April 2011 

NASA/CR–2011-217084 

N+3 Advanced Concept Studies for Supersonic 

Commercial Transport Aircraft Entering Service in 

the 2030-2035 Period 

 

H. Robert Welge, John Bonet, Todd Magee, Daniel Tompkins, and Terry R. Britt 

Boeing Research & Technology, Huntington Beach, California 

Chet Nelson and Gregory Miller 

Boeing Commercial Airplanes, Seattle, Washington 

Douglas Stenson, J. Brent Staubach, and Naushir Bala 

Pratt & Whitney, East Hartford, Connecticut 

Robert Duge, Mark O’Brien, Robert Cedoz, and Andrew Barlow 

Rolls Royce Liberty Works, Indianapolis, Indiana 

Steve Martins, Phil Viars, and Adam Rasheed 

General Electric, Niskayuna, New York 

Michelle Kirby and Chris Raczynski 

Georgia Institute of Technology, Atlanta, Georgia 

Kevin Roughen, Steven Doyle, and Katherine Alston 

M4 Engineering, Long Beach, California 

Juliet Page and Kenneth J. Plotkin 

Wyle Laboratories, Arlington, Virginia 
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April 2011 

NASA/CR–2011-217084 

N+3 Advanced Concept Studies for Supersonic 

Commercial Transport Aircraft Entering Service in 

the 2030-2035 Period 

H. Robert Welge, John Bonet, Todd Magee, Daniel Tompkins, and Terry R. Britt 

Boeing Research & Technology, Huntington Beach, California 

Chet Nelson and Gregory Miller 

Boeing Commercial Airplanes, Seattle, Washington 

Douglas Stenson, J. Brent Staubach, and Naushir Bala 

Pratt & Whitney, East Hartford, Connecticut 

Robert Duge, Mark O’Brien, Robert Cedoz, and Andrew Barlow 

Rolls Royce Liberty Works, Indianapolis, Indiana 

Steve Martins, Phil Viars, and Adam Rasheed 

General Electric, Niskayuna, New York 

Michelle Kirby and Chris Raczynski 

Georgia Institute of Technology, Atlanta, Georgia 

Kevin Roughen, Steven Doyle, and Katherine Alston 

M4 Engineering, Long Beach, California 

Juliet Page and Kenneth J. Plotkin 

Wyle Laboratories, Arlington, Virginia
Available from: 

NASA Center for AeroSpace Information 

7115 Standard Drive 

Hanover, MD 21076-1320 

443-757-5802 


Table of Contents 

1.0 Executive Summary ...................................................................................................... 9

2.0 Design Requirements (Task 3.1 & 3.2) ...................................................................... 11

3.0 Initial Reference Systems and Technologies (Task 3.3) ............................................. 20

4.0 Engine Development and Technologies (Task 3.3 & 3.4) .......................................... 35

5.0 Preliminary Engine Analysis and Trades (Task 3.5) .................................................. 41

6.0 Airframe/Engine Analysis and Trades (Task 3.5) ...................................................... 46

7.0 Technology Prioritization, Selection and Roadmapping (Task 3.6) ........................... 83

8.0 Conclusions ................................................................................................................. 92

Appendix A: Boeing Engine Summary Results and Airframe Roadmaps .......................93

(PROPRIETARY - NOT INCLUDED) 

Appendix B: General Electric Engine Development and Roadmaps ................................94

(PROPRIETARY - NOT INCLUDED) 

Appendix C: Pratt & Whitney Engine Development and Roadmaps ...............................95

(PROPRIETARY - NOT INCLUDED) 

Appendix D: Rolls-Royce Engine Development and Roadmaps .....................................96

(PROPRIETARY - NOT INCLUDED) 

Appendix E: Appendix E: Achievable Sonic Boom Levels Through Continued 

Configuration Studies (Wyle Labs) ...........................................................97

Appendix F: Boeing Airframe Technology Roadmaps ..................................................110

(PROPRIETARY - NOT INCLUDED) 

Appendix G: Aeroelastic Analysis Report (M4 Engineering) ........................................111


Submitted to NASA LaRC: 

Lori Ozoroski, Technical Monitor Peter Coen, NASA Principal Investigator 

Program Management: 

Tony Antani (BR&T) Peter Radloff (BCA) 

Principal Investigator: Bob Welge 

Co-Investigator: Chet Nelson and Todd Magee 

Report Authors: John Bonet, Terry Britt, Greg Miller, Daniel Tompkins

Technical contributors in addition to authors: 

Boeing: 

Aerodynamics/Performance/Weights: 

Brandon Huelman, Eric Adamson, Steve Hollowell, Josh Stengel, Kevin Lutke, Jan Murphy 

Acoustics 

Alan Mortlock 

Configuration: 

Tom Derbyshire, Greg Oakes 

Propulsion: 

Edward Lawson, Gary Galerne, Ed Kowalski, Kim Nguyen 

Marketing: 

Rhodri Thomas 

Structures/Materials: 

R. Terry Britt, Thomas Tsotsis, Edward White, Brian Foist, Daniel Chen 

Systems & Flight Controls: 

James Huang, David Hyde, Kamal Shweyk 

Propulsion OEMs: 

Pratt & Whitney: 

Naushir Bala, J. Brent Staubach, Douglas Stetson 

Rolls-Royce Liberty Works: 

Andrew Barlow, Robert Cedoz, Robert Duge, Mark O‘Brien

General Electric: 

Steve Martens, Phil Viars, Adam Rasheed, Louise Chang, Wontae Hwang 

Georgia Institute of Technology 

Michelle Kirby, Chris Raczynski 

M4 Engineering 

Kevin Roughen, Steven Doyle, Katherine Alston 

Wyle Laboratories 

Juliet Page, Ken Plotkin 


Abstract 

Boeing, with Pratt & Whitney, General Electric, Rolls-Royce, M4 Engineering, Wyle Laboratories and 

Georgia Institute of Technology, conducted a study of supersonic commercial aircraft concepts and 

enabling technologies for the year 2030-2035 timeframe. The work defined the market and 

environmental/regulatory conditions that could evolve by the 2030/35 time period, from which vehicle 

performance goals were derived. Relevant vehicle concepts and technologies are identified that are 

anticipated to meet these performance and environmental goals. A series of multidisciplinary analyses 

trade studies considering vehicle sizing, mission performance and environmental conformity determined 

the appropriate concepts. Combinations of enabling technologies and the required technology performance 

levels needed to meet the desired goals were identified. Several high priority technologies are described in 

detail, including ―roadmaps‖ with risk assessments that outline objectives, key technology challenges, 

detailed tasks and schedules and demonstrations that need to be performed. A representative configuration 

is provided for reference purposes, along with associated performance estimates based on these key 

technologies. 
8 

THIS PAGE INTENTIONALLY LEFT BLANK 
9

1.0 Executive Summary

This is the final report by Boeing to NASA under Contract NNL08AA16B ―Advanced Concept Studies for 

Supersonic Commercial Transport Aircraft Entering Service in the 2030-2035 Period‖, Paragraph 11 

Deliverables/Documentation Requirements. It summarizes the work and findings, with non-proprietary 

information in the main report, and proprietary information in appendices. 

NASA‘s current projects have been aimed at developing tools and technologies that will help supersonic 

aircraft to enter service in N+1 (2012-15) and N+2 (2018-20) timeframe. Boeing supports NASA‘s objective 

to identify and assess advanced vehicle and propulsion concepts, as well as corresponding technologies, for a 

new generation of supersonic commercial aircraft which could be in service by the 2030-35 timeframe 

(―N+3‖). NASA‘s vision is that this new generation of commercial aircraft will extend the benefits of 

supersonic travel to a potential market with a broader segment of the public, carrying a larger number of 

passengers to improve economic viability, while meeting the increasingly stringent environmental 

requirements in noise and emissions anticipated being in place in 2030-35 timeframe.

The specific objective of the NASA N+3 study was to methodically identify and evaluate conventional and 

unconventional commercial supersonic configurations including closely integrated aircraft/propulsion 

concepts and prioritize technology developments needed to surmount future barriers. Results are supported 

by analysis and detailed assessment of the pros/cons of different approaches. This information was used to 

identify technology and prediction methods capability gaps, technology requirements, risks and their 

mitigation approaches, and to develop N+3 technology development/validation/maturation plans and 

roadmaps.

The initial effort under this contract was aimed at defining the design goals and metrics based on market 

conditions and NextGen requirements for supersonic aircraft entering service in the 2030-2035 time period. 

The majority of effort was devoted to defining/evaluating configurations and engine architectures, 

defining/evaluating enabling technologies, and prioritizing the technologies. Roadmaps of the most 

promising technologies and technology combinations were prepared and reported in February 2010.

Configuration ideas were distilled from the initial effort of the entire N+3 team to collect configuration and 

technology ideas. Forecasts of engine performance and design features by Rolls-Royce, Pratt & Whitney, 

and General Electric enabled initial screening of several candidate configuration and engine combinations. 

Technologies were identified which would enable more slender and flexible airframes, reduce engine noise, 

lower sonic boom, and provide improved drag and fuel consumption. Ultimately, the ―Icon-II‖ Boeing‘s 

recommended configuration and reference engine were developed, taking advantage of expected 

configuration enabling technologies. Performance benefits including a 5% reduction in operational empty 

weight and 10% reduction in cruise drag that come from application of various advanced technologies were 

assumed in sizing this ―concept plane‖. The ―Icon-II‖ represents a low boom supersonic airliner concept of 

the 2030-2035 time period with 120 passengers and ―trans-Atlantic+‖ range.

Section 2 of this report contains the Boeing forecast of the market and regulatory environment that a 

supersonic airliner may face in the ―N+3‖ timeframe, and design goals that might make it feasible. The 

material also appears in a separate report delivered in January 2009. It concludes that a potentially viable 

percentage of future travelers would be willing to pay a fare premium to save time, and this could constitute 

an attractive business opportunity for airlines and manufacturers of future supersonic-capable aircraft. 

Such aircraft would require 4000-5000nmi range capability, reasonably high fuel efficiency and flexible 

operational characteristics in order to be economically competitive. Low emissions, noise & sonic boom 

will also be essential.

Section 3 describes our methodical approach to initially identifying and evaluating promising configuration 

directions and technological innovations. It employed a traditional brainstorming workshop, and the 

Interactive Reconfigurable Matrix of Alternatives (IRMA) tool at Georgia Tech to help guide the notional 
10

application and integration of ideas. The activity identified several specific categories of configurations 

and technology combinations that served as the point of departure for more detailed studies.

Section 4 presents brief, non-proprietary statements from General Electric, Pratt & Whitney and RollsRoyce regarding their forecasts of emerging engine technologies, features and performance in the N+3 

timeframe. Proprietary appendices A, B, C & D contain more extensive proprietary discussion and 

supporting data, organized in parallel with the overall report. The proprietary Boeing Appendix A includes 

figures comparing engine options from all three companies, so it should not be shared with them.

Section 5 is a preliminary scoping of the requirements for an N+3 engine, based initially on the nominal 

aerodynamic performance and weights of the 765-072B aircraft from N+2 as a ―point-of-departure‖. It 

employed the MDAO tools and methods from N+2, and provided both the nominal requirements expected 

for the engine, and a preliminary look at the overall vehicle performance that might be expected during the 

remainder of the study. This part of the study also illuminated some areas for improving the propulsion and 

propulsion integration through advanced technology and innovative configurations. Proprietary Appendix 

A presents the proprietary data and discussion associated with Section 5.

Section 6 describes the configuration and more detailed engine assessments that reveal promising avenues 

of technology and configuration development, and areas of greatest challenge. With some assumptions 

about advanced technologies and innovative configurations, some measure of their significance to 

developing an N+3 aircraft was gained. It includes a forecast of achievable sonic boom levels, and a 

preliminary assessment of the system-wide impact of supersonic operations on emissions and within the 

NextGen ATC framework. Proprietary data and discussion from Section 6 appears in proprietary Appendix 

A.

Section 7 discusses the methodology and key non-proprietary results of the technology roadmaps that are 

offered to guide technology development in the coming decades. Proprietary discussion and roadmaps for 

the propulsion system from GE appear in Appendix B, from Pratt & Whitney in Appendix C, and from 

Rolls-Royce in Appendix D. Airframe technology roadmapping is discussed in proprietary Appendix A, 

and the corresponding roadmaps are in the proprietary Appendix F. These roadmaps were discussed and 

presented separately in February 2010.

Section 8 presents overall N+3 conclusions.
11

2.0 Design Requirements (Task 3.1 & 3.2)

2.1 Market Conditions (Task 3.1)

Several key considerations are behind the market condition forecast. First is the potential market size and 

economic benefit. It will be a global market that depends on the world population and the global economy. 

Political & economic freedoms, personal & commercial financial resources, and the propensity of 

individuals and business to travel will dictate the demand. An international aerospace project of the future 

faces uncertain availability of resources—both raw materials and fuel—and must promise profitability to a 

variety of stake-holders worldwide.

The second key consideration is fuel prices and their volatility. Along with their commodity price and 

sustained availability comes an environmental impact related cost that will likely appear in the form of 

taxes and carbon offsets.

The final key consideration is the environment, both in terms of meeting future strict regulations, and in 

terms of doing the right thing for our planet. Public concerns over NOx, stratospheric water vapor addition 

and CO2 emissions will argue for fuel-efficient airplanes and lower cruise altitudes (maximum 55,000ft). 

Contrail persistence has also become a concern, though this should not present problems at the altitudes 

which supersonic aircraft will be operating. Airport and community noise will be a challenge for all 

airplanes of the future--- more so for supersonic aircraft which require very high exhaust velocities and low 

effective bypass ratio at cruise. Minimizing sonic boom is an especially tough technical challenge, 

particularly if the boom loudness of a airliner of significant size and weight (over 150,000lbs climb weight) 

is to be reduced to a level acceptable for over-land supersonic cruise, at least in designated corridors.

The degree of technological success toward fuel efficiency, low noise, low emissions, and low sonic boom 

will to a large degree determine the ultimate viability in the future marketplace.

2.1.1 Potential Market

One estimate of the potential size of the supersonic passenger market can be made from Figure 2.1.1. 

Using qualitative indices that measure a passenger‘s willingness to pay versus the schedule and service 

quality he/she demands, the data shows a relatively small segment of the overall market amenable to 

premium airline ticket prices for supersonic travel—initially only frequent business travelers (the ―Road 

Warriors‖), and some portion of those currently using business jets. In the upper right are travelers who are 

willing to pay to reduce overall trip time by avoiding ordinary airport procedures. These parameters were 

identified in the N+2 market requirements study and carry over to the N+3 time period. One difference is 

that in the N+3 timeframe, a portion of the premium traffic may be already carried by supersonic (or high 

subsonic) business jets. Also, continued technology improvements may increase the payload-range 

capability of supersonic airliners and may allow supersonic over-land flight, potentially improving the 

market potential and lowering the price of flights for time-critical travel. If successful, this trend could 

potentially also attract some passengers from the full-fare economy and regular business travel price 

segments.

Typically, under today‘s conventional business model, a route with demand of at least 100 passengers per 

day allows an airline to justify a direct flight. Assuming supersonic flights could corner 10% to 20% of a 

given market, then only markets with demand above about 1000 passengers per day would support 

supersonic service. In Figure 2.1.2 are one recent month‘s worth of passenger demand (data points) versus 

distance of the flight, along with the number of markets (curve, right-side vertical axis) that represents. 

The target market is shown by the smaller oval. With the Boeing Current Market Outlook forecast as a 

guide, demand within this target should increase substantially by the N+3 timeframe, but it will still be a 

relatively small segment of the entire market. If the vehicle concept is flexible enough to also operate at 

lower cost and speed, the market could grow to about the area within the larger bounds (parallelogram). 

Somewhere between 2000nmi and 4000nmi is the shift from domestic to intercontinental ranges, and 

demand in this segment may not grow significantly. A similar dataset, but for long-range flights only, is 
12

plotted in Figure 2.1.3, showing the large amount of premium airline travel just under 4000nmi, then a gap 

between 4000nmi and 5000nmi, and a second large group between 5000nmi and 7000nmi. It will therefore 

be essential for a supersonic transport to initially serve this demand for 4000nmi (+/-) range, but longer 

ranges should be an objective as enabling technologies mature in the N+3 (and beyond) time frame.

A poll of corporate travelers concludes that schedule is their first consideration when choosing flights. 

Results from that poll are shown in Figure 2.1.4, illustrating that many factors have an influence, but none 

as large as schedule. Aircraft type seems to have the least influence of all, but that might not be true for a 

unique supersonic design, especially with the recognition that ―schedule‖ also might be served by flying 

faster. Historical demand for seats on the Concorde in spite of very high ticket prices is evidence of that 

impact. A relatively efficient supersonic aircraft, particularly one able to maintain high speed over land, 

might offer a segment of the market the ultimate in time-saving, point-to-point service with price that is 

reasonably close to traditional subsonic service. Depending on the route, it might be possible for a given 

aircraft (single tail number) to provide departures per day.

The argument for setting trans-Atlantic as a minimum design range is made in Figure 2.1.5, where the New 

York to London market stands out as having by far the largest current demand for full, business and 

premium fare travel. Several other trans-Atlantic and similar range markets are significant. But high 

utilization of a supersonic airplane becomes an issue at these ranges on east-west routes. While the 

airplane would be capable of flying the route several times per day, travelers might not be eager to adjust to 

less convenient departure or arrival times than the current subsonic fleet already supports. So efficient 

utilization of a long range supersonic airplane might include having the airline fly a given tail number 

aircraft on a variety of ranges, payloads, routes, and even speeds throughout the 24-hour day to capitalize 

on the operational productivity.

Actual one-way fares paid in the 3rd quarter of 2006 for NYC-LON flights are shown in Figure 2.1.6. The 

data demonstrate that about 75 passengers per day paid over $2000 one-way fare then, and some pay up to 

$5000. This was of course after the retirement of Concorde which charged substantially more for a faster 

supersonic flight than these premium subsonic fares. By the time of N+3, this market will have grown, and 

several others are expected to be substantially larger than today. A straightforward lesson from Concorde 

was that offering supersonic service generates demand for it, in excess of the latent demand for premium 

fare travel. 

If additional technological successes can further improve eventual range capability, reduce fuel burn costs, 

and provide operational and speed flexibility (including low boom design), additional viable markets could 

be opened and ticket prices reduced to be more competitive with conventional subsonic flights.

2.1.2 Fuel Price

The availability of petroleum-based fuels will likely fall through the N+3 timeframe, but be replaced in part 

or in whole by synthetic or biological sources. But, regardless of the source, the price of fuel will most 

likely rise, and probably disproportionately fast when compared to other expenses incurred to manufacture, 

own and operate an airplane. This will place even greater importance on keeping the efficiency in seatmiles per pound of fuel (the primary performance Figure of Merit, ―FOM‖, for N+3 aircraft) high for any 

aircraft of the future. The infusion of N+3 technology shows the potential to minimize the incremental fuel 

cost compared to subsonic aircraft to the extent that operations would still be profitable at reasonably low 

ticket prices.
13

2.1.3 Environmental Constraints

Mounting regulation of noise and emissions could render a non-compliant aircraft obsolete before it flies, 

so noise and emissions are critical design requirements. Taking an example from the HSCT/HSR program 

of the 1990‘s, goals then were

- No measureable adverse impact on stratospheric ozone.

- Compliance with then-year airport and community noise standards.

- No environmental damage from sonic booms.

- Compliance with all then-year requirements for low and high altitude aircraft

 engine emissions (including airport NOx, CO2, ...).

Additionally, if transonic/supersonic flight over land is to be viable, sonic booms must not only avoid 

―environmental damage‖ to animals, humans, and property, but also be reduced in intensity to a level that 

the vast majority of the over-flown population agrees is not annoying or disruptive.

Fundamentally, minimizing weight and drag (required thrust) are the most important ways to minimize 

community noise and emissions, including CO2. But advancements in controlling the airflow and turbomachinery noise, improved combustor technology, and shaping the aerodynamics to minimize sonic boom 

will be essential to meeting the ever-more challenging goals facing an aircraft designed for the N+3 time.

2.2 Design Goals (Task 3.2)

Based on the marketing assessment, and results of the N+2 studies for 2025 airplanes 1, a set of general 

design goals, guidelines and assumptions were initially established internally by Boeing to get the N+3 

studies started. These are listed below:

 100-150 passengers in 2-class arrangement with baseline interior (target 130)

 1.6-1.8 Mach cruise speed

 55,000ft or lower cruise altitude (for emissions).

 4000nmi supersonic range (trans-Atlantic+) with 6000nmi range target for Asian routes

 0.95 Mach or lower below 39,000ft for ATC margins

 Subsonic below 41,000ft for ATC margins

 3.8 seat nmi/lb fuel (0.26 lb/seat/nmi) or better supersonic fuel burn

 Sonic boom as low as practical for an aircraft of this size

o Less than Concorde over water

o Consider ―threshold Mach‖ over land if very low boom levels cannot be achieved

o Consider ―boom softening‖ (e.g. 0.7psf) near coastal areas & and along over-land 

corridors if very low overpressures appear infeasible with a realistic configuration

The guidelines were then combined with the suggested design goals by NASA shown below:

 Sonic Boom: 65-70 PLdB low boom flight, 75-80 PLdB ―unrestricted‖ flight over water.

 Airport Noise: 20-30 EPNdB cum below Stage 3

 Cruise Emissions: NOx 5g/kg fuel and particulate & water vapor mitigation

 Cruise Speed: Mach 1.3-2.0 low boom flight and unrestricted flight

 Range: 4000-5500 n.mi.

 Payload: 100-200 passengers

 Fuel Efficiency: 3.5-4.5seat nmi/lb fuel

 

1 N+2 Supersonic Concept Development & Systems Study, July 2009, final report to NASA
14

Using the above information and the results of the future market assessment, several conclusions were 

drawn to use as guidance for the remainder of the engineering activity associated with the vehicle design. 

The general conclusions are shown in the left side of the table 2.2.1. Based on the conclusions shown, the 

engineering guidelines as listed in the right side of the table were used for the vehicle design work.

2.3 Representative Program Development Schedule

To develop the technology roadmaps discussed later in this report, a representative timeline leading to the 

entry-into-service (―EIS‖) date of 2035 was required to encourage developmental milestone consistency 

across all study participants. The one developed and used in this study is shown in Fig 2.3.1. This timeline 

is a generic version of development and certification histories typical of recent commercial airliners. The 

chart also shows a notional set of certification and regulatory milestones relating to supersonic aircraft 

noise and associated ―readiness levels‖.

Figure 2.1.1 Willingness to pay vs schedule (and quality) demanded by customers.

Leisure Travelers

Bizjet 

Willingness Users

To Pay

Schedule/Service Quality 

Demanded

„Road 

Warriors‟

„Pragmatic 

Business 

Travelers‟ „Reluctant 

Business 

Travelers‟

Business Travelers

„Visiting 

Friends and

Relatives‟

„Holiday &

Leisure‟

Ad hoc

Charter

„Price Inducible

Opportunists‟

Air Elite

• Delta Air Lines affiliate

• 300+ aircraft

• GV - Lear Privatair

• Lufthansa affiliate

• BBJ scheduled service

• DUS-EWR/ORD

• MUC-EWR

• 50 + aircraft

~9%

~9%

Private

Owners

Fractiona

l

Owners

~14%

~19%

Ownership

„Hybrids‟ 

Total: ~1%

Of Total

US Pass.

~20%

~27%

Members

hip

Programs

Market

Gap
15

Figure 2.1.2 Measure of one recent month’s demand (points) and number of markets served (curve) 

versus distance of a trip. Blue oval is target, green area is potential if cost & speed are flexible.

Figure 2.1.3 Number of premium passengers per day, versus range.

0

250

500

750

1000

1250

0 1000 2000 3000 4000 5000 6000 7000 8000

Range

Small number of markets 

large enough to support 

Premium Travel Options

“Premium” passengers per day
16

Figure 2.1.4 Corporate passengers’ ranking of factors influencing their choice of airline.

a)

0

500

1000

1500

2000

2500

NYC-LONLON-HKGLAX-TYO

LON_TYO

PAR-TYONYC-PAR

LON-SIN

NYC-TYO

SFO-TYO

NYC-SEL

LON-LAX

LAX-TPE

LAX-SEL

LON-SFO

BOS-LON

SFO-SEL

FRA-TYOSFO-HKG

TPE-SFO

F

C

Y-full

Y-disc
17

b)

Figure 2.1.5 Passenger demand each way (vertical axis) on the top 20 routes in 2006. a) Distribution 

of all fares. b) Distribution of full and premium fares. F=first class, C=business, Y-full=full fare 

coach, and Y-disc=discount fair coach.

Figure 2.1.6 Actual one-way fares paid for NYC-LON for first, business and coach class seats in 3rd

quarter 2006.

0

100

200

300

400

500

600

700

800

900

1000

NYC-LON

LON-SIN

LON_TYO

LON-HKGLAX-TYO

NYC-TYO

LON-LAX

PAR-TYOSFO-TYO

LON-SFO

BOS-LONNYC-PAR

LAX-TPE

LAX-SELNYC-SEL

FRA-TYOSFO-HKG

SFO-SEL

TPE-SFO

F

C

Y-full
18

Table 2.2.1 Engineering Design Guidance Based on the Marketing Study. 

Marketing Conclusions Engineering Guideline

100-150 passengers (in 2-class arrangement) baseline 

interior, target ~130 seats

100 pass. , 130+ with optional seating

1.6-1.8 Mach cruise speed & need alternative operation plan 

to increase utilization (sub-sonic, hybrid ownership...)

1.8 design limit

Cruise altitude limited to 55,000ft (emissions) <= 55,000 ft

4000nmi min. supersonic range (trans-Atlantic +) 6000nmi 

objective to open up Asian routes

4000 nmi minimum range

Cruise M <= 0.95 below 39Kft for ATC margins. No 

supersonic speeds below 41Kft for ATC margins

Compatible with ATC and traffic

All SS mission

Supersonic fuel burn less than 0.26 lb/seat/nmi (3.8 seat 

nmi/lb) set as a plausible economic and environmental 

target (1% / year beyond N+2)

Study Goal for min fuel aircraft and 

point of reference for single metric 

designs

Sonic boom as low as practical (< Concorde over-water), 

consider ―threshold Mach‖ over-land, and ―boom softening‖ 

for operations in coastal regions and selected over-land 

corridors

Balanced 100 Seat config in the 80 

PLdB class, ―Low Boom‖ metric 

aircraft in the 70 PLdB class

(eventual goal is 65-70 PLdB)

Over-land and low-yield operational solution needed Technology Goals; low boom & good 

fuel efficiency vs. Mach, possibly 

―Threshold Mach‖ cruise 
19

Figure 2.3.1 Program Development Timeline Used for Reference in the Roadmap Development.

