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Gulfstream 5 Sets Pace For Long-Range Bizjets

DAVID M. NORTH/SAVANNAH, GA.

The G5 is likely to enter service 18 months prior to its closest competitor, Bombardier's Global Express

Gulfstream Aerospace's newest business jet, the Gulfstream 5, offers corporate operators an 6,500-naut.-mi. aircraft--a performance guarantee the company made when the program was started in 1992.



The G5 was granted its FAA certification on Apr. 11, after first receiving provisional certification in December, 1996. While Gulfstream was off in its final certification estimate by some five months, the provisional type certificate allowed the aircraft manufacturer to deliver three aircraft to its own completion centers in 1996 and another six G5s in the first quarter of this year.

While Gulfstream has had to increase the maximum takeoff and landing gross weights of the G5 to accommodate aircraft weight gains, and slip the final delivery schedule to operators by some 4-8 weeks, the G5 program is much closer to the company's plan than many other aircraft development programs have been in the past. Gulfstream's goal was to maintain the 6,500-naut.-mi. range with eight passengers at Mach 0.80 and it appears that the final production aircraft will do exactly that.

The less than two-month delay in deliveries to customers was partially as a result of an earlier decision to build the G5 and the G4SP on the same production line. Gulfstream realized that the differences in the G5 from its predecessor made that a difficult task. So now the G5 is separated from the G4SP at the wing mating junction, and the G5 is completed on a different line. Another delay was caused by a requirement to stiffen an upper wing stringer in 8-10 aircraft after stress analysis revealed a barely substandard margin.

The differences between the G4 and the G5 are more than the stretched fuselage and new engines. Gulfstream officials and pilots made a strong effort to elicit operators' comments in what they wanted to see in the new aircraft. Where possible, those recommendations have been incorporated into the new business jet. The G5 customer technical review board provided recommendations on the overall design of the aircraft and cabin, maintainability and reliability considerations, and input on vendor selection and management.



The instrument panel of the Gulfstream 5 is dominated by the six 8 X 8-in. Honeywell multifunction displays. The displayed primary flight, system and navigation information is similar to that in later Gulfstream 4s, but the system controls on the overhead panel have been simplified. A Honeywell/GEC Marconi head-up display, scheduled for certification later this year, will be optional equipment.


One comment by earlier Gulfstream operators resulted in a G5 that has better harmonization of flight controls, and an aircraft that at least feels easier to fly than the earlier line of Gulfstreams.

I had the opportunity to determine whether this claim was accurate during a recent evaluation flight from Gulfstream's Savannah facility. The flight was with John O'Meara, Gulfstream's deputy director of flight test operations, in G5 No. 505. This same aircraft had been used to complete High Intensity Radiated Field (HIRF) testing as well as lightning tests. This aircraft had just finished its function and reliability test flights and was soon to be turned over for delivery to a customer.

Prior to delivery to one of Gulfstream's completion centers, No. 505's wing was to be replaced with a new wing. In three of the earlier aircraft, Gulfstream found that the wings delivered by Northrop Grumman's facility in Dallas were slightly deformed and provided lateral trim anomalies at high speeds. These wings were not certifiable and were to be replaced prior to customer delivery.

During the preflight, O'Meara detailed some of the changes incorporated in the G5 from the G4SP series. The main cabin door was moved to the rear, so that passengers would enter behind the avionics compartment. The rear baggage door was enlarged 40%, and a unique winched hoist was added, partly to accommodate the placement of the aircraft's two batteries located in the rear hold and other heavier baggage. The maintainability incorporated into the G5 was evident in the location and accessibility of its key systems, including the auxiliary power unit, hydraulic and fuel components.

The G5's wing, winglets and trailing edge components are a newer design, compared to the G4 of the 1980s. The aircraft also incorporates a new vertical fin and a new larger span horizontal tail and elevators.

