scispace - formally typeset
SciSpace - Your AI assistant to discover and understand research papers | Product Hunt

Proceedings ArticleDOI

Economic viability assessment of NASA's blended wing body N3-X aircraft

12 Jul 2017-

AbstractNumerous novel aircraft concepts are under development that aim to achieve dramatic increases in efficiency and reductions in emissions in comparison to current aircraft. Research into these concepts typically focuses on performance aspects to establish whether the aircraft will be capable of meeting developmental goals. However, the final goal of such concepts is to progress to viable commercial products. Economic viability assessments are therefore an integral part of the development process to ensure a sustainable industry. The key question to address is whether a high efficiency aircraft concept can translate into an attractive product from an economic perspective. This research performed an economic viability assessment of NASA’s N3-X aircraft, a blended wing body aircraft with a distributed boundary layer ingesting propulsion system. The sensitivity of the aircraft’s direct operating cost to changes in acquisition price and maintenance cost was predicted to establish maximum cost margins for the aircraft. In a May 2017 fuel price scenario, the N3-X could be no more than 25% more expensive than the baseline aircraft to remain economically viable. Introducing a carbon tax or fuel price jump widens the margin for increased costs. Aircraft cost estimates for the aircraft predict an acquisition cost from 11–37% more expensive than the baseline. In combination with the direct operating cost sensitivity analysis, the N3-X is predicted to need to capture 30% of the aircraft market up to 2035.

Summary (4 min read)

1 Introduction

  • The development of new, more efficient technology is an integral part of the growth of the aviation industry.
  • The key aspects of this goal are the reduction of aviation’s energy consumption (i.e. fuel use) and the reduction of emissions, especially carbon dioxide, oxides of nitrogen, and noise.
  • The development of new aviation technology can span a timeline that means a new aircraft takes more than a decade to move from concept to a commercial product.
  • Given the risk and uncertainty of novel technology, a large body of research covering all aspects of each novel technology is necessary.

2 Case Study Definition

  • Following the established performance characteristics of the selected baseline aircraft, mission level goals have been set for the N3-X aircraft in terms of payload and range requirements.
  • The N3-X is therefore ideally required to achieve a mission range of at least 7500 nmi at Mach 0.84 with a full payload (payload mass equal to the aircraft maximum of 53,570 kg).
  • In order to achieve the required efficiency improvements, the aircraft makes use of a number of novel technologies in both the airframe and the propulsion system.
  • The aircraft propulsive power is provided by a distributed propulsion system consisting of an array of propulsor fans which ingests the boundary layer of the airframe, along with free stream air.
  • The embedded engine and propulsor array location provide noise shielding to achieve the required noise targets [6].

3 Method

  • There are numerous goals when optimising an aircraft design, such as achieving a low fuel consumption, operating empty weight, or cost.
  • They can typically be split into two categories; Parametric Cost Models (PCM) and Manufacturing Process Cost Models (MPCM) [7].
  • Parametric cost models make use of historical data to establish a statistical relationship between variables.
  • In the case of cost estimation, this will be between the cost of the aircraft and the design parameter or parameters found to correlate well with cost.
  • There is insufficient design detail at the preliminary stage to enable a cost estimate based on manufacturing process, whilst novel aircraft are not typically covered by the historical data used to create parametric cost estimating relationships.

Boundary Layer Ingestion

  • The boundary layer ingesting propulsion system of the N3-X was simulated from an integrated / net propulsive force perspective.
  • Inlet mass flow characteristics were approximated as the mass flow averaged properties for the entire inlet stream for all flow conditions [9].
  • The propulsor array’s performance was otherwise calculated using conventional one-dimensional gas dynamics methods.
  • The propulsors were assumed to have a variable area nozzle [4].
  • Fan mass flow, efficiency, and pressure ratio at alternative power settings for propulsors in the array were determined from a scaled fan map.

Aircraft Performance Simulation

  • Conventional aircraft mission simulation tools are designed to support standard aircraft configurations and propulsion systems.
  • No improvements to air traffic management were assumed for 2035.
  • The aircraft are therefore assumed to cruise at a fixed altitude.
  • Weights and dimensions for the N3-X were obtained from referenced sources[4, 5, 12] in combination with a 3-D model of the aircraft available in the public domain [13].
  • Performance obtained from the simulation model of the baseline aircraft was verified against actual payload-range performance information available for the baseline aircraft[14].

3.2 Economic Modelling

  • The economic performance of a product or project may be represented by identifying the operating cost and revenue produced.
  • The useful life and residual value of an aircraft at the end of its life depends on operator policy [15].
  • Amongst some of the methods available the application of the concept of Net Present Value calculation (NPV) is quite prevalent.
  • Direct operating cost was calculated as cost per flight.
  • Therefore, the inflation rate is accounted for within the rate of return term, whilst the cash flow values are in terms of the value of money at the start of the project.

Airframe

  • Both manufacturing process and parametric cost models are not ideal for predicting the cost of a novel aircraft.
  • Given the difficulty of predicting the cost of novel technology, any cost estimate comes with a degree of uncertainty that can be represented by a confidence interval.
  • Aircraft manufacturers will have well developed models for predicting the cost of a new project and setting a list price for the aircraft.
  • It may be assumed that the N3-X will use a large proportion of composites in its construction.
  • It should be noted that the cost estimate does not include a price increase to ensure a profit margin.

Engine

  • Cost estimating relationships for aircraft engines typically rely on thrust as the primary variable.
  • It is less useful for the N3-X’s engines which are predominantly power-producing engines.
  • All the engine useful work would therefore go towards producing thrust rather than power.
  • As with the airframe costs, a number of models and relationships were selected for estimating the engine cost: Weight and thrust liner regression fits Younossi et al [25] Birkler et al [26].
  • The relatively larger error of the estimate from the models by Younossi et al suggests it should be excluded from the cost estimating process.

Other Components

  • Whilst there are established methods for predicting the cost of engines and airframes, the availability of models for estimating the cost of the remaining components is limited.
  • The weight of the superconducting motors and generators was predicted using a correlation of shaft power to weight [4].
  • Instead, a cost estimating relationship provided by Roskam correlating shaft power to the cost of propellers was used [21].
  • Using such methods does lead to a degree of uncertainty in the cost estimate.
  • The cost of the superconducting systems and array is minimal compared to the total cost of the airframe and main engines (2-3% of the total cost for the N3-X).

Uncertainty

  • As has been identified, the cost-estimating relationships are reliant on fits to historical data, leading to inherent uncertainty in the estimates they produce.
  • For the purposes of this research, a 50% confidence interval will be used, i.e. there is a 50% certainty that the actual price will lie within ± 0.675 times the standard deviation.
  • Given that the estimate is being applied to a novel aircraft, there is a higher possibility of costs being greater than expected.
  • This suggests that a distribution which favours values higher than the mean may be more suitable.
  • By combining the two analyses, it is possible to identify whether the cost (including the confidence interval) coincides with the viable cost margin predicted by the cost sensitivity analysis.

4.1 Direct operating cost comparison

  • The overall direct operating cost also includes the remaining cost factors listed in Section 3.
  • A reduction in fuel consumption will lead to a relatively smaller reduction in the direct operating cost.
  • Taking this value, the direct operating cost saving possible for the design 7500 nautical mile mission is approximately 23% .
  • The breakdown of cost components highlights a key aspect of the direct operating cost of a high efficiency aircraft.
  • If the acquisition price and maintenance cost for the N3-X is assumed to be the same as that of the baseline aircraft, fuel contributes to approximately 10%–18% of the overall operating cost .

4.2 N3-X Acquisition Price Estimate

  • Cost estimates for the N3-X were made using the previously identified models.
  • The Rand model by Resetar et al and Younossi et al produces a significantly lower cost estimate than Roskam’s model (Table 5).
  • Assuming that the aircraft would not cost less than the mean cost estimate, the N3-X could be anywhere between 11% and 37% more expensive than the baseline aircraft (Rand models with 50% confidence interval).
  • The Rand model estimate was selected for the further analyses, as it enables the use of confidence intervals.
  • The airframe cost estimate also includes the cost estimates for the propulsion system (engines, array, and superconducting electrical system).

4.3 Sensitivity Analysis

  • With the cost of the baseline aircraft as the starting point, the direct operating cost of the N3-X was estimated with acquisition price and maintenance cost increases between 0% and 100% of the baseline values.
  • This value drops to approximately 10% were the aircraft’s maintenance cost to be twice that of the baseline .
  • Three potential scenarios have been considered in the present research.
  • The cost of emissions adds a further element to the aircraft’s direct operating cost and would, for CO2 emissions, increase in proportion with fuel consumption.
  • Financing the aircraft purchase through other sources or a drop in interest rate reduces the yearly interest repayment and hence reduces direct operating cost.

4.4 Aircraft Market

  • The previous analyses have assumed that 154 aircraft are produced in the first lot.
  • The more aircraft that are produced and sold, the faster the cost of the aircraft development program may be paid off.
  • Given the assumptions used in creating the cost estimate, the number of aircraft to break even for an aircraft list price equal to the baseline would be approximately 200 .
  • The remaining question is whether demand in the aircraft market up to 2035 could support in the region 160 new aircraft.
  • If costs were to lie at the upper limit of the 50% confidence interval, just under 50% of the new aircraft market would need to be captured by the N3-X (assuming the current economic scenario).

5 Conclusions

  • The research has presented a framework for the assessment of the economic viability of an aircraft from an economic perspective.
  • In combination with cost-estimating tools, the framework may be used to predict whether the aircraft can achieve a reasonable price point and the number of aircraft sales that might be required to meet the requisite price.
  • The fuel price and carbon tax scenarios highlight the influence that economic conditions have over the viability of the aircraft.
  • Both manufacturers and operators may therefore be more willing to invest in developing a novel aircraft such as the N3-X.
  • From the operator’s perspective, investment in expensive novel aircraft may nevertheless reduce direct operating costs, assuming costs stay within acceptable margins.

Did you find this useful? Give us your feedback

...read more

Content maybe subject to copyright    Report

Economic Viability Assessment of NASA’s Blended Wing Body
N3-X Aircraft
C. Goldberg
, D. Nalianda
P. Pilidis
and R. Singh
§
Cranfield University, Bedfordshire, MK43 0AL, United Kingdom
Abstract
Numerous novel aircraft concepts are under development that aim to achieve dramatic increases in
efficiency and reductions in emissions in comparison to current aircraft. Research into these concepts
typically focuses on performance aspects to establish whether the aircraft will be capable of meeting
developmental goals. However, the final goal of such concepts is to progress to viable commercial products.
Economic viability assessments are therefore an integral part of the development process to ensure a
sustainable industry. The key question to address is whether a high efficiency aircraft concept can
translate into an attractive product from an economic perspective.
This research performed an economic viability assessment of NASA’s N3-X aircraft, a blended wing
body aircraft with a distributed boundary layer ingesting propulsion system. The sensitivity of the aircraft’s
direct operating cost to changes in acquisition price and maintenance cost was predicted to establish
maximum cost margins for the aircraft. In a May 2017 fuel price scenario, the N3-X could be no more
than 25% more expensive than the baseline aircraft to remain economically viable. Introducing a carbon
tax or fuel price jump widens the margin for increased costs. Aircraft cost estimates for the aircraft
predict an acquisition cost from 11–37% more expensive than the baseline. In combination with the
direct operating cost sensitivity analysis, the N3-X is predicted to need to capture 30% of the aircraft
market up to 2035.
Nomenclature
Acronyms
BLI = Boundary layer ingestion
BWB = Blended wing body
CER = Cost-estimating relationship
DOC = Direct operating cost
IRR = Internal rate of return
MPCM = Manufacturing process cost model
PCM = Parametric cost model
SEE = Standard error of estimate
SFC = Specific Fuel Consumption
TERA = Techno-economic and Environmental Risk Assessment
TRL = Technology readiness level
Symbols
1 Introduction
The development of new, more efficient technology is an integral part of the growth of the aviation industry.
Whilst a modern aircraft is superficially similar to its predecessors, the tools and technologies used in their
design have led to dramatic improvements in efficiency in comparison to their predecessors. As with any
Research Assistant, Propulsion Engineering Centre, Cranfield University.
Lecturer, Propulsion Engineering Centre, Cranfield University.
Head of Centre, Propulsion Engineering Centre, Cranfield University.
§
Professor Emeritus Gas Turbine Engineering, Cranfield University.
1
Proceedings of 53rd AIAA/SAE/ASEE Joint Propulsion Conference 2017, AIAA Propulsion and Energy Forum,
10 - 12 July 2017, Atlanta, GA, USA, Paper number AIAA 2017-4604
DOI:10.2514/6.2017-4604
©2017 AIAA. This is the Author Accepted Manuscript.
Please refer to any applicable publisher terms of use.

commercial industry, a core driver behind the development of new technologies is to offer a product that
increases profitability. In aviation, this is typically gained through reductions in fuel consumption, a cost that
can account for more than a quarter of an aircraft’s direct operating cost [1]. However, the global community
in the 21
st
century has become increasingly aware of its impact on the environment. This awareness has
added an additional goal to the development of new technology: the mitigation and reduction of industry’s
impact on the environment. The key aspects of this goal are the reduction of aviation’s energy consumption
(i.e. fuel use) and the reduction of emissions, especially carbon dioxide, oxides of nitrogen, and noise. The
goals of reducing energy consumption lies in line with the typical course of development in aviation to lower
fuel consumption and hence reduce fuel cost. However, aviation bodies have targeted dramatic reductions
in energy consumption and emissions that cannot be met without the development of revolutionary new
technologies [2, 3].
As commercial entities, airlines and manufacturers are naturally profit-oriented. It is therefore inevitable
that the decisions made will be influenced by economics, be it operating strategies or the purchase of new
assets. In a high fuel price environment, the financial penalties of operating older, less-efficient aircraft are
high. The purchase of new aircraft and interest in new technology is therefore relatively lower. In an opposite
scenario, the cost of operating older aircraft is less significant as fuel contributes less to the overall operating
cost. Older aircraft may therefore be brought out of storage rather than investing in new technology [1]. It
is therefore vital that new technologies can be shown to have the potential to provide profitable solutions to
manufacturers, owners, and operators and ensure that they are commercial viable.
The development of revolutionary or novel technologies entails a higher degree of risk than the evolutionary
development of conventional technology. Novel concepts require the investment of significant time and money
to ensure that the technology can move from a low technology readiness level (TRL) preliminary design through
to certification and commercial use. The development of new aviation technology can span a timeline that
means a new aircraft takes more than a decade to move from concept to a commercial product. Reflecting
this, aviation’s developmental goals also span long timelines, with NASA’s Subsonic fixed wing project settings
goals for 2035+ and Flightpath 2050 setting a goal for 2050. Long timelines contribute further uncertainty
to the development of new technology, as the environment in which the new technology must operate (in
terms of global policy, taxation, economic environment and fuel price) is an unknown. Given the risk and
uncertainty of novel technology, a large body of research covering all aspects of each novel technology is
necessary. Research at the preliminary stage typically focuses on predicting the performance characteristics
of the technology. Given the commercial orientation of the industry, it is vital to ensure that new aircraft
concepts remain profitable whilst also meeting established developmental goals.
This research presents the techno-economic analysis of a novel aircraft concept, NASA’s N3-X, designed
for a 2035+ to achieve 60% fuel saving versus a 2005 entry-into-service aircraft (the Boeing 777-200LR). The
aim of the research was to assess the economic benefits of the N3-X in comparison to the baseline aircraft
and to present a framework for predicting the economic viability of novel aircraft concepts.
2 Case Study Definition
The present research focuses on a case-study of the NASA N3-X conceptual aircraft, developed by Felder
et al [4, 5]. The N3-X aircraft is designed to reduce fuel/energy consumption by at least 60% relative to
a conventional 2005 entry-into-service aircraft. Following the established performance characteristics of the
selected baseline aircraft, mission level goals have been set for the N3-X aircraft in terms of payload and
range requirements. The N3-X is therefore ideally required to achieve a mission range of at least 7500 nmi
at Mach 0.84 with a full payload (payload mass equal to the aircraft maximum of 53,570 kg). In order to
achieve the required efficiency improvements, the aircraft makes use of a number of novel technologies in both
the airframe and the propulsion system. The aircraft propulsive power is provided by a distributed propulsion
system consisting of an array of propulsor fans which ingests the boundary layer of the airframe, along with
free stream air. Electrical power for the propulsor fans is produced by a pair of turbojet/turbogenerator type
engines through a superconducting system, cooled by liquid hydrogen. The N3-X airframe is a blended wing
body planform with main engines assumed to be embedded within the airframe (Figure 1). The embedded
engine and propulsor array location provide noise shielding to achieve the required noise targets [6]. Fuel burn
and emissions targets are achieved through utilisation of the boundary layer ingesting distributed propulsion
system and a blended wing body airframe [5].
2

65.5 m (215 ft)
41 m (135 ft)
Distributed Propulsor Array
Ingested Boundary Layer
Blended Wing Body
Embedded Engine
Figure 1: N3-X aircraft diagram
3 Method
There are numerous goals when optimising an aircraft design, such as achieving a low fuel consumption,
operating empty weight, or cost. However, an optimised aircraft design does not guarantee a profitable
solution, as competitors and alternative options may offer a more attractive solution. It is therefore useful to
apply tools that can compare performance and economics against these alternatives.
Aircraft costs resulting from performance are relatively easily identified as an extension of performance
assessments. However, further costs are contributed as a part two key uncertain costs: the aircraft’s ac-
quisition price and value, and its maintenance cost. This complicates the assessment of novel technology
from an economic perspective. Cost predictions may be created for aircraft in a number of ways. They can
typically be split into two categories; Parametric Cost Models (PCM) and Manufacturing Process Cost Models
(MPCM) [7]. These two categories of model attempt the overcome the difficulties of estimating the cost of
an engineering project from different perspectives and at different levels of fidelity. Parametric cost models
make use of historical data to establish a statistical relationship between variables. In the case of cost estima-
tion, this will be between the cost of the aircraft and the design parameter or parameters found to correlate
well with cost. The relationship between the dependent variable cost and its independent variables can be
determined using a regression analysis to create a cost estimating relationship (CER). MPCM models support
a bottom-up design process, which assess each component and the processes required for its manufacture,
building up to an estimation of the total aircraft cost. However, both techniques are difficult to apply to novel
or preliminary designs. There is insufficient design detail at the preliminary stage to enable a cost estimate
based on manufacturing process, whilst novel aircraft are not typically covered by the historical data used
to create parametric cost estimating relationships. This is therefore an aspect that must be addressed when
attempting to predict the economic performance of a novel concept. Research by Nalianda et al. developed
a sensitivity analysis method which predicts the influence that the two key costs have over an aircraft’s direct
operating cost [8]. The sensitivity analysis may be used to compare the direct operating cost of a novel aircraft
to that of a baseline aircraft to assess whether a novel concept is profitable and provides a good return on
investment. Using this form of analysis, the design of a new conceptual aircraft may be assessed from a
manufacturers or operators perspective for any fuel cost and/or emissions taxation scenarios. Subsequently,
the maximum viable acquisition price and maintenance cost for the aircraft may be predicted. For a given
set of novel technologies that are included in the design, a decision may then also be made as to whether the
established maximum cost boundaries are achievable. This method circumvents the difficulty of predicting
the acquisition or maintenance cost of a novel concept.
3.1 Performance Modelling
Boundary Layer Ingestion
The boundary layer ingesting propulsion system of the N3-X was simulated from an integrated / net propulsive
force perspective. Inlet mass flow characteristics were approximated as the mass flow averaged properties for
the entire inlet stream for all flow conditions [9]. The propulsor array’s performance was otherwise calculated
using conventional one-dimensional gas dynamics methods. The propulsors were assumed to have a variable
area nozzle [4]. Fan mass flow, efficiency, and pressure ratio at alternative power settings for propulsors in
the array were determined from a scaled fan map.
3

Turbomachinery
Engine modelling and simulation was performed using an in-house gas turbine performance assessment tool
[10]. Using the tool, a model of the engine can be created from a selection of modules to simulate the engine
thermodynamic performance and predict gas properties of the individual gas turbine components. This in
turn allows for a detailed simulation of the overall engine performance.
The propulsive power for the baseline aircraft is provided by a pair of twin spool turbofan engines. The
performance of the power plants was simulated using public domain data available for the GE90-115B turbofan
engine. The performance data with which the engine was simulated and verified included sea level static thrust
(514kN) mass flow (1641kg/s) and bypass ratio at cruise (between 7.1 and 8.9) [11]. The design point of
the engine was fixed at a cruise altitude of 35,000 feet and Mach 0.85.
The main engines of the N3-X are required to provide power for the aircraft propulsor array through a
superconducting electrical system. The engines are therefore primarily power producing, although a small
amount of core nozzle thrust is produced to counteract the engine drag. Power requirements are defined by
the propulsor array, with each of the main engines providing half of the required power, including an assumed
transmission loss of 0.2% [5]. The engines were sized for the aerodynamic design point, with cruise defined
at 40,000ft and Mach 0.84 [12]. A number of key engine parameters for the simulated baseline and N3-X
engines are listed in Table 2. Further engine design and component efficiency parameters for the N3-X main
engines as assumed for this study may be found in the referenced sources [4, 5, 12].
Table 2: Engine simulation parameters for the baseline aircraft and N3-X main engines
Parameter Baseline N3-X
Design Point
Operating Pressure Ratio 42 64
Turbine Entry Temperature (K) 1503 1811
Bypass Ratio 7.8 N/A
Mass Flow Rate (kg/s) 658 20.4
Net Thrust (kN) 88.2 3.9
SFC (g/kNs) 15.4 N/A
Power Output (MW) N/A 14.6
Sea Level Static
Turbine Entry Temperature (K) 1755 1867
Mass Flow Rate (kg/s) 1648 52.3
Net Thrust (kN) 514 13.5
Power Output (MW) N/A 34.1
Aircraft Performance Simulation
Conventional aircraft mission simulation tools are designed to support standard aircraft configurations and
propulsion systems. However, there are a limited number of tools available to enable the simulation and
integration of the novel propulsion system architecture of the N3-X. Therefore, a custom aircraft performance
model was created for this study, to combine conventional aircraft simulation methods with a module to
simulate a novel and highly integrated propulsion system [9]. The mission performance model applied a point
mass approximation of the aircraft. Block fuel burn was estimated by splitting the aircraft mission into taxi,
take-off, climb, cruise, descent, and landing segments. No improvements to air traffic management were
assumed for 2035. The aircraft are therefore assumed to cruise at a fixed altitude.
Weights and dimensions for the N3-X were obtained from referenced sources[4, 5, 12] in combination with
a 3-D model of the aircraft available in the public domain [13]. Weights and dimensions for the baseline
aircraft were obtained from publicly available sources[14]. Performance obtained from the simulation model
of the baseline aircraft was verified against actual payload-range performance information available for the
baseline aircraft[14]. The simulated baseline aircraft indicated a maximum payload range of 7,474 nautical
miles (<1% error), a maximum fuel range of 9,242 nautical miles (<1% error), and a maximum ferry range
of 10,218 nautical miles (2.7% error).
4

3.2 Economic Modelling
The economic performance of a product or project may be represented by identifying the operating cost and
revenue produced. Operating cost may be split into two components, direct and indirect [1]. Direct costs can
be easily associated with a project, such as materials, labour, or maintenance. Indirect costs are typically more
difficult to attribute to a single project, and will include administrative staff salaries and similar miscellaneous
costs. Although indirect operating costs must be included in a company-wide assessment, it includes costs
which may be distributed over a range of projects. Therefore, direct operating cost is more useful as a point
of comparison. The present study is considered from the perspective of an airline operator and assumes the
outright purchase and operation of a new aircraft. The direct operating cost is therefore the summation of
the following components [1]:
Fuel
Emissions taxation
Maintenance (engine and airframe)
Insurance
Depreciation
Interest repayment
Crew salary
Both fuel cost and emissions taxation are related to aircraft performance parameters as determined by an
aircraft mission simulation. The emissions taxation component enables the simulation of alternative scenarios
and policies, such as carbon taxation. The remaining components are financial rather than performance
related and can contribute around three quarters of the overall aircraft operating cost [1]. Assuming the
aircraft is purchased through financing - rather than leased - interest on the cost must be repaid over the
aircraft life. Depreciation is not a direct outflow of money, however, it represents the decrease in value of
the aircraft over its life. The useful life and residual value of an aircraft at the end of its life depends on
operator policy [15]. For the present work, residual aircraft value was assumed to be 10% of the initial value
over a 20-year useful life. Insurance cost depends on the risk of operation, and was assumed to be 0.5% of
the aircraft value per year for the present research [1].
Investment cost analyses are often performed to assist in project and investment decisions. Amongst some
of the methods available the application of the concept of Net Present Value calculation (NPV) is quite
prevalent. NPV is an economic valuation concept that accounts for the fact that incomes or expenditures in
the future have less impact than their value at present. Further, a project’s profit and loss are weighted by
making use of a discount factor. Often the discount factor applied is the interest rate, or the weighted average
cost of capital (WACC), a value which accounts for the weighting of costs a company may attribute to debt
and equity. The discount factor represents the return on investment that would be required to exceed the
return achieved by investing the money elsewhere. When comparing a selection of project investments, the
one offering the highest NPV is the one most likely to be selected. Alternatively, the Internal Rate of Return
(IRR) may be calculated. This value is the rate for which the project NPV breaks even, i.e. expenditures
exactly cancel out revenue. A project should ideally exceed the minimum required return rate to be considered
a suitable investment. This minimum is represented by the WACC, which is 7-8% for the airline industry [16].
In the present work, the NPV analysis was made in terms of the difference in direct operating cost between
the baseline aircraft and N3-X, as revenues were assumed to be equal. The project IRR was subsequently
calculated based on this DOC difference, with a NPV formulation as follows [8]:
X =
life
X
n=1
∆DOC
(1 + IRR)
n
(1)
In this formulation, X is equal to the difference in aircraft purchase cost), ∆DOC is the difference in direct
operating cost, and IRR is the real rate of return for which the project NPV is equal to zero. The term n
represents the years in the aircraft’s economic life, up to the assumed maximum of 20 years. Direct operating
cost was calculated as cost per flight. Fuel cost and emissions cost were calculated on a cost per flight basis
from the performance analysis. Insurance, depreciation and interest repayments were calculated as costs per
year and were subsequently distributed over the number of missions flown per year. Maintenance cost and
crew salary were per flight hour terms scaled to the length of the flight. A maintenance severity curve was
included to scale maintenance cost per flight hour to the flight length and flights per year. Flight cycles per
year were scaled based on flight length and reference data on the B777-200LR [17].
The effect of inflation can be included in the calculation by either modifying the cash flow or the rate
of return. In the first case, the cash flow is inflated using the current inflation rate and discounted using a
5

