strategy

7 Politics and Regulations
7.1 Global - ICAO
7.1.1 ICAO Standards and Recommend Practices on Aircraft Noise
7.1.2 ICAO Standards and Recommend Practices on Emissions
7.2 United States – FAA
7.2.1 FAR 91.817 Civil aircraft sonic boom
7.2.2 FAR 36 Noise Standards Aircraft Type and Airworthiness Certification
7.2.3 FAR 34 Fuel Venting and exhaust Emissions requirements
7.2.4 FAR 25.773/91.175 Cockpit View
7.2.5 FAR 25.841 Cabin Pressurisation
7.2.6 FAR ETOPS (Extended Range Twin-Engine Operations)
7.3 Europe – EASA
7.4 Asia-Pacific, Africa, South-America
7.5 Airport Noise
7.6 Politics and Public Perception

8 Concept Comparison – Subsonic vs. Supersonic Business Jet
8.1 SWOT Analysis
8.2 Risk Assessment
8.2.1 Risk Identification and Description
8.2.2 Risk Estimation
8.2.3 Risk Evaluation
8.3 SSBJ Competitor Analysis
8.4 Aircraft Comfort

9 Conclusion

10 Outlook

11 Executive Summary

12 References

13 Attachments
13.1 Subsonic Business Jet – Models on the Market and in Development (58)
13.2 Specific Fuel Consumption (SFC) trends for various engine types (72)
13.3 SSBJ Programme Cost Estimation Calculator (Excel) based on DAPCA IV model
13.4 CAEP Working Paper CAEP/8-WP/35 – Extract Notional Roadmap
13.5 Declaration of Authorship

II Abbreviations

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III Figures

Figure 1: Gulfstream G650 (2)

Figure 2: Content of Master Thesis - Subsonic versus Supersonic Business Jets

Figure 3: Development Aircraft Bell X-1 - 1947

Figure 4: Tupolev Tu-144 [left image] and Concorde [right image (7) ]

Figure 5: Summary Supersonic Aircraft Progress (10)

Figure 6: Mach number vs. Cruise Travelling Time for a distance of 4,000 nm (7,408 km)

Figure 7: Worldwide development number of billionaires 1996 – 2010 (16)

Figure 8: Successful Business Strategy by Michael Porter (19)

Figure 9: Sound wave propagation at various velocities (22)

Figure 10: Illustration Sonic Boom – N-Shaped wave (adapted from (24) )

Figure 11: Mach number vs. Drag

Figure 12: Lift/Drag ratios as a function of Mach number (27) (28)

Figure 13: Propulsion Efficiency Characteristics (Ref (30) , p 9)

Figure 14: Illustration of Aircraft ranges

Figure 15: Gulfstream business jet aircraft models (35)

Figure 16: Gulfstream Low-Shock Supersonic aircraft (36)

Figure 17: JAXA Low Sonic boom model S3CM with reduced sonic boom signature

Figure 18: NASA Involvement in Supersonic Research

Figure 19: Atmospheric radiation exposure (48)

Figure 20: Comparison Maximum Range

Figure 21: Comparison Cruise Speed

Figure 22: Comparison Maximum Take-off Weight (MTOW)

Figure 23: Comparative noise levels of various engine types (49)

Figure 24: Noise Scale (50)

Figure 25: Aircraft Engine Emission (51)

Figure 26: Business Aviation contribution to climate change (52)

Figure 27: Passenger Traffic Demand Growth 1950 - 2009 (54)

Figure 28: Business jets and Turboprop fleet size 2001 - 2010 (56)

Figure 29: Business Aircraft deliveries versus corporate profit (56)

Figure 30: Business aviation forecast 2011-2021

Figure 31: Supersonic Business Jet Market Demand Curve

Figure 32: Summary Market Studies

Figure 33: Product Lifecycle (64)

Figure 34: Simple Linear Example SSBJ Life Cycle Cost Calculation

Figure 35: Elements of Life Cycle Cost (65)

Figure 36: Typical Aircraft design life cycle from concept definition to EIS (67)

Figure 37: Engine development cost driver

Figure 38: Programme cost elements – 300 Aircraft

Figure 39: Aircraft unit cost versus cumulative output

Figure 40: SSBJ Profit margin optimisation

Figure 41: Cost elements for engine maintenance (78)

Figure 42: Operational and Maintenance Cost Comparison

Figure 43: SSBJ Marketing mix (81)

Figure 44: Sonic Boom Rulemaking Process

Figure 45: ICAO Noise limits (Ref. (85) p 22)

Figure 46: Noise margin relative to chapter 3 limits by class of aeroplane Ref. (85) p 25

Figure 47: Aircraft noise certification reference points

Figure 48: Comparison of NOx Regulations for Subsonic and Supersonic Aircraft Ref. (87) p 56

Figure 49: Concorde variable nose system to enhance cockpit visibility

Figure 50: Balance between Strength/Opportunities and Weaknesses and Threats

Figure 51: Results Probability – Impact Analysis

Figure 52: Gulfstream G550 – Cabin Dimensions and Layout

Figure 53: Aerion SSBJ – Cabin Dimensions and Layout

Figure 54: Small SSBJ as a key for Hypersonic Transport

Figure 55: SonicStar - Hypermach Concept (98)

Figure 56: NASA Hypersonic Aircraft X43A (99)

IV Tables

Table 1: Gulfstream G650 Specification (3)

Table 2: Main Aircraft Specification Tu-144S (8) and Concorde (9)

Table 3: Aerion SSBJ Specification (30)