Reference N+3 Supersonic Timeline for Roadmaps

2025

Propulsion System Development

Prod Engine

Technology Development

Pre- Type Cert. Effort

Non-recurring

Feasibility

Authority to

Proceed

Business Case

First

Flight

TRL

5

TRL

6

Certification

and Delivery

Ground and 

Flight Test

TRL 5: Tested in Simulated Environment

MRL 5: Manufacturing Process Developed

IRL 3: System Physical Mockup Ground Tested

2035

Tech Integrated 

in System

Demonstrations

TRL 6: Tested in Relevant Environment

MRL 6: Manufacturing Process Demonstrated

IRL 4: Prototype Subjected to Representative Flight Environment

TRL 8: System Proven to Work

MRL 8: Maturity Demo

IRL 5: Fab, launch and Operations

TRL 2: Basic Principles Observed

MRL 0: NA

IRL 0: NA

TRL

2

TRL

4

TRL 4: Tech components established to work together

MRL 4: Manufacturing Processes Identified—Breadboard in Lab

IRL 1: Concept Systems Analysis Completed

TRL

3

TRL 3: Physically Validated Analytical Predictions/Not Integrated

MRL 3: Manufacturing Concepts Identified

IRL 0: N/A

Years

2012 2020 2030

Firm Config

3+ Years

First

Flight

Concept Dev

Initial Concept Defined

Preliminary Des Cycles

Product Development Cycles

Prelim Concept

SB Flt Demo

ICAO Rulemaking

CAEP 10

Draft Stds & Cert Criteria

Mod SB Flt Demo

2025

Propulsion System Development

Prod Engine

Technology Development

Pre- Type Cert. Effort

Non-recurring

Feasibility

Authority to

Proceed

Business Case

First

Flight

TRL

5

TRL

6

Certification

and Delivery

Ground and 

Flight Test

TRL 5: Tested in Simulated Environment

MRL 5: Manufacturing Process Developed

IRL 3: System Physical Mockup Ground Tested

2035

Tech Integrated 

in System

Demonstrations

TRL 6: Tested in Relevant Environment

MRL 6: Manufacturing Process Demonstrated

IRL 4: Prototype Subjected to Representative Flight Environment

TRL 8: System Proven to Work

MRL 8: Maturity Demo

IRL 5: Fab, launch and Operations

TRL 2: Basic Principles Observed

MRL 0: NA

IRL 0: NA

TRL

2

TRL

4

TRL 4: Tech components established to work together

MRL 4: Manufacturing Processes Identified—Breadboard in Lab

IRL 1: Concept Systems Analysis Completed

TRL

3

TRL 3: Physically Validated Analytical Predictions/Not Integrated

MRL 3: Manufacturing Concepts Identified

IRL 0: N/A

Years

2012 2020 2030

Firm Config

3+ Years

First

Flight

Concept Dev

Initial Concept Defined

Preliminary Des Cycles

Product Development Cycles

Prelim Concept

SB Flt Demo

ICAO Rulemaking

CAEP 10

Draft Stds & Cert Criteria

Mod SB Flt Demo
20

3.0 Initial Reference Systems and Technologies (Task 3.3)

This section describes a methodical approach to initially identifying promising configurations and 

technological innovations. It employed a traditional brainstorming workshop, and the Interactive 

Reconfigurable Matrix of Alternatives (IRMA) tool at Georgia Tech to help guide the notional 

configuration concepts and technology ideas. Following some formal Systems Engineering processes to 

select configuration and technology alternatives, the activity provided several categories of preliminary 

configurations and technology combinations that served as the point of departure for more detailed studies.

3.1 - Process Overview and Background- Submitted by Georgia Institute of Technology

The Boeing Company solicited input from the Georgia Tech (Ga. Tech) Aerospace Systems Design 

Laboratory (ASDL) to facilitate a workshop for concept selection for the aircraft. Working closely with 

Boeing, General Electric, Pratt & Whitney, and Rolls-Royce, ASDL formalized a custom process and 

created tools specifically for the concept selection activity based on past experience in similar programs. 

The overall goal of the workshop was to downselect a few operational, airframe and engine concepts for 

further analysis and study. The workshop required coordination between the partners prior to the actual 

events of the workshop to create the interactive tools which would aid in workshop activities. 

The workshop for N+3 Supersonic concept selection was centered on using an Interactive Reconfigurable 

Matrix of Alternatives (IRMA) as a tool to aid in the discovery of configurations. IRMA is a systematic 

qualitative procedure that is unique to the conceptual design process developed by ASDL2. It was created to 

provide an ―audit-trail‖ to define reference systems upon which quantitative analysis could be performed in 

a traceable, structured and systematic manner. IRMA builds on the concept of a Morphological Analysis 

created by Fritz Zwicky. Zwicky states that ―within the final and true world image everything is related to 

everything, and nothing can be discarded a priori as being unimportant.‖3

Given the complexity of the new systems, there are millions of possible alternatives in the hyperspace of 

requirements, technologies and responses. Not all these alternatives could be quantitatively compared 

within the practical time limits imposed by the program management. To overcome this issue, a qualitative 

brain-storming exercise was developed by ASDL to prioritize and down-select the important requirements 

and alternatives with feedback from disciplinary experts and program management. This allowed for the 

quantitative process of the down-selected alternatives to be much more manageable.

The IRMA is a combination of Systems Engineering techniques such as Matrix of Alternatives, MultiAttributes Decision Making (MADM) and Technique for Ordered Preference by Similarity to Ideal 

Solutions (TOPSIS). 

Figure 3.1.1 depicts the Interactive Reconfigurable Matrix of Alternatives (IRMA) which was created for 

the N+3 Supersonic workshop. These tools provided a process for functionally decomposing the problem, 

identifying alternatives and technologies to meet the functions, and identifying the solutions that meet the 

top level needs. These tools and processes provided a mechanism for encouraging collaborative 

communication at the early stages of conceptual design.

The general procedure for selecting a system through the Morphological Matrix of Alternatives was as 

follows:

- Functionally decompose the existing system

- For each function, list all the possible ways in which it might be satisfied

- Examine the matrix for the possible new permutations

The last step offers great ambiguity, which the ASDL developed IRMA process was attempting to solve. 

The IRMA process included a dynamic dashboard for visualizing the effects of each decision. When a 

 

2 Zwicky, Fritz, ―Morphological Astronomy‖, The Observatory, Vol. 68, No. 845, Aug. 1948.

3 Zwicky, Fritz, ―Discovery, Invention, Research through Morphological Approach‖, 1969.
21

selection was made, incompatible options were filtered out thereby facilitating down-selection. The 

interactive nature of the IRMA tool allowed for the Boeing team to understand the impact of decisions at 

the initial point of decision making. In a collaborative group such as seen at the N+3 Supersonic workshop, 

this tool provided a mechanism for understanding the impacts of the order of decisions as well as 

facilitating discussions among group members. 

3.2 – Pre-Workshop Steps

In order to create an IRMA and have a successful workshop for selecting advanced vehicle concepts, a fair 

amount of systems engineering activities occurred prior to the workshop. 

Figure 3.1.1 depicts the necessary general steps used to create the IRMA to prepare for the workshop. This 

section will describe the details and major outcomes of each step.

These steps were carried through by a subset of workshop participants who had demonstrated technical 

competence in systems engineering techniques as well as the technical aspects for the problem at hand. The 

subgroup for the development of the N+3 Supersonic IRMA consisted of representatives from The Boeing 

Company as well as representatives from each engine company. The representatives from the engine 

companies provided input and guidance supporting engine technologies and integration issues. 

Pre-workshop Step 1: Identify a set of customer requirements

Preparation for the workshop first began with understanding the needs of the customer. Supersonic 

commercial travel continues to offer a potentially viable, profitable option for cutting travel time and 

allowing for easier business and international travel. However, with the current push towards more 

environmentally friendly aircraft, both in the subsonic and supersonic regime, NASA has issued an 

aggressive set of goals which will drive next generation supersonic commercial aircraft design. 

Figure 3.2.2 illustrates the various goals NASA has set for future supersonic aircraft design. The N+3 

Supersonic initiative strives to develop N+3 Supersonic vehicle concepts to meet the most aggressive set of 

goals: reduction of sonic boom, cumulative noise, cruise emissions, and fuel efficiency. These requirements 

provided the initial constraints for the N+3 Supersonic initiative and direct IRMA construction. 

Pre-workshop Step 2: Define problem in terms of requirements

Once the customer (i.e., NASA) had issued a set of requirements, and the overall project goal established, 

the requirements were translated such that the problem could later be mapped to realizable engineering 

characteristics. This report has discussed the need for supersonic commercial aviation and how the aircraft 

fleet will change as a result. This information, coupled with NASA‘s goals, helped formulate the overall 

problem: to design advanced concept, improved performance supersonic aircraft which can fit the need for 

commercial supersonic aviation while also meeting aggressive environmental standards. Therefore, the 

problem could be understood as one primarily involving aircraft architecture; changes to the aircraft 

architecture would either enhance or detract from the vehicle performance relative one or more of NASA‘s 

goals. In order to thoroughly address vehicle performance, the specific vehicle systems that most affect 

performance were identified and targeted as important areas for the conceptual design process. The Boeing 

team noted that design changes made to the aircraft fuselage, wing, stability and control system, propulsion, 

and fuel systems would most impact the vehicle‘s performance. 

Pre-workshop Step 3: Decompose requirements in terms of functional taxonomy

Once the targeted areas of vehicle architecture were defined, it was important to break down the 

architecture in terms of its functional components. This was the first step in building the morphological 

matrix essential to IRMA. Using the sub-categories defined by Boeing (i.e. fuselage, wing, stability and 

control, propulsion, fuel) as a starting place, the vehicle was functionally broken down into its parts. These 

functional ―parts‖ served as points of decision for each concept created. Design decisions were then made 

at this level of detail, ensuring that the concepts were built from the ―bottom up‖ with much freedom to 

generate the N+3 concepts that would best address NASA‘s goals. 
22

In order to begin vehicle decomposition, it was important to know the vehicle components which make up 

each subsystem as these generate decision making points in the IRMA. The functional decomposition was 

completed by Boeing and the engine companies in keeping with the fuselage, wing, stability and control, 

propulsion, and fuel categories. A complete visualization of the finished functional taxonomy can be seen 

in Figure 3.2.3. 

Pre-workshop Step 4: Identify alternatives to decomposition and compose morphological matrix

Once the functional taxonomy was complete, each entry to the decomposition was given possible 

alternatives that could function in a vehicle design. For example, an airplane may realistically have 1 or 2 

wings. Therefore these are the two alternatives which would populate the ―number of wings‖ category. 

These alternatives served as possible ―choices‖ in the IRMA, guiding the users in creating vehicle concepts. 

The alternatives were populated across a row for each entry created in the functional taxonomy. Once the 

alternatives were entered, the morphological matrix was complete and the backbone for the IRMA was set. 

The complete morphological matrix created by Boeing and the engine companies for the N+3 Supersonic 

workshop is shown in figure 3.2.4.

Pre-workshop Step 5.1: Create conditional relationships of functional decomposition

Once the morphological matrix was complete, the dynamic nature of the matrix was set up. This was done 

through the creation of a compatibility matrix which summarizes the conditional relationships within the 

functional decomposition. The goal of conditional relationships was to eliminate alternatives that are 

physically incompatible with each other. For example, if the user initially selected the aft shape of the 

fuselage to be a tail spike, it is physically impossible to have the propulsion system also located in the aft 

fuselage. Therefore, the alternatives under these categories on other rows of the matrix would be removed 

as alternatives for the vehicle configuration. 

It is important to note that the incompatibilities dealt with merely reflect those vehicle attributes which 

were impossible by the laws of physics or by engineering standards. These incompatibilities did not reflect 

combinations of attributes which may be uncommon or suggested against. This allowed for more freedom 

in generating concepts. It is important that the users applied their engineering judgment when making 

decisions to ensure the designs were not only physically possible, but also logical, as incompatibilities 

cannot account for engineering logic. 

The compatibility matrix was filled in by those who helped populate the morphological matrix. This matrix 

is symmetrical and at minimum, consists of the numbers 1 and 0. A 0 indicates that two alternatives are 

incompatible while a 1 indicates they are compatible. The compatibility covers alternatives in the same row 

as the attribute in question as well as those alternatives in other rows that affect other aspects of the vehicle 

architecture. Additionally, the matrix was enhanced by using the number 2 to indicate when two 

alternatives were not only compatible, but also that using those two alternatives together provides a benefit 

to using just one or the other. When an alternative was selected, any alternatives that would couple with the 

previously selected one and thereby improve performance were highlighted for the user to view. 

A section of the compatibility matrix created for the N+3 Supersonic workshop is shown in Figure 3.2.5. 

Once the compatibility matrix was completed, it was linked to the morphological matrix to enable dynamic 

decision making. The results of the compatibility were automatically reflected to the user with each choice 

made during the workshop. This can be seen in Figure 3.7. The red cells indicate those options which had 

been ruled out due to the incompatibility matrix. Which cells appear red was a result of choices selected 

previously in the decision making chain (these choices were marked with a green ―yes‖) and helped to 

drive vehicle concept design. The cells that appeared purple were options that had not yet been chosen but 

would enhance the overall design if chosen. This reflected a number ―2‖ in the compatibility matrix. This 

was a function of IRMA and will be discussed in more detail in the workshop section of this report. Note

that Figure 3.2.6 does not reflect work done at the workshop, it merely indicates the functionality of the 

built in compatibility matrix. 
23

Pre-workshop Step 5.2: Identify and discuss attributes of each row of the decomposition

Once the backbone of the IRMA was completed, it was important to go over the results of the functional 

decomposition to ensure it is comprehensive. Additionally, it was also important to discuss each attribute 

and alternative to ensure that the function and meaning of each was understood by all those involved. 

Understanding the importance of each attribute was crucial to the next pre-workshop step. Additionally, it 

allowed the users to scrutinize the choices they made in the functional decomposition to ensure that the 

problem could be adequately addressed with those attributes listed in the matrix. 

Pre-workshop Step 6: Rank order decomposition based on relative importance to requirements

Using the discussions begun in step 5.2, it was important to set up the basics for IRMA scoring by 

identifying the importance of each functional attribute to the problem. IRMA scoring ensured that those 

decisions which most directly impact the NASA goals get weightings reflecting their importance. For 

example, fuel efficiency is highly affected by the aircraft propulsor type. Therefore, the functional attribute 

―propulsor type‖ was given a high rating such that it would count highly towards the overall score of the 

vehicle concept. Additionally, knowing the propulsor type was an attribute highly affecting fuel efficiency, 

the user was given a logical place to start the decision making process. Because of the incompatibility 

matrix, the order in which decisions are made affect the vehicle architecture options available towards the 

end of the decision making chain. Therefore, it was important to begin making decisions with those 

attributes that would most highly affect the vehicle‘s performance. 

Each attribute was evaluated for its effect on each one of NASA‘s goals. The attributes were marked as 

having a high impact, medium impact, low impact, or no impact on a specific goal. The impact could be 

positive or negative and was accounted for during the workshop when scoring each alternative. The ―highnone‖ scale allowed the user to think of the problem qualitatively rather than quantitatively while still 

capturing the importance of a specific attribute. Once the attributes were rated, the stage was set to allow 

for more logical, effective decision making, allowing those decisions which were more critical to vehicle 

performance relative to a certain goal to occur early on in the chain of decisions. 

This step was performed both pre-workshop and during the workshop. Conducting this exercise prior to the 

workshop helped users ensure that the matrix was complete and its entries were understood. Conducting the 

exercise during the workshop helped check the work done before the workshop and brought all participants 

together. It was important that the rankings were as accurate as possible, as they ended up driving the 

decision making process heavily.

Pre-workshop Step 7: Select optimal suitable reference systems

Before groups could come together and begin to brainstorm unique vehicle concepts at the workshop, it 

was important that everyone be given a frame of reference in which they must make decisions. This frame 

of reference included a baseline vehicle as well as the type of mission for which the vehicle was being 

designed. 

The baseline vehicle provided a reference system for users when they were scoring alternatives in the 

workshop. During the workshop, each alternative was given a score (1-10) reflecting how well they 

contribute to the customer goals. In this case, the score reflected how well an alternative will improve 

performance towards specific NASA goal. Knowing the features of the baseline, the user was able to make 

these decisions relative to existing systems. Additionally, choosing a reference mission was important prior 

to the workshop. In order to minimize confusion, it was important to stipulate reference conditions ahead of 

time so everyone could understand the context in which they were brainstorming. The N+3 Supersonic 

team selected the 765-076E as the baseline aircraft and assumed a 100 passenger aircraft for all concepts 

created. Having these guidelines gave structure to the workshop and ensured the participants are able to 

effectively contribute to the overall workshop process. 
24

Pre-workshop Step 8: Exercise IRMA

The steps of the workshop and details on how the IRMA was used to aid dynamic decision making will be 

discussed in the next section of this report. A complete IRMA, ready for a workshop, is depicted in Figure 

3.2.7. Again, this IRMA is a notional example and does not reflect real decisions made prior to the 

workshop.

3.3 – Workshop Steps

The work prepared prior to the workshop created tools and resources to facilitate a more streamlined 

execution of the workshop steps. These workshop steps were composed of small group breakout activities 

and larger group down-selection activities. This workflow is depicted in Figure 3.3.1 and this section will 

describe in more detail the major accomplishments of each of the steps involved in the workshop and the 

outcomes. 

Workshop Step 1: Participant Planning and Pre-workshop review 

The information provided in the pre-workshop activities contributed to the creation of the tools that will be 

available to the workshop participants. The IRMA, information on specific technologies, the baseline 

vehicle, mission requirements and the NASA goals were provided to each of the teams. The IRMA 

integrated the decomposition of requirements, the alternatives in the matrix of alternatives and the 

compatibility matrix in an interactively accessible format. 

The workshop participants consisted of a subset of the individuals who participated in the pre-workshop 

activities and other technical experts. These participants were selected by their past experience in specific 

technology areas, configuration design or their broad understanding of engineering trades. The purpose of 

the Workshop Step 1 was to orient the participants to the mission that they are designing for and the steps 

that they will be required to go through during the workshop days. 

An orientation for the tools that will be available to them was provided along with reference vehicle and 

mission information. Furthermore, each of the groups was required to select architectures that relate to each 

of the functional metrics. These metrics were specified by NASA and refined in the earlier phases of the 

program. 

Workshop Step 2: Score Matrix of Alternatives

The participants were broken up into three groups consisting of an averaged level of experience both on 

years of experience and technical expertise. These groups worked together to identify the initial aircraft 

configurations for each of the NASA Goals or ―Metrics of Interest‖ (MOI). The teams investigated a single 

MOI and qualitatively ranked the benefit of each characteristic relative to the MOI. The groups identified 

the characteristics with high benefits progressing from medium to identifying characteristics with low or no 

benefit to the MOI. This progressive identification of relative benefit supplied the team with a general 

―order of selection‖ to be used in the future. A snapshot of the exercise is depicted in figure 3.3.2.

Upon identifying the order of selection, the teams progressed in the specified order and ranked the 

alternatives associated with the metrics of interest. This ranking was then used to facilitate discussions for 

assessing the benefit and tradeoffs between configuration options. For a given metric, starting with the high 

impact characteristics, the elements within each row were scored based on their value to the specified 

metrics, where 1 is low and 10 is high. The teams progressed in the specified order of selection, ranking 

each of the alternatives. A snapshot of selected results are depicted in Figure 3.3.3 below. The teams 

repeated step 2 until all the MOI were evaluated. Once the order of selection was identified and the 

alternatives scored, the teams had the information necessary to begin exercising the IRMA to select 

concepts. 
25

Workshop Step 3: Down-Select Group Concepts

For a specific MOI, each characteristic was considered in assigned order, and the team began to discuss and 

select alternatives for that characteristic. As alternatives were selected, any incompatible options in other 

characteristic rows turn red, and any enhancing options turn purple. As compatibility allows, the team, 

ideally, specified the highest ranked alternative on each row for a given MOI. A configuration was 

complete once there was an option selected for each characteristic. Figure 3.3.4 shows an example of such 

an intermediate result for a few characteristics. The resulting configurations represented the corners of the 

design space and will be used for sensitivity analysis once the workshop process is complete. Figure 3.3.5 

shows the results of the configuration selection for one of the groups participating in the workshop. 

Workshop Step 4: Sketch group concepts

In order to bring the concept to life and understand different interpretations of the integration aspect of the 

design choices, each member of the group sketched each of the proposed aircraft. The teams then compared 

individual sketches for each of the different aircraft and reached group consensus on what the aircraft 

should look like. Based on the results of the discussions, the team redrew the concepts, incorporating any 

changes. An example of one of the groups‘ original interpretations and final drawing is depicted below in 

Figure 3.3.6.

Workshop Step 5: Down-select among group concepts

At this stage of the workshop, there were at least three concepts to meet each of the NASA goals and in 

order to arrive at a select few configurations to apply technologies towards, the teams regrouped and 

presented their concepts. Each team presented their concept sketch and provided discussion of the rationale 

for their configuration selection. Since different alternatives for each of the vehicle characteristics provided 

advantages and disadvantages, individually as well as integrated, the teams discussed the expected pros and 

cons for their concepts.

Once all the groups had discussed their concepts, the large group down-selects to one or two concepts per 

metric. To facilitate the down-select, the group compared the concepts to each of the metrics of interest 

based on the perceived pros and cons of each concept. The groups then discussed commonalities amongst 

all concepts, configuration selection issues and integration issues which could have led to reassessing the 

configuration selection. Upon reaching consensus, the large group arrived at a concept or two for each 

metric as well as repeating the concept selection process to identify a configuration that represents a 

compromise between all metrics. An example of the results of the large group discussion is depicted below 

in Figure 3.3.7.

Workshop Step 6: Final workshop configuration and sketch workshop concepts

Upon reaching consensus amongst the larger group, the concepts were reviewed for completeness and 

sketches were drawn by a selected individual to bring the concepts to life. This final sketch up provided a 

mechanism for discussion as well as a product of the workshop. Figure 3.3.8 depicts the results from the 

N+3 Supersonic workshop. These drawings were used as a starting point in future steps of the contracted 

work.

3.4 – IRMA Process Payoff

By utilizing the ASDL created IRMA process, the N+3 Supersonic team was able to develop several 

alternatives for evaluation utilizing a systematic approach with documented decisions. By exercising the 

interactive tool, the teams were able to gain an enhanced understanding of the systems selections for the 

vehicle characteristics and the impacts of selecting a particular alternative without the need to exercise 
26

lengthy and expensive analysis. The tool‘s dynamic nature and extensible, flexible framework allowed for 

the down-select process to be rapidly repeated in order to select multiple configuration alternatives. This 

tool also facilitated discussions related to all major components of the aircraft and the integration issues. 

The process used for exercising the tool provided a systematic process to obtain a sufficient set of reference 

systems and a mechanism for documenting the decisions that were made over the course of the workshop. 

The resulting files were given to the participants for use in further analysis in the later phases of the 

contract or any follow-on work. 

