2010_4930 Supersonic Vehicle Systems 2020 - 2035

Supersonic Vehicle Systems for the 2020 to 2035 Timeframe

H. Robert Welge1, Chester Nelson2 and John Bonet3

The Boeing Company

Abstract

Over the preceding 5 years, NASA has engaged industry to revisit the subject of commercial supersonic transports as part of its Fundamental Aeronautics Program in response to emerging environmental goals and perceived progress in some key enabling technologies. These NASA-sponsored studies were centered on years 2020 to 2025 (N+2) and 2030 to 2035 (N+3) technology readiness timeframes. In order to conduct these studies, Boeing built an integrated multidisciplinary team, with a wide cross-section of the industry, to capture a diverse spectrum of ideas and backgrounds. This team developed designs and identified technologies to address the N+2 and N+3 goals. The results concluded that the N+2 supersonic airliner concepts are unlikely to meet both fuel efficiency and sonic boom mitigation goals simultaneously. A 30- to 40-passenger concept aircraft could potentially approach the low-sonic-boom goals, and a 100-passenger (dual class) concept could meet the stated fuel efficiency goals. A preferred N+3 conceptual design (airframe, engine, and technology suite) for the 2035 timeframe was defined. This concept aircraft, called the Icon-II, shows the potential to meet or exceed nearly all the N+3 goals. Supporting technologies (engine and airframe) were defined, grouped into categories, and roadmapped in the long term (TRL 6) and near term (next 2 or 3 years) as a NASA-industry resource for long-term R&D planning in subsequent years.

I. Introduction N the 1990s, NASA and U.S. industry were heavily engaged in developing enabling technologies for a commercially viable second-generation supersonic transport. This class of aircraft, selected as a reference platform for technology development work, was referred to as the High Speed Civil Transport (HSCT). A

large NASA-sponsored component of this effort, called the High Speed Research (HSR) program, provided significant advances in fundamental aerodynamics, materials, structures, propulsion, acoustics, and systems technologies centered on a Mach 2.4, 300-passenger HSCT concept. Along with a number of other aerospace development programs, the HSCT/HSR research effort was discontinued in the late 1990s due to widespread budget cutbacks and new priorities. A reassessment of the extreme challenges in meeting stringent environmental and economic goals showed that it was unlikely for such an HSCT to become a viable commercial product in the foreseeable future, especially given the inability to fund the remaining propulsion and airframe technology development within available NASA and industry resources. It was also felt that some time interval would be needed to understand how such goals were escalating due to worldwide changes in economic trends in the airline industry, and the evolving regulatory regime—especially those related to more stringent noise, emissions, and airworthiness standards.

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1 Project Manager, Boeing Research and Technology, 5301 Bolsa Ave, MC H45-E405,

Huntington Beach CA 92647, AIAA Associate Fellow 2 Boeing Technical Fellow, Boeing Commercial Aircraft Co., P.O. Box 3707, MC OR-MM

Seattle, WA 98124-2207, Non-member 3 Propulsion Manager, Boeing Research and Technology, 5301 Bolsa Ave, MC H45-E408,

Huntington Beach CA 92647, Non member

American Institute of Aeronautics and Astronautics

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28th AIAA Applied Aerodynamics Conference28 June - 1 July 2010, Chicago, Illinois

AIAA 2010-4930

Copyright © 2010 by The Boeing Co. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.

By the year 2000, a worldwide industry consensus developed that the proposed 300-passenger Mach 2.4 HSCT would have been “overkill” for nearly all potential customers and that a smaller, slower, lower cost class of aircraft would be more likely to succeed. In subsequent years, Boeing continued low-level internally funded investigations of various hypothetical future aircraft, including smaller supersonic airliners, and worked to develop methods for reducing sonic booms and integrating airframe and engine concepts to meet more stringent airport noise regulations. Significant conceptual and preliminary design efforts on proposed supersonic business jet concepts were conducted by several companies, and some continue to this day. Boeing carried out several feasibility studies of supersonic business jets as a possible technological and regulatory “stepping stone” to eventual next-generation supersonic airliners. Boeing also, for a time, carried on a serious program to develop a ”Sonic Cruiser” aircraft, designed to fly long ranges efficiently at speeds near Mach 1 using near-term constituent technologies later applied to the 787.

Since 2005, NASA has engaged industry to reassess the future of commercial supersonic flight in light of better understood environmental goals and the need to assess continued progress in key enabling technologies. This new activity over the last several years is the subject of this paper. Industry teams were initially assembled under the banner of “N+2” studies, and later for “N+3” (where, in NASA terminology, these represent studies two and three technology generations beyond aircraft currently serving the commercial fleet). The corresponding timeframes referenced for these studies were chosen by NASA to represent the years 2020-2025 and 2030-2035, respectively. The design goals NASA proposed for these activities are given in Table 1.

Table 1. NASA guidelines for N+ studies.

N+2 N+3 Environmental Goals

Sonic Boom (Linear Theory Goal) 65 to 70 PLdB 65 to 70 PLdB Airport Noise (cum below Stage 3) Stage 3–10 to 20 dB cum Stage 3–20 to 30 dB cum Cruise Emissions (NOx g/kg of fuel) Limited Consideration Cruise EINOx 5 or less

Performance Goals Cruise Mach 1.6 to 2.0 1.3 to 2.0 Range (nmi) 4000 to 6000 4000 to 6000 Payload (passengers) 25 to 100 100-200

In addition to the work described here, other topics studied but not discussed to limit the scope of this paper are (1) structural concepts, aeroelastic control, and material properties using a finite element model (FEM); (2) a limited assessment of atmospheric impacts; and (3) Numerical Propulsion Simulation System (NPSS) coupling with a parametric model of the airframe and the multidisciplinary analysis using this system.

Fuel Efficiency (passenger-miles per pound of fuel) >3.0 3.5 to 4.5

For the studies described in this paper, The Boeing Company was the primary contractor to NASA Langley, with contributions from the following subcontractors:

General Electric Pratt & Whitney Rolls-Royce Liberty Works

Georgia Institute of Technology M4 Engineering Wyle Laboratories

II. Discussion

A. Market Study and Design Requirements The basic payload-range performance of projected supersonic transport aircraft could be easily met with

technologies that are well in hand today if freed from commercial economic considerations (for both operators and manufacturers), environmental standards, and civil aircraft safety and certification requirements. The challenge, then, is to provide the basic mission capability while simultaneously satisfying the same kind of community noise and emissions standards, airworthiness requirements, and market economics considerations as other future aircraft are expected to encounter. In addition, supersonic aircraft will have to satisfy special considerations for supersonic-unique characteristics such as sonic boom and operations at higher altitudes. For these reasons any study of future supersonic technology requirements and identification of feasible aircraft concepts require careful consideration of future airline market scenarios, certification requirements, and environmental compliance.

Several key considerations contributed to the assessment of market-driven future airplane requirements. First is the potential market size and economic benefit provided by such an aircraft. Such aircraft will operate in a global marketplace that depends on the world population demographics and the state of the global economy. Political and economic freedoms, personal and commercial financial resources, and the propensity of individuals and business to


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travel will dictate the supersonic service demand in given market segments. An international aerospace project of the future could face uncertain availability of resources—both raw materials and fuel—and must promise profitability to a variety of stakeholders worldwide under varying scenarios.

The second key consideration is future fuels: their price volatility and availability. The economic viability of any future supersonic aircraft must account for the fact that even fully optimized supersonic aircraft will require larger, more powerful engines (core size) and sturdier structures; have significant “wave drag”; and thermodynamically will have less efficient specific fuel consumption than their equivalent year subsonic cousins.

