G650: As good as it gets?

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When Gulfstream begins assembling the first of its next-generation executive jets in October, the milestone will mark the realisation of the first clean-sheet aircraft design and type certificate for the company since the start of the Gulfstream II in the early 1960s.

t will also be the acid test of a new-build philosophy designed to halve part counts and build time down from the 14 weeks it takes to construct a "green" G550, today's flagship.

The result promises to be well worth the wait. Tomorrow's line leader, the G650, set for a first flight in 2009, certification in 2011 and service entry in 2012, will be "the longest-range, highest-speed, largest aircraft Gulfstream has ever built", says Nick Chabraja, chief executive of General Dynamics.

Chabraja made the comments at a March unveiling ceremony of the programme at Gulfstream's headquarters in Savannah, home of the new $100 million 28,400m2 (306,000ft2) assembly plant for the G650.

 g650
 © Gulfstream
The G650

The largest and most spacious aircraft in Gulfstream's portfolio, the G650 has already received an immense amount of engineering and windtunnel attention to assure it will display exemplary handling characteristics and be the fastest business jet in anyone's hangar.

"The data confirms we'll get to M0.925," says Pres Henne, senior vice-president for programmes, engineering and test at Gulfstream.

The "5" digit is key, as it makes the G650's top speed one-half of 1% greater than today's fastest business jet, the M0.92 maximum mach number Cessna Citation X.

Gulfstream's confidence is the result of more than 1,400h of windtunnel tests at seven locations, including the European Transonic Wind Tunnel where the company tested for the first time in its history a semi-span 9%-scale model at full-scale Reynolds numbers, providing the most accurate real-world lift and drag results.

"Not being able to test to full scale has been the bugaboo on previous aircraft," says Henne. Gulfstream also tested its windtunnel model out to M1.0 to validate the computational fluid dynamics (CFD) model at the aircraft's design dive speed of M0.99. "We sometimes flight test beyond M1.0," Henne adds.

Much more than speed fuelled the internal launch decision for the $1 billion development programme in 2005, however. Gulfstream several years before reached out to its advanced technology customer advisory team (ATCAT), which is comprised of a cross-section of owners from the 70 countries that have purchased Gulfstream aircraft.

"The ATCAT gave us the confidence that this aircraft will be a market leader," says Henne. The 75 customers, working in four committees including flight operations and maintenance, had been meeting twice a year for three days at a time in Savannah, crafting a "design list".

Included in the "desirements" was an aircraft with more width and speed than the G550, more range being a secondary consideration. "If you can go further, great," Henne recalls of the list.

Gulfstream then translated the design list into direct and indirect design requirements. In the performance realm, the aircraft's range would be more than 12,965km (7,000nm) at a cruise speed of M0.85 (the G550 can fly 12,490km at its cruise speed of M0.80) or more than 9,260km at M0.90 (the G550 can fly 11,110km at its high speed cruise of M0.85).

Maximum take-off weight would have to come in at less than 45,360kg (100,000lb), allowing the aircraft to use weight-capped key business aviation hubs like Teterboro near New York.

Take-off distance would be similar to the G550, less than 1,830m (6,000ft), landing distance would be 915m or less and maximum operating altitude would be 51,000ft, the same as for the G550.

LARGER WINDOWS

For passengers, the aircraft would have a wider and taller cabin - 7.6cm (3in) taller and 35.6cm wider than the G550 - putting it on par with the Bombardier Global Express cabin, but with larger windows.

The G650's new trademark oval windows are 71cm wide and 133cm apart with eight windows on each side. Gulfstream also rotated the windows upward 8.6cm to make for more comfortable viewing of the ground.

The G550 has 14 windows, each at 66cm wide and 124cm apart, in total yielding 16% less window area than the G650. By comparison, the Bombardier Global 5000 has nine more windows, but each measures only 27.9 x 40.6cm.

