Sanjay Garg

Glenn Research Center, Cleveland, Ohio

Overview of Propulsion Controls and 

Diagnostics Research at NASA Glenn

NASA/TM—2012-217718

October 2012

AIAA–2012–4255
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Sanjay Garg

Glenn Research Center, Cleveland, Ohio

Overview of Propulsion Controls and 

Diagnostics Research at NASA Glenn

NASA/TM—2012-217718

October 2012

AIAA–2012–4255

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

48th Joint Propulsion Conference and Exhibit

cosponsored by the AIAA, ASME, SAE, and ASEE

Atlanta, Georgia, July 30–August 1, 2012
Acknowledgments

The author will like to thank all the members of the Controls and Dynamics Branch for their enthusiasm and initiative in 

performing the research documented in this paper, and for providing the graphics and information for the paper. The Branch 

members including civil servants and contractors are: Rachael Bis, Joseph Connolly, Amy Chicatelli, Jeff Csank, Dennis Culley, 

John DeLaat, Christopher Fulton, Ten-Huei Guo, George Kopasakis, Jonathan Litt, James Liu, William Maul, Ryan May, Kevin 

Melcher, Daniel Paxson, Joseph Saus, Donald Simon, Shane Sowers, Thomas Stueber, Randy Thomas and Edmond Wong. The 

author will also like to thank the various NASA program/project managers who have supported these research efforts.

Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

5301 Shawnee Road

Alexandria, VA 22312

Available electronically at http://www.sti.nasa.gov

Trade names and trademarks are used in this report for identification 

only. Their usage does not constitute an official endorsement, 

either expressed or implied, by the National Aeronautics and 

Space Administration.

Level of Review: This material has been technically reviewed by technical management. 

This report contains preliminary findings, 

subject to revision as analysis proceeds.
Abstract

With the increased emphasis on aircraft safety, enhanced performance and affordability, and the need to reduce 

the environmental impact of aircraft, there are many new challenges being faced by the designers of aircraft 

propulsion systems. The Controls and Dynamics Branch (CDB) at NASA (National Aeronautics and Space 

Administration) Glenn Research Center (GRC) in Cleveland, Ohio, is leading and participating in various projects 

in partnership with other organizations within GRC and across NASA, the U.S. aerospace industry, and academia to 

develop advanced controls and health management technologies that will help meet these challenges through the 

concept of an Intelligent Engine. CDB conducts propulsion control and diagnostics research in support of various 

programs and projects under the NASA Aeronautics Research Mission Directorate and the Human Exploration and 

Operations Mission Directorate. The paper first provides an overview of the various research tasks in CDB relative 

to the NASA programs and projects, and briefly describes the progress being made on each of these tasks. The 

discussion here is at a high level providing the objectives of the tasks, the technical challenges in meeting the 

objectives and most recent accomplishments. References are provided for each of the technical tasks for the reader 

to familiarize themselves with the details.

NASA/TM—2012-217718 1
Intelligent Propulsion Systems—Control System Perspective

The control system enabling technologies for Intelligent Propulsion Systems are show above. These can be 

organized into three broad categories—active component control, advanced health management, and distributed 

fault tolerant control.

Engine components such as combustors, fans and compressors, inlets, nozzles etc. are designed for optimum 

component performance within some overall system constraints and the control design problem has been to 

transition the operating point of the engine from one set point to another in a most expedient manner without 

compromising safety. With the advancements in information technologies, the component designers are beginning 

to realize the potential of including active control into their component designs to help them meet more stringent 

design requirements and the need for affordable and environment friendly propulsion systems. 

The need to have more reliable and safe engine service, to quickly identify the cause of current or future 

performance problems and take corrective action, and to reduce the operating cost requires development of 

advanced diagnostic and prognostic algorithms. The objective for this technology development is to maximize the 

“on wing” life of the engine and to move from a schedule based maintenance system to a condition based system. 

Implementation of these concepts requires advancements in the area of robust and adaptive control synthesis 

techniques, and development of new hardware such as smart sensors and actuators. Attention will also need to be 

paid to integration of the active component control and diagnostics technologies with the control of the overall 

engine system which will require moving from the current analog control systems to distributed control 

architectures.

Ref: Garg, S., “NASA Glenn Research in Controls and Diagnostics for Intelligent Aerospace Propulsion Systems,” 

2005 AIAA Infotech@Aerospace Conference, Arlington, VA, October 2005.

NASA/TM—2012-217718 2
NASA Aeronautics Program Structure

(Effective FY13)

The NASA Aeronautics Research Mission program structure consists of five major programs: Fundamental 

Aeronautics (FAP) , Aviation Safety (ASP), Airspace Systems, Aeronautics Test, and Integrated Systems Research 

(ISRP), with each of these programs having 2 or more projects. The CDB activities are primarily in the various 

projects under FAP and ASP, with a small participation in the Environmentally Responsive Aviation (ERA) project 

of ISRP.

The Fundamental Aeronautics Program (FAP) went through a reorganization in FY12, and the projects listed are 

as the program will be implemented in FY13 (Fiscal Year 2013—the government fiscal year is from October 1 to 

September 30). For FY12, the FAP consisted of four projects—Subsonic Fixed Wing (SFW), Subsonic Rotary Wing 

(SRW), Supersonics (SUP) and Hypersonics (HYP). The FAP was restructured to have the 4 projects shown in the 

chart for FY13 onwards—HYP project was eliminated with some of the critical hypersonics research work 

combined with a relevant supersonics research into the new High Speed (HS) project; the Aeronautical Sciences 

(AS) project was created to focus investment in fundamental technology and tools development which are crosscutting, i.e., have applicability across a wide range of flight speeds; and the Subsonic Fixed Wing (SFW) and 

Subsonic Rotary Wing (SRW) projects were renamed the Fixed Wing (FW) and Rotary Wing (RW) projects, 

respectively, with content focused on technologies that are directly relevant to the objectives of these projects.