Along with the commodity price of future fuels and the need for sustained availability, are likely environmental impact related fuel costs that will appear in the form of taxes and/or carbon offsets, or simply the likelihood that sustainable low net-carbon bio-fuels or bio-/synthetic fuel blends are likely to be higher priced. Expected improvements in the fuel efficiency of all classes of future aircraft and the retirement of older less efficient aircraft will be of benefit in reducing the overall impact of aviation fuel use. Due to the unique duty-cycle of aircraft, and their inherent sensitivity to weight and volume, it is generally much easier for cars and other surface transportation to migrate toward some form of electric or electric-hybrid propulsion, fuel cells, natural gas, or hydrogen combustion for primary propulsion. Natural gas and hydrogen are particularly unsuited for supersonic aircraft due to steep weight and volume trades versus performance. For most civil aircraft, and supersonics in particular, a reformulation of gas or coal into synthetic jet fuel or bio-fuel blends seems a much more likely scenario if conventional sources become strained. Hypothetically, a large scale shift of surface transportation away from liquid fossil fuels, could also reduce some of the demand pressure on fossil-based aviation fuels, helping to maintain widespread availability in the coming decades. However, as liquid fossil fuels become a smaller part of the total energy solution, increases in their price will have a reduced inflationary effect on the rest of the economy, which could sustain fuel price increases that represent larger changes in “real dollars”.

Supersonic aircraft will of necessity always be somewhat larger, heavier, more expensive, and need to carry a greater fuel load than their subsonic cousin to achieve equivalent payload-range. Economic viability therefore depends on providing significant value to passengers and airplane operators in terms of time-related savings, while using innovative design and technology to minimize the additional operating costs of the supersonic vehicle. The benefits of significantly shorter flight times to the passenger are fairly obvious and carry a high potential value for those who must travel frequently or those for whom health issues currently discourage long-haul travel. For the operator, such time-related savings can include not only an increased number of trips-per-day asset utilization, but also reduced cost of crew and flight-hour-based maintenance and reduced need for in-flight catering, large galley and lavatory capacity, and extra cabin volume normally required for long-haul subsonic flights. The latter reductions of course have a favorable impact on airplane zero fuel weight, which can help narrow the total operating cost gap with subsonics.

The “march of technology” has generally favored supersonics for eventually reducing the size/cost gap to a favorable increment. For example, most engine and airframe technology advances for subsonics also have applications to supersonic types. A number of additional technologies that heavily benefit supersonics (e.g., higher temperature materials, variable cycle engines, variable inlets) have more limited application to subsonics and have much less impact there. Those two facts, coupled with the strong sensitivity of supersonic aircraft size and performance to technology changes, mean that the slope of improvement of supersonic aircraft over time tends to converge with that of subsonics, asymptotically approaching an offset that provides future economic viability for supersonics, at least in a number of markets. These trends with technology have been noted in the past, but it seems that successive development programs in the 1960s through the 1990s that attempted to accelerate supersonic technology have consistently aimed too far in the future or attempted to push the goals beyond the limits of what can be achieved by a sustainable development effort.

In any event, the economic feasibility of supersonic transportation will require that its mission performance be designed to match market segments where there is sufficient demand and sufficient time-related benefits to counter the incremental supersonic aircraft operating costs over a reasonable range of price uncertainty in future sustainable fuel prices.

The third key category for future requirements consideration is the environment, both in terms of meeting future strict regulations and in terms of public perception and doing the right thing for our planet. Public concerns over NOx, stratospheric water vapor addition, and CO2 emissions will necessitate supersonic transports with improved fuel efficiency relative to those studied in the past, and cruise at lower cruise altitudes (maximum 55,000 ft) to significantly reduce any potential atmospheric impacts. The potential “blanket effect” of persistent contrails has also become a concern for commercial aircraft, though this should not be a factor for supersonic aircraft due to their higher cruise altitudes at which supersonic aircraft will be operating. Airport and community noise will be a


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challenge for all airplanes of the future, more so for supersonic aircraft, which require very high exhaust velocities and lower effective bypass ratio at cruise.

Mounting regulation of noise and emissions could render a noncompliant aircraft obsolete before it flies, so noise and emissions are critical design requirements. Taking an example from the HSCT/HSR program of the 1990s, the goals then were as follows:

� 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 and CO2).

Additionally, if transonic/supersonic flight over land is to be viable, sonic booms must not only avoid adverse environmental impacts to animals, humans, and property, but they also must be reduced in intensity to a level that the vast majority of the over-flown population agrees is not annoying or disruptive. Minimizing sonic boom is an especially tough technical challenge, particularly if the boom loudness of an airliner of significant size and weight (over 150,000-lb cruise weight) is to be reduced to a level acceptable for over-land supersonic cruise. Initially at least, achievable low-boom levels may only allow supersonic over-land flight in designated corridors. Fundamentally, minimizing airframe 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 turbo-machinery noise and improved combustor technology will be essential to meeting the ever-more challenging goals facing an aircraft designed for the N+3 timeframe. 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 of supersonics in the future marketplace.

Matching airplane payload-range requirements to a potentially viable market is very important to the feasibility of any future supersonic aircraft, for without the ability to establish an economic foothold in the market such an aircraft will not be a viable business proposition for either the builders or the operators. While Concorde established a very small and loyal clientele willing to pay several times the normal subsonic first class ticket prices to save hours across the Atlantic, its limited service and very high operating costs do not make it a practical economic model for any future supersonic aircraft. Anecdotically, many Concorde frequent flyers have sought to reduce door-to-door travel time in its absence by moving to long-range business jets and charter aircraft. It is often speculated that once supersonic services are well established and the benefits of significant time savings are “discovered” by more travelers, that additional market demand will be “stimulated” and a natural economy of scale will cause ticket prices to fall. Although this could hypothetically occur, at least initially a future supersonic aircraft will need to ensure economic viability in competition against conventional subsonic premium travel (e.g., international business and first class travelers and portions of the business jet user community) without a significant ticket surcharge such as the first generation supersonic (Concorde and TU144) required.

One indication of the potential size of the initial N+2/N+3 supersonic passenger market can be obtained from Fig. 1. Using qualitative indices that measure a passenger’s willingness to pay versus the schedule and service quality he/she demands, the data show a relatively small but potentially viable 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. In the 2035 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 more passengers normally flying in the full-fare economy and regular business travel price segments.

Data for long-range flights only, plotted in Fig. 2, show that a large amount of premium airline traffic for current city pairs occurs just under 4000 nmi, and a second large group exists between 5000 and 7000 nmi. It will therefore be essential for an N+2 supersonic transport to initially serve this demand for a 4000-nmi(+/-) range, but longer ranges should be an objective as enabling technologies mature in the N+3 (and beyond) timeframe.


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Based on the marketing assessments, environmental considerations, and data from previous studies, a set of

general design, guidelines, and assumptions were initially established internally by Boeing to get the 2020 to 2035 studies started. These are listed below:

� 100 to 150 passengers in two-class arrangement with baseline interior (target 130) � 1.6 to 1.8 Mach cruise speed � 55,000 ft or lower cruise altitude (for emissions)

Air Elite

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• Delta Air Lines affiliate

• 300+ aircraft

GV - Lear Privatair • Lufthansa affiliate

• BBJ scheduled service

• DUS-EWR/ORD

• MUC-EWR

• 50 + aircraft

PrivateOwners

~9%

~9%

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~14%

~19%

Ownership ‘Hybrids’ Total: ~1%

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~20%

~27%

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Programs

Market Gap

Figure 1. Willingness to pay versus schedule (and quality) demanded by customers.

