at lewis field glenn research center controls and dynamics branch engine performance deterioration...

Controls and Dynamics Branch at Lewis FieldGlenn Research Center

Engine Performance Deterioration Mitigation Control- A retrofit approach

Dr. Sanjay GargBranch Chief

Ph: (216) 433-2685FAX: (216) 433-8990

email: [email protected]://www.lerc.nasa.gov/WWW/cdtb

Presented at: Aerospace Guidance and Control System Committee MeetingBoulder, CO, March 1, 2007

Research Performed by: Jonathan Litt – Army Research LabShane Sowers – Analex


OverviewOverview

• Motivation

• Architecture Description

• Steady State Evaluation

• Transient Evaluation

• Piloted Simulation

• Conclusions


Source: AIA PC 342 Committee on Continued Airworthiness Assessment Methodology Initial Report on Propulsion System and APU Related Aircraft Safety Hazards 1982 Through 1991

Propulsion Related Accidents & Incidents 1982 - 1991

Includes all Part 25 Category Transports Aircraft Data - Turboprop, Low Bypass, High Bypass Turbofans. (Does not include data from former Soviet Union and satellite countries’ products.)

0

5

10

15

20

25

30

35

40

Nu

mb

er

of

Even

ts

Level 4 - Severe Consequenses

Level 3 - Serious Consequenses

Uncontained

Propulsion System Malfunction + Inappropriate Crew Response

(PSM+ICR)


Example PSM+ICR Turbofan AccidentsExample PSM+ICR Turbofan Accidents

Rejected Takeoff Events at or above V1 (30 Turbofan Events, 5 Hull Losses, 1 Fatal)

• 13 June 1996; Garuda Indonesian Airways DC10-30; Fukuoka, Japan (Contributing event: fracture of a HPT stage 1 blade)

• 19 October 1995; Canadian Airlines DC10-30ER; Vancouver, Canada (Contributing event: progressive HPC blade failures)

Shutdown / Throttle Wrong Engine (27 Turbofan Events, 2 Hull Losses, 1 Fatal)

• 8 January 1989; British Midland Airways 737-400; near East Midlands Airport, UK (Contributing event: fan blade failure)

Loss of Control (14 Turbofan Events, 11 Hull Losses, 7 Fatal)

• 24 November 1992; China Southern Airlines 737-300; Guangzhou, China (asymmetric thrust - stuck throttle)

• 31 March 1995; Tarom Romanian Airlines A310; near Balotesti, Romania (asymmetric thrust - stuck throttle)

Autonomous Propulsion System TechnologyAutonomous Propulsion System Technology- Reduce PSM+ICR incidents

Reduce/Eliminate human dependency in the control and operation of the propulsion system

Diagnostics/PrognosticsAlgorithms Are Being Developed

Demonstrate Technology in a relevant environment

Vehicle Management System

Self-Diagnostic Adaptive Engine Control System

• Performs autonomous propulsion system monitoring, diagnosing, and adapting functions

• Combines information from multiple disparate sources using state-of-the-art data fusion technology

• Communicates with vehicle management system and flight control to optimize overall system performance

Engine Condition/Capability

Performance Requirement

Model-Based Fault Detection

Fuzzy Belief

Network

Data Fusion

p

FADEC

u

controlsignals

Sensoroutput

PLA

Real EngineClosed Loop Control

NMPCmin J

Optimizer

State/Parameter Est. +

-

xP ˆ,

y

y

vw

Eng. Model

Eng. Model

REF

p

FADEC

u

controlsignals

Sensoroutput

PLA

Real EngineClosed Loop Control

NMPCmin J

Optimizer

State/Parameter Est. +

-

xP ˆ,

y

y

vw

Eng. Model

Eng. Model

REF


PILOT WORKSHOP at GRC - 2002PILOT WORKSHOP at GRC - 2002

OBJECTIVE: Get direct input from pilots that will be used to help define the APST project plan

GOALS:• Under all flight regimes, identify what processes or procedures associated with propulsion system management could be candidates for autonomous operation• Identify what propulsion system information or control features will be helpful in managing the integration of propulsion with flight control for normal and abnormal operations• Identify what “sensory” information, other than the engine instruments, is used by the pilots in operation and control of the propulsion system for all flight regimes


• The conclusions of 2002 NASA Glenn Pilot Workshop fell into three main categories– Control

• Thrust asymmetry control• Thrust response rate variation between engines• Propulsion Controlled Aircraft• Operating envelope expansion for emergency operation