The Aviation Safety Program (ASP) went through a restructuring in 2010 and the current program structure is 

reflected in the chart. CDB has a significant activity under the VSST (Vehicle System Safety Technologies) project 

of ASP with a small task under the SSAT (System-wide Safety & Assurance Technology) project. Additionally 

CDB does research on engine icing detection and mitigation under the VSST project which is a collaborative effort 

with the AEST (Atmospheric Environment and Safety Technologies) project. 

Detailed information about the ARMD programs is available at: http://www.aeronautics.nasa.gov/programs.htm

NASA/TM—2012-217718 3
CDB Tasks Under NASA Aeronautics Research

The Controls and Dynamics Branch (CDB) tasks under the NASA Aeronautics Research Program, and the 

program/project that support these tasks, are listed above. The task relationships to projects, as of August 2012, is briefly

discussed below, and the tasks are discussed in a little more detail in the rest of the paper.

Fundamental Aeronautics Program

Distributed Engine Control and Model Based Engine Control : These efforts are currently under the SFW project, but will 

transition to the AS project in FY13 as part of the Controls sub-project. 

Pressure Gain Combustion: This effort is currently under the SFW project. It is expected to continue under the Combustion 

sub-project of AS project.

Dynamic Systems Analysis: This is a new start in FY13 under the MDAO (Multidisciplinary Analysis and Optimization) 

sub-project of the FW project. No detail is provided on this task in the paper since this effort has not yet started.

Active Combustion Control: Major effort under this task will transition from the SUP project to the AS project in FY13 

under the Combustion sub-project. Small efforts will continue in support of the ERA project under the ISRP. Also a small 

effort will support technology maturation under the new Fixed Wing project.

Aero-Propulso-Servo-Elasticity: This effort, currently under the SUP project, will continue under the new High Speed 

project in FY13.

Turbine Based Combined Cycle (TBCC) Dynamic Modeling and Control: This effort will be discontinued in FY13 with 

the cancellation of the HYP project. The TBCC leadership is in discussions with Army and Air Force to provide support to 

their Hypersonics Research programs.

Aviation Safety Program

Gas Path Health Management: This effort will continue under the VSST project.

Integrated Resilient Propulsion Control: This effort on enhanced engine response control was carried over into 

VSST from the previous IRAC (Integrated Resilient Aircraft Control) project and is now complete.

Robust Propulsion Control: This effort will continue in VSST as part of addressing the “Loss of Control” 

technical challenge.

Run-time Validation of Complex Systems: This effort will continue under the VVFCS (Verification and Validation 

of Flight Critical Systems) element of SSAT project.

NASA/TM—2012-217718 4
Human Exploration and Operations Programs——CDB Activities

In 2009, the NASA Explorations Systems program was restructured to reflect the priorities of the new 

administration. The Constellation Program was cancelled and replaced by the Explorations Systems Development 

program which includes the Orion Multi-Purpose Crew Vehicle (MPCV), Space Launch System (SLS), and Ground 

Systems Development and Operation (GSDO) programs. CDB has tasks in system modeling and fault management 

technology development under the SLS and GSDO programs. Additionally, the previous Exploration Systems 

Technology program was reorganized as the Advanced Exploration Systems (AES) program. CDB has a small 

activity ongoing under one of the projects in the AES program.

For the SLS program, under the SEI (Systems Engineering and Integration) project, CDB is supporting various 

aspects of the Mission and Fault Management effort which is led by MSFC (Marshall Space Flight Center).These 

efforts are focused first on ensuring crew safety/survival and secondly on ensuring mission success. Under the 

Engines project of the SLS program, CDB is working in collaboration with MSFC and Pratt & Whitney Rocketdyne 

to develop methods and system models to characterize the J-2X engine performance parameters from test data, and 

to ensure that the test-data used for such characterization is not faulty. 

For the GSDO program, CDB is working with KSC (Kennedy Space Center) under the Advanced Ground 

Systems Maintenance element to develop functional fault models of the Cryogenics Testbed and selected ground 

support equipment subsystems, to be able to perform detection and isolation of subsystem faults and failures during 

testing and launch operations.

For the AES program, CDB is supporting the Modular Power Systems project and leading the development of a 

health management and control architecture for modular power systems, with elements of the architecture to be 

tested on system components.

Detailed information about the HEOMD programs is available at: 

http://www.nasa.gov/directorates/heo/home/index.html

NASA/TM—2012-217718 5
Distributed Engine Control (DEC)

Distributed (decentralized) engine control involves the development of multiple new technologies for 

implementation on the turbine engine system. One key requirement is to enable a modular architecture which allows 

the heavy processing capability critical for advanced control algorithms to be location independent. This preserves 

the ability of designers to use familiar commercially available processing components, capabilities, and tools. A 

digitally networked ECU (Engine Control Unit) can be located anywhere, even on the airframe, with minimal 

system impact.

This also requires that electronics be embedded in control components which must remain on the engine. For most 

of these components, high temperature electronics are critical to alleviate the weight impact of cooling electronics 

and for long term reliability. However, high temperature electronics are relatively primitive compared to 

commercially electronic components. This creates system constraints for control system operation and performance.

Distributed control on turbine engines requires an entirely new portfolio of technologies beyond high temperature 

electronics to be able to design, analyze, and optimize control systems for continued performance improvement of 

the turbine propulsion system. Capability to test and validate the operation of high temperature capable control 

components such as sensors and actuators requires development of new hardware-in-the-loop test capability. 

Research efforts include: analyzing the requirements for different data communication architectures for 

decentralized control; studying the impact of distributing the current functions of the Engine Control Unit among the 

various control components; performing reliability analysis of different architectures etc.

NASA GRC in collaboration with Air Force Research Lab and industry partners, through the Distributed Engine 

Control Working Group (DECWG), is conducting research on various technologies to enable distributed engine 

control.