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Figure 2. Number of premium passengers per day versus range.


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� 4000-nmi supersonic range (trans-Atlantic+) with 6000-nmi range target for Asian routes � 0.95 Mach or lower below 39,000 ft for ATC margins � Subsonic below 41,000 ft 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

� Less than Concorde over water � Consider “threshold Mach” over land if very low boom levels cannot be achieved � Consider “boom softening” (e.g., 0.7 lb/ft2) near coastal areas and along over-land corridors if very

low overpressures appear infeasible with a realistic configuration These Boeing internal design guidelines were more focused than those covered by the range of parameters in

NASA’s suggested design N+2/N+3 design goals in Table 1. Using the previous information and the results of the future market assessment study, several conclusions were

drawn to use as guidance for the remainder of the engineering activity associated with the vehicle design. The seat-nmi/lb fuel was used as the primary Figure of Merit (FOM) by which to measure or evaluate the different configurations and to assess the results of the trade studies. The general conclusions are shown in the left side of Table 2. Based on the conclusions shown, the engineering guidelines as listed in the right side of the table were used for the remaining N+2/N+3 vehicle conceptual design work. Table 2. Engineering design guidance based on the marketing study.

B. Air Vehicle Concept Exploration As illustrated in Fig. 3, near-term technological progress should enable viable supersonic business jets (SSBJ)

with a reasonable degree of sonic boom reduction within the near term (N+1). With roughly another 10 years of development (N+2 or 2020 to 2025 timeframe), progress could 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 conceptual design models -072B and -076E (to be discussed later), respectively, represent concept aircraft for each of those categories. The N+3 (2030 to 2035 timeframe) studies have identified a path whereby an aircraft such as the 107B or “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 2030 to 2035 timeframe using the enabling technologies identified.

These representative configuration concepts in Fig. 3 were the result of concept exploration studies conducted in two phases. The first phase focused on the more near term 2020 to 2025 (N+2) entry into service (EIS) date, and the second phase focused on a 10-year later EIS of 2030 to 2035 (N+3). The integrated vehicle projected performance characteristics are therefore offset by the 10-year spread, with the later EIS having improved airplane performance

Marketing Conclusions Engineering Guideline 100 to 150 passengers (in two-class arrangement) baseline interior, target ~130 seats

100 passengers, 130+ with optional seating

1.6 to 1.8 Mach cruise speed and need for alternative operation plan to increase utilization (e.g., subsonic, hybrid ownership)

1.8 Mach design limit

Cruise altitude limited to 55,000 ft (emissions) <= 55,000 ft 4000-nmi min. supersonic range (trans-Atlantic +) 6000-nmi objective to open up Asian routes

4000-nmi minimum range

Cruise Mach <= 0.95 below 39,000 ft for ATC margins. No supersonic speeds below 41,000 ft 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 overland corridors

Balanced 100-seat config in the 80-PLdB class, “low boom” metric aircraft in the 70-PLdB class (eventual goal is 65 to 70 PLdB)

Over-and and low-yield operational solution needed

Technology goals; low boom and good fuel efficiency vs. Mach, possibly “threshold Mach” cruise


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levels but accompanied by a longer development time and a more aggressive technology suite. This paper discusses the nearer term work first (N+2), then the longer term N+3 studies followed by a discussion and comparison of the two to give a broad view of the potential that could be expected for supersonic transport performance in the coming 25 years if the associated technology developments needed to achieve these performance levels are brought to fruition.

The general objective for the studies was to develop a representative commercial supersonic aircraft conceptual design with the potential to overcome the cruise efficiency, weight, durability, and handling/ride qualities challenges while having acceptable airport noise, sonic boom, and high-altitude emissions. The vehicle concepts incorporated a high degree of component integration and a good balance between the practical design requirements and technology. The performance design guidelines were as discussed in the Market Study and Design Requirements portion of this paper (Section II.A).

1. 2020 to 2025 Timeframe Initial N+2 studies used concept aircraft from the High Speed Research/High Speed Commercial Transport

(HSR/HSCT) programs in the 1990s as a point of departure. These aircraft were in the 300-passenger, 750,000-lb class, but the basic configuration development, testing, and research formed a large database from which to begin the work here.

The overall scale of a 100-passenger 2020 airplane falls between the larger HSR/HSCT concept planes and smaller SSBJ concepts as shown in Fig. 4, having no overlap with either. Little direct comparison to previous work will be possible without relying on basic scaling, and a few of the detailed configuration analyses (e.g., addressing aero/propulso/servoelasticity, planform optimization, engine-airframe matching) from the other projects will be directly applicable. As a result, the year 2020 N+2 work necessarily included supplemental investigations and reassessment of areas of risk that might have already been more fully addressed in the other programs.

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Figure 3. Supersonic technology horizons.


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The first steps in the N+2 work began with a first order analysis to scope the performance potential of a notional efficient Concorde-sized vehicle, carrying 50 first class or 100 dual class passengers with the objective of significantly improving the seat-mile fuel burn and emissions over first generation SST’s. A representative engine concept was selected from a matrix of available in-house study engines, installing them on scaled versions of two of the best final HSR configurations at constant wing loading and thrust loading. A preliminary configuration was assembled from promising features and sized. A 30- to 40-passenger candidate alternate concept was also developed, starting with existing internal and NASA trade-study results, to provide a configuration that could potentially achieve significantly lower sonic boom levels. Both the large and small configurations were developed further using a combination of interactive and automated design methods.

Studies of larger aircraft began with two examples derived from concept aircraft of the NASA HSR/HSCT Program. One was the 765-070A based on a scaled 1080-2015 configuration, or “2015-TC.” The other was the 765-071B based on the 1080-2154 configuration, or “2154 HISCAT,” which promised lower noise, lower transonic drag and increased structural stiffness near the engines. These vehicles are illustrated in the upper left portion of Fig. 5.

Figure 4. Size and weight of 100-passenger N+2 studies compared to other supersonic airplane studies.

76% 2015TC 765-070

76% 2154 HISCAT 765-071

HSCT/HSR N+2Airframe &

Engine Sizing

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The 765-072BChosen as Best

“Green” Supersonic Airliner

Figure 5. Development of the N+2 study concept starting from the HSR database.


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Performance sizing for the 765-070A and 765-071B was completed to set thrust and wing area for Mach 1.8 cruise with 47 passengers and fixed 300,000-lb takeoff gross weight (TOGW) attempting to meet the fuel burn target of 0.3 lb fuel per passenger-mile (i.e. minimum FOM=3.33) on a long-range mission. The sizing was repeated for several study engines. These sizing results led to configurations that were essentially 76% scale versions of the corresponding HSR originals as indicated in the upper left hand portion of Fig. 5.

A sensitivity to varying passenger count (i.e., changing the weight of passengers plus their accommodations) and cruise Mach indicated the range that the 765-071B could fly if TOGW were fixed at 300,000 lb. Cruising at high subsonic Mach number for part of a mission could extend range, providing some compensation for the lost speed. But choosing to slow to Mach 1.2 would cost both speed and range (at least without an alternate engine cycle), indicating that the advantage of possibly flying at “threshold Mach” to avoid booms at ground level must be weighed against possible penalties in performance. The incremental economic value of speed was not included, so it is not clear whether that would be a favorable trade. Figure 5 also illustrates how range and passenger count trade against one another. Clearly there is a cost in range at fixed takeoff weight for hauling more passengers, but seat-mile economics generally favor more passengers, so the best design will just meet the required range. Considering fuel burned and emissions indicated on Fig. 5 results in the same general conclusions.