An enhanced cabin environment includes an industry-leading pressurisation that will yield a 4,850ft cabin at FL510 or a 2,800ft cabin at FL410, the lowest available. The cabin will also have lower sound levels and fully renewed air volume every 90s.

g650-general-arrangement

Although conceived as a replacement for the G550, in service since 1993 with more than 200-plus aircraft fielded, Gulfstream later decided to build the new aircraft and continue G550 and G450 production, spawning the need for a new manufacturing facility where it could take full advantage of 3D design tools being used to develop the aircraft concurrently.

Implicit in the requirements for manufacturing of the new aircraft were increased use of composites, standardised parts and significantly fewer of them, lean manufacturing and precision assembly, elements that combined would make for the faster production and help secure the ultimate goal of an aircraft that is for all practical purposes, always ready to fly - 99.75% or greater reliability and 90% or more availability.

With larger, more powerful Rolls-Royce BR725 engines and new wing design, featuring composite winglets, 13% more wing area, 1.83m additional span and 6° more sweep than the G550, the aircraft has a higher cruise speed that will cut nearly 1h from the time it takes to fly an existing ultra-long-range business jet for a 17,315km trip (Geneva to Sydney, for example).

For a 5,555km trip, Gulfstream estimates the G650 will burn 7,257kg (16,000lb) of fuel at M0.85, almost 910kg less fuel than the G550 for the same trip and about 1,360kg less than the Bombardier Global Express XRS, a savings that translates to more than 4t less CO2 generated.

A variant of the G550's BR710 engine, the BR725 features a 1.27m-diameter fan (up 5cm from the BR710 fan) and a 24-blade swept-design fan with a solid titanium case.

The core has a two-stage shrouded high-pressure turbine and new three-stage low-pressure turbine, up one stage from the BR710. As the a whole, the engine features 4.6% higher bypass ratio (4.1:1 compared with 3.84:1) and provides 16,100lb (71.8kN) of take-off thrust, flat rated to IAS 15°C (59°F), up 4.6% from the BR710, and an additional 12.6% thrust for climb.

Thrust to weight for the engine is 3% improved at take-off and 11% in climb, and specific fuel consumption is 4% better in cruise, down to 0.657 at M0.85.

From an environmental view, the BR725 will be 33% quieter, generate 5% less NOx and 10% less smoke than the BR710, coming in at 16dB below Stage 4 noise limits.

R-R has four of the eventual five engineering test engines up and running and is on schedule to deliver the first of four flight-test engine sets to Gulfstream early next year to support first flight of the G650 in the second half of the year.

A superior performer, the engine is not designed to be retrofitted to earlier Gulfstream jets in part because the attach mounts are 7.62cm wider for the new engine and the nacelles are different.

The composite nacelles, built by Spirit Aero­Systems, also the manufacturer of the G650 wing, include a new high-efficiency thrust reverser that generates higher flow rates, hence increased reverse thrust for more stopping power.

Although it has the same maximum diameter of the BR710 nacelle, built by Vought, the BR725 nacelle has a new inlet cowl for the larger-diameter fan of the new engine. Along with the nacelles, Vought also builds the wings for the G550 and other Gulfstream aircraft.

FIRST COMPOSITES

The G650 will also have a Fokker-built composite horizontal stabiliser and elevator combination, the first application of composites for flight critical structures for the company.

Other composite structures include the wing-body fairing and main landing gear doors, built by Nordam, floor boards and rudder, also built by Fokker, and radome, built by Saint-Gobain.

More than elegant, the G650's new longer, wider Spirit-built metal wing, featuring 33° sweep at the quarter-chord point for reduced shock strength, are key to its performance prowess.

Wingspan is 30.35m, just 5cm shorter than the 30.4m fuselage length. Although the planform and aerofoils are new, the basic wing is similar to the G550's in that there are no leading edge devices or drag-producing flap-tracks and associated fairings. Wing area is increased 8% to 119m2 for more lift, with an additional 0.9m span per side for improved span loading and decreased induced drag.

