NBAA: Rewinged Gulfstream G280 raises the bar

Dallas
Source: Flightglobal.com
This story is sourced from Flightglobal.com

Gulfstream’s G280 is a direct descendant of the Israel Aerospace Industries (IAI) 1125 Astra, but the super-midsize business jet that debuted in 2012 has nothing in common with its predecessor.

The original Astra wing was modified and mated to a larger fuselage to field the Galaxy. The Galaxy design was acquired by Gulfstream and rebranded the G200. The G200 featured a cabin cross-section on par with its large-cabin Gulfstream brethren.

While passengers liked the Galaxy’s roomy cabin, its small Astra-derived wing gave it relatively poor take-off field performance. To take the high ground in the super-midsize segment, Gulfstream would need to develop an entirely new wing for the G280.

SHARED CROSS-SECTION

Gulfstream kept most of the fuselage with its large cross-section cabin as well as some subsystems, but little else of the G200 Galaxy-series as it was fashioned into the G280.

The G200’s wing had an area of 34.3m2 (369ft2), a slight enlargement over the Astra’s 29.4m2 airfoil. The G200’s maximum take-off weight (MTOW) was, however, more than 50% greater than the Astra’s, and leading-edge slats and Krueger flaps were needed to give the G200 acceptable field performance.

The G280’s wing is perhaps the most significant improvement on the legacy design. The new supercritical wing has a 1.5m (4.92ft) larger span, increasing the area to 46m2. Swept at 30º to 5º more than the G200, the new wing helps the G280 cruise at Mach 0.84, a M0.04 improvement over the G200. Now the G280 wing has a fixed leading edge, reducing complexity and maintenance costs.

In addition to significantly increasing runway and cruise performance, the new wing has another notable knock-on effect.The G200 has an aft fuselage fuel tank located between the lavatory and aft baggage compartment. The G280’s larger available wing volume allows for the removal of that tank, allowing walk-through access to the baggage compartment.

The additional found area is now available for the cabin, with total cabin volume increasing from 24.58m3 (683ft3) to 26.48m3. While the length of the cabin seating area has been increased slightly, most of the additional found space has been allocated to the lavatory, one that Gulfstream claims is the largest in its segment. Removal of the fuel tank also allowed Gulfstream to add two windows per side, further enhancing the airy feel of the cabin.

Rounding out the notable changes to the G280 are new engines and an improved flightdeck. Two Honeywell HTF7250G turbofans replace the G200’s Pratt & Whitney Canada PW306 engines, offering an additional 7kN of thrust per side. Gulfstream increased MTOW thrust to weight ratio from 0.341:1 to 0.385:1.

Up front, the G200’s dated Rockwell Collins ProLine 4 avionics suite has been replaced by the ProLine Fusion-based PlaneView280 flightdeck. The G280’s PlaneView system features three 15in liquid crystal displays and embodies Gulfstream’s common crew resource management philosophy for its entire product line.

PREVIEW FLIGHT

Gulfstream originally launched the G280 in 2008 as the G250. First flight of the prototype aircraft was in December 2009 from IAI’s factory in Tel Aviv, Israel.

In 2011, Gulfstream rebranded the aircraft as the G280 after noting concerns that the Mandarin characters for "250" can be read by some Chinese-speakers as “imbecile”.

Type certification by the US Federal Aviation Administration (FAA) was approved in August 2012. Regulators in Europe, Canada and China followed in 2013. Just prior to the one-year anniversary of its FAA certification, Flight International was invited to put the G280 through its paces at Gulfstream’s Dallas Love Field completion centre.

The preview aircraft was serial number 2004, registered as N280GD. It was the first aircraft with a completed interior and had the optional Intercontinental package, which offered upgraded navigation and communication capabilities.

I accompanied Gulfstream test pilot Bob Wilson as he accomplished the straight forward pre-flight walk-around inspection. Unlike the G200, whose wing had a booted leading edge for de-icing, the G280 has a hot leading edge, a feature more befitting of such a capable aircraft.

The main landing gear is a trailing-link design incorporating carbonfibre brakes. In my numerous business jet evaluation flights, I have come to appreciate trailing-link designs as they cushion some of my less-than-optimal landings.

Access to the large, pressurised 3.4m3 aft baggage compartment is via a plug-type door beneath the left engine. As mentioned earlier, removal of the G200’s aft fuselage fuel tank allows the aft baggage compartment to be accessed from the cabin both on the ground and in flight.

Flightdeck entry is from the cabin, and once settled into the left-hand seat, I used the centre pillar alignment balls to obtain the correct seating position. On the overhead panel, individual aircraft system control panels were logically arranged. The flight guidance control panel was centred on the glareshield panel and was bracketed by LCD standby instrument displays and standby multifunction controllers (SMCs). The forward panel was dominated by three large multifunction LCD displays. The centre pedestal featured two FMS panels forward of the throttle quadrant, with flight control and trim panels located aft.

