Airtest – Gulfstream G.IV

With operators continually requiring more range and better fuel efficiencies, Gulfstream continued to develop their aircraft culminating with the G. 111. However, over the last few years with the introduction of the Canadair Challenger 601 and Dassault Falcon 900, the competition has been able to very much close the gap of the Big Iron Leader. So to maintain their number one position in the marketplace, Gulfstream had to go back and carefully do their homework.

The Company opted to stay with the proven method of developing an evolutionary design enabling them to draw on the vast technical and operational expertise gained with the G. 11 and G. 111 Thus it was announced that the G. IV would be developed to meet the following operational criteria:

• An IFR range of at least 4000 nautical miles with a 16001b payload (eight passengers and baggage)

• Long-range cruise speed of at least Mach . 80 (459kts) and a maximum cruise speed of at least Mach . 85 (500kts)

• Balanced field length of 5100 feet ISNsealevel)

• Accommodation for up to 19 passengers plus crew of 3

• Comfortable interior to match the range

• New generation, reliable and quiet turbofans

• Advanced CRT avionics and digital flight guidance systems

• Certification to FAR 25 and full compliance with FAR 36, stage Ill noise standards.

These parameters, announced in March 1983, so impressed sufficient potential owners to place orders for 85 aircraft by the summer of 1984. The order book now stands at over 100 units representing the largest dollar backlog in general aviation history at over US$1. 5 billion. The bulk of these orders coming during an economic recession – proof once again that an efficient business aircraft is now recognised as a vital business tool.

Gulfstreams have always provided a comfortable business environment, commencing with the G. I. which had a fuselage length of 64. 0 feet; this was stretched to 79. 9 feet in the g. 11 and then to 83. 1 feet in the G. 111. Now the fuselage has been stretched yet again to 88. 3 feet in the G. IV giving a very spacious cabin with a floor length of 45. 1 feet allowing unlimited flexibility for interior arrangements. The demonstration aircraft was divided into seven compartments. The flight deck, the entrance area include a forward lavatory, a forward conference area, the main passenger cabin, the galley, the main toilet area and the baggage compartment which is also accessible in flight. The additional 4. 5 feet cabin stretch over the G. 111 may encourage some operators to install a comfortable crew rest area to take full advantage of the G. IV’s 10 hour plus range. Additional forward cabin space was gained by relocating some of the avionics, normally located in the forward righthand cabin, to a new avionics bay just aft of the radome and a new avionics bay/refreshment centre on the lefthand forward cabin aft of the entrance door. Having seen two G. IV interiors, I found both to be luxuriously appointed, well finished and incorporating everything one might wish for in a well equipped home. Even spending 17 hours at a time in the cabin was a pleasant experience allowing us to arrive in Sydney totally refreshed. A very different experience from undertaking the same journey in a crowded airliner.

The 12 large oval windows, a Gulfstream trademark, make for easy viewing of the passing scenery and provide a spacious airy feeling to the cabin, not available in other business transports. The selection of colours in the demonstration aircraft proved to be a very subtle and soothing choice, although this is influenced by personal preference. Choice of interior design being limited only by the owners imagination.

Gulfstream engineers paid particular attention to aerodynamics and the reduction of drag, ensuring the G. IV’s guaranteed performance data (long range cruise 0. 8 Mach BFL 5,100 feet, Range 4000nm). With an investment of over 1000 hours of wind-tunnel testing the engineers developed a wing, fuselage and nacelle combination that yielded performance advantages over the already excellent G. 111. This wind-tunnel development revealed that to maintain the same drag value as the G. 111 at Mach 0. 8, the nacelles had to be moved aft 17in from the familiar Spey installation and because the intake area was increased by 50% the nacelles were installed slightly higher resulting in a thrust line some Bin higher than the G. 111

The aft movement and greater weight of the Tays also influenced the 5 feet span increase of the tailplane preserving the G. 111 pitch axis handling.