The interior of No. 505 was spartan, with test equipment still installed. Gulfstream officials are allowing a 6,700-lb. cabin outfitting allowance, which they say equates to close to a 4.0-lb.-per-cu.-ft. outfitting allowance and one of the better of the larger cabin-class corporate jets. Part of the reduction in outfitting weight requirements from an earlier higher limit can be traced to weight savings in the potable water tanks, lavatory water tank, carpeting and the aircraft's acoustical package. The extensive use of single-ply Nomex in the construction of the galley, credenza and tables accounts for a 600-lb. saving, Gulfstream officials claim. The taste of individual customers can vary, but a $4-million price tag for the cabin completion is standard.

Once I was in the left seat, and O'Meara in the right seat, he started the AlliedSignal APU. The APU has been quieted on the G5 by the design and acoustic lining in the exhaust. I found that getting into the seat was made easier by the long track of the seat rail. The cockpit of the G5 is longer than that of the G4 by 1 ft. O'Meara then went on to detail some of the improvements made in the G5 to improve reliability and offer redundancy. Both features were important in light of ETOPS, although the Gulfstream series of business jets has an enviable safety record, both for ETOPS and overall.

The two engine-driven, variable speed, constant frequency alternators used in the G4 were replaced by four engine-driven AC alternators tied to constant speed drives. The majority of the G5 electrical equipment is DC-powered, thus transformer rectifiers are required, but at a weight saving over DC generators. The APU has its own alternator.

The same attention for redundancy was built into the hydraulic system on the G5. The two engine-driven hydraulic pumps on the G4 were replaced by four on the G5. A electrically-driven auxiliary hydraulic pump provides backup power, if required.

To accommodate customer requests, there is a three-zone climate control installed on the G5, allowing for separate settings possible for the cockpit, and the front and rear sections of the longer cabin.

The overhead panel housing the engine start switches and system controls have been simplified in the G5. There are approximately half the controls on the overhead panel compared with the G4. Many of the cockpit improvements were urged by O'Meara to lessen pilot workload. The 350 circuit breakers in the G4 cockpit were narrowed to 100 essential breakers, with the remaining ones put in the electronic equipment rack behind the cockpit on the G5.

Both of the BMW/Rolls-Royce BR710 engines were started, with maximum temperature reaching 486C on the 26C day. Maximum allowed starting temperature is 700C. Fuel flow was 690 lb./hr./eng. at idle. O'Meara then cycled through the systems displayed on the Honeywell center multifunction display prior to taxi. The layout of the system symbology was one of the most comprehensive but logically displayed I have ever seen in an aircraft.



Cabin configuration for the longer fuselage Gulfstream 5 can accommodate up to 19 passengers, but 13-15 seats would be optimal. The company has a 6,700-lb. outfitting weight allowance. Gulfstream is doing the completions for the Gulfstream 5 in Savannah, Ga., and Long Beach, Calif.

The ramp weight of the G5 was 55,950 lb. and included 7,100 lb. of fuel. There was only the two of us in the aircraft for the flight. Basic operating weight was 48,816 lb. for the test aircraft. Maximum ramp weight of the G5 is 90,900 lb. and maximum fuel volume is 41,300 lb. The takeoff decision speed and rotation speed was calculated to be 115 kt., while the takeoff safety speed was 122 kt.

I taxied from the Gulfstream ramp to the active runway at the Savannah airport. I found the steer-by-wire nose wheel steering to be effective during the taxi. The hydromechanical brakes took a short time to get used to, but after a time the correct pressure on the rudder pedals was applied.

Once on the runway, I advanced the two power levels to full power, with the FADEC adjusting for the required setting. Takeoff acceleration was brisk at the light gross weight and takeoff roll was close to 2,500 ft. After the gear and flaps were retracted, the rate of climb was close to 5,000 fpm., while staying at 250 kt. The altitude of 20,000 ft. was reached in 6 min. and the rate of climb was 3,700 fpm. at 300 kt. An air traffic control restriction required us to stay at 23,000 ft. for 1 min.

An altitude of 35,000 ft. was reached in 12 min. and the rate of climb was close to 3,000 fpm. Prior to reaching this altitude, a 180-deg. turn was required to stay within the operating area.