After demonstrating with the 765-070A and 765-071B concept airplanes that the performance targets for 2020 were feasible, an N+2 specific configuration, the 765-072, was synthesized including design features that would assist in integrating an airplane with at least some degree of sonic boom “softening”. It was initially defined and analyzed interactively within a Boeing conceptual design tool. A Python-based MDA (Multi-Disciplinary Analysis) was also employed to run thousands of design perturbations, single-objective MDO, and multi-objective (Pareto) optimizations.

At the conclusion of these optimizations and several cycles of interactive design, the final 765-072B configuration emerged, shown in Figure 5 lower right. Its fuel burn and emissions looked promising, so additional refinement and analysis were performed at higher fidelity using a ModelCenter-based MDA/O system. The characteristics of the resulting N+2 072B concept is shown on Fig. 6.

Further study variations of range, passenger count, and Mach number in the design space around the 765-072B type concept are shown in Fig. 7. The fuel efficiency metric (FOM) is plotted versus range; a separate curve is shown for each of 25, 50, and 100 passengers; and a separate plot is shown for each cruise Mach of 1.6, 1.8, and 2.0.

Figure 6. Initial N+2 concept: 765-072B.


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For a cruise Mach of 2.0, none of the combinations of range and passengers will reach the FOM goal of 3. Further, at Mach 2, a 6000-nmi range is not feasible and the 5000-nmi, 100-passenger point did not meet the wing loading constraint. The Mach 1.6 and 1.8 plots are very similar. None of the 6000-nmi points meets the wing loading constraint imposed for approach speed and top-of-climb sonic boom level. Only one range/passenger combination exceeds the project FOM goal of 3: the 4000-nmi range and 100 passengers. So, in the absence of a more stringent sonic boom requirement, the best compromise payload-range design point for N+2 was chosen to be the 4000-nmi range, 100 passengers, and a cruise speed of Mach 1.6 to 1.8, depending on detailed operating cost index trades.

With the 4000-nmi and 100 passengers selected, several manual iterations and MDO side studies were conducted to lower the sonic boom level of the 100-passenger 765-072B concept. It became clear that the configuration afforded little opportunity to lower the boom significantly using conventional shaping technology by 2020/2025 without substantially compromising the weight or drag and adding unreasonable development risk. With the 765-072B just meeting the performance requirements, it appears that it has no performance margin that would allow for further boom reduction. The final 765-072B is shown in Fig. 8; the performance numbers are summarized in Table 3.

To illustrate what kind of configuration might be required to significantly reduce the sonic boom levels, a 40% lighter gross weight, 30-passenger concept aircraft was introduced as an alternative technology platform to the 100-passenger 765-072B. This alternative concept was configured to meet the kind of aggressive boom requirements proposed by NASA, trading payload capacity and fuel efficiency. It was initially sized to have a Takeoff Gross Weight (TOGW) of 180,000 lb, with similar wing loading and thrust loading as the 765-072B.

The E variant of the 765-076 (shown in Fig. 9) has overwing nacelles to enable shielding of fan noise and a significantly lower risk from runway slush or tire foreign object damage (FOD). Large canard surfaces were omitted to avoid potential leading-edge vortex ingestion by the engines. V-tails were chosen to aid engine noise shielding and to provide added opportunity for sonic boom tailoring.

The model 765-076E surface definition was created with sufficient constraints to ensure the ability to package internal components and degrees of freedom to achieve the projected sonic boom targets. The 765-076E sonic boom target signature was based on a linear analysis of the concept’s lift and volumetric degrees of freedom. The signature was analyzed with the Zephyrus wave propagation code. Based on experience with recent internal studies, the design was projected to achieve the desired sonic boom target wave form and cruise performance goals using an experimentally validated set of higher order design tools.

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Figure 7. Combined range, Mach, and passenger trade results.


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WING CANARD VERTICALAREA (sf) 4600 210 335VOLUME - 0.0327 0.0389ASPECT RATIO 2.6 2.71 1.37TAPER RATIO 0.045 0.275 0.281LE SWEEP (deg) 68/40 40 39.4TE SWEEP (deg) -15/6 0 0MAC (in) 1082 117 207XREF (in) 1692 592.2 2509.8SPAN (ft) 115 23 21

PILOT EYEX = 450Y = -24Z = 29.8

285.9523 10

116.85

MAC

1082.22

MAC

1099.71

LC

817.80

LV

FS 1600

PILOT EYEX = 450Y = -24Z = 29.8

NOTIONAL CGX = 1692

2820235

10

51843 1.8

207.45

MAC

14 x H40x14.5-19MLG TIRES

2 x H22x8.25-10NLG TIRES

352.2029 4

1381.82115 2

418.5534 11

9 First36-in pitch

90 Economy32-in pitch

Class (%) Carts Cart Ratio LavatoryRatio

AttendentRatio

First 9.1 3 0.333 9 -Economy 90.9 5 0.055 45 -Total - 8 0.081 33 25

MINIMUM CROSS SECTIONS1/50

FS 717TYPE I42 X 66

FS 1306TYPE III20 X 36

FS 1917.5TYPE I42 X 66 APB

FRONT PRESSURE BULKHEAD EE BAY APUFS 1600

Figure 8. Final 765-072B vehicle.

Figure 9. 765-076E general arrangement.

The performance of the 765-076E paired with an engine to be discussed later is shown in Table 4. As noted in

the table, the fuel efficiency FOM metric is only 1.57 due in part to low-boom design compromises, the projected state of N+2 technologies, and the smaller passenger count. Other parameters are also listed.

The sonic boom wave propagation is shown in Fig. 10. The ground signature of 91.5 PLdB is much improved over the 765-072B’s 108 PLdB shown in Fig. 6. The 765-076E configuration should be able to provide ~91 PLdB after several cycles of nonlinear CFD-based boom optimization (which was beyond the scope of the N+2 study).


11

The N+2 study identified some achievable levels relative the initial goals set forth in the preceding section. The capabilities of the two study concepts (-072B and -076E) are summarized in Table 5. This table shows that the -072B will meet the N+2 performance goals, but not the sonic boom goals. While the -076E has a much lower boom signature, it still does not meet NASA’s sonic boom goals (though its projected overpressure level of 0.7psf is very favorable compared to the Concord’s 2+psf, and could allow supersonic flight in some over-land corridors). The 076E also does not meet the minimum range or FOM efficiency goals of the study.

Some key enablers are necessary to achieve the performance and environ-mental performance numbers discussed here for the 2020/2025 timeframe. A summary of key enablers is as follows:

� Aero-propulsion servo-elastic design and evolved fly-by-wire, multifunction surfaces, and multi-input/multi-output design.

� Configuration features that enable both low boom and low drag. � Configuration optimization via CFD and FEM and MDA/MDO tools. � Inlets and nozzles that are simple, efficient, and low noise. � Durable engine materials and reduced SFC optimized engine cycles. � Design for low speed performance, handling, field performance, and noise. � Credible and achievable certification requirements (e.g., boom, loads, emissions).

