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FLIGHT TEST: Gulstream G450 - Heir apparent

The G450, the latest in Gulfstream's family of business jets, enters service next year. Can it live up to its illustrious predecessors? We assess its performance

If one aircraft cemented Gulfstream's success in the business jet market, it is the long-range, large-cabin GIV. Production of the GIV, improved GIV-SP and rebranded G400/G300 has totalled 537 aircraft - far more than any other Gulfstream - and it is not the end of the story. Production continues with the next-generation G450 and G350.

Certificated in August, the G450 began life in 2001 as the GIV-X, the third generation of a business jet family that began with the original GIV, launched in 1985, and continued with introduction of the GIV-SP in 1993. In 2002, the GIV-SP was rebranded the G400 and last month production transitioned to the new G450, with entry into service planned for the second quarter of next year.

Over that time, competition in the long-range segment has not stood still, with Dassault improving its Falcon 900 and Bombardier introducing the Global 5000 derivative of its ultra-long-range Global Express. The $33.5 million G450 carries eight passengers 8,060km (4,350nm) at Mach 0.8, 465km further than the G400. This compares with 7,630km at M0.8 for the $34.65 million Falcon 900EX. At M0.85, the G450 flies 6,485km, almost 955km further than the G400. This compares with 8,880km at M0.85 for the $33.5 million Global 5000, which enters service late next year.

The G450 shares the 88.3m2 (950ft2) wing of the GIV/G400, but with several minor differences. About half of the vortex generators have been removed from the wing's upper surface and the actuator rod for the trim tab on the left aileron, previously exposed, is now covered in a canoe fairing. Flow visualisation tests led to removal of all vortex generators above the cockpit and the addition of stakes on the engine nacelles that measurably reduce compressibility drag.

Big enhancements

Some of the biggest enhancements the G450 offers will be appreciated by its pilots. One common complaint was the small size of the GIV/G400 cockpit. The fuselage has been extended 0.305m (1ft) and main entry door moved aft 0.914m, allowing a lengthened cockpit. The extra length eases flightdeck entry and exit, and alleviates the feeling of being shoehorned into the cockpit.

The G450's cockpit and forward fuselage are essentially identical to the ultra-long-range G550's, with the same PlaneView integrated flightdeck, head-up display (HUD) and enhanced vision system (EVS) as standard equipment. PlaneView is based on Honeywell's Primus Epic avionics and features four 355mm (14in) -diagonal liquid crystal displays in landscape format. The EVS displays images from Kollsman's undernose infrared camera on Honeywell's HUD, which has a 30° x 25° field of view.

As with the GIV/G400, the motive power is two Rolls-Royce Tay turbofans. The G450's Tay 611-8Cs introduce full-authority digital engine control (FADEC) and feature a 20mm (0.8in) -wider fan than in the G400's 611-8s. The larger fan and turbine enhancements reduce specific fuel consumption by about 2%. Thrust at sea level is unchanged at 13,850lb (61.6kN), but hot and high performance is improved, with 5% more thrust at 5,000ft and ISA +20°C. Cruise thrust above 30,000ft is increased by 3-5%.

FADEC and turbine material and cooling changes increase temperature margins and extend turbine life, with time between overhauls increased from 8,000h to 12,000h. New lightweight, low-drag Nordam thrust reversers have been incorporated. The Tay has proved to be a reliable engine, with an in-flight shutdown rate significantly lower than the minimum for 180min extended twin-engined operations (ETOPS).

Advanced cockpit

The G450 is the latest aircraft to receive Gulfstream's PlaneView advanced cockpit, after the G550 and G500. With certification of the shorter-range G350 earlier this month, the company has a common cockpit across all four of its large-cabin aircraft, allowing them to share a single pilot rating. The four large displays are arranged conventionally across the cockpit. Each display can be configured in either a full-screen or lateral-segmented one-third/two-thirds window format. The one-third portion is further divided into two independent one-sixth-screen windows.

PlaneView is best compared with Dassault's EASy integrated flightdeck, installed in the competing Falcon 900EX, which is based on the same Honeywell Primus Epic avionics, but differs in execution. Dassault divides information into two categories, with tactical information on each pilot's primary display and strategic information on two displays stacked vertically in the centre of the panel to form a shared workspace. While in EASy the primary flight display (PFD) occupies the outboard two-thirds of each pilot's display, in PlaneView it occupies the inboard two-thirds.

