787 No-Bleed Systems: Saving Fuel and Enhancing Operational Efficiencies

by Mike Sinnett, Director, 787 Systems

The Boeing 787 Dreamliner features a unique systems architecture that offers numerous advantages to operators. The new airplane’s use of electrical systems reduces fuel usage and increases operational efficiency.

The primary differentiating factor in the systems reasons behind the move to ■ expanded range and reduced fuel consumption architecture of the 787 is its emphasis on a more eleCtric airplane due to lower overall weight. electrical systems, which replace most of the ■ reduced maintenance costs and improved pneumatic systems found on traditional com­ Recent advances in technology have allowed reliability because the architecture uses fewer mercial airplanes. Boeing to incorporate a new no-bleed systems parts than previous systems. One of the advantages of the no-bleed electri­ architecture in the 787 that eliminates the The 787’s no-bleed systems architecture cal systems architecture is the greater efficiency traditional pneumatic system and bleed manifold will allow the airplane’s engines to produce thrust gained in terms of reduced fuel burn — the and converts the power source of most functions more efficiently — all of the high-speed air pro­ 787 systems architecture accounts for predicted formerly powered by bleed air to electric power (for duced by the engines goes to thrust. Pneumatic fuel savings of about 3 percent. The 787 also example, the air-conditioning packs and wing anti- systems that divert high-speed air from the engines offers operators operational efficiencies due to ice systems). The no-bleed systems architecture rob conventional airplanes of some thrust and the advantages of electrical systems compared offers operators a number of benefits, including: increase the engine’s fuel consumption. to pneumatic systems in terms of weight and ■ improved fuel consumption, due to a more Boeing believes that using electrical power is reduced lifecycle costs. efficient secondary power extraction, transfer, more efficient than engine-generated pneumatic This article explores the 787’s no-bleed and usage. power, and expects the new architecture to extract systems architecture and explains how the ■ reduced maintenance costs, due to elimination as much as 35 percent less power from the engines. airplane’s efficiencies are realized. of the maintenance-intensive bleed system. Conventional pneumatic systems generally develop ■ improved reliability due to the use of modern more power than is needed in most conditions, power electronics and fewer components in causing excess energy to be dumped overboard. the engine installation.

06 aero quarterly qtr_04 | 07 787 NO-BLEED SYSTEMS ARCHITECTURE Figure 1

The 787’s no-bleed systems architecture replaces the traditional pneumatic system and the bleed manifold with a high-power electrical system that, in addition to the traditional electrical system functions, supports a majority of the airplane functions that were traditionally performed via bleed air.

RAT P G

P M SG

HX P Engine M SG Battery ECS M XFR CTAI P M M SG APU NGS SG P P M M CTAI ECS XFR M SG HX P Engine

M SG

HX Heat Exchanger

XFR Trans / Rectifier SG Starter Generator RAT Ram Air Turbine P Hydraulic Pump M Motor CTAI Cowl Thermal Anti-Ice

Electrical Electrical power is more Hydraulic efficient than Pneumatics engine-generated Fuel pneumatic power. Ram Air

07 WWW.boeing.com/commercial/aeromagazine COMPARISON OF BLEED AND NO–BLEED ENGINE BUILDUP Figure 2

A comparison of typical engine buildups of a no-bleed engine (left) and the traditional bleed engine.