2. 2030 to 2035 Timeframe Reference Systems and Technologies. Due to the nature of the long-range planning and unknowns for the

2030/2035 timeframe, it was decided that Georgia Tech Aerospace Systems Design Laboratory (ASDL) would take the lead to facilitate a workshop for concept and technology selections for this timeframe. Working closely with

Table 3. 765-072B vehicle performance. Table 4. 765-076E small low boom supersonic vehicle performance (with the 765-072B for comparison).

765-072B 765-072B 765-076E Wing Area, ft2 4058 Wing Area, ft2 4058 2517 Passengers 100 Passengers 100 30 Payload, lb 21,000 Payload, lb 21,000 6300 Cruise Mach 1.6 Cruise Mach 1.6 1.6 TOGW, lb 316,786 TOGW, lb 316,786 178,581 OEW, lb 150,240 OEW, lb 150,240 88,390 Thrust/Engine, lb thrust 64,688 Thrust/Engine, lb thrust 64,688 41,133 Total Fuel, lb 146,028 Total Fuel, lb 146,028 84,373 Block Fuel, lb 126,243 Block Fuel, lb 126,243 72,740 Range, nmi 4000 Range, nmi 4000 3799 FOM (Seat*nmi/fuel burned) 3.17 FOM (Seat*nmi/fuel burned) 3.17 1.57

Figure 10. 765-076E as-designed shaped ground signatures at M = 1.8, 162,000 lb, Altitude of 49,000 ft, and CL = 0.1117.


12

Table 5. N+2 study compliance matrix.

Guidelines for Study 765-072B 765-076E Environmental Goals Sonic Boom (Linear Theory Goal) 65 to 70 PLdB ~ 100

~ 90

Airport Noise (cum below Stage 3)

industry participants, a formalized custom process and tools were developed 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 that would aid in workshop activities.

The workshop for 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 ASDL. 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.

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. To overcome this issue, a qualitative brainstorming exercise was developed to prioritize and downselect the important requirements and alternatives with feedback from disciplinary experts and program management. This allowed for the quantitative process of the downselected alternatives to be much more manageable.

IRMA combines systems engineering techniques such as Matrix of Alternatives, Multi-Attributes Decision Making (MADM), and Technique for Ordered Preference by Similarity to Ideal Solutions (TOPSIS). 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 attempted to solve. The IRMA process included a dynamic dashboard for visualizing the effects of each decision. When a selection was made, incompatible options were filtered out, thereby facilitating downselection. The interactive nature of the IRMA tool allowed for the team to understand the impact of decisions at the initial point of decision-making. In a collaborative group such as seen at the workshop, this tool provided a mechanism for understanding the impacts of the order of decisions as well as facilitating discussions among group members.

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. Fig. 11 depicts the necessary general steps used to create the IRMA to prepare for the workshop.

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 IRMA consisted of representatives from all the program participants who provided input and guidance in supporting technologies and integration issues.

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 downselection activities. This workflow is depicted in Fig. 12.

Upon reaching consensus among 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 provided a mechanism for

Stage 3–10 to 20 dB (Sideline Vj ~1100 ft/s)

Minus 15 Minus 18

Cruise Emissions (NOX g/kg of fuel) Limited consideration Not evaluated Not evaluated Performance Goals Cruise Mach 1.6 to 2.0 1.6 1.6 Range (nmi) 4000 to 6000 4000 3799 Payload (passengers) 25 to 100 100 30 Fuel Efficiency (passenger-miles per pound of fuel) >3.0 3.17 1.57


13

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

Figure 11. Pre-workshop activity sequence.

Pre-Workshop Tasks

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

Figure 12. Workshop workflow diagram.

discussion as well as a product of the workshop. Fig. 13 depicts the results from the workshop. These drawings were used as a starting point in future steps for this phase of the work.

Concept Development and Technology Identification. With the workshop described previously as a background and a point of departure, preliminary brainstorming for configuration features and technologies


14

Figure 13. Concept categories for the 2030/2035 timeframe: configuration and technology development.

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 overwing inlets. With sufficient development, such features and several generally applicable technologies could advance substantially and become practicable within the 2030/2035 timeframe. Two more radical alternative configurations, an oblique “scissor” wing and a joined wing concept, were also briefly examined in light of the expected enabling 2030/2035 technologies.

Selected configurations employing technologies representing promising and addressable concepts from the Reference Systems and Technologies Workshop described previously are shown in Fig. 14. The first is configuration 1C, which has a variable sweep “arrow” wing. Its promise is low fuel burn, which 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 earlier N+2 study. It has a fixed wing and a V-tail that is 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 recommended 2030/2035 reference airplane, which will be discussed later. A joined wing and oblique “scissor” wing configuration were investigated to explore significantly different configuration alternatives. Finally, remotely-driven fan technology was applied to a generic supersonic airframe, but preliminary analysis indicated that, at least as applied to this problem, it offered no net benefits overall and presented high technical risks.

When comparing the aerodynamic performance of these candidate concepts, it was found that all can achieve about the same lift-to-drag ratio at the design point (e.g., Mach 1.8 cruise), except the joined wing that as drawn has significantly more wetted area in the large joined tail. The consequent skin friction drag hinders the performance of the joined wing at all Mach numbers.

At subsonic Mach, there is an aerodynamic advantage of variable sweep in the “swing-wing” configuration. Variable sweep is also responsible for an 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 trim flaps on the aft deck. Configuration 2C could roughly match configuration 1C at low supersonic Mach. The scissor wing appears to have significantly higher L/D at all Mach numbers 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. A brief Computational Fluid Dynamics (CFD)


15

� Low fuel burn/low boom “arrow wing” (1C)

– Swing wing: weight penalty, drag advantage– Evaluate for low fuel burn, low boom

� Based on reference N+2 low boom -076 concept (2C)– Decided to avoid weight of swing wing proposed in June 09 on

concept 2A

� Alternate general arrangement concepts :

– Joined-wing

– Scissor-wing

� Completed a preliminary study of remote fan.– Not favorable trade as drawn– HSR “boost fan” tri-jet concept more workable

Add image

Figure 14. Preliminary configurations for study.

study demonstrated that 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 at high sweep angles. It was also assumed that the wing pivot and fairing between the wing and body could not eventually be designed to not compromise the aerodynamics at any condition. With these caveats in mind, the likely maximum practical cruise Mach number for the scissors wing is set at 1.4.

Area and thrust sizing for configurations 1C and 2C determined that 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 would probably add another constraint in the form of a lower bound on wing area that still offers potential for sufficient boom reduction.

Considering the costs, risks, and uncertain net benefits of either variable geometry or the other alternative configurations, configuration 2C became the point of departure for developing the Icon-II, the reference N+3 technology concept airplane. Because the alternative configurations would have required extensive detailed design, and potentially reconsideration of the basic requirements in order to fairly assess their potential, (e.g. cruise Mach for the scissor wing), 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 in the transonic thrust-drag-pinch region for acceleration. 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 and benefits of more detailed design and analysis of a similar configuration during ongoing experimental low-boom validations, the 2C was selected as the basis for the Icon-II reference airplane.

Selected Reference System for 2030/2035—The Icon-II. A first step in developing the Concept 2-C into the Icon-II reference configuration was doing a preliminary sizing and incorporating the best-performing N+3 engine (to be described in Section II.C). Results are shown in Table 6. The first result is from sizing only thrust to maximize range for Configuration 2C at Mach 1.6 with wing area and maximum takeoff gross weight (MTOGW) fixed. The resulting range is 4600 nmi. Using preliminary estimates of 10% reduction in operational empty weight (OEW) and 6% potential reduction cruise drag, and sizing both the wing area and thrust to minimize weight at fixed 4000-nmi


16

Table 6. Thrust and area + thrust sizing of configuration 2C, with and without preliminary estimate of weight and drag reduction via technology.

range, the theoretical takeoff gross weight is reduced substantially. Unfortunately, the proportions of the indicated configuration were not geometrically feasible because the large overwing nacelles and landing gear did not integrate into such a small wing. Using a 5000-nmi range instead, and repeating the trial sizing, relieved 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 overwing inlets can be designed using similar technology.

