A program was completed with joint industry and government funding to apply fiber optic technologies to aircraft. The technology offers many potential benefits. Among them are increased electromagnetic interference immunity and the possibility of reduced weight, increased reliability, and enlarged capability by redesigning architectures to use the large bandwidth of fiber optics. Those benefits can be realized if fiber optics meets the unique requirements of aircraft networks. Many independent efforts have been made in the development of the systems, known as cable plants, to link opto-electronic components. The FLASH program built on that work. Over the last two years, FLASH expanded on the cable plant efforts by building components based on a cohesive aircraft plant system concept. The concept was rooted in not just optical performance, but also cost, manufacturing, installation, maintenance, and support. To do that, the FLASH team evaluated requirements, delineated environmental and use conditions, designed, built, and tested components, such as cables, connectors, splices and backplanes for transport aircraft, tactical aircraft, and helicopters. In addition, the FLASH team developed installation and test methods, and support equipment for aircraft optical cable plants. The results of that design, development, and test effort are reported here.

Until now, there has been no reasonably priced high-density avionics fiber optic connector. AVMAC^TM connector assemblies, designed to meet this need, consist of Berg AVMAC connectors (F/O contacts), Gore ribbon cable, and HiRelco^TM special self-locking plugs and receptacles. Berg Electronics' MACII multifiber array connector has been used in the telecommunications industry for over 10 years. The 18-fiber version was modified to meet the avionics environment, by using high temperature plastic and epoxy. Also, modified cable assembly techniques were developed for the special cable used. W.L. Core and Associates designed and manufactured the high temperature ruggedized ribbon cable, using patented GORE-TEX^TM ribbon buffer to protect the 18 polyimide coated fibers in the harsh environments specified for avionics applications. New materials were introduced to the commercial Gore ribbon design to meet the McDonnell Douglas Aerospace temperature specifications. The HiRel connector design incorporates the optical fiber ribbon contact and cable assembly into a modified close tolerance Mil-C-83723 connection system to meet the environmental requirements and withstand the high vibration of modern aircraft, and also provide an environmental seal and strain relief. The ability to assemble the connector around a pre-terminated optical link is a key feature, which minimizes assembly and maintenance time over cable assembly life. McDonnell Douglas Aerospace is testing AVMAC qualification cables.

The use of fiber optic data transmission media can make significant contributions in achieving increasing performance and reduced life cycle cost requirements placed on commercial and military transport aircraft. For complete end-to-end fiber optic transmission, photonics technologies and techniques need to be understood and applied internally to the aircraft line replaceable units as well as externally on the interconnecting aircraft cable plant. During a portion of the Honeywell contribution to Task 2A on the Fly- by-Light Advanced System Hardware program, evaluations were done on a fiber optic transmission media implementation internal to a Primary Flight Control Computer (PFCC). The PFCC internal fiber optic transmission media implementation included a fiber optic backplane, an optical card-edge connector, and an optical source/detector coupler/installation. The performance of these optical media components were evaluated over typical aircraft environmental stresses of temperature, vibration, and humidity. These optical media components represent key technologies to the computer end-to-end fiber optic transmission capability on commercial and military transport aircraft. The evaluations and technical readiness assessments of these technologies will enable better perspectives on productization of fly-by-light systems requiring their utilizations.

Fiber optic connectors and splices were designed for connection of multi-fiber cables within the aircraft environment as part of the FLASH program. These devices use novel `multi-fiber positioners' to secure and precisely position multiple mating pairs of individual optical fibers to achieve excellent light throughput characteristics. The multi-fiber positioner is a micromachined structure that includes multiple V-grooves in anisotropically etched silicon. Prototype splices were developed to create a 4- channel optical splice suitable for aircraft application. The multi-fiber positioner is mounted on a flexible polymeric `elevator' and housed within a protective metal shell. The splice and shell design have been developed to facilitate user-friendly operation. The shell assembly includes a novel method for cable attachment and provides an environmental seal. This splice design should allow practicable field use in adverse conditions. Prototype connectors were developed including a 4-channel connector housed in a MIL-C 38999 (shell size #11) and a 16-channel connector (shell size #19). The multi-fiber positioner is mounted within the connector shell using a `floating- contact' concept to provide vibration isolation and allow physical end-face contact. The fiber terminus and rear shell designs have been developed to facilitate user-friendly operation. The rear shell includes new methods for cable attachment and seals for environmental and EMI/RFI protection.