While we were able to climb directly to 51,000 ft. in the relatively lightweight test aircraft, many operations would entail long flights with a maximum payload. The Gulfstream 5 has the ability to reach 41,000 ft. on initial climb, starting with a maximum ramp weight of 90,500 lb. on a standard day +10C. Time to reach 20,000 ft. is 7 min. while burning 990 lb. Time from sea level to 30,000 ft. is 12 min. with a total fuel usage of 1,560 lb. Total time to reach 41,000 ft. is 24 min. and fuel burn is 2,440 lb., according to Gulfstream figures.

During the slow climb, now in autopilot, I was able to better examine the flight displays. The six-tube Honeywell SPZ8500 system is state of the art for any class of aircraft. The primary flight displays and engine information is presented logically and with pilot workload considered. One change from the G4SP layout was placing the higher speeds at the top of the airspeed bar, rather than at the bottom as in the G4SP. Gulfstream pilots have been especially active in industry groups in trying to eliminate controlled flight into terrain, and the G5 cockpit layout and displays reflects the emphasis on good situational awareness.

The G5's APU had been shut down on the ground, but O'Meara said that the unit had repeatedly been started at 43,000 ft., after being cold-soaked, and delivers full power at 45,000 ft. The AlliedSignal unit is capable of running at 51,000 ft.

At 45,000 ft., the rate of climb was 1,600 fpm. at Mach 0.80 and the fuel flow was 1,550 lb./hr./eng. It had taken 17 min. to reach this altitude. The rate of climb decreased to close to 500 fpm. prior to reaching 51,000 ft., and the total fuel burn had been close to 2,700 lb. during the altitude hold and turns required to stay within the restricted area. Total time to reach 51,000 ft. was just shy of 26 min. O'Meara estimated we had 2.5 hr. of flight at this altitude with adequate reserves remaining. It was indicating a -9C day at this altitude. The cabin altitude was 6,000 ft. at 51,000 ft. with a pressure differential of 10.14 psi.

Gulfstream is testing the fatigue life of the G5 to two lifetimes, and the fuselage has been requalified to 17.2 psi., because of the increase in pressure differential from the G4 to the G5. One test completed earlier to meet European certification standards was failing the outer pane of a cabin window and then achieving a cabin differential of 42 psi. with the window inner panel still intact.

Other changes incorporated into the G5 to reach current FAA requirements include the capability of isolating right and left-side pitch and roll controls if a control jams. Also, there is now a secondary pitch control should both elevators become locked and the normal control of the elevators through the elevator trim tab becomes effective. There is also a triple safety latch on the engine reversers to prevent deployment in flight. An FAA special condition requires that there is a second pressure bulkhead to prevent cabin pressure loss in the G5, in the event of an engine rotor burst at altitude.

At 51,000 ft., a cruise setting resulted in a Mach 0.81 speed and a fuel flow of 1,030 lb./hr./eng. At this altitude, I made some 45-deg. banked turns without buffet, while holding close to 1.4g in the turn. O'Meara said that the G5 wing had been designed specifically for high altitude and long-range flight, but also with the comfort of the passenger in mind. O'Meara said that the wing provided them much better stall margins throughout the flight regime than they had expected.

Roll control at this altitude was positive, and I had no difficulty in establishing a bank angle and then holding it. The longer wings of the G5 place the ailerons farther out the wing, giving it a higher mechanical advantage. Gulfstream also has increased the ratio of the hydraulically power-boosted ailerons.

Following flight at 51,000 ft., I descended to 45,000 ft., a more representative altitude for a long-range flight. At this altitude, maximum power provided a speed of Mach 0.88 with a fuel flow of 1,560 lb./hr./eng. The aircraft gross weight was 52,700 lb. and the temperature was -1C.

Gulfstream is attempting to lower the specific fuel consumption (SFC) of the G5 to offset the 1,500-lb. weight gain during development. This weight gain made it necessary to increase the maximum takeoff weight from 89,000 lb. to 90,500 lb. The unanticipated weight gain is attributed to Gulfstream, the Northrop wing, the Fokker tail and 500 lb. for the engine, nacelle and thrust reversers. Weight reduction efforts include the removal of a steel structure around the FADEC.