– Diagnostics• Fault detection and isolation for vibration and potential

engine shutdowns• Health and usage monitoring

– Indications to pilots• Fault signals• Vehicle status under autopilot, especially concerning

throttle movement and split throttles

Results from PILOT WORKSHOPResults from PILOT WORKSHOP

• Engine Control Logic Is Developed Using A “Nominal” Engine Model…But “Nominal” Engine Does Not Exist

TimePLA

Thr

ust

Nominal Engine withFixed Control Normal

Variation

NormalVariation

Degraded Engine withFixed Control

Mea

sure

of

Per

form

ance

Typical Current Engine ControlTypical Current Engine Control

Control Logic

Limit Logic

EngineFan Speed Schedule

PLA N2c

N2

eN2 WFc WF y

FADEC – Full Authority Digital Engine Control

+

-

• Since Thrust cannot be measured, another parameter such as Fan Speed (N2), which correlates to Thrust, is regulated

Asymmetric Thrust Accident InformationAsymmetric Thrust Accident Information• Aircraft asymmetric thrust accidents have been identified as a concern in the

AIA/AECMA study on PSM+ICR [1]: “A further area of concern was power asymmetry resulting from a slow power loss, stuck

throttle, or no response to throttle coupled with automatic controls. Flying aids, such as the auto-pilot and auto-throttle, can mask significant power asymmetry until a control limit is reached. At this point, the flight crew has to intervene, understand the malfunction, and assume control of an airplane which may be in an upset condition. Better indications and/or annunciations of power asymmetry could warn crews in advance and allow them time to identify the problem and apply the appropriate procedures.”

• The following description of past asymmetric thrust accident is taken from an FAA Policy Statement on aircraft thrust management systems (TMS) [2]:

1. Sallee, G.P., and Gibbons, D.M., “AIA/AECMA Project Report on Propulsion System Malfunction Plus Inappropriate Crew Response (PSM+ICR), Volume I,” (Aerospace Industries Association and The European Association of Aerospace Industries, November 1, 1998).

2. FAA Policy Statement, “FAA Policy on Type Certification Assessment of Thrust Management Systems,” FAA Policy Statement Number ANM-01-02, March 2002. http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/0f670523ec44af9f86256ce9004c4539

March 31, 1995, Tarom Airbus Model A310-300, Bucharest, Hungary: The airplane crashed shortly after takeoff. The Romanian investigating team indicated that the probable cause of the accident was the combination of an autothrottle failure that generated asymmetric thrust and the pilot's apparent failure to react quickly enough to the developing emergency.

Report Conclusion: Data from these accident investigations have provided evidence that it is incorrect to assume that the flightcrew will always detect and address potentially adverse TMS effects strictly from inherent operational cues.

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/0f670523ec44af9f86256ce9004c4539


Model-Based Controls and DiagnosticsModel-Based Controls and Diagnostics

GroundLevel

Engine Instrumentation• Pressures• Fuel flow• Temperatures• Rotor Speeds

Actuator Commands• Fuel Flow• Variable Geometry• Bleeds

Ground-Based Diagnostics• Fault Codes• Maintenance/Inspection

Advisories

On-Board Model & Tracking Filter

• Efficiencies • Flow capacities• Stability margin• Thrust

Selected Sensors

On Board

SensorValidation &

Fault Detection

Component Performance

Estimates

Sensor Estimates

Sensor Measurements

Actuator Positions

Adaptive Engine Control

• Applicable only to future systems• Still in research mode with many technical changes to overcome


THE NEEDTHE NEED

• There is a need to develop a “simplified” approach to maintaining throttle to thrust relationship in the presence of engine degradation, and detecting thrust asymmetry situations. The approach “shall”:

• Be retrofitable to existing FADEC systems

• Leverage the extensive investment in existing FADEC control logic – specially in terms of limits imposed for operational life and safety

• Be mostly software/logic additions – not require any new sensors or actuation hardware

• Have “reasonable” development, verification and implementation costs

Control Logic

Limit Logic

EngineFan Speed Schedule

PLA

T_des

N2

eN2 WFc WF y

FADEC – Retrofit

Thrust Model

Thrust Estimator

+-

N2c Modifier

delN2c

N2cmod +

+

-

T_est

Addition to Existing FADEC Logic

Engine Performance DeteriorationEngine Performance Deterioration Mitigation Control (EPDMC)Mitigation Control (EPDMC)