Whilst the wing appears to be the same as that on the G. 111 it is in fact a new structure based on the FAA’s fail-safe criteria; and through this review, the engineers were able to reduce the structural components by 30%, saving 8701bs in weight and still find room for an additional 12001bs of fuel, increasing each wing’s capacity to 14,7501bs. The changes were instigated to give the G. IV a higher cruise speed without the penalty of additional drag. The engineers achieved this by creating more lift inboard and delaying the high drag onset at higher subsonic Mach numbers. The three wing planks of the G. 111 have now been replaced by a single one on the top. Twenty three ribs have been removed from the structure and inspection panels have been moved to the bottom of the wing.

The leading edge has been extended slightly and drooped by one degree and the tips have been twisted two degrees. Also a slight widening of the tips has resulted in an increased surface area to 950sq ft from 935sq ft. Calculations show the new wing achieves 5% less drag at high speeds allowing an increase of . 02 to . 025 Mach over the old wing. However, during flight testing it was found that low speed stall characters were no quite as good as they could be so to increase the pre-stall buffet and create an aerodynamic fence to control stall propagation the engineers added four-vortilons and a stall strip to the underside of each wing. ‘Vortilons’, a McDonnell Douglas invention, are small fences that extend ahead of the wing and are toed in 11 degrees to straighten the local airflow with the advantage of not creating any additional drag as do the normal over-wing fences.

To maintain the traditional Gulfstream feel the entire trailing edge and inboard one-third of the wing were retained. The ailerons and elevators are boosted by dual hydraulic actuators with actual airloads fed back to the pilot in flight. Ailerons and elevators have conventional trim-tabs operated by the four way trim button located on the control column.

Flaps are selected 1 O degrees for takeoff, 20 degrees and 39 degrees for approach and landing. The tailplane incidence is automatically altered to increase available tail-down effort a few seconds after the flaps are selected. This always keeps the control column in a central position. A dual stall prevention system operates a stick shaker and pusher at a predetermined range of airspeeds above the aerodynamic stall dependant upon height and angle of attack. Both systems must agree before the pusher can operate. To counter Mach tuck at speeds over 0. 082 the elevator trim tab will automatically operate to produce a noseup trim change. The G. IV retains the six spoilers of the G. I11. The outer two panels deflect to 43 degrees when acting as spoilers in association with the ailerons. All six panels will deflect up to 26 degrees when used as speed brakes and after touchdown all six panels will rise to 55 degrees for lift-dumo. The rudder is fully powered and has a feel spring which can be displaced for trimming.

Hydraulics have also been simplified, rather than switching back and forth from 1500psi to 3000psi the G. IV used a constant pressure system that maintains 3000psi. The total system is comprised of a primary system, an auxiliary system and an emergency system. Should the hydraulic system fail, the undercarriage can be blown down with the aid of a nitrogen bottle. The two major systems maintain pressure generated by engine driven pumps, whilst the emergency system maintains its pressure through an electrically driven hydraulic pump.

Undercarriage on the G. IV is identical to that used on the G. 11I with the exception that a higher strength 300m steel is used resulting in a weight saving of 127Ibs, and the incorporation of electrical signalling (fly-by-wire) for the brakes and steering. The Goodyear brake-by-wire system already used on the Concorde, Airbus A310 and General Dynamics F-16, is 18% more efficient than the current systems and offers smoother stopping and generally better ground handling. The system operated through pedal transducers which send a signal to an electronic control unit which in turn sends a signal to the hydraulics and anti-skid system.

The steer-by-wire system incorporated in the G. IV is the same Dowty system already as used on the Canadian Challenger 601. This is a fail-passive electronic system which obtains its input from either the tiller on the captain’s side or from the rudder pedals on either side. The tiller provides a steering authority of plus or minus 82 degrees whilst the rudder pedals have an authority of plus or minus 7 degrees – a very effective system.