Figure 3.1.1 – Interactive Matrix of Alternatives for Conceptual Design Formulation
27

Figure 3.2.1 – Pre-Workshop Activity Sequence

Figure 3.2.2 – NASA Goals for Next Generation Supersonic Aircraft

Set of customer 

requirements

Define 

problem in 

terms of 

requirements

Decompose 

requirements 

in terms of 

functional 

taxonomy

Rank order 

decomposition 

based on 

relative 

importance to 

requirements

Identify 

alternatives to 

decomposition 

and compose 

morphological 

matrix

Identify and 

discuss 

attributes for 

each row of 

decomposition

Create 

conditional 

relationships 

of functional 

decomposition

Select optimal 

suitable 

reference 

systems 

IRMA

Quantification Method

(Example Level 1 Tools)

Sonic Boom Perceived Loudness - PLdB 70 - Low Boom 

80 – Unrestricted

65 - Low Boom 

75 – Unrestricted

MDBOOM*, MDPLOT*, 

Zephyrus*, Loudboom*, 

PCBOOM

Airport Noise Cum below stage 3 – 

EPNdB -20 -30

JEN7A* (jet), INLET3*, 

AFTFAN7* (turbine), 

RDIFF*, CDUCT* (fan)

Cruise Emissions Cruise NOx – g/kg of fuel 5

< 5 with Particulate 

and H2O Mitigation

BADA, BFFM2*, Wyle Labs 

Proprietary Code

Cruise Speed Mach Number 1.3 2 Aero: Panel codes

Payload Passengers 100 200 CATIA

Range Nautical Miles 4000 5500 CASES*

Fuel Efficiency Passenger-miles per lb of 

fuel 3.5 4.5 CASES*

* Boeing Proprietary Codes

Metric N+3 Minimum Goal N+3 Stretch Goal
28

Figure 3.2.3 - Functional Decomposition of Vehicle Characteristics

Figure 3.2.4 – N+3 Supersonic Morphological Matrix
29

Figure 3.2.5 – Portion of Compatibility Matrix

Figure 3.2.6 – Example of IRMA Dashboard with several selections. (Red cells indicate incompatible 

options. Purple cells indicate enhanced design options.)
30

Figure 3.2.7 – Notional IRMA Prior to Workshop

Figure 3.3.1 – Workshop Workflow Diagram

Pre-Workshop 

Tasks

Score Matrix of 

Alternatives

Score Matrix of 

Alternatives

Score Matrix of 

Alternatives

Break Out 

Groups

Down-Select

Down-select

Down-Select 

Group Concepts

Down-Select

Down-select

Sketch Group 

Concepts

Down-select 

Workshop 

Concepts

Sketch Workshop 

Concepts

Big Group
31

Figure 3.3.2 – Step 2: Identification of Relative Benefit

Figure 3.3.3 – Scoring the Alternatives

Metric of Interest: Fuel Efficiency

Benefit of Wing Join with respect 

to Fuel Efficiency ranked as High 

Benefit of Propulsor Arrangement with 

Order of Selection

respect to Fuel Efficiency ranked as None 

Metric of Interest: Fuel Efficiency

Benefit of Wing Join with respect 

to Fuel Efficiency ranked as High 

Benefit of Propulsor Arrangement with 

Order of Selection

respect to Fuel Efficiency ranked as None 

Metric of Interest = Cumulative Noise

Remote fan scores a 10 with respect to 

cumulative noise

Fixed cycle turbofan scores a 5 with 

respect to cumulative noise

Variable cycle turbofan scores an 8 with 

respect to cumulative noise
32

Figure 3.3.4 – Intermediate Results from the IRMA

Figure 3.3.5 – Team Y’s Configuration Results from IRMA process

Selections are made 

according to the order of 

selection

Selection “yes” from 

the drop down box

As selections are made 

incompatible elements 

turn red

Selections are made 

according to the order of 

selection

Selection “yes” from 

the drop down box

As selections are made 

incompatible elements 

turn red
33

Figure 3.3.6 – Concept sketches

Figure 3.3.7 – Large group configuration down-selection

Number of Fuselages Team Z:

Cumulative Noise

Team Y:

Cumulative Noise

Team Z:

Cumulative Noise

Wing-Body Blend 1 1 2

Aft Shape None Moderate Blend Fairing

Nose Shape Conventional Aft-Deck Body Flap

Number Conventional Conventional Conventional

Location 2 2 1

High Lift System Low Low Low

Cruise aero Slotted Flap Slotted Flap Slotted Flap

Join Active flow control Active flow control Active Flow Control

Swing None None None

Morphing IN flight-varible None IN flight- variable Winglet Both Both Both

Pitch Effecter None None None

CG Control Canard 3-Surface Canard

Location Active Active Active 

Integration Above Wing Above Wing Above Wing

Propulsor Arrangement Embedded Podded Embedded

Propulsor Type Single Multiple Multiple

Energy Conversion Variable cycle turbofan Remote Fan Variable cycle turbofan

Power Augmentation Intercooler/Recoup Cycle Fuel Cell conentional turbofan (Brayton)

Inlet Geometry None Fuel Cell None

Inlet Shape Variable Area Variable Area Variable Area

Inlet Type 2-D 2-D w-D

Nozzle Geometry External Compression Mixed Compression External Compression

Nozzle Shape Variable Area Variable Area Vairable Area

Nozzle Type 2-D 2-D 2-D

Ejector C-D SERN SERN

option with prop type Yes No Yes

Compiled Team: 

Cumulative Noise

1

Moderate Blend

Aft-Deck

Convenventional

1

Low

Slotted Flap

Active Flow Control

None

IN flight- variable

Variable Camber

None

3-Surface - put engines inside VT

Active

Above Wing

Podded Multiple

Remote Fan

Intercooler / Recoup Cycle

None

Fixed Area - due to external compression

2-D

External Compression

Vairable Area

2-D

SERN

Yes

Number of Fuselages Team Z:

Cumulative Noise

Team Y:

Cumulative Noise

Team Z:

Cumulative Noise

Wing-Body Blend 1 1 2

Aft Shape None Moderate Blend Fairing

Nose Shape Conventional Aft-Deck Body Flap

Number Conventional Conventional Conventional

Location 2 2 1

High Lift System Low Low Low

Cruise aero Slotted Flap Slotted Flap Slotted Flap

Join Active flow control Active flow control Active Flow Control

Swing None None None

Morphing IN flight-varible None IN flight- variable Winglet Both Both Both

Pitch Effecter None None None

CG Control Canard 3-Surface Canard

Location Active Active Active 

Integration Above Wing Above Wing Above Wing

Propulsor Arrangement Embedded Podded Embedded

Propulsor Type Single Multiple Multiple

Energy Conversion Variable cycle turbofan Remote Fan Variable cycle turbofan

Power Augmentation Intercooler/Recoup Cycle Fuel Cell conentional turbofan (Brayton)

Inlet Geometry None Fuel Cell None

Inlet Shape Variable Area Variable Area Variable Area

Inlet Type 2-D 2-D w-D

Nozzle Geometry External Compression Mixed Compression External Compression

Nozzle Shape Variable Area Variable Area Vairable Area

Nozzle Type 2-D 2-D 2-D

Ejector C-D SERN SERN

option with prop type Yes No Yes

Compiled Team: 

Cumulative Noise

1

Moderate Blend

Aft-Deck

Convenventional

1

Low

Slotted Flap

Active Flow Control

None

IN flight- variable

Variable Camber

None

3-Surface - put engines inside VT

Active

Above Wing

Podded Multiple

Remote Fan

Intercooler / Recoup Cycle

None

Fixed Area - due to external compression

2-D

External Compression

Vairable Area

2-D

SERN

Yes
34

Figure 3.3.8 Concept Category Sketches as a Point of Departure for Further 

Development.
35

4.0 Engine Development and Technologies (Task 3.3 & 3.4)

This section contains non-proprietary discussion of the engine development and technologies by General 

Electric, Pratt & Whitney, and Rolls-Royce U.S. (Liberty Works). Sub-sections 4.1, 4.2 and 4.3 were 

prepared and submitted independently by the respective engine companies, and formatting and content are 

not strictly consistent. Independent proprietary discussion and data are found in Appendices B, C & D.

4.1 General Electric Engine Technology Inputs

4.1.1 General Electric Introduction

GE Global Research and Aviation supported Boeing‘s contract from NASA on these N+3 Supersonic 

System Studies. GE‘s support included propulsion system support through the development of an 

advanced variable cycle engine (VCE) propulsion system to meet the vehicle requirements and 

environmental goals. The overall goals are shown in Figure 3.2.2. They cover sonic boom, airport noise, 

fuel efficiency, and emissions. The sonic boom, cruise speed, payload, and range were essentially used by 

Boeing to set the propulsion requirements that GE used to design the propulsion system. The airport noise, 

cruise emissions, and fuel efficiency were targets that GE assessed based on the propulsion system 

developed.

The baseline propulsion system was a variable cycle engine with advanced technology assumptions 

appropriate for a 2025-30 TRL 6 technology availability date. The engine architecture includes features 

such as:

 Variable Cycle Technologies

 Advanced Thermal Management

 Axisymmetric Plug (Axi-Plug) Exhaust with Noise Reduction Technologies

 Transonic Thrust Augmentation

Together these technologies provide an advanced propulsion system anticipated to meet the vehicle 

requirements and environmental goals.

Assessments of the jet noise produced by the propulsion system during takeoff were made to ensure the 

propulsion system meets the targets provided by Boeing such that the overall airport noise goal is met. The 

exhaust system proposed in this study provides very high performance due to the Axisymmetric plug 

configuration, and jet noise reduction features to take advantage of the capabilities of the variable cycle 

engine to allow higher jet exhaust velocities to be achieved with lower noise levels. 

Emission levels are estimated based on the engine cycle and anticipated operational limits of the current 

TAPS combustor. The emission assessment was likely the most difficult to perform as very limited 

emission data exists at the very aggressive engine conditions used in this study. It was required to reduce 

the operating temperature of the propulsion system to meet the current emission goals. It will be required 

to move to an alternate combustor concept during future studies to retain the highest thermal efficiency 

possible with this system. 

The fuel efficiency goal is targeted through the high thermal efficiency of the engine, smaller diameter, and 

lighter weight due to the variable cycle features and the high performance exhaust, as well as using 

moderate thrust augmentation during transonic operation.

A number of trade studies were made looking at ways to reduce the combustor temperature while 

maintaining the high thermal efficiency of the propulsion system. These included intercooling and 

interturbine combustion. The results indicate the best trade for the propulsion system to meet the emissions 

goal was to reduce the operating temperature and accept a small SFC and weight impact.

Roadmaps were developed for the most critical technologies and a list of future work efforts was included. 

All of these items are covered in detail in Appendix B
36

4.1.2 General Electric Propulsion System Overview

The advanced Variable Cycle Engine uses advanced level technologies, and other technologies aimed at an 

entry into service (EIS) date of 2035. The engine architecture includes variable cycle features and 

advanced thermal management. The high performance Axi-Plug exhaust includes jet noise reduction 

technologies.

The advanced thermal management system enables the engine to be designed at a higher overall pressure 

ratio (OPR) for improved thermal efficiency and enhanced engine life while operating at sustained high 

core temperature during cruise.

Also, as part of this program, advanced low NOx combustor concepts and technologies were investigated to 

determine the ability of the propulsion system to achieve the N+3 cruise emission goal. The combustor 

concepts and technologies and the impact on cruise NOx emissions are discussed in Appendix B. The 

impact of the combustor exit temperature (T4) on cruise NOx emissions, engine performance, and weight is 

also discussed in Appendix B.

The exhaust system is critical for supersonic vehicles since the nozzle performance strongly impacts the 

efficiency of the propulsion system as well as enabling jet noise technologies. The VCE propulsion system 

also features an Axi-Plug exhaust system. The exhaust has variable area capability to ensure high 

performance throughout the flight envelope. The exhaust system also provides for a thrust reversing 

system. 

The exhaust also has a feature that augments the mixed temperature of the exhaust by a moderate amount. 

This system has minimal impact on exhaust performance. Due to the low augmentation temperature and 

use of advanced materials, no additional cooling is required when the augmentation is on.

4.2 Pratt & Whitney Engine Technology Inputs

4.2.1 Pratt & Whitney Initial Aircraft and Propulsion Concepts

Initial propulsion and aircraft concepts were generated through a joint brain storming session with Boeing, 

Pratt & Whitney, General Electric, and Rolls-Royce. This effort was conducted at Georgia Institute of 

Technology and employed various qualitative assessment techniques. The outcome of this activity 

identified six aircraft concepts that addressed the key N+3 supersonic metrics. These concepts are 

described in section 3 of this report. From this effort several critical propulsion observation were made that 

set the technology direction pursued by Pratt & Whitney.

Observation 1: A low boom aircraft design is essential for meeting overland supersonic noise requirements. 

Low boom aircraft designs are inherently long and slender such that aerodynamic loading and compression 

characteristics are distributed to reduce the ground level boom. From a propulsion airframe integration 

perspective this suggested that engine length is a design degree of freedom that could be exploited for 

overall system advantage.

Observation 2: Low airport noise is critical. Current N+1 (2013-2018 EIS) subsonic engines under 

development by industry will drive bypass ratio higher to minimize noise and reduce fuel burn. Pratt & 

Whitney‘s gear technology will allow this trend to continue without incurring the weight penalties 

associated with high bypass ratio. By the N+3 time frame subsonic aircraft will likely have bypass ratios 

on the order of 20-30 and far exceed the N+3 supersonic airport noise goals. Any supersonic system will 

need to meet, or more likely, exceed N+3 supersonic airport noise goals. 

Observation 3: In a high energy cost future, fuel burn dominates aircraft cash operating cost per seat mile 

and CO2 production goes directly with fuel burn. Therefore, reducing fuel burn can be used as a surrogate 

for reducing CO2 and improving economics. NOx production will be a challenge, but is not unique to 

supersonic aircraft and can be assumed to be solved by subsonic technology efforts.
37

From these three observation Pratt & Whitney focused its efforts on innovating solutions that met boom, 

airport noise, and fuel burn/CO2 goals. The design implications of satisfying low airport noise and 

efficient low boom supersonic flight drive the engine in diametrically opposed design directions. Low 

airport noise requires an engine with high bypass ratio while efficient supersonic flight requires an engine 

with low bypass ratio. Pratt & Whitney focused primarily on finding solutions to this dichotomy. 

4.2.2 Pratt & Whitney Propulsion Concepts

Pratt & Whitney engaged in an internal brainstorming activity to identify propulsion concepts that align 

with the direction described in the P&W proprietary section 4.1 of Appendix C. The concepts were 

qualitatively developed based on historical experience, physical review, and innovative brainstorming. 

Each concept was then categorized by the four elements of a jet engine (inlet, propulsor, gas generator, and 

nozzle) and performance estimated. These concepts are discussed and prioritized in the Pratt & Whitney 

proprietary Appendix C. The most promising of these concepts were then refined, quantified, and 

integrated with the vehicle as described in section 5.0

4.2.3 Pratt & Whitney Analysis & Trades

The traditional approach for executing designs with diametrically opposed requirements is to optimize the 

system to a Pareto front at which point any further improvement with respect to one goal must come at the 

expense of the other. If none of these compromise solutions are acceptable from a business or 

environmental perspective then investment in technology is required to move the pareto front. To date, 

technology has been insufficient to meet a minimum threshold of acceptability for commercial operations 

and after a half century of research, there are no commercial supersonic transports in service. Congruent 

with NASA N+3 goals, Pratt & Whitney pursued concepts and technologies that will enable diametrically 

opposed goals to be met or exceeded. 

The challenge of meeting both low airport noise and low fuel burn supersonic flight was assessed by point 

designing engines at the extreme of the Pareto front defined by current technology. Conceptually this is 

illustrated in figure 4.2.1. These two design solutions are referred to as Pareto limit engines. The 

difference in the design characteristics between these two engines represents the physical barriers that need 

to be overcome with new technology. The magnitude of the gap determines the closure strategy. If the gap 

is narrow then it is likely that combinations of incremental technologies can close it. If on the other hand 

the gap is large then fundamentally new and innovative approaches will need to be pursued. 

The two Pareto limit engines were obtained by mining the Pratt & Whitney N+2 supersonic parametric data 

base established in 2008. An engine was selected that maximized the economic figure of merit (seat*nmi / 

block fuel) without concern for airport noise and then a second engine was identified that minimized airport 

noise without regard for economics. These two engines showed that economical supersonic (M=1.6) flight 

required engine fan pressure ratios on the order of ~3, and conversely, low airport noise required the jet 

velocity to be less than 1100ft/s and a fan pressure ratio on the order 1.7. These engine attributes were then 

enforced as requirements and both engines re-evaluated at the N+3 base aircraft mission-thrust profile. 

Results are shown in the Pratt & Whitney proprietary Appendix C. This activity demonstrated that an N+3 

engine must be able to vary its fan airflow and fan pressure ratio almost 2X to satisfy both low airport noise 

and efficient supersonic flight. Conventional fan architectures can not meet this design range and new 

propulsor concepts are required.

Concepts that potentially allow a 2X fan flow and meet the required fan pressure ratio range were 

identified. See Pratt & Whitney proprietary Appendix C. An observation of these systems is that they 

increased frontal area, i.e., when the engines are in low bypass mode there is significant frontal area that 

does not swallow flow and results in drag. This is true whether the fans are remote off the engine axis or 

concentric similar to emerging military 3rd stream concepts. Figure 4.2.2 shows an integrated propulsion 

aircraft assessment of an auxiliary fan arrangement. The auxiliary fans are remote and are engaged only for 

around the airport operations and cocooned with an aerodynamic fairing at supersonic cruise. Vehicle 

assessment showed that the net drag of the vehicle increased 10% at supersonic cruise due to the increased 

frontal area. This translates into a 10% thrust increase to offset the drag and at constant fuel flow this 
38

would require turbine specific fuel consumption to be reduced ~10%. This TSFC short-fall potentially 

could be made up with a variety of the candidate gas generator technologies identified in section 4.0. 

However, these gas generator technologies will pertain to any vehicles in the N+3 time frame, subsonic or 

supersonic. Therefore, as a practical matter, technologies that negate the drag need to be identified for N+3 

supersonic transports if they are to be competitive economically and acoustically. Technologies that reduce 

the drag associated with auxiliary fans are discussed in Pratt & Whitney proprietary Appendix C along with 

propulsion airframe integration solutions.

In addition to the propulsor concepts described above several gas generator technologies were investigated. 

Since gas generator technologies are equally applicable to subsonic, supersonic, industrial, and marine 

application, they were not studied in as much detail. Pratt & Whitney primarily focused on refining 

discriminating supersonic technologies. However, of the gas generator technologies identified in section 

4.0 of Appendix C, two stood out as having twice the potential of the other technologies. These two 

technologies are discussed in greater detail in the Pratt & Whitney proprietary Appendix C.

4.2.4 Pratt & Whitney Technology Prioritization.

Boeing accessed the aircraft system impact of the initial engine technologies provided by Pratt & Whitney 

by applying sensitivity coefficients. The engine technologies that had the greatest system potential were 

then refined through quantitative analysis and integration with the vehicle. This refinement was conducted 

by applying the NASA NPSS engine modeling environment. Integration with the vehicle was conducted by 

providing Boeing with traditional data packs for various groupings of technologies. This approach was 

used because the physical characteristics of very low TRL technologies were not sufficiently developed to 

parametrically model in NPSS across the flight envelope. Also, it was not practical within the scope of this 

contract to assess technologies individually one at a time because of their confounded nature, 

dimensionality, and limited physics modeling for low TRL concepts. Therefore, the technologies were 

grouped into bundles that were independent based on physics mechanisms. Three data packs were 

provided that reflected:

 Baseline enabling concept (data pack STF1841)

 Advanced gas generator concepts  Technology Bundle 1 (data pack TB1)

 Advanced propulsor/inlet concepts  Technology Bundle 2 (data pack TB2)

The details each technology bundle is described in the Pratt & Whitney proprietary Appendix C

4.2.5 Pratt & Whitney Road Mapping

Roadmaps for the baseline and technology bundles were established and are provided in the Pratt & 

Whitney proprietary Appendix C. These roadmaps were developed to give a holistic view of the activity 

required to mature each technology. It should be emphasized that the technology concepts as put forth are 

still very notional. The roadmaps emphasize 5 elements that need to be executed. They are:

 Develop physics models for each concept. These models need to be able to address design and off 

design performance from an aerodynamic, thermal, structural, kinematic, and controls perspective.

 Propulsion Airframe Integration Optimization. Parametric exploration of the best mission,

aircraft, engine, and integration. Establish the relevant environment for technology development 

and validation.

 Analysis-of-Alternatives (AOA). Assess concept alternatives as physics is refined and integration 

issues identified.

 TRL Progression Testing from bench tests through supersonic flight demonstrators

 Engine development leading to a 2035 entry into service.
39

4.3 Rolls-Royce Engine Technology Inputs

4.3.1 Rolls-Royce Process

Rolls-Royce was asked to develop an engine solution for Boeing‘s -072B supersonic civilian cruiser. In 

order to meet mission requirements the engine needed to meet three critical sizing points as shown in Table 

4.3.1. Other requirements for the mission were to have a 1100 ft/sec jet velocity at takeoff and demonstrate

lower NOx emissions from the N+2 levels. Emissions were assessed at takeoff, subsonic climb and 

supersonic cruise. It was directed by Boeing that the NASA NOx emission index method be used

4

345

0.37 1471

3

3

439

0.0041941 e T

P

NOxEI

T

  











 











 

Since many advanced engines lead to higher pressures and temperatures an amended version of the relation 

can be found in the proprietary Appendix D. Additional customer requirements were a 0.5 high-pressure 

bleed as well as an 80 hp power extraction. Generic inlet and exhaust curves were supplied by Boeing in 

order to provide installed engine performance.

In order to meet or exceed each of the requirements set by Boeing and NASA, new technologies needed to 

be defined for the 2035 timeframe. A large list of new or updated technologies was initially assessed at a 

qualitative level before a technology solution was defined and resulted in a subset of the original list. The 

truncated list was then incorporated into a full engine model where a design space of overall pressure ratio 

(OPR), fan pressure ratio (FPR), turbine inlet temperature (HPT RIT) and other parameters were defined 

and explored. Using this process an optimum solution was found and still met all requirements. Once an 

engine was defined data and scaling rules were sent to Boeing to assess the engine at the aircraft level. The 

scaling rules were supplied so that the engine could be made larger or smaller as the aircraft requirements 

changed.

4.3.2 Rolls-Royce Technology Prioritizing, Selection, and Roadmapping

An essential part of the NASA N+3 studies was to assess each technology‘s worth to the engine system. 

Once an acceptable engine was chosen a sensitivity study commenced. For the sensitivity study each 

technology was assessed in terms of drag, weight, fuel burn and noise. The fuel burn was assessed by 

looking at the cruise condition, the drag has been assessed to be just a function of engine diameter and 

finally the emissions and noise were assessed at the takeoff condition. Only the takeoff condition was used 

for emission assessment during the sensitivity study. There were two reasons the delta at takeoff, rather 

than the supersonic condition, was applicable to the study. First during the optimization of the cycle in 

4.3.1 it was noted that the variation in NOxEI did not change much across environmental conditions when 

comparing different technology suites. Secondly the amended version of the NOxEI equation is baselined 

to a sea-level static condition. Using the sensitivities found in the technology assessment a prioritized 

technology list was generated which highlighted what technologies needed to be roadmapped for future 

development. It should be noted that the technologies chosen were found to be specific to supersonic 

engines. Specific data associated with the prioritizing, selection and roadmapping efforts are shown in the 

Rolls-Royce proprietary Appendix D.
40

Figure 4.2.1 P&W, Interrogating designs at the Pareto limits provide insight to the magnitude of the 

technologies required to satisfy both airport noise & low fuel burn.

Figure 4.2.2 P&W Cocooned auxiliary fans increase drag 10% and require a 10% SFC improvement 

to overcome the drag (hold Mach) with 10% more thrust at constant fuel flow 

Table 4.3.1 Engine Requirements

Condition Altitude 

[ft] Mach No. ΔTamb [deg F]

Cruise 55000 1.6 0

Pinch Point 40550 1.13 0

Takeoff 0 0.25 27
41

5.0 Preliminary Engine Analysis and Trades (Task 3.5)

Non-Proprietary

5.1 Point of Departure Vehicle

The N+2 765-072B configuration4, Figure 5.1, and corresponding optimum NPSS engine definition were 

used as the point of departure vehicle for assessing the impact of N+3 engine technologies. The -072B 

concept is a 100 passenger vehicle capable of 4000nmi total range, with a cruise M=1.6 and a TOGW of 

approximately 300,000lb. 

In order to provide context for the results of the N+3 studies, the background of the N+2 -072B vehicle is 

summarized in the following discussion. This vehicle was the product of a detailed series of N+2 system 

level trade studies. In order to capture the interactions between the various analysis disciplines (geometry, 

aero, weights, propulsion, mission performance, takeoff performance), an in-house MDAO model was 

employed. The system level trades considered passenger count, cruise Mach, cruise range, and engine 

cycles over a defined supersonic non-stop mission profile.

For the engine cycle trades, a series of candidate engines cycles from engine manufacturers were evaluated. 

These were provided to the MDAO model in the form of installed thrust and fuel flow tables for a reference 

thrust. Jet velocity (Vj) served as a surrogate for propulsion noise. It was generally understood that a low 

diameter engine is needed for best supersonic aerodynamic performance, and a low Vj to minimize the jet 

noise. However, because of the fundamental physics of turbine engines, minimizing Vj results in a large 

diameter engine, and vice versa. A trade study was performed on several engine cycles having low 

diameter, low Vj, or a compromise between diameter and Vj. Following the trades, a preferred concept was 

selected. The N+2 -072B / NPSS configuration optimized for minimum jet velocity is the point of departure 

vehicle and source for the initial thrust requirements. 

5.2 Initial Engine Requirements

Each engine company (OEM) was provided with the same set of thrust and SFC targets, inlet and nozzle 

performance schedules, bleed and HPx off-takes, and flight profile data. Relevant inputs are summarized as 

follows:

A) Key cycle points

 Cruise (sizing Point): 55,000 ft, Mach 1.6, ISA 

 Pinch Point: 40,550 ft, Mach 1.13, ISA 

 Takeoff: Sea Level, Mach 0.25, ISA + 27 deg F

 

B) Customer Requirements

 80hp extraction

 0.50 pps high pressure bleed

C) Installation/Integration

 The baseline inlet design is an external compression tailored 3D inlet of fixed geometry. 

Reference inlet recovery, spillage drag, bleed drag maps were supplied. 

 The baseline nozzle design is a two-dimensional convergent-divergent nozzle with variable area 

ratio. Data supplied included drag coefficients and gross thrust coefficients.

 The inlet and nozzle data were used at the discretion of each engine manufacturer, depending upon 

their configuration.

 

4 N+2 Supersonic Concept Development & Systems Study, July 2009, final report to NASA
42

D) Mission Definition

 The supersonic mission profile is displayed in Figure 5.2

The engine OEMs would then provide data packs of key engine data. They provided engine size, weight, 

and scaling exponents. Several iterations were made with the OEMs, based on changes to cycle settings 

and/or geometry.

The values for power extraction and bleed airflow in the Customer Requirements, above, are reference 

values. In actuality they would be highly dependent on airplane size and systems architecture details. The 

reference values used represent optimistic levels for a generic small future airliner at cruise conditions, 

assuming technology progress in the future energy efficiency of airplane systems, cabin systems, and 

vehicle thermal management. If scaled current year (~787 type) airplane systems were assumed, the 

resulting engine performance would likely show increases in SFC up to 0.3-2.4% (depending on airplane 

size and mission profile) relative to the decks supplied by the engine companies based on the reference 

levels shown. All airplane level performance in the N+2 and N+3 studies was computed based on 

propulsion decks using the reference extraction levels which were held constant regardless of airplane size 

or configuration details being considered. This assumption has made the primary configuration and 

technology increments under study easier to track.

5.3 Engine & Vehicle Sizing Process

The Boeing medium fidelity parametric airplane model, along with the provided engine data, was modeled 

in the similar MDAO environment as was used on the N+2 studies. The engines were nominally considered 

to be under-wing podded engines on the -072B configuration. 

For each of the trade study points, the concept was re-optimized through ―sizing‖ to maximize the cruise 

efficiency Figure of Merit (FOM) = Seat*nmi/lbs of block fuel, by varying the wing area and engine size 

(reference thrust). Each engine and airplane combination was sized holding range and payload constant, 

allowing TOGW to vary. The MDAO model resized the airframe as the engine, wing and fuel load 

changed. When the wing area is scaled, the MDAO model recalculates all the aerodynamics, weights, and 

resulting performance. When the reference thrust is scaled, the MDAO model changes engine size/weight, 

along with the thrust and fuel flow tables. When the engine size changes (diameter, weight, length) the 

nacelle will also change. So the aerodynamics must be recalculated. All of these will affect the 

performance. 

The aircraft optimization was subjected to the following constraints:

 Greater than 300 fpm rate of climb (ROC) anywhere in the mission

 Less than 10,000 ft balanced field length with noise derate (tradable)

 Sufficient fuel volume in the wing (desired) or wing and fuselage (required)

 Less than 78 psf wing loading (W/S) maximum wing loading @ T/O

 4000 nmi range with a 100 passenger, cabin, 1.6Mach cruise speed

The implication of using the N+2 modeling method for the N+3 studies is the following. Because range is 

held constant, for a parametric model this means that the vehicle can scale down. Therefore, vehicle weight 

and required thrust goes down. Since the engine configurations offered for the N+3 studies had the 

potential for higher performance than the N+2 reference engine, the vehicle could be resized by several 

thousands of pounds, leading to fairly substantial changes in vehicle performance. 