Ref.:, Culley, D.E., “Transition in Gas Turbine Control System Architecture: Modular, Distributed and 

Embedded,” GT2010-23226, ASME Turbo Expo 2010, Glasgow, UK, June 14-18, 2010.

NASA/TM—2012-217718 6
DEC Control Architecture and Requirements

The development of Hardware-in-the-Loop (HIL)capability for distributed engine control is critical for 

understanding how to best implement control architecture for various engine applications. It provides a means to 

analyze and quantify system performance in order to advance new technologies. NASA GRC is working with Rolls 

Royce Liberty Works to develop a HIL capability for distributed engine control research. This HIL environment 

will allow engineers to design control systems in simulation and then continue that development through hardware, 

all within a common environment. 

The HIL system will use common simulation tools and develop libraries of modular control components. Each 

control component will be defined by its functional capability and interconnected to the larger system through a 

structured interface definition. This provides great flexibility and allows the system to be easily partitioned and 

scaled. The requirements of each system component can be defined and validated before proceeding to hardware 

development. When hardware is available, it can replace its simulated version and the system operated in hard realtime mode.

The diagram shows the rigidly structured interaction of each control module operating through well-defined 

interfaces (the vertical flow between components). The user interface is able to peer inside the simulated modules 

(the horizontal flow between data structures) to analyze exactly what is happening with the data flow inside of each 

modular element. Actual hardware components function exactly the same way but have less visibility because they 

are forced to communicate strictly through the communication interface.

The intention of the HIL system is to enable multiple organizations to interact in the requirement definition and 

design of control system components, and to provide the tools which can quantify the performance and system level 

benefits of advanced control technologies.

NASA/TM—2012-217718 7
Model Based Engine Control

Model-based engine control (MBEC) is being developed as one of the advanced engine control system 

methodologies to improve turbofan engine performance and efficiency. In current engine control architectures, the 

typical design approach is to regulate a measurable variable such as fan shaft speed (Nf) or engine pressure ratio 

(EPR), which is strongly correlated with thrust. This is done since engine thrust is not a measurable parameter from 

typical on-board engine sensors. Additionally, limits on allowable fuel flow are imposed based on a conservative 

approach to maintain adequate stall margin and temperature margin for safe operation of the engine throughout its life.

MBEC will enable operation of an engine using a direct feedback of thrust providing the ability to have a tighter 

control of the main parameter of interest for engine performance at various deterioration levels throughout its life 

cycle or unexpected disturbances. In addition, MBEC will allow operation with less conservative safety margins, 

since all safety margins currently are designed to an end of life engine, whereas an on-board model can provide a 

more accurate margin for the actual condition of the flight engine. The reduction in the safety margins for newer 

engines will increase fuel efficiency, which links to the critical aeronautics research goals. Direct control of thrust 

will help maintain a tight bound on variations in the engine throttle to thrust response as the engine ages. The 

longer-term pay-off of this research is to have a personalized control for each specific engine, which adapts to the 

condition of the engine to not only maintain the most efficient operation throughout its lifetime but also increase the 

useful operating life.

Ref.: Connolly, J., “Model-Based Engine Control of a Commercial Class Turbofan Engine using an Optimal Tuner 

Approach,” 48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit and 10th International Energy 

Conversion Engineering Conference Atlanta, GA, Jul-Aug. 30-1, 2012

NASA/TM—2012-217718 8
Active Combustion Control—Combustion Instability Suppression 

Demonstrated

Lean combustion concepts for aircraft engine combustors are prone to combustion instabilities. Mitigation of 

instabilities is an enabling technology for these low-emissions combustors. Prior research at NASA Glenn Research 

Center has demonstrated active control to suppress a high-frequency combustion instability in a combustor rig 

designed to emulate an actual aircraft engine instability experience with a conventional, rich-front-end combustor. 

The current effort is developing further understanding of the problem specifically as applied to future lean-burning, 

very low-emissions combustors. 

A prototype advanced, low-emissions aircraft engine combustor with a combustion instability has been identified 

and previous work has characterized the dynamic behavior of that combustor prototype. The combustor exhibits 

thermo-acoustic instabilities that are related to increasing fuel flow and that potentially prevent full-power operation. 

A simplified, non-linear oscillator model and a more physics-based sectored 1-D dynamic model have been 

developed to capture the combustor prototype’s instability behavior. Utilizing these models, the NASA Adaptive 

Sliding Phasor Average Control (ASPAC) instability control method has been updated for the low-emissions 

combustor prototype. 

Active combustion instability suppression using the ASPAC control method has been demonstrated experimentally 

with this combustor prototype in a NASA combustion test cell operating at engine pressures, temperatures, and flows. 

A high-frequency fuel valve was utilized to perturb the combustor fuel flow. Successful instability suppression was 

shown using a dynamic pressure sensor in the combustor for controller feedback. Instability control was also shown 

with a pressure feedback sensor in the lower temperature region upstream of the combustor. It was also demonstrated 

that the controller can prevent the instability from occurring while combustor operation was transitioning from a 

stable, low-power condition to a normally unstable high-power condition, thus enabling the high-power condition. 

Ref.: DeLaat, J.C.; Kopasakis, G.; Saus, J.R.; Chang, C.T.; Wey, C.: “Active Combustion Control for Aircraft GasTurbine Engines—Experimental Results for an Advanced, Low-Emissions Combustor Prototype” 50th AIAA 

Aerospace Sciences Meeting, Nashville, TN, January 2012. AIAA-2012-0783.

NASA/TM—2012-217718 9
Simplified Models for Pressure Gain Combustion Systems

Pressure gain combustion (PGC) is being investigated for potential application to gas turbines. Here, the pressure 

rise (as opposed to a conventional combustor loss) yields higher engine thermal efficiency and specific power. In 

any potential application, system studies must be undertaken. These require component models which can generate 

meaningful performance predictions over a range of flight conditions and parameter variations. Furthermore, these 

models must compute solutions very quickly due to their being exercised over many parameters. This is a particular 

challenge for PGC devices which are fundamentally unsteady, and therefore result in time dependent limit cycle 

solutions rather than single, steady-state operating points. The modeling effort illustrated above has taken the least 

complex approach possible, while maintaining this essential time dependence. The project has produced several 

codes that close in approximately the time it takes to click a mouse, and which produce performance estimates 

consistent with higher fidelity CFD (Computational Fluid Dynamics) models. 

