Can Main Electrical Service Line Be Anchored To Rooftop

The 787 Dreamliner is powered by new-generation engines from GE and Rolls-Royce that offer improvements in fuel consumption, racket, and emissions.

By Stephen F. Clark, Senior Technical Fellow, Propulsion Systems

Engine manufacturers take adult systems that stand for nearly a two-generation jump in technology.

The 787 uses new engines from GE and Rolls-Royce. Advances in engine engineering are the biggest correspondent to the airplane's overall fuel efficiency improvements. The new engines correspond a two-generation jump in technology over the 767.

This article gives an overview of the basic features of the 787 propulsion system, comparing it to the 767 system it replaces. The article focuses on how the design achieves fuel consumption, racket, and emissions improvements and discusses operating and maintainability features every bit well as overall cost-of-buying reduction benefits.

The evolution of airplane engines

Starting in 2002, Boeing'south analysis indicated a strong market place demand for a twin-alley airplane with 767-class payload capability at significantly enhanced range. This finding was consequent with airline evolution from a hub-and-spoke to a point-to-point operational model. Enabling enhanced range in this seat class demanded significant advances in overall airplane design with a large portion of this burden given to the propulsion system.

Boeing and engine manufacturers approached this challenge by improving fuel fire in iii traditional performance areas and introducing a meaning architectural innovation (see fig. one):

• Higher propulsive efficiency through increased featherbed ratio.
• Higher engine thermal efficiency through increased overall pressure ratio and improved component efficiencies.
• Improved thrust-to-weight ratio through the awarding of advanced materials.
• Introduction of a novel dual-apply electric power generation system that doubled as the engine start arrangement.

Figure ane: 787 Engines

Comparison of GEnx-1B and Rolls-Royce Trent g with a tabular array that compares key characteristics of these engines to 767 engines.

GE GEnx-1B
Rolls-Royce Trent 1000
	787 Engines: GEnx-1B Trent thousand		767 Engines: GE CF6-80C2 RR RB211-524G/H
Featherbed Ratio	~x		~5
Overall Force per unit area Ratio	~50		~33
Thrust Class	53,000–74,000 lbf		53,000–63,000 lbf
Fan Diameter	111–112 in		86–93 in
Specific Fuel Consumption	15% lower		Base
Noise	ICAO Chapter 4		ICAO Chapter 3
Emissions	CAEP/8 (2014)		CAEP/2

In addition to the improved fuel burn down requirements, the 787 propulsion system as well had to meet more stringent dissonance and emissions requirements. Finally, in order to maximize the upper-case letter value of the aeroplane, Boeing decided that the propulsion systems should be designed for total interchangeability betwixt the ii engine types.

Electrical Power Organisation

A main foundation of the 787 compages was the incorporation of the variable frequency starter generator (VFSG) system (run into fig. 2). The VFSG delivers many benefits:

• Replaces the heritage bleed air organisation used to feed the airplane's environmental control organisation, thereby realizing directly weight savings through the emptying of relatively heavy bleed air components such equally regulation valves, ducting, and coolers.
• Eliminates the energy loss of the drain air system pre-cooler.
• Eliminates the throttling losses of bleed air provided from discrete engine compression stages.
• Eliminates the single-purpose air turbine starters and their associated oil system and maintenance.
• Simplifies the auxiliary power unit (APU) design to be a shaft power-only machine.
• Provides high flexibility with existing drome basis support infrastructure.
• Is fully self-contained with its ain lubrication system and the ability to be disconnected self-protectively, manually or remotely, through flight deck controls.

Figure 2: Starter generator

The variable frequency starter generator delivers many benefits, including the replacement of the heritage drain air system.

Variable Frequency Starter Generator

The 787 main electric ability generation and start system is a four-channel variable frequency system with two 250 kVA VFSGs on each of the two main engines. The power from these generators is supplied to the primary load buses through generator feeders and generator circuit breakers (see fig. 3).

Figure iii: 787 Engine start organisation schematic—GEnx

The variable frequency starter generator is a half dozen-pole machine within an aluminum housing driven directly from the main engine gearbox. The generator is a brushless, three-stage, alternating current, and variable frequency synchronous machine. Information technology has a nominal rating of 235 volts alternate current (VAC), 250 kVA, three phases, and 360–800 Hz output.

Controlling each VFSG is a dedicated generator control unit (GCU). The GCU is a line replaceable unit (LRU) housed inside the aft electrical equipment bay. The GCU's principal part is to provide voltage regulation and error electric current limiting while in the generate mode. The GCU as well supports the principal engine start function.

Managing the ability distribution betwixt the VFSGs is the jitney ability command unit (BPCU). The BPCU performs several functions:

• Controls motorbus configuration and engine wellness monitoring.
• Provides standby organisation command, generating source load management, and main and APU engine horsepower load direction.
• Acts as the electrical power system communication gateway with other systems and flying deck.

Built-in redundancy in the BPCU enhances arrangement reliability and operational flexibility.

The mutual motor offset controllers (CMSCs) are used to control the VFSG start role and properly regulate torque during the commencement sequence. In one case the engine is started, the CMSC switches over to controlling the cabin air compressors, thereby performing a 2d function.

The electrical kickoff arrangement affords maximum flexibility from a variety of power sources: APU generators, external power cart, and cross engine (contrary engine VFSGs). The VFSG arrangement provides full maintenance diagnostics for both the entire system and all LRUs.