When it was initially noticed that vehicle performance was in some cases significantly beyond the goal, an 

investigation was performed into the feasibility of the MDAO model results. The investigation confirmed 

the powerful compounding effects of the optimization method. For instance, a lower SFC means less fuel 

used during a mission, leading to lower weight and drag. A smaller fan diameter due to higher specific 

thrust results in lower drag. Therefore, when the vehicle and engine are resized, the lower drag leads to less 
43

fuel, resulting in lower weight, and therefore lower wing area. The outcome of the investigation confirmed 

that the MDAO was predicting reasonable results.

5.4 Overall Engine and Vehicle Performance Assessment With -072B Configuration

Efficiency 

All engine concepts demonstrate innovative approaches to achieving an adaptive cycle capable of high 

performance for the given requirements. They have aggressive cycle parameters such as high OPR and 

turbine temperatures. All engine concepts resulted in efficiency FOM values which exceeded the goal of 

3.5, ranging in values from 18% to 38% better than the goal. Such fuel efficiency increases could be 

feasible with technologies such as sophisticated inlet flow management, advanced materials, efficient 

thermal management systems, and transonic thrust augmentation, which enables reductions in engine size.

TOGW

All configurations resulted in vehicles with TOGW‘s well below the N+2 optimum baseline of ~300,000 

lbs. They were between about 220,000 – 280,000 lbs. The un-scaled fan diameters range from about 76 to 

91inches; when resized during the optimization process, the fan diameters ranged from about 60 to 80 

inches. This compares favorably to the optimized N+2 fan diameter of about 95in. The un-scaled engine 

weights range from about 8200 to 12000 lbs; when resized during the optimization process, the weights 

were in general much lower than the optimized N+2 weight of nearly 12000lbs. The ability of the engine 

concepts to resize well below the N+2 optimum reflects the benefits of the advanced technologies which 

were incorporated. However, it was found that, much below 270,000lb TOGW, the proportions of the 100-

passenger body relative to the wings and nacelles made it impossible to re-draw a reasonable configuration 

with the predicted sizing (i.e. the sizing re-optimization would drive the configuration into a part of the 

design space where the vehicle would no longer re-integrate). In such a case, the design range was 

increased above the 4000nmi minimum before re-cycling the configuration.

Emissions

All configurations noted challenges with achieving the emissions targets. The OEMs were given the 

following empirical equation to calculate emissions, based on legacy programs such as HSR:

4

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3

439

0.0041941 e T

P

NOxEI

T

  











 











 

Although initially used, this equation was considered not entirely applicable to the N+3 studies. To reduce 

the potential for over predictions, the results were factored down based on literature research and 

consultation with subject matter experts. Other calculation methods were also employed. While some 

reduction relative to N+2 was found, it was generally concluded that the goal could be met only if cycle 

temperatures were reduced. This would, however, adversely affect efficiency FOM.

Noise

In general, the engine configurations were sized such that a Vj target of 1100 ft/s or less was met at sideline 

noise conditions. If the Vj target was exceeded and additional noise-mitigating technologies were included, 

further acoustic assessments were performed to justify having sufficient potential to meet the noise targets 

with deeper derates, more aggressive nozzle designs, and/or changes to the airframe.
44

Figure 5.1 Configuration 765-072B low fuel burn configuration from NASA N+2 

study.

Body Volume Updated

(Net Body volume decreased to 

14282cuft or 142cuf/pass)

Wing/Body fairing houses

two post 4-wheel truck

Nacelle contain 

83.55” Fan Hi-BPR

60,000lbs SLST/engine

• 2-D inlet

• 2-D Nozzle

Design Weight is 300,000lbs

Design Mach=1.8

Overall Length 241‟

Design payload is 100 pass -dual class

Payload 25,000lbs

Vertical Only 

aftbody

Wing Reference 

Area=3988sqft

Body Volume Updated

(Net Body volume decreased to 

14282cuft or 142cuf/pass)

Wing/Body fairing houses

two post 4-wheel truck

Nacelle contain 

83.55” Fan Hi-BPR

60,000lbs SLST/engine

• 2-D inlet

• 2-D Nozzle

Design Weight is 300,000lbs

Design Mach=1.8

Overall Length 241‟

Design payload is 100 pass -dual class

Payload 25,000lbs

Vertical Only 

aftbody

Wing Reference 

Area=3988sqft
45

Figure 5.2: Supersonic Mission Profile
46

6.0 Airframe/Engine Analysis and Trades (Task 3.5)

Preliminary brainstorming for configuration features and technologies identified several configuration 

categories and several technologies that influenced the specific study airplanes. Configuration features of 

interest included very long and slender bodies, minimum thickness lifting surfaces, variable geometry 

wings, and over-wing inlets. With sufficient development, such features and several generally applicable 

technologies could advance substantially and become practical within the N+3 timeframe. This section 

describes a variety of configurations assembled to serve the dual purposes of evaluating these features and 

technologies, and selecting the most promising N+3 configuration. Two more radical alternative 

configurations, an oblique ―scissor‖ wing and a joined wing concept, are also briefly examined in light of 

the expected enabling N+3 technologies.

6.1 Configuration Development

High body fineness is one of the general features expected in the N+3 generation of supersonic airplanes. 

While a long slender body has some potential for wave drag reduction, the primary appeal is the 

opportunity to shape and minimize the sonic boom. But weight and flexibility are concerns that will put 

practical limits on what degree of configuration slenderness for boom is realistic. Rather than using extra 

material or adding internal structural components, the most promising remedy allowing significant 

slenderness increases seems to be active structural mode control and aerodynamic load (e.g. gust & 

maneuver) alleviation as part of an integrated flight control system. A relatively smaller but important 

benefit can be expected from using tailored stiffness materials that might be developed. A slender body 

would unfavorably reduce the cross-section of the flight deck and obstruct pilot vision, likely demanding a 

full-time forward external vision system (XVS). 

Higher fineness ratio wing planforms (minimum thickness and greater quarter chord sweep angles) are 

required for minimizing the sonic boom of N+3 airplanes, presenting flexibility problems similar to those 

of slender bodies. Such surfaces can be expected to have flutter and limit cycle oscillation (LCO) issues. 

Low-frequency ―hump mode‖ flutter may exist at points in the normal operating envelope, and on very 

long bodies the structural mode frequencies may be on the same order as the frequencies of the flight 

control system. As the aircraft structure deflects, alignment of the engine inlets and nozzles may change,

and structural vibrations of the lifting surfaces may couple with oscillating deflections of the fuselage. 

Tailored structural concepts and materials will help, but the most promising solutions are also likely to 

require the addition of active control of the structure and loads. A very slender N+3 airplane would 

probably need a complete aero- propulso- servo- elastic (APSE) control system to stabilize the aircraft and 

structure, relieve gust and maneuver loads, and avoid flutter throughout the flight envelope.

A configuration feature identified as being of potential interest is variable wing geometry in the form of 

variable sweep. While it offers some promise of ―fine-tuning‖ the configuration for climb, acceleration, 

cruise and any boom control phases of flight, the most attractive feature of variable sweep is a potential 

improvement in low-speed performance (e.g. take-off field length, engine-out climb, approach speed, takeoff and approach thrust requirements). An interesting alternative to symmetrical swing-wings is the 

oblique ―scissor‖ swing-wing which could offer the same low speed advantages and capture fuel burn 

savings at lower supersonic Machs. Such a concept could even offer efficient flight at ―threshold Mach‖, 

thereby offering an alternative ―no boom‖ operational solution over land.

Nacelles for all the study airplanes for N+3 are over the wing. It sacrifices the favorable supersonic 

interference potential that is inherent in lower mounted nacelles, and requires inlets and engines to be more 

tolerant of distortion. But over-wing nacelles promise better shielding of noise sources from inlets, 

turbomachinery, nozzle and jet exhaust, and allow more freedom to integrate the area and lift distributions 

during the sonic boom design tailoring. The inlets for N+3 study airplanes project the use of ―diverter-less‖ 

nacelles, relying on alternate upstream or internal boundary layer management through a combination of 

shape optimization, suction panels and active flow control (AFC) devices. These features may be combined 
47

with aerodynamically tailored 3D inlets that offer high pressure recovery and compact (shorter, lighter) 

installations with minimal moving parts.

Some technologies required for a swing-wing or oblique ―scissor‖ wing airplane (e.g. reliable, fail-safe &

compact bearings and actuation systems) are applicable to those configurations exclusively. But most 

structural, aerodynamic, boom reduction and systems technologies for N+3 would benefit any 

configuration by roughly the same amount. The net benefit however, is not always easy to quantify for an 

individual technology. For example, some technologies are enabling technologies rather than ones that 

directly provide weight, L/D or SFC improvements. For example, the APSE control system mentioned 

above would essentially add weight, volume and complexity to an airplane, and save weight on only heavy, 

slender structures. But it might enable an otherwise infeasible slender body and wing combination, for 

which the payoff comes in design options that lead to a better overall configuration solution. Other 

examples of enabling technologies are lightweight shaped composite armor for firewalls and containing a 

burst engine rotor, which is key to enabling podded or other close side-by-side engine arrangements; high 

toughness/low density material that reduces weight in lightly loaded areas of minimum gage; and materials 

for high temperature & acoustic loads for aft decks, noise shielding and nozzles.

6.2 Detailed Studies of Selected Concepts and Technologies

This section outlines selected configurations employing technologies representing promising and 

addressable concepts from the preliminary Georgia Tech workshop which are shown in Figure 6.2.1. The 

first is configuration 1C that has a variable sweep ―arrow‖ wing. Its promise is low fuel burn that might 

result from tailoring the performance across the flight envelope, and low boom. Next is configuration 2C, a 

scaled-up version of the model 765-076E reference low boom airplane from the N+2 study5. It has a fixed

wing and a V-tail expected to help tailor the sonic boom and to shield aft engine and exhaust jet noise. 

Configuration 2C is the basis for ―Icon-II‖, the Boeing recommended N+3 reference airplane which will be 

discussed at length later. A joined wing and oblique ―scissor‖ wing configuration are used to explore 

significantly different configuration alternatives. Finally, ―remote fan‖ technology is applied to a generic 

supersonic airframe to explore its potential. Note: the number designations for these configurations signify 

nothing more than the order of their original graphical layout, and the letters signify revisions (typically 

minor) of the original ―A‖ model.

A central task of the N+3 project is to assess the impact of technology. It could affect the choice of engine, 

the choice of airframe, and determine the ultimate performance of the airplane. With several engines and 

several airframes under consideration, answering some preliminary questions about matching, and sizing 

optimization is necessary to properly balance the performance. At one extreme, using each combination for 

every study and assessment would be comprehensive, but could be formidable, and, at the other, a hasty 

reduction to a single combination or single condition could hide important results. A series of preliminary 

sizing studies help answer some important questions about how to proceed with the broader 

engine/airframe studies. Proprietary engines from each of the engine companies are employed. Their 

weight, size and performance represent the engine companies‘ forecasts for technology at the N+3 level 

and under N+3 noise, performance and emissions requirements. Each engine and its performance is 

described in more detail in the separate appendices B, C & D. NPSS engines from the 765-076E (scaled) 

and the 765-072B from N+2 are also used for reference. For these preliminary studies, the airframe 

technology is assumed to be at the outer limits of ―N+2‖ in light of the aggressive general arrangement of 

the ―-076‖ type, with thin surfaces, novel engine integration, and high body fineness ratio. Some important 

questions about how to proceed can be addressed using these preliminary studies.

First, does the choice of configuration have a large effect on the relative evaluation of the engines? The 

answer is no, based on results from sizing the thrust to maximize range for the 765-072B and 765-076E 

airplanes from N+2 using each of 4 engines, including the N+3 study engines supplied by the three engine 

companies. Because these results are based on proprietary engine company data, they appear together in 

Proprietary Appendix A, and separately in Appendices B, C & D. For each airplane, MTOGW was fixed 

 

5 N+2 Supersonic Concept Development & Systems Study, July 2009, final report to NASA
48

(300,000lb for the -072B and 180,000lb for the -076E) and wing area was fixed (3988 sq ft for the -072B 

and 2516 sq ft for the -076E). The relative range achieved using the various engines is about the same for 

each airplane, demonstrating that the configuration does not strongly affect the engine evaluation.

Does the choice of cruise Mach number have a large effect on the relative evaluation of the engines? No, 

not according the results from sizing thrust for maximum range on the 765-072B, with each of four 

engines, at 1.6 & 1.8 Mach. The relative range from each of the engines is about the same at the two cruise 

Machs. Results are in Proprietary Appendix A.

Does wing area have a large effect on the relative evaluation of the engines? Again, no, based on similar 

thrust sizing results where wing area of Configuration 1C was first held fixed at 4700 sq ft (sufficient for 

carrying nearly all required fuel in wing tanks), then changed to 3800 sq ft (nominally the value that 

maximizes range, but requires fuel tanks within the fuselage). These results can be found in Proprietary 

Appendix A.

These preliminary results provide some confidence that a study using a single engine/airframe combination 

should provide a general result without much risk of overlooking some unique benefit or issue arising from 

a specific combination. Thus, a single configuration, 2C, is used for the incremental technology effects 

assessment with an expectation that the results will be generally applicable. The choice of Configuration 

2C is discussed later.

6.2.1 Low Fuel Burn/Low Boom Swing “Arrow” Wing: Configuration 1C.

Configuration 1C is described in Figure 6.2.2, with details of the planform and a three-view in Figure 6.2.3. 

Table 6.2.1 summarizes the features of this configuration. The swing-wings have the potential to nearly 

double the overall wing span of the configuration at lower subsonic Mach, resulting in nearly 4 times the 

aspect ratio. As configured here, 1C has three surfaces for trim, and only forward noise shielding is 

provided by the over-wing nacelle installation since there is little aft deck area. 5000lb is estimated for the 

wing pivot and actuation system, and 15,000lb is estimated for the relatively high aspect ratio movable 

outboard panels. A complete breakdown of the weight is provided in Table 6.2.2. Some fuel volume in the 

wing is lost due to the pivot joint and actuator, and overall volume increases because of the thickness 

assumed for the pivot. The swing-wing geometry assumed is based on in-house experience with variable 

sweep concepts incorporating lessons learned from the design of the B-1 bomber and more recent in-house 

design studies. The strake has constant sweep located to avoid shedding a vortex that might be ingested by 

the engine. High aspect ratio and sweep of the moveable wing panels, and the absence of an aft deck to 

support the engines suggest that APSE might be a challenge for this configuration.

Variable sweep configurations show lower drag in the transonic speed range, and large potential drag 

reduction at landing and takeoff conditions (along with an increase in low-speed lift at alpha which 

improves approach/touchdown attitudes). To fully exploit the advantages, re-optimized engine cycles 

should be matched to the airframe, but that was not within the scope of the present activity. As a result, the 

ultimate integrated benefit of variable sweep remains unmeasured, but the significant costs can already be 

estimated. A comprehensive evaluation would require significant design, engine-airframe MDO, and 

multi-point aero optimization efforts.

Unfortunately, many low-boom supersonic configurations are not sized by low-speed performance 

exclusively, since the wing loading can be constrained by climb profile and boom considerations, and the 

low supersonic ―thrust pinch‖ often sizes the engine. So the principal advantages of variable sweep are not 

always realizable. While some improvements in wing pivot bearing and actuation design have been made 

since aircraft like the F-14 and B-1, variable sweep still requires relatively heavy and bulky bearings and 

actuation systems that will inevitably reduce the available fuel volume within the wing, and add to the 

overall configuration cross-section and weight. Compared to a contemporary fixed planform selected to 

provide a good compromise between high and low speed performance (e.g. the 2C or -072 types), a swingwing of similar size provides only a modest aerodynamic advantage anywhere in the mission profile except 
49

in the mid-subsonic to low speed regime the wing can be nearly unswept. A lower landing speed does 

become possible and engines may be de-rated further to meet takeoff noise goals (without the need for 

airframe shielding). Some future applications of a ―swing-wing‖ general arrangement can‘t be entirely 

ruled out. However, if sufficient noise reduction can be obtained through variable cycle engines, airframe 

shielding, and low-impact suppressor nozzles, and field performance is automatically met by the relatively 

low wing loading required for low sonic boom designs, then the overall incremental benefit of the variable 

sweep wing may not be worth the added risk and complexity.

6.2.2 Configuration 2C, 100 passenger scaled 765-076E from N+2.

Configuration 2C is described in Figure 6.2.4, with a three-view and characteristics in Figure 6.2.5. It is 

essentially the 765-076E configuration from N+2 but scaled and re-integrated to accommodate 100 

passengers at 300,000lb MTOW. Notable features are the V-tail for noise shielding and boom control, and 

the fin-tip pods for housing ballast to tune the V-tail structural dynamics and potentially help volume 

tailoring for low boom. The planform represents a typical compromise of a fixed-wing for supersonic 

cruise and low speed performance and handling. The 2C represents technology closely tied to the levels 

assumed for the final N+2 reference configuration, but some elements of this larger cousin would require 

―N+2+‖ enablers (e.g. materials mix and APSE flight controls) even prior to any application of specific 

N+3 advances. The characteristics in Table 6.2.3 and the weight breakdown in Table 6.2.4 show further 

details. Configuration 2C will serve as the point-of-departure for developing the N+3 ―Icon-II‖ Boeing 

recommended study airplane. The 2C is designated configuration 765-107A as shown here, and becomes 

765-107B after developing into the ―Icon-II‖ concept which rolls in all applicable N+3 technologies and an 

increase in payload to 120 passengers and cargo.

6.2.3 Alternate Concept: Joined Wing (3B)

The joined wing concept shown in Figure 6.2.6, detailed in Figure 6.2.7, was identified for its possible 

structural efficiency, stiffness in structural modes important for dynamic conditions, and an unexplored 

potential to favorably affect the boom by directing shocks aft of the otherwise trailing re-compression. 

Characteristics of the configuration are in Table 6.2.5.

As this joined wing concept was studied further, it was realized that an undesirable feature of the high tail 

is that it would reflect some engine noise downward. More significantly, the promised structural 

advantages are not certain. Thin supersonic tail surfaces offer little buckling resistance from end-loads, and 

the inherent relief of critical high static loads through bending of an ordinary cantilever wing is limited by 

this stiff arrangement. The stiffness of the nacelle attached to the wing might not be improved over an aftdeck alone. A more detailed Finite Element Model (FEM) structural analysis and design would be 

necessary to identify and maximize any structural advantages of a joined wing. Table 6.2.6 is a breakdown 

of the weight, with no advantage assessed for the joined structure. This particular weights summary also 

includes a heavier, older technology engine than the others, but if a credible structural weight assessment 

and design could be made of the joined wing concept, then its performance could be compared to other 

configurations by installing equivalent engines.

Optimizing the twist and camber of the wing and tail for minimum drag in Tranair changes the lift 

distribution by an amount comparable to what was achieved using the same process for the 765-076F in the 

N+2 study. Figure 6.2.8 shows these results at 1.8 Mach and 0.12 CL for configuration 3B. A drag 

reduction of 8 counts is achieved by reducing peak Mach numbers over the wing slightly, and shrinking the 

area over which they appear, evident in Figure 6.2.9. Nearly 30 counts remain between the drag of this 

highly constrained optimum and the forecast, but tail size and other features of the integrated configuration 

have not been refined from their initial values. It is likely that a simultaneous design for drag and boom 

would be necessary to explore the low sonic boom potential of this concept—an effort significantly beyond 

the scope of the present study.
50

The trial drag optimization resulted in a more aft center of lift, as shown in Figure 6.2.10, creating a 

challenge to balancing the airplane, payload and fuel. So, while the aft area in the joined tail might be good 

for boom, and maybe for supersonic trim, it is unfavorable for subsonic trim and loadability. A canard or 

longer strake might help, but would add wetted area and drag at their intersection with the body. It is also 

possible that the extra wetted area of the tail (a source of both weight and drag) would offset any potential 

APSE benefit of the joined wing arrangement, and that any boom advantage would be realized over only a 

small range of operation. A significant effort of CFD and FEM analysis and design would be required 

before assuming the advantages.

6.2.4 Alternate Concept: Oblique “Scissor” Wing (4B)

The oblique ―scissor‖ wing configuration is an attractive and somewhat radical alternative for a supersonic 

transport. An example in configuration 4B is shown in Figures 6.2.11 and 12. It offers the possibility of 

nearly twice the lifting length as a conventional wing of comparable size. A straight load path across the 

wing root, potential to align the center of lift with the payload, and the ability to transform from a nearly 

optimum unswept flapped low speed wing at high lift conditions to a highly swept supersonic configuration 

with an entirely subsonic leading edge make this an attractive alternative to the traditional ―swing-wing‖.

But the oblique ―scissor‖ wing was originally aimed at low supersonic cruise, so most supersonic design 

and testing has been done at Mach numbers less than about 1.4, and most early CFD analysis (typically 

Euler) neglected important viscous effects. A significant concern on this concept was that ―real flow‖ 

viscous effects could limit the maximum Mach number at which this type could cruise efficiently and 

without airframe buffet. A brief CFD study was conducted to understand this risk issue. Figure 6.2.13 

shows viscous CFD results from CFD++ at 1.4 Mach and 3 deg AOA on a wing-body representative of the 

4B. 40 million grid elements are used for a solution at a flight Reynolds number of 2 million/ft. With the 

wing swept 60 degrees (for a normal Mach number near 0.7 across the airfoil), the boundary layer on the 

trailing edge of the downstream wing is separating. Any higher Mach would require higher sweep, and the 

problem would be exacerbated. Careful design could help minimize the affect, but probably not eliminate 

it unless other sacrifices were made.

While the oblique ―scissor‖ wing offers nearly twice the lift length of a conventional configuration, and, 

therefore, some natural reduction in boom overpressure and PLdB, it offers few design alternatives for 

shaping the boom beyond simply reduced over-pressure ―N-wave‖. Therefore, an optimized 

―conventional‖ configuration that exploits all of the advances through the N+3 timeframe remains the more 

promising concept if true low-boom is to be achieved.

Employing the oblique ―scissor‖ wing concept for operation at threshold Mach is attractive. It could be a 

fall-back position in case boom regulation is strict. At lower supersonic speeds, there is potential for higher 

efficiency, particularly if landing or takeoff conditions size the wing area, and boom considerations would 

not influence the wing loading or any other characteristics of the supersonic design. The highest possible 

threshold Mach would probably be chosen, both for the obvious advantage of speed, and for the less 

obvious advantage of avoiding the increasing sensitivity of focused booms to maneuvering near the speed 

of sound. The ability of the ―scissor‖ wing to provide so much low-speed performance (i.e. L/D) from a 

configuration with favorable supersonic drag might allow simpler and lighter engines, having both 

performance and cost advantages. But the true performance potential would be realized only after 

matching the engine characteristics to the airframe, similar in scope to what was done on the HSCT, and 

that is not a part of this N+3 study. Future studies should consider re-visiting this concept for supersonic 

flight at shorter ranges (e.g. U.S. trans-continental) with reduced fuel burn potential if reduced cruise Mach 

is an option.

6.2.5 Preliminary Airframe Comparisons

Comparing the aerodynamic performance of the these candidate concepts in Figure 6.2.14, all can achieve 

about the same lift-to-drag ratio at a point (e.g. Mach 1.8 cruise) except the joined wing 3B that, as drawn, 
51

has significantly more wetted area in the large joined tail. The consequent skin friction drag hinders the 

performance of the joined wing 3B at all Mach numbers. At subsonic Mach, the aerodynamic advantage of 

variable sweep is evident in the ―swing-wing‖ increment for the 1C configuration, shown with and without 

variable sweep. Variable sweep is also responsible for part of the advantage of configuration 1C over 2C at 

low supersonic Mach, but a significant portion of the advantage at supersonic speeds is achievable from 

varying camber with simple flaps on the aft deck. Configuration 2C is shown without optimum aft deck 

flap deflections, but could roughly match configuration 1C at low supersonic Mach. The scissor wing 4B 

appears to have significantly higher L/D at all Mach below cruise, especially at subsonic Mach. Not 

apparent at this level of analysis, however, is whether the range factor Mach*L/D/SFC could be as high at 

lower supersonic Mach as at cruise Mach of 1.8, where all aircraft of this study were aimed. As the brief 

CFD study demonstrates, the promise of an oblique scissor wing configuration is tempered by the risk of 

buffeting and potential stability and control issues arising from viscous flow effects. The data shown for the 

scissor wing also presumes a joint and fairing between the wing and body that does not compromise the 

aerodynamics at any condition. With these challenges in mind the likely maximum practical cruise Mach 

number for the Configuration 4B is set at 1.4. The two curves for the 765-107A and 107B ―Icon-II‘ will be 

discussed later. Area+thrust sizing ―thumbprint‖ charts for configurations 1C and 2C are in Figures 6.2.15 

and 6.2.16 as examples of the information available to assess the airplanes. For both configurations, cruise 

range could be increased if the wing area and thrust were lowered from their original values, but fuel 

volume, second-segment climb gradient, and thrust margin constrain the area and thrust to remain about the 

same as their original values. Additionally, the aggressive sonic boom targets for N+3 would probably add 

another constraint in the form of a lower bound on wing area that still offers potential for sufficient boom 

reduction.

6.3 “Icon-II” Airframe and Engine, Configuration 765-107B. 

-- Description of Preferred Designs

6.3.1 Icon II Airframe

Considering the costs, penalties, and uncertain benefits of variable geometry or the other alternative 

configurations considered, configuration 2C became the point of departure for developing the ―Icon-II‖, 

Boeing‘s reference N+3 technology concept airplane. Because the alternative configurations 3B and 4B 

would have required extensive detailed design, and potentially reconsideration of the basic requirements 

(e.g. cruise Mach for the scissor wing 4B) in order to fairly assess their potential, both were not considered 

to be viable reference aircraft. Between 1C and 2C, the swing-wing 1C seemed attractive for the possibly 

lower approach speed, improved climb-out performance and noise, and lower thrust required for thrust 

pinch. But a large part of the advantage of 1C would have to come from sizing the wing down. Not only 

would a smaller wing require significant volume in the body for fuel tanks, but raising the cruise wing 

loading might prevent achieving the aggressive boom goals. Any aerodynamic advantages must overcome 

the increased structural weight of the pivot and highly swept outboard wing to realize a net performance 

advantage, and that performance advantage must be large enough to justify the complexity and cost of 

designing, building and maintaining the joint and actuator. Considering these challenges facing the 1C, and 

the fact that 2C has comparable cruise performance, along with another cycle of more detailed design and 

analysis of a similar configuration for the N+2 Experimental Validation project, 2C was selected as the 

basis for ―Icon-II‖ reference airplane.