Table 4: Raytheon SSBJ Low Boom Configuration (38)

Table 5: Raytheon SSBJ High Boom Configuration (38)

Table 6: Sukhoi S-21 (S-21G) SSBJ Specification (39)

Table 7: SAI Specification ( 40)

Table 8: Tupolev Tu-444 Specification (42)

Table 9: Comparison of identified SSBJ parameters with the G650 and the Concorde

Table 10: Summary: Supersonic Business Jet Specification

Table 11: Worldwide business jet deliveries 1998 - 2010(56)

Table 12: Business jet deliveries 2006 – 2010 with a price of above 40 Million USD (56) (57)

Table 13: SSBJ demand - 40 Million USD (100 %)

Table 14: Estimated RDTE Costs of Aircraft Programs in the past and future

Table 15: Percentage of Cost by Design Cycle Phase—New Designs (67)

Table 16: Input parameter to calculate SSBJ programme cost - Modified DAPCA IV Cost Model

Table 17: Results SSBJ programme cost - Modified DAPCA IV Cost Model

Table 18: Aircraft Purchase Price Calculation

Table 19: Cost-Volume-Profit Analysis in Million USD

Table 20: Profit margin optimisation – High Performance Configuration

Table 21: Aircraft noise charges* (Hamburg airport) (78)

Table 22: Operational and Maintenance Cost Comparison

Table 23: SSBJ SWOT Analysis

Table 24: Risk Identification (Register) and Description

Table 25: SSBJ Competitor Analysis

1 Introduction

On the 26th of August 2010 the new “ultra-large-cabin ultra-long-range” Gulfstream G650 business jet (see figure 1) reached Mach 0.995 during its flight test campaign (1). This is almost the speed of sound (Mach 1) and inspires one to say, why not fly faster than the speed of sound! Reduce travelling time in the commercial business aviation segment. This is, however not a completely new vision. Many companies and research facilities have already spent a lot of time and investment in studies to investigate the feasibility of supersonic flight. Entry Into Service (EIS) for the new Gulfstream G650 is scheduled for 2012.

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Figure 1 : Gulfstream G650 (2)

The following Table 1 summarises the main performance parameter of the G650 aircraft. The parameters range, cruise speed, MTOW, etc. have been selected and serve as a basis to allow an appropriate comparison between the G650 as the latest “high end” Subsonic Business Jet and potential in future Supersonic Business Jets (SSBJ) within this subject Master Thesis. With the impressive maximum range of nearly 13,000 km the G650 can connect Dubai with New York or London with Buenos Aires within almost 14 hours.

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Table 1: Gulfstream G650 Specification (3)

Gulfstream business rival Bombardier Aerospace also announced in October 2010 two new “high end” models, the Global 7000 and 8000 with a maximum range of 7,300 nm (13,520 km) and 7,900 nm (14,631 km) at cruise speed Mach 0.85. Entry Into Service is scheduled for 2016 (Global 7000) and 2017 (Global 8000) (4). A comprehensive overview of business jets in service and in development is given in attachment 13.1.

A Supersonic Business Jet flying at Mach 2 cruise speed could virtually halve the travelling time, which would enormously enhance the mobility and flexibility. In order to achieve this ambition a paradigm shift is required. New technologies must be established, the impact on the environment must be understood and minimised, existing regulations must be changed to permit overland flight restrictions and the product still needs to be economically viable. All of the above aspects must be considered and will be subject for discussion within this Master Thesis (See also figure 2).

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Figure 2 : Content of Master Thesis - Subsonic versus Supersonic Business Jets

Discussions regarding the introduction of a Supersonic Business Jet (SSBJ) have been on-going for decades. However, until now no project has been officially launched to develop and build a SSBJ. This indicates that the required maturity of the market has not been reached.

To understand the state of the business and barriers to entry, this document will first analyse and summarise the history of Supersonic Transport (SST). There are no successes without motivation. For that reason, all possible motives will be deliberated. The main part and backbone of this thesis will be a detailed discussion of all identified and involved aspects. The gained conclusions will serve as a basis to allow a comprehensive comparison between Subsonic and Supersonic Business Jets. This will be supported by a SWOT analysis and a risk assessment. The key points will be summarised to derive the most reasonable conclusions regarding the readiness of small SSBJs, highlight associated risks and provide recommendations. Further fields of studies and future visions round up this subject Master Thesis.

2 History of Supersonic Travelling

The first manned supersonic flight (> Mach 1) of an aircraft was achieved more than 60 years ago in October 14th 1947 (5). A development aircraft named the Bell X-1 (see figure 3) successfully broke through the sound barrier and reached a maximum speed of Mach 1.06 at 13,100 m. In 1954, a further advanced Bell X-1 reached even speeds of Mach 2.4 at an impressive altitude of 27,400 m (89,895 ft).

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Figure 3 : Development Aircraft Bell X-1 - 1947

The first successful supersonic flight of the Bell X-1 led to a new era resulting in many military supersonic aircraft and later also civilian supersonic aircraft. Mid 1950's a U.S. consortium consisting of Lockheed, Boeing, General Electric (GE), Pratt and Whitney (P&W) started to develop a civilian Supersonic Transport (SST) aircraft. The aircraft was intended for carrying of 250-300 passengers at cruising speed up to Mach 3 for the range of 7,000 – 8,000 km. After more than one decade of study, principal design work and competition, the U.S. federal government finally selected Boeing in 1959 to build the first prototype for the country's first supersonic transport (SST) (6). Twenty-six airlines ordered 122 aircraft, however government funding was withdrawn in 1971. The entire project was cancelled before the Boeing 2707 prototype was ever built. The main reasons were; far greater costs than expected, environmental and technical concerns. In parallel, the Anglo-French Concorde and the Soviet Union Tupolev 144 (Tu-144) were developed. The first flight of a civilian Supersonic Transport was performed by the Tu-144 on the 31st December 1968 followed just two month later by the Concorde.

