The large Honeywell primary flight displays show numerous perameters without clutter.
The Gulfstream V wing is larger and holds more fuel than its predecessor on the GIV
At a glance, the Gulfstream V looks much like its predecessor, the GIV, but closer investigation reveals it to be a substantially different aircraft. Initially the GV was conceived as a development of the GIV, but the market demand for greater range drove Gulfstream towards fundamental changes.
The wing, for example, is new. Although built using the same materials and spacing of ribs and stringers as the GIV wing, it is aerodynamically different, it is larger, and holds more fuel. Gulfstream designed its own wing section to meet the GV's diverse operational requirements. Typical cruise altitudes will be between 41,000 ft (12,500m) and 51,000 ft and cruise speeds between Mach 0.8 and 0.88, yet these high-speed requirements could not be met at the expense of low-speed handling qualities and field performance. The GIV's simple Fowler flaps are retained, but are larger.
A "standard" supercritical aerofoil section was deemed unsuitable because of adverse trim-drag and pitching-moment effects caused by aft loading - and because the cusped trailing-edge would not have accommodated the flap mechanism and maintained a clean wing. The GIV winglet was found not to work well with the new wing - so the GV winglet is longer, with an increased blend radius introduced to reduce interference drag.
The new wing contributes significantly to the GV's increased range both by its improved aerodynamic efficiency and greater fuel capacity. The BMW Rolls-Royce BR710 turbofans, which replace the Rolls-Royce Tay Mk611-801s in the GIV, contribute a 15% reduction in specific fuel consumption. The net result is an impressive 57% improvement in range over the GIV-SP, which translates into a guaranteed 12,000km (6,500nm) range for the GV.
The fuselage, although stretched by 2.1m, still looks very Gulfstream-like, with the same six oval cabin windows per side of its predecessors. Inside, however, good use has been made of the extra volume; the cockpit is 0.3m longer and baggage capacity has been increased by 34%. The pressurisation differential has been increased to give a 6,000 ft cabin altitude at the maximum operating altitude of 51,000 ft.
The GV's capability of carrying eight passengers 12,000km at M0.8 means that it could spend many of its operating hours over the oceans. Because of this, Gulfstream has designed the aircraft to meet the requirements applied to commercial extended-range twin-engine operations, although they are not not a criterion for business-jet certification.
The GV has increased redundancy in the electrical system - a 40kVA generator on each engine and a third on the auxiliary power unit (APU) - and hydraulic system (two pumps per engine). A full technical description of the GV has appeared in Flight International (31 January-6 February, 1996).
WEATHER FRUSTRATION
Flight International was able to fly a development GV at Gulfstream's factory in Savannah, Georgia. Our aircraft, the third development GV, appropriately registered N503G5, had flight-test equipment racks in the cabin, little cabin insulation and early engines not to production specification. It was not possible, therefore, to assess cabin noise levels. It was possible, however, to gain a good impression of the aircraft's handling and performance. Even that was not to be without its frustrations, because an intensively active weather system, including thunderstorms and a tornado alert, was moving slowly north-eastwards across the entire eastern third of the USA. Randy Gaston, Gulfstream's chief test pilot, and I both considered the turbulence in which we at one stage became unavoidably embroiled to be as bad as either of us had experienced in many years.
Impressive cabin layout
The cockpit, like the cabin of aircraft 503, was devoid of production trim, but the layout was nevertheless instantly impressive because of its clear and uncluttered appearance. Although the centre console is wide, and the seats have no sideways travel, it was reasonably easy to get into the seat and to adjust it for reach, height and recline; there are adjustable armrests and a five-point harness. There is insufficient room for a flight bag beside the seat. The field of view is good, although each thick windscreen side-pillar is intrusive and one had to become used to peering round it, particularly when, say, turning on to finals in the visual circuit. Each pilot can just see the wingtip on his side of the aircraft, but only by craning to look rearwards through the side window. The rudder pedals are adjustable, with an unlocking lever behind the column, on the lower edge of the instrument panel.
The GV is equipped with Honeywell's SPZ-8500 integrated digital avionics, and the comprehensive nature of this package became clear almost from the moment the brief pre-start checklist was initiated. In this instance, the APU had already been started to test the electronics in the cabin. Normally, the APU would provide electrics and bleed air for cabin cooling on the ground and for engine start (primarily on the ground, but also in the air in an emergency). The AlliedSignal RE220 APU is in the tailcone and its controller is in the overhead panel, which is a well-laid-out square of systems controllers, mostly with push-button selector indicators.