A first step in developing the ―Icon-II‖ was doing a preliminary sizing and incorporating the best 

performing N+3 engine. Results are shown in Table 6.3.1. The first result is from sizing only thrust to 

maximize range for Configuration 2C at Mach 1.6 with wing area and MTOGW fixed. The resulting range 

is 4600 nmi. Using preliminary estimates of 10% reduction in operational empty weight (OEW) and 6% 

potential reduction in cruise drag, and sizing both the wing area and thrust to minimize weight at fixed 

4000nmi range, the theoretical takeoff gross weight is reduced substantially. Unfortunately, the 

configuration is not feasible because the over-wing nacelles and landing gear do not integrate into such a 

small wing. Using 5000nmi range instead, and repeating the sizing relieves some of the integration 

challenge, but not all. The cruise speed sensitivity proved to be relatively flat; changing from 1.6 Mach to 

1.8 Mach has little effect, assuming that equally efficient over-wing inlets can be designed using similar 

technology. 
52

From an airline‘s perspective, the most promising resolution would likely be to maintain the original 

300,000 lb design MTOGW and trade away some of the range (nearly trans-Pacific, as shown in the last 

two lines of Table 6.3.1) for an increase in cabin size. This would immediately improve the seat nmi/lb 

figure of merit through additional seats, with initially modest cost in total fuel burn. On this basis, the 

vehicle was re-drawn for a 120 passenger dual-class version, and now the impact of technology can be 

more carefully assessed.

Structural concepts from N+3 applied to the ―Icon-II‖ airplane include some advanced materials, as shown 

in Figure 6.3.1. Also assumed is an active APSE control system to alleviate gust and maneuver loads, 

tailor the configuration (e.g. spanload) for optimum efficiency, control the flexible airframe, and actively 

suppress flutter. In addition to the materials and control system advancements, authority to design and 

certify the structure based on reliability, rather than allowable stress as is traditional, is assumed. The 

weight saved should be comparable to that saved by advanced materials and an APSE control system. 

Progress in airframe optimization is expected to deliver some additional reduction in weight by the N+3 

timeframe.

At the top of the list of aerodynamic technologies applied to the ―Icon-II‖ is hybrid laminar flow control 

(HLFC) on at least the wing, and possibly the tail. Riblets would cover all other surfaces for reduced 

turbulent skin friction. In addition to their basic drag reduction, application of HLFC and riblets would 

have the favorable side effect of eliminating some excrescence by smoothing over some manufacturing 

seams. Flex hinges and morphing flap geometry would also address some excrescence, particularly when 

controls are deflected. Progress in CFD-based design should provide overall improvement, and specific 

assistance in integrating the propulsion system and optimizing in the presence of propulsion induced flowfields. Some unfavorable aspects of over-wing inlets should be mitigated by improvements to design 

methodology. Active control systems should permit significantly aft CG, and fine-tuned drag reduction 

throughout the envelope. Advancements in high-lift aerodynamics might contribute to maximum lift and 

drag reduction through configuration sizing relative to field performance, approach speeds, and community 

noise constraints.

Airframe noise is improved by some of the same features that reduce drag. Some examples are flex hinges, 

sealed & morphing leading edge geometry, flush antennas & air data system sensors, and streamlined 

landing gear fairings. Noise from the propulsion system is reduced by the wing shielding inherent in overwing nacelles, acoustic liners for the inlet and nozzle, chevrons or actively controlled exhaust jet edge 

flow-field, and shielding by the V tail.

Boom is addressed in N+3 primarily through airplane general arrangement and the assumption of improved 

simultaneous optimization for drag and boom, and slender configurations that offer design freedom. Overwing nacelles also offer some design freedom to affect boom with minimum consequences elsewhere. A 

nose boom for adding forward body length might be beneficial. Even more nose length could be added by 

using a retractable probe like the Gulfstream ―Quiet Spike‖, at some penalty in weight and complexity. 

But, there is generally little to be gained in PLdB for front shock reduction below the level attainable in the 

rear of the aircraft. Regulation and certification criteria are unknown, but expected to be challenging. 

Advanced design methods and configuration strategies provide hope that the challenge can be met.

A careful ―bottoms up‖ estimate of the benefit of these technologies applied to Configuration 2C results in 

about 5% reduction in OEW, and 10% reduction in cruise drag. These values are the basis for performance 

improvements between the ―N+2+‖ levels assumed for the initial N+3 study airplanes, and the final ―IconII‖, designated 765-107B. Comparing the 765-107B ―Icon-II‖ to configuration 765-107A (i.e. an 

intermediately refined configuration 2C with 100 passenger body and no aft deck flap optimization), Figure 

6.2.13 demonstrates the advantage in lift-to-drag ratio afforded by this reduction in drag. 

A three-view of the ―Icon-II‖ configuration, 765-107B, is shown in Figure 6.3.2. It is essentially the 

Configuration 2C, but with ride control vanes, a moderate fixed nose boom, and a slightly broader fuselage 

that accommodates 120 passengers in a dual class arrangement, shown in Figure 6.3.3. The cabin 

accommodates 50 passengers in a spacious ―executive‖ interior arrangement, as shown in Figure 6.3.4, 
53

demonstrating one of the alternative cabin utilization concepts. If seating comfort were reduced for an ―all 

tourist‖ charter type configuration, around 130 passengers could be accommodated.

The drag of the 765-107B is explained in Figure 6.3.5. It shows that scaling the 765-076E up to the 100 

passenger Configuration 2C changed the cruise lift-to-drag ratio (L/D) a small amount, from 8.3 to 8.47. 

The cruise L/D increases to 9.46 once the 10% drag reduction from N+3 technology is applied and the 

fuselage has been grown to accommodate 120 passengers. Comparing the L/D of the 765-107B to some of 

its predecessors, Figure 6.3.6 shows better L/D for the HSR 2015TC6, but a pretty close match to a 2015TC 

with revised technology predictions and scaled 76% to be about the same size (i.e. airplane size plays a 

significant role in L/D differences due to Reynolds number and excrescence scaling). The benefit of N+3 

technology over N+2 is evident when compared to the 765-072B from N+2.

6.3.2 Icon II Engine

6.3.2.1 General Description

The N+3 goals call for low cruise emissions (~5 g/kg NOx), high range (4000-5500nmi), and high fuel 

efficiency (3.5-4.5 seat nmi/lb fuel at 4000-5000nmi). For trade study purposes, ―stretch goals‖ beyond the 

NASA N+3 goals, partly based on desirable market economics, were specified for the ―Icon-II‖ vehicle 

configuration. These called for, among other things, increased range (4800-5000nmi) and fuel efficiency (4 

- 5 seat nmi/lb fuel). The Icon-II vehicle sizing was performed for fixed wing area and a fixed TOGW of 

300k lb (tied to approach speed limits and top-of-climb boom design point). The engines were resized to 

maximize range.

The ―Icon-II‖ airframe was paired with an N+3 technology level reference engine (referred to as the ―Icon‖ 

engine). This is a notional engine meant to represent the most promising combinations of technologies 

disclosed by the engine OEMs, and is used as a concept engine for trade studies only. The Icon 

‖composite‖ propulsion concept represents no particular OEM‘s design and does not imply commitment 

from any OEM to design or develop such an engine, especially regarding weight and geometry. As 

described later, this notional engine provides projected propulsion performance levels which enable the 

Icon-II airframe to meet the basic N+3 performance requirements and even approach the ―stretch‖ goals. 

6.3.2.2 Methodology

To create the Icon engine configuration, all engine technologies were reviewed in order to determine which 

technologies were a) common, and b) most beneficial. The performance data for the Icon engine is based 

on the N+2 -072B NPSS data. Factors were applied to the data such that its vehicle range would meet the 

N+3 stretch goals. Further details are in proprietary Appendix A.

6.3.2.3 .Results

An overview of the engine configuration can be seen in Table 6.3.2 and Figure 6.3.7.

6.3.3 Icon II Performance

Figure 6.3.8 is a thumbprint sizing chart showing the as-drawn 765-107B ―Icon-II‖ having some margin in 

wing area and thrust (de-rated as required to meet projected noise) in the configuration. Where the 

approach speed and second segment climb gradient constraints meet, a small advantage in increased range, 

reduced thrust, reduced wing area, and improved seat nmi/lb fuel FOM could be achieved if another sizing 

cycle had been allowed. Changing the wing area and thrust to achieve this would be a first step in the 

 

6 High Speed Civil Transport—2015 Technology Baseline Airplane Configuration, D6-82527-3, April 

2000, NAS1-20220
54

development of this configuration. The table in Figure 5.2 presents the mission profile used to evaluate the 

airplane.

6.3.4 Icon II Noise

As described in Section 6.3.1, advances in noise reduction, suppression and efficiently integrated shielding 

should give the N+3 generation of aircraft an advantage over the N+2 generation. Starting at the levels of 

airport and community noise predicted for the study aircraft of the N+2, the Icon-II gains from better high 

lift performance, light weight and low impact ejector/suppressor nozzles and effective shielding that is 

more efficiently integrated into the configuration. The noise level of the ―Icon-II‖ is expected to keep pace 

with the ever more strict noise requirements.

6.3.5 Icon II Structural Arrangement

The structural arrangement assumed for the 765-107B ―Icon-II‖ is essentially the same as for the 765-076E 

from the N+2 study, with appropriate adjustments for the effects of airplane size and passenger cabin 

dimensions on the floor height, window spacing, stowage bins, landing gear sizing, fuel tank volume 

allocations, etc.. The wing has multiple spars and the thin outboard wing has little volume for anything but 

structure. The wing tip and tail tip are solid. A torque box gives rigidity to the thin aft deck, allowing it to 

resist and transmit tail loads, but supplemental external keel structures in the aft deck, as on the 765-076E, 

might be unavoidable. The fuselage is essentially monocoque, but a supplemental internal keel beam is 

likely. Landing gear will match those described in Table 6.2.3 for configuration 2C, and the main gear 

bays demand innovative structure to route wing carry-through loads, and articulate mechanisms to ensure 

compact stowage with minimum fairing.

6.3.6 Progress toward the goals

A comparison of the capabilities of the ―Icon-II‖ 765-107B against the goals is shown in Table 6.3.3. In 

every category, the airplane is forecast to exceed the minimum goals, and often reaches the stretch goals.

6.4 Technology Trade Studies

6.4.1 Aeroelastics & Material Trades (submitted by M4 Engineering)

The initial assessment of technology benefits was based on experience with previous vehicle development 

activities. Technologies selected in the loads and aeroelasticity area included; active gust load alleviation 

(GLA) and maneuver load alleviation (MLA), active flutter suppression, and aero-propulsive-servoelasticity (APSE). In order to better quantify the benefits associated with aeroelastic and material 

technologies on flutter, detailed analyses were conducted on a relevant configuration. The starting point for 

these analyses was the final FEM from the NASA NRA N+2 studies. The model was first modified to 

provide a more relevant baseline for the N+3 analyses where the structural layout was modified to improve 

load paths. The model is shown in Figure 6.4.1. The baseline titanium strength sized model was provided 

to M4 Engineering Inc. for aeroelastic studies to assess flutter margins and to determine potential benefits 

of active flutter suppression. A range of materials was considered, including the baseline titanium design, 

aluminum, a baseline composite and an advanced composite. The material properties are shown in Table 

6.4.1.

The flutter speed margins were based on the flight envelope of the N+2 system studies as shown in Figure 

6.4.2. Starting with strength sized models for all four materials, flutter analyses were conducted to establish 

margins. The titanium and aluminum configurations did not meet flutter margin requirements. The 

composite configuration vehicles are stiffer and suppress the flutter mechanism present in the more flexible 

metallic configurations. The details of these analyses are provided in the M4 Final Report provided as an 

attachment. The titanium and aluminum configurations then went through a resizing process using the 

aeroelastic optimization capability in MSCSoftware NASTRAN to meet both the strength and flutter 
55

requirement. Table 6.4.2 summarizes the results. The column marked  ̳Baseline‘ shows the structural 

weight for the 4 configurations sized for both strength and flutter. The column marked with ‘FSS‘, for 

Flutter Suppression System, shows the structural weight with just strength requirement, and provides an 

upper bound of weight reduction when implementing a flutter suppression system. The addition of the 

flutter constraint to the sizing of the all titanium vehicle results in the addition of 7282 lb of structural 

weight (6.3% OWE) to the baseline vehicle. For an all aluminum construction, the flutter penalty is 

34,390 lb of structural weight (19.7% OWE). The flutter characteristics present in these configurations 

could be mitigated through the use of an active flutter suppression system, which could result in a 

significant avoidance of structural weight. The details of the analysis are provided in the M4 final report 

and this report has been provided as an attachment in Appendix G.

Based on the technology assessments and detailed analyses performed, a roadmap has been developed for 

developing and improving the technologies to support the N+3 timeframe as shown in section 7. 

6.4.2 Sonic Boom

The forecast sonic boom levels for the N+3 vehicle concepts represent a mix of classical Jones-SeebassGeorge-Darden theory of sonic boom minimization, emerging N+2 technology advancement, and 

predictions of future N+ 3 developments assuming the appropriate investments are made.

The basic principles of how to reduce the sonic boom of supersonic aircraft with classical signature shaping 

has been available for decades. Seebass and George published ―Sonic boom Minimization Including Front 

and Rear Shock Waves‖ in 1969. This paper laid out the basic principles and theory, and proposed the 

minimum sonic boom an aircraft concept might achieve as a function of aircraft weight, length, Mach and 

altitude. What was absent at the time was:

1. Definition of what sonic boom loudness would be acceptable to the public at large

2. Significant innovation in the areas of aerodynamics, propulsion, and structures (to minimize 

aircraft physical size and weight)

3. Technological progress in flight controls and in various ASE disciplines (to handle the required 

long, slender, thin-winged aircraft designs) 

4. Validated, high fidelity analysis tools to accurately predict a configuration‘s sonic boom level at 

all regions of its supersonic flight envelope 

5. Flight verifications of the shaping theory

6. Definition of a feasible compromise between aircraft features selected for sonic boom 

minimization criteria and features to meet performance, safety, emissions, and noise 

requirements.

Much of the subsequent HSR sonic boom related work in the 1990‘s, and a substantial portion of the 

NASA and industry funded sonic boom research since then, has been directed toward addressing each of 

these areas. In addition, research has also focused on the MDO problem of defining aircraft features like 

weight, length, planform, general arrangement that would place a concept design space where the high 

speed lines could potentially be optimized to achieve the configuration‘s low boom objectives with the 

available design tools. In 1998, Seebass revisited minimum achievable sonic boom as defined by the 

classical Jones-Seebass-George-Darden theory, with his paper on ―Sonic Boom Minimization‖ presented 

at the Special Course on ―Fluid Dynamics Research on Supersonic Aircraft‖ held at the von Karman 

Institute for Fluid Dynamics (VKI). For reference, based on the method of that paper, an aircraft of the 

―Icon-II‖ size, length, Mach, and altitude, would have a ―Seeb minimum‖ potential boom loudness level of 

79PLdB.

Our expectation is that between now and the technology readiness date for an N+3 supersonic airliner, 

assuming the continued necessary investment in sonic boom mitigation technology, significant progress 

will be made in at least three more recent promising areas of sonic boom design development research. 

These progress areas would include:

 Expanded use of MDO and higher order tool suites (CFD, FEM‘s) applied to classical JonesSeebass-George-Darden theory of sonic boom minimization. This approach focuses on 
56

minimizing the sonic boom on a ―macro‖ level by changes to the overall lift and volume 

distribution. This is done by maximizing the effective length and minimizing the weight of the 

aircraft with effective MDO design, as well as tailoring the general arrangement of the aircraft to 

achieve target lift and volume distributions with minimal compromises to overall performance 

parameters.

 Enhanced use of emerging optimization capabilities coupled with advances in computing power to 

work both full configuration and configuration component features on a ―micro‖ level to take 

advantage of near-field aerodynamics and exploitation of non-linear effects. This potential resides 

in using wave interference, wave cancellation, nacelle shaping and positioning, etc. to manipulate 

the near-field signature well before the fully formed far-field signature develops and ―freezes‖ on 

its way to the ground.

 Developments in harnessing the potential of active flow control, unsteady aerodynamics, energy 

manipulation, active geometry morphing, etc... at a micro level for the benefit of sonic boom 

mitigation

It is important to recognize that although we expect significant progress to be made in sonic boom design 

capability, we also believe a trade will remain between utilizing the emerging technology for the exclusive 

purpose of sonic boom reduction versus the purpose of improved performance, reduced emissions, reduced 

costs and so forth. Consequently we have only forecast the ―Icon-II‖ as having boom levels at ~77PLdB, 

even though its optimum signature is assumed to be distinctly non-SEEB. While we foresee the possibility 

of an aircraft in the same size/weight category of the ―Icon-II‖ possibly achieving a lower bound of 65-

70pldb if all the sonic boom technology potential is realized, the 65-70PLB level may come at a 

substantial performance /economic /fuel-burn penalty which may constitute an unfavorable compromise.

In addition to Boeing‘s own assumptions as to the future pace and direction of low boom design 

technology, Wyle Labs has proposed fine-tuning the source/multi-pole distribution, as demonstrated in the 

Wyle Labs GENGS tool (see non-proprietary Appendix E), to drive that boom level down to the goal. 

Translating the theoretical description of the off-body pressure field into practical aircraft geometry or load 

is among the many challenges facing development of low boom technology maturity in the N+3 timeframe.

6.4.3 NextGen System Wide Environmental Assessment of Technology Impacts 

(submitted by Wyle Labs)

Pursuing advanced aircraft designs and NAS technologies is a vital component of a comprehensive strategy 

to reduce aviation environmental impacts, including those related to climate forcing. The aviation industry 

is pursuing various transformational concepts for environmentally-friendly subsonic and supersonic aircraft 

to be introduced into the NAS within the NextGen framework and beyond. N+3 vehicle concepts presently 

offer the most ambitious targets in terms of environmental impact reduction from the source. In terms of 

emissions and fuel burn, NASA‘s Subsonic N+3 program (Table 6.4.3) aims to achieve a set of highly 

stringent targets:

 More than 80 percent reduction in LTO Nitrous Oxide (NOx) emissions compared to CAEP 2 

standards,

 Mitigation of contrail formation, which have a climate forcing effect,

 More than 70 percent improvement in fuel efficiency compared to current Stage 4 aircraft,

 The preponderance of alternative fuel use.

These stringent goals for emissions and fuel burn are to be pursued in concert with an equally stringent goal 

to reduce noise at the source. What is more, the Boeing Team N+3 Supersonic concepts and Technology 

Programs under study are targeting a supersonic transport vehicle—injecting additional environmental 

considerations, namely sonic boom and stratospheric emissions. Hence, even though achieving win-win 

outcomes for all the environmental effects associated with future aircraft is possible, there are several 

design tradeoffs and operational constraints that make aggressive NextGen goals for environmental impact 
57

mitigation challenging and require further development in order to achieve a technology readiness level 

suitable for incorporation into a viable future supersonic aircraft.

There are notable gaps in the current body of aviation climate change research and there is further progress 

to be had on the accurate modeling of cruise emissions, especially stratospheric emissions, which would be 

relevant to the vehicle concepts considered under this study. Wyle modeled the emission distribution across 

the NAS (Figure 6.4.3) for a 2025 NextGen condition that would likely only see the introduction of a few 

N+1 and N+2 concepts7. This modeling exercise showed that cruise emissions by a select vehicle class 

(Single-aisle/medium-haul) produce over 60 percent of domestic US emissions. The modeling of a 

supersonic business jet with a frequency of 85 daily operations proved to contribute less than 1 percent of 

total NAS emissions.7 This shows that from a system-level perspective, the largest impacts, and the 

potential for their mitigation currently lies within a particular market segment and a smaller supersonic 

transport market is unlikely to alter that picture. Yet other concerns with high altitude supersonic 

operations, namely climate forcing issues remain. 

There is still an ongoing effort to understand and accurately model non-CO2 climate forcing effects by 

aircraft emissions during the cruise phase of flight, where emissions are directly injected into Upper 

Troposphere (UT) or the Stratosphere as would be the case for high altitude supersonic transport 

operations. These emissions, including SO2, Particulate Matter (PM), H2O, have local and transient effects 

on irradiative forcing, through reactions that impact ozone, formation of contrail and other direct/indirect 

PM effects. PM is of particular concern for aviation due to its direct effects on human health, including 

respiratory and cardiac complications.8

The total climate forcing effect of non-CO2 emissions is believed to equal the CO2 emissions produced by 

aircraft operations.9 However, the scientific community still lacks a thorough understanding of these 

interactions at high altitude. Further observational and modeling research is needed before their effects on 

climate change can be accurately accounted for. Despite these gaps, the cruise emissions that Wyle 

modeled for a separate NRA provide a good start for understanding the proportionality and distribution of 

emissions across the NAS and the effects of introducing advanced supersonic vehicles on NextGen goals 

for environmental mitigation. Such an approach can also serve to help prioritize the various emissions and 

performance technology programs by providing a system wide assessment of their contributions and 

benefits relative to one another.

Another approach to evaluate the environmental performance of advanced vehicles is to measure their 

impacts in relation to their productivity in the NAS and/or the capacity they serve. We generally found that 

this becomes a challenge for supersonic vehicles of which the value served in the NAS is one of time 

saved.10 It is exceedingly difficult to quantify the value of time saved in the NAS as a result of supersonic 

operations and compare those benefits to the environmental footprint of the vehicle. Hence, analyzing the 

emissions and climate change effects of future supersonic aircraft currently faces two analytical challenges: 

(a) existing gaps in scientific understanding and modeling of stratospheric emissions, and (b) the difficulty 

of concluding an effective tradeoff metric for the vehicle that communicates its benefit in relation to its 

impact.

 

7 Rachami J., Page J., Zhou L., ―Environmental Modeling of Advanced Vehicles in NextGen‖, AIAA 2009-

6981, 9th AIAA Aviation Technology, Integration and Operations (ATIO) / Aircraft Noise and Emissions 

Reduction (ANERS) Conference, September 2009.

8 Environmental Protection Agency (EPA). Health and the Environment. Available: 

http://www.epa.gov/particles/health.html

9

Intergovernmental Panel on Climate Change (IPCC) (2000). Aviation and the Global Atmosphere, chap 6, 

Potential Climate Change from Aviation.

10 Rachami, J., and Page, J., ―Sonic Boom Modeling of Advanced Supersonic Business Jets in NextGen‖, 

48th Annual AIAA Aerospace Sciences Meeting, AIAA 2010-1385, January 2010.
58

Figure 6.2.1 Preliminary configurations for study.

Figure 6.2.2 Walk-around chart of Configuration 1C, 3 surface swing “arrow” wing.

Swing wing

5000lb

Challenges: APSE issues arise from high AR, 

high sweep and minimal aft deck to support 

engines.

Constant sweep strake to 

avoid vortex ingestion.

Wing/Body fairing houses

two axle 4-wheel truck

High AR and sweep

15000lb

Forward noise 

shielding by wing

 Low fuel burn/low boom swing ―arrow wing‖ (1C)

 Reference N+2 low boom -076 scaled up (2C)

 Alternate Concept: Joined Wing (3B)

 Alternate Concept: Scissor Wing (4B)

 Remote fan proposal
59

Figure 6.2.3 Three-view and characteristics of Configuration 1C, swing “arrow” wing.

89.8ft

259.4 ft
60

Table 6.2.1 Characteristics of Configuration 1C, swing “arrow” wing.
61

Table 6.2.2 Preliminary, un-cycled weights for Configuration 1C, “swing–wing”.
62

Figure 6.2.4 Walk-around chart of 100 passenger Configuration 2C /“765-107A”, 

(scaled from N+2 765-076E) 

Figure 6.2.5 Three-view and characteristics of Configuration 2C 

107.6

242 ft

Over-wing Nacelles; 

configured with aft 

deck and tails for noise 

shielding & boom

Cranked planform 

is cruise/subsonic 

Fin-tip pods for flutter compromise

balancing
63

Table 6.2.3 Characteristics of Configuration 2C. 

N+3 Concept 2C

Weights (Targets)

Maximum Taxi Weight (MTW) (lb.) 303,000

Maximum Takeoff Weight (MTOW) (lb.) 300,000

Maximum Landing Weight (MLW) (lb.) 240,000

Engine Type

SLST (lb) 60,000

Fan diameter (in.) 86.44

Overall Dimensions

Overall Length (ft., in.) 242.0

Fuselage Length (ft., in.) 242.0

Passenger Cabin Length (ft) 96

Wing

ESDU Reference Area (sq. ft.) 3964

Span (ft.) 107.6

Outboard LE Sweep (o) 52

ESDU Reference Area LE Sweep (o) 57.40

Empennage and Canard

Horizontal Stabilizer Area (ref., sq. ft.) 420.5

Combined Vertical Tail Area (exposed, projected, sq. ft.) 420.5

Combined Canard Area (exposed, projected, all-moving, sq. ft.) 0.00

Passenger and Baggage Capacities

Pass. Count 100

Total Cargo Capacity (cuft) 900cuft

Landing Gear

Wheel base (ft., in.) 1564

Main Landing Gear Track (ft., in.) 305

Main Landing Gear Truck Size (width x length, in.) Dual Tandem

Main Landing Gear Tire Size H40x14.5-19

Nose Landing Gear Tire Size H22x8.25-10
64

Table 6.2.4 Preliminary, un-cycled weights for Configuration 2C

Model N+3 Concept 2C Rev. INITIAL, MCTCB, N+3, LONG CON-DI

Growth 300,000 lb

FC Description Weight CG

01 Wing Structure 40460 2213

02 Horizontal Tail Struture 4570 2611

03 Vertical Tail Structure 1740 2306

04 Fuselage Structure 15720 1452

05 Main Landing Gear 7400 2109

07 Nose Landing Gear 1010 1004

08 Forebody Controls 0 0

Structure Total 70900 2044

09 Inlet Structure and Systems 4620 2245

10 Cowling 2160 2388

11 Pylon/Strut 1820 2380

12 Engine 18940 2359

13 Nozzle 5680 2531

14 Installation (incl. fairings) 1340 2380

15 Engine Accessories, Controls, & Start System 200 2403

Propulsion Pod Total 34760 2376

23 Fuel System 4110 2117

24 APU/EPU 610 1060

27 Instruments 830 1099

28 Surface Controls 3460 1998

29 Hydraulic Power System 2210 1901

30 Pneumatic System 0 0

32 Electrical System 2330 1483

33 Electronics 510 1885

34 Flight Provisions 760 600

35 Passenger Accomodations 10340 1552

37 Cargo Compartment 580 2647

38 Emergency Equipment 600 1541

39 Environmental Control Systems 1190 2279

40 Ice Protection 210 2497

49 Exterior Markings 590 1722

50 Load and Handling 0 0

55 Customer Options 800 6318

Systems & Fixed Equipment Total 29130 1856

Manufacturer's Empty Weight (MEW) 134790 2089

97 Standard and Operational Items 5360 1660

Operational Empty Weight (OEW) 140150 2072
65

Figure 6.2.6 Configuration 3B, preliminary Joined Wing.