Engine pattern Highlights

Both 787 engine manufacturers incorporated the latest technology offerings from their extensive enquiry and product maturation programs.

The GE engines:

• Leverage the highly successful GE90 composite fan blades with the latest swept aerodynamics.
• Incorporate an entirely new composite fan case for significant weight savings.
• Field the enhanced twin annular pre-swirl combustion system that achieves significant emission reductions while preserving low pattern factor for turbine durability as well as excellent re-low-cal characteristics.
• Introduce surface air-oil coolers to compactly decline the VFSG and engine oil heat.
• Incorporate state-of-the-art titanium aluminide (Ti-Al) blades in the last two stages of the seven-stage low pressure turbine. Ti-Al achieves pregnant weight savings over traditional nickel alloy.

The Rolls-Royce engines:

• Incorporate the latest swept aero hollow-fan-bract engineering science evolved from the predecessor Trent 900 engine.
• Utilise the proven benefit of the Trent three-spool engine architecture. In the case of the Trent grand, the three-spool design affords intermediate pressure power off-accept with demonstrated benefits in engine operability and fuel consumption.
• Comprise surface coolers for meaty and efficient rejection of VFSG and engine oil heat.
• Design the Trent 1000 with the latest computational fluid dynamics-enabled 3D aerodynamics for loftier efficiency and depression noise.
• Allow power to exist extracted for each VFSG through the second of the three engine shafts. This unique solution using the Trent k engine compages brings with it lower engine idle speeds, which reduce fuel burn down and noise on the 787.

New nacelle features improve on legacy designs

The nacelle design (come across fig. 4) maximizes composite and weight-saving materials to better maintenance cost and fuel burn down. Highlights include:

• A single-piece inlet barrel construction for low dissonance.
• Lightweight blended fan cowls.
• A proven translating sleeve thrust reverser organisation that utilizes compact land-of-the-fine art v,000 pounds per square inch (psi) hydraulic actuation.
• Advanced titanium alloy exhaust system components.
• A single-piece aft fairing.
• Blended diagonal brace.
• Advanced titanium alloy strut.

Effigy 4: Nacelle design: expanded view

This view of the nacelle shows the inlet, fan cowls, thrust reverser, frazzle plug, and nozzle.

Extensive engine and flight testing

The 787 propulsion system was rigorously tested, both to accomplish bones certification and to demonstrate full service readiness and extended operations (ETOPS) capability when the 787 entered service (see fig. 5).

Figure v: Engine test programme

Intense engine development and 787 flight test programs contribute to the engines' service readiness and durability.

Accumulated Feel at Entry into Service (EIS)
>12,000	>xv,000	>iv,800	>1,800
Engine Test Hours	Engine Cycle	Flying Test Hours	Flights

The engine exam program incorporated more than than twenty defended test engines between the two engine manufacturers. Beyond testing for basic engine certification, each engine type completed 3,000 cycles of ETOPS flight testing. The engine test program was started far in advance of the Boeing flying examination program. Multiple flight exam beds identified necessary modifications prior to the Boeing flight test program. A two-year, half-dozen-airplane 787 flying test program led to blazon certification in August 2011 and entry into service in October 2011.

Flight deck controls and displays

The 787 propulsion controls are designed for maximum commonality with the 777 architecture, while incorporating the latest customer-driven improvements.

The cockpit provides engine-starting controls, forwards and reverse thrust manual control, autothrottle control, and engine-indicating and crew-alerting system (EICAS).

During normal operation of the plane, the flight crew monitors engine information on the principal flying display (run across fig. 6). The display tin can be gear up to bear witness the full normal brandish, both primary and secondary engine parameters, or an abbreviated compact brandish with simply master parameters.

Effigy vi: Flight deck displays

The flying deck displays can exist prepare to show the total normal display with both primary and secondary engine parameters (left) or an abbreviated compact brandish with only master parameters (eye). A normal display (right) shows the location of engine-indicating and coiffure-alerting system (EICAS) messages.

The normal brandish is the default display. The flight crew may select the compact brandish when both engines are operating commonly. When the compact display has been selected, the normal display appears if:

• An engine is starting.
• An engine has failed.
• An engine is close downwardly.
• A secondary parameter goes out of normal operating range.
• The display is selected by the flying coiffure.

To the right of the engine parameter display on the EICAS principal display is the location for displaying flight coiffure alerting messages. The text of alert, caution, and advisory messages is displayed to warning the flight crew to non-normal conditions.

Engine health direction system

The 787 propulsion arrangement incorporates the latest generation of central maintenance and engine wellness management systems.

Fundamental maintenance system. Through centralized fault reporting, the 787 onboard maintenance arrangement (OMS) aids the airline mechanic in rapidly isolating faults and guiding the appropriate maintenance action (see fig. seven). The OMS is an essential tool in maintaining rapid plane turnaround rates and maximizing dispatchability.

Figure seven: Onboard maintenance organization

The 787 onboard maintenance organisation helps mechanics rapidly isolate faults and guides advisable maintenance action.

Engine health management organisation. Each engine manufacturer provides a defended engine wellness monitor that has vibration monitoring and fan trim balancing functions and sophisticated engine parameter trending for maintenance planning.

Summary

The new-generation engines powering the 787 aeroplane offer operators improvements in fuel consumption, dissonance, and emissions. Both GE and Rolls-Royce have developed avant-garde engine systems that deliver about a two-generation spring in applied science.

Source: https://www.boeing.com/commercial/aeromagazine/articles/2012_q3/2/

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