Shown in the chart are a simple schematic of a pressure gain combustor in a gas turbine engine, and a notional 

combustor which was sized using the present model. The complete combustor is comprised of many smaller 

combustion chambers, each undergoing the same limit cycle. The model focuses on just one of these chambers. The 

center figure shows a typical limit cycle output from the model. Here the exit plane distribution of pressure, 

temperature, and velocity are shown (normalized by combustor entry conditions). At each operating point, such 

output is averaged to provide a single total pressure and temperature representing the equivalent steady performance 

at that operating point. A typical combustor performance map based on these averages is shown in the lower left.

The unsteady model and averaging method have now been implemented in NASA’s Numerical Propulsion System 

Simulation (NPSS) which allows the PGC component to be integrated with other gas turbine components into a 

complete engine simulation. A throttle line calculation (idle to max. power) is shown for a small power generation 

facility. Here, the baseline specific fuel consumption is shown as a function of shaft power (throttle setting) for the 

baseline engine and for the same engine with PGC. The reduction in SFC is quite impressive. 

Ref.: Paxson, D. E., Kaemming, T. A., “Foundational Performance Analyses of Pressure Gain Combustion 

Thermodynamic Benefits for Gas Turbines,” AIAA paper 2012-770, January, 2012

NASA/TM—2012-217718 10
Supersonic Propulsion System Modeling and Control

For the NASA Supersonics, project, the overall objective is to perform the research to advance the technology so 

that the industry will be in position to develop supersonic cruise vehicles such as a civil transport. There are many 

technical challenges remaining for the supersonic vehicle technology development, such as sonic boom reduction 

for overland flight, emissions (NOx ) reduction, fuel efficiency, materials, control and handling qualities, etc. 

The objective of the Aero-Servo-Elasticity (ASE) task and specifically the Aero-Propulso-Servo-Elasticity 

(APSE) task is to develop dynamic models for integrated propulsion and airframe systems and associated control 

designs to study overall vehicle performance, such as vehicle stability and vehicle ride quality as well as overall 

efficiency. The future supersonic transport vehicles are expected to be slender body with a highly flexible structure. 

Initial studies have shown that there is a potential for significant coupling between the flexible modes and the engine 

dynamics which can result in unacceptable ride qualities. Therefore the objective of the overall APSE effort is to 

develop higher fidelity propulsion system dynamics, understand the coupling issues with flexible modes and design 

conceptual control logic to mitigate the effects of such coupling. The types of modeling employed are volume gas 

dynamics with component performance characteristics - lump and stage-by-stage, Computational Fluid Dynamics 

(CFD), and parallel flow path modeling. Control designs involve feedback controls loop shaping, and engine 

schedules for compressor Inlet Guide Vanes, fan bypass, and exit nozzle area.

In the chart, the first row shows the baseline variable cycle engine diagram, components that have been modeled 

with associated control designs, and an example thrust response due to atmospheric turbulence. The second row 

shows the variable geometry multi-flow path nozzle design with sonic boom abatement, initial CFD modeling and 

responses. The third row shows the inlet concept design, a test Schlieren image, and modeling results. The forth row 

shows a diagram for a Parallel flow path stage-by-stage compressor modeling and an example response of stage 7 at 

100 percent speed under a certain flow distortion signature.

Ref.: Connolly, J.W., Kopasakis, G., Paxson, D.E., Stuber, E., and Woolwine, K., “Nonlinear Dynamic Modeling 

and Controls Development for Supersonic Propulsion System Research ,” 47th Joint Propulsion Conference and 

Exhibit; 31 Jul. - 3 Aug. 2011; San Diego, CA.

NASA/TM—2012-217718 11
Hypersonic Propulsion System Control—Overview

Control research for a Turbine Based Combined Cycle (TBCC) propulsion system is being conducted as part of 

the Hypersonic project under the NASA Fundamental Aeronautics Program. The ongoing work is to develop tools 

to aid the design of control algorithms to manage a TBCC airbreathing propulsion system during the critical 

operating period when the propulsion system transitions from one cycle to another, referred to as mode transition. 

The first step underway is developing computational models for each component of the propulsion system. These 

component models will be collected under a common programming format for an overall propulsion system 

computational model. 

Current research is focused on developing the computational models to simulate an airbreathing TBCC propulsion 

system inlet. The TBCC inlet aerodynamic design being modeled is that of the Combined-Cycle Engine (CCE) 

Testbed. The CCE Testbed is a large-scale hardware model of an aerodynamic design that was verified in a smallscale screening experiment. The CCE Testbed has been designed for experiments in the NASA GRC 10- by 10-Foot 

Supersonic Wind Tunnel (SWT). This mixed compression inlet system is suitable for experiments focusing on mode 

transition studies. The modeling approach includes employing existing state-of-the-art simulation codes, developing 

new dynamic simulations, and performing system identification experiments on the CCE Testbed in the SWT. The 

developed computational models will be available for control studies prior to hardware buildup. The system 

identification experiments will characterize the necessary dynamics to be represented in the models for control 

design. The primary objective for the CCE Testbed is to experimentally investigate and develop methods of mode 

transition for a TBCC type propulsion system. Ideally, these hardware tests will result in a demonstration of an inlet 

system capable of maintaining inlet operability and safety margins with maximum performance through all flight 

conditions including mode transition. The CCE large scale inlet testing Phase I and Phase II have been completed—

Phase I focused on quantifying inlet performance for the transition Mach Nos., while Phase II focused on 

conducting System Identification experiments to collect data to develop control models of the inlet.

