Civil Air Transport: a Fresh Look at Power-By-Wire and Fly-By-Light

CIVIL AIR TRANSPORT: A FRESH LOOK AT POWER-BY-WIRE AND FLY-BY-LIGHT

Gale R. Sundberg National Aeronautics and Space Administration Lewis Research Center Cleveland, Ohio 44135

Abstract the NASA Lewis study. The single electrical power system provides higher component utilization with signifi- Power-by-wire (PBW) is a key element under sub- cant reductions in parts count, weight, failure modes, sonic transport flight systems technology with poten- and cost of ownership. tial savings of over 10 percent in gross take off weight and in fuel consumption compared to today's The PBW technology eliminates the need for hydrau- transport aircraft. The PBW technology substitutes lic actuation and for engine bleed air to supply cabin electrical actuation in place of centralized hydraul- comfort and anti-icing. It enables integral starter/ ics, uses internal starter-motor/generators and elimi- generators for engine starting and power generation to nates the need for variable engine bleed air to supply be used with advanced energy-efficient engines without cabin comfort. gearboxes. These changes significantly improve fuel efficiency and reduce aircraft weight. Improved safety The application of advanced fiber optics to the and dispatch reliability combined with lower mainte- electrical power system controls, to built-in-test nance and direct operating costs are additional tangi- (BITE) equipment, and to fly-by-light (FBL) flight con- ble benefits. trols provides additional benefits in lightning and high energy radio frequency (HERF) immunity over exist- According to the study, eliminating the engine ing mechanical or even fly-by-wire controls. This paper bleed for powering the environmental control system will review the program plan and give a snapshot of the (ECS) and for anti-icing provided the largest single key technologies and their benefits to all future air- fuel savings of any proposed change. An electric motor craft - civil and military. driven ECS with electric impulse driven de-icers are the proposed replacements. Introduction Subsequent to the NASA Lewis study, additional NASA in response to a directive from the U.S. Sen- technologies have emerged. The application of advanced ate has developed a mu1 tiyear technology development fiber optics to the electrical power system controls, and validation plan that will help the United States to built-in-test (BITE) equipment, and to fly-by-light retain its leadership in aeronautics research and tech- (FBL) flight controls provides additional benefits in nology and compete in the international marketplace for ligntning and high energy radio frequency (HERF) immu- future civil aircraft. One of the key elements under nity over existing mechanical or even fly-by-wire subsonic transport flight systems technology is power- control s. by-wire (PBW) with potential savings of over 10 percent in gross take-off-weight (GTOW) and fuel consumption This paper wi 11 review the program plan and take a compared to today's aircraft (Ref. 1). Fly-by-light fresh look at some of the key technologies and their (FBL), which is the replacement of electronic data benefits to all future aircraft - civilian and military. transmission, mechanical control linkages, and elec- Figure 1 shows the payoffs and the major tasks planned tronic sensors with optical components and subsystems, for the PBW element. Figure 2 summarizes the primary is another key element. elements of the FBL/PBW 5-yr program plan under the Civil Transport Initiative. In the NASA Lewis Research Center study reported in Ref. 1 the stated benefits are shown to be possible The Electrical Powerplant through the integration of an advanced secondary electrical power system into a civil transport aircraft The heart of the electrical power system is a using a Boeing 767 as a baseline. While the particu- multiredundant, fault tolerant, microprocessor con- lar benefits may depend on aircraft size and type, trolled, power management and distribution (PMAD) sys- engines, and specific electrical and flight control tem. It incorporates bidirectional inverters driven systems, the range of improvements is consistent with through a high frequency, resonant utility bus connected available advanced technologies. to internal starter-motorlgenerators, thereby eliminating gearboxes and the need for separate APU's and engine The primary weight reduction occurred in the sec- starters. The high frequency utility bus permits all ondary power system when the base1 ine hydraul ic, pneu- the advantages of ac for stability, fault clearing, dif- matic and electrical subsystems were replaced with a ferential monitoring and control, as well as significant single, advanced high frequency, sinusoidal power man- crew/technician safety because of its low energy per agement and distribution (PMAD) system with control led pulse nature and ease of ground fault interruption.. energy flow and load management. An advanced fly-by- Figure 3 shows a typical utility bus architecture for an wire flight control system using electrical actuators ac PMAD system using advanced electronic switching for and advanced low fixed bleed high bypass ratio engines power conditioning, control, distribution, protection contribute the remaining major advantages according to and a fault tolerant architecture (Ref. 1).