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Figure 4 : Tupolev Tu-144 [left image] and Concorde [right image (7) ]

The Tu-144 had a tragic start when the first production Tu-144 crashed at the Paris Air Show in 1973. The aircraft went into commercial service, flying cargo in 1975 and then released for passengers in 1978. Nevertheless, due to safety issues the planes were grounded and removed from service following another crash in 1978. It was also believed that a lack of the passenger market in the former Soviet Union contributed to this decision. Later modified variants continued to fly as test beds for research of supersonic flight aircraft. The Concorde was in contrast more successful. Scheduled services for the Anglo-French Concorde began officially on Wednesday the 21st of January 1976. The decision to retire the Concorde at the end of October 2003, after almost 28 years of service and 140 Million flight miles, carrying in total more than 2.5 million passengers was prompted by compelling technical and economic reasons. One main reason was the tragic crash, which occurred on the 25th July 2000 where all 100 passengers including the crew died. As consequence the passenger demand declined. It should be noted that accident root cause investigation concluded that it was not directly caused by a technical defect of the Concorde. Prior to the accident the Concorde had been the safest operational passenger airliner in terms of passenger deaths-per-kilometers travelled with zero. The following table 2 shows the specification of the Tu-144S and the Concorde aircraft respectively.

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Table 2: Main Aircraft Specification Tu-144S (8) and Concorde (9)

In total 20 Concords have been built (including 6 development aircraft), which from an economical point-of-view, was a disaster considering the enormously high development costs. The Tu-144 and Concorde might have looked similar, but the Concorde was superior in its avionics and capabilities. Both aircraft generated a high noise during start, landing and flight and the exhaust emissions were also considerably high compared to conventional subsonic aircraft such as the Boeing 747 jumbo jet, which entered the market at the same time (1970). The following figure 5 gives a broad overview of the development and progress of military and commercial Supersonic Aircraft over time. Since 2003, no commercial Supersonic Aircraft is in service.

In the military segment Supersonic Aircraft were more successful like the Lockheed F-104 “Starfighter” with more than 2500 built (First flight 1954, EIS 1958) or the McDonnell Douglas F-4 Phantom II (First flight 1958, EIS 1960) with more than 5000 built and operated.

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Figure 5 : Summary Supersonic Aircraft Progress (10)

Analysis and understanding the history is always a very beneficial instrument for all projects planned in future. Based on the past experience presented, it can be concluded that the success of SSBJs are based on three concurrent measures: Technical; Environmental and Economic. This is discussed further in sections 4 Technical Aspects, 5 Environmental Aspects and 6 Economic Aspects.

In addition, the public perception and the regulations must be changed to permit commercial overland supersonic flight. All the related problems must be addressed and/or compromised before supersonic business travelling can become a real success. The need for mobility and reduced travelling time is continuously moving in a growing globalised world, despite the numerous challenges and the financial setback caused by the global economic recession.

Extensive studies in respect to the feasibility of SSBJs have been conducted and were published in the Aeronautical Journal (Ref (11), (12) and (13)). The articles served as basic background information for this thesis. The next chapters will go into more detail in order to understand the various problems, compare subsonic versus supersonic and to identify the potential solutions to the known problems.

3 Motivation

The motivations behind the use of developing supersonic aircraft are:

- Mobility, Range and Travelling Time
- Prestige, both for customer and company
- Efficient use of free Airspace at high Altitudes
- Developing for the future - Platform for new Technologies
- Generate Profits
- Possibility of developing Supersonic Cargo Transport and Supersonic Non-Civil Applications

These points are discussed in the following sub paragraphs.

3.1 Mobility, Range and Travelling Time

The authors understanding of the definition for Mobility is the degree of freedom to travel from one place to another. The distance, time (duration), price and comfort are seen as relevant parameter which form the way of mobility. Distance and time are in a close relationship. The further the place is to go, the longer it will take to get there. There exists different ways of travelling: by Car, Bus, Train, Ship, Bicycle, etc. and lastly by aircraft. Travelling by aircraft is up-to-date the fasted mode of transport and typically used for longer distances.

The price for mobility is of high importance. Business jet customers are most likely to value time over money. They want to travel independently in order not to rely on any scheduled flights. The main target groups identified for SSBJs are Governments, Companies and Private Persons including leasing and fractional ownerships.

Globalisation has become the dominant economic paradigm. In economic terms, globalisation refers to the growing economic integration of the world (14). Since World War II the pace, scope and scale of globalisation has accelerated immensely, in particular, within the last 25 years. The need for more travelling can be directly correlated. This is a critical business tool in the modern day industry, where time equals money.

The travelling time is an important aspect. The range is the distance an aircraft can fly between take-off and landing. The range is mainly depending on the fuel capacity and fuel consumption (Aircraft efficiency). An example for a range of 4,000 nm (7,408 km) against different travel times as a result of different speeds (or way of travelling) is presented in figure 6 below.