On this occasion, as I was strapping in, the six Honeywell cathode-ray-tube (CRT) displays were already alive. Together, the displays provide flightpath, navigation, engine and systems information. Each pilot has a large and clear primary flight-display (PFD) and navigation display (ND), positioned side by side. The centre panel houses the engine-instrument and crew-alerting system (EICAS) displays, one above the other. On the glareshield in front of each pilot is a display controller by which the pilot can set his own PFD and ND and the centrally located EICAS CRTs. The selections made are shown on a small CRT integral with each display controller. The lower EICAS display is divided vertically in two; on the left are crew warnings - red for emergency, amber for rectification and blue for information (audio alerting tones accompany the initial display of these messages); on the right, systems "synoptics" (schematic diagrams), can be displayed.
The menu of EICAS synoptics includes: doors and hatches, so that the status of each can be easily checked; AC power; brakes (applied brake pressure and temperatures); hydraulics; and, particularly useful, flight controls (showing the positions and movement of all primary and secondary controls). This latter display is essential for control checks before take-off and for monitoring control deflection in flight.
The BR710 engines have full-authority digital engine-control (FADEC). The operating benefits of the FADEC became evident from the time engine starting is contemplated. In the overhead panel there is an engine-starting controller incorporating a start master switch which is selected to on, after which the relevant left or right engine start switch is pressed. Once positive low-pressure-spool RPM is indicated, fuel is introduced by moving the relevant fuel control (located towards the rear of the centre console) to on. Thereafter, the start sequence is automatic and, if unsatisfactory, will be discontinued by the FADEC.
A significant element of the Honeywell avionics suite is the flight-management system (FMS) - its major functions are shown in the diagram. For the purpose of our flight, a simple profile of a climb to 45,000ft, manouevring in a defined airspace and descent to return to Savannah via a global-positioning-system approach was programmed into the FMS. The take-off weight was 26,200kg (the maximum permitted is 41,000kg), Savannah's Runway 18 was used, the temperature was 24íC, the surface wind from 200í at 7kt (13km/h) and the broken cloudbase was about 1,800ft. Savannah is about 40ft above sea level, and the take-off speeds were: V1 114kt, VR 114kt, and V2 122kt.
SIGNIFICANT POWER
There was only a short distance to taxi from Gulfstream's ramp to the holding point for Runway 18. The GV's parking brakes are set and released by a T-handle on the captain's side of the centre console, which is turned and pushed down to release the brakes. Quite a significant amount of power was needed to start the aircraft rolling.
Once under way, taxiing speed was easily controlled, primarily by using a little reverse thrust - which provoked a clearly audible growl from the engines - or by use of the smooth Dunlop carbon-disc mainwheel brakes. The reverse thrust is controlled by subsidiary "roll-over" levers mounted at the top of and to the front of the power levers. The nose-wheel steering is electrically controlled and hydraulically operated. There is one tiller, on the captain's side-panel. Steering the aircraft was without fuss, the control being positive with fairly powerful self-centering.
By the time the holding point was reached, Gaston had set the flap to 20í (there is also a 10í flap setting to meet the second-segment climb gradient on runways with significant obstacles). The take-off brief was short and to the point: discard the nose-wheel steering from the start of the roll, use rudder to keep straight and push the power levers to the front of the quadrant; if the take-off had to be aborted, close the throttles and select reverse thrust (still usable even if only one engine was functioning) and keep straight using rudder and brake.
The spoilers had been armed for automatic operation so that, the moment the power levers were closed, they would have deployed to kill any lift the wing was generating and to assist retardation. Happily, the abort procedure was not needed.
Pushing the power levers fully forward gives the FADEC the authority to set and monitor take-off power. Doing so, however, seemed to take time; spool-up of the big-fan engines was noticeably slow (subjectively, I would have said about 5-7s, and thus within the 8s certification limit) and initial acceleration of the aircraft was leisurely. Once about 30kt was reached, however, an impressive surge of acceleration took place, and the GV rotated rapidly and unstuck cleanly. Gear and flaps were retracted by Gaston with no noticeable trim change, and a rate of climb of nearly 6,000ft/min (30.48m/s) was seen, at 250kt, before levelling off at the 3,000ft altitude cleared by air-traffic control (ATC). Even bearing in mind the GV's light weight on this occasion, the mild temperature and an airport virtually at sea level, this was still an impressive performance.