The cursor control devices (CCD) are also distinctly different. Instead of EASy's two centre-console trackballs, the PlaneView cursor controls are handgrips mounted on the cockpit sidewalls, reminiscent of a fighter's switch-festooned throttle. The cursor is slewed by a thumb controller, while the "ENTER" function uses an index-finger trigger switch. The cursor is "jumped" from display to display with three buttons located just above the slew control. In EASy the cursor is slewed from display to display with the trackball. And while EASy has a rotary knob on the CCD panel to change display scales, I found PlaneView's CCD thumb scrollwheel easier to use.

On the G450 three multifunction control display units (MDU) on the centre console interface with the triplex synchronous flight-management systems (FMS) as well as navigation and communication radios and datalink. The EASy has two centre-console multifunction keyboards. While in EASy most interface is via pull-down menus, in PlaneView most tasks can be accomplished either using pull-down menus or MCDU keystrokes. For pilots moving from conventional glass-cockpit aircraft, PlaneView may provide an easier transition than EASy.

Hand flying

While both manufacturers' CCDs are functional and easy to use, their differing locations in the flightdeck is noteworthy. Cockpit duties are usually broken down into pilot flying (PF) and pilot not flying (PNF) tasks. With the autopilot off, typically the PF flies and the PNF performs tasks such as entering route changes into the FMS. Pilots typically use their outboard hand to fly the aircraft and in the PlaneView cockpit, with the autopilot off, the PF must remove his hand from the yoke to use the CCD. This should remind him he is no longer flying, and that the task perhaps should be accomplished by the PNF.

HUDs are becoming commonplace in business jet cockpits, but Gulfstream is the first manufacturer with a certificated EVS. The Kollsman-developed All Weather Window is a cooled indium antimonide staring-array (320 x 240 pixels) sensor mounted beneath the nose of the aircraft.

The sensor operates at wavelengths of 1-5µm, covering the near and medium IR "windows" of atmospheric transmissivity. Approach and runway lights are visible in the lower window, 1-2µm, background features in the higher one, 3-5µm. EVS can allow visual-like operations in reduced visibility conditions such as fog, smoke, haze or night, allowing the pilot to see far beyond the range of an unaided eye.

Flying the G450

Flight International was given the opportunity to evaluate the G450 during a recent test flight from Gulfstream's Savannah, Georgia plant. Jake Howard, lead G450 project pilot, conducted the preflight inspection of the third development aircraft, serial number 4003. This aircraft was the avionics workhorse for the certification programme and features a production-representative flightdeck and engines. The engine nacelles did not have the production drag-reducing strakes installed.

While the G450 will typically seat 13 passengers in either a forward or aft galley configuration, aircraft 4003's cabin was configured for flight test operations with no interior sidewall panels and only a computer workstation installed. A new vacuum lavatory and conformal potable-water tank combine to give the G450 a larger, 4.79m3 (170ft3) heated and pressurised baggage compartment accessed through a door under the left engine and in the air through the lavatory at the aft end of the cabin.

Seated in the cockpit, I used the coloured alignment balls on the centre pillar to find the design-eye seating position. The balls have horizontal lines to further refine eye position, critical when using the HUD/EVS. Howard started the Honeywell auxiliary power unit (APU) in preparation for engine start. The new APU is significantly quieter than the GIV's and has a demonstrated 6,000h mean time between failures in the regional market. The APU drives a 40kVA electrical generator and can be operated in flight at altitudes up to 37,000ft.

Aircraft position for initialisation of the three inertial reference units was taken from the dual GPS receivers. FMS initialisation and pre-start tasks were easily accomplished, Howard using the PlaneView electronic checklist (ECL) to ensure completion. As in the EASy flightdeck, the ECL does not sense switch or system status.

Both engines were started individually with bleed air from the APU. I used the PlaneView electronic charts menu to display Savannah's airport diagram, which allowed us to track our progress on the airfield as the aircraft symbol moved on the chart. This should help avoid runway incursions.

 Howard set the flaps to 20° and I used the yoke-mounted pitch trim switch to set the elevator trim position. For normal operations the horizontal stabiliser moves only in relation to flap position. In the G400 the flap and stabiliser interconnect is a torque tube running from the main wheel well to the tail. In the G450 this is replaced by a horizontal stabiliser electronic control unit, saving weight and increasing reliability.

Getting to grips

On the runway I advanced the throttles and hit the throttle-mounted TOGA (take-off/go-around) button. The autothrottles advanced power to a setting of 1.65 EPR (engine pressure ratio). At 80kt (148km/h) indicated airspeed I removed my left hand from the nosewheel steering tiller and took the yoke from Howard. With 6,078kg (13,400lb) of fuel and a zero fuel weight of 18,694kg, including one passenger, V1 was called at 119kt. Approximately 14kg of yoke force was required to attain a 10° nose high take-off attitude at the VR of 124kt. A 20° climb angle was needed to maintain 142kt (V2 +10kt) as the gear was retracted.