1365 U.S. Government work not protected by U.S. copyright. The characteristics of the advanced PMAD system Pushing the intelligence down to the power switch and provide the conduit to the benefits for PBW in civil circuit level enables easy verification, validation, transport and perhaps certain military aircraft. The status, and maintainability. It provides step-by-step resonant, high frequency (>lo kHz) link drive enables transitions from manual to autonomous controls. Inte- either multiphase low frequency ac sources or dc sources grated health monitoring, incipient fault prediction and to operate at their optimum voltage and frequency at the a controlled evolution of power and avionic systems are input. Since the main inverters switch at the zero readi ly accommodated with each node communicating with crossing of either current or voltage, they minimize other nodes via simple, common words. This enables dis- power losses, component stress, EMI/EMC and the need for tributed intelligence for fault containment, fault tol- heavy, bulky filters. The high frequency bidirectional erance, and autonomous control without massive software conversion and synthesis significantly reduces the size investments. and mass of the electronics components, controls and systematics. Electro-optical Controls The key benefit, however, comes in the ability to The fly-by-light (FBL) controls are proposed as a drive all kinds of motors (including rugged induction replacement of electrical data transmission, mechanical motors with high temperature capability) in either control linkages and electronic sensors with optical direction with independent control of torque, speed and components and subsystems. They circumvent electromag- maximized, efficient operation over the entire speed netic interference (EMI) concerns in applying digital range. In effect, all load control including variable controls by providing lifetime immunity to signal EM1 speed motor drive is accomplished by sorting and steer- without need for shielding. The FBL technology will ing the high frequency sinusoidal pulses to the appro- demonstrate optical sensors and interfaces with improved priate power switch, motor winding or energy storage lightning and HERF immunity. element. Voltage regulation, power quality and energy flow are determined and managed at all times and within The FBL program will identify, develop, and evalu- specified limits. Multiple levels of redundancy are ate an optical sensor suite. The sensors will be easily accommodated in the system, providing fault integrated into innovative electro-optical based fault- containment, fault recovery, and maximized end-to-end tolerant architectures using optical networks and efficiency. multiplexer/demultiplexer techniques. Performance and reliability assessments of the fault tolerant processors El ectr i cal Actuation and architectures will provide a basis for developing hardware and software for flight test and inservice Existing electrical actuation technology in the eval uat i on. 5- to 50-hp range will be adapted to the flight control and other actuation requirements on an aircraft. Proto- Several ongoing activities will feed technology type electrical actuators operating from the distributed into the FBL program: the fiber optical control system power bus will be built and demonstrated in a full integration (FOCSI) program, the optical propulsion avionics control environment. management interface system being designed into the advanced transport operating system aircraft, and a The electric actuators would replace hydraulic fiber optical transmitter/receiver with a dc 4-GHz band- actuators, servovalves, and mechanical control linkages. width. An extensive data base and experimental investi- An advanced electrical actuation system includes elec- gation of lightning effects on digital electronics will tromechanical and/or electrohydraulic actuators, load serve as a baseline for assessing FBL enhancements to receivers, redundant digital data buses, and remote ter- the flight control system. minals. Electrical actuators perform the same functions as hydraulic actuators with lower weight, higher effi- Summary ciency and without sizing restrictions. The goal of the FBLIPBW program is to accomplish The digital data bus and electro-optical sensors credible flight tests and demonstration of full author- and controls promise to be a much lighter weight, more ity, all digital FBL/PBW transport aircraft systems. reliable and EM1 immune approach than fly-by-wire or Performance will be evaluated in the stress of flight mechanical controls. Also, many functions previously environments. The program will use the NASA advanced done with hardware can now be done with software. This transport operating system aircraft. Using parallel may include such functions as control surface damping operation of experimental equipment on the basic air- and trim. craft will maximize flight test safety. Status and Health The flight tests will be designed to verify and evaluate the integrated system. FAA participation and Microchip level BITE will be built into the hard- coordination wi 11 be integral to developing a prototype ware to provide a "fingerprint", which may include com- certification model. ponent characteristics, test information and validation parameters. Such smart BITE chips could provide health Reference self-testing for pre-flight checkout, for in-flight status and for maintenance assistance and records. 1. Hoffman, A.C. et al., Advanced Secondary Power System for Transport Aircraft, NASA TP-2463; May The keys to autonomous, growable power and control 1985. systems are simple, smart, replicative logic structures.

1366 POWER-BY-WIRE TECHNOLOGY HERE IS WHAT WE PLAN TO DO

DEMONSTRATE FAULT TOLERANT ELECTRICAL POWER SYSTEM ELIMINATE CATASTROPHIC POWER FAILURES

SAFE FOR PASSENGERSICREW USE ELECTRIC ACTUATION AND ENVIRONMENTAL I CONTROL SYSTEM; VARIABLE SPEED PUMPS I 0 IMMUNE TO LIGHTNING, HERF * OPERABILITY MAINTAINABILITY

PBW SAVES * ELIMINATES BLEED PENALTY AUTO CHECK-OUT 10% NC WEIGHT * INCORPORATES INTEGRAL * SMART EQUIPMENT & CABLE STARTERiGENEflATORS GRS90-001 11

FIGURE 1. - MAJOR TASKS AND BENEFITS OF POWER-BY-WIRE TECHNOLOGY.

ARCHITECTURE DESIGN & SENSOR INTEGRATION ENGlNE 6 AlRFRAME -?!?% I VERIFICATION

& EVALUATION

DEVELOPMENT ALL-ELECTRIC ARCHITECTVRE I A (FLIGHT EVALUATIO~?

ELECTRICAL E3 ENGINE I 1~~:pqJ ARCHmC EM ACTUATORS

FIGURE 2. - ELEMENTS OF FLY-BY-LIGHT/POWER-BY-WIRE PROGRAM.

1367 I & &

Bi-directional B i-di rectional Bi-directional Bi-directional converter converter Ram air converter converter turbine

Dual high-vol tage , high- frequency buses

Bi-directional Bi-directional converter with converter with charge control - charge control --

Uninterrupted Hot dc battery bus Bc computer bus

BC Left dc bus Right battery bus BC

4 ECSl air-conditioner ECS2 air-conditioner controllerhotor BC --+I- BC El--- controllerhotor Left flight control bus BC * I Transformer Transformer High frequency to 400-Hz synthesizer

400-Hz bus I I Low-voltage bus Low-voltage bus 400-Hz bus

Left utility bus I BC I I High frequency to 400-Hz synthesizer

I 400-Hz bus I I Low-voltage bus I I I

I I1 1 I Left galley bus

BC bus controller BI bus isolator ECS environmental control system

FIGURE 3. - ADVANCED POWER DISTRIBUTION SYSTEM.