• The proposed retrofit architecture:

• Adds the following “logic” elements to existing FADEC:• A model of the nominal throttle to desired thrust (T_des) response• An estimator for engine thrust (T_est) based on available measurements• A modifier to the Fan Speed Command (delN2c) based on the error between desired and estimated thrust

• Since the modifier appears prior to the limit logic, the operational safety and life remains unchanged

EPDMC Testbed ArchitectureEPDMC Testbed Architecture

• Engine– Full envelope, nonlinear

Component Level Model– Represents a large

commercial turbofan engine

Parts of EPDMC Testbed ArchitectureParts of EPDMC Testbed Architecture

• Engine Control– Typical Full Authority

Digital Engine Control (FADEC) type controller

– PLA in, fuel flow out

– Fan speed is controlled


• Nominal Engine Model– Piecewise linear model– Scheduled on percent

corrected fan speed


• Thrust Estimator– Piecewise linear Kalman filter– Based on Nominal Engine Model– Provides optimal estimation of variables in a least

squares sense subject to sensors selected


• PI Control with Integrator Windup Protection– Performs outer loop PLA

adjustment– Stops integrating error when

PLA limit is reached


EPDMC EvaluationEPDMC Evaluation

• The purpose of the evaluation is to determine– The steady state accuracy of the thrust estimator at

many operating points and degradation levels with various types of uncertainty (model mismatch, nonlinearities, noise)

– How well the outer loop control is able bring the thrust back to the nominal level in steady state

– How well the outer loop control is able to maintain a nominal thrust response over a typical flight trajectory with a deteriorated engine


• Evaluation was performed in two phases– Steady State– Transient

• Assumptions– 10 health parameters, two each (efficiency and flow

capacity) for each of the five major components– Worst case degradation 5% in each health parameter– Health parameters degrade at their own pace, pretty

much independent of each other no restrictions placed on simulated deterioration except upper limit of 5%

EPDMC EvaluationEPDMC Evaluation

Outer Loop Control off

Steady State EvaluationSteady State Evaluation• Thrust performance deterioration with engine degradation

• Thrust estimation error is << Thrust deterioration => Thrust estimate can be used effectively for performance recovery

Outer Loop Control on

Steady State EvaluationSteady State Evaluation

Outer Loop Control off

• EPDMC maintains “close” to nominal thrust performance- even with high levels of engine degradation


Transient EvaluationTransient Evaluation

• Trajectory is takeoff/climb/cruise

• It passes through or near the linearization points

• No airframe is included, the engine is operating as if it were in a wind tunnel


Transient EvaluationTransient Evaluation

• Nominal Engine with and without Outer Loop Control


Transient EvaluationTransient Evaluation• Degraded Engine with and without Outer Loop Control


Flight SimulatorFlight Simulator

THROTTLESTICK

PEDALS

INSTRUMENTATIONDISPLAY

HEADS UPDISPLAY

SCREEN

““Piloted” Evaluation of ArchitecturePiloted” Evaluation of Architecture

Segment 1 2 3 4 5

Fan Speed 86% 90% 88% 82% 86%

Indicated Airspeed

290 knots 290 knots 290 knots 290 knots 290 knots

Heading 270º 270º 270º 270º 270º

Altitude 32,000 feet

Climb 33,000 feet

descend 32,000 feet

Duration 3 minutes - 3 minutes - 3 minutes

• Pilot-in-the-loop in a fixed-base simulator• Maintain airspeed and heading while following profile - Three cases: Nominal, 1 engine degraded – OLC Off/On


Pilot Workload During Transient FlightPilot Workload During Transient Flight

Very ClearIncrease inWorkload WithOuter LoopControl Off


ConclusionsConclusions• Developed a controls architecture that would maintain throttle

to thrust relationship as the engine degrades– Addresses one of the major issues of propulsion related workload

identified during a pilot workshop– Requires “minor” additions to existing FADEC logic– Preliminary simplified simulation results encouraging

• Current research focusing on implementing the architecture on the fan speed correction over the whole engine operating envelope and performing more detailed evaluations

• Need to address some of the potential challenges for implementation:– Pilots are used to relating throttle setting to fan speed– Acoustics issues related to two engines running at different but very

close fan speeds (Beat frequency)

at lewis field glenn research center controls and dynamics branch engine performance deterioration...

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propulsion system management

dynamics branch source

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takeoff events