NASA Technical Memorandum 106151

Status of the Fiber Optic Control SystemIntegration (FOCSI) Program

Robert J. BaumbickLewis Research CenterCleveland, Ohio

May 1993

NASA

https://ntrs.nasa.gov/search.jsp?R=19930018864 2018-07-09T17:27:16+00:00Z

STATUS OF THE FIBER OPTIC CONTROL SYSTEM INTEGRATION

(FOCSI) PROGRAM

Robert J. BaumbickNational Aeronautics and Space Administration

Lewis Research CenterCleveland, Ohio 44135

ABSTRACT

This report presents a discussion of the progress made in the NASA/NAVY Fiber Optic Control System Integration (FOCSI) program. Thisprogram will culminate in open-loop flight tests of passive opticalsensors and associated electro-optics on an F-18 aircraft. Cur-rently, the program is in the final stages of hardware fabricationand environmental testing of the passive optical sensors andelectro-optics.

This program is a foundation for future Fly-by-Light (FBL) pro-grams. The term Fly-by-Light is used to describe the utilization ofpassive optical sensors and fiber optic data links for monitoringand control of aircraft in which sensor and actuation signals aretransmitted optically. The benefits of this technology for advancedaircraft include: improved reliability and reduced certificationcost due to greater immunity to EME (electromagnetic effects),reduced harness volume and weight, elimination of short circuitsand sparking in wiring due to insulation deterioration, lower main-tenance costs (fewer components), greater flexibility in databusprotocol and architecture, absence of ground loops and higheroperating temperatures for electrically passive optical sensors.

INTRODUCTION

Fly-by-Light is used to describe the utilization of passive opticalsensors and fiber optic data links for monitoring and control ofaircraft in which sensor and actuation signals are transmittedoptically. The benefits of this technology for advanced aircraftinclude: improved reliability and reduced certification cost due togreater immunity to EME (electromagnetic effects), reduced harnessvolume and weight, elimination of short circuits and sparking inwiring due to insulation deterioration, lower maintenance costs(fewer components), greater flexibility in databus protocol andarchitecture, absence of ground loops and higher operatingtemperatures for electrically passive optical sensors. Table Iidentifies the benefits of optical technology for aircraft.

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TABLE I

FEATURES BENEFITS

Immunity to electromagnetic Improved reliability and re-effects duced certification costs

Lower weight and volume for Increased payload and/or rangedata links

No sparking or short circuits

No ground loops

Wavelength and temporalmultiplexing

Improved safety, no danger ofexplosions or fire

Reduction of signal noise

Greater flexibility in design-ing protocol and architecture

If optical technology is to replace electrical/mechanical technol-ogy in control and monitoring functions of advanced aircraft, itmust be demonstrated that optical technology can provide one or allof the following: solution of an existing problem; provide newfunctional capability; lower direct operating or acquisition costs;and/or improve safety. In addition, credible flight demonstrationsmust be performed and substantial in-flight operating data oncomponents and optical subsystems must be obtained to establishreliability data on optical components and systems. Standards forconnectors, fiber cables and interfaces along with specificationsfor testing must be established. Retraining of maintenance person-nel will also be required.

The ADOCS (Advanced Digital Optical Control System) (ref. 1) pro-gram was the first large scale effort to demonstrate the use ofoptical sensors in active flight control systems for helicopters.Optical sensors providing information to the helicopter controlincreased ballistic and electromagnetic survivability along withreduced weight, volume and maintenance time. In this programoptical sensors measured the position of flight control surfacesand hydraulic pressure. The optical sensors were integrated withexisting mechanical and hydraulic components. Flight tests wereconducted in 1987. Total flight time accumulated was over 126 hourswithout any major failures of the optical sensors.