The climb was continued to 45,000ft, brakes-off to level-off taking 16min despite a couple of steps introduced by ATC and the need to navigate around the worst of the atrocious weather - solid to 37,000ft in places. (The GV's anti-icing system consists of bleed air for wing and engine-inlet protection and electrical heating for the windscreens and cockpit side windows.)
Throughout the flight, within an area and a block of flight levels defined by ATC, orientation was instantaneous by reference to the ND, where the area boundaries were shown (from the local-area database) as if on a chart, while a miniature outline of the aircraft showed its position. Use of the flight-director controller to select a heading generated a purple cursor line across the ND to indicate the aircraft's predicted course through the area.
BOOSTED CONTROLS
The GV's primary flying controls include hydraulically boosted ailerons with manual reversion, and hydraulically powered spoilers (three spoiler panels per side, with the outer two panels on each side providing roll control in conjunction with the ailerons). The spoilers also perform the airbrake function through progressive, symmetrical, extension and act as ground spoilers - with an automatic mode, through a weight-on-wheels microswitch and a power-levers-closed sensor.
Hydraulically boosted elevators with manual reversion provide longitudinal control, while a hydraulically powered rudder with manual reversion and an artificial feel system takes care of yaw control. Trimming is via tabs on the port aileron and each elevator. Control is through a divided "coolie hat" electric pitch-trim switch on the outer horn of each control yoke, with manual trim wheels either side of the centre console, and conventional trim wheels for aileron and rudder on top of the centre console. The electrically controlled variable-incidence tailplane is used for automatic trim compensation during flap selection. There is a pilot-operated disconnect for ailerons and elevators to allow the control runs to be divided if one became jammed.
The GV was very pleasant to handle, the controls being well harmonised, readily responsive to moderate forces, and having "feel" - all typical of a well-contrived power-assisted system in this size of aircraft. The manoeuvrability at 45,000ft was particularly impressive, with buffet boundaries sufficiently generous to allow level turns at 45í and 60í of bank at M0.8 without the onset of buffet.
The stick force per g seemed moderate, although Gaston recommended trimming the aircraft in these turns. The aircraft was admittedly light, but there was ample power to maintain M0.8 in sustained turns. I would have liked to handle the GV in a similar manner at 51,000 ft to verify the flight-manual chart, which indicates that the buffet boundaries appear to remain comfortably generous at that altitude.
All this says much for the capability of the GV's new wing, but high-altitude, high-bank-angle, high-g manouevring is hardly typical of normal business-jet operations; indeed passenger comfort has clearly rated highly among the design priorities for the GV. The FMS has a reduced-bank mode for more comfortable turns if airspace considerations permit such leisurely manoeuvres. The pressurisation system maintains a low, 6,000ft, cabin altitude when the aircraft is at 51,000ft, the air conditioning provides a high-volume throughput of fresh air, and the cockpit and cabin have a total of three temperature sensors and controllers - one for each of three zones.
EXCELLENT DISPLAYS
For much of this flight, extensive use had to be made of the excellent Honeywell PFD because of the weather conditions and because it allowed the high-altitude, high-speed manoeuvres to be flown reasonably accurately. The display is large and therefore has room to display numerous parameters without clutter (for example, airspeed, Mach number, angle of attack, altitude, cleared level, altimeter setting, decision height, heading, course, and vertical speed), all in addition to its primary task of being an attitude and horizontal-situation indicator. The symbology is clear, easy to read and does not seem to suffer washout with rapid changes in ambient light conditions. Similarly the main (upper) EICAS display was first-class, clearly showing the main engine parameters through digital/analogue presentations, with subsidiary systems information in digital format to the right (see diagram).
A quick look at the GV's static stability indicated a positive reaction to disturbances longitudinally and neutral stability laterally. Rudder deflections with the yaw damper in operation were met with instant suppression of the oscillation, but usually with a residual angle of bank of about 10í. With the yaw damper switched off, however, the GV was a different aircraft, a similar rudder "doublet" provoking pronounced dutch roll with no natural damping.
Monitoring several cycles indicated that there was no sign of divergence, but the only way to stop the phenomenon was to break the couple with aileron.