Ref.: Stueber, T.J., Vrnak, D.R., Le, D.K., and Ouzts, P.J., “Control Activity in Support of NASA TBCC Research,” 

NASA TM–2010-216109, January, 2010.

NASA/TM—2012-217718 12
Hypersonic Propulsion System Control—HiTECC

The High Mach Transient Engine Cycle Code, HiTECC, initially developed by Spiritech Advanced Products, 

Inc., via a NASA NRA (NASA Research Announcement) award, is a collection of propulsion system simulation 

components configured to simulate a complete turbine based combined cycle (TBCC) propulsion system. The 

HiTECC simulation includes code for the following components: turbine engine and inlet, dual-mode scramjet 

(DMSJ) and inlet, and an aft nozzle. Furthermore, HiTECC is coded to include heat transfer models, fuel flow 

models, hydraulics models, kinematic models, and a control system. The original HiTECC configuration was a 

simulation for a general propulsion system design and the modular components allow for propulsion system 

changes. This feature enables the use of HiTECC to consider alternate inlet designs, DMSJs, or other turbine 

engine models. 

Since HiTECC was designed as a propulsion system simulation toolbox that employs the MathWorks, Inc. 

MATLAB software as a programming platform, the geometry, actuators, and control systems can be easily 

modified. This flexibility made the HiTECC simulation software readily modifiable to suitably represent the CCELIMX as it was configured in the GRC 10- by 10-Foot SWT. 

The HiTECC wind tunnel model has the simulation geometry defined to match the CCE-LIMX within 

±2 percent error with respect to the actual hardware geometry. This configuration includes mass-flow plugs and 

cold pipe assemblies, instead of a turbine engine or DMSJ, representative of the CCE-LIMX experiments. 

Furthermore, this version of the HiTECC package did not need the components that simulate a thermal or fuel 

management system. Configured in this manner, the HiTECC wind tunnel model serves as a computational test bed 

capable of testing mode transition procedures and control algorithms. 

Csank, J.T., Stueber, T.J., “A Turbine Based Combined Cycle Engine Inlet Model and Mode Transition Simulation 

Based on HiTECC Tool,” 48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, July 30 – August 

1, 2012, Atlanta, GA

NASA/TM—2012-217718 13
An Integrated Architecture for Aircraft Engine Performance Trend 

Monitoring and Gas Path Fault Diagnostics

Aircraft engine performance trend monitoring and gas path fault diagnostics are closely related technologies that 

assist operators in managing the health of their gas turbine engine assets. Trend monitoring is the process of 

monitoring the gradual performance change that an aircraft engine will naturally incur over time due to 

turbomachinery deterioration, while gas path diagnostics is the process of detecting and isolating the occurrence of 

any faults impacting engine flow-path performance. Today, these functions are conventionally performed based on 

the post-flight processing of a small number of engine snapshot measurements collected each flight. Often, this 

processing does not happen until several days after the flight has occurred causing significant diagnostic latency. 

Additionally, the resulting health information is only available off-board. 

An enhanced architecture has been designed to address these limitations by migrating portions of the conventional 

ground-based functionality on-board. This is done to enable the real-time continuous monitoring of engine health, 

the earlier diagnosis of faults, and the estimation of unmeasured engine performance parameters that can be directly 

applied for on-board controls and health management applications. The architecture contains two engine models 

designed to operate in parallel. The first model, referred to as the real-time adaptive performance model (RTAPM), 

continuously self-tunes internal tuning parameters that allow it to match the performance level of the physical 

engine. Performance parameter estimates produced by the RTAPM can be used for controls purposes. The second 

model, referred to as the performance baseline model (PBM), serves as a baseline of recent past engine 

performance. Residuals between the engine and PBM outputs are analyzed for fault diagnostic purposes. The 

applicability of this approach for reliable fault detection and isolation with improved latency was demonstrated 

using a detailed engine dynamic simulation.

Ref.: Simon, D. L., “An Integrated Architecture for Onboard Aircraft Engine Performance Trend Monitoring and 

Gas Path Fault Diagnostics,” NASA/TM-2010-216358, Proceedings of The 2010 JANNAF Joint Subcommittee 

Meeting, Colorado Springs, CO, May 3-7, 2010.

NASA/TM—2012-217718 14
Vehicle Integrated Propulsion Research (VIPR)

On-engine testing is a necessary component of aircraft Engine Health Management (EHM) technology 

development, required to demonstrate the technology against a known system “ground truth” state. However, the 

cost to conduct such testing is often prohibitive, making engine test opportunities rare. To address this need, NASA, 

working in collaboration with the U.S. Air Force and Pratt & Whitney, is conducting a series of ground-based, onwing, engine tests of EHM technologies. This series of tests, referred to as Vehicle Integrated Propulsion Research 

(VIPR), is being conducted on a U.S. Air Force Boeing C-17 Globemaster III aircraft equipped with four Pratt & 

Whitney F117 high bypass turbofan engines. The VIPR series of tests will include both “nominal” and “faulted” 

engine operating scenarios. The first VIPR test took place in 2011, and additional testing is planned for 2013 and 

2014. 

One of the NASA EHM technologies under test as part of VIPR is a model-based gas path health management 

architecture. This architecture consists of a self-tuning engine model and associated diagnostic logic designed to 

detect and isolate any gas path system faults. The self-tuning engine model includes a Kalman filter-based tracking 

filter that processes gas path sensor measurements and adjusts model tuning parameters to capture engine 

performance variations. The architecture’s diagnostic logic continuously monitors for rapid or abrupt performance 

changes in the engine. If a performance change is detected, the diagnostic logic analyzes the observed change and 

classifies a root cause for the fault. Unlike conventional gas path health management methods that are primarily 

performed based on a limited number of snapshot measurements, the enhanced model-based gas path health 

management architecture enables the real-time processing of streaming measurement data. The benefits of this 

approach include real-time monitoring/trending of engine performance and the diagnosis of incipient gas path faults 

with reduced diagnostic latency. The VIPR testing is acquiring engine data at steady-state and transient operating 

scenarios, both when the engine is operating nominally and under known fault conditions. This provides actual 

engine data vital for evaluating and maturing the model-based gas path health management architecture. 