A feasibility study (ref. 2-3), initiated in 1985 by NASA/DOD,concluded that fiber optic technology had the potential to improveoperational reliability of advanced aircraft because of the attri- A,butes listed in table I. A program, cofunded by NASA and the NAVY,called FOCSI (Fiber Optic Control System Integration), evolved witha design study (ref. 4-6) of the architecture for full opticalflight and propulsion control of aircraft. Following the designstudy, a hardware development program was initiated to build,

environmentally test and fly (in piggyback fashion) a represen-tative set of passive optical sensors for the flight and propulsionsystem of an advanced F-18 aircraft (fig. 1). In addition to pro-viding credible flight demonstrations of optical sensors andoptical components in an advanced aircraft environment, the FOCSIprogram also involved a significant number of sensor vendors withexperience in this technology area. As a result of the flight teststhe program will provide information on the installation, mainten-ance and operational problems in advanced aircraft. The remainingpart of this report will deal with the FOCSI hardware developmentprogram.

FOCSI HARDWARE DEVELOPMENT

Prior to the flight tests with the full set of FOCSI hardware, somepreliminary flight tests were conducted with four passive, opticalsensors installed and flown on another research aircraft (F15 HIDECtestbed) at NASA Dryden. This program was valuable to the vendorswho participated, enabling them to evaluate sensor performancethrough comparison with the production sensors. The optical sensorsflown included: a compressor inlet temperature sensor, (which usesfluorescent decay); PTO (power takeoff shaft) speed (which usesFaraday magneto-optic effect); turbine discharge gas temperature(which uses the blackbody radiation principle); and, PLA (powerlever angle, which uses a wavelength division multiplexed (WDM)code plate to measure position). Preliminary flight test data forthese sensors are shown in figure 2. Generally the sensors per-formed well and compared favorably with the production sensors.These sensors have flown for a minimum of 6 hours with some of thesensors collecting up to 12 hours of flight time. Valuable informa-tion on installation problems and handling problems was obtainedfrom these preliminary tests.

OPTICAL HARDWARE FOR PROPULSION CONTROL

The FOCSI propulsion sensors are shown in figure 3. The type ofmeasurement along with the optical modulation technique and thevendor supplying the sensor are also shown in this figure. Typicalsensors delivered for the flight tests are shown in figure 4. Thesensors were all environmentally tested to the MILSPEC requirementsfor engine mounted hardware. Sensor range specifications are shownin table II.

A wide variety of physical phenomena are employed in these sensorsfor converting the measurand into an optical effect that can bemeasured in an aircraft environment. Engine air inlet temperatureis measured by taking advantage of the temperature dependence ofthe fluorescence decay rate of certain crystals. The compressorinlet temperature sensor uses the Fabry Perot principle whichfilters or attenuates (through destructive interference) particular

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wavelengths, depending on the optical path length of the FabryPerot cavity. The optical path length changes with temperaturethrough both a change in cavity spacing and index of refraction ofthe material in the cavity. Fan speed is measured by using thePockels effect. The Pockels effect is the change in index of 'refraction of certain birefringent crystals when subjected to anelectric field. The electric field variation is caused by couplinginto the- eddy current sensor used to measure fan speed. Compressorspeed is measured by using the Faraday effect. The Faraday effectcauses rotation of the polarization of incoming light when thelight passes through certain isotropic materials which have strongmagneto-optic characteristics. The optical speed sensor is locatedin the alternator. The magnetic field variation results from therotor of the alternator. Turbine discharge gas temperature ismeasured by detecting and measuring the amount of blackbody radia-tion, predictable from Planck's law, from a material heated by thehot gas. Actuator positions are measured by using WDM code plate orWDM (2 lambda) analog ratio. These WDM sensors operate on part orall of the spectrum of broad band light. The broad band light isdispersed unto the modulating medium (i.e., code plate or variabletransmissive medium.

The sensors will be integrated with a centralized electro-opticsmodule. The electro-optic architecture (EOA) is discussed furtherin the report.

