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  • FLIGHT TEST: Cessna Citation Soverign - Mid-size marvel

FLIGHT TEST: Cessna Citation Soverign - Mid-size marvel

Cessna's Citation Sovereign business jet has great field performance and can take eight passengers coast to coast across the USA

Although there are a several aircraft in the mid-size business jet category, recently most manufacturers have concentrated on launching larger designs. But while Bombardier developed the Challenger 300, Dassault the Falcon 2000EX and Raytheon the Hawker Horizon for the burgeoning super mid-size segment, Cessna saw an opportunity in the traditional mid-size market, where no all-new aircraft were being launched.

When it announced the Model 680 Sovereign at the 1998 National Business Aviation Association convention, certification and first deliveries were planned for 2002, but the programme was delayed while Cessna worked on other business jets. First flight was not until February 2002, and US type certification was received in June this year. Customer deliveries began last week, in the run-up to NBAA 2004.

Cessna's first all-new business jet since the Mach 0.92 Citation X, the Sovereign is not the fastest, largest or longest-range offering in the mid-size market. But what it does offer is a large cabin, exceptional field performance and the ability to take eight passengers from coast to coast in the USA - all at a typically equipped price of $14.2 million. The Sovereign costs about $1.6 million more than Bombardier's mid-size Learjet 60, yet can carry 10 passengers 4,630km (2,500nm) while the Learjet can carry only four over that distance. The Sovereign can carry eight passengers 4,985km, just 760km short of the capability of the larger-cabin, $3.6 million more- expensive, super mid-size Challenger 300.

While the Sovereign typically cruises more slowly than either of those aircraft, it can operate out of shorter fields. At maximum take-off weight (MTOW), at sea level and in standard day conditions, the Sovereign needs only 1,090m (3,580ft), while the Challenger 300 needs 1,450m and the Learjet 60 1,660m. At maximum landing weight (MLW), the Sovereign needs only 808m of runway, less than the Learjet 60's 1,042m but more than the Challenger 300's 796m. Hot and high performance is also noteworthy, with the Sovereign able to carry eight passengers from Aspen, Colorado to Teterboro, New Jersey with instrument flight rules reserves on a 35°C (95°F) day.

The Sovereign shares its fuselage diameter and nose section with the faster Citation X. But at 7.37m, its cabin is 0.21m longer than the X's, and typically seats nine compared with eight.

The typical floorplan has a single seat opposite the entry door and eight more in a double-club arrangement. Higher-density configurations are available for up to 12 passengers. The seats have armrests that stow to the side of the seat back, affording more room.

Fifteen elliptical windows provide an airy cabin environment. An externally serviced full lavatory is located at the aft end of the cabin. Baggage can be carried either in a centreline closet aft of the lavatory or in the tailcone compartment. The heated 2.83m3 (100ft3) compartment has a 450kg (1,000lb) capacity, but is not pressurised. A large door with integral steps, below the left engine nacelle, provides easy access to this large hold.

Fault analysis

The Sovereign's development and certification flight-test effort totalled more than 3,000h and involved three aircraft - a prototype and two development aircraft built on production tooling. The development programme included a number of firsts for Cessna. It was the first Citation to use the Maintenance Steering Group (MSG 3) process to develop a maintenance programme through fault analysis, which should result in a significant reduction in scheduled maintenance costs. The Sovereign is also Cessna's first aircraft to have a Level D flight simulator - developed and operated by FlightSafety International - in place before first customer delivery.

Flight International was invited to fly the Sovereign at Cessna's Wichita, Kansas production facility. Cessna senior demonstration pilot David Bodlak conducted the pre-flight exterior inspection, pointing out some of the Sovereign's features. Like the Citation X, the Sovereign lacks windscreen wipers, because the cockpit windows have a water-repellent coating. A blower, mounted in the forward equipment bay, clears any stubborn residue.

Housed in the right side of the nose compartment is a large fire-suppression bottle for the tailcone baggage compartment. Should a fire be detected, the tailcone-mounted auxiliary power unit's (APU) fire bottle is discharged into the baggage hold. The nose bottle's contents are then metered into the compartment to provide 180min of fire protection.

This may seem like overkill in a mid-size business jet, but the Sovereign can carry eight passengers from California to Hawaii and there is nowhere it can be diverted to en route.

Most of the pre-flight inspection can be conducted from ramp level, but a ladder is required to check oil levels in the 5,688lb-thrust (25.3kN) Pratt & Whitney Canada PW306C engines.

Although the Sovereign is pleasing to the eye, its vertical stabiliser appears somewhat stout. In an effort to ensure the Sovereign would fit into the maximum number of hangars, the aircraft's overall height was limited to 6.2m. A T-tail arrangement would have increased vertical stabiliser effectiveness, but at the cost of higher structural weight, so Cessna chose to go with a "thick" fin and mounted the horizontal stabiliser a quarter of the way up. A number of vortex generators at the base of the fin smooth airflow over the rudder and tailcone.

Acoustic silencing

Entry to the cabin is via an integral door and ladder. The manual counterbalanced door has roller overcentre locks instead of Cessna's usual locking-pin arrangement. The door has a stiff outer seal to maintain cