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Technical Paper

Viable Designs Through a Joint Probabilistic Estimation Technique

A key issue in complex systems design is measuring the ‘goodness’ of a design, i.e. finding a criterion through which a particular design is determined to be the ‘best’. Traditional choices in aerospace systems design, such as performance, cost, revenue, reliability, and safety, individually fail to fully capture the life cycle characteristics of the system. Furthermore, current multi-criteria optimization approaches, addressing this problem, rely on deterministic, thus, complete and known information about the system and the environment it is exposed to. In many cases, this information is not be available at the conceptual or preliminary design phases. Hence, critical decisions made in these phases have to draw from only incomplete or uncertain knowledge. One modeling option is to treat this incomplete information probabilistically, accounting for the fact that certain values may be prominent, while the actual value during operation is unknown.
Technical Paper

Variable Cycle Optimization for Supersonic Commercial Applications

Variable cycle engines (VCEs) hold promise as an enabling technology for supersonic business jet (SBJ) applications. Fuel consumption can potentially be minimized by modulating the engine cycle between the subsonic and supersonic phases of flight. The additional flexibility may also contribute toward meeting takeoff and landing noise and emissions requirements. Several different concepts have been and are currently being investigated to achieve variable cycle operation. The core-driven fan stage (CDFS) variable cycle engine is perhaps the most mature concept since an engine of this type flew in the USAF Advanced Tactical Fighter prototype program in the 1990s. Therefore, this type of VCE is of particular interest for potential commercial application. To investigate the potential benefits of a CDFS variable cycle engine, a parametric model is developed using the NASA Numerical Propulsion System Simulation (NPSS).
Technical Paper

Test Results for a Fuel Cell-Powered Demonstration Aircraft

A fuel cell powered airplane has been designed and constructed at the Georgia Insitute of Technology to develop an understanding of the design and implementation challenges of fuel cell-powered unmanned aerial vehicles (UAVs). A custom 448W net output proton exchange membrane fuel cell powerplant has been constructed and tested. A demonstrator aircraft was designed and built to accommodate this powerplant and the fuel cell powered aircraft has performed seven test flights to date. Test data show that the aircraft performance validates the models used for design and optimization and that the fuel cell aircraft is capable of longer endurance, higher performance test flights.
Technical Paper

Technology Assessment of a Supersonic Business Jet

This paper presents a quantitative process to track the progress of technology developments within NASA’s Vehicle Systems Program (VSP) as implemented on a Supersonic Business Jet (SBJ). The process, called the Technology Metric Assessment and Tracking (TMAT) process, accounts for the temporal aspects of technology development programs such that technology portfolio assessments, in the form of technological progress towards VSP sector goals, may be tracked and assessed. Progress tracking of internal research and development programs is an essential element to successful strategic endeavors and justification of the pursuit of capital projects [1].
Journal Article

Superconducting Machines and Power Systems for Electric-Drive Aeropropulsion

Societal demands of recent years have increasingly pressured the development of greener technologies in all sectors of the nation's transportation infrastructure, including that of civilian aviation. This study explores the concept of electric-drive aeropropulsion, aided by high-temperature superconducting technology, as an enabler for enhancing the environmental characteristics at the air-vehicle level. Potential improvements in the areas of aircraft noise, emissions, and energy efficiency are discussed in the context of supporting the latest strategic goals of leading governmental organizations.
Technical Paper

Quiet, Clean, and Efficient, but Heavy - Concerns for Future Fuel Cell Powered Personal Air Vehicles

Unfortunately, the promises of efficient, clean, quiet power that fuel cells offer are balanced by extremely low power densities and great infrastructure-related challenges. Studies by government and industry have investigated their feasibility for primary propulsion in light aircraft. These studies have produced mixed results but have tended to rely on integrating fuel cells into existing airframes, with respectably-performing light sport planes being turned into underpowered show planes with horribly compromised range and payload capabilities. Fuel cells today are in the earliest phases of technological development. As an aircraft propulsion system, they are as advanced as the Wright's reciprocating engine was a hundred years ago.
Technical Paper

Probabilistic Analysis of an HSCT Modeled with an Equivalent Laminated Plate Wing

The High Speed Civil Transport (HSCT), a supersonic commercial transport currently under development, presents several challenges to traditional conceptual design. The current historical database used by many commercial transport design processes only include data for subsonic transports and therefore does not apply to innovative new configurations such as the HSCT. Therefore, physics-based, preliminary design tools must be used to model the characteristics of advanced aircraft in conceptual sizing routines. In addition, the evaluation of the aircraft design space often requires the analysis of many configurations in order to assess the impact of design constraints and determine the attainable range of system level metrics, a process which is very time consuming in both modeling and computer run time.
Technical Paper

New Approaches to Multidisciplinary Synthesis: An Aero-Structures-Control Application Using Statistical Techniques

An evolving aircraft synthesis simulation environment which offers improvements to existing methods at multiple levels of a design process is described in this paper. As design databases become obsolete due to the introduction of new technologies and classes of vehicles and as sophisticated analysis codes are often too computationally expensive for iterative applications, the design engineer may find a lack of usable information needed for decision making. Within the environment developed in this paper, rapid sensitivity analysis is possible through a unique representation of the relationship between fundamental design variables and system objectives. The combined use of the Design of Experiments and Response Surface techniques provides the ability to form this design relationship among system variables and target values, which is termed design-oriented in nature.
Technical Paper

New Approaches to Conceptual and Preliminary Aircraft Design: A Comparative Assessment of a Neural Network Formulation and a Response Surface Methodology

This paper critically evaluates the use of Neural Networks (NNs) as metamodels for design applications. The specifics of implementing a NN approach are researched and discussed, including the type and architecture appropriate for design-related tasks, the processes of collecting training and validation data, and training the network, resulting in a sound process, which is described. This approach is then contrasted to the Response Surface Methodology (RSM). As illustrative problems, two equations to be approximated and a real-world problem from a Stability and Controls scenario, where it is desirable to predict the static longitudinal stability for a High Speed Civil Transport (HSCT) at takeoff, are presented. This research examines Response Surface Equations (RSEs) as Taylor series approximations, and explains their high performance as a proven approach to approximate functions that are known to be quadratic or near quadratic in nature.
Technical Paper

Methodology for Assessing Survivability Tradeoffs in the Preliminary Design Process

Aircraft survivability is a key metric that contributes to the overall system effectiveness of military aircraft as well as to a lower life cycle cost. The aircraft designer, thus, must have a complete and thorough understanding of the interrelationships between the components of survivability and the other traditional disciplines as well as how they affect the overall life cycle cost of the aircraft. If this understanding occurs, the designer can then evaluate which components and technologies will create the most robust aircraft system with the best system effectiveness at the lowest cost. A synthesis and modeling environment is formulated and presented that will allow trade-off studies and analysis of survivability concepts to be conducted. This environment then becomes the testbed used to develop a comprehensive and structured probabilistic methodology, called the Probabilistic System of System Effectiveness Methodology (POSSEM), that will allow these trades to be conducted.
Technical Paper

Method for the Exploration of Cause and Effect Links and Derivation of Causal Trees from Accident Reports

The ultimate goal of knowledge-based aircraft design, pilot training and flight operations is to make flight safety an inherent, built-in feature of the flight vehicle, such as its aerodynamics, strength, economics and comfort are. Individual flight accidents and incidents may vary in terms of quantitative characteristics, circumstances, and other external details. However, their cause-and-effect patterns often reveal invariant structure or essential causal chains which may re-occur in the future for the same or other vehicle types. The identification of invariant logical patterns from flight accident reports, time-histories and other data sources is very important for enhancing flight safety at the level of the ‘pilot - vehicle -operational conditions’ system. The objective of this research project was to develop and assess a method for ‘mining’ knowledge of typical cause-and-effect patterns from flight accidents and incidents.
Technical Paper

Implementation of a Physics-Based Decision-Making Framework for Evaluation of the Multidisciplinary Aircraft Uncertainty

In today's business climate, aerospace companies are more than ever in need of rational methods and techniques that provide insights as to the best strategies which may be pursued for increased profitability and risk mitigation. However, the use of subjective, anecdotal decision-making remains prevalent due to the absence of analytical methods capable of capturing and forecasting future needs. Negotiations between airframe and engine manufacturers could benefit greatly from a structured environment that facilitates efficient, rational, decision-making. Creation of such an environment can be developed through a parametric physics-based, stochastic formulation that uses Response Surface Equations as meta-models to expedite the process.
Technical Paper

Impact of Sampling Technique Selection on the Creation of Response Surface Models

This paper evaluates and compares a variety of sampling techniques, including both classical and modern Designs of Experiments, to create a more structured approach to selecting the most apt DoE for a specific type of problem. Six different designs are investigated through a design analysis for a notional commercial aircraft. The appropriateness of each sampling technique is determined based on a number of criteria, including code execution time, independent variable correlation, and distribution of data points throughout the design space. Additionally, the resulting models are evaluated using a systematic procedure for checking quality to quantify the accuracy and predictive capability of a given model.
Technical Paper

Identification and Evaluation of Technologies for the Development of a Quiet Supersonic Business Jet

The success of business jets like the Citation X, the fastest civil aircraft in use after the Concorde, highlights the need for speed to improve business and globalization. Currently, developing a supersonic business jet has many technical and economical impediments. These obstacles include sonic boom, emissions and noise requirements problems that are easily meet or do not exist for subsonic aircraft. A baseline aircraft, defined by an optimization process, is the starting point for this study. However, this baseline aircraft does not meet the sonic boom, emissions and noise requirements, which are very strict. Companion studies to this one indicate that it may be possible to meet emissions and noise requirements, but it is clear that technology infusion is necessary for the future viability of this aircraft concept to succeed.
Technical Paper

Formulation of an IPPD Methodology for the Design of a Supersonic Business Jet

The growth of international markets as well as business partnerships between U.S. and Asian-based firms has lead to an increased interest in an economically viable business jet capable of supersonic cruise and trans-Pacific range with one stop over (or non-stop trans-Atlantic range)1. Such an aircraft would reduce the travel time to these regions by as much as 50% by increasing cruise Mach number from roughly 0.85 to 2.0. In response to this interest, the 1996 AIAA / United Technologies / Pratt & Whitney Individual Undergraduate Design Competition has issued a Request for Proposal for the conceptual design of a supersonic cruise business jet. The design of this aircraft considered both performance and economic issues in the conceptual design phase. Through the use of Response Surface Methodology (RSM) and Design of Experiments (DoE) techniques, the aerodynamics of this vehicle were modeled and incorporated into an aircraft sizing code, FLOPS.
Technical Paper

Forecasting the Impact of Technology Infusion on Subsonic Transport Affordability

The design of complex systems, such as commercial aircraft, has drastically changed since the middle 1970's. Budgetary and airline requirements have forced many aerospace companies to reduce the amount of time and monetary investments in future revolutionary concepts and design methods. The current NASA administration has noticed this shift in aviation focus and responded with the “Three Pillars for Success” program. This program is a roadmap for the development of research, innovative ideas, and technology implementation goals for the next 20 years. As a response to this program, the Aerospace Systems Design Laboratory at Georgia Tech is developing methods whereby forecasting techniques will aid in the proper assessment of future vehicle concepts. This method is called Technology Impact Forecasting (TIF). This method is applied to a medium-range, intra-continental, commercial transport concept.
Technical Paper

Forecasting Technology Uncertainty in Preliminary Aircraft Design

An evolved version of the Technology Identification, Evaluation, and Selection (TIES) method is presented that provides techniques for quantifying technological uncertainty associated with immature technologies. Uncertainty in this context implies forecasting. Forecasting the impact of immature technologies on a system is needed to provide increased knowledge to a decision-maker in the conceptual and preliminary phases of aircraft design. The increased knowledge allows for proper allocation of company resources and program management. The TIES method addresses the milestones encountered during a technology development program, the sources of uncertainty during that development, a potential method for bounding and forecasting the uncertainty, and a means to quantify the impact of any emerging technology. A proof of concept application was performed on a High Speed Civil Transport concept due to its technically challenging customer requirements.
Technical Paper

Facilitating the Energy Optimization of Aircraft Propulsion and Thermal Management Systems through Integrated Modeling and Simulation

An integrated, multidisciplinary environment of a tactical aircraft platform has been created by leveraging the powerful capabilities of both MATLAB/Simulink and Numerical Propulsion System Simulation (NPSS). The overall simulation includes propulsion, power, and thermal management subsystem models, which are integrated together and linked to an air vehicle model and mission profile. The model has the capability of tracking temperatures and performance metrics and subsequently controlling characteristics of the propulsion and thermal management subsystems. The integrated model enables system-level trade studies involving the optimization of engine bleed and power extraction and thermal management requirements to be conducted. The simulation can also be used to examine future technologies and advanced thermal management architectures in order to increase mission capability and performance.
Technical Paper

Development of an Object Oriented Vehicle Library for Automated Design Analysis

In today’s emerging parametric and probabilistic design environments, disciplinary or multidisciplinary analysis data are represented efficiently with the use of metamodels. Each metamodel is an efficient replacement for a particular design analysis tool. An object oriented library is developed in this paper to represent vehicle configuration in a generic manner and assist the analysis data collection for the metamodeling process. The library is used to produce input files for design analysis tools. It can also be used to create preprocessors for integration environments used in the design process. This allows for smoother integrations of analysis programs within such environments as the environment now needs only replace data in one central input file rather than a file for each analysis tool.
Technical Paper

Development of a Multi-Mission Sizing Methodology Applied to the Common Support Aircraft

A methodology is developed for the rapid quantification and exploration of the design space of a multi-mission vehicle. This method is applied to the Common Support Aircraft, a vehicle with four separate missions, to determine which is most critical to size the vehicle. The Airborne Early Warning mission is shown to be critical for sizing the Common Support Aircraft. Furthermore, the method developed gives a feel for the excess capability of the aircraft in its other support roles. Finally, this methodology is shown to be useful in the creation of balanced requirements for multi-mission vehicles.