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Figure 6 : Mach number vs. Cruise Travelling Time for a distance of 4,000 nm (7,408 km)

It should be noted that only the cruise travelling time has been considered for this particular calculation. The time needed for taxiing, take-off, approach, decent and landing has been omitted, as this is not considered an aircraft trait and more a random variability. Mach 0.5 represents the normal cruise speed of a Turboprop type business jet typically used for shorter distances. Turboprops normally have a better effectiveness on shorter distances compared to fan engine type business jets. The cruise travelling time for a distance of 4,000 nm (7,408 km) would be about 14 hours. In comparison, a conventional business jet like the G650 would need about 8 hours. A SSBJ jet flying at Mach 2 could arrive after only 3.5 hours which provides a further time reduction.

3.2 Prestige

The Prestige to fly faster than the speed of sound and to own an aircraft which not many people can afford is another motivational aspect. The definition for the word “Prestige” found in the Cambridge dictionary is quoted as follows “respect and admiration given to someone or something, usually because of a reputation for high quality, success or social influence” (15). Prestige value motivates many rich consumers to purchase more expensive and more advanced technology aircraft than they otherwise would. Private business jets are a status symbol showing that the owner belongs to the group of the richest people in the world. Even “only” to rent a plane or fractional ownership is showing extensive wealth. The Gulfstream G650 is currently the most expensive business jet with a price between 60 and 70 million USD on the market, but if SSBJs enter the market, the G650 will be easily overtrumped in price. The money spent for the interior and furniture can also go into the regime of millions. According to Forbes an American business and financial magazine (16), the number of super-rich people is continuing growing. Since 1996 the numbers have more than doubled. More than 400 are situated in the U.S. and Canada (North America) followed by 200 Billionaires in Europe. The BRIC countries (Brazil, Russia, India and China) are in third place and have shown a strong increase in the last decade. The worldwide development of the number of Millionaires is similar.

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Figure 7 : Worldwide development number of billionaires 1996 – 2010 (16)

In respect to potential customers for expensive SSBJs this is a positive development. It is also a prestige for the SSBJ manufacturer to have a high end product in their portfolio. This can have a positive effect on the remaining products, therefore used as an appropriate marketing instrument. A small sized SSBJ could fulfill a lucrative niche market.

3.3 Efficient use of free Airspace at high Altitudes

The efficient use of free airspace above 45,000 ft (13,716 m) is identified as another reason. The airspace refers to a portion of the atmosphere controlled by a particular country on top of its territory and territorial waters unless otherwise defined a country´s airspace is used by other country´s aircraft for over flight purposes or for the reasons of reaching an airport lying on the country´s territory (the freedoms of the air as defined by ICAO). ICAO Article 1 postulates that every state has complete and exclusive sovereignty over the airspace above its territory (17).

Two fixed-route systems have been established for air navigation. Between 1,200 ft (366 m) above the surface up to but not including 18,000 ft (5,486 m) above mean sea level and secondly so-called Jet-routes are defined from 18,000 (5,486 m) to 45,000 ft (13,716 m) above mean sea level. Jet-routes are designated to indicate frequently used routings. Above 45,000 ft (13,716 m) normally no direct Air Traffic Control (ATC) routes are applicable and thus point-to-point flight is possible, therefore flying above 45,000 ft (13,716 m) will avoid commercial airline traffic. Since commercial airline traffic is continuously growing the avoidance of highly busy traffic routes will be even more relevant.

Additional positive effects are that at certain altitudes above adverse weather and turbulence can be avoided. Airstream resistance is significantly reduced allowing greater range on the same fuel load. The adverse effect of jet streams can also be minimised (headwind) and the positive effect (tailwind) maximised. The jet stream is defined as a band of air that moves around the earth at relatively high speeds up to 300 km/h. Two jet streams exist: the “polar jet stream”, found over the mid-latitudes at altitudes of 20,000 ft (7,000 m) to 40,000 ft (12,000 m), and the weaker “sub-tropical jet stream”, found near ± 30º at greater altitudes of 30,000 ft (10,000 m) to 50,000 ft (16,000 m) (18).

Conventional Subsonic Long-Range Business jets like the Bombardier Global series 5000/7000/8000 or the Gulfstream G550/650 have or will have a maximum certified altitude of 51,000 ft (15,545 m) and can make already use of these advantages. A SSBJ could also make use of the free airspace above 51,000 ft (15,545 m) which gives a further operational advantage.

The absolute maximum altitude regardless of aircraft type is 60,000 ft (18,288 m) without special permission from the authorities like FAA (uncontrolled airspace).

3.4 Platform for new Technologies

The development of Supersonic Business Jets can be a platform to improve and maturely future-oriented new technologies. As such a successful SSBJ can be the flagship of an aircraft manufacturer supporting and promoting its entire fleet. Hence, the development of such a product will assist in the progress and verification of advanced supersonic design required to make SSBJ´s technically reliable, environmentally friendly, economically attractive and competitive. The sustainable success of key sections such as aerodynamics, structures, propulsions, performance and materials are of high importance and considered essential. The new established know-how and technologies can be transferred and used effectively in different business segments. In particularly, supersonic aerodynamic long range cruise efficiency, efficient thermal protection to withstand sustained high temperatures, propulsion efficiency including emissions, lightweight materials and advanced avionics and control systems are of special interest.

3.5 To Generate Profit

Supersonic Business Jets can only become successful if there is a Return of Investment (ROI). Manufacturers will only enter the market with a new product or service when it generates adequate profit. The same statement is valid for potential operators. An exclusive niche product such as a SSBJ has the potential for success. According to Michael Porter Note^[1] a successful business strategy is based on product differentiation i.e. to be better than the competition or cost leadership i.e. cheaper than the competition. A SSBJ would belong to the product differentiation category (See also Figure 8).