Gulfstream retained the excellent dual-channel solid-state AC electrical system that was certified under FAR 25 in December 1982. This system introduced on,the G. I11, is a variable speed constant frequency type utilising two engine-driven alternators and two electronic converters to produce 48 KVA of 115 volt AC power at a precise 400hz, as well as 500 amps of 28 volts DC power. As a back-up there is a third identical alternator driven by the auxiliary power unit which has been flight-rated; the aircraft can, in fact, be dispatched, with the APU running. In addition, should all three fail; there is a fourth hydraulically driven standby generator to power the essential bus. The system is completely automatic, reducing pilot workload, however, if the crew feel left our of the action, there is a manual override feature.

The electrical system leads us into what must currently be the most advanced flight-deck iri aviation. Experience gained with Sperry equipment installed in the G. 11 and G. 11I led to the development and installation of the fully integrated, digital, Sperry SPZ-8000 System as standard equipment on all G. IV aircraft. The major components comprise six full colour CRT cockpit displays featuring flight reference, engine performance, monitoring and alert/warning functions. Dual fail operational/fail passive flight guidance (autopilots) systems including autothrottles. Dual flight management systems providing vertical and lateral navigation and full real time performance management. D. ual digital air data systems and a digital colour weather radar-system.

Two 8 by 8 inch colour CRTs mounted side by side at each flight station comprise the EFIS (Electronic Flight Instrument System) portion of the flight deck. One is used for primary flight data whilst the second is used for radar and navigation displays. Should either malfunction, the information can be transferred to the other. Ahead of the centre console are another two CRTs, identical to the EFIS display but mounted on their side. These two comprise the EICAS (Engine Instrument and Crew Alerting System). Should one of these displays fail the information can be transferred to the other CRT but not to the EFIS CRTs. This may be possible at a later date. However, all six tubes are interchangeable.

Additionally, the EFIS CRTs are backed up by a conventional artificial horizon, airspeed indicator and altimeter. The EICAS CRTs are backed up by a digital readout, located on the captain’s panel, that has a left and right column displaying _the five vital parameters of engine operation. The EICA? CRT EPA, TGT LP Turbine, HP turbine and fuel flow in a round dial format with ‘digital readouts for fine adjustments on the left hand side. Whilst the right hand side displays oil pressure, oil temperature, environmental system, hydraulic system and fuel data in a digital format. The second EICAS CRT is used as a flight deck message centre. The left side of the display is normally blank and reserved for alerting the crew of a systems failure. The messages are coded in white for systems in operation, amber for those switched off and red for failures. The right hand side of the CRT is used to display systems configurations that can be called up by the crew for review.

There are three generators driving the six CRTs, normally one per pair,· however each has the capability to drive up to four CRTs. The symbol generators obtain their information from the two flight management systems, the flight guidance systems, the crew alerting system and the various avionics sensors via a Sperry Avionics Standard Communications Bus (ASCB). Use of this system provides considerable weight and cost savings over the older ARING systems.

The dual flight management systems (FMS) combine navigation and performance management to provide a complete automatic takeoff to touchdown capability anywhere in the world. To enable the FMSs to operate they are linked into six primary systems which are:

NAVIGATION (a worldwide database updated every 28 days. the dual Honeywell Laseref II inertial reference systems, VOR/ DME, VLF/OMEGA and GPS);

MAP (displayed on the second EFIS CRTs);

FLIGHT PLAN (as presented to the FMS);

ENGINE DISPLAY (from the EICAS);

AUTOPILOT/AUTOTHROTTLE; and

PERFORMANCE (from database includes engine, airframe and flight manual)

At the time of writing, the autothrottle system had not been certified although Gulfstream expected certification in early 1988.

The last item in this review of the systems is the source of power- the remarkable Rolls Royce Tay. The G. IV continues the successful partnership that Gulfstream and Rolls Royce have enjoyed for three decades. Rolls Royce, like Gulfstream, uses the evolutionary process to develop their new generation turbofan, successfully combining the core of the highly reliable Spey with the low pressure systems of the RB211.