Citations
More filters

Journal ArticleDOI
Abstract: Following high-profile government and industry studies, electric aircraft propulsion has emerged as an important research topic. This article surveys the scholarly and business literature on fixed-wing aircraft propelled in whole or in part by electricity. This includes all-electric, hybrid electric, and turboelectric architectures. We introduce a classification of electric aircraft, technology factors, and performance parameters. Next, we present an overview of electrical components and electric propulsion architectures. We survey existing commercial products, prototypes, demonstrators, and conceptual studies, and develop a list of potential benefits and disadvantages of electric propulsion with estimates of potential benefit. We present an introduction to power electronics, electric machines, and batteries for aircraft designers, and explore the emerging problem of aircraft thermal management. We review modeling, simulation, and multidisciplinary optimization capabilities, and identify current shortcomings. We conclude that the electric aircraft design problem introduces new coupling between previously distinct disciplines, such as aerodynamics and propulsion, which may only become apparent with high-fidelity, physics-based analysis. High-fidelity multidisciplinary design analysis and optimization of electric aircraft, including safety and economic analysis, remains an open challenge.

149 citations


Cites background from "Economic viability assessment of NA..."

  • ...[109] examines the sensitivity of N3-X economics to maintenance cost and concludes that uncertainty in maintenance cost is an acceptable risk....

    [...]


Journal ArticleDOI
13 Apr 2020
Abstract: Electrification of the propulsion system has opened the door to a new paradigm of propulsion system configurations and novel aircraft designs, which was never envisioned before. Despite lofty promises, the concept must overcome the design and sizing challenges to make it realizable. A suitable modeling framework is desired in order to explore the design space at the conceptual level. A greater investment in enabling technologies, and infrastructural developments, is expected to facilitate its successful application in the market. In this review paper, several scholarly articles were surveyed to get an insight into the current landscape of research endeavors and the formulated derivations related to electric aircraft developments. The barriers and the needed future technological development paths are discussed. The paper also includes detailed assessments of the implications and other needs pertaining to future technology, regulation, certification, and infrastructure developments, in order to make the next generation electric aircraft operation commercially worthy.

28 citations


Additional excerpts

  • ...The most technologically overwhelmed notional design from NASA in the subsonic segment, the N3-X design, was assessed for many N+3-time framed environmental performance targets such as for noise and NOx emission [52], fuel burn [22,23], and for economic viability [108]....

    [...]


BookDOI
18 Jan 2018
Abstract: This article was first published in 2001. This is an examination of practices in aircraft evaluation and selection. It clarifies the fleet planning methodologies and defines decision-making processes that are relevant to the environment, offering insights into how selections are being made for a range of airlines and market conditions.

7 citations


Journal ArticleDOI
Abstract: The concept of turboelectric-distributed propulsion (TeDP) has become integral to engineering because of its ability to generate electricity. However, social science compels careful evaluations of TeDP’s environmental and economic impacts—out of caution, such elements must be taken up before TeDP is put into practice. Responding to this call, this research investigates TeDP’s economic and environmental viability with a case study of the National Aeronautics and Space Administration’s (NASA) proposal for a TeDP aircraft, N3-X, using technical aspects and real data integration. The economic assessment measures NASA’s N3-X economic added value for aviation manufacturing, operations, and investors as well as net present value, internal rate of return, and payback period. Meanwhile, the environmental assessment looks at carbon monoxide and dioxide and oxides of nitrogen. The economic and environmental evaluation results establish the viability of TeDP.

2 citations



References
More filters

05 Jan 2009
Abstract: Meeting NASA's N+3 goals requires a fundamental shift in approach to aircraft and engine design. Material and design improvements allow higher pressure and higher temperature core engines which improve the thermal efficiency. Propulsive efficiency, the other half of the overall efficiency equation, however, is largely determined by the fan pressure ratio (FPR). Lower FPR increases propulsive efficiency, but also dramatically reduces fan shaft speed through the combination of larger diameter fans and reduced fan tip speed limits. The result is that below an FPR of 1.5 the maximum fan shaft speed makes direct drive turbines problematic. However, it is the low pressure ratio fans that allow the improvement in propulsive efficiency which, along with improvements in thermal efficiency in the core, contributes strongly to meeting the N+3 goals for fuel burn reduction. The lower fan exhaust velocities resulting from lower FPRs are also key to meeting the aircraft noise goals. Adding a gear box to the standard turbofan engine allows acceptable turbine speeds to be maintained. However, development of a 50,000+ hp gearbox required by fans in a large twin engine transport aircraft presents an extreme technical challenge, therefore another approach is needed. This paper presents a propulsion system which transmits power from the turbine to the fan electrically rather than mechanically. Recent and anticipated advances in high temperature superconducting generators, motors, and power lines offer the possibility that such devices can be used to transmit turbine power in aircraft without an excessive weight penalty. Moving to such a power transmission system does more than provide better matching between fan and turbine shaft speeds. The relative ease with which electrical power can be distributed throughout the aircraft opens up numerous other possibilities for new aircraft and propulsion configurations and modes of operation. This paper discusses a number of these new possibilities. The Boeing N2 hybrid-wing-body (HWB) is used as a baseline aircraft for this study. The two pylon mounted conventional turbofans are replaced by two wing-tip mounted turboshaft engines, each driving a superconducting generator. Both generators feed a common electrical bus which distributes power to an array of superconducting motor-driven fans in a continuous nacelle centered along the trailing edge of the upper surface of the wing-body. A key finding was that traditional inlet performance methodology has to be modified when most of the air entering the inlet is boundary layer air. A very thorough and detailed propulsion/airframe integration (PAI) analysis is required at the very beginning of the design process since embedded engine inlet performance must be based on conditions at the inlet lip rather than freestream conditions. Examination of a range of fan pressure ratios yielded a minimum Thrust-specific-fuel-consumption (TSFC) at the aerodynamic design point of the vehicle (31,000 ft /Mach 0.8) between 1.3 and 1.35 FPR. We deduced that this was due to the higher pressure losses prior to the fan inlet as well as higher losses in the 2-D inlets and nozzles. This FPR is likely to be higher than the FPR that yields a minimum TSFC in a pylon mounted engine. 1