Figure 6.2.7 Three-view and characteristics of Configuration 3B, preliminary Joined Wing.

104.6ft

242 ft
66

Table 6.2.5 Characteristics of Configuration 3B, preliminary Joined Wing.

N+3 Concept 3B

Weights (Targets)

Maximum Taxi Weight (MTW) (lb.) 303,000

Maximum Takeoff Weight (MTOW) (lb.) 300,000

Maximum Landing Weight (MLW) (lb.) 240,000

Engine Type

SLST (lb) 60,000

Fan diameter (in.) 83.55

Overall Dimensions

Overall Length (ft., in.) 242.0

Fuselage Length (ft., in.) 242.0

Passenger Cabin Length (ft) 96

Wing

ESDU Reference Area (sq. ft.) 0.0

Span (ft.) 114.0

Outboard LE Sweep (o) 45

ESDU Reference Area LE Sweep (o) 1684.5

Empennage and Canard

Horizontal Stabilizer Area (ref., sq. ft.) 1071.4

Combined Vertical Tail Area (exposed, projected, sq. ft.) 477.8

Combined Canard Area (exposed, projected, all-moving, sq. ft.) 0.02

Passenger and Baggage Capacities

Pass. Count 100

Total Cargo Capacity (cuft) 900cuft

Landing Gear

Wheel base (ft., in.) 1346.88

Main Landing Gear Track (ft., in.) 429.9

Main Landing Gear Truck Size (width x length, in.) Dual Tandem

Main Landing Gear Tire Size H40x14.5-19

Nose Landing Gear Tire Size H22x8.25-10
67

Table 6.2.6 Preliminary, un-cycled weight breakdown of Configuration 3B, preliminary Joined 

Wing. Note: No weight advantages assessed for joined structure. Engine is a heavier, N+2 technology 

model.
68

Figure 6.2.8 Cumulative lift distributions on the Joined Wing config 3D and the N+2 config 765-

076F, before and after Tranair design of twist and camber for minimum drag. Mach=1.8, CL=0.12

Figure 6.2.9 Mach contours before (“Seed”) and after Tranair design of twist and camber on the 

wing and tail at 1.8 Mach and 0.12 CL.

Twist & camber of wing & tail designed to 

minimize drag (pressure + skin friction)

at M=1.8, cruise CL=0.12

Seed Tranair design

-8ct

(Status is +30ct from forecast)
69

Figure 6.2.10 Center of lift on seed and drag optimized configurations. Balancing payload fuel & 

airframe would be more challenging on the optimized configuration.

Figure 6.2.11 Configuration 4B Oblique “Scissor” Wing.

ESDU MAC/4

seed design
70

Figure 6.2.12 Scissor Wing dimensions

Figure 6.2.13 CFD++ viscous analysis of an oblique “scissor” wing & body like config 4B. Mach 1.4, 

angle of attack 3 deg, 40 million grid elements, Reynolds number 2 million/ft. 

Scissor Wing config. 4B, M=1.4, AOA=3deg

Surface Streamlines

Flow separation 

indicated along 

down-stream wing 

T.E. at cruise

Optimal/variable 

fairings a challenge

flow

CFD++ analysis

40M grid elements

Re 2M/ft

(Full-scale flight )

112.2 ft

259.4 ft

208.3 ft unswept
71

Figure 6.2.14 L/D vs Mach for a nominal climb, accel. and cruise flight profile. (Carlson-Middleton 

linearized panel solution + calibration factors and flight adjustments) 
72

Figure 6.2.15 Area+thrust sizing “thumbprint” of configuration 1C.
73

Figure 6.2.16 Area+thrust sizing “thumbprint” of configuration 2A, predecessor to 2C, the seed to 

the eventual “Icon-II.
74

Table 6.3.1 Thrust and Area + Thrust sizing of Configuration 2C, with and without preliminary 

estimate of weight and drag reduction via technology.

Weight (lbs) Range (nmi)

Engine change alone

Mach 1.6 300k 4600

With Preliminary Weight & 

Drag Projections

10% OEW Reduction

(preliminary estimate)

6% Cruise Drag Reduction

(preliminary estimate)

Mach 1.6 220k 4000

Mach 1.6

Mach 1.8

275k

277k

5000

5000

Mach 1.6

Mach 1.8

300k

300k

5400

5350

Figure 6.3.1 Advanced materials & structural concepts assumed for N+3.

Mini canard/RCV

for trim and structural

mode control

Advanced Metals/MMC/CMC

(nose & main landing gear, hot 

wash)

High Strength/Modulus 

composites 

Tough, low density composites

Tailored stiffness

Light Weight Composite Armor

Light weight thermal protection

Mini canard/RCV

for trim and structural

mode control

Advanced Metals/MMC/CMC

(nose & main landing gear, hot 

wash)

High Strength/Modulus 

composites 

Tough, low density composites

Tailored stiffness

Light Weight Composite Armor

Light weight thermal protection

Advanced Metals/MMC/CMC

(nose & main landing gear, hot 

wash)

High Strength/Modulus 

composites 

Tough, low density composites

Tailored stiffness

Light Weight Composite Armor

Light weight thermal protection
75

 

Figure 6.3.2 Three-view of the “Icon-II” 765-107B.

Model DATA TABLE (as drawn airplane)

N+3 765-107B Wing Horizontal RCV Vertical

ITEM ESDU Total Projected Projected

Area to CL 4200 4471.1

Exposed 445.48 78.13 445.48

Reference 4200 445.48 78.13 445.48

Aspect Ratio 2.90 2.72 3.15 2.00 3.15

Taper Ratio 0.169 0.198 0.20 0.198

LE Sweep angle 57.59 48 58 48

Dihedral, TE 12 12 45 -20 45

T/C 0.024 0.024 0.030 0.030 0.030

Tail Volume 0.102 0.102 0.066 0.0413

Span , in 1323.6 1323.6 534.6 75.0 534.6

Root Chord, in 782.1 283.4 125.0 283.4

Tip Chord, in 131.8 56.0 25.0 56.0

M.A.C. in 534.1 703.9 195.1 86.1 195.1

X 1/4 mac 2196.6 2071.4 2711.6 293.9 2711.6

Y, mac 252.4 335.7 41.2 335.7

Tail Arm, in. 515.0 1902.7 515.0

262 ft

110 ft 4in
76

 

Figure 6.3.3 Cabin layout for 120 passengers, dual class, in “Icon-II” 765-107B.
77

 

Figure 6.3.4 Cabin layout for 50 passenger, executive class “Icon-II” 765-107B.

Executive/All First Class
78

Figure 6.3.5 Drag tracking from 765-076E to Concept 2A to 765-107B “Icon-II”.

Figure 6.3.6 Drag tracking from HSR 2015TC and N+2 765-072B.

M=1.6, CL=.14, Alt=47,000ft

8.3

8.47

9.46

7

7.5

8

8.5

9

9.5

10

765-076E Concept 2a 765-107B

L/D

M=1.8, CL=.12, Alt=51,000ft

10.05

9.09

8.54

9.09

7

7.5

8

8.5

9

9.5

10

10.5

HSR 2015TC 76% scale 2015 with

revisted tech

756-072B 765-107B

L/D
79

Table 6.3.2 Configuration parameters of the “Icon-II” engine (un-scaled).

Figure 6.3.7: Icon Engine Configuration Chart

Ref. Thrust (27F, SLS, Augm.) [lbf] 66000 - 68000

Ref. Thrust (27F, SLS, Non-Augm.) [lbf] 57000 - 59000

Cruise SFC (50k, M1.6, 90% power) 

[lbm/hr/lbf] 0.77 - 0.79

Diameter [in] 81 - 84

Total Length [in] 560 - 570

Engine+Nozzle Weight [lbm] 11000 - 11300

Advanced bleedless inlet 

with shock control

Advanced variable area 

nozzle

Designed for civil 

applications

Adv materials

High OPR Compressor

Cooled cooling air

High efficiency

Adv Materials Turbine

CMC

High efficiency

Low emissions, 

pressure rise combustor

Adaptive Fan/Cycle Duct-integrated burner

Low Jet Velocity
80

Figure 6.3.8 Thumbprint sizing chart for “Icon-II” 765-107B. Thrust is de-rated as required for 

estimated noise. 

Table 6.3.3 Comparison between N+3 goals and forecast for “Icon-II” 765-107B.

Metric Min Goal Stretch Goal Icon-II

Sonic Boom 70-80 65-75 65-75

Noise -20 -30 -30

Cruise Emissions 5 <5 ~5

Speed 1.3 2 1.6-1.8

Range 4000 5500 5900-4800

Payload 100 200 50-130

Seat-nmi/lb fuel 3.5 4.5 4-5

FOM = 

4.90

4.85

4.95

5.0

FOM = Seat * Nautical Miles

Block Fuel
81

Figure 6.4.1 Structural Layout

Table 6.4.1 Material Properties

Figure 6.4.2 Flight Envelope
82

Table 6.4.2 Structural Weight Summary

Table 6.4.3 – NASA Subsonic N+3 Program Goals

Figure 6.4.3 – NAS-Wide Emission Distribution for Modeled 2025 Scenario 

(Baseline NextGen and N+1 and N+2 Subsonic and Supersonic Fleet and Operations)

Table 1. NASA’s Environmental Targets for Three Generations of Aircraft Technology

Criteria / Technology

N+1 Generation: 

Conventional Tube 

& Wing (2010)

N+2 Generation: 

Unconventional 

Hybrid Wing Body 

(2020)

N+3 Generation 

(2030-2035)

Noise (Cumulative 

below Stage 4) - 32 dB - 42 dB

Better than - 71 dB (55 

LDN at average airport 

boundary)

LTO NOx Emissions 

(below CAEP 2) -70% -80%

Better than -80% plus 

mitigate formation of 

contrails

Performance: Aircraft 

Fuel Burn -33% -50% Better than -70% plus non-fossil fuel sources

Performance: Field 

Length -33% -50% Exploit metroplex concepts

Source: Adapted from NASA Overview of NRA solicitation (N+3 Pre-Proposal Conference)
83

7.0 Technology Prioritization, Selection and Roadmapping (Task 3.6)

7.1 Propulsion Technologies

7.1.1 Background

The goal of Task 6 is to calculate an aggregated benefit at the vehicle level. This benefit is composed of the 

individual benefits or decrements that a technology offers in terms of propulsion-specific quantities. 

―Propulsion-specific‖ refers to the engine itself, in addition to integration technologies such as inlets and 

nozzles. The fundamental quantities of interest were changes in engine weight, diameter (or drag for inlets 

and nozzles), SFC, noise, emissions, and thrust. The respective engine OEM‘s assessed the fundamental 

quantities for engine technologies, whereas Boeing assessed the nozzle and inlet technologies with a few 

exceptions.

7.1.2 Methodology

Sensitivities were calculated based on variations in parameters on a resized engine from the -072B baseline. 

This exercise was performed in order to determine, for instance, the effect of a 1% change in engine thrust, 

diameter, or SFC on vehicle FOM and TOGW. Then the following equation was employed:

D

D

Param W

W

Param SFC

Wf

Param Fn

Fn

Param Param 





 





 





 





 

Where

Param = Vehicle-level parameter (FOM, TOGW)

Fn = Net thrust

Wf = Fuel flow

SFC = Specific Fuel Consumption

W = Weight (engine)

D = Diameter (engine)

and

Param

Fn

Param





Wf

Param





W

Param





D

Param





FOM 2.366 -2.05 -0.238 -0.694

TOGW -1.503 1.161 0.285 0.571

The emissions and noise benefits were not explicitly calculated, but considered inputs from engine OEM 

analyses.

After calculation of vehicle-level benefits, statistical analyses were performed. The first section of the 

analysis consisted of constructing histograms that indicated which technologies showed the most benefit. 

An example histogram is shown in Figure 7.1. In the second section of the statistical analysis, the cost and 

risk indices (i.e. low, medium, or high) were assigned values, and the benefits were then divided by the 

indices. These indices were 1 for low, 3 for medium, and 5 for high risk or cost. An example of such a chart 

can be found in Figure 7.2. Such a chart is meant to delineate which technologies show the best balance 

between benefit, risk, and cost; essentially, the further out a technology lay on the horizontal and vertical 

axes, the more promising it is. For the simplified example in Figure 7.1 and Figure 7.2, Tech 1 shows high 

benefit, low risk, and low cost; in contrast, Techs 5-7 show low benefit, high risk, and high cost. Therefore, 

the cluster of Techs 5-7 would be eliminated from further consideration. An ―overall weighted benefit‖ 

metric was defined which aimed to combine the benefits of reductions in sonic boom, noise, and emissions, 

and increases in fuel efficiency. These benefits, if available, were individually multiplied by weighting 

factors and then summed. The weighting factors were 1 for sonic boom reduction, 1 for noise reduction, 1 

for fuel efficiency increase, and 0.2 for emissions reduction. The reason for assigning 0.2 to the emissions 
84

reduction was because technologies which had emissions benefits were typically significantly higher than 

the other benefits, and could have skewed the data. The technologies, changes to fundamental values, and 

vehicle aggregated benefits are contained in the proprietary Appendices A through D.

7.1.3 Technology Families

Approximately 90 propulsion-related technologies were considered and analyzed per the described process. 

Of these technologies, approximately 25% were deemed for consideration for detailed roadmapping. A 

typical reason for exclusion is that a technology could represent significant benefits in terms of SFC and 

emissions, but also demonstrated a weight penalty which far outweighed the overall potential fuel 

efficiency benefit. 

Upon analyzing all technologies which were considered for detailed roadmapping, technology groups or 

―families‖ were evident. These shall now be described.

7.1.3.1 Adaptive Fan/Cycle

The constraints of the design space for this vehicle call for propulsion systems which are met with 

competing requirements. For instance, the engines must be low-noise during take-off, which implies 

traditional high BPR turbofans, which also require high mass flows. However, during cruise, the engines 

must have high thrust in proportion to inlet area, which implies a smaller diameter and low BPR (i.e. a 

turbojet). To address these competing demands, advanced configurations should adapt mass flow and/or 

effective fan pressure ratio.

The broad classification of ―Adaptive Fan/Cycle‖ is meant to describe configurations in which the inlet 

mass flow is adjusted during operation, the variation of which enables high cycle performance. This can be 

achieved by several means. Whereas in traditional turbofans the fan flow is distributed between the bypass 

and core, such advanced concepts may result in an additional diversion, generating a separate mass flow 

which enables advanced thermal and noise management. By varying the flow in an optimal manner, 

significant potential for reductions in engine diameter, weight, and noise exist.

Less than five technology concepts were roadmapped in detail. The primary affected goal is fuel efficiency, 

with benefits greater than 10% but less than 25%. The secondary goal affected is sonic boom reduction, due 

to reductions in TOGW on the order of 15-20%. Additionally, Adaptive Fan/Cycle systems are seen to 

have potential benefit for noise reduction during take-off.

7.1.3.2 Compressor

Advances in material technology for compressor components are deemed to have the potential for 

significant performance improvements. The family of ―Compressor‖ describes these material technology 

advancements. Improving the microstructure of discs could lead to higher compressor operating 

temperatures and therefore higher discharge pressures. This results in higher OPRs for engines of smaller 

diameter and weight. Less than five technology concepts were roadmapped in detail. The primary affected 

goal is fuel efficiency, with a benefit between 5 and 10%; the secondary affected goal is sonic boom, due to 

reductions in TOGW on the order of 5%.

7.1.3.3 Turbine

Advances in turbine technologies are primarily in the field of materials development. Fundamentally, high 

temperature materials enable the turbine to run at much higher temperatures. With the increase in 

temperature capability, the turbine requires less cooling. Reductions in cooling, along with the higher 

turbine temperature, increase thermal efficiency while also reducing engine weight. Of the few 

technologies which were roadmapped, an example is CMC components. The primary goal affected was 

fuel efficiency, with benefits between approximately 10 and 20%; the secondary affected goal is sonic 

boom, due to reductions in TOGW on the order of 5-15%.
85

7.1.3.4 Combustor

The family ―Combustor‖ describes advanced combustion concepts which can significantly improve 

emissions and fuel efficiency. Examples of such concepts would be those in which combustion occurs such 

that volume is maintained and therefore pressure is increased. These concepts might also include high 

temperature-capability materials and advanced controls on ignition and mixing to ensure the leanest 

possible ignition. Less than 5 technologies were roadmapped in detail. The primary goal affected was 

emissions, with estimated benefits of greater than 70% reduction. The secondary goal affected was fuel 

efficiency, with up to 5% improvement due to SFC reductions.

7.1.3.5 Cycle/System

The term ―Cycle/System‖ is a broad classification for those technologies which offer optimized cycle 

performance. Improving compressor and turbine efficiencies through advancements in modeling and 

materials could lead to large SFC reductions. Other examples of Cycle/System technologies are advanced 

thermal management systems such as cooled cooling air, and increasing the ability of fuel to retain heat 

prior to combustion. Five technologies were roadmapped, and they primarily affected fuel efficiency, up to 

25%. A secondary affected goal was emissions, with more than an 80% improvement.

7.1.3.6 Inlet

As the mission for this vehicle requires sub- and supersonic flight phases, the propulsion system must be 

able to adapt for maximum performance and operability. The term ―Inlet‖ refers to technologies which 

ensure sufficient mass flow to the engine and high pressure recovery, while minimizing noise, SFC, and 

distortion effects throughout all flight conditions. Some technologies such as auxiliary inlet doors enable 

the inlet to meet the mass flow demands of low speed, high power situations. Other technologies would 

enable aggressive flow turning to shorten the diffuser length, or changing the shape of the nacelle during 

flight through the use of advanced materials and control systems. Four technologies were roadmapped. 

They primarily benefitted fuel efficiency, with benefits between 5-10%. Due to potential for weight 

reductions, the secondary goal affected was sonic boom, with an average of 1% improvement. 

7.1.3.7 Nozzle

To perform efficiently, provide sufficient take-off thrust, and still meet stringent noise requirements, the 

propulsion system must have a sophisticated exhaust system. The family ―Nozzle‖ refers to these 

technologies. Nozzle technologies must be able to operate efficiently at subsonic speeds, where fixed 

geometries have had a successful history, and at supersonic high altitude conditions, where variable 

geometries enable a broad range of operating capabilities. While variable area configurations have been 

successfully applied to military platforms, further steps are required to apply similar technologies for a 

commercial application. Some nozzle technologies show potential for the shielding of jet velocity noise 

through the use of innovative mass flow channeling afforded by adaptive cycle engines. This category also 

encompasses technologies which augment the thrust at certain Mach number ranges, enabling lower dry 

thrust, therefore reducing engine size and weight and increasing vehicle efficiency over a given flight 

range. Five nozzle technologies were roadmapped. They primarily benefit fuel efficiency, up to 20%. The 

secondary benefit is in noise reduction, with near 10% improvements.

7.2 Airframe Non-Proprietary

7.2.1 Technology Identification, Screening and Prioritization

The airframe technology items were identified and developed building off the results of the Initial 

Reference System and Technologies workshop described in Section 3.0. Each Engine Company developed 

their own technologies items and all are covered in detail in the respective proprietary Appendices.

Boeing started from a company-wide survey of ongoing technology and vehicle development work, past 

studies such as HSR and other industry efforts such as that from NIA. The goals and objectives of the N+3 

supersonic vehicle study program were reviewed with the appropriate personnel working on the 
86

technologies with the request to identify the items that would be applicable to this N+3 supersonic work. 

This activity generated about 100 technology items that were then grouped under the following categories: 

• Safety and Airworthiness

• Sonic Boom

• Noise

• Engine Efficiency and Durability (covered in Section 7.1)

• Aeroelastics and Flight Controls 

• Airframe Structures and Materials

• Aerodynamic Efficiency

• Systems

• MDO (Multidisciplinary Optimization)

The 100 items were reduced to 34 through an initial screening process that considered the most promising 

and applicable technologies for this application. The following criteria were used during the initial 

screening process:

• Fuel Efficiency

• Development time to TRL 6

• Fundamental Quantity Benefit i.e. Drag, noise etc

• Tech Rank relative to each of the Concepts shown in Section 3 

• Risk

• Integration Issues

• Current TRL

• Description

• Cost for TRL 6

Following the initial screening process, more detailed quantitative values were assigned to each technology 

for the criteria shown above. 

Resized mission performance for the 072B reference configuration was evaluated by incrementally varying 

each of the fundamental quantity items of drag, empty weight (OEW), thrust and SFC. The following 

equation, similar to that shown in Section 7.1, was then developed based on the resizing results and the 

partial derivative values determined as shown below:

These results are therefore based on a direct impact on the fuel burned FOM. The assessed values for each 

of the 34 technologies were used with the above equation to get an overall FOM (figure of merit, 

seat*nmi/fuel burned) and the results used to rank the technologies from best to worst to obtain the top 

items for further study. The top 34 items ranked in order is shown in Table 7.1. Then as discussed in 

Section 7.1, histograms were constructed that indicated which technologies showed the most benefit and 

the risk indices were assigned values, and the benefits were then divided by the indices and histograms 

were constructed as illustrated in Figs 7.1 and 7.2. 

The detailed results of the technology evaluations are contained in Appendix A. 

7.2.2 Affordability Analysis

An attempt was made to determine the best-value of the technologies by applying NASA‘s Process Based 

Economic Analysis Tool (P-BEAT). This process is summarized in Figure 7.3. A few technologies were 

identified to test the ability to apply the process. Needed quantities were identified to execute the process. 

Based on the far term nature of the work the necessary information was not available in sufficient detail to 

make the analysis meaningful. So the effort was discontinued. 
87

7.2.3 Roadmaps

The top technologies indicated in Table 7.1 were then combined with related technologies identified in the 

discussion of Section 7.2.1 and grouped into categories. These categories were: 

1. Sonic Boom—Design Methods

2. Sonic Boom– Active Technology Mitigation 

3. Noise—High Lift 

4. Propulsion Integration—Inlet and Nozzle

5. Aeroelastics & Flight Controls* 

6. Composites & Metals* 

7. Structural Concepts* 

8. Aerodynamic Efficiency

9. Aircraft Systems* 

The supersonic technologies were compared side-by-side with the Subsonic Super Ultra Green Aircraft 

Research (SUGAR) work being done by Boeing in an attempt to highlight the exclusively supersonic items. 

They were compared on the basis of Subsonic Only, Mixed and Supersonic only. We built the supersonic 

technology roadmaps with this as a point of departure and focused on the supersonic only and the 

supersonic applications for the mixed. But we found that some can‘t be segregated and those are identified 

by the * in the roadmap listing above. 