Experience gained through 32 million hours of pey operations and the proven results of RB211 technology, gamed on aircraft such as the Boeing 747, 757 and Lockheed L-1011, gave Rolls Royce the confidence to set the initial Time Between Overhaul (TBO) for the Tay at 7000 hours. This is the same TBO as currently enjoyed on the Spey and one of the highest amongst business transport aircraft, a significant contribution to lower operating costs.

Gulfstream initially adopted a takeoff rating of 12,420Ibs of thrust this, despite the fact that Rolls Royce have successfully demonstrated the engine to 15,000lbs of thrust and that the engine has been certified to 13,850Ibs of thrust in the Fokker F100 installation. Subsequent flight testing, however, has shown that the aircraft meets or exceeds all performance guarantees except balanced field length which was established at 6,100 ft – one thousand feet more than the 5,100 feet guarantee. Gulfstream will now take advantage of the engine’s thrust reserves and boost the engine to 13,850lbs of takeoff thrust, which combined with a new takeoff technique, should ensure a balanced field length of even less than the 5,100ft guarantee. The modification to uprate the power is apparen!ly only a fuel control adjustment making the whole process relatively simple.

Adding comfort to G. IV operators; should be the knowledge that the Tay in the F100 installation will accumulate at four to five times that expected on the G. IV, thus ensuring a rapidly maturing engine with the inherent TBO extensions commensurate with extensive inflight experience.

The Tay engine has allowed the G. IV to be significantly quieter than the standards required under FAR 36 Stage 3, and provided a 16% saving in fuel consumption over the Spey at Mach . 80 cruise speeds. This engine will be around for many years to come.

Flying in the G.IV

Having had the pleasure of experiencing several sectors in the G. IV, amounting to over 23 hours, I was able to form a fairly good impression of the aircraft. My first exposure to the G. IV as a passenger was from New Orleans to Los Angeles. This leg was flown at FL 450 and initially M. 83, then M. 855 which showed the high speed capability of the aircraft and allowed a good appreiation of noise levels. There was a definite increase in wind noise as the aircraft accelerated from M. 83 to M. 855 but the levels were still low compared to many other aircraft and one could still converse at normal levels The second leg, involving a pre-dawn departure, was from Los Angeles to Papeete, Tahiti, a distance of 3,584nm. There were eight persons on board with a considerable amount of baggage plus with 29,000lbs of fuel (5001bs less than maximum). Our ramp weight was 71,8001bs. (400lbs less than max). At this weight I anticipated a longer takeoff roll and slower climb than we had· experienced out of New Orleans the day before when the aircraft was light; but this was indiscernible with the aircraft rocketing down the runway and reaching its initial cruise level of FL 390, 24 minutes after brakes release. Fuel consumed at top of climb was 2,2001bs and the rate of climb just prior to level off exceeded 1,100 ft per minute. The climb was conducted at 300KIAS/M. 75 with the changeover occurring at FL 320. Once we levelled off I decided to recline and berth two chairs and managed several hours of undisturbed, comfortable sleep in the now very quiet environment. When I awoke Gulfstream Crew Chief Billy Parker, had cooked up a marvelous breakfast which he had laid out in the rear conference area where together with three of my fellow passengers we enjoyed a level of luxury in long range flight not experienced by airline travellers of today.

We encountered average headwinds of only 11 knots on our way to Papeete with a final cruise altitude of FL 430. At this level, our fuel burn had dwindled to a miserly 2,400 lbs/hr for a constant long range cruise of M. 80 +. Touchdown was 8 hours 15 minutes after takeoff with 5,000lbs of fuel remaining – sufficient to allow an approach at Papeete and proceed safely to Raratonga as our alternate if necessary.

There being no airliner expected, the terminal at Papeete was closed so it took a little while to organise refuelling. However, 51 minutes after touchdown we were airborne again, this time with a ramp weight of 71,500Ibs as the surface temperature of 28°C only allowed 28,700Ibs of fuel into the tanks. We reached top of climb, FL 390, 22 minutes after brakes release with a total fuel burn of 2,000 lbs.