OPTICAL HARDWARE FOR FLIGHT CONTROL

The FOCSI flight control sensors are shown in figure 5. Similarinformation, as provided for the propulsion sensors on the vendors,modulation techniques and parameters measured is provided in thisfigure. These sensors were also environmentally tested to MILSPECrequirements. Table II provides specifications for the sensorranges.

Most of the sensors in the flight control measure position. Theposition sensors cover a number of different optical modulationtechniques (WDM digital, analog, etc.). Other flight controlsensors measure pressure using an analog modulation techniquecalled microbending and an air data temperature sensor which usesthe same fluorescence decay optical modulation technique as is usedfor measuring engine inlet temperature.

Figure 6 is a drawing of the optical fiber runs in the aircraftalong with the number of connectors in each optical circuit.

Flight tests of the optical hardware will be performed on the F-18System Research Aircraft (SRA) at NASA Dryden. These tests will bepiggyback tests of the optical hardware with the data from theoptical sensors compared to comparable production sensors.

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TABLE II

MEASUREMENT

Inlet temperatureCompressor inlet temperatureCompressor speedFan speedCompressor variable geometryFan variable geometryTurbine exhaust gas temperatureExhaust nozzle positionStabilizer positionRudder positionTrailing edge flap (TEF)Leading edge flap (LEF)Throttle lever angle (TLA)Nose wheel steering (NWS)Total pressure (air data)Air data temperaturePitch stick positionRudder pedal position

SPECIFICATIONS FOR RANGES

-65 to 300 degrees F-65 to 540 degrees F817 to 18553 rpm +/- .1% FS3981 to 15267 rpm +/- .1% FS-3.5 to 52.5 degrees0 to 2.7 inches700 to 2500 degrees F0 to 6.923 inches+/- 3.56 inches+/- .665 inches+/- 4.05 inches+/- 67.5 degrees+/- 65 degrees+/- 75 degrees1.25 to 80 inches Hg-100 to 450 degrees F+2.02 to -1.01 inches+/- .75 inches

ELECTRO-OPTIC ARCHITECTURE FOR PROPULSION AND FLIGHT SENSORS

One objective of this program is to develop a standard interfacefor the optical system. The sensor and electro-optics designers arerequired to meet the interface specifications for wavelength,optical power and data rates. The standard interface allows theelectro-optics to handle any type of optical sensor, attached toany connector port, requiring only a change in the software toaccommodate the sensors. Table III identifies the cards and cardfunctions for the electro-optics module.

TABLE III

Decode CPU

CARD FUNCTION

Supplies broadband light(750nm-950nm) to the sensors.Uses two LED's

Charge-coupled device (CCD)optical to electrical converter

Accepts electrical signals fromoptical receiver card and con-ditions data for CPU

Processes the data and convertsto engineering units

ELECTRO-OPTICS CARD

A/D optical source card

A/D optical receiver

Data acquisition card (DAC)

5

Time rate of decay (TRD) Custom card for fluorescencesensor

EOA CPU Conditions and formats data for1553 bus

Converts the electrical 1553 to1553/1773 converter optical 1773 data format

Power supply Supplies power to all modules

The flight control electro-optics module and cards installed in themodule are shown in figure 7 (a). A diagram of the electro-opticsis shown in figure 7 (b). The optical source card contains 10 LEDpairs (each pair has a 150 nm bandwidth). The LED's feed a 10 x 10port passive coupler connected to optical fibers, which are in turnconnected to the sensors. The large optical bandwidth is requiredby the digital code plate sensors. A smaller bandwidth source couldaccommodate the other sensors. The optical sources operate continu-ously 9 millisec (ms) on and 1 ms off. The 1 ms off period isrequired to clock out the data from the CCD array. The opticalreceiver consists of a 2-dimensional charge-coupled device (CCD)which is self-scanning. The optical signal from each sensor isfocused on a specific location of the 2-dimensional array. Sensor1 occupies row 1 followed by 3 blank rows, followed by sensor #2with 3 blank rows, etc. The sensor signals enter the opticalreceiver and are focused unto the CCD array. Prior to focussing,each optical signal passes through a dispersing element that sepa-rates the 150 nm modulated signal into as many as fifteen 10 nmstripes. The CCD array output is processed and formatted by the CPUand passed to the 1553/1773 processor card which sends the signalsto the data collection system onboard the aircraft. The fluores-cence sensor requires a separate sensor /electro-optics card toprovide a different specific wavelength range and to process theresulting optical signal. In the propulsion EOA, separate cards forthe fluorescence, blackbody and speed sensors are required.