50005000

275k277k

Mach 1.6Mach 1.8

4000220kMach 1.6

54005350

300k300k

Mach 1.6Mach 1.8

6% Cruise Drag Reduction(preliminary estimate)

10% OEW Reduction(preliminary estimate)

With Preliminary Weight & Drag Projections

4600300kEngine change alone

Mach 1.6

Range (nm)Weight (lbs)

50005000

275k277k

Mach 1.6Mach 1.8

4000220kMach 1.6

54005350

300k300k

Mach 1.6Mach 1.8

6% Cruise Drag Reduction(preliminary estimate)

10% OEW Reduction(preliminary estimate)

With Preliminary Weight & Drag Projections

4600300kEngine change alone

Mach 1.6

Range (nm)Weight (lbs)

TOGW & Range sensitivity to the combined Weight, Drag & Engine technology assumptions, using Config 2C (“N+2 +”)

Base is config 2C(“N+2+” technology)

Direction for “Icon-II” Development

Un-cycled weight.Re-draw will not integrate.

Direction for “Icon-II” Development

Un-cycled weight.Re-draw will not integrate.

From an airline’s perspective, the most promising compromise would likely be to maintain the original 300,000-lb design MTOGW and trade for some more range (nearly trans-Pacific) and an increase in cabin size as shown in the last two lines of Table 6. This would immediately improve the seat nmi/lb figure of merit through additional seats, with an initially modest cost in total fuel burn. On this basis, the Icon-II was redrawn for a 120-passenger dual-class version on which the impact of individual candidate technologies could be more carefully assessed.

A careful bottoms-up estimate of the benefit of these technologies applied to Configuration 2C resulted in some changes to the initial estimates to about 5% reduction in OEW and a 10% reduction in cruise drag. These updated values are the basis for performance improvements between the N+2+ levels assumed for the initial study airplanes and the final 765-107B Icon-II to be discussed below.

A three-view of the final Icon-II configuration, 765-107B, is shown in Fig. 15. It is essentially the Configuration 2C, but with anti-aero/propulsor/servoelastic ride control vanes, a moderate length fixed-nose for boom, and a slightly broader fuselage that accommodates 120 passengers in a dual-class arrangement as shown in Fig. 16. As shown the cabin could also accommodate 50 passengers in a spacious “executive” interior arrangement, demonstrating one of the alternative cabin utilization concepts. If seating pitch comfort were reduced to that for a typical all-tourist, charter-type cabin, around 130 passengers could be accommodated.

The final performance numbers for the 765-107B are given in Table 7. A comparison of the capabilities of the Icon-II 765-107B against the goals is shown in Table 8. In every category, the airplane is projected to meet or exceed the minimum requirements, and often reaches the stretch goals.

C. Propulsion Architecture and Technologies This section summarizes the propulsion system study as it relates to the configuration development. Completely

covering that work here would make this paper unreasonably long. Therefore, the propulsion system development and performance will be the subjects of future paper.


17

Model DATA TABLE (as drawn airplane)N+3 765-107B Wing Horizontal RCV Vertical

ITEM ESDU Total Projected ProjectedArea to CL 4200 4471.1Exposed 445.48 78.13 445.48

Reference 4200 445.48 78.13 445.48Aspect Ratio 2.90 2.72 3.15 2.00 3.15Taper Ratio 0.169 0.198 0.20 0.198

LE Sweep angle 57.59 48 58 48Dihedral, TE 12 12 45 -20 45

T/C 0.024 0.024 0.030 0.030 0.030Tail Volume 0.102 0.102 0.066 0.0413

Span , in 1323.6 1323.6 534.6 75.0 534.6Root Chord, in 782.1 283.4 125.0 283.4Tip Chord, in 131.8 56.0 25.0 56.0

M.A.C. in 534.1 703.9 195.1 86.1 195.1X 1/4 mac 2196.6 2071.4 2711.6 293.9 2711.6

Y, mac 252.4 335.7 41.2 335.7Tail Arm, in. 515.0 1902.7 515.0

262 ft

110 ft 4 in

Figure 15. Three-view of the Icon-II 765-107B.

Figure 16. Cabin layout for 120 passengers, dual class, in Icon-II 765-107B.


18

The initial 2020/2025 concept development leading to the 765-072B and 765-076 concepts discussed previously employed Boeing study engines (see Fig. 5). They were selected by choosing a 100- or 30-passenger type of relevant airframe configuration, installing one of several available engines, and then sizing both thrust and wing area to maximize range. Any secondary impact on the configuration was also assessed in case it might change the simple conclusion that range decides the best engine.

Table 7. Mission summary for 765-107B Icon-II (with comparison to the 765-072B and 765-076E).

765-072B 765-076E Icon-II (765-107B)

Wing Area, ft2 4058 2517 4200 Passengers 100 30 120 Payload, lb 21,000 6300 27,000 Cruise Mach 1.6 1.6 1.8 TOGW, lb 316,786 178,581 300,000 OEW, lb 150,240 88,390 134,540 Thrust/Engine, lb thrust 64,688 41,133 68,000 Total Fuel, lb 146,028 84,373 139416 Block Fuel, lb 126,243 72,740 121057 Range, nmi 4000 3799 4930 FOM (Seat*nmi/fuel burned) 3.17 1.57 4.89

For the initial configuration and trade studies of the 765-072B and 765-076, a series of six candidate engines cycles was developed, three from Pratt & Whitney and three from Rolls-Royce. A best engine cycle was selected based on the results from this study group and used for the discussions of the 2020/2025 concepts and trades in the previous Section B.

Table 8. Comparison between N+3 goals and forecast for Icon-II 765-107B.

During the 2020/2025 effort, a dual-spool, mixed-flow turbofan (MFTF) engine with a high-pressure-ratio fan was modeled in the widely-available Numerical Propulsion Simulator System (NPSS). The MFTF was selected because it is a proven architecture that has been used for years, and its modeling characteristics are well understood. A simple block schematic of the MFTF is shown in Fig. 17. Current engine technologies, represented by parameters such as component efficiency, were modeled using public domain data, which were then modified to reflect the technology level expected to exist in the N+2 timeframe. The baseline efficiencies were not tied to a particular year and were adjusted as appropriate for the year of consideration and the configuration. The NPSS model was created using several modularized function files that allowed for easy updates to the model as new data or results were made available.

The NPSS was integrated into a Multidisciplinary Analysis and Optimization model (MDAO). The MDAO process has the capability to optimize engine-airframe combinations in a way previously unavailable (see Fig. 18). Traditional methods assumed nacelle scaling correlations to grow and shrink the nacelle based on the thrust

Metric Min Goal Stretch Goal Icon-II Sonic Boom 70 to 80 65 to 75 65 to 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

Figure 17. NPSS model schematic.


19

169171-035

Fnref, FPR, OPR

T41Max, ExT, ThR Geometry

PerformanceTO & Mission*

Aerodynamics

MassProperties

Propulsion

Nacelle ScalingCrz Alt, Crz Mn

Vjet, Derate

Optimizer (Design Explorer)•Selects values for variables•Checks Constraints•Checks Objectives

•Design Variables•Design Constraints•Design ObjectivesStart

VARIABLES

Nacelle Lines

Nacelle Drag

VehicleL/D, etc.