NASA/TM—2012-217718 15
Enhanced Propulsion Control Modes for Emergency Operation

Previous in-flight emergencies in which flight control has been partially or totally lost, have required pilots to 

learn how to fly the damaged aircraft using the engines. Pilots have used differential thrust successfully for 

maneuvering on several occasions. Other examples of mid-air or on-the-ground crises, such as runway incursions or 

attempted take-offs from the wrong runway, have resulted in deadly accidents. However, it has been speculated that 

in some cases there is a potential safety improvement possible through the incorporation of additional propulsion 

system capability. For instance, it is possible to use differential thrust to replace or augment the function of a 

damaged rudder and vertical tail. However, the engine response is sluggish compared to traditional flight control, 

and their control moments tend to be relatively weak.

Research into achieving enhanced engine responsiveness to address these situations has revealed that the 

potential exists to greatly improve engine performance through control system modifications alone, albeit with a 

slightly increased risk to the engine. This risk is mitigated, however, by the overall safety improvement to the 

distressed vehicle. Enhanced propulsion control modes for emergency flight operation have been developed and 

demonstrated in simulation. Specifically, the two modes are Overthrust and Fast Response, which relate to 

emergency situations such as runway incursion and loss of flight control effectiveness, respectively. Piloted 

evaluation in a flight simulator has been performed using a full envelope nonlinear four-engine transport aircraft 

simulation. The incorporated engine model is the Commercial Modular Aero-Propulsion System Simulation 40k (CMAPSS40k) with realistically achievable enhanced propulsion control modes. Comparisons against the same 

aircraft/engine simulation utilizing a standard propulsion control have shown significant improvement in flight 

stability and control, and in reduced required takeoff distance for these emergency scenarios.

Ref: Litt, J.S., Sowers, T.S., Owen, A.K., Fulton, C., Chicatelli, A., “Flight Simulator Evaluation of Enhanced 

Propulsion Control Modes for Emergency Operation,” AIAA 2012-2604, Infotech@Aerospace 2012, Garden 

Grove, CA, June 19-21, 2012. 

NASA/TM—2012-217718 16
Engine Icing: Simulation, Detection, and Mitigation

Over the past 20 years, there have been over 200 reported cases of aircraft engine power loss due to the accretion 

of ice crystal particles in the compression system of commercial turbofan engines. The majority of the work in 

response to this aviation safety concern has focused on understanding the mechanism by which particles in high icewater content (HIWC) conditions can accrete on compressor stator blades, understanding the environmental 

conditions in which accretion can occur, and related regulatory guidance. While avoidance of HIWC conditions and 

compressor redesigns are the ideal long-term solutions, a systems level analysis highlights some near-term 

capabilities.

To this end, simulation studies were conducted using the C-MAPSS40k (Commercial Modular Aero-Propulsion 

System Simulation for a 40,000 lb thrust engine) engine model. Low Pressure Compressor maps that include the 

effect of blockage due to ice accretion were generated and integrated into the C-MAPSS40k simulation. Using this 

capability in conjunction with the realistic engine controller of C-MAPSS40k, research has shown that the engine 

rollback phenomenon is caused by the normal behavior of the engine controller responding to operational limits 

being encountered. As the ice accretion builds up, the decreased mass flow requires higher fan speed to maintain the 

commanded thrust, however, the engine controller limits the fuel flow to maintain the core speed at the maximum 

safe limit, resulting in a drop in the fan speed. This is the first known publicly available simulation demonstration 

that the observed thrust rollback is potentially caused due to the coupling of the engine control with the ice accretion 

effects. It was also shown that the change in engine performance associated with ice accretion can be detected by 

the existing sensor suite. When combined with the knowledge that the aircraft is operating in HIWC conditions, this 

could trigger the detection of ice accretion in the engine compression system. Future work seeks to determine 

various means of preventing ice accretion or mitigating the impact of the blockage.

Ref.: May, R.D., Guo, T-H., Veres J.P., Jorgenson, P.C.E., “Engine Icing Modeling and Simulation (Part 2): 

Performance Simulation of Engine Rollback Phenomena,” 2011-38-0026, SAE International Conference on Aircraft 

and Engine Icing and Ground Deicing, Chicago, IL, Jun 13-17, 2011. 

NASA/TM—2012-217718 17
Integrated Flight and Propulsion Control

The Vehicle System Safety Technologies (VSST) project under the Aviation Safety Program is tasked with 

developing, implementing and, validating advanced control systems for the safety of current and future aircraft 

flight operations. One of the challenging theme tasks under the VSST project is to address the “Loss-of-Control” of 

the aircraft. Since the propulsion system is one of the most powerful actuators for multi-engine aircraft, it is 

conceivable that an integrated flight and propulsion control (IFPC) system can be an effective way to control an 

aircraft to avoid entering an undesirable portion of the flight envelope or to help maneuver beyond the currently 

allowable envelope. Furthermore, under the previous Integrated Resilient Aircraft Control project of the Aviation 

Safety Program, research results showed that under certain conditions the engine can be operated with an enhanced 

response, both in terms of overthrust and faster thrust response, within a pre-defined risk of engine failure. This 

makes the integration of flight and propulsion control even more feasible for application.

However, the current flight and propulsion controllers are designed and operated separately. An integrated flight 

and propulsion control system can potentially increase the safety dramatically by utilizing propulsion system as a set 

of flight effectors. This research includes the evaluation of existing control theory analysis, specification of 

integration goals and requirements, assessment of the interactions of flight control and engine control, defining the 

interface between flight and propulsion control, and preliminary design demonstration of the integration of flight 

and propulsion control.

This is a joint research effort among NASA and its industry partners.