Winglets are canted outboard from the vertical more so than for the G550 to boost performance. Henne says the wing is 8% more efficient than the G550 wing due as its maximum lift over drag point occurs at Mach 0.055 faster.

"We got the peak efficiency out to M0.855," Pres said earlier this year, "and this aircraft will be used in the M0.90 range a lot."

Wing leading and trailing edge design as well as a continuously varying aerofoil work together to reduce the effects of drag-producing shock waves at high speeds. As a result of the higher wing sweep, engineers increased the sweep and throw of the ailerons to boost roll authority.

All 20,050kg of jet fuel will be held in the G650's wet wings. Like the G550, the G650 uses a heated fuel return system to ensure fuel flow during high-altitude, long-duration flights at low temperatures.

New for the G650 is the fuel quantity monitoring system (FQMS), built by Zodiac subsidiary, Intertechnique. The system uses a distributed architecture that prevents a single failure from masking fuel quantity.

Gulfstream says the FQMS sensor arrangement - a combination of low-level, high-level, temperature and fuel characteristic sensors - will eliminate fuel stratification issues, and testing is under way to prove out the design using a one-third scale wing mock-up developed by Intertechnique.

Other G650 fuel features include larger diameter fuel tubing and electronically controlled refuelling that result in a maximum imbalance of 90kg, while the tanks can be filled in as little as 26min under 3.44bar (50lb/in2) pump pressure, down a factor of two from the 45min needed to completely fill the G550.

Fuel removal will also be quicker by a factor of two, down to 2h from 4h for the G550 assuming a pump pressure of -0.55bar.

Not to be outdone by the wings, the fuselage too will have new-found graceful curves. "It's almost unreal looking," says Henne of the first completed nose article, so smooth it did not require sanding before being painted.

gulfstream g650 cutaway small

Behind the perfect skin is a new bonding process developed by risk-sharing partner Stork Fokker, supplier of the empennage and metal fuselage panels.

The process results in a 60% reduction in fasteners, which went a long way toward reducing the overall part number and part count by half. The nose article is now being used in a test facility.

LEAN MANUFACTURING

As part of an overall lean manufacturing process in the new plant, the panels are built up by first bonding stringers and doublers to the skin, after which panels are mounted into integrated panel assembly cells for automated riveting to the machined frames.

Precision carts are used to move the fuselage sections, built with harnesses, hydraulic, oxygen and fuel lines as well as avionics components, actuators and controls installed, through the workstations, a method that maintains reference points and eliminates the need to hoist the barrels.

Wire harnesses are modular, minimising wire-to-connector pinning during assembly and saving installation time. Gulfstream initially plans to build 35-45 aircraft a year. The plant has the capacity to construct 90.

Gulfstream proved its design philosophy on a full-scale fuselage section, bending and twisting the article to as much as 265% of its limit load (limit load is the maximum load the section is expected to see at least once in its design life) with the structure in each case returning to its original shape and no disbonding.

g650-g550-cabin-comparison

The barrel was also pressure tested to 1.26bar to validate the new window box structure designed for the larger windows. The G650's fuselage no longer has a round cross-section, but rather an oval that is wider at the bottom to increase roominess and height while decreasing drag.

Gulfstream used the load-bearing capability of the composite cabin floor to minimise the weight penalty brought on by the more complex shape. Henne says the aircraft was designed around the cabin, with the ultimate choice in width a compromise between Gulfstream and its parent company, General Dynamics.

Development aids for the project include Catia V5 and Enovia 3d, model-based 3D design packages that give engineers the ability to simulate systems and structures and avoid interference issues.

Engineering and manufacturing elements of the programme were completed in parallel, with Delmia software used to develop and simulate an ergonomically efficient manufacturing process.

The company also brought in the Georgia Institute of Technology, and the Savannah College of Art and Design to help with cabin interior design, work that resulted in a 3D virtual cabin computer model and ultimately, a full-scale cabin mock-up.