We accelerated to 300kt and climbed to 15,000ft for our transit to the working area over the Atlantic Ocean. Once in the area, shown clearly on the PlaneView integrated navigation (I-Nav) display, we descended to 3,000ft for a climb to cruise altitude. Climbing out of 3,000ft the autothrottle set a climb EPR of 1.53 and automatically adjusted the thrust level throughout the climb. Passing 10,000ft, a speed of 300kt was maintained until passing flight level 273 (27,300ft) where Mach 0.75 was held. The aircraft levelled at FL410 just 16min after the start of the climb and with a fuel burn of 705kg. At maximum take-off weight, Gulfstream says, the G450 can climb directly to FL410 and reach it 2min sooner than the G400.

Once level, a calibrated 220kt yielded 426kt true airspeed, or M0.75. Total fuel flow for the 23,388kg aircraft was 1,070kg/h. Accelerating to M0.8/453kt, total fuel flow at our light weight was just 1,135kg/h. At M0.85/483kt total fuel flow was 1,390kg/h.

While unable to evaluate the acoustical environment, I noted that the cabin altitude at FL410 was just 5,300ft. At the aircraft's FL450 ceiling, this increases to 6,000ft. As with the G550, cabin air is not recirculated, and a constant supply of fresh air is provided to the passengers. The 12 Gulfstream-signature oval windows provided a bright cabin.

In response to complaints about window fogging in the GIV/G400, the G450 has the same heated cabin windows as the G550. The G450 also has the G550's quieter environmental control system, and its three-zone digital temperature control system.

The G450 has a large wing, which at maximum take-off weight has a loading of just 380kg/m2, lower than the larger G550's. While still level at FL410, a series of 60° angle-of-bank steep turns at M0.8 produced no buffet, the nose tracking smoothly across the horizon. Like the G550, the G450 autopilot has an emergency descent mode (EDM). If the aircraft is above FL400 with the autopilot engaged, a rise in cabin altitude to 8,000ft will trigger the EDM, the autopilot initiating a 90° left turn and starting a descent at MMO/NMO (M0.88/340kt calibrated). The autothrottle will engage and retard the throttles to idle for a rapid descent. The speedbrakes must be deployed by the pilot.

Howard manually raised the cabin altitude to 8,000ft to trigger the EDM. As advertised, the throttles were retarded to idle and a left-hand turn initiated. At M0.88 I extended the speedbrakes, and a descent rate of over 6,000ft/min was attained. Howard then restored normal cabin pressurisation and disengaged the autopilot for a descent to 15,000ft.

Level at 15,000ft, three stalls were performed. In the clean configuration, with 3,992kg of fuel, the aircraft was slowed at 1kt/s in idle power. At an angle-of-attack (AoA) indication of 0.7, a pitch limit indicator appeared on the PFD and HUD. At 0.75 AoA the airspeed tape turned amber to signify the slow-speed condition. At 127kt indicated and 0.85 AoA, the stick shaker activated. Pulling through the shaker slowed the G450 to 117kt, where the stick pusher fired at 1.0 AoA. No airframe buffet preceded either the shaker or pusher, the wings remaining level throughout the stall. Normal flight was regained by relaxing yoke backpressure and advancing the throttles.

Reality block

The flaps were set to 20° for a take-off configuration stall. In a 20° angle-of-bank turn the aircraft was again slowed at 1kt/s. The shaker triggered at 113kt, with the pusher firing at 105kt. Ailerons and rudder were used to roll wings level as recovery to normal flight was again attained by relaxing yoke backpressure and advancing the throttles. The third and final stall was in the landing configuration, gear down and flaps set to 39°. In wings-level flight the shaker activated at 109kt, with the pusher firing at 100kt. Again no airframe buffet preceded the shaker or pusher. A descent was initiated, and gear and flaps retracted as the aircraft was accelerated out of the stall.

Area work complete, ATC issued vectors to Brunswick, Georgia's Golden Isles airport. The autopilot and autothrottle were engaged and the I-Nav display used to access the approach charts for the airport. Using the CCD I was easily able to select and activate the instrument landing system (ILS) approach to runway 7. At 2,000ft, and on an intercept heading for the ILS localiser, I armed the approach mode of the autopilot.