NASA/TM—2012-217718 18
Engine Simulation Software Packages

It is important to have access to publicly available realistic engine dynamic simulations to be able to perform 

meaningful engine control and diagnostics research. The Controls and Dynamics Branch has created various engine 

simulations in the Matlab/Simulink environment which are available to U.S. citizens for downloading from the 

NASA GRC software repository. This chart provides information on the various engine simulations that are 

available for download.

C-MAPSS40k, which is the latest in the suite of software packages, introduces a number of new features 

including an iterative solver and detailed compressor stall models. C-MAPSS40k also includes an “industry 

standard” controller for use as a baseline against which to compare new controllers and architectures. With these 

capabilities, users in academia, industry, and government have access to a generic, high-fidelity engine simulation 

that can be used to quickly develop, simulate, and test new control system components and architectures, and 

diagnostic algorithms. C-MAPSS40k is being used extensively by NASA researchers in support of the Aviation 

Safety and Fundamental Aeronautics Programs research efforts, and by our industry partners for NASA sponsored 

as well as internal research efforts.

Also, recently, the author recorded a 1 hour video on “Fundamentals of Aircraft Engine Control” as part of the 

NASA Engineering and Safety Center (NESC) web lecture series on Guidance, Navigation and Control applications 

across NASA programs. This lecture is available as indicated, and provides a good overview for students in the 

senior level propulsion class as well as controls engineers interested in pursuing research in engine control and 

diagnostics.

Ref: May, R. D., Csank, J. T., Lavelle, T. M., Litt, J. S., Guo, T. -H., “A High-Fidelity Simulation of a Generic 

Commercial Aircraft Engine and Controller,” Joint Propulsion Conference, Nashville, TN, July 25-28, 2010.

NASA/TM—2012-217718 19
3rd GRC Propulsion Control and Diagnostics Workshop

The 3rd GRC PCD (Propulsion Control and Diagnostics) Workshop was held on February 28 to March 1, 2012, at 

the Ohio Aerospace Institute, Cleveland, Ohio. The objectives of the workshop were to: Disseminate information to 

the research community about the propulsion control and diagnostics research being done at by RHC (Controls and 

Dynamics Branch) in support of various projects under the NASA Aeronautics Research Mission Directorate 

(ARMD) programs; Get feedback from peers on value of the research and validity of the technical approach; and 

Identify opportunities for potential collaboration and sharing of tools and methods. 

The workshop consisted of: Overview presentations on ongoing research in aircraft engine control and diagnostics 

at NASA, DoD (Department of Defense) and Engine manufacturers; Detailed presentations on the RHC PCD 

research efforts—progress to date and future plans, and tools and simulations available for public use; and One-onone discussions between NASA researchers and attendees to answer any questions and identify potential 

collaboration opportunities. There were over 65 attendees from academia, industry and government with a large 

portion being from the industry. The feedback from the attendees has been extremely positive in terms of the 

workshop meeting the stated objectives and the opportunity it provides for networking within the aero-propulsion 

control and diagnostics research community.

The presentations from the workshop are available at the CDB website as indicated in the chart above. Below is a 

sample of overall feedback provided by some of the attendees:

• "I learned quite a bit from the workshop and found it very valuable" - Industry Participant

• "Covered a lot of material, did it concisely, little wasted time" - Industry Participant

• "This was an essential and extremely valuable workshop with highly relevant and high quality presentations. 

The high regard with which industry value this event is indicated by the large number of attendees. Well 

done!" - Small Business Participant

NASA/TM—2012-217718 20
Mission and Fault Management for the SLS Project

NASA’s Space Launch System Project (SLS) is a contractor build with government oversight/insight effort. 

NASA Glenn currently supports SLS systems engineering and integration under a sub-project known as Mission 

and Fault Management (M&FM). M&FM is responsible for developing analyses and algorithms for normal 

operation, abort conditions, caution & warning situations, and redundancy management—efforts that are focused 

first on ensuring crew safety/survival and secondly on ensuring mission success. In these areas, NASA Glenn covers 

the vehicle’s Thrust Vector Control (TVC) and Electrical Power System (EPS) subsystems. Early M&FM efforts 

have been focused on identifying and developing required capabilities and processes. The SLS Project completed a 

System Requirements and System Definition Review in the March-April 2012 timeframe and is currently working 

toward a Preliminary Design Review. NASA Glenn is currently working the four areas shown here:

• Goal Tree/Success Tree (GT/ST)—Responsible for developing a GT/ST for the entire Core Stage ascent 

phase. As planned, the GT/ST will be used early in the design process to identify gaps and overlap in abort 

conditions/triggers which cover failure modes that threaten the crew. 

• System Engineering Model—New SysML-based tools are being used to model and coordinate the 

development of M&FM algorithms with subsystem designers and the flight software team.

• Integrated Vehicle Failure Model—This model seeks to capture the propagation of faults through SLS 

systems, subsystems, and components. Early models are qualitative and can be used to determine whether or 

not designs meet requirements for fault management. This allows for changes to be made earlier in the design 

process when changes are less costly.

• Sensor Data Qualification—Monitors data from flight critical sensors at the flight computer to determine if 

they reflect the true system state. Uses multiple algorithms and persistence to minimize the probability of a false 

positive or false negative detection. Bad data is flagged so that it is not used by higher-level M&FM algorithms.

NASA/TM—2012-217718 21
NASA Extended Testability Analysis Tool

During the Ares I Upper Stage (US) Project, Functional Fault Models (FFMs) and testability analyses provided 

significant new capabilities for assessing the ability of early US designs to meet requirements for fault detection and 

isolation. Design schematics and Failure Modes and Effects Analyses (FMEA) were used as the basis for creating 

FFMs of the US subsystems in COTS modeling software. The COTS software provides a graphical framework for 

capturing the design architecture shown in system schematics; the failure modes associated with systems 

components; and the way the failure modes propagate from one subsystem or component to another. The COTS 

software generates a Dependency Matrix (D-Matrix) which maps each failure mode to the set of sensor-based 

logical tests that are available for detecting the failure modes.