Gulfstream had earlier built an advanced flight control "iron bird" test rig to gain confidence in its choice of fly-by-wire for the G650, the first FBW control system application in the company's history. Dassault was the first to introduce FBW on a business jet with the Falcon 7X, which was certificated in April 2007.

g650-key-features.

While the G650 cockpit from the pilot's perspective will look much like the G550, so much so that Gulfstream hopes to offer a common type rating for the two aircraft, the innards of the control system are radically different.

Gone are the mechanical connections from the control column and rudder pedals to the flight-control surfaces. Instead the FBW system will collect electrical inputs from the cockpit controls, process the information through Thales-built redundant flight control computers, which will also impose flight envelope checks, and send control signals to Parker Aerospace-built dual electro-hydrostatic actuators at the control surfaces and spoilers.

The envelope protection will eliminate the need for a stick pusher by providing stall protection at low airspeeds and buffet margin at high airspeeds.

QUADRUPLE REDUNDANCY

Safety is paramount in the system. The two computers driving the three-axis primary flight control system each have two dissimilar channels and each channel can command every control surface, for quadruple redundancy.

Each actuator is powered by redundant hydraulic pumps that feature 50% more flow than in the G550 and internal hard-over protection. If there are issues with both primary flight control systems, the G650 has a completely independent safe mode that includes a three-axis back-up flight-control unit that is designed for "get home" purposes. 

In the hydraulic system, the last lines of defence are self-contained electric backup hydrostatic actuators (EBHA) with independent power sources.

Back-up systems notwithstanding, continuous electrical power is virtually assured on the G650 with two 40kV engine-driven generators, one 40kV APU driven generator and one 15kV deployable ram air turbine.

Additional get-home power is provided by two new lithium-ion dedicated batteries for back-up of the flight-control system, one battery for the actuator controller and flight-control computers, the other for uninterruptible power to the EBHAs. There are also two dedicated batteries for emergency cabin and over-wing lighting.

New efficiency and weight savings in the electrical system will be realised with the G650's solid state power distribution system, which will be used for non-flight-critical electrical loads including water, taxi lights, pulse lights, landing lights, cockpit window heat and cabin window heat.

The system eliminates 400 circuit breakers by using solid state power controllers instead, cuts weight by 135kg compared with previous systems and removes the need for more than 5km of wiring, says Gulfstream.

Pilots will be treated to the zenith in avionics systems with the Planeview II package, an evolution of the Honeywell Primus Epic-based Planeview I integrated avionics suite in other Gulfstream aircraft.

The cockpit features four 14in adaptive LCD screens as in the G550, but with a new 5in display called the standby multifunction controller, a screen that provides back-up flight displays in an emergency but is nominally available for refuel control, cabin pressure control, weather radar control, hydraulic and oil level display, tyre pressure and post-shutdown oil quantity capture. The system automatically reverts to its back-up flight display mode when power is lost.

Planeview II features synthetic vision, EVS II and a Rockwell Collins HGS-6000 head-up display as standard equipment, the combination being a foundation for qualifying for Category 1 approaches down to 100ft above the runway.

Along with being RNP 0.1 capable, the cockpit will be equipped for FANS-1, controller-pilot datalink, WAAS GPS, LPV approaches, Honeywell INAV flight planning and automatic emergency descent for pressurisation emergencies.

NO SIDESTICKS

Gulfstream opted to keep the interconnected control columns, built by Rockwell Collins, for the new aircraft rather than using sidestick controllers, in part so that pilots would be aware of control inputs being made by the autopilot.

Henne says technology for active sidestick controllers is not yet mature. A full-motion simulator and maintenance trainer for the G650 will be ready for pilot training in 2011 at FlightSafety's Savannah facility, says Gulfstream.

Pilots will also have brake-by-wire control with electrically commanded and controlled and hydraulically actuated brakes. Along with a brake temperature monitoring system, the G650 will have a new tyre pressure monitoring system as well as a new parking brake system featuring an ergonomic control handle.

A landing gear control and indication system will replace the complex interplay of linkages, bungees and timer valves previously used to sequence gear and doors.