Included in the attempts to lower fuel burn are the reshaping of the engine nacelle, installing lower drag vortex generators on the wing, removing the windshield wipers in favor of a pneumatic air system and reworking the antenna fairings. Improvements to the BR710 production engine include a fully faired bypass duct and super polishing the high-pressure turbine blades. These modifications should give the entry into service aircraft a 3-5% improvement in SFC over flight test aircraft, Ed Flinn, Gulfstream chief customer engineer, said.

A high-speed descent was made with the speed brakes extended at a initial speed of Mach 0.88 and at idle power. The deployment of the speed brakes did not provoke a pitch change and the rate of descent was 5,800 fpm.

At 16,000 ft., I held altitude at idle power with a deceleration of one kt./sec. for the 52,500-lb. aircraft. The G5's stickshaker activated at 107 kt., and the stick pusher forced the control column 1-in. forward of center with a 70-lb. force and without a feeling of negative Gs. With the G5 in the landing configuration, the shaker went off at 94 kt. and the stick pusher activated at 87 kt. Both recoveries were normal with the addition of power and keeping the nose lowered. There was no tendency of the wing to drop during either stall.

O'Meara said that during the flight test program, they found it impossible to stall the G5 at 10,000 ft. with flap settings of zero, 10 deg. and 20 deg. At the 10-deg. and 20-deg. flap settings, the pilots ran out of elevator control before reaching the stall. At a 39-deg. flap setting at 10,000 ft., there was an aerodynamic stall when the aircraft reached 19 units of angle of attack. It was in the low- to mid-20,000-ft. altitudes where they would experience a wing roll of more than the 20-deg. FAA limitation at stall, necessitating the stick pusher. At the higher altitudes, the stall was defined when the G5's nose would slightly pitch up, without a wing drop.

In the aftermath of recent aircraft accidents tied to icing problems, the FAA required special testing in the event of an ice-congested tailplane stall. O'Meara said that they accomplished a zero-g pushover with simulated ice forms on the horizontal stabilizer without difficulty.

We then descended en route to the Brunswick, Ga., Glynco airport to do several touch-and-go landings. I found that the G5 was extremely stable at the lower altitudes and in the approach, even with gusting winds above 15 kt. The visibility from the cockpit afforded an excellent view of other aircraft traffic at the uncontrolled airport. The first approach was flown at 125 kt. in automatic throttle and the second one was at 115 kt. in the same mode. Both landings were smoother than the approach deserved, because of ground effect and the trailing link design of the G5's main landing gear.

I found the pitch forces at rotation speed to be lighter than expected, but in complete accord with the overall harmony of the G5's flight control system. The sensitivity and responsiveness of the flight controls might not equate to a sports car, but they certainly rank with a luxury sedan and not a truck.

During the return flight to Savannah, the G5 had a fuel flow of 1,640 lb./hr./eng. at 5,000 ft. at an indicated airspeed of 250 kt. The final landing at Savannah was on an ILS with a direct crosswind nearing 15 kt. The G5 was planted firmly on the runway and, with use of thrust reversers and moderate braking, the aircraft was easily slowed to a taxi speed in near 5,000 ft. The brake system registers the peak temperature of the brakes on the landing roll and displays it on the system page for calculation of brake energy for the next takeoff.

Total fuel burn for the 1.7-hr. flight was 5,650 lb., which included the climb to 51,000 ft., the stall sequence, two touch-and-go landings, a return to Savannah at a low altitude and the final landing.

There are few operational options available to customers with all that Gulfstream offers as standard equipment. One such option will be a Honeywell/GEC Marconi head-up display. Certification on the G5 is expected in the third quarter of this year. The HUD will have a feature that automatically declutters the flight information on approach.

While No. 505 was not equipped with a enhanced ground proximity warning system, the AlliedSignal Aerospace unit will be installed on customer aircraft.