The ETA Tool was developed under the Ares I US project as stand-alone software tool that extends the testability 

analysis and reporting capabilities provided by the COTS modeling software. The ETA Tool uses the COTS model 

information and the D-MATRIX to determine: overlap or gaps in the detection of failure modes; tests that are not 

useful for detecting faults; if failure modes can be isolated via unique detection signatures; whether failure modes 

originating in a specific component can be isolated to that component; and failure modes that cannot be detected if a 

given sensor fails.

Having seen the capabilities of the ETA Tool, the COTS software vendor expressed interest in integrating those 

capabilities into the COTS software. A government/industry partnership was subsequently implemented to conduct 

the integration. ETA Tool capabilities are now available as part of the COTS tool and also as a stand-alone software 

package through the NASA Glenn software catalog.

Ref.: Maul, William, A.; Fulton, Christopher, E., “Software Users Manual (SUM): Extended Testability Analysis 

(ETA) Tool”, NASA/CR–2011-217240, November 2011.

NASA/TM—2012-217718 22
SLS Engines Project Pre-Test Prediction and Post-Test Analysis

NASA Glenn support for the SLS Engine Project is focused on developing analytical approaches to predict 

engine performance prior to testing and to analyze test data to support post test review. 

ESMART (Embedded System Model Analysis and Reporting Tool) is a software simulation tool that is being 

developed to provide pre-test predictions of the J-2X engine and J-2X PowerPack. To generate pre-test predictions, 

an engine model with a mixture of physics-based and empirical equations is used. This simulation is capable of 

modeling both nominal and off-nominal operation. The initial data is then expanded by capturing hardware 

redundancy of the sensors and adding stochastically-based sensor noise characteristics for realism. A spreadsheetbased user interface provides a convenient mechanism for setting up the simulation/analysis. Results are generated 

in a format for compatibility with analysis tools like WinPlot. ESMART is currently being used to support the 

definition of test conditions and the selection of the red-line limits needed to protect the engine. 

An important element of post-test analysis of the engine data is understanding the health of the individual 

sensors. NASA Glenn Sensor Data Qualification (SDQ) algorithms are being used to analyze J-2X test data for 

faulty sensors. SDQ algorithms analyze signal and noise levels, and compare responses of hardware redundant 

sensors or heterogeneous sensors to identify those sensors that do not accurately reflect the physical state of the 

engine. A multi-algorithm approach and phase-dependent thresholds reduce the likelihood of false alarms. Results 

are captured in spreadsheet form where failed sensor signal information is detailed. Additionally, SDQ generates a 

WinPlot script that plots time traces for the failed sensor signals which allow experts to visually confirm the SDQ 

results.

The work discussed here has been initiated in the last couple of years and there are no publications yet on this 

work. Information on prior J-2X modeling effort is available in the reference listed below.

Ref: Sowers, T., Santi, L., Butas, J., “Selection of Sensors for J-2X Test Data Reduction”, IPS-I-04, 54th JANNAF 

Propulsion Meeting, Orlando, Florida, December 8-12, 2008.

NASA/TM—2012-217718 23
Concluding Remarks

The Controls and Dynamics Branch (CDB) at NASA Glenn Research Center is working in strong partnership 

with industry, academia and other government agencies to develop the propulsion control and health management 

technologies that will help meet NASA’s Aeronautics Research Mission and Human Exploration and Operations 

Mission objectives. For the Aeronautics Research Mission, CDB is conducting research in: Distributed Engine 

Control architectures and technologies development, Model-Based Engine Control, Active Combustion Control, and 

High Speed Propulsion System Dynamic Modeling and Control, to help meet the objectives of the Fundamental 

Aeronautics Program; Gas Path Health Management, Enhanced Engine Response Control, and Robust Propulsion 

Control to help meet the goals of the Aviation Safety Program; and health management technologies development to 

help meet the challenge for safe and efficient operation of the Space Launch System.

Our aim is to use the public resources in a most efficient manner to make a significant contribution to the 

aggressive goals that have been set by the administrator in the latest strategic plan for NASA, and to ensure that our 

activities are aligned with the goals of the NASA Missions that we participate in. We take a systems level approach 

to ensure that the various components of a control or diagnostic system work together as an integrated system to 

achieve the desired objectives. CDB also actively pursues opportunities to disseminate information on our 

technology development efforts to the aerospace research community by presenting papers at technical conferences, 

holding the GRC Propulsion Control and Diagnostics Workshop on a bi-annual basis, and making available various 

software tools for enabling advanced research in propulsion control and diagnostics.

NASA/TM—2012-217718 24

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Overview of Propulsion Controls and Diagnostics Research at NASA Glenn 

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14. ABSTRACT

With the increased emphasis on aircraft safety, enhanced performance and affordability, and the need to reduce the environmental impact of 

aircraft, there are many new challenges being faced by the designers of aircraft propulsion systems. The Controls and Dynamics Branch 

(CDB) at NASA (National Aeronautics and Space Administration) Glenn Research Center (GRC) in Cleveland, Ohio, is leading and 

participating in various projects in partnership with other organizations within GRC and across NASA, the U.S. aerospace industry, and 

academia to develop advanced controls and health management technologies that will help meet these challenges through the concept of an 

Intelligent Engine. CDB conducts propulsion control and diagnostics research in support of various programs and projects under the NASA 

Aeronautics Research Mission Directorate and the Human Exploration and Operations Mission Directorate. The paper first provides an 

overview of the various research tasks in CDB relative to the NASA programs and projects, and briefly describes the progress being made 

on each of these tasks. The discussion here is at a high level providing the objectives of the tasks, the technical challenges in meeting the 

objectives and most recent accomplishments. References are provided for each of the technical tasks for the reader to familiarize themselves 

with the details. 

15. SUBJECT TERMS

Turbofan engines; Sensors; Actuators; Fault detection; Engine control 

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