Confidence in the cockpit and cabin will be the realm of the G650 integration test facility (ITF), which includes a fully functional flightdeck and cabin electronic mock-ups that simulate the complete aircraft in terms of systems, including the network architecture and wiring.

The ITF will remain intact throughout the programme as a tool to evaluate flightdeck software or hardware upgrades, troubleshoot issues with cabin functions or investigate proposed upgrades or changes.

Gulfstream has similar testbeds for the G550 and G450, although not to the fidelity of the G650 ITF, which includes a transparent floor that allows engineers to view the flow of fluids through piping under the floor.

Gulfstream is targeting 99% availability for the G650 due to planned maintenance, including airworthiness directives and alerts. In the areas of scheduled maintenance under the MSG-3 programme, however, the company is targeting an availability of 97%, up four points from the G550.

For unscheduled maintenance, the goal is an availability of 95%, up three points from the G550. To make that happen, G650 line replaceable units are being designed to be removed and replaced in 30min, more built-in-test equipment is being incorporated into equipment and Gulfstream is asking vendors for improved mean time before failure and health and trend monitoring on key components.

In operation, Gulfstream's PlaneConnect option will automatically email an operator about maintenance status while an aircraft is in flight.

In keeping with its focus on the cabin, Gulfstream has designed the G650 so that no single-point failure will result in a loss of cabin functionality.

This means a toilet will always flush, water will always be available and will drain, voice communications cabin to ground will always be available, there will never be a complete loss of cabin lighting and at least one entertainment source will always available.

The cabin also features Gulfstream's largest main entry door, more than 1.83m tall at the entry area and equipped with a handrail extended to the end of the stairs for support all the way to the ground.

The G650 will have 5.52m3 (195ft3) usable volume in the baggage compartment, up 11% from G550, with 2.93m2 floor area, up 9% from G550.

There is a 109 x 90.7cm exterior door that is 8% larger than the G550's and is 10cm lower to the ground for easier bag loading. The pressurised heated area is also accessible in flight to FL510. Gulfstream is building five aircraft for the 18-month, 1,800h Part 25 flight-test campaign, two of which will represent production aircraft.

PARTS FLOWING

As of late September, Henne says roughly 92% of the 3D models needed to build the aircraft had been released, parts were "flowing" and the ITF had been powered up.

First panels are to be completed in October. General Dynamics in July had reported that 100 of the 500 letters of interest from potential customers had been converted to firm orders, and the company planned to convert most of the remaining 400 by year's end. Gulfstream would not comment on the current order status.

G650 could be zero/zero candidate

Gulfstream is leading an industry effort to develop a combined synthetic and enhanced vision system that pilots could use in the near future to fly an aircraft to the ground in virtual visual flight rules conditions regardless of the actual weather, with few or no ground aids.

Referred to as equivalent visual operations (EVO) by the US Federal Aviation Administration, the operation is a natural next step for most of the equipment that will be standard on the G650, namely the SV-PFD synthetic vision and EVS II enhanced vision system. It is conceivable that an EVO system could be realisable by the time the G650 goes into service in 2012.

Gulfstream will not provide details on its approach, just that engineers and pilots are evaluating an EVO system. Industry consensus however points to "fused" system that will combine a computer-generated synthetic view (SV) of the terrain derived from an on-board terrain and obstacle database with a sensor-based infrared view ahead of the aircraft, similar to the output of today's enhanced vision systems.

Appropriately equipped and trained crews in the USA and Europe today can use an EVS view through a head-up display in place of their natural vision descent to 100ft (30.5m above the ground for a Category 1 instrument approach, which normally has a 200ft minimum descent altitude. One missing link for descending lower at the moment is a sensor that can validate the terrain and obstacle data in real time, independent of weather effects that can "blind" an EVS, such as dense fog. Candidate technologies for the missing link include millimetre wave radar or possibly modified weather radar.