217 citations


"Economic viability assessment of NA..." refers background or methods in this paper

  • ...The present research focuses on a case-study of the NASA N3-X conceptual aircraft, developed by Felder et al [4, 5]....

    [...]

  • ...The propulsors were assumed to have a variable area nozzle [4]....

    [...]

  • ...Further engine design and component efficiency parameters for the N3-X main engines as assumed for this study may be found in the referenced sources [4, 5, 12]....

    [...]

  • ...The weight of the superconducting motors and generators was predicted using a correlation of shaft power to weight [4]....

    [...]

  • ...Weights and dimensions for the N3-X were obtained from referenced sources[4, 5, 12] in combination with a 3-D model of the aircraft available in the public domain [13]....

    [...]


Proceedings ArticleDOI
05 Jan 2009
Abstract: Meeting NASA's N+3 goals requires a fundamental shift in approach to aircraft and engine design. Material and design improvements allow higher pressure and higher temperature core engines which improve the thermal efficiency. Propulsive efficiency, the other half of the overall efficiency equation, however, is largely determined by the fan pressure ratio (FPR). Lower FPR increases propulsive efficiency, but also dramatically reduces fan shaft speed through the combination of larger diameter fans and reduced fan tip speed limits. The result is that below an FPR of 1.5 the maximum fan shaft speed makes direct drive turbines problematic. However, it is the low pressure ratio fans that allow the improvement in propulsive efficiency which, along with improvements in thermal efficiency in the core, contributes strongly to meeting the N+3 goals for fuel burn reduction. The lower fan exhaust velocities resulting from lower FPRs are also key to meeting the aircraft noise goals. Adding a gear box to the standard turbofan engine allows acceptable turbine speeds to be maintained. However, development of a 50,000+ hp gearbox required by fans in a large twin engine transport aircraft presents an extreme technical challenge, therefore another approach is needed. This paper presents a propulsion system which transmits power from the turbine to the fan electrically rather than mechanically. Recent and anticipated advances in high temperature superconducting generators, motors, and power lines offer the possibility that such devices can be used to transmit turbine power in aircraft without an excessive weight penalty. Moving to such a power transmission system does more than provide better matching between fan and turbine shaft speeds. The relative ease with which electrical power can be distributed throughout the aircraft opens up numerous other possibilities for new aircraft and propulsion configurations and modes of operation. This paper discusses a number of these new possibilities. The Boeing N2 hybrid-wing-body (HWB) is used as a baseline aircraft for this study. The two pylon mounted conventional turbofans are replaced by two wing-tip mounted turboshaft engines, each driving a superconducting generator. Both generators feed a common electrical bus which distributes power to an array of superconducting motor-driven fans in a continuous nacelle centered along the trailing edge of the upper surface of the wing-body. A key finding was that traditional inlet performance methodology has to be modified when most of the air entering the inlet is boundary layer air. A very thorough and detailed propulsion/airframe integration (PAI) analysis is required at the very beginning of the design process since embedded engine inlet performance must be based on conditions at the inlet lip rather than freestream conditions. Examination of a range of fan pressure ratios yielded a minimum Thrust-specific-fuel-consumption (TSFC) at the aerodynamic design point of the vehicle (31,000 ft /Mach 0.8) between 1.3 and 1.35 FPR. We deduced that this was due to the higher pressure losses prior to the fan inlet as well as higher losses in the 2-D inlets and nozzles. This FPR is likely to be higher than the FPR that yields a minimum TSFC in a pylon mounted engine. 1

133 citations


12 Sep 2011
Abstract: The performance of the N3-X, a 300 passenger hybrid wing body (HWB) aircraft with turboelectric distributed propulsion (TeDP), has been analyzed to see if it can meet the 70% fuel burn reduction goal of the NASA Subsonic Fixed Wing project for N+3 generation aircraft. The TeDP system utilizes superconducting electric generators, motors and transmission lines to allow the power producing and thrust producing portions of the system to be widely separated. It also allows a small number of large turboshaft engines to drive any number of propulsors. On the N3-X these new degrees of freedom were used to (1) place two large turboshaft engines driving generators in freestream conditions to maximize thermal efficiency and (2) to embed a broad continuous array of 15 motor driven propulsors on the upper surface of the aircraft near the trailing edge. That location maximizes the amount of the boundary layer ingested and thus maximizes propulsive efficiency. The Boeing B777-200LR flying 7500 nm (13890 km) with a cruise speed of Mach 0.84 and an 118100 lb payload was selected as the reference aircraft and mission for this study. In order to distinguish between improvements due to technology and aircraft configuration changes from those due to the propulsion configuration changes, an intermediate configuration was included in this study. In this configuration a pylon mounted, ultra high bypass (UHB) geared turbofan engine with identical propulsion technology was integrated into the same hybrid wing body airframe. That aircraft achieved a 52% reduction in mission fuel burn relative to the reference aircraft. The N3-X was able to achieve a reduction of 70% and 72% (depending on the cooling system) relative to the reference aircraft. The additional 18% - 20% reduction in the mission fuel burn can therefore be attributed to the additional degrees of freedom in the propulsion system configuration afforded by the TeDP system that eliminates nacelle and pylon drag, maximizes boundary layer ingestion (BLI) to reduce inlet drag on the propulsion system, and reduces the wake drag of the vehicle.

