Graham Warwick/MONTREALCutaway drawing by Tim Hall/LONDON
When Bombardier conceived the Global Express, it "-wanted to put a stake in the ground beyond anything that existed". As flight-testing of the ultra-long-range business jet gets under way, the Canadian manufacturer remains confident that its aircraft offers an unrivalled combination of comfort and performance at a competitive price.
Three design objectives shaped the Global Express: performance, cabin comfort and reliability. The performance goals set were challenging, particularly the requirement to combine long range and high speed with good low-speed characteristics for short-field capability. Bombardier's desire to offer the largest business-jet cabin available only made the performance goals more challenging, while the requirement for airliner reliability drove system redundancy to new levels for business aircraft.
One more objective shaped the overall programme: Bombardier's need to spread the cost of developing the Global Express across its own divisions and other aerospace companies. As a result, half of the C$800 million ($600 million) development cost is carried by Bombardier and the rest by nine risk-sharing partners. This required a lengthy joint-definition phase, during which the participants agreed the interfaces between their parts of the aircraft before beginning detailed design.
Bombardier's view of the ultra-long-range market has changed little since "Project Global Express" was unveiled in 1991. The range goal then was 9,250km (5,000nm) at Mach 0.85, with eight passengers and four crew, but this was increased to accommodate the market-defining city pair of New York-Tokyo, and is now 12,000km at M0.8. This translates into 11,700km at M0.85 and the original 9,250km at the aircraft's M0.88 high-speed cruise.
Market studies showed that the increasing globalisation of business, and growing dissatisfaction with airline service, would drive the need for long-range corporate aircraft. The Global Express was conceived to link businesses in North America with the Far East, Middle East and South America; Europe with the Far East and South Africa; and vice versa - all with secure non-stop service under the owner's control.
Long-range confidence
"Our confidence in the market for ultra-long-range aircraft continues," says John Lawson, president of Bombardier's Canadair Business Aircraft division. The company's estimate of the ultra-long-range market is still for 500-800 aircraft over the next 15 years, he says.
The programme is based on selling 250 aircraft, with the break-even point at around 100, and production of two a month over the life of the programme - a production rate which is now achieved with the Canadair Challenger. By the roll-out on 26 August, the company had 53 firm orders for the $34 million aircraft.
More than half of the orders have been placed by international customers, with slightly less than half from the traditionally dominant North American market. Customers include operators of other manufacturers' large business-jets, with the Global Express orderbook containing more operators of the Gulfstream IV than of the Challenger, Lawson claims.
Bombardier Aerospace executive vice-president of engineering, John Holding ,says that the design objectives of the Global Express (officially designated the BD 700) were to provide "the longest range at the highest speed from the shortest runways of any available or planned business jet". Take-off field length at the 41,280kg maximum take-off weight is 1,550m (5,100ft); landing distance at the 35,650kg maximum landing weight is 780m.
The key to combining a maximum operating Mach number of 0.9 with an approach speed of 125kt (230km/h) lies in the wing. The Global Express is an all-new design: the aircraft has the same 2.7m fuselage cross-section as that of the Challenger, and the same 14.6m cabin length as that of the Canadair Regional Jet. The architectures of many systems are based on those used successfully on both, but the wing is all-new.
The wing is sized by the need to house fuel for the 12,000km design mission; shaped by the desire to cruise virtually shock-free at M0.85; and equipped with high-lift devices to provide what Holding describes as "superb low-speed handling characteristics". The result is a supercritical wing with 28.5m span, 35ísweep, leading-edge slats and winglets.
Bombardier describes the wing as "third-generation supercritical". Its first such wing was designed for the Challenger, and improved for the Regional Jet. The Global Express wing is the result of some 100 design iterations using computational fluid-dynamics (CFD). Over the past 15 years, Canadair has developed its own CFD codes for transonic wing design and has a Cray J916 supercomputer.
CFD allowed the company to limit windtunnel testing to just two promising wing planforms, designated the W10 and W11, and an optimisation of the W10 planform, dubbed the W20, which was selected as the final wing geometry. The wing was created from a family of two-dimensional sections which were derived from the desired pressure-distribution using inverse aerofoil-design methods. Three-dimensional optimisation then ensured that the pressure isobars on the wing were swept to minimise drag.
"CFD was used to design 100% of the external lines of the Global Express," says Holding. Areas of concern were the winglets, wing/body fairing and engine integration. CFD was also used in the design of the high-lift system, and to predict the maximum lift-coefficient with slats and single-slotted Fowler flaps deployed.
Bombardier says that winglets result in a lower aircraft weight for the mission. Several design iterations were evaluated in a bid to avoid flow separation at the junction of the winglet with the cambered wing. The final design avoids unsweeping of the pressure isobars at the wingtip. Design of the wing leading-edge fillet and wing/body fairing relied heavily on Canadair's transonic CFD codes, says advanced-aerodynamics section chief Dr Fassi Kafyeke.