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Figure 8 : Successful Business Strategy by Michael Porter (19)

The product differentiation strategy characterises unique product attributes that are special valued by the customer (20). A Supersonic Business Jet will have those unique attributes. Superior flight performance and an exclusive design will be very attractive for the customer. The futuristic and extravagant aircraft shape will draw potential customers’ attention and therefore serves as a marketing instrument. The high product functionality will justify the high premium price that the manufacturing company specifies. The high price is also needed to compensate for the enormously high research and development costs associated with such a superior product.

Due to the non-existence of SSBJs the company that makes first entry into the market will have a monopoly position and the resulting benefits. SSBJ customer will have less power for price negotiation because of no alternative products.

The business case will be further discussed in section 6 Economic Aspects.

3.6 Supersonic Cargo Transport

Another incentive where an SSBJ can be used is supersonic cargo. The transport of urgent/perishable goods such as organs needed for surgery or medicine can be carried within short durations and therefore help humans. Critical Aircraft on Ground (AoG) parts can also be expeditious transported in order to reduce costly aircraft downtimes.

3.7 Supersonic Non-Civil Applications

Finally, a SSBJ can also be adapted for non-civil aircraft applications. One possible use would be the modification to a ferret aircraft equipped with special radar and surveillance systems. The SSBJ could also be used for time critical military cargo transport.

4 Technical Aspects

In order to understand the strengths and weaknesses of supersonic flight, there are several technical aspects that need to be fully understood, these are addressed in the following subparagraphs.

4.1 Basics of Supersonic Flights

4.1.1 Definitions for Mach Number and Speed of Sound

In order to understand travelling at supersonic speed, it is important to familiarise with the so-called Mach number Note^[2]. The Mach number is a non-dimensional unit to measure speed and is defined as the ratio of the speed of an object (aircraft) in relation to the speed of sound. It can be expressed in following formula:

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The sound is a longitudinal pressure wave that propagates in a material medium. Under stationary conditions (non-moving object), the pressure waves propagate three-dimensionally in all directions equally (see figure 9 top left). The speed of sound “a” for ideal gases can be expressed as follows (21):

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For a given fluid the speed of sound “a” varies at and is independent of pressure. For medium air the speed of sound is proportional to the square root of the temperature: [km/h]. Hence, it can be concluded that in a colder environment the speed of sound is higher than in a warmer environment. For example an aircraft flying at sea level at 15°C (288.15 K) the speed of sound is approximately 1,220 km/h. At 11 Km altitude (ISA standard atmosphere: T= -56.5 °C = 216.65 K) the speed of sound is only about 1,060 Km/h. Consequently an aircraft flying at an altitude of 11 km with a speed of 1,060 km/h fly’s Mach 1. 2,120 km/h would be equivalent to Mach 2. Between 11 and 20 km altitude the temperature is constant (tropopause) and consequently the speed of sound remains unchanged.

4.1.2 Subsonic, Transonic and Supersonic Speed

The different speed regimes can be distinguished into Subsonic, Transonic and Supersonic Speed. For Subsonic speed the Mach number is below 0.8. The range between Mach 0.8 and Mach 1.2 is called Transonic and above Mach 1.2 the range is called Supersonic Speed (See figure 9). In the transonic regime some of the airflow is supersonic and some is not (transition zone). Speeds above Mach 5 are called Hypersonic. The figure below illustrates the sound wave propagation at the different speeds (22).

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Figure 9 : Sound wave propagation at various velocities (22)

When an aircraft is moving through air faster than the speed of sound (Mach 1), it will experience a different aerodynamic reaction from the air when flying at subsonic speed. This will be further discussed in the next sections.

4.1.3 Sonic Boom

Sonic boom can be described as an impulsive noise similar to thunder with duration less than one second. As discussed in section 4.1.2 it is caused by an aircraft flying faster than the speed of sound, meaning greater than Mach 1. During flight pressure fluctuations (waves) analogous to the water waves caused by a ship´s bow moving in water are generated (see figure 10 right). Above the speed of sound these pressure waves combine and form so-called shock waves, which travel from the release point three-dimensional in all directions (See figure 9 bottom left and right). If the shock waves arrive at the ground they will be recognised as a sonic boom, normally a deep double boom. The sonic boom can have an immense impact on the environment. There exist two types of waveforms depending on the boom signature: N und U-type (23). N-waves are formed during steady state flights and it is shaped like the letter N. In opposite, U-waves are a result of transient manoeuvres. N-waves have a positive peak overpressure caused by the bow wave which is followed by a linear decrease in the pressure until the rear shock caused by the tail wave returns to ambient pressure. Figure 10 illustrates the phenomenon.

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Figure 10 : Illustration Sonic Boom – N-Shaped wave (adapted from (24) )

The pressure difference Dp is the noise that is detected by the ear. The noise is normally expressed in Decibel [dB] a logarithmic unit and gives a relative measure of sound intensity. The sound intensity level can be calculated using following equation (Ref (25); pp 452-453):

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The logarithmic sound intensity level scale matches the human sense of hearing. Doubling the intensity increases the sound level by 3 dB due to the logarithmic function. The average home sound intensity level is about 50 dB (0.0063 Pa). The human pain threshold is about 110 – 130 dB (6.3 – 63 Pa) depending on the noise frequency. According to (Ref (9), p 764) the Concorde generated overfly noise levels when flying at Mach 2 at an altitude of 52,000 ft (15,545 m) is 93 Pa. This equates to approximately 133 dB. In addition, Concorde emitted a take-off noise between 110 – 120 dB which has also always been a problem and led to human annoyance. The sonic boom level is influenced by aircraft size, shape, speed and altitude (temperature/ pressure). Larger and heavier aircraft produce larger booms because they displace more air along their flight path than smaller aircraft. Above Mach 1.3 the effect becomes smaller. To make SSBJs competitive and attractive new technologies must be developed to reduce noise emissions. Possible sonic boom noise reduction methods are presented as part of the Design and Manufacture Organisations within chapter 4.2.