We will describe the nature of the activity which surrounds the development of the `Fly-by-Light' Cable Plant in the FLASH Program in conjunction with McDonnell Douglas Aerospace. We will describe the characteristics of the technology and the activities which we are engaged in to provide a robust, environmentally stable system. The environmental constraints which have been tested to ensure the applicability of this technology will be described. We have dealt with worst case conditions, and fed back this information to the design for aircraft systems. This program is oriented to satisfy the needs of fighter aircraft, with an extendibility to helicopters. The products developed should see use in large volume markets, such as, devices used as shared storage for clusters of computers, in local area networks, High Performance, highly parallel computers and multimedia systems. It represents a new technique of wiring buildings for all kinds of optical transmission whether it be parallel, or multichannel serial based. It represents a new technique to deal with embedded sensors.

The Fly-By-Light Advanced Systems Hardware (FLASH) program developed Fly-By-Light (FBL) and Power-By-Wire (PBW) technologies for military and commercial aircraft. FLASH consists of three tasks. Task 1 developed the fiber optic cable, connectors, testers and installation and maintenance procedures. Task 3 developed advanced smart, rotary thin wing and electro-hydrostatic (EHA) actuators. Task 2, which is the subject of this paper,l focused on integration of fiber optic sensors and data buses with cable plant components from Task 1 and actuators from Task 3 into centralized and distributed flight control systems. Both open loop and piloted hardware-in-the-loop demonstrations were conducted with centralized and distributed flight control architectures incorporating the AS-1773A optical bus, active hand controllers, optical sensors, optimal flight control laws in high speed 32-bit processors, and neural networks for EHA monitoring and fault diagnosis. This paper overviews the systems level testing conducted under the FLASH Flight Control task. Preliminary results are summarized. Companion papers provide additional information.

The Fly-By-Light Advanced System Hardware (FLASH) program is developing and demonstrating dual use fly-by-light hardware for flight control systems on military and commercial aircraft. Under the transport aircraft portion of this program, we and our industry teammates are demonstrating two representative fly-by-light systems. These fly-by-light demonstrations include a ground demonstration of a partial primary flight control system and a flight demonstration of an aileron trim control system. This paper describes these and discusses the dual use fly-by-light hardware developed for transport aircraft as well as the associated FLASH program demonstrations.

Requirements for future advanced tactical aircraft identify the need for flight control system architectures that provide a higher degree of performance with regard to electromagnetic interference immunity, communication bus data rate, propulsion/utility subsystem integration, and affordability. Evolution for highly centralized, digital, fly-by-light flight/propulsion/utility control system is achieved as modular functions are implemented and integrated by serial digital fiberoptic communication links. These adaptable architectures allow the user to configure the fly- by-light system to meet unique safety requirements, system performance, and design-to-cost targets. This paper presents results of the open and closed loop system demonstrations of Fly-By-Light Advanced System Hardware architecture building blocks integrated with SAE AS-1773 communication bus at MDA.

Development costs of Fly-by-Light flight control systems have increased as complexity of these systems expands; the list to integrate and test includes fiber optic components, multiple-channel digital processors, fault tolerant software, multiple sensors, engine control, air data sensors, targeting sensors, and navigation system. Flight control hardware tests have been traditionally performed using manned flight simulators linked to the hardware for interactive tests with the aircraft's aerodynamic flight characteristics. This flight simulator environment requires additional fiber optic tests besides hosting the flight hardware. Flight simulators are expensive to operate and difficult to obtain schedule time which exacerbates program cost. The approach used in FLASH Task 2C program keeps the fiber optics, the flight processor hardware in the more friendly laboratory environment, and adds the aircraft aerodynamics and control actuator simulation using a laboratory PC linked to the flight hardware. This provides effective flight representation at a much lower cost than flight simulators, and permits full laboratory access for the critical flight software. This paper describes how their capability is applied to test fly-by-light aircraft control systems.