I did have the opportunity to fly the EGPWS in the FlightSafety International simulator at the Gulfstream facility on the day before my G5 flight. My first approach from the left seat in the simulator was to the Aspen airport. This gave me the chance to see all of the features of the unit meant to eliminate controlled flight into terrain. The voice calls and the red danger zones displayed on the multifunction display gave me more than adequate warning to miss the mountains around the Colorado airport.

The price of the G5 is $29.5 million in 1996 dollars, with an escalation capped at 3% annually. Normal contract requirements requires a $2-million deposit at contract signing and then a payment of $5 million 12 months prior to delivery and another $10 million six months before delivery. The balance and escalation costs are collected at the green aircraft delivery.

Gulfstream has accumulated over 70 orders for the G5, with the first open delivery date near the beginning of 2000. Total backlog of aircraft is 104, counting both G4SPs and G5s. While Gulfstream in recent years has been delivering near 30 aircraft annually, the company plans to increase the total production rate to 60 aircraft by 1999.

Gulfstream Aircraft Vice Chairman Bryan Moss is both bullish on the future prospects of the G5 as well as the health of corporate aviation. He attributes this bullishness to the changing pattern of business air travel and the need for long-range flights, especially in the Far East. The expanding use of fractional ownership of corporate jets is showing more business people the flexible, secure and comfortable means of transportation afforded by business jets, Moss said.

The ability of Gulfstream to meet its performance guarantees with the G5 has provided a true challenge for Bombardier with the comparable performance and size of its Global Express, now in flight test. Gulfstream has a potential lead of almost 18 months in putting an aircraft into service before the Global Express. Once both aircraft are in operation, the marketplace will determine the order split and the overall need for a long-range corporate jet in the $35-million category.

Gulfstream 5 Specifications

Engines:
Two BMW Rolls-Royce BR710A1-10 turbofan engines with a
takeoff static thrust rating of 14,750 lb. each.
Weights:
Maximum ramp weight 90,900 lb. (41,232 kg.)
Maximum takeoff weight 90,500 lb. (41,050 kg.)
Maximum landing weight 75,300 lb. (34,156 kg.)
Maximum zero fuel weight 54,500 lb. (24,721 kg.)
Manufacturer's bare empty weight 39,500 lb. (17,917 kg.)
Outfitting allowance 6,700 lb. (3,039 kg.)
Typical operating weight empty 48,000 lb. (21,773 kg.)
Typical payload (eight pax) 1,600 lb. (725 kg.)
Typical zero fuel weight 49,600 lb. (22,499 kg.)
Maximum fuel 41,300 lb. (18,734 kg.)
Dimensions:
Overall length 96.5 ft. (29.4 meters)
Overall height 25.9 ft. (7.9 meters)
Wing span 93.5 ft. (28.5 meters)
Cabin length 50.1 ft. (15.3 meters)
Cabin height 6.2 ft. (1.9 meters)
Cabin width 7.3 ft. (2.2 meters)
Cabin volume 1,699 cu. ft. (47.3 cu. m)
Baggage compartment volume 226 cu. ft. (6.4 cu. m)
Cockpit length 12.9 ft. (3.9 meters)
Performance:
Cruise speed, max cruise power, 60,000 lb. at 35,000 ft. 510 kt. Mmo limit
Specific range at 65,000 lb., 5,000 ft. at Mach 0.8 185 naut.mi./1,000 lb. fuel
FAA takeoff distance at 90,500 lb. 6,041 ft. demonstrated
FAA takeoff distance at 85,100 lb. 5,240 ft. demonstrated
FAA landing distance at 75,300 lb. 3,172 ft. demonstrated
Maximum range, Mach 0.80, eight pax,
four crew and NBAA IFR reserves 		6,500 naut. mi.
Maximum allowable Mach Mach 0.885
Maximum cruise speed Mach 0.87
Maximum cruise altitude 51,000 ft. (15,545 meters)
Cabin pressure differential 10.17 psid.
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