OEW, etc.

Dia, Len

Fnref, Wt

TO, CI, Crz, Idle

Fn & Wf, Vjet

TOFL, TOGW, Range, OEWFuel Burn, ROC, ICA, etc.

NPSSParametric Model

169171-035

Fnref, FPR, OPR

T41Max, ExT, ThR Geometry

PerformanceTO & Mission*

Aerodynamics

MassProperties

Propulsion

Nacelle ScalingCrz Alt, Crz Mn

Vjet, Derate

Optimizer (Design Explorer)•Selects values for variables•Checks Constraints•Checks Objectives

•Design Variables•Design Constraints•Design ObjectivesStart

VARIABLES

Nacelle Lines

Nacelle Drag

VehicleL/D, etc.

OEW, etc.

Dia, Len

Fnref, Wt

TO, CI, Crz, Idle

Fn & Wf, Vjet

TOFL, TOGW, Range, OEWFuel Burn, ROC, ICA, etc.

NPSSParametric Model

Figure 18. NPSS integration and optimization process.

required, whereas the thrust and fuel flow for the engine was merely scaled within the sizing program. NPSS allowed an engine deck to be created with each sizing iteration, providing a more accurately sized engine for different thrust requirements. As the reference thrust for the engine deck is the required thrust, there is no longer any need to scale thrust and fuel flow in the sizing program, increasing the accuracy of the analysis. In addition, NPSS estimates the engine diameter, which allows more accurate inputs to geometry than the assumed correlations.

The 2030/2035 timeframe called for more stringent stretch goals beyond the NASA N+3 goals, which is partly based on desirable market economics. The Icon-II vehicle configuration as discussed previously addressed these goals, and they were accordingly imposed on the engine for this vehicle. The later 2030/2035 timeframe studies obtained inputs from the engine manufacturers and used data sets as supplied by each of them in the sizing studies. A summary of the content of these data sets is as follows:

� GE: � Variable cycle technologies � Advanced thermal management, exhaust and noise reduction technologies, and thrust augmentation

� Pratt & Whitney: � Variable fan airflow and fan pressure ratio to address conflicting noise and efficiency goals � Baseline configuration combined with advanced technology bundles

� Rolls-Royce/Liberty Works: � Adaptive cycle � Low-emissions adaptive combustor, advanced fuels, CMC turbine hardware, and highly efficient

components Based on the information exchanged with the engine companies, Boeing modified the NPSS model to reflect the

best of the best for application to the Icon-II vehicle. The Icon-II airframe was paired with an Icon engine. This is a notional engine meant to represent the most promising combinations of technologies disclosed by the engine original equipment manufacturers (OEM) 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. This notional engine provides projected propulsion performance levels that enable the Icon-II airframe to meet the basic 2030/2035 performance requirements and even approach the stretch goals.


20

To create the Icon engine configuration, all engine technologies were reviewed in order to determine which technologies were common and most beneficial. The performance data for the Icon engine are based on the N+2 765-072B NPSS data with factors applied based on these common and beneficial technologies.

Table 9. Configuration parameters of the Icon-II engine (unscaled).

An overview of the engine performance is shown in Table 9 and the configuration in Fig. 19.

As mentioned previously, more information about the propulsion system development and performance will be published later in a companion paper.

D. Technologies

Ref. Thrust (27F, SLS, Augm.) [lbf] 66000 - 68000Ref. 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 - 84Total Length [in] 560 - 570

En ht [lbm] 11000 - 11300gine+Nozzle Weig

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

Figure 19. Icon-II engine configuration features.

With several airframes and engines under consideration, a series of preliminary sizing studies were conducted to determine how to proceed with the broader engine/airframe trades and technology assessments. Study results found that the choice of configuration, Mach number, or wing area did not have a significant effect on the choice of the engines. Therefore, there was confidence that a study using a single engine/airframe combination would provide a general result without much risk of overlooking some unique benefit or issue arising from a specific combination. Thus, a single configuration (2C) was used for the incremental technology effects assessment, with an expectation that the results will be generally applicable.

The airframe and engine technology items were identified and developed building on the results of the initial Reference System and Technologies Workshop described previously.

1. Airframe Technology Identification, Screening, and Prioritization Boeing started from a companywide survey of ongoing technology and vehicle development work, past studies

such as HSR, and other industry efforts such as that from the National Institute of Aerospace. The goals and objectives of the supersonic vehicle study program were reviewed with the appropriate personnel working on the technologies with the request to identify the items that would be applicable to this supersonic work. This activity generated about 100 technology items.


21

The 100 items were reduced to 34 through an initial screening process that considered the most promising and applicable technologies in terms of their direct impact on aircraft performance and environmental compliance. The following criteria were used during the initial screening process:

� Fuel efficiency � Development time to TRL 6 (Technology Readiness Level) � Fundamental quantity benefit; that is, drag, noise, and so forth � Tech rank relative to each of the concepts shown in Section II.B � 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 765-072B reference configuration was evaluated by incrementally varying each of the fundamental quantity items of drag, empty weight (OEW), thrust, and SFC. The following equation was developed based on the resizing results and the partial derivative values determined as shown in equation (1):

�Drag

.(Drag)

)(Parameter�OEW

.(OEW)

)(Parameter�SFC

.Flow)_(Fuel

)(Parameter

.(Thrust)

)(Parameter�Parameter �

��

��

��

��

��

��

��

590913251052

�Thrust

3662FOM(1)

The results were, therefore based on a direct impact on the fuel burned as the key economic and emissions

metric. The assessed impacts for each of the 34 technologies were used with Eq. (1) to get an overall system-level impact on the 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. Technology items which would serve as enablers for fabrication or certification of selected configuration features but which had negligible direct fuel burn impact once adopted were considered separately as part of the vehicle concept development process. The top 10 performance items ranked in order are shown in Table 10.

Table 10. The top 10 airframe performance technologies.

FOM Rank Technolgy Fuel BurnedBenefit

1 Reliability-Based Design and Certification > 10%

2 Active Laminar Flow

3 Structural Health Management 5-10%

4 Active GLA/MLA

5 Riblets (limitied application) < 5%

6 Low-speed High-Lift devices

7 Aero-Servo-Propulsive-Elasticity (ASPE)

8 Reliable CG Control

9 Passive Laminar Flow

10 Morphing bumps (Control Cp Distribution)


22

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.

The top technologies were then combined as appropriate with related technologies identified in the previous discussion and grouped into categories. These categories were:

1. Sonic Boom—Design Methods 2. Sonic Boom–Active Technology Mitigation 3. Community Noise—High Lift, Reduced Jet Velocities 4. Propulsion Integration—Inlet and Nozzle 5. Aeroelastics and Flight Controls* 6. Composites and Metals* 7. Structural Concepts* 8. Aerodynamic Efficiency 9. Aircraft Systems*

With these categorizations as a point of departure, nine airframe technology roadmaps in the previous categories were developed that focused on the supersonic only and the supersonic applications for the mixed. Some could not be segregated; those were identified (see items marked with an asterisk), but included anyway to form a complete set. These roadmaps described the goals and objectives for each technology category, performance area and impact, technical description, risk assessment, current TRL, major milestones, deliverables, tasks, schedule, and major milestones. From the resulting roadmaps, the key milestones over the first 3 years from the roadmaps are shown in Fig. 20.