Fly-by-Light control systems offer higher performance for fighter and transport aircraft, with efficient fiber optic data transmission, electric control surface actuation, and multi-channel high capacity centralized processing combining to provide maximum aircraft flight control system handling qualities and safety. The key to efficient support for these vehicles is timely and accurate fault diagnostics of all control system components. These diagnostic tests are best conducted during flight when all facts relating to the failure are present. The resulting data can be used by the ground crew for efficient repair and turnaround of the aircraft, saving time and money in support costs. These difficult to diagnose (Cannot Duplicate) fault indications average 40 - 50% of maintenance activities on today's fighter and transport aircraft, adding significantly to fleet support cost. Fiber optic data transmission can support a wealth of data for fault monitoring; the most efficient method of fault diagnostics is accurate modeling of the component response under normal and failed conditions for use in comparison with the actual component flight data. Neural Network hardware processors offer an efficient and cost-effective method to install fault diagnostics in flight systems, permitting on-board diagnostic modeling of very complex subsystems. Task 2C of the ARPA FLASH program is a design demonstration of this diagnostics approach, using the very high speed computation of the Adaptive Solutions Neural Network processor to monitor an advanced Electrohydrostatic control surface actuator linked through a AS-1773A fiber optic bus. This paper describes the design approach and projected performance of this on-line diagnostics system.

For many years, programs have focused on single optical fiber sensors for each measurement required on an engine. Sensor systems therefore required signal processing for each of these individual sensors. While this approach provided the best individual sensor for each measurement, the system cost and complexity suffered. BFGoodrich has begun a new program focused on developing an optical fiber engine sensor suite based on one single sensing mechanism to monitor the majority of the measurements on an engine. The sensors will be optically multiplexed to a single signal processing unit thereby reducing cost, weight and size for the overall system. This program is a joint effort among three BFGoodrich divisions: Aircraft Sensors Division (Rosemount Aerospace), Aircraft Integrated Systems Division and Engine Electrical Systems Division. The program is described and results to date on choosing and developing the single sensing mechanism are presented.

A Litton LN-200 fiber optic gyro IMU has been successfully adapted to provide flight control and AHRS data messages via a dual rate AS-1773A fiber optic interface to the FLASH demonstration system. To provide a rugged, reliable demonstration unit, the production LN-200 IMU is mounted in an adaptive housing along with the circuitry to convert the LN-200 RS-485 SDLC electrical interface to the FLASH 1773A fiber optic interface. A dc/dc converter is also incorporated to provide the additional voltages required for LN-200 and conversion circuitry operation. Software modifications to generate the requisite output data from the LN-200 IMU incremental angle and velocity data were developed for the VFCS program. Following integration, the FLASH IMU completed demonstration testing at Litton and was delivered to McDonnell Douglas in February 1996. There, the unit successfully completed laboratory flight control testing in the integrated fiber optic configuration.

Flight control system architects are increasingly integrating aircraft control and management functionality. This functional integration increases performance and cost of ownership requirements on the communication pathways. Optical signal transmission is an attractive approach to satisfying these system requirements. Investigations and demonstrations of optic signaling are needed to validate applicability of fiber based communication systems to the new system architecture performance and cost requirements. Honeywell's activities associated with the Fly-By-Light Advanced System Hardware (FLASH) program have produced a system including key optical interface elements and accomplished preliminary demonstrations needed to validate flexible, optical based aircraft control and avionic systems. The Honeywell Primary Flight Control System included Active Hand Controllers, Primary Flight Control Computers and smart actuation subsystem elements interfaced through various optical implementations and communication protocols. These successful implementations and demonstrations provide an excellent baseline for the processes, tools and materials required to make Fly-by-Light avionic systems marketable.

The Fly-by-Light Advanced Systems Hardware (FLASH) program developed Fly-by-Light technologies for flight control and vehicle management of military and commercial aircraft. The FLASH program established requirements, performed a trade study, and selected the Dual Rate AS1773 fiber-optic data bus as the baseline interconnection means between equipment designed, built, and demonstrated by FLASH team-mates. This paper cites the lessons learned in using the AS1773 data bus. This includes the individual problems that users experienced and the overall problems of working with immature data bus components.