REGULATORY CHANGES

Just as important as the technical solutions are the regulatory changes that will be required. A joint US and European working group under the auspices of RTCA and Eurocae WG-79 is meeting this week in Bordeaux, France to, among other tasks, plot out the potential future for enhanced flight vision systems and EVO by crafting a consensus-based advanced vision system concept of operations (conops).

Rather than jumping straight into a plan for a "zero/zero" system that would let pilots land with zero forward or down visibility, representatives will first develop conops for vision technologies that will extend today's EVS-aided minimums.

The group, consisting of government and industry volunteers, could later begin developing technology-agnostic minimum aviation system performance standards (MASPS) for EVO, a first step to developing new rules and consistent standards that would allow manufacturers to build certificatable equipment to perform the procedures. The primary purpose of the meeting in Bordeaux is to approve MASPS for the EVS systems that have already been approved on a case-by-case basis.

Gulfstream has two representatives on the RTCA committee (SC 213), highlighting the importance the company is placing on EVO. Pilots of Gulfstream aircraft with both synthetic and enhanced vision (not fused) today are already seeing benefits of merging the two technologies. In one example, pilots are using the extending runway centreline feature of SV-PFD to point their eyes in the right direction to acquire runway lights when it comes time to transition to natural vision from the EVS.

ROLLS-ROYCE BR725 SUCCESS IS A FAMILY AFFAIR

The bedrock principle of Rolls-Royce's approach to creating a new turbofan engine for the Gulfstream G650 was low risk: upgrade the proven BR710-family engine platform and incorporate latest technologies from its "toolbox" of other engine programmes.

What has emerged from R-R laboratories after much fine tuning, however, is a "Formula 1 engine for the corporate market", says Rainer Hönig, director of the BR725 and future corporate and regional engine programmes at R-R.

Hönig says the development of the BR725 has been innovative due to the compressed schedule, with first engine test runs taking place in late April, just over one month after the programme was unveiled by Gulfstream. The first engine incorporated more than 1,600 measurement points in the low-pressure system (fan and low pressure turbine), transmitting information wirelessly to the test group. The second engine was used for a 150h endurance test that simulates an entire lifetime of operations by running at redline conditions.

"It exceeded our expectations," says Hönig of the test. "We're very confident the rest of the programme will go just as smoothly."

TECHNOLOGY

That confidence in part comes from transferring technologies from other successful R-R programmes, including the swept fan blade design from the Trent 800 for the Boeing 777 and the combustor design for the BR715, which powers the Boeing 717. For the high-pressure turbine, R-R is for the first time on a corporate aircraft actively controlling the tip clearance on both stages of the high-pressure turbine, a feature also used on Trent engines. By controlling the distance between the shroud and turbine blade tips by cooling the turbine casing, the manufacturer is able to reduce losses over the tips and optimise the turbine performance to improve cruise fuel burn.

Overall, specific fuel consumption for the BR725 is 4% lower than for the BR710, the engine for the Gulfstream G550 and other corporate aircraft. The BR710 has shrouded blades on the first HPT stage and no shrouds on the second. R-R also improved the HPT efficiency through 3D computational fluid dynamics (CFD) modelling of various core components and moving to elliptical leading edges on the HPC blades.

For the LPT, a third stage was added to account for the larger fan diameter - 127cm (50in) compared with 122cm for the BR710 - and used three-dimensional modelling to reduce the parts count for the section. The company took weight out of the compressor where possible using 3D CFD modelling, part of a larger push to increase the thrust-to-weight ratio of the engine up 3.6% from the BR710.

Thrust-to-weight was also increased by moving to a new accessory gearbox and modular architecture electronic engine control unit brought over from the Trent 1000 development programme for the Boeing 787. R-R also moved to composites to reduce weight where possible, including fan outlet guide vanes and front spinner.

Testing of various engine components is under way at four sites around the globe, with delivery of the first two test engines to Gulfstream in Savannah expected by early 2009. Future key tests include crosswind, bird strike and fan blade-off tests, says Hönig.