The propulsion EOA has separate electro-optics cards for the speedsensors, exhaust gas temperature sensor and inlet temperaturesensor. The remaining sensors interface with the same EOA as usedin the flight control.

The configuration for collection of the data on the FOCSI aircraftis shown in figure 8. Each EOA provides a 1553 output data formatwhich is converted to the optically equivalent 1773 format and isthen transmitted to the aircraft data collection system where it isconverted back to the 1553 format for recording. The electro-opticsused for the conversion between 1553/1773 and 1773/1553 formats isbeing provided to the FOCSI program by the Navy. The hardware is aproduct of the Navy SHARP program (Standard Hardware for AvionicsResearch Program). The optical signals can then be compared to the

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production electrical sensors which are located, in most casesadjacent to the optical sensors.

CONCLUDING REMARKS

Successful transition of Fly-by-Light technology to productionaircraft will depend on flight demonstrations similar to those inthe FOCSI program. Significant in-service time is required toestablish a reasonable history for the technology. The true bene-fits of this technology and it's impact on safety and aircraftcosts have yet to be evaluated. However, continued testing andcontinuous improvement in components must continue or this technol-ogy may never achieve it's full potential. The experience obtainedfrom this program is valuable in promoting optical technologytransfer to production aircraft, both military and commercial. Thisprogram will yield valuable information on the installation, main-tenance, troubleshooting and installed testing which will betransferred to the aircraft industry. This program also involves alarge number of vendors who have gained valuable experience inpackaging their particular product for an aircraft environment.

Problems of standardization of optical components as well asproduction challenges associated with integrating optical systemsinto aircraft need to be addressed. To complete this phase of theFly-by-Light program, a closed-loop flight demonstration of all-optical closed-loop operation of one or more control surfaces andthe propulsion system needs to be performed. A demonstration ofactive control will establish the true credibility of thistechnology.

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REFERENCES

1. Dones, F.; and Glusman, S.I.: Advanced Digital Optical ControlSystem (ADOCS). Volume I. U.S. Army report USAAVSCOM TR90-D-11A, Nov. 1990. (Available from DTIC as AD-B152137L.)

2. Poumakis, D.J.; and Davies, W.: Fiber-Optic Control SystemIntegration. NASA CR-179569, 1986.

3. Poppel, G.L.; Glasheen, W.M.; and Russell, J.C.: Fiber-OpticControl System Integration. NASA CR-179568, 1987.

4. Poppel, G.L.; and Glasheen, W.M.: Electro-Optic Architecturefor Servicing Sensors and Actuators in Advanced AircraftPropulsion Systems. NASA CR-182269, 1989.

5. Seal, D.W.: Multiplexing Electro-Optic Architectures forAdvanced Aircraft Integrated Flight Control Systems. NASACR-182268, 1989.

6. Glomb, W.L.: Electro-Optic Architecture (EOA) for Sensors andActuators in Aircraft Propulsion Systems. NASA CR-182270,1989.

/M51are

400

Airspeed 200I

02600

Altitude 2400

2200

16000Optical sensor

— — — Production sensorCore — —

speed, 14000(RPM)

12000 I I I

0 10 20 30 40 50

Time of flight (sec)

(a) Core speed sensor; Faraday effect (Bendix Corp.).