After two decades of research and development, optical fiber and photonics are finally at the threshold of application to flight-critical systems in military and commercial aircraft. Flight tests and laboratory tests have demonstrated that photonic components, sensors and optical fiber can withstand the harsh environments of aircraft applications and meet the safety requirements necessary to achieve certification by the military and the Federal Aviation Administration.

This paper describes present day wind-measuring and air-data systems, the limitations of these systems, and the formation of a consortium to develop solutions using the laser Doppler velocimeter (LDV). The LDV concept is discussed as well as the issues related to developing such systems. Significant progress towards making practical, reliable, and affordable eye-safe LDV systems is being gained through the many systems built to date and flight tests. The technical goal of this program is to demonstrate that small, low-power, diode pumped, 2 micrometers wavelength, eye-safe coherent LDV systems can be built and flown on both high-performance military fighter aircraft and advanced military attack helicopters. An industry-government consortium will develop LDV systems with the name Laser Wind and Hazard Profiler.

Raytheon has developed and is certifying fault-tolerant low- cost distributed Control-By-Light^TM technology for use in the next generation of Civil, Regional, and General Aviation aircraft. Distributed Control-By-Light^TM holds significant promise when applied to complex sensor/actuator systems such as aircraft controls. CBL^TM systems replace mechanical, hydraulic and electrical controls presently used to monitor, control and display flight, engine, and utility functions, and has substantial weight, cost, safety, and performance advantages over today's mechanical and Fly-By- Wire techniques. This paper describes the system concepts and outlines the formal certification program presently underway.

Raytheon Aircraft Company has developed an architecture and protocol for implementing aircraft and vehicle control systems, based on fiber optics and fault-tolerant distributed control concepts. The processor and protocol technology base are derived from commercial open-standard, high-volume products which when coupled with proven fault- tolerance techniques provide substantial cost reductions versus competing protocols. Products based upon this architecture are presently being certified for aircraft control applications in General Aviation, and are beginning to find applications in civil transport and military applications. The system uses an open architecture fiber optic based serial data network, known as the Adaptive Standard PredictivE Network. This paper provides a technical introduction to the ASPEN^TM data bus technology. ASPEN has been developed by Raytheon Aircraft for its aircraft applications, and is available for use by other members of the aircraft industry as a standard. Descriptions of the systems being developed which use ASPEN as a component, as well as the techniques used to achieve critical level development assurance, are outside the scope of this paper.

A Sagnac distributed sensor based on placement of one or more fiber gratings in the Sagnac loop may be used to measure local strain, integrated strain and the position and location of time varying events. This sensor is described as well as its application to aircraft and spacecraft. Examples are also given of how fiber optic gratings can be applied to a variety of strain sensing situations that are applicable to aerospace.

We present a device which has potential for use as a fiber sensor. The device is formed by leading two of the output parts of a multiport coupler (eight port coupler) of square form, back to two of the input ports to form a double ring resonator structure. A 4 X 4 square fused coupler with coupling coefficient Kl equals 0.348 II and an excess loss of about 0.5 dB and a loop loss of about 2 dB was fabricated in our laboratories. The double ring resonator was formed as described. By modulating one ring with Pz element, the finesses of the device as approximately 30. Therefore, the two rings may provide one ring as a reference arm and the other ring as a sensing arm. Thus, the device may have potential for use as a sensitive fiber optic sensor.

The DARPA Fly-by-Light Advanced System Hardware (FLASH) program is aimed at practical fiber optic component development for next generation aerospace systems. For aircraft control, large numbers of linear position sensors are generally needed on the vehicle. In particular, these are needed for closed loop control of flight surfaces in which the sensor continuously monitors actuator position in order to provide feedback to the control system. In this paper, we briefly describe the principle of operation, design and operational characteristics of a long stroke length (20 cm, 7.9 inches) wavelength encoding multimode fiber optic linear position sensor developed for the FLASH program.

As a part of the Fly-by-Light Advanced Systems Hardware (FLASH) DARPA Technology Reinvestment Program, we have integrated a time-rate-of-decay optical fiber temperature sensor with an existing air data transducer. Optical fiber communications hardware for AS-1773 communications were also integrated with the system. This paper presents the results of the integration testing and demonstrations performed on the sensor and communications hardware.