The resulting roadmaps are presented in the proprietary Appendix F. However the key milestones over the 

first five years from the roadmaps are shown figure 7.4. 
88

Table 7.1 Results of the Technology Ranking

FOM Rank Technolgy

1

Reliability-Based Design and Certification

2

Active Laminar

3

Structural Health Management

4

Active GLA/MLA

5

Riblets (limitied application)

6

Low-speed High-Lift devices

7

Aero-Servo-Propulsive-Elasticity (ASPE)

8

Reliable CG Control

9

Passive Laminar

10 Morphing bumps (Control Cp Distribution)

11 Synthetic Jets Fuselaage

12 Plasma

13 Structurally Integrated Energy Management

14 Highly efficienct and flexible, thin film solar cell

15 High-Efficiency Thermal-Electric Energy Harvesting

16 AFC High Lift

17 Synthetic Jets Wing

18 Advanced Metals

19 Hingeless Control Surfaces

20 Tailored Structural Stiffness

21 Active Flutter Suppression

22 Highly Integrated Subsystems (multifunctional structures)

23 Ultra-High-Modulus, Ultra-High-Strength Fibers

24 Thermoplastic Composites

25 High-Temperature Polymer Composites

26 Multifunctional Nano-Composite

27 Nano-electronics 

28 Very Tough Composites

29 Metal-Matrix Composites

30 Active TE

31 Hingeless Control Surfaces with Fowler Motion

32 Control Surface Deflection through LE or TE Warping

33 Supersonic Microjets

34 Off-Body Energy Addition
89

Figure 7.1: Example Histogram

Figure 7.2: Example Benefit/Cost vs. Benefit/Risk Chart

BENEFIT (i.e. FOM Increase, Sonic Boom Decrease, Emissions 

Decrease, Noise Decrease)

-25

-20

-15

-10

-5

0

5

10

15

20

25 Tech 1 Tech 2 Tech 3 Tech 4 Tech 5 Tech 6 Tech 7

TECHNOLOGY BENEFIT [%]

BENEFIT (i.e. FOM Increase, Sonic Boom Decrease, 

Emissions Decrease, Noise Decrease)

Tech 1

Tech 2

Tech 3

Tech 4

Tech 5

Tech 6 Tech 7

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

16

18

20

22

-10 -5 0 5 10 15 20 25

Benefit/Risk Index Benefit/Cost Index
90

Figure 7.3 Summary of Affordability Process

• N+3 Supersonics Metrics & FOMs

• Vehicle Technologies Morph Matrix

Boeing 

Performance 

Engineering

Boeing 

Affordability 

Engineering

80% Uncertainty 

Region

Cost Uncertainty

Best Value Attribute Score Cost to Mature to TRL 6

Qualitative Technology 

Value Analysis

Task 5

Technology 

Evaluation

Task 6

Vehicle 

Evaluation Desirability (weighted FOMs) Life Cycle Cost 

(Develop, Production. O&S)

Quantitative Vehicle 

Concept Value Analysis

New Best 

Value

-$8,000,000 $2,000,000 $12,000,000

Feature Cnt

Mass Elec Lbs

Mass Non Elec Lbs

Hyd PSI

Platform Override

Number Components

Production Qty

Material Workability

Precision Fact Override

Op Hrs Struct

Dev Cost Sensitivity - Pgm: CEV Service Module Jon 

Study: SM_Govt_Baseline Number: 8

$3,458,061,865

$2,203,154,650

$923,550,046

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

$710,000,

000

$1,210,00

0,000

$1,710,00

0,000

$2,210,00

0,000

$2,710,00

0,000

$3,210,00

0,000

$3,710,00

0,000

$4,210,00

0,000 Prob DEV $K: Pgm: CEV Service Module Jon Study: 

SM_Govt_Baseline Number: 8

Subsystem-Level

Vehicle Cost 

Estimates & Drivers

Task 6

Vehicle 

Evaluation Desirability (weighted FOMs) Life Cycle Cost 

(Develop, Production. O&S)

Quantitative Vehicle 

Concept Value Analysis

New Best 

Value

-$8,000,000 $2,000,000 $12,000,000

Feature Cnt

Mass Elec Lbs

Mass Non Elec Lbs

Hyd PSI

Platform Override

Number Components

Production Qty

Material Workability

Precision Fact Override

Op Hrs Struct

Dev Cost Sensitivity - Pgm: CEV Service Module Jon 

Study: SM_Govt_Baseline Number: 8

$3,458,061,865

$2,203,154,650

$923,550,046

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

$710,000,

000

$1,210,00

0,000

$1,710,00

0,000

$2,210,00

0,000

$2,710,00

0,000

$3,210,00

0,000

$3,710,00

0,000

$4,210,00

0,000 Prob DEV $K: Pgm: CEV Service Module Jon Study: 

SM_Govt_Baseline Number: 8

Subsystem-Level

Vehicle Cost 

Estimates & Drivers Desirability (weighted FOMs) Life Cycle Cost 

(Develop, Production. O&S)

Quantitative Vehicle 

Concept Value Analysis

New Best 

Value

-$8,000,000 $2,000,000 $12,000,000

Feature Cnt

Mass Elec Lbs

Mass Non Elec Lbs

Hyd PSI

Platform Override

Number Components

Production Qty

Material Workability

Precision Fact Override

Op Hrs Struct

Dev Cost Sensitivity - Pgm: CEV Service Module Jon 

Study: SM_Govt_Baseline Number: 8

$3,458,061,865

$2,203,154,650

$923,550,046

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

$710,000,

000

$1,210,00

0,000

$1,710,00

0,000

$2,210,00

0,000

$2,710,00

0,000

$3,210,00

0,000

$3,710,00

0,000

$4,210,00

0,000 Prob DEV $K: Pgm: CEV Service Module Jon Study: 

SM_Govt_Baseline Number: 8

Subsystem-Level

Vehicle Cost 

Estimates & Drivers

• Vehicle Characteristics Morph Matrix

• Performance & Sizing Analysis 

(Subsystem-level information)

N+3 Affordability Task Progression

(“Affordability” = Cost vs. Benefit)
91

SONIC BOOM

CUMULATIVE NOISE

CRUISE EMISSIONS

FUEL EFFICIENCY

AERODYNAMICS PROPULSION (ENGINE OEM-SPECIFIC)

STRUCTURE AIRCRAFT SYSTEMS

Initial SB Framework

Final SB Framework

Propogation Aero and FEM

Para Geom and CFD

Obj Ftns and Constrains Otimization Technique

Parametric Requirements

Current Contract Commplete 

2011 2012 2013 2014 2015

MJ Shock mods

MJ WT Test go-ahead MJ FS sys des & demo plan

MJ 3-D wt demo

OBH Benefit ana

OBH WT demo

OBH Pwr Sys & demo plan

HCl Prelm Conceps Feasability HCl WT Test

ASE Lidar gust sensor ASE physics, CFD Structure

ASE hingeless cont surf ASE Active wing control

ASE Improved actuators ASE benefit ana

ASE real time algorithims

Mat cost benefit ana

Mat target applications

MAT new forms & processes

RBD metrics and des app

Struct integrated antennas SHM hot spot monitoring Struct powr retern and EME

Adaptive struct low rate deformation

RBD and SHM benetift ana

MDO BL stability morphing ans camber

Passive LFC WT Test

Active LF extent and location

Active LF veh assessmt

Riblets app studies

Active LF breadbd bench tests

Sys cand techs and risk

Sys tech dev plan

Sys tech feasability demo

Sys tech maturation status

Low Emissions 

Combustor

Test

Variable Area Noz sys reqmts

Variable Area Noz layout & control

Ejector Noz sys reqmts

Inlet fluidic control reqmts

Inlet fluidic feasability

Inlet fluidic bench test Inlet mold line lips bench test

Adv. Combustor

Rig Test

Compressor w/ heat exchanger

Noise reducing nozzle 

Augmentation Dev for 

Adv Nozzle

Variable Area Noz trade study

Adaptive Cycle Test

Cont. Mold Line Lip (CMLL) 

Sys Req. 

CMLL feasibility CMLL Bench Test

Figure 7.4 Key Milestones from the Roadmaps
92

8.0 Conclusions

The objectives of this study were to define and evaluate integrated configuration and propulsion concepts 

for supersonic aircraft entering service in the 2030-2035 timeframe, to identify and prioritize key 

technologies to enable such aircraft, and to develop corresponding technology development roadmaps. A 

study was conducted to determine potential market and regulatory conditions in the time frame of interest, 

and those results were used to determine the design requirements and performance and environmental goals 

for the study aircraft. A separate contract with Sensis provided involvement, input to and requirements 

from their studies for the NextGen airspace system. Using the design requirements thus determined, 

configurations and technologies were identified early in the program to set the vehicle categories and top 

level technology areas for study. This was done in a group setting with all program participants 

contributing to the results. 

Following the initial configuration and technology identification exercise—each engine company and the 

airframe team members proceeded to develop: (1) a more detailed set of appropriate vehicle concepts, (2) 

representative engine architectures, and (3) a detailed set of technologies that would be applicable to these

vehicle configurations and engine architectures. Trade studies were conducted using size-optimized 

vehicle mission performance to identify the primary candidates in all areas. 

Conceptual design studies resulted in the recommendation of a fixed wing configuration with V-tails and 

upper surface engines as the technology reference concept plane for N+3. This vehicle, Boeing model 

number 765-107B, was nicknamed ―Icon-II‖. Sizing and mission analysis of the Icon-II concept showed 

that if the constituent enabling technologies achieved their projected levels, similar aircraft should have the 

potential to meet or exceed all the N+3 goals set out at the beginning of the study. 

As shown in Figure 8.1, near-term technological progress should enable technically viable SuperSonic 

Business Jets (SSBJ‘s) with a reasonable degree of sonic boom reduction within the next decade (N+1). 

With roughly another ten years of development, progress should be sufficient to allow a type of relatively 

fuel-efficient supersonic airliner of roughly 100 seats or a low-boom airliner of somewhat smaller size (at 

some fuel efficiency penalty). The Boeing models -072B and -076E, respectively, represented concept 

planes for each of those categories in the previous N+2 study. The N+3 studies have identified a path 

whereby an aircraft like the Icon-II would have the potential to provide 100 or more passengers in capacity, 

increased range, lower boom, reduced takeoff noise, and significantly increased fuel efficiency by the N+3 

time frame.

The Icon-II concept plane is configured to carry 120 passengers in a two class, single aisle interior, cruise 

at Mach 1.6-1.8 with a range of about 5000 nmi. At design range, the concept showed a fuel efficiency of 

more than 4.5 seat-nautical-miles/pound of block fuel. Recent advances in low-boom shaping technology 

indicate that a configuration with the design features of Icon-II is projected to achieve a sonic boom 

environmental goal level of 65-75 PLdB, airport/community noise levels potentially quieter than 30 

EPNdB cumulative below Stage III/Chapter 3, and attain cruise NOx emissions of EI= 5g/kg. 

To achieve these performance levels, the highlights of the technologies incorporated in the vehicle concept 

are:

 Improved metallic and composite materials and structural concepts (including improved ballistic 

protection for airplane systems and structure for engine disk burst, rim release,and FOD), 

reliability based design, active load alleviation and active aeroelastic (APSE) control

 Aerodynamic devices including hybrid laminar flow, riblets, morphing leading and trailing edges 

and selective use of active flow control

 Noise-shielded upper surface nacelles, employing advanced liners and duct treatments, and 

potentially low-impact/low NPR suppressor nozzles, 

 Optimized low sonic-boom design coupled with multi-point drag optimization and configuration 

refinement based on improved Multi-Disciplinary Optimization (MDO) 
93

 Advanced light weight, high energy efficient airplane systems including electronic forward 

external vision systems, automated CG monitoring/control, and thermal management

 Advanced light weight bleedless inlets with compact light-weight diffusers, high distortion 

tolerance, and variable area nozzles with low jet velocities and a duct integrated burners 

 Adaptive fans and other variable cycle engine features, low emission pressure rise combustors, 

high OPR compressors, and turbines with advanced materials/ advanced cooling

A prioritized list of engine and airframe technologies has been determined using mission performance 

based trade factors. The top 34 airframe technologies, broad engine technologies and a 5 year milestone 

summary for all technical areas is included in Section 7 of this report. Because of the competitive nature of 

the roadmaps, details of the roadmaps are contained in a series of Proprietary Appendices to this nonproprietary document. 

Figure 8.1 Supersonic Technology Horizons.

0

50

100

150

2010 2020 2030 2040 Year Airplane Size (seats)

“N+1” “N+2” “N+3”

765-072B

Min. fuel burn

100+passengers

(boom < Concorde)

765-107B “Icon-II”

N+3 BASELINE

Low fuel burn & low boom

765-076E

N+2 Low boom 

Low boom SSBJ Technology Baseline

0

50

100

150

2010 2020 2030 2040 Year Airplane Size (seats)

“N+1” “N+2” “N+3”

765-072B

Min. fuel burn

100+passengers

(boom < Concorde)

765-107B “Icon-II”

N+3 BASELINE

Low fuel burn & low boom

765-076E

N+2 Low boom 

Low boom SSBJ Technology Baseline
94

Appendix A: Boeing Engine Summary Results and Airframe Roadmaps

(NOT INCLUDED)
95

Appendix B: General Electric Engine Development and Roadmaps

(NOT INCLUDED)
96

Appendix C: Pratt & Whitney Engine Development and Roadmaps

(NOT INCLUDED)
97

Appendix D: Rolls-Royce Engine Development and Roadmaps

(NOT INCLUDED)
98

Appendix E: Achievable Sonic Boom Levels Through Continued Configuration Studies (Wyle Labs) 

NASA has introduced a set of supersonic technology goals (Figure E.1). In order to achieve these goals, a 

set of design and analysis tools must be developed and refined and integrated into an effective integrated 

state of the art knowledge base: Sonic Boom minimization Technology. At present, various elements of the 

design, integration, optimization and analysis toolset have been prepared, but significant work remains to 

bring the technology to a readiness level suitable for serious design consideration. The remaining sections 

of this chapter will discuss the current state of the art in sonic boom tools, an application of the 

optimization technology (conducted under the current contract) to a realistic supersonic transport 

configuration, and a discussion of the various elements of the sonic boom technology roadmap. Where 

possible the nomenclature used in the Sonic Boom Technology Roadmap (long term schedule and short 

term schedule and costs) are referenced in bold italics.

Figure E.1 – NASA Supersonic Vehicle Goals

State of the Art, 2010 and Future Technology Needs

Sonic Boom Prediction

Considerable resources have been applied to the refinement of sonic boom prediction methodologies. One 

such model whose development has been funded in a large part by NASA is the PCBOOM propagation 

model11. PCBoom is a full ray trace sonic boom program that calculates sonic boom footprints and 

signatures from flight vehicles performing arbitrary maneuvers. It computes detailed ground signature 

shapes starting from a variety of near-field signature definitions. PCBoom has its roots in the NASA sonic 

boom program written by Thomas12 in the early 1970s. Initial development consisted of adding focus 

 

11 Page, J.A., Plotkin, K.J., and Wilmer, C.W., ―PCBoom Version 6 Technical Reference and User 

Manual‖, Wyle Research Report WR 09-20, August 2009.

12 Thomas, C.L., "Extrapolation of Sonic Boom Pressure Signatures by the Waveform Parameter Method," 

NASA TN D-6832, June 1972.
99

boom prediction capability13. Further development, through a series of versions,14,15,16 extended the 

original code (which computed boom on a single ray for a single flight condition) to handle full maneuvers 

and a variety of aircraft source inputs. There have been improvements to the algorithms, such that boom 

aging is now handled by waveform steepening and shock fitting,17 rather than Thomas's waveform 

parameter method.18 Three dimensional ray tracing algorithms19 have replaced Thomas's original flat earth 

layered ray equations, although Thomas's original ray equations are present as an option and much of the 

logical flow is retained.

PCBoom6 has the following capabilities:

 Specification of the vehicle as an F-function, a data line of Δp/p, via data from a CFD solution, as 

a simple form from a library of aircraft, or as a blunt hypersonic body. There is a launch vehicle 

mode, which includes the effect of the vehicle itself plus the effect of an underexpanded rocket 

plume.

 Matching of CFD solution inputs to mid-field via an Euler full potential code.20

 Ray tracing through a 3-D stratified atmosphere over either flat earth or over a WGS-84 ellipsoidal 

earth.

 Specification of arbitrary maneuvers in either local Cartesian coordinates or in geographic latitude 

and longitude.

 Calculation of superboom signatures at focal zones, and also the secondary post-boom signatures a 

distance away from the geometric focus.

 Calculation of boom along particular rays, or on rays across the full width of the boom carpet.

 Calculation of shock structures, either as a simple Taylor structure or via molecular relaxation 

absorption processes.

 Calculation of spectra and a variety of loudness metrics for ground booms.

 Calculation of the effect of finite ground impedance on boom signatures.

 Effects of wind and terrain on boom propagation.

There still remain areas where further research is required. In the Sonic Boom Technology Roadmap these 

are referred to as Analysis Tools. These Analysis Tools are further refined in the near term roadmap as 

Sonic Boom Propagation Tools whose elements are explained in more detail in the following paragraphs.

Focusing – This area requires detailed investigation of the nature of sonic boom focusing for low-boom 

aircraft and to assess and improve the adequacy of methods to model focused sonic boom waveforms under 

realistic conditions. To date, analysis of focusing from candidate low boom aircraft has been limited and 

has not adequately accounted for the complexity of their F-functions including off-design F-functions. A 

NASA NRA program has been established to investigate sonic boom focusing analytically and 

experimentally and to assess the suitability of current modeling techniques and physical understanding for 

focused sonic boom signature prediction.

 

13 Plotkin, K.J., and Cantril, J.M., "Prediction of Sonic Boom at a Focus", Wyle Laboratories Research 

Report WR 75-7, October 1975. Also, AIAA Paper 76-2, January 1976.

14 Plotkin, K.J., ―PCBoom3 Sonic Boom Prediction Model, Version 1.0e‖, Wyle Research Report WR 95-

22E, October 1998.

15 Plotkin, K.J., and Grandi, F., "Computer Models for Sonic Boom Analysis: PCBoom4, CABoom, 

BooMap, CORBoom," Wyle Research Report WR 02-11, June 2002.

16 Plotkin, K.J., Page, J.A., and Haering, E.A. Jr., ―Extension of PCBoom to Over-The-Top Booms, 

Ellipsoidal Earth, and Full 3-D Ray Tracing,‖ AIAA 2007-3677, May 2007.

17 Middleton, W.D., and Carlson, H.W., "A Numerical Method for Calculating Near-Field Sonic-Boom 

Pressure Signatures," NASA TN D-3082, November 1965.

18 Thomas, C.L., "Extrapolation of Wind-Tunnel Sonic Boom Signatures Without Use of a Whitham FFunction," NASA SP-255, Third Conference on Sonic Boom Research, Schwartz, I.R., (Ed.), October 

1970, pp.205-218.

19 Schulten, J.B.H.M., "Computation of aircraft noise propagation through the atmospheric boundary 

layer," NLR TP 97374, December 1997.

20 Kandil, O.A., Yang, Z., and Bobbitt, P., "Prediction of Sonic Boom Signature Using Euler-Full Potential 

CFD with Grid Adaptation and Shock Fitting," AIAA-2002-2543, June 2002.
100

Weather – A thorough investigation of the effects of weather on sonic booms needs to be explored. 

Current models include the effects of stratified atmospheric temperature, wind and humidity profiles, but 

little validation work has been done investigating the propagation of sonic booms through varied 

atmospheric conditions such as rain and clouds. While methodologies exist for predicting sonic boom 

ground impacts from winds aloft, no comprehensive analysis of the impacts of gross climate features, such 

as the jet stream on both operations and subsequent sonic boom cumulative impacts has been performed. 

Previous NASA studies assessing the impacts of future vehicles on the NextGen concept of operations and 

computation of system wide environmental impacts should be extended to include the cumulative 

environmental impacts of weather features. System wide modeling tools exist today in a suitable form that 

analyses could be accomplished in the short term which account for such items as the impact of seasonal jet 

stream variation and the impact of contrail avoidance trajectory rerouting on CONUS cumulative sonic 

boom impacts. Atmospheric turbulence has been addressed in recent work; however limited empirical 

datasets exist with high fidelity atmospheric turbulence data, with which to validate and assess current 

turbulence modeling. Also a more comprehensive understanding of the impact realistic turbulent 

environments (seasonal, regional, local terrain effects) have on sonic boom signatures is needed.

Over the Top Booms – Propagation tools for prediction of OTT booms have been established.21 

Assessments of OTT sonic booms from Concorde operations have been performed but experimental 

validation datasets including comprehensive weather data are limited.

Terrain – Incorporation of terrain capability in PCBoom includes the effects of ground altitude and 

impedance changes on predicted ground boom signatures. At present there are no benchmark datasets from 

which to compute validation studies of propagation over varying ground impedance and altitude terrain. 

Methodologies for propagation of sonic booms into canyons (natural or urban) from which one would 

expect sound reflections do not currently exist. Consideration of potential regulatory requirements to 

minimize human audibility in areas such as the Grand Canyon National Park could conceivably necessitate 

development of such a propagation model. Anecdotal observations of recent NASA sonic boom testing 

such as the House Vibes experiment22 indicate that reflections of sonic booms off residential homes 

(especially garage doors or other flat surfaces) create sounds that could impact human subjective response. 

Models for predicting reflected or secondary acoustic elements in urban or natural environments do not 

currently exist.

Transmission of Booms Indoors – The potential for acceptable supersonic flight lies in the concept of 

sonic boom minimization through shaping sonic booms, whose shocks (and associated loudness) are lower 

than those of conventional N-waves. The benefit of shaping for direct outdoor listening has been well 

demonstrated in the laboratory, and is fully consistent with mainstream understanding of hearing and 

perceived loudness. The indoor perception of sonic booms is more complex23, with three components:

• The audible and perceptible (felt) indoor boom, which is simply the outdoor boom filtered by the noise 

reduction characteristics of the building

• Tactile motion of the building, which is governed by the structural response characteristics of the structure

• Rattling of the building and of objects inside the building. This is a secondary effect, dependent on both 

building structural response and the nature of items which can potentially rattle.

Current state of the art has identified methods for prediction of the onset of window rattle24,25 but 

significant work remains in the assessment of suitable indoor metrics which are reflective of human 

response.

 

21 Reference to Boeing Zyphrus (?) Code for OTT / Secondary Booms

22 Klos, J. et all, ―Vibroacoustic response of residential housing due to sonic boom exposure: a summary of 

two field tests‖, Noise Con 2008, July 2008.

23 Plotkin, K.J., Sizov, N.V., and Morgenstern, J.M., ―Examination of Sonic Boom Minimization 

Experienced Indoors‖, AIAA Aerospace Sciences Meeting, AIAA 2008-0057, January, 2008.

24 Sizov, N. et all, ―Measured rattle threshold of residential house windows‖, Noise-Con 20078.

25 Sizov, N.V., and Scholl, D.J., ―Wavelet-based detection for rattle of residential house windows‖, InterNoise 2009, August 2009.
101

Threshold Mach – Some of the current designs for supersonic business jet and transport aircraft26 target 

overland slightly supersonic cruise flight at conditions such that the sonic boom will not reach the ground. 

This is known as supersonic flight below Mach Cutoff (typically Mach 1.0 – 1.2). It is a flight speed below 

the speed of sound at the ground, and under certain atmospheric and operational conditions where 

atmospheric refraction due to inherent temperature gradients will cause the sonic boom to curve upwards 

before intersecting the ground, thereby avoiding the creation of a sonic boom. The physical phenomena of 

Threshold Mach has been demonstrated; however the practical application in the NextGen system needs to 

be examined in more detail in order to assess the viability of such a concept. Examination of the benefits of 

dynamic routing on such operations, a realistic assessment of time based weather changes on system wide 

flights as well as a more detailed experimental benchmark dataset from which to validate the 3D ray tracing 

and prediction of Threshold Mach is needed.

Euler Full Potential Mid-Zone Method

In order to more accurately predict the aerodynamic field surrounding the vehicle and obtain a better 

representation of the sonic boom source function, it is customary to utilize Computational Fluid Dynamics, 

such as an Euler solver. While this often improves the order of the sonic boom modeling (from simple 

linearized volume and lift to incorporation of higher order acoustic sources such as multipoles), it comes 

with a significant computational cost. Today‘s CFD codes principally consider uniform atmospheric 

environment and are valid locally in the vicinity of the aircraft. A propagation model such as PCBoom is 

required to compute the effects of propagation of the vehicle signature through a varying atmosphere. 

When working with CFD flowfield solutions, the critical issue is coupling the highly detailed numeric near 

field into locally axisymmetric ray tracing. In the past, Ting and Darden's MMOC27 and Page and Plotkin‘s 

multipole method28,

29 provided partial solutions. These are basically one or two zone methods, with two 

zone methods generally having an interface to ray tracing. MMOC was a two zone method where near 

field CFD was coupled to Method of Characteristics propagation. Plotkin30 outlined a possible three-zone 

method, with full CFD interfacing to a second order CFD-like region and then to ray tracing.

An alternate technique to the multipole method which has been incorporated into PCBoom, employs a 3D 

Euler-Full Potential (EFP) code developed by Eagle Aeronautics and Old Dominion University.31 This is a 

computationally accurate method for bridging the gap between CFD acoustic near-field predictions and 

linearized far-field acoustic propagation. It propagates signatures from CFD near-field to the far-field 

based on the full-potential equation with a grid adaptive shock fitting scheme. The EFP method extracts 

flowfield data from a CFD solution for either structured or unstructured CFD codes and propagates it to the 

acoustic far-field where a pressure cylinder is extracted and provided to PCBoom for continued 

propagation to the ground using geometrical acoustics. 

Far-field CFD for Sonic Boom – To date very limited flight measurement data and corresponding CFD 

predictions are available for validation of the near-field CFD32, the mid-field EFP propagation and 

 

26 Rachami, J., and Page, J., ―Sonic Boom Modeling of Advanced Supersonic Business Jets in NextGen‖, 

48th Annual AIAA Aerospace Sciences Meeting, AIAA 2010-1385, January 2010.

27 Darden, C.M., ―An Analysis of Shock Coalescence Including Three-Dimensional Effects With 

Application to Sonic Boom Extrapolation,‖ NASA Technical Paper 2214, 1984.

28 Page, J.A., and Plotkin, K.J., ―An Efficient Method for Incorporating Computational Fluid Dynamics 

Into Sonic Boom Prediction‖, AIAA-91-3275, Sept. 1991.

29 Plotkin, K.J., and Page, J.A., ―Extrapolation of Sonic Boom Signatures from CFD Solutions,‖ AIAA2002-9022, January 2002.

30 Plotkin, K.J., ―Theoretical Basis for Finite Difference Extrapolation of Sonic Boom Signatures,‖ 1995 

NASA High-Speed Research Program Sonic Boom Workshop, NASA Conference Publication 3335, edited 

by D.G. Baize, July 1996.

31 Kandil, O.A., Yang, Z., and Bobbitt, P., "Prediction of Sonic Boom Signature Using Euler-Full Potential 

CFD with Grid Adaptation and Shock Fitting," AIAA-2002-2542, June 2002.

32 Haering, E.A., et all, ―Airborne Shaped Sonic Boom Demonstration Pressure Measurements with 

Computational Fluid Dynamics Comparisons‖, 43rd AIAA Aerospaces Sciences Meeting, AIAA 2005-

0009, January 2005.
102

ultimately the far-field ground sonic boom signature for shaped low-boom vehicles. Some wind tunnel 

measurements and corresponding CFD predictions have been performed for shaped sonic boom vehicles.33 

Further refinement of the CFD prediction models and gridding algorithms need to be investigated in order 

to improve the off-body CFD prediction capability, improve modeling fidelity, avoid numerical dispersion 

of shocks and improve computational efficiency.

Low Boom Optimization – Goals and Targets

Boom Optimization Tool

The key concept to minimizing sonic boom is vehicle shaping, such that the boom at the ground is a midfield shape that has not yet evolved into a far field N-wave.34

 George and Seebass35,36 showed that an 

optimal low boom F-function is that shown in Figure E.2. The signature begins with a delta function, 

which Jones37 had shown is the optimal for arbitrarily far N-waves. Since one is looking for a mid-field 

signature, some of the energy from the delta can be "hidden" behind it, in a region with slope gentle enough 

that it does not steepen into a shock. The F-function is defined by five or six constants, defined in the 

equation at the top of the figure. The equivalent area is algebraically related to the F-function, and is 

defined by the equation at the bottom of Figure E.2. 

Figure E.2 – George-Seebass minimum boom solution, including front and rear shocks

The F-function in Figure E.2 will, at its design point, yield a ground signature that falls into a family 

illustrated in Figure E.3. George and Seebass showed that, for a given weight and length, this model 

yielded the optimal lowest shock strength. They also established the minimum length needed to obtain a 

shockless boom.

 

33 Graham, D.H., et all, ―Wind Tunnel Validation of Shaped Sonic Boom Demonstration Aircraft Design‖, 

43rd AIAA Aerospace Sciences Meeting, AIAA 2005-0007, January 2005.

34 McLean. F.E., "Some Nonasymptotic Effects on the Sonic Boom of Large Airplanes," NASA TN D2877 (1965)

35 George. A.R., and Seebass, R, "Sonic Boom Minimization Including Both Front and Rear Shocks", 

AIAA Journal 9 (1971) 2091-2093.

36 Seebass. A.R, and George, A.R, "Design and Operation of Aircraft to Minimize Their Sonic Boom," 

J.Aircraft, 11 (9), 509-517, September 1974.

37 Jones, L.B., "Lower Bounds for Sonic Bangs", Journal of the Royal Aeronautical Society 65 (1961) 1-4
103

Figure E.3. Family of booms in George-Seebass optimal model

There are two limitations to George and Seebass's theory. The first is that it is ideal, with the vehicle 

geometry restricted to shapes defined by the equation at the bottom of Figure E.2. The second is that it is 

written only for the total boom, the sum of volume and equivalent lift volume, under the aircraft. Sonic 

boom is three dimensional, with boom off-track being just as important as on-track, and for a given 

configuration the mix of volume and lift will change with off-track azimuth angle.