400

Airspeed 200

020000

Altitude 10000

0

Optical sensor

Turbine 2000 — — — Production sensordischarge

gas 1000temperature

F) 0 20 40 60 60 100 120Time of flight (sec)

(b) Turbine discharge gas temperature; blackbody radiation (Conax Buffalo).

Figure 2—Flight test data of FOCSI sensors from F15 flights.

9

140

120

100Power 80leverangle, 60(deg)

40

20

015:41:45 15:42:15 15:42:45 15:43:15 15:43:45

Time

600

1 Airspeed 400

20080000

Altitude 40000

0

Compressor 400 Optical sensor

inlet – – – Production sensortemperature 0

-4000 200 400 600 800 1000 1200 1400 1600

Time of flight (sec)(c) Temperature sensor, time rate decay (Rosemount Corp.)

Optical sensor– _ – – Production sensor

(d) NASA Lewis PLA sensor, WDM digital.Figure 2.—Concluded.

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Engine sensor, variable exhaustnozzle (BEJ)

Fan variable geometry 7 Compressor inletlinear position sensor; I temperature sensor; /—Turbine exhaust gasLitton/WDM digital code —7 1 Puget Sound/Fabry Perot / temperature sensor;

Inlet temperature sensor 1i Compressor variable geometry// Conax/BlackbodyRose mount/flourescent rotaposition sensor;decay RFIM/phA —1— +ice AB flame detector;

Core speed sensor; LBendix/Faraday effect -J Fan speed sensor;

Banks/Pockets effect`— Vaiable exhaust nozzle

linear position sensor;BEVWDM analog ratio

Figure 3.— FOCSI propulsion sensors.

Engine sensor Engine sensorCore speed sensor Turbine discharge temperature

Faraday effect Blackbody radiation(Bendix Corp.) (Conax Buffalo)

Engine sensor, Light-off detector (AMETEK)

Engine sensor, compressor variablegeometry (BEI)

Aircraft sensor Nose wheel steeringWDM (Allied Signal Bendix)

Figure 4.—FOCSI flight qualified optical sensors.

11

Rudder(Litton Poly-Scientific)

WDM LinearStabilizer

(Litton Poly-Scientific)WDM Linear—

T-- Trailing Edge Flap(BEI Motion Systems)

i Analog Gradient Filter Linear

- Pitch Stick(BEI Motion Systems)Analog Gradient Filter Linear

Power Lever Control(Litton Poly-Scientific)

WDM Rotary— - j

Air Data Temperature(Rosemount, Inc.)Fluorescent Time Rate of Delay

- Rudder Pedal(Litton Poly-Scientific)

\ WDM Lineari

Leading Edge Flap(Allied Signal - Bendix) r

WDM Rotary

iTotal Pressure

(Babcock & Wilcox)Analog Microbend

Figure S.— FOCSI flight control sensors.

i vi

Electro-Optic Architecture(Litton Poly-Scientific)

12

J

Rudder Power Lever Control

(Litton Poly-Scientific) (Litton Poly-Scientific)

Stabilizer Air Data Temperature(Litton Poly-Scientific) (Rosemount, Inc.)

Aileron Pitch Stick(BEI Motion Systemsf-- (BE/ Motion Systems)

Leading Edge Flap Rudder Pedal

(Allied Signal-Bendix) (Litton Poly-Scientific)

Electro-Optic Architecture Total Pressure(Litton Poly- Scientific) (Babcock & Wilcox)EOA Nose Wheel Steering

(130 Motion Systems)250 Inches

RNose Wheel Steering Sensor

650 Inches

Leading Edge Flap Sensor

7001nches

Power Lever Control Sensor

550 InchesRudder Sensor

575 Inches Stabilizer Sensor

300 InchesRudder Pedal Position Sensor

300 Inches Air Data Temperature Probe

Fiber Length 200 Inches Pitch Stick Position SensorNo Bulkhead Connectors

550 Inches

Aileron Sensorr--r Air DataFiber Optic Total Computer

Pressure Sensor New Existing Pneumatic LinePneumatic o0o

Line

48 Inches Pitot Tube

= Bulkhead Connectors Pneumatic Tee Section

Figure 6.—Aircraft optical fiber runs and connectors for FOCSI.

