Engine Performance Deterioration Mitigation Control - A retrofit approach

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Engine Performance Deterioration Mitigation
Control- A retrofit approach

• Dr. Sanjay Garg
• Branch Chief
• Ph [phone]
• FAX [phone]
• email sanjay.garg_at_nasa.gov
• http//www.lerc.nasa.gov/WWW/cdtb

Presented at Aerospace Guidance and Control
System Committee Meeting Boulder, CO, March 1,
2007 Research Performed by Jonathan Litt
Army Research Lab Shane Sowers Analex
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Overview

• Motivation
• Architecture Description
• Steady State Evaluation
• Transient Evaluation
• Piloted Simulation
• Conclusions

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Propulsion Related Accidents Incidents 1982 -
1991
Source AIA PC 342 Committee on Continued
Airworthiness Assessment Methodology Initial
Report on Propulsion System and APU Related
Aircraft Safety Hazards 1982 Through 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.)
Uncontained
Propulsion System Malfunction Inappropriate
Crew Response (PSMICR)
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Example PSMICR 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)

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Autonomous Propulsion System Technology- Reduce
PSMICR incidents
Reduce/Eliminate human dependency in the control
and operation of the propulsion system
Engine Condition/Capability
Performance Requirement
Demonstrate Technology in a relevant environment
Diagnostics/PrognosticsAlgorithms Are Being
Developed

• 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

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PILOT 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

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Results from PILOT WORKSHOP

• 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

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Typical Current Engine Control

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

• Engine Control Logic Is Developed Using A
  Nominal Engine ModelBut Nominal Engine Does
  Not Exist

Nominal Engine with Fixed Control
Normal Variation
Normal Variation
Measure of Performance
Thrust
Time
PLA
Degraded Engine with Fixed Control
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Asymmetric Thrust Accident Information

• Aircraft asymmetric thrust accidents have been
  identified as a concern in the AIA/AECMA study on
  PSMICR 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

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.

1. Sallee, G.P., and Gibbons, D.M., AIA/AECMA
   Project Report on Propulsion System Malfunction
   Plus Inappropriate Crew Response (PSMICR),
   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/0/0f670523ec44a
   f9f86256ce9004c4539

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Model-Based Controls and Diagnostics

• Actuator
• Commands
• Fuel Flow
• Variable Geometry
• Bleeds

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

Actuator Positions
Adaptive Engine Control

• On-Board Model
• Tracking Filter
• Efficiencies
• Flow capacities
• Stability margin
• Thrust

Component Performance Estimates
Selected Sensors
Sensor Validation Fault Detection
Sensor Estimates
Sensor Measurements
On Board

• Ground-Based Diagnostics
• Fault Codes
• Maintenance/Inspection Advisories

Ground Level

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

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THE 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

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Engine Performance Deterioration 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

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EPDMC Testbed Architecture

• Engine
• Full envelope, nonlinear Component Level Model
• Represents a large commercial turbofan engine

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Parts of EPDMC Testbed Architecture

• Engine Control
• Typical Full Authority Digital Engine Control
  (FADEC) type controller
• PLA in, fuel flow out
• Fan speed is controlled

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Parts of EPDMC Testbed Architecture

• Nominal Engine Model
• Piecewise linear model
• Scheduled on percent corrected fan speed

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Parts of EPDMC Testbed Architecture

• 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

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Parts of EPDMC Testbed Architecture

• PI Control with Integrator Windup Protection
• Performs outer loop PLA adjustment
• Stops integrating error when PLA limit is reached

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EPDMC 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

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EPDMC Evaluation

• 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

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Steady State Evaluation

• Thrust performance deterioration with engine
  degradation

Outer Loop Control off

• Thrust estimation error is ltlt Thrust
  deterioration
• gt Thrust estimate can be used effectively for
  performance recovery

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Steady State Evaluation
Outer Loop Control off
Outer Loop Control on

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

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Transient 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

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Transient Evaluation

• Nominal Engine with and without Outer Loop
  Control

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Transient Evaluation

• Degraded Engine with and without Outer Loop
  Control

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Flight Simulator
INSTRUMENTATION DISPLAY
HEADS UP DISPLAY
SCREEN
THROTTLE
STICK
PEDALS
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Piloted Evaluation of Architecture

• 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

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
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Pilot Workload During Transient Flight
Very Clear Increase in Workload With Outer
Loop Control Off
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Conclusions

• 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)