4.1.4 Supersonic Cruise Efficiency

In order to fulfil the required mission capability the Supersonic Business Jet need to achieve suitable levels of cruise efficiency. The required efficiency levels must be retained in all flight regimes such as transient, transonic, take-off and landings. There are two principal elements to supersonic cruise efficiency, firstly: propulsion efficiency and secondly: the airframe aerodynamic efficiency. The aircraft aerodynamic efficiency is normally optimised for one flight condition (design point). The Breguet Note^[3] range equation for a jet engine driven aircraft is as follows (applicable for cruise travelling) (Ref (26)):

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Figure 11 : Mach number vs. Drag

The first term (cL/cD) represents the lift/drag (L/D) ratio which is a measure of the aerodynamic efficiency of an aircraft. With high lift and low drag the aircraft can maximise the range. The second term represents the propulsion efficiency in form of burned fuel per thrust generated. The third term is the measure of structural efficiency i.e. minimise fixed aircraft weight (m2). It should be noted that this is the simplified version of the range equation applicable for constant speed, angle of attack, lift and drag coefficient. This varies typically during flight. To find a plausible answer whether there is a future for Supersonic travelling it is important to fully understand the problems. The main technical problem of supersonic travelling is caused by aerodynamics laws. The natural laws change significantly from subsonic `Compressible Flow` to Supersonic `Incompressible Flow`. Compressible flow has a variation in density. In opposite, `Incompressive Flow` behaves more like a liquid. The aircraft drag is increasing with aircraft speed (See figure 11). The maximum drag is at Mach 1 with a decreasing characteristic towards greater Mach numbers. Consequently, enormous power in form of thrust delivered by the engines is needed to overcome the increase in drag. The following figure 12 shows typical L/D relationships for different Mach numbers.

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Figure 12 : Lift/Drag ratios as a function of Mach number (27) (28)

Typically L/D ratios for modern subsonic aircraft vary between 18 and 21. Past supersonic aircraft had only an L/D ratio of 7 to 8. In fact, the Concorde L/D ratio reduces from about 12 at Mach 0.95 to about 7.5 at Mach 2.0 (Ref (9), p 25). In comparison, the G650 has estimated about 20 for subsonic cruise speed conditions. A compromised solution is the variable sweep geometry configuration, which has a better subsonic performance but less supersonic aerodynamic efficiency compared to non-swept wing design. Variable sweep wings can be extended for low speeds to create more lift and folded back at high speed to reduce drag. The disadvantage of the variable sweep design is additional weight, increased complexity and associated higher costs. The problem with low L/D ratio is that more thrust in the form of engine power is needed to overcome the higher drag. The two G650 Rolls-Royce BR725 engines therefore provide 17,000lbs thrust each. Thrust is the difference between outlet and inlet velocity of the mass flow of air passing through the jet engine. To generate thrust the engines burn fuel resulting in heat, which is used to accelerate the air passing through the turbine and nozzle. This is also known as the Brayton Note^[4] cycle. Hereafter, the fuel consumption increases with supersonic speed, which has again an adverse effect on the environment (exhaust emission, fuel non-renewable energy, etc.) and operational costs.

For higher aircraft speeds above Mach 1 turbojet engines with a low bypass ratio are typically selected. They provide the best propulsion efficiency compared to Turboprops or high bypass Turbofan engines used for subsonic speeds. The propulsion efficiency for jet engines can be calculated using following expression (29):

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with: vExit = engine exhaust gas speed and v = aircraft speed in [km/h, m/s]

If the engine exhaust gas speed equals the aircraft speed, the propulsion efficiency is 1 (100 %). The different engine types Turboprop, Turbofan and Turbojet and the associated propulsion efficiencies are illustrated in figure 13 (Ref (30), p 9).

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Figure 13 : Propulsion Efficiency Characteristics (Ref (30) , p 9)

The propulsion efficiency of a Turbojet engines increases with speed up to Mach 3 to 4. Nevertheless the Specific Fuel Consumption (SFC) is still much higher compared to subsonic engine concepts (see also attachment 13.2). The SFC represents how much fuel the engine burns each hour per thrust generated. The Concorde had a SFC at cruise speed of 1.18; this means that about 20,000 kg of fuel is burned per hour (Ref (9), p 220). The engine thrust can be boosted by 50% by using an afterburner (Ref (30), p 175). The afterburner is a simple nozzle formed tube attached to the turbine where fuel is directly injected and burned. The disadvantages are even higher fuel consumption and incredibly high noise and exhaust emissions. The Concorde´s afterburner was only used during take-off and to accelerate the aircraft though Mach 1 up to Mach 1.7 (Ref (9), p 93). For cruise flight conditions the afterburner was switched off in order to save fuel.