A most unique aspect of the G280’s flightdeck was its cursor control devices (CCDs). Rather than employing a track pad and ball device on the pedestal, the CCD was a control stick-like device located on the cockpit sidewall. In many ways, they remind me of the F-16’s hands-on-throttle-and-stick (HOTAS) controls: with push buttons, a scroll wheel and a thumb-actuated cursor slew button. Upon reflection, this was not surprising, as the device’s design was heavily influenced by a former F-16 experimental test pilot.

Wilson started the auxiliary power unit and pre-start checks were accomplished with reference to the electronic checklist. While not available for our flight, Gulfstream is developing an electronic performance database for quick reference through the FMS. The engines are equipped with full authority digital engine control systems, and starts required little pilot interaction. Both engines reached “idle” in less than 30s.

The flaps were set to 20º prior to releasing the parking brake, a silver lever that would look at home in a classic sports car, for taxiing to Love Field’s runway 31R. During the taxi, I found the tiller-controlled nose wheel steering (NWS) allowed for smooth and precise tracking of taxiway centrelines. Limited NWS (+/-3º) was available via the rudder pedals, but was suitable only for negotiating straight taxiways.

ENHANCED FIELD PERFORMANCE

With its higher thrust-to-weight ratio and lighter wing loading, the G280 needs about 20% less runway than its G200 predecessor, so 1,448m (4,750ft) versus 1,853m at MTOW, sea level and standard atmospheric conditions.

Simulating a segment from Aspen Colorado, we would perform the initial take-off with the engine bleeds off. With a field elevation of 7,838ft MSL on a 25ºC day, this configuration allows the G280 to carry an additional 204kg (443lb) of payload 120nm (222km) further than the typical “bleeds-on” configuration.

With a single press of the engage button, the autothrottle advanced the engines to 90.7% N1, and the G280 accelerated briskly. Tiller NWS was used to track the runway centreline until Wilson announced “pilot’s controls” at 80KIAS (knots-indicated air speed). On his cue, I released the tiller and placed my left hand on the yoke. I found yoke pitch forces to be somewhat high when I pulled aft at VR (114KIAS). Once airborne, pitch force changes encountered during the acceleration and clean-up were easily countered by the stabiliser pitch trim.

An initial climb speed of 250KIAS was captured, as we turned towards the working area. Once established westbound, I engaged the autopilot in the “flight level change” mode. Passing about 35,000ft, M0.75 was captured and held until reaching our cruise altitude of 43,000ft. At MTOW and standard atmosphere +10ºC, the G280 can climb directly to 43,000ft in under 23min.

Test day time to level off was an impressive 17min, a time that included several turns directed by air traffic control. Once level, the G280 accelerated at climb power to M0.84 (high-speed cruise). I manually set 90.7% N1 (total fuel flow 2,050pph) to hold this high-speed cruise condition.

Ambient temperature was standard atmosphere -5ºC and resultant true airspeed was 478kt (885km/h). I then retarded the power and slowed the G280 to M0.80, a more economical cruise speed. Total fuel flow decreased to 1,530pph while true airspeed slowed to 452kt. Decreasing cruise speed by M0.04 reduced total fuel flow by about 25% while only costing 26kt of true airspeed. With four passengers, Gulfstream quotes an NBAA IFR range of 3,000nm at M0.84 and 3,600nm at M0.80.

COMFORTABLE CABIN

While at 43,000ft, I left the flight deck to sample the G280’s sizeable and luxurious cabin. Gulfstream offers three interior configurations for the G280. Ours, the Universal, featured a three-place divan and had seating for nine and berthing for four passengers. The passenger cabin was always the G200’s strong point, and the G280 is no exception.

Gulfstream claims the G280 cabin has an industry-leading low noise level, and I found test day cruise conditions level allowed for easy conversation at normal voice levels. Additionally, the G280’s cabin pressurisation system is designed to enhance passenger comfort. The system maintains a maximum delta P of 9.2psi, which yields a cabin altitude of only 6,400ft at 43,000ft. As a point of reference, most commercial airliners have a cabin altitude in excess of 8,000ft at that altitude. Finally, the environmental control system does not recirculate stale cabin air, but provides fresh air at all times.

PROTECTIVE MEASURES

After returning to the cockpit, Wilson and I discussed the automatic descent mode (ADM) resident in the PlaneView avionics. With the autopilot engaged at altitudes above 34,000ft, if cabin altitude exceeds 10,000ft, the ADM will be triggered to descend the aircraft to 15,000ft MSL in hopes of reviving the assumed incapacitated flight crew. To do this, ADM turns the aircraft 90º to the left and lowers the nose to capture maximum operating limit speed. Additionally, the autothrottle will return power to “idle” to quicken the descent, “waking up” even if it was not previously engaged.