The ducting used to pass the pressurized air valves. There is no need to regulate down the hydraulic system around the airplane employs check valves and supplied com­pressed air. Instead, the compressed pre‑coolers, and is itself made of titanium, which air is produced by adjustable speed motor com­ The hydraulic system in the 787 no-bleed archi­ adds hundreds of pounds of weight to the airplane. pressors at the required pressure without significant tec­­ture is similar to the one in the traditional The electric system is also inherently easier energy waste. That results in significant improve­ architecture. There are three independent sys­ to monitor and control, and produces only enough ments in engine fuel consumption. tems — left, center, and right — that collec­tively power as needed. The power, which comes off the support primary flight control actuators, landing generators at variable frequencies, is conditioned gear actuation, nose gear steering, thrust engines in the electronics bay before being distributed to reversers, and leading/trailing edge flaps. the appropriate systems. The primary power source for the left and right In the traditional architecture, the engines provide systems are engine-driven pumps mounted on the majority of secondary airplane systems power the engine gearbox. In addition, the left and right 787 no-bleed systems architecture needs in pneumatic form; in the no-bleed archi­tec­ systems are each powered by an electric-motor- ture, the engines provide the majority of airplane driven hydraulic pump for peak demands and for The 787 no-bleed systems architecture is shown systems power needs in electrical form via ground operations. schematically in figure 1. On the 787, bleed air is shaft-driven generators. The traditional airplane The key difference between the traditional only used for engine cowl ice protection and pres­ pneumatic bleed system architecture results in and 787 hydraulic system is the power source surization of hydraulic reservoirs. The electri­fied less than optimum engine efficiency. Eliminating for the center system. In the traditional architec­ functions are wing deicing protection, engine start­ the pneumatic bleed results in a more efficient ture, the center system is powered by two large ing, driving the high-capacity hydraulic pumps, and engine operation due to reduced overall airplane air-turbine-driven hydraulic pumps, which operate powering the cabin environmental control system. level power requirements — the airplane does not at approximately 50 gallons per minute (gpm) at In this architecture, the power sources for the draw as much horsepower off the engine in cruise, 3,000 pounds per square inch (psi) to meet peak electrical system are engine-driven and auxiliary- so it doesn’t burn as much fuel. The corresponding hydraulic demands for landing gear actuation, power-unit (APU)-driven generators, while the power predicted improvement in fuel consumption, at high lift actuation and primary flight control during sources for the hydraulic system are engine-driven cruise conditions, is in the range of 1 to 2 percent. takeoff and landing. During the remainder of the and electric-motor-driven hydraulic pumps. The Moreover, the no-bleed architecture allows flight, two small (approximately 6 gpm) electric- engine-driven hydraulic power sources in the significant simplification in engine buildup due driven hydraulic pumps power the center system. no-bleed architecture are similar to those in the to the elimination of the pneumatic system In the 787 no-bleed architecture, the center traditional architecture. and associated pre-coolers, control valves, and hydraulic system is powered by two large (approxi­ In the no-bleed architecture, electrically driven required pneumatic ducting. Figure 2 compares mately 30 gpm at 5,000 psi) electric-motor-driven compressors provide the cabin pressurization typical engine buildups of no-bleed engine and hydraulic pumps. One of the pumps runs through­ function, with fresh air brought onboard via the traditional bleed engine. out the entire flight and the other pump runs only dedicated cabin air inlets. This approach is during takeoff and landing. The higher pressure significantly more efficient than the traditional of the 787’s hydraulic system enables the airplane bleed system because it avoids excessive energy to use smaller hydraulic components, saving both extraction from engines with the associated space and weight. energy waste by pre-coolers and modulating 08 aero quarterly qtr_04 | 07

Figure 3

The 787’s electrical system uses a remote distribution system that saves weight and is expected to reduce maintenance costs.

TRADITIONAL 787

External Power E/E Bay 2 x 115 Vac, 90 kVA Forward E/E Bay

External Power 115 VacFeeder 115 Vac 230 VacFeeder Generator Generator 1 x 120 kVA 2 x 250 kVA

Aft E/E Bay External Power 115 Vacor 2 x 115 Vac, 90 kVA Loads 28 Vdc Wire Loads

Remote Power APU Generator APU Generator Distribution Unit 2 x 225 kVA

Centralized Distribution: Remote Distribution: Circuit Breakers, Relays, Solid-State Power Controllers and Contactors and Contactors

electrical system simplest and the most efficient generation method supplied by four auto-transformer-rectifier units because it does not include the complex constant that convert 235 VAC power to ±270 VDC. The The 787 uses an electrical system that is a hybrid speed drive, which is the key component of an ±270 VDC system supports a handful of large- voltage system consisting of the following voltage integrated drive generator (IDG). As a result, the rated adjust­able speed motors required for the types: 235 volts alternating current (VAC), 115 generators are expected to be more reliable, require no-bleed architecture. These include cabin VAC, 28 volts direct current (VDC), and ±270 VDC. less maintenance, and have lower spare costs pressurization compressor motors, ram air fan The 115 VAC and 28 VDC voltage types are tradi­ than the traditional IDGs. motors, the nitrogen-generation-system compressor tional, while the 235 VAC and the ±270 VDC The electrical system features two electrical/ used for fuel-tank inerting, and large hydraulic voltage types are the consequence of the no-bleed electronics (E/E) bays, one forward and one aft, pump motors. electrical architecture that results in a greatly as well as a number of remote power distribution The system, as shown in figure 3, features two expanded electrical system generating twice as units (RPDU) for supporting airplane electrical forward 115 VAC external power receptacles to much electricity as previous Boeing airplane models. equipment. The system saves weight by reducing service the airplane on the ground without the APU The system includes six generators — two per the size of power feeders. A limited number of and two aft 115 VAC external power receptacles engine and two per APU — operating at 235 VAC 235 VAC elec­trical equipment is supplied from the for maintenance activities that require running the for reduced generator feeder weight. The system aft E/E bay, while the majority of airplane electrical large-rated adjustable speed motors. also includes ground power receptacles for airplane equipment, being either 115 VAC or 28 VDC, are servicing on the ground without the use of the APU. supported by the forward E/E bay and RPDUs as engine and apu start The generators are directly connected to shown schematically in figure 3.T he RPDUs are the engine gearboxes and therefore operate at a largely based on solid-state power controllers The 787’s engine-start and APU-start functions variable frequency (360 to 800 hertz) proportional (SSPC) instead of the traditional thermal circuit are performed by extensions of the method that to the engine speed. This type of generator is the breakers and relays. The ±270 VDC system is has been successfully used for the APU in the 09 WWW.boeing.com/commercial/aeromagazine APU SYSTEMS ELIMINATED IN THE NO-BLEED ARCHITECTURE Figure 4

This diagram of an APU for a 767-400 airplane shows the pneumatic portions that will be eliminated in a no-bleed architecture.