Much attention was devoted to the aft fuselage, because of the large engine nacelles. Over a series of iterations, the fuselage was stretched and recontoured to minimise interference. Area-ruling of the fuselage, and careful contouring of the nacelle and pylon, have resulted in "virtually shock-free flow" between the engines and fuselage at M0.85, says Kafyeke.
Canadair responsibility
As design authority for the Global Express, Canadair is responsible for aerodynamic design, aircraft performance, structure and systems layout, interface definition and certification. The company drew up the system-performance specifications against which bids from potential risk-sharing partners were evaluated. "We buy systems, not components," says Holding, who adds: "Suppliers like the arrangement."
Partners are responsible for the detailed design, installation and performance of their systems. They carry the non-recurring development expenses in return for fixed-price contracts to deliver production systems. They are responsible for the integration of their systems, and many have their own test rigs.
Bombardier has divided its share of the programme between its four aerospace companies: Canadair builds the nose; Shorts manufactures the forward fuselage, horizontal stabiliser and fairings; de Havilland produces the rear fuselage and vertical stabiliser; and Learjet is responsible for flight testing, in Wichita. De Havilland is also responsible for final assembly, in Toronto, while the newly acquired Innotech Aviation completion centre in Montreal will be responsible for outfitting Global Expresses.
Of the nine risk-sharing partners, Mitsubishi Heavy Industries is supplying the wing and centre fuselage; BMW Rolls-Royce is providing the powerplant; Messier-Dowty International is developing the landing gear; the flight controls are from Sextant Avionique; Parker Bertea Aerospace is supplying the hydraulic and fuel systems; Honeywell is furnishing the avionics; Lucas Aerospace is delivering the electrics; AlliedSignal Aerospace is providing the auxiliary power-unit (APU); and the air-management system is from Leibherr Aerospace.
Mitsubishi delivers the wing in two pieces, to be joined by de Havilland to the Airbus-style combined centre wing-box and centre fuselage-barrel structure, also produced in Nagoya, Japan. The firm will deliver the sections fully stuffed with components supplied by other risk-sharing partners, including Sextant flight controls.
Each wing half has four-segment leading-edge slats, three-segment trailing-edge flaps, aileron and six spoiler panels. Winglets, ailerons, flaps and spoilers are composite. Other composite components on the Global Express include the wing/body fairings, cabin floor, rear pressure-bulkhead, nacelles, rudder, elevators and horizontal stabiliser - the latter is Bombardier's first composite primary structure.
Bombardier's systems-design philosophy is that the Global Express should provide the level of reliability passengers expect. The target is 99.5% despatch and mission-completion reliability, achieved by providing the redundancy required for airline extended-range twinjet operations and using airliner-standard systems.
Bombardier considered fly-by-wire controls, but could not convince its customers of the benefit. Instead, the flight-control architecture is similar to that of the Challenger/Regional Jet. Primary controls are fully powered, and designed to allow safe flight following a dual hydraulic failure. Cable runs are duplicated, with an automatic disconnect in the event of control jam. Ailerons and elevators each have two power-control units; the rudder has three. The trimmable horizontal stabiliser has dual electric motors.
Secondary flight controls include dual-spoiler electronic-control units driving electrically signalled, hydraulically actuated, outer multi-function panels, to assist the ailerons and improve roll handling; and the inboard hydraulically controlled ground spoilers. Dual-flap/ slat electronic-control units command the dual-motor slat and flap power-drive units, connected by rigid driveshafts to ball-screw actuators. Sextant supplies primary and secondary controls, partnered by Parker Bertea and Sundstrand.
Bombardier says that the Global Express will have a natural aerodynamic stall. As the slats do not extend all the way to the fuselage, the inner wing will stall first, providing a natural recovery. Because of the T-tail, however, the aircraft will be equipped with a stall-protection system with stick shaker and pusher, to preclude a deep stall.
ELECTRICAL design
The electrical system is a departure for Bombardier. Lucas proposed variable-frequency power generation, which the company says is lighter, more efficient and more reliable than the constant-frequency system used in the Challenger/Regional Jet. Two 40kVA variable-frequency generators are mounted on each engine, providing four independent AC buses, backed up by a 45kVA APU-mounted generator and a 9kVA ram-air turbine.
An electrical-management system controls power generation and distribution, automatically reconfiguring the system and prioritising loads in the event of a failure. The system includes two cockpit control/display units, designed to reduce pilot workload, and circuit-breakers in the cockpit have been reduced by about 75%, Bombardier says. Lucas teamed with Leach to develop the electrical system, and suppliers include Eldec and SAFT.