Settling into the second leg proved to be very easy. The demonstrator has a very comfortable interior finished in pleasant tones of grey. This combined with the low noise levels, ozone filters and smooth handling of the aircraft produced a very relaxed environment. With the added distraction of watching ‘Prizzis Honour’ on the inflight entertainment centre, the time passed rapidly.

Universal had done an excellent job of predicting the winds on the Los Angeles/Papeete leg. However, they weren’t quite so lucky 011 the Papeete/Sydney leg with the winds being some 30 to 50 knots stronger than forecast. Six hours into the flight with a TAF for Sydney that read CAVOK, the abominable realities of the Sydney ATC system reared its ugly head. Due to the stronger headwinds and lower fuel uplift out of Papeete we only had sufficient fuel for 40 minutes holding above all our reserves. Sydney advised they wanted sixty minutes – one could be excused for thinking that inflight refuelling of corporate jets is routine in Australia! After some discussion of our alternatives we asked Sydney how much holding we could expect. A short time later the reply was “Expect no holding”. Needless to say as Sydney loomed on the horizon we heard only two other aircraft in the air, flew in on a straight-in approach to runway 34 and didn’t see another aircraft. The Gulfstream pilots were dismayed, to say the least, at our quaint fuel policies.

We touched down in Sydney 8 hours and 53 minutes after takeoff from Papeete, covering a distance of 3,318nm. Our final cruise level was FL 450 which produced a total fuel flow of 2,200lbs/hr and we had 3,400lbs remaining in the tanks – we would in fact have had our 60 minutes holding over and above reserves.

Stepping off the aircraft in Sydney I felt totally refreshed and relaxed. In fact, if need be, I could have stepped on board again to undertake the return journey. I have never experienced this on previous trans-Pacific flights. Usually, at the end of the trans-Pacific ordeal, one hopes for a quick and painless death.

Two days later, on a pilot demonstration from Sydney to Melbourne for some circuits, then back to Sydney (our original destination was Avalon but the crosswind was blowing at 40kts). I was able to fly the G. IV myself. I found the EFIS display with vertical tapes depicting altitude and airspeed a little difficult to get used to but I am certain that with a little time one could find this system very easy to fly. However, reverting to raw data could be difficult as the EFIS display requires no scan.

The G. IV felt positive but firm in the ailerons while pitch seemed light. The overall feel was very good and the aircraft was nice to hand fly. We commenced our descent for an ILS approach to Melbourne’s runway 27. The G. IV’s clean aerodynamics made the aircraft difficult to slow down without the aid of speed brakes, although once deployed they proved to be very effective and produced very little attitude change. Even though the conditions were blustery, the aircraft was easy to handle on the ILS.

Vref was bugged at 133kts and due to the gusty conditions and unfamiliar aircraft I flew the final approach at ref plus 10. The aircraft did not slow down as I had anticipated when I closed the throttles and I did not achieve a smooth landing, but with practice this aircraft would be a delight to fly. Control down the runway on the touch and go was excellent through the rudder pedal connected nosewheel steering. Acceleration was brisk and rotation produced interceptor like climbs at these low weights. Power had to be hauled back quickly to keep the aircraft within the Melbourne pattern and maintain 3,000 feet. Dave Foster was next into the left hand seat and as he fies a G. IIB, had little trouble transitioning to the G. IV producing a greaser on his first landing. No one else achieved that distinction on the day though we all returned to Sydney thoroughly impressed by the G. IV. Gulfstream Aerospace set out to build the world’s finest executive transport jet. A design without compromise to provide unequalled performance, efficiency, dependability and quality. They offered performance guarantees that stipulated a cruise speed of M. 85, long range cruise of M. 80, a theoretical range of 5,136nm, balanced field length of 5,100 feet and a landing distance of 3,200 feet. They have met all these criteria and produced an aircraft capable of a one stop trans-Pacific flight with eight persons on board maintaining a long range cruise of M. 80. I hope we can look forward to perhaps seeing one or two of these fine aircraft in Australia in the future.