These limitations are relaxed in the Generalized George-Seebass (GENGS) model developed by Wyle.42,41 

There are two generalizations. The first is to define the F-function as an arbitrary number of segments, as 

sketched in Figure E.4. The equation at the top of E. 2 then becomes

     



   

n

i

i i i F y B y C H y

1

 1

(1)

where Bi, Ci and λi are segment-by-segment generalizations of the original single parameters and H is the 

Heaviside step function. The nose delta is not a separate element, but is defined by a pair of segments 

forming a triangle. Equation (1) is not ideal, but allows for realistic requirements such as engines and 

empennage. Its deviation from ideal can be quantified by comparison with the original form. The 

equivalent area is then

      



   

n

i

e i i i i A x B I x x l C I x x l

1

3 1 2 1 4 ; , ; ,

(2)

where I2 and I3 are closed form algebraic expressions similar to the elements in the equation at the bottom 

of Figure E.2.

Figure E.4. Generalized multi-segment F-function
104

The second extension is to allow azimuthal variation. A true three dimensional F-function can be 

decomposed into distributions of multipoles.38 This is a logical extension of Walkden's original lifting 

body theory39 which represented the F-function as volume (monopole) and lift (dipole) components. 

Equation (1) is further generalized to

       









  

k

i

in

n

in in F y n B y C H y

1

1

0

, cos  

(3)

where the decomposition is both in longitudinal segments i and azimuthal harmonic order n, There are now 

many more components to solve for, but there are also many more constraints since minimum shock 

strength is sought off track as well as on track.

This generalized method has been implemented in graphical interactive version used for manual steering of 

optimization, Figure E.5, and a batch version suitable for use in an automated optimization system.

Figure E.5. Graphical manually steered generalized George-Seebass model (GENGS)

Application of the Manually Steered Optimization Analysis 

The 3D Generalized George-Seebass analysis methodology described in the previous section was 

developed for NASA under a separate NRA effort and leveraged in this study. GENGS serves as a 

constraint based on the physical reality of the optimum George-Seebass solution. The GENGS 

methodology was executed using manual steering to obtain a target low-boom concept F-function and 

associated ground sonic boom metrics. This process was applied in order to demonstrate application of the 

Low-Boom Technology Optimization and better understand its role in low-boom configuration 

development and provide deeper insight in order to effectively develop the low-boom technology roadmap.

Vehicle sonic boom characteristics for the configuration -2A vehicle (Figure E.6) was provided to Wyle by 

Boeing in the form of an Excel file containing undertrack centerline lift and volume distributions (Figure 

 

38 George, A.R., "Reduction of Sonic Boom by Azimuthal Redistribution of Overpressure", AIAA Journal, 

7, 2, February 1969.

39 Walkden, F., "The Shock Pattern of a Wing-Body Combination, Far From the Flight Path", Aeronautical 

Quarterly, IX (2), 164-194, 1958.
105

E.7) predicted by linear aerodynamic analyses. This vehicle starting point is not an optimized low-boom 

vehicle; however it is reflective of a closed and sized configuration and is the result of incorporation of 

boom reduction concepts, such as slender airframe, highly swept swing wings, integrated nacelles and aft 

deck, into the configuration. The source characteristics include airframe features such as tails and nacelles 

are lumped in with the appropriate lift and volume pieces.

Figure E.6 –Configuration -2A40

Figure E.7 – Configuration – 2A Sonic Boom Linearized Aero (Lift and Volume) Source Description

The optimization process was developed to provide suggested source target improvements including higher 

order poles as would be present in a CFD solution. For this analysis we did not have CFD results available, 

so a starting cylinder was created analytically from the linearized undertrack data. The data was 

manipulated by using a Cosine(azimuth) function to estimate the lift component at other roll angles (Figure 

E.8). The lift and volume were summed and converted to an F-function for all roll angles in 1 degree 

increments. The F-function was scaled back to dP/P and a complete pressure cylinder was created.

 

40 A description of the -2A vehicle is provided in Section 6.2
106

Figure E.8 – Starting pressure cylinder

The original provided pressure distribution (dP/P) is based on a radius of 1000 Ft. This is too large for the 

GENGS Cylinder optimization process because much of the initial aging (where there are a lot of dramatic 

changes) are not included in a 1000 Ft radius cylinder, and hence lost. Since our starting point contains 

only the n=0 and n=1 multipole terms, reducing the cylinder radius did not require a full multipole analysis. 

The sonic boom source description was reworked so that the dP/P is representative of a cylinder with radius 

of one-half body length. In the case of the -2A vehicle, this is 121 Ft. The scaling from F-fcn to dP/P is 

provided in Equation 4.

R

M





2

2

(4)

where 

 1.4

and 

1

2

  M  and 

R 121ft

The GENGS optimization process is designed to start with a CFD solution with the axial coordinate origin 

located at the noise of the aircraft. So the first axial coordinate of the initial pressure rise (nose cone) in the 

Cylinder file was adjusted aft along the Mach angle representing the undertrack intersection of the nose 

shock with the cylinder at the 0.5 R/L radius.

The strength of the starting multipoles present in the cylinder may be computed using the GENGS 

preprocessor program Poles. The order 0 (volume) and 1 (lift) multipoles are provided in Figure E.9 for the 

configuration -2A concept vehicle for the undertrack azimuth. The black lines indicate the numerical 

multipole fit to the source dP/P data while the red lines are the approximated finite number of multipole 

segments used for the starting point in the optimization process.

F-Fcn-Lift as f(phi)

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

0.0000 50.0000 100.0000 150.0000 200.0000 250.0000 300.0000 350.0000 400.0000

X FFL

0

15

30

45

60

75

90

105

120

135

150

165

180
107

Figure E.9 – Configuration -2A multipoles of order 0 (volume) and 1 (lift)

With the starting configuration defined, the interactive (human steered) process of undertrack optimization 

can begin. This analysis leveraged a recently completed Wyle NASA NRA41,42 entitled ―Low Boom 

Supersonic Vehicle Shaping Tools‖ under NASA Task Order No. NNL08AA27T. This technology is 

outlined earlier in this section. The manually steered optimization allows one to interactively edit the 

source multipole distribution and visualize the ground signature and loudness. For this process the 

signature aging characteristics were created based on flight at Mach 1.8 at 51,000 Ft through the US 

Standard atmosphere using PCBoom43. 

The manually steered optimization process concentrated only on the undertrack signature and relied on the 

introduction of higher order multipoles to achieve reduced ground booms. Figure E.10 documents the 

starting source F-function parameters (top left quadrant) the starting source F-function (bottom left 

quadrant), the ground boom signature parameters (top right quadrant) and ground boom signature (bottom 

left quadrant). This is based on the finite number of segments fit to the n=0 and n=1 order poles. For this 

source F-function, the maximum shock is at the rear of the aircraft of magnitude 1psf and is driving the 

loudness level to 90.69 PLdB. Optimization will therefore attempt to better shape the aft segment of the Ffunction and reduce the rear shock by introducing higher order multipoles (order n=2, quadrupoles). 

Examination of CFD solutions for slender supersonic configurations suggested that quadrupoles contain 

initially a negative pulse followed by a positive and a second negative pulse. 

 

41 Plotkin, K. J., ―Sonic Boom Shaping in Three Dimensions‖, 15th AIAA / CEAS Aeroacoustics

Conference, AIAA 2009-3387, May 2009.

42 Plotkin, K. J., ―Low Boom Supersonic Vehicle Shaping Tools, Including Three-Dimensional Effects‖, 

Wyle Research Report WR 09-15, June 2009.

43 Page, J.A., Plotkin, K.J., and Wilmer, C.W., ―PCBoom Version 6 Technical Reference and User 

Manual‖, Wyle Research Report WR 09-20, August 2009.

Approximate with a Finite Number 

of Multipole Segments
108

Figure E.10 – Starting -2A Source and Ground Boom Signature and Loudness 

After several interactive iterations, it was determined that introduction of the quadropole terms shown in 

Figure E.11 (top left inset) created a multi-step aft shock. Further refinement of the multipole source 

distribution (Figure E.12) eventually yielded a target F-function which obtained balanced front and rear 

maximum shock strengths (approximately 0.5 psf) and resulted in a reduced loudness level of 84.9 dB, a 

reduction of almost 6dB from the starting point. An illustration of the undertrack signature evolution as it 

advances and ages through the atmosphere is provided in Figure E.13. Evident is the evolution of the 

higher order multipoles into an aft ―sawtooth‖ like signature, reminiscent of the quiet spike technology 

responsible for significant reduction of sonic boom levels from the front half of the ground boom signature.

Figure E.11 – Intermediate -2A Source and Ground Boom Signature and Loudness
109

Figure E.12 - Final -2A Manually Steered Source and Ground Boom Signature and Loudness

Figure E.13 – Final Manually Steered and Optimized Configuration Propagation History

An integral part of the optimization process is retention of the key configuration characteristics such as 

weight and length. The length of the vehicle is represented by the F-function length and preserving this 

value retains the original configuration length. Weight is represented by the integration of the lift from the 

vehicle and is manifest by the integral of the axial lift term from the n=1 multipole. Since the n=0 and n=1 

multipoles were essentially preserved during this manually steered optimization process, these key 

configuration characteristics were retained. 

P(t) at 51kFt

P(t) at 50kFt

P(t) at 40kFt

P(t) at Ground
110

Higher order multipoles beyond n=2 were not exploited in this analysis. Potential improvements to the 

azimuthal redistribution of boom might be found by introducing additional terms. The software suite 

provides for this analysis using optimizer steering – a task unsuitable for ―human‖ (manual) steering. A 

parametric investigation of sonic boom target shaping with automated optimizer steering could help to 

better understand the potential improvements such poles will provide, specifically when considering boom 

signature across the entire carpet and not just undertrack. Development of the knowledge base for potential 

higher order multipole benefits as well as an understanding of the applicability across configuration types 

(smaller business jets, larger transports, symmetric and asymmetric configurations and vehicles with nonplanar lifting surfaces such as joined wings) is required to advance the technology readiness level of the 

sonic boom optimization target development. 

Preferred objective functions and targets – is how the sonic boom source optimization technology is 

referred to in the sonic boom technology roadmap. The current optimization methodologies employed in 

this study explained in the previous section, focused on perceived loudness (PLdB) as the metric of choice. 

However at present, the regulatory framework for future commercial supersonic flight remains undefined. 

Considerations of cumulative sonic boom impacts and possible indoor and outdoor listening environments 

have the potential to introduce additional metrics into the optimization process. The proper balance 

between objective functions and targets when considering ground boom metrics must be explored further. 

Survey Potential Objective Function Parameters – When exploring GENGS optimization using automated 

rather than manually steered optimization, a series of objective function parameter boundaries must be 

defined. A systematic investigation of these functions for various classes of supersonic low-boom aircraft 

should be performed. It is conceivable that different sets of objective functions are more effective for 

smaller vehicles such as business jets than for larger transport aircraft. Also conventional symmetric 

slender wing-body aircraft will require different optimization guidance than novel concepts such as oblique 

wing or joined wing low-boom aircraft. 

An expansion of the GENGS optimization concept to other flight altitudes (such as cruise-climb profiles), 

to other Mach numbers (such as would be encountered for lower range missions) and the incorporation of 

flight over different terrain conditions (mountains, over water flight etc...) is needed. Expansion of the 

optimization from a single operating condition across the carpet width, to a full mission based optimization 

and ultimately a system-wide optimum will be needed in order to guide the detailed design process. 

Expansion of the optimization technology will be required before any significant low-boom design 

investment will be made.

Integrate tools to define targets – At present the link between the configuration parameters and the 

GENGS optimization targets does not exist. There is a distinct decoupling of the vehicle surfaces and the 

off-body target pressure distribution. The first step is to integrate the existing design suite of tools with the 

optimization targets so that achievable and reasonable configuration changes are driving the optimization 

process, not just the intermediate pressure or F-function distribution. The configuration shape responsible 

for yielding an aerodynamic pressure solution with the optimized and desired higher order poles is not 

defined by this process. Additional configuration shaping design work is required to determine the changes 

required in the lifting surfaces which will yield the desired non-linear effects. The development of 

multidisciplinary design optimization toolsets which will permit rapid design of alternate configurations 

which can produce these desired higher order multipole signatures is a one of the technology areas 

requiring additional investment. 

Configuration and Target Links Understood – With the integrated configuration – optimization target tool 

developed, systematic configuration perturbations can be explored in order to better understand the full 

three-dimensional higher order impact configuration changes have on the higher order multipoles from the 

sonic boom perspective. An examination of these relationships will lead to potential rapid prototyping 

improvements in the design methodology and more robust vehicle designs.
111

Appendix F: Boeing Airframe Technology Roadmaps

(NOT INCLUDED)
112

Appendix G: Aeroelastic Analysis Report (M4 Engineering)

G.1 Introduction 

The SOW between Boeing and NASA contains the following description in Task 3.6: ―The contractor shall 

conduct detailed studies on the most promising technologies and technology combinations determined in task 

3.5. ... The contractor shall ... use a higher order level of analysis tools to ensure benefit and penalty trends are 

not a function of tool fidelity.‖ M4 is supporting this effort by extending the trade study process with detailed 

analysis using higher fidelity structural models. The approach taken is to perform multiple aeroelastic analyses 

including FEM based weight prediction to quantify effect on weight of technologies and configuration 

parameters. This work is based on Boeing‘s N+2 FEM with updates for the N+3 effort. This model is for the 

765-076E configuration described in reference 1 and shown in Figure G.0.1.

Figure G.0.1: 765-076E general arrangement [2]. This figure depicts the vehicle planform with an initial 

structural layout. The structural layout was revised for use in the analyses in this effort.
113

G.1.1 Performance Summary

Based on the aeroelastic FEM received from Boeing, the baseline FEM for this study has been developed. This 

work is described here:

Task 1: Establish Sensitivity of Vehicle Weight to Active Flutter Suppression Technology

 Completed

o Strength analysis

 Received strength sized FEM from Boeing

 Define regions not included in global sizing (Detail design of local reinforcements 

not addressed in this effort)

o Flutter analysis

 Flutter analysis of strength sized vehicle

 Add local panel stiffness to remove local modes

o Optimization setup

 Definition of design regions for use in trade studies

 Definition of minimum gage

o Structural sizing with flutter constraints to quantify effect of flutter suppression technology

Task 2: Establish Sensitivity of Vehicle Weight to Material Property Technologies

 Completed

o Material trade study for four materials with and without flutter constraints

G.1.2 Issues/Concerns

No reportable technical issues exist at this time.

G.2 Strength Analysis

G.2.1 Assumptions

The following assumptions are made in the N+3 strength analysis:

 Basic load set of 8 cases

 Linear aerodynamics and linear structure

 Minimum gauge thickness of 0.040‖

 Local reinforcements not addressed in this effort

 270 property regions grouped in the eighteen portions of the structure shown in Figure G.0.2 through 

Figure G.0.10

a) b)

Figure G.0.2: (a) Fuselage Spine, (b) Fuselage Skin
114

a) b)

Figure G.0.3: (a) Floor, (b) Bulkheads

a) b)

Figure G.0.4: (a) Forward Landing Gear Bay, (b) Aft Walls

a) b)

Figure G.0.5: (a) Inboard Wing Upper Skin, (b) Inboard Wing Lower Skin

a) b)

Figure G.0.6: (a) Inboard Wing Ribs, (b) Inboard Wing Spars (Forward Carry-through and Aft)
115

a) b)

Figure G.0.7: (a) Inboard Wing Leading Edge, (b) Mid Wing Upper Skin

a) b)

Figure G.0.8: (a) Mid Wing Lower Skin, (b) Mid Wing Ribs

a) b)

Figure G.0.9: (a) Mid Wing Spars, (b) Fins
116

a) b)

Figure G.0.10: (a) Skin Below Fins, (b) Spars Below Fins

G.2.2 Load Conditions

The load conditions used in this study were developed by Boeing [3]. These include both symmetric and antisymmetric maneuvers as well as landing, a lateral ground maneuver and a simple gust condition. The load 

conditions (Limit loads) are:

 +2.5/-1.0G subsonic

 +1.2/-0.0G supersonic

 25°/sec roll subsonic

 Landing

 0.5G lateral ground maneuver

 1.5G pitch-up supersonic 

The strength requirement enforced is:

 No material yielding at limit load

G.2.3 Material Properties

Materials considered in the material trade study include a conventional Aluminum, an Advanced Titanium, as 

well as baseline and improved Graphite Epoxy materials. The properties used for these materials are shown in 

Table G.0.1.

Table G.0.1: Material properties used in N+3 material trade study.

Al Ti Baseline Comp Improved Comp

2024-T62 5AI-5V-5Mo-3Cr 11/11 email 11/11 email

E Msi 10.6 16.0 30.6 39

E (q-iso) Msi 10.6 16.0 11.1 13.9

Ftu ksi 63 56 68

Fty ksi 50 180 37 45

eall (Limit) in/in 0.004717 0.011250 0.003363 0.0032614

rho lb/in^3 0.10 0.16 0.056 0.056
117

G.2.4 Stress Results for Titanium Configuration

As discussed in the Interim Report [4] elements in the wing/fuselage joint region with stress greater than 180ksi 

were removed from consideration for the optimization studies. Additionally the minimum gauge thickness was 

set to 0.040‖. To decrease the time the optimization analysis took to run, design regions, as provided by 

Boeing, that resulted in similar optimized thickness were grouped together. This reduced the total number of 

design regions to optimize from 535 to 270. Figure G.0.11 shows the von Mises stress envelope of the eight 

load conditions for the strength optimized upper and lower skin (note that the set of elements removed are not 

included in the results).
118

a)

b)

Figure G.0.11: Stress results showing maximum von Mises stress across all load conditions for (a) upper 

skin, and (b) lower skin. (Limit loads)
119

G.3 Flutter Analysis

G.3.1 Assumptions

The following assumptions are made in the N+3 flutter analysis:

 Linear aerodynamics and linear structure

o Character of linear results at transonic conditions were confirmed to be similar to those at 

high subsonic conditions

 Actuator compliance not modeled at control surfaces (preliminary nature of configuration)

 One mass condition considered 

 2 percent structural damping (g) assumed

G.3.2 Flight Conditions

The flight conditions for flutter analysis are derived from the N+2 flight envelope as shown in Figure G.0.12. 

The flutter requirement is:

 No flutter below 1.15 times the dive speed for all Mach numbers in the flight envelope.

Figure G.0.12: N+2 flight envelope [1] with conditions identified as critical for flutter identified in green.

G.3.3 Flutter Results

Based on the results presented in the Interim Report [4] a transonic flutter case and a supersonic flutter case 

were defined to determine the weight penalty to satisfy the flutter constraint.

Transonic (Mach 0.99)

 Velocity (in/sec): 11501.1 11560.5 13033.6

 Q (lb/in^2): 8.5696E-9 3.5600E-8 9.7554E-8

Supersonic (Mach 1.8)
120

 Velocity (in/sec): 20911.1 20911.1 21948.0

 Q (lb/in^2): 6.8557E-9 2.8323E-8 4.5629E-8

The last flight condition listed above represents 1.5 times the dive speed (events highlighted in Figure G.0.14).

Using a conservative flutter constraint of 0% damping for modes 7 through 15, as well as the strength 

constraint, the structure was optimized for each of the eight strength analyses and the two flutter analyses. For 

the Titanium material, the resulting structural weight is 18.5% larger than the strength only optimized structure 

(46,587 lbs).

Flutter analysis results of the strength only sized configuration and the strength and flutter sized configuration 

for Titanium are shown for various Mach numbers in Figure G.0.13 and Figure G.0.14. These results show 

frequency and damping as a function of equivalent airspeed and have vertical lines indicating the dive speed 

and flutter requirement. For each of these analyses, flutter is identified within the flight envelope for the 

strength only sized configuration. This is seen as crossing of 2% damping at speeds below the dive speed. The 

strength and flutter sized configurations show flutter does not occur below the dive speed for these Mach 

numbers. The flutter mode shape for the strength only sized configuration is shown in Figure G.0.15.

While the strength sized metallic configurations exhibited flutter within the flight envelope, the composite 

configurations did not. A comparison of the flutter data for the critical aeroelastic modes is shown in Figure 

G.0.16. It is noted that the composite configuration exhibits higher wind-off frequencies with a similar 

frequency ratio to that of the Titanium configuration.
121

Strength Sized Strength/Flutter Sized

a)

b)

Figure G.0.13: N+3 flutter results for strength sized and strength/flutter sized configurations.
122

Strength Sized Strength/Flutter Sized

c)

d)

Figure G.0.14: N+3 flutter results for strength sized and strength/flutter sized configurations (events specified for optimization highlighted).
123

Figure G.0.15: N+3 flutter results for strength sized configurations (M∞=0.99, V∞=400KEAS).
124

a)

b)

Figure G.0.16: N+3 flutter results for strength sized configurations: a) Titanium, b) baseline 

composite (M∞=0.99).
125

G.4 Optimization Results

The structural weight comparisons for all four materials with and without flutter constraints are shown in 

Table G.0.2. Note that the configurations sized without flutter constraints are representative of an ideal 

flutter suppression system (FSS). Note that while the Titanium material results in the lightest weight for 

the cases with FSS, the composite materials achieve comparable weights when flutter constraints must be 

satisfied by the airframe.

Figure G.0.17 through Figure G.0.20 show the breakdown of the weight of the different portions of the 

structure for each of the materials. The weight of the inboard wing and fuselage skin increases 

significantly to meet the flutter requirement in for both metallic materials.

Table G.0.2: Optimization results for structural weight (lb).

Baseline With FSS

Aluminum 104,956 70,566

Baseline Composite 48,791 48,791

Improved Composite 45,556 45,556

Titanium 46,587 39,305

Figure G.0.17: N+3 Weight Summary for Titanium Material.

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Weight, lbs

Strength Optimized

Strength and Flutter Optimized
126

Figure G.0.18: N+3 Weight Summary for Aluminum Material.

Figure G.0.19: N+3 Weight Summary for Baseline Composite Material.

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Weight, lbs

Strength Optimized

Strength and Flutter Optimized

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Weight, lbs

Strength Optimized

Strength and Flutter Optimized
127

Figure G.0.20: N+3 Weight Summary for Improved Composite Material.

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Weight, lbs

Strength Optimized

Strength and Flutter Optimized
128

G.5. Conclusion

Material trade studies have been performed for the Boeing N+3 configuration. There materials included 

consideration of strength and flutter constraints. The weight savings relative to a conventional Aluminum 

material are shown in Table G.0.3. The following conclusions are made:

1. Strength sized configurations for both metallic materials were found to have flutter within the 

flight envelope.

2. The lightest weight structure is achieved for the Titanium structure in which flutter constraints are 

satisfied by a flutter suppression system. Recent active aeroelastic control research suggests such 

a flutter suppression control law might be achievable [5]. 

3. Sizing results for composite structure show significant weight savings relative to an Aluminum 

configuration. This is especially true for the case in which flutter constraints must be satisfied by 

the structure.

Table G.0.3: Optimization results for structural weight.

Baseline With FSS

Aluminum N/A -33%

Baseline Composite -54% -54% 

Improved Composite -57% -57%

Titanium -56% -63% 
129

G.6 References

1. Boeing, N+2 Supersonic Concept Development and Systems Integration, Version 1.0, July 2009, 

Huntington Beach, CA.

2. Kutzmann, A., General Arrangement 765-076E, Revision A, June 30, 2009, Huntington Beach, CA.

3. Chen, D., ―M4 Engineering Boeing 076E Data‖, CD, 09-21-2009.

4. ―N+3 Aeroelastic Analysis Task 1 Interim Report‖

5. Roughen, K.M., M4 Engineering, NASA S4T - Simultaneous Flutter Suppression, Gust Load 

Alleviation, and Ride Quality Assurance for Supersonic Aircraft at Transonic Conditions, ―Final 

Report‖, September 30, 2009.

6. Baker, M. L. and Lenkey, P. W., ―Parametric Flutter Analysis of the TCA Configuration and 

Recommendation for FFM Design and Scaling‖, Report CRAD-9306-TR-3088.

7. Fogarty, T., and Baker, M. L., ―MSC/NASTRAN Flutter Analysis of TCA with Lateral and 

Directional Control Laws‖, HSR Program memorandum, 6/30/1998.

8. Baker, M.L., Mendoza, R., and Hartwich, P.M., ―Transonic Aeroelastic Analysis of a High Speed 

Transport Wind Tunnel Model‖, presented at AIAA/ASME/ASCE/AHS/ASC Structures, Structural 

Dynamics, and Materials Conference and Exhibit, 40th, St. Louis, MO, AIAA-99-1217, Apr. 12-15, 

1999.

9. Bendiksen, Oddvar O, ―Transonic Flutter and the Nature of the Transonic Dip,‖ CEAS International 

Forum on Aeroelasticity and Structural Dynamics, Madrid, Spain; 5-7 June 2001. pp. 273-286.

10. Bendiksen, Oddvar O, ―Role of Shock Dynamics in Transonic Flutter,‖ AIAA Dynamics Specialists 

Conference, Dallas, TX; Apr. 1992. pp. 401-414.

11. B. Perry, W. Silva, J. Florance, C. Wieseman, A. Pototzky, M. Sanetrik, R. Scott, D. Keller, and S. 

Cole, ―Plans and Status of Wind-Tunnel Testing Employing an Aeroservoelastic Semispan Model,‖ 

48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 

Honolulu, HI, April 2007.

12. Rodden, W.P., Harder, R.L., and Bellinger, E.D., ―Aeroelastic Addition to NASTRAN,‖ NASA CR3094, 1979.

13. Giesing JP, Kalman TP, Rodden WP, ―Subsonic unsteady aerodynamics for general configuration,‖ 

AFFDL-TR-71-5, 1971
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N+3 Advanced Concept Studies for Supersonic Commercial Transport 

Aircraft Entering Service in the 2030-2035 Period 

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NNL08AA16B

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Welge, H. Robert; Bonet, John; Magee, Todd; Tompkins, Daniel; Britt, 

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Barlow, Andrew; Martins, Steve; Viars, Phil; Rasheed, Adam; Kirby, 

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Katherine; Page, Julet; Plotkin, Kenneth J.

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Boeing, with Pratt & Whitney, General Electric, Rolls-Royce, M4 Engineering, Wyle Laboratories and Georgia Institute of Technology, conducted a study of 

supersonic commercial aircraft concepts and enabling technologies for the year 2030-2035 timeframe. The work defined the market and 

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15. SUBJECT TERMS

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