Extreme surface heat is another by-product of Supersonic flight. It is actually compression and skin friction that causes an extreme temperature rise of the air surrounding the aircraft. At Mach 2 the temperature can go above 130°C at the nose cone (Ref (9), p 27). The lightweight materials used in the aeronautical industry such as aluminium, magnesium and composites have all a relative low temperature resistance. These materials would need to be replaced by heavier more temperature resistant materials, which have a negative effect on weight and therefore aircraft efficiency. There is also the possibility of using more expensive ceramic materials as used on the Space Shuttle. The deterioration of the aircraft engines and structure is also much higher compared to subsonic aircraft, which increases the maintenance costs due to the reduced maintenance intervals caused by high thermal stress levels exposed to in service. Speeds above Mach 2 accelerate the temperature effect and should be avoided to make a SSBJ economically attractive. In addition to cruise efficiency appropriate take-off and landing performance must be maintained.

4.1.5 Aircraft Range Considerations

The supersonic aircraft range will be a key factor for success. Long ranges such as the subsonic Gulfstream G650 or the Bombardier G7000/8000 will offer, give a significant operational advantage. The G650 has a maximum range at cruise speed of about 13,000 km and allows non-stop flights between Dubai and New York or London and Buenos Aires as illustrated in figure 14 below. The distance between London and Buenos Aires is about 6,900 nm (12,800 km).

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Figure 14 : Illustration of Aircraft ranges

Transatlantic flight capability is the minimum requirement and therefore essential for the success of a SSBJ. The distance between New York and London is about 3,500 nm (6,500 km) and between Chicago and London is about 4,000 nm (7,408 km). Based on the facts presented it can be concluded that 4,000 nm (7,408 km) is the absolute minimum range for a SSBJ. All ranges above will significantly improve the sales volume and allow a SSBJ to be competitive compared to conventional subsonic business jets. To achieve a comparable total range of a Subsonic Business jet (> 7,000 nm) a Supersonic Business Jet with 4,000 nm (7,408 km) range will have to make one refuelling stop, which will reduce the competitive advantage in travelling time.

4.2 Design and Manufacturer Organisations

The next subchapters summarises the identified design and manufacturer organisations involved in the research and development of Supersonic Business Jets. They are listed in alphabetical order.

4.2.1 Aerion Corporation

The Aerion Corporation is an advanced aeronautical engineering organisation headquartered in Reno, Nevada, U.S, founded in 2002 by the U.S. billionaire Robert Bass (31). The company was solely formed for the purpose of developing, manufacturing and commercialising a supersonic business jet. The following table 3 shows the proposed product specification. All information has been extracted from the Aerion homepage.

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Table 3: Aerion SSBJ Specification (31)

The proposed Aerion SSBJ is mainly based on the F-104 Starfighter design equipped with existing Pratt & Whitney JT8D-219 engines. The Aerion is designed to fly subsonic (Mach 0.99) and also Supersonic (Mach 1.6). The adaptation of existing platforms is Aeron’s approach to manage risks and reduce development costs. According to Aerion the aircraft will meet latest noise (ICAO Stage 4/Chapter 4 noise) and also ICAO exhaust emission standards. The selected JT8D-219 engine has a By-pass Ratio of 1.7 and will generate 19,600 pounds thrust each. No afterburner is required to achieve the Mach 1.6 cruise. The Time Before Overhaul (TBO) of the engines is projected to be 3000 hours. In comparison, the Gulfstream G650 Rolls-Royce BR725 engine has a TBO of 10,000 hours. Flying subsonic will avoid noise boom effects and therefore allow overland flights without amending the existing regulations which permits passenger supersonic overland flights. The Aerion’s natural laminar flow wing shall reduce total airframe drag by up to 20 percent versus previous delta wing technology used on the Concorde and Tu-144. The wings will be made from carbon epoxy material to accomplish structural rigidity and low weight. The certification of the Aerion SSBJ is planned for 2015. Aerion has received about 50 letters of intent which gives a total order volume of 4 Billion USD (80 Million times 50 Aircraft). At the moment discussions are ongoing with potential partner companies to start development and manufacturing the jet.

4.2.2 Dassault Aviation SA

Dassault Aviation (32) SA is a France based company founded in 1930s that operates in the global civil and military aviation industry. The Company is specialised in the design, manufacture and sale of combat aircraft (Mirage, Rafale) and executive business jets such as the Falcon business jet family (7X, 900 Series, 2000 Series). Dassault Aviation employees about 12,000 people and generated a total revenue of 4.2 Billion € in 2010 (33). The Dassault Aviation shareholders are with 50.55 % Groupe Industriel Marcel Dassault (Dassault Family), 46.32 % EADS France and the remaining 3.13 % are owned by private Investors. Dassault Aviation has been designated to lead a European Research and Development programme on supersonic aircraft (See section 4.3.1 HiSAC). The dual experience in business aviation and combat aircraft has been used by Dassault Aviation to investigate in the feasibility on a supersonic Falcon business jet concept in 1997-2000 (Falcon SST with cruise speed of 1.8 Mach and a range of 4,000 nautical miles). This was stopped due to the non-availability of a reliable and durable Mach 2 jet engine which meets the required performance specification. The global transport crisis beginning 2000 contributed to the decision to park the supersonic project.

4.2.3 Gulfstream Aerospace Corporation (GAC)

Gulfstream Aerospace Corporation (GAC) (34) based in Savannah, Georgia U.S is a major producer of business jet aircraft. GAC is a subsidiary of General Dynamics with about 90,000 employees worldwide. The total revenue generated by General Dynamics in 2010 was 32.5 Billion USD. The aerospace section contributed with an amount of 5.3 Billion USD to the total revenue (35). A series of eight business jets aircraft offering different comfort, range and speeds are within the current portfolio.