116 citations


"Economic viability assessment of NA..." refers background or methods in this paper

  • ...Fuel burn and emissions targets are achieved through utilisation of the boundary layer ingesting distributed propulsion system and a blended wing body airframe [5]....

    [...]

  • ...Weights and dimensions for the N3-X were obtained from referenced sources[4, 5, 12] in combination with a 3-D model of the aircraft available in the public domain [13]....

    [...]

  • ...Further engine design and component efficiency parameters for the N3-X main engines as assumed for this study may be found in the referenced sources [4, 5, 12]....

    [...]

  • ...The present research focuses on a case-study of the NASA N3-X conceptual aircraft, developed by Felder et al [4, 5]....

    [...]


Proceedings ArticleDOI
04 Jan 2011
Abstract: A Turboelectric Distributed Propulsion (TeDP) system differs from other propulsion systems by the use of electrical power to transmit power from the turbine to the fan. Electrical power can be efficiently transmitted over longer distances and with complex topologies. Also the use of power inverters allows the generator and motors speeds to be independent of one another. This decoupling allows the aircraft designer to place the core engines and the fans in locations most advantageous for each. The result can be very different installation environments for the different devices. Thus the installation effects on this system can be quite different than conventional turbofans where the fan and core both see the same installed environments. This paper examines a propulsion system consisting of two superconducting generators, each driven by a turboshaft engine located so that their inlets ingest freestream air, superconducting electrical transmission lines, and an array of superconducting motor driven fan positioned across the upper/rear fuselage area of a hybrid wing body aircraft in a continuous nacelle that ingests all of the upper fuselage boundary layer. The effect of ingesting the boundary layer on the design of the system with a range of design pressure ratios is examined. Also the impact of ingesting the boundary layer on off-design performance is examined. The results show that when examining different design fan pressure ratios it is important to recalculate of the boundary layer mass-average Pt and MN up the height for each inlet height during convergence of the design point for each fan design pressure ratio examined. Correct estimation of off-design performance is dependent on the height of the column of air measured from the aircraft surface immediately prior to any external diffusion that will flow through the fan propulsors. The mass-averaged Pt and MN calculated for this column of air determine the Pt and MN seen by the propulsor inlet. Since the height of this column will change as the amount of air passing through the fans change as the propulsion system is throttled, and since the mass-average Pt and MN varies by height, this capture height must be recalculated as the airflow through the propulsor is varied as the off-design performance point is converged.

86 citations


"Economic viability assessment of NA..." refers background or methods in this paper

  • ...Weights and dimensions for the N3-X were obtained from referenced sources[4, 5, 12] in combination with a 3-D model of the aircraft available in the public domain [13]....

    [...]

  • ...Further engine design and component efficiency parameters for the N3-X main engines as assumed for this study may be found in the referenced sources [4, 5, 12]....

    [...]


Book
01 Jun 2001
Abstract: Selecting the right aircraft for an airline operation is a vastly complex process, involving a multitude of skills and considerable knowledge of the business. Buying the Big Jets has been published since 2001 to provide expert guidance to all those involved in aircraft selection strategies. This third edition brings the picture fully up to date, representing the latest developments in aircraft products and best practice in airline fleet planning techniques. It features a new section that addresses the passenger experience and, for the first time, includes regional jet manufacturers who are now extending their product families into the 100-plus seating category. Overall, the third edition looks at a broader selection of analytical approaches than previously and considers how fleet planning for cost-leader airlines differs from that of network carriers. Buying the Big Jets is an industry-specific example of strategic planning and is therefore a vital text for students engaged in graduate or post-graduate studies either in aeronautics or business administration. The book is essential reading for airline planners with fleet planning responsibility, consultancy groups, analysts studying aircraft performance and economics, airline operational personnel, students of air transport, leasing companies, aircraft value appraisers, and all who manage commercial aircraft acquisition programmes and provide strategic advice to decision-makers. It is also a valuable tool for the banking community where insights into aircraft acquisition decisions are vital.

73 citations


"Economic viability assessment of NA..." refers background in this paper

  • ...The remaining components are financial rather than performance related and can contribute around three quarters of the overall aircraft operating cost [1]....

    [...]

  • ...Older aircraft may therefore be brought out of storage rather than investing in new technology [1]....

    [...]

  • ...Operating cost may be split into two components, direct and indirect [1]....

    [...]

  • ...In aviation, this is typically gained through reductions in fuel consumption, a cost that can account for more than a quarter of an aircraft’s direct operating cost [1]....

    [...]

  • ...As has previously been identified [1, 29], low fuel costs reduce the incentive for operators to invest in new, more efficient aircraft....

    [...]


Frequently Asked Questions (1)
Q1. What are the contributions in "Economic viability assessment of nasa’s blended wing body n3-x aircraft" ?

This research performed an economic viability assessment of NASA ’ s N3-X aircraft, a blended wing body aircraft with a distributed boundary layer ingesting propulsion system.