With the high-altitude portion of the flight complete, a descent was initiated to medium altitude to investigate the G280’s slow-speed handling qualities. During the descent, I accelerated the G280 to maximum operating limit speed of M0.85. Numerous visual and aural cues were provided to alert me to the impending overspeed. At the limit speed, I found the G280’s response to small sharp control inputs in all three-control axes to be well damped, an admirable trait. Had the autopilot been engaged during our high-speed descent, it would have raised the nose to slow the aircraft to M0.83, another helpful automatic protection feature.

At 15,000ft MSL, I was able to evaluate the G280’s slow-speed handling qualities. Like the high-speed condition, the G280 autoflight system has two modes designed to prevent inadvertent slow-speed excursions and stalls.

The first uses the autothrottle to maintain a safe speed if the autopilot is holding an altitude or tracking a glide path. Even if the autothrottle is not engaged, it will “wake up” to prevent a stall.

The second is when the autopilot is trying to maintain a commanded vertical speed. Should the commanded climb rate exceed that available with the current power setting, the autopilot will lower the nose to maintain a safe speed.

To see how the G280 would handle the unlikely event of slow-speed excursion, we first set up for a clean configuration stall. While slowing in idle power at about 1kt/s, the stick shaker activated at 141KIAS. Ignoring this warning, I continued to hold back-pressure until the stick pusher fired at 131KIAS. Aircraft response to small control inputs in all three axes at speeds above the pusher was good. After the pusher fired, forward yoke was applied to break the stall and power advanced to facilitate a rapid recovery to normal flight conditions.

Two other stalls, one in a take-off configuration (gear up, flaps at 20º down) and the other in a landing configuration (gear down and flaps full) were performed. In both these cases, the stick shaker provided ample warning of the impending stall, while the pusher provided an initial nose down pitching motion to break the stall.

RUNWAY SAFETY

With the slow speed evaluation complete, we preceded to Abilene, Kansas, for pattern work, as upon return to Love Field, we would have to do a full stop landing. En route to Abilene, I continued to familiarise myself with the PlaneView avionics. I especially liked its inherent flexibility, with more than one way to accomplish many tasks. Additionally, the ability to split displays in half and one quarter greatly enhanced usability and situational awareness.

The initial approach to Abilene was a coupled required navigation (RNAV) approach to runway 35R for a full stop landing. The G280’s autoflight system admirably tracked both the lateral and vertical approach paths. New to the G280 is its brake-by-wire system, which has an autobrake capability. On
touchdown out of the RNAV approach, the autobrakes smoothly and rapidly slowed the G280. The autobrakes also have a rejected take-off (RTO) mode, a great safety-enhancing feature we were also able to sample at Abilene.

The most challenging event we accomplished at Abilene was an engine failure scenario. New to the G280 is its fly-by-wire rudder with back-driven rudder pedals. During the up and away portion of my evaluation, I had found rudder pedal forces to be well harmonised with pitch and roll forces, a sign that Gulfstream had gotten it right.

In case of an engine loss, the G280 has a thrust compensation module that automatically deflects the rudder to counteract an asymmetric thrust condition. Unlike the Boeing 787 thrust asymmetry compensation system, which seeks to stop all yawing motion, the G280’s system only commands about two-thirds of the required rudder deflection. Shortly after take-off from Abilene’s runway 35L, Wilson pulled the right engine to idle to simulate an engine failure. While I visually picked up the yawing motion, the thrust compensation module input to the rudder caused the pedals to displace, confirming the need for left rudder.

At maximum power, only about half of the available rudder trim was needed to zero out forces for co-ordinated flight. Once level on downwind, I centred the rudder trim as we slowed and configured for a hand-flown, single-engine visual approach.

On final approach, I found the fly-by-wire rudder enabled me to precisely counteract the yawing motions caused as I modulated thrust to maintain the target approach speed.

To my surprise, Wilson called for a go-around at 50ft AGL. Much like the power loss on departure event, the fly-by-wire rudder and thrust compensation module allowed me to easily counteract yawing motions generated by the asymmetric thrust. Once climbing away from the runway with the gear retracted, Wilson gave the right engine back to me for our return to Love Field and full stop landing.

FULLY-FLEDGED GULFSTREAM

The Gulfstream brand has enjoyed unequalled cachet with the jet set. When Gulfstream purchased the Galaxy product line to expand into the super-midsize segment, they made a commitment. While a capable aircraft in its own right, the G200 (née Galaxy) was not seen by some as being a real
Gulfstream.

With the G280, Gulfstream has honoured its commitment. Its larger supercritical wing and more powerful engines give it class-leading range and cruise speed. The PlaneView flightdeck with three large displays and graphical flight planning capability eases pilot workload while increasing situational awareness. The large cross-section cabin offers stand-up height as well as class-leading quiet. At a glance, the only thing missing from the G280 are Gulfstream’s signature oval windows. Closer inspection, however, reveals that they are there – they are just turned 90º.