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Figure 15 : Gulfstream business jet aircraft models (35)

Gulfstream is heavily involved in the research and development of a Supersonic Business Jet concept. In order to reduce the sonic boom noise effect an extendable aircraft nose spike is proposed (quiet spike). The spike extends during supersonic flight and divides the bow shock into several less intense pressure waves (see figure 16). This results in that the sonic boom noise shape changes from N-shape to a more moderate S-shape. This reduces the sonic boom effect.

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Figure 16 : Gulfstream Low-Shock Supersonic aircraft (36)

The concept was already successfully flight tested on a NASA Boeing F15 test aircraft (2006) and is patent-registered by Gulfstream. The Gulfstream Quite Supersonic Jet (QSJ) shall have a cruise speed of Mach 1.8 and a MTOW below 100,000 lb (37). The market price will be between 70 and 100 Million USD. However, until the regulations have been changed to permit U.S supersonic overland flights Gulfstream will not enter the market with a SSBJ.

4.2.4 Mitsubishi Heavy Industries (MHI)

Mitsubishi Heavy Industries, a Japanese company with headquarter in Tokyo was founded in 1884. About 70,000 employees are working for MHI in 2010. MHI has a wide range portfolio and also offers products and services for the aeronautical industry in form of components for aircraft and engines. In 2008 Mitsubishi Aircraft Corporation announced to build a Regional Jet (MRJ) with a capacity of 70 to 90 passengers. In the past MHI was involved in the research of supersonic flights but did never proceed any further.

4.2.5 Raytheon Aircraft Company

The Raytheon Aircraft Company, since 2007 owned by Hawker Beechcraft presented on the 2003 FAA Civil Supersonic Aircraft Workshop a low and a high boom SSBJ concept. Hawker Beechcraft (38) has 8,000 employees worldwide and headquartered in Wichita, Kansas U.S.

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Table 4: Raytheon SSBJ Low Boom Configuration (39)

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Table 5: Raytheon SSBJ High Boom Configuration (39)

4.2.6 Sukhoi-Gulfstream

The Sukhoi-Gulfstream consortium developed beginning 1990s the concept for a supersonic business jet, named the S-21G (The letter G stands for Gulfstream). Due to low market resonance for commercial supersonic air travel, the project was waved and Gulfstream finally left 1992 the consortium. However, Sukhoi continued with the research and development of the S-21 concept. There exists a two engine configuration aircraft the S-21G and a three engine configuration the S-21.

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Table 6: Sukhoi S-21 (S-21G) SSBJ Specification (40)

4.2.7 Supersonic Aerospace International (SAI)

Supersonic Aerospace International (SAI) based in Las Vegas, U.S., founded in 2001 is a company that want to develop a marketable SSBJ. SAI contracted Lockheed Martin Skunk Works with a budged of 25 Million USD to assess the feasibility of a SSBJ. In October 2004 SAI unveiled its design for an SSBJ at the National Business Aviation Association (NBAA) annual convention (41). The SAI's Quiet Small Supersonic Transport (QSST) is a low-boom aircraft designed to allow supersonic flight over land.

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Table 7: SAI Specification (41)

4.2.8 Tupolev PSC

Tupolev PSC (Public Stock Company) is a Russian aerospace and defence company, headquartered in Moscow. Tupolev and other Russian aerospace companies have been united by former President Putin in 2006 to United Aircraft Corporation (UAC) (42). The Tu-444 is the second generation supersonic passenger aircraft based on previous supersonic experience such as the Tu-144 (43).

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Table 8: Tupolev Tu-444 Specification (43)

4.3 Research Projects

Several research projects have been launched and completed to investigate the environmental and technical feasibility of a SSBJ. The projects are discussed within the next subparagraphs.

4.3.1 Environmentally High Speed Aircraft (HiSAC)

The HiSAC European Supersonic Transport 26 Million Euro research project was launched in 2005 involving 37 partners from 13 countries. The project was led by Dassault Aviation with main stakeholders were Sukhoi, EADS, Rolls-Royce, Volvo and public research institutes and ended in October 2009 (44). The main project objective was to establish the technical feasibility of an environmentally compliant supersonic small size transport aircraft (S4TA). Hence, following different aircraft configurations have been investigated.

- Low noise configuration to meet ICAO Stage IV – 10 dB
- Long range configuration (>5,000 nm)
- Low boom configuration
- Variable geometry configuration (Swept wing design)
- High subsonic with supersonic capabilities (cruise speed a Mach 0.95, with supersonic capabilities up to Mach 1.2)
- Low supersonic (cruise speed a Mach 1.2)

The general aircraft targets like cruise speed (Mach 0.95 to 1.8), range (4,000 to 5,000 nm), field performances (BFL of 6,000ft), cabin size (8 to 20 passengers) were used as baseline design points.

Despite the notable technical progress, which was made, the project finally concluded based on the results gained, that the maturity of the specific technologies identified for all the concepts was rather low and more research was deemed necessary. To meet all the relevant requirements tradeoffs need to be made i.e. range vs. emissions, speed vs. noise, emissions, costs etc.

[...]

^[1] Note: Michael Porter (born 1947) is Professor at the Harvard Business School teaching business and economics

^[2] Note: The Mach number is named after Prof. Dr. Ernst Mach (1838-1916), Mathematician, Physicist

^[3] Note: The Brequet range equation is named after Louis Charles Breguet (1880-1955), Aviation pioneer

^[4] Note: The Brayton cycle is named after George Brayton (1830-1892), Engineer