Descending the GV, power levers closed and spoilers (airbrakes) deployed, resulted in a rate of descent of 6,000ft/min at M0.8. A snap selection of full spoiler deflection produced a sharp pitching moment, but gradual deployment (as designed) caused little trim change. The roll characteristics of the GV were slightly improved with the spoilers deployed.
STALLS CURTAILED
During the descent, the diabolical weather again intruded to frustrate a full sequence of stalls and an engine shut-down. About 5 min flying in severe "chop", sufficiently bad to make it impossible to read instruments, caused no distress to the GV, however, and no systems failed as a result. The weather radar gave a clear picture of the areas likely to be turbulent, but they were virtually unavoidable.
Once clear of the weather, and after a visual check to make sure the anti-icing system had kept the wings clean, a "stall" to the point of stick push was tried with the flaps fully extended and gear down. The aircraft weight was by then down to 24,700kg. Stall warning occurred at 89kt and stick push at 84kt - corresponding to the stall speed for our weight and configuration computed by the FMS and displayed as a speed ribbon on the PFD.
Roll control approaching the stall became noticeably less crisp, and I would have liked to explore the GV's characteristics near the stall more extensively, in all configurations, but the weather precluded this.
Instead, a GPS-coupled approach to Runway 18 at Savannah was flown next, and the accuracy and assurance with which the autopilot and autothrottle coped with this descent and approach were a pleasure to watch. Preselected speeds (270kt on the descent - the rough-air speed, once again because of the weather) and preset altitudes were captured and maintained smoothly and precisely. The hold and procedure turn, held in the FMS' local database, were also flown with no more contribution from the pilots than mode setting and monitoring. The electrically controlled variable-incidence tailplane countered flap selections quickly and smoothly (as it did later, when I flew a circuit and approach manually). Once heading inbound, a 2.9í computed approach path was captured and flown to a 400ft minimum. The aircraft's position laterally and vertically was shown throughout on the NDs.
Disconnected autopilot
At 400ft, the autopilot was disconnected and a full-stop landing tackled. The approach speed was 125kt, and Gaston recommended closing the power levers at about 50ft. The early power-off technique worked well, but the GV has a disconcertingly flat touchdown attitude. Any inclination to execute a normal flare immediately increases the lift on the large, clean wing in ground effect, causing ballooning. To avoid this, the stick has to be held forward to fly the aircraft on to the ground, with the resultant fear (for me at least, as a newcomer to the GV) of touching down nosewheels first.
This did not happen, but the nosewheels did touchdown a mere second or two after the main wheels. A combination of automatic lift-dump (through spoiler deployment) and reverse thrust, via the upper and lower clamshell-door deflectors, resulted in impressive deceleration; reverse thrust would normally be cancelled at 60kt, as in this case, but could be used to a full stop if needed in an emergency.
While taxiing back to the marshalling point for a final take-off which was to include a simulated engine failure at rotation, Gaston assured me that I would "hardly notice" the failure. This proved to be a slightly extravagant prediction because, when he did "fail" the engine just before rotation, I allowed some roll and yaw to develop once we became airborne. When I woke up to the situation, however, it was easily corrected by the application of rudder and aileron. The single-engine climb was easy to fly, and the foot forces easy to maintain and then to trim out. I flew a simulated asymmetric circuit to a simulated single-engine landing - all of which, at our low all-up weight, was something of a non-event.
Gulfstream's V is extremely well equipped and versatile. The design goal clearly has been to make a large business jet with intercontinental capability that is a world leader. The GV has the ability to cruise high and fast, well above congested flight levels, but with good field performance allowing it to be operated from relatively small airfields when necessary. The aircraft gives the impression of having been designed without compromise: the cockpit has as much pilot appeal as any I have flown.
None of this comes cheaply. Some $800 million has been spent on development and the GV sells for around $36 million a copy. It is an expensive asset and many will have to be sold to recover the development costs.
Because the GV is a complex aircraft, it was not easy to assess its capabilities in one flight of just 1h and 20min. I would, for example, have liked to have experienced the aircraft at 51,000ft, to have spent more time at or near the stall, flying in the circuit, on touch-and-go landings, and to have flown a coupled go-around. Similarly, a comprehensive exploration of the GV's sophisticated systems would have required an article as bulky as the flight manual.
From one relatively short flight, it has not been possible to acquire more than an impression of the GV - albeit a very favourable one.
Source: Flight International