10 aero quarterly qtr_04 | 07 The 787 utilizes an electro-thermal ice protection scheme, in which several heating blankets are bonded to the interior of the protected slat leading edges.

Next-Generation 737 airplane family. In this method, system air inflow can be adjusted in accordance power delivery are eliminated. This should result the generators are run as synchronous starting with the number of airplane occupants to achieve in a significant improvement in APU reliability and motors with the starting process being controlled the lowest energy waste while meeting the air-flow required maintenance. by start converters. The start converters provide requirements. Figure 4 shows the APU for a 767-400 air­ conditioned electrical power (adjustable voltage plane, identifying the pneumatic portions that will and adjustable frequency) to the generators during be eliminated in a no-bleed electrical architecture. wing ice protection the start for optimum start performance. Moreover, taking advantage of the variable fre­ Unlike the air turbine engine starters in the quency feature of the 787 electrical system, the In the traditional architecture, hot bleed air is traditional architecture that are not used while APU operates at a variable speed for improved extracted from the airplane bleed system and the respective engines are not running, the start performance. The operating speed is based on distributed through the areas of the wing leading converters will be used after the respective engine the ambient temperature and will be within a edge that need ice protection. For each wing, one is started. The engine- and APU-start converters 15 percent range of the nominal speed. valve controls the flow of the bleed air to the wing will function as the motor controller for cabin leading edge, while a “piccolo” duct distributes the pressurization compressor motors. heat evenly along the protected area of the wing summary Normally, both generators on the APU and both leading edge. In addition, should ice protection on generators on the engine are used for optimum the leading edge slats be required, a telescoping A key benefit expected from the Boeing 787’s start performance. However, in case of a generator duct supplies bleed air to the slats in the extended no-bleed architecture is improved fuel consump­ failure, the remaining generator may be used for position. The spent bleed air is exhausted through tion as a result of more efficient engine cycle and engine starting but at a slower pace. For APU holes in the lower surface of the wing or slat. more efficient secondary power extraction, power starting, only one generator is required. The 787 utilizes an electro-thermal ice protec­ transfer, and energy usage. The power source for APU starting may be tion scheme, in which several heating blankets are Eliminating the maintenance-intensive bleed the airplane battery, a ground power source, bonded to the interior of the protected slat leading system is also expected to reduce airplane main­ or an engine-driven generator. The power source edges. The heating blankets may then be energized­ tenance needs and improve airplane reliability for engine starting may be the APU generators, simultaneously for anti-icing protection or sequen­ because there are fewer components on the engine-driven generators on the opposite side tially for deicing protection to heat the wing leading engine installation; there are no IDGs, pneumatic engine, or two forward 115 VAC ground power edge. This method is significantly more efficient ducts, pre-coolers, valves, duct burst protection, sources. The aft external power receptacles may than the traditional system because no excess and over-temperature protection; and there is be used for a faster start, if desired. energy is exhausted. As a result, the required ice no compressed air from the APU, resulting in a protection power usage is approxi­mately half that simplified and more reliable APU. environmental control system of pneumatic systems. Moreover, because there The 787 no-bleed architecture also features are no-bleed air exhaust holes, airplane drag modern power electronics and motors that will In the 787 electrical architecture, the output of the and community noise are improved relative to provide increased overall reliability, decreased cabin pressurization compressors flows through the traditional pneumatic ice protection system. costs, and improved performance. Finally, the low-pressure air-conditioning packs for improved architecture means reduced airplane weight, efficiency.T he adjustable speed feature of elec­ reduced part count, and simpler systems instal­ apu trical motors will allow further optimization of lation. For more information, please contact airplane energy usage by not requiring excessive Lori Gunter at [email protected] As in a traditional architecture, the APU in the energy from the supplied compressed air and no-bleed electrical architecture is mounted in later regulating it down through modulating valves the airplane tail cone, but it provides only electrical resulting in energy loss. power. Consequently, it is much simpler than the Avoiding the energy waste associated with APU for the traditional architecture because all of down regulation results in improvements in engine the components associated with the pneumatic fuel consumption, and the environmental-control- 11 WWW.boeing.com/commercial/aeromagazine