Hydraulic-system architecture is similar to that of the Challenger/Regional Jet - a triplex system providing dual redundancy on critical flight controls. Fuel is stored in "wet" main and centre wing-box tanks and an aft-fuselage bladder tank. Maximum fuel load is 18,600kg. Fuel from the aft and centre tanks is transferred to the main wing tanks, from where two AC-motor pumps and a back-up DC pump feed fuel to the engines. A fuel-quantity management system balances the left and right tanks.
Bombardier says that the integrated air-management system has an "Airbus" architecture. The system performs air-conditioning, cabin-pressurisation and anti-icing functions. Dual air-cycle cooling packs with ozone converters and bleed-air filters supply 1.36m3/min/ person of fresh air - increasing to 1.87m3/min/ person with pilot-selectable recirculation, which can be used to warm or cool the cabin rapidly.
Dual digital pressurisation-controls are linked to the flight-management system and the 0.67bar (9.7lb/in2) pressure-differential provides a 6,000ft cabin altitude at 45,000ft, increasing to 7,230ft at the aircraft's 51,000ft service ceiling. Engine bleed-air is also used to de-ice the wing slats and fixed leading edges: the tail is not de-iced. A bleed-management system switches between low-pressure (fifth stage) and high-pressure (eighth stage) compressor air to improve engine efficiency.
Messier-Dowty's contribution includes the nosegear and trailing-arm main gear - both dual-wheel - low-pressure tyres, carbon brakes and brake-by-wire and steer-by-wire systems. The dual digital brake/anti-skid system provides pilot-selectable, three-level autobraking capability. BFGoodrich and Hydro-Aire are suppliers to Messier-Dowty.
BMW Rolls-Royce's BR710-48 turbofan for the Global Express also powers the rival Gulfstream V ultra-long-range business jet, but is optimised for the Bombardier aircraft. Changes include thrust ratings, accessories, bleed-air management, full-authority digital engine-control software, and inlet and nozzle orientation.
The engine, with a 1.2m-diameter wide-chord fan, produces 65.3kN (14,690lb) take-off thrust and is flat-rated to ISA+20íC. It was certificated in August, and approval of the Global Express version is expected in February 1997. International Nacelle Systems, a Shorts/ Hurel-Dubois joint venture, is supplying the nacelle and target-type thrust-reverser to BMW R-R.
BMW R-R is also a partner in development of AlliedSignal's RE220(GX) APU for the Global Express. This all-new, digitally controlled, APU, also used in the GV, will be certificated for operation up to 45,000ft, in-flight starting up to 37,000ft and engine starting up to 30,000ft. The APU is mounted in the tailcone, for reduced noise and improved access, and can be replaced in 45min, Bombardier says.
Step inside suite
Honeywell's Primus 2000XP integrated-avionics suite is built around three computers which provide a fail-operational automatic flight-control system, four-screen electronic flight-instrument system (EFIS), two-screen engine engine-instrument and crew-alerting system (EICAS), dual flight-management systems and dual autothrottles. The EFIS and EICAS have large, 200 x 250mm, cathode-ray-tube displays.
The standard suite includes triple laser inertial-reference systems and digital air-data computers, a global-positioning system and the traffic-alert and collision-avoidance system. There are provisions for satellite communications, and a fintip-mounted antenna. Honeywell has integrated AlliedSignal's enhanced ground-proximity warning system (with terrain database) into the Primus 2000XP for EFIS display.
The EICAS displays system synoptics, as well as engine instruments and crew-alerting and status messages. Ametek is supplying the four data-acquisition units used by the EICAS and the central aircraft-information and maintenance system, which is designed to simplify maintenance by logging faults and identifying faulty line-replaceable units. These are located under the cabin floor, accessible via a crawlspace, and target replacement time is 20min.
All this will be of secondary interest to Bombardier's real customer - the chief executive who can approve an outlay of $34 million for a completed Global Express. Cabin comfort is the aircraft's major selling point. From the starting point of the Regional Jet's 14.6m-long, 2.5m-wide cabin, Bombardier has dropped the floor by 51mm, to give a 1.9m cabin height, and enlarged the cabin windows by 25%.
The design requirements were for a three-compartment cabin with a large galley and lavatory aft and a crew rest-area and small lavatory forward. The engines are located entirely aft of the flat rear pressure-bulkhead, as is the 5m3 (175ft3) baggage compartment, and Bombardier is predicting a cabin noise level of 50dB.
The first Global Express to have an interior installed will be the fourth aircraft, due to join the 2,000h flight-test programme by mid-1997. The first customer aircraft will be delivered to Bombardier's Montreal completion centre in late 1997, ready to enter service immediately following certification in May 1998.
Although the Global Express has rivals ranging from Dassault's smaller Falcon 900EX through the Gulfstream V to Boeing's larger 737-700 business jet, Bombardier and its risk-sharing partners remain confident that the aircraft's combination of range, speed and cabin size will ensure the programme's success.
Source: Flight International