13

sEws ,module ^ 1553 board'

^

/

^'

gig

^ ^^ ~^, 1773 board*

^~ -Supplied uy Naval x"ivn:csCenter

(a) poos/eoA built »y LITTON, Aircraft sVAaemsmodule.

----- ---------

o tical fit ,,: , Parallel11 ZAD

100/140 micronoptical fiber Source card I

Drive Data acquisition card

Outgoing spectrum ParallelCL 110Drive

CL Cz

750 950

DriveControlstate machine

Address

C

-\7 decode

WDIVI SRAM

AnalogReceiver card

WDM(3 modules)

Analog 0

processing100/140 micron Fiber

optical fiber array

bulkhead I GRIN lens ­: (View from

CCD

;;;OGor at, ^n 2—9 array

(b)vvoIVIsoA functional block oiagmm.

Figure 7­ EI ectro- optics unit for flight control.

Processorcard

2

^

14

Airfame EOA (MCAIR)Flight control Optical

Electrical data . 1-TRD• 1-WDM source

data • 1-WDM receiver0 0 • 1-CPU /1 553 RT0 • 1-1553 controller

• 2-1773 converters

9data

• 1 -Power supplyAirborne data

acquisition --- interface --- Fiber optic data bus (NASA) Electrical data bus

O O I data OpticalL----

Engine EOA (General Electric)• 1-WDM position

0 0 0 • 1-WDM speedMission

computerMaintenancesignal data

Electrical data • 1-T1 tempO O • 1-T5 temp

• 1-LOD EOA(Bus converter • 1-1573 bus interface

controller) • 1-Power supply

Figure 8.—FOCSI architecture for on board flight test data collection

15

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

May 1993 Technical Memorandum4. TITLE AND SUBTITLE 5- FUNDING NUMBERS

Status of the Fiber Optic Control System Integration (FOCSI) Program

WU-505-62-506. AUTHOR(S) -

Robert J. Baumbick

7- PERFORMING ORGANIZATION NAMES) AND ADDRESS(ES) 8. PERFORMING ORGANIZATIONREPORT NUMBER

National Aeronautics and Space AdministrationLewis Research Center E-7832Cleveland, Ohio 44135-3191

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National Aeronautics and Space AdministrationWashington, D.C. 20546-0001 NASA TM-106151

11. SUPPLEMENTARY NOTES

Responsible person, Robert J. Baumbick, (216) 433-3735.

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

Unclassified - UnlimitedSubject Category 35

13. ABSTRACT (Maximum 200 words)

This report presents a discussion of the progress made in the NASA/NAVY Fiber Optic Control System Integration(FOCSI) program. This program will culminate in open-loop flight tests of passive optical sensors and associatedelectro-optics on an F-18 aircraft. Currently, the program is in the final stages of hardware fabrication and environ-mental testing of the passive optical sensors and electro-optics. This program is a foundation for future Fly-by-Light(FBL) programs. The term Fly-by-Light is used to describe the utilization of passive optical sensors and fiber opticdata links for monitoring and control of aircraft in which sensor and actuation signals are transmitted optically. Thebenefits of this technology for advanced aircraft include: improved reliability and reduced certification cost due togreater immunity to EME (electromagnetic effects), reduced harness volume and weight, elimination of shortcircuits and sparking in wiring due to insulation deterioration, lower maintenance costs (fewer components), greaterflexibility in databus protocol and architecture, absence of ground loops and higher operating temperatures forelectrically passive optical sensors.

14. SUBJECT TERMS 15. NUMBER OF PAGES17

Fiber optics; Optical sensors; Fiber optic based controls; Fly-by-light 16. PRICE CODEA02

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