Flaps were extended to 10°, the autothrottle slowed the aircraft to and held 180kt calibrated. Further extending the flaps to 20° slowed the aircraft to 160kt. With the localiser captured, and just before ILS glideslope capture, the gear was extended. As the flaps were extended to 39°, the autothrottle was set to hold the 22,345kg aircraft at a target speed of 131kt (VREF + 5kt) on final approach. The autopilot did an admirable job of tracking both localiser and glideslope.

At 200ft radar altitude (RA) I disengaged the autopilot and flew the rest of the approach visually. At 50ft the autothrottle slowly retarded the engines to idle for the flare manoeuvre. Passing 25ft light aft yoke pressure was required to start the flare. After initially rounding out a few feet high I was able to milk the aircraft down to the runway, where the flaps were set to 20° for a touch and go. After advancing the throttles, Howard called "Rotate" at 125kt indicated. Once airborne with the aircraft cleaned up, a climb to 2,000ft positioned us for another approach to runway 7.

The I-Nav display and CCD were again used to select the GPS approach to runway 7. With the autopilot engaged I lowered the HUD combiner glass and checked I was still in the correct seating position. Howard put the protective cover behind the combiner, allowing me to see HUD symbology and EVS imagery, but not the real world. The entire approach and full-stop landing was hand flown using only the HUD and EVS.

A target speed of 131kt indicated was again held. Passing the final approach fix, the FMS provided vertical-navigation guidance for a 3.06° glidepath on the non-precision approach, ensuring arrival at the visual descent point in a stabilised condition. I found the flight director's (FD) guidance easy to follow on the HUD. The autopilot was engaged for the approach, allowing me to fully concentrate on flying the aircraft.

On final the runway was clearly visible with EVS, providing a near-visual environment. As the lack of peripheral vision while looking through the HUD would hinder a visual flare, a flare cue is provided and came into view at 100ft RA. At 50ft, as the throttles were retarded to idle, the cue started to move up towards the flightpath marker. At approximately 25ft I captured the flare cue and tracked it as the aircraft flared and alighted on the runway. While not a feather-soft touchdown, it was smoother than my first visual attempt had been. Idle reverse thrust and light wheel braking stopped the aircraft.

The take-off from Brunswick for return to Savannah was performed only using HUD and EVS, my view of the outside world again blocked. While accelerating down the runway Howard retarded the right throttle to idle passing V1 (119kt indicated) and announced "engine failure". With maximum take-off power set (1.65 EPR) approximately 3/4 of the available rudder was needed to keep the aircraft tracking down the runway. Once airborne, full left rudder and a left bank of less than 5° was required to keep the aircraft tracking straight ahead. The G450's rudder has a load limiter, and during the climb-out full rudder deflection was achieved with only 30kg pedal force. Once level at 2,000ft, with gear and flaps retracted, there was more than enough rudder trim available to zero out pedal forces during the short cruise to Savannah.

The approach for the full-stop landing was a hand-flown single engine ILS to Savannah's runway 36. As with the GPS approach, only the HUD and EVS would be used to fly the entire approach to touchdown. With an engine shut down, the autothrottle can be used to maintain approach speed, but since the right engine was only at idle for our approach I would have to bring airspeed into my instrument crosscheck.

On final I found the FD's guidance in the HUD allowed me to track the localiser and glideslope accurately. The thrust director in the HUD also provided good cues, helping maintain a target speed with 39° flap of 128kt indicated. Around half of the available rudder trim was required to maintain coordinated wings level flight on final. At 100ft RA the flare cue appeared. Passing 50ft, I slowly retarded the left throttle to idle while putting in right rudder to counteract the trim setting.

Able successor

Again I captured the flare cue and rounded the aircraft out for touchdown. Full reverse thrust on the left engine and moderate wheel braking quickly brought the aircraft to a halt. The EVS picture in the HUD allowed me to keep the aircraft tracking down the runway's centreline, even with the asymmetric reverse thrust. After taxi back to the Gulfstream ramp, shut down and post-flight checks were easily accomplished.

The G450 is the latest entry into the large-cabin, long-range business-jet segment. With a strong inheritance from the GIV/G400, the G450's forward fuselage and cockpit, its flightdeck and many of the systems are identical to the larger G550's. The cabin shares the same cross-section and, while shorter than the G550's, is long enough to provide three interior zones plus a large baggage hold.

Priced to compete with the Falcon 900EX and Global 5000, the G450 is a major advance over the GIV/G400. The PlaneView cockpit with standard EVS is clearly an outstanding addition that enhances flight safety. The Falcon may be more fun to fly, perhaps, but the G450 is an able heir to the GIV's reputation for robust performance and will meet any pilot's demands for operational flexibility and mission assurance.