S O N IC B O O M

C U M U L A T IV E N O IS E

C R U IS E E M IS S IO N S

F U E L E F F IC IE N C Y

A E R O D Y N A M I C S P R O P U L SIO N (E N GIN E O E M -S P E C I F IC )

S T R U C T U R E A IR C R A F T S Y S TE M S

In it ial S B F rame wo rk

F ina l S B F rame wo rk

P ara Ge o m a n d C F D

Ob j Ftn s an d Co n st ra in sC urre n t C o nt ra ct C ommple te

2 01 1 2 0 12 2 01 3

M J Sh o ck mod sM J W T T es t g o-a he a d

M J 3-D w

O B H B en e fit a n a

O BH W T de mo

H C l P re lm C on c ep s Fe a sa b ility H C l W T T e s t

A SE Lida r gu s t s e n so r A S E ph y s ic s , CF D S t ruc tu reA S E be n e fit a na

A SE re al t ime a lg o rit h imsM at c o s t b en e fit a n a

M at t a rg e t a p p lic a t io n sRB D me t ric s an d de s ap p

SH M h o t s p ot mon it orin gS t ruc t in t e gra t e d a nt e n na s

R B D a nd S HM be n et ift an a

A c tiv e LF e xte n t a n d lo ca t io n

R ib le t s a p p s tud ie s

S ys c an d te c h s a n d ris k

Sy s t ec h de v pla n

Sy s te c h fe a sa b ilit y d emo

Varia ble A re a No z s y s re q mt s

In le t fluid ic c o nt ro l re q mts

In le t flu id ic fe a sa b ility

A u g me n ta t ion D ev fo r A d v No zzle

Va riab le A re a N o z t ra de s tu d y

A da p t iv e Cy c le T e s tC o nt . M o ld Lin e Lip (C M LL) S y s R e q.

C M LL fea s ibilit y

Figure 20. Key technology milestones.

2. Propulsion Technology, Identification, Screening, and Prioritization Technology benefits are 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 OEMs assessed the fundamental quantities for engine technologies, whereas Boeing assessed the nozzle and inlet technologies with a few exceptions.

To assess the performance impact of the individual technologies, sensitivities were calculated based on 765-072B vehicle resizing and determining the changes in the vehicle level performance. This exercise was performed 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 (2) was employed:


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DD

ParamWW

ParamSFCWf

ParamFnFn

ParamParam ��

��

��

��

��

��

� (2)

where

Param = Vehicle-level parameter (FOM, TOGW) Fn = Net thrust Wf = Fuel flow SFC = Specific fuel consumption W = Weight (engine) D = Diameter (engine) And the partial derivative values were:

Param Fn

Param�

�W

Param�

�D

Param�

�Wf

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. Results from this analysis are shown in Table 11: From the resulting roadmaps, the key milestones over the first

3 years from the roadmaps are also included in Fig. 20.

Table 11. Engine technologies.

III. Conclusions Since 2005, NASA has engaged industry to reassess the future of commercial supersonic flight in light of

environmental goals that are better understood and the need to assess continued progress in key enabling technologies. The corresponding timeframes referenced for these studies were chosen by NASA to represent the years 2020 to 2025 (N+2) and 2030 to 2035 (N+3), respectively.

Qualitative indices that measure a passenger’s willingness to pay versus the schedule and service quality he/she demands show that a relatively small but potentially viable segment of the overall market is 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. This group constitutes a potentially viable market segment to support initial commercial supersonic service on multiple routes beginning in the N+2 timeframe if sufficient airplane efficiency and environmental standards are achieved through innovative design and key enabling technologies identified in these studies. It is reasonable to project that such an hypothetical market foothold could be expanded in the N+3 timeframe and beyond as better technology provides improved economics, longer ranges, and eventually routine low-boom over-land supersonic flight operations.

Engine Type or Sonic Boom (Through Component Fuel Efficiency Weight Reduction) Additional Items

Adaptive Fan/Cycle 10% to 25% 15% to 20% Takeoff noise Compressor 5 to 10 5 None Turbine 10 to 20 5 to 15 Combustor 5 NA Emissions reductions >70% Cycle/System Tech Bundle Up to 25 Emissions reductions >80% Inlet Tech Bundle 5 to 10 1 Nozzle Tech Bundle Up to 20 Noise ~10 EPNdB


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The top-level results are summarized in Table 12. (The performance results for these concepts were shown in Table 7.) The results concluded that the N+2 supersonic airliner concepts are unlikely to meet both fuel efficiency and sonic boom mitigation goals simultaneously. A 30- to 40-passenger concept aircraft could potentially approach the low-sonic-boom goals, and a 100-passenger (dual class) concept could meet the stated fuel efficiency goals with N+2 technologies. A preferred N+3 conceptual design (airframe, engine, and technology suite) for the 2035 timeframe was defined. This concept aircraft, called the Icon-II, shows the potential to meet or exceed nearly all the N+3 goals. Supporting technologies (engine and airframe) were identified, grouped into categories, and roadmapped in the long term (TRL 6) and near term (next 2 or 3 years) as a NASA-industry resource for long-term R&D planning in subsequent years. Table 12. Study compliance matrix and study conclusions.

N+2 Guidelines

Acknowledgments This report was prepared for NASA Langley Research Center under Contract NNL08AA16B, Orders

NNL08AC35T and NNL08AC76T. Lori Ozoroski was the Technical Monitor, and Peter Coen was the NASA Principal Investigator.

The authors want to thank the following for their contributions to this effort: From Boeing:

Todd Magee, Greg Miller, Daniel Tompkins, Terry Britt, Edward White, Steve Hollowell, Brandon Huelman, Eric Adamson, Josh Stengel, Kevin Lutke, Jan Murphy, Alan Mortlock, Tom Derbyshire, Greg Oakes, Edward Lawson, Gary Galerne, Ed Kowalski, Kim Nguyen, Rhodri Thomas, Thomas Tsotsis, Brian Foist, Daniel Chen, James Huang, David Hyde, Kamal Shweyk, Fred Roos, Roger Clark, Peter Camacho, Aaron Kutzmann, Dave Bruns, Brandin Northrop, Tony Gonzales, and Tom Smith, Tony Antani and Peter Radloff.

And members of the subcontracting teams: General Electric Pratt & Whitney Rolls-Royce North American Technologies Inc. (Liberty Works®) Georgia Institute of Technology Aircraft System Development Lab (ASDL) M4 Engineering Wyle Laboratories

for Study 765-072B 765-076E N+3 Goals 765-107B EnvironmentalGoals

Sonic Boom (Linear Theory Goal)

65 to 70 PLdB ~ 100 ~ 90 65 to 70 PLdB 65 to 75

Airport Noise (cumulative margin below Stage 3)

Stage 3–10 to 20 dB cum (Vj ~1100 ft/s)

Minus 15 Minus 18 Stage 3–20 to Minus ~30 30 dB cum

Cruise Emissions (NOX g/kg of fuel)

Limited Consideration Not evaluated

Not evaluated

Cruise EINOx ~5 <5

Performance Goals Cruise Mach 1.6 to 2.0 1.6 1.6 1.3 to 2.0 1.6-1.8 Range (nmi) 4000 to 6000 4000 3799 4000 to 6000 5900 to 4800 Payload (passengers)

25 to 100 100 30 100 to 200 50 to 130

Fuel Efficiency (passenger-miles per pound of fuel)

>3.0 3.17 1.57 3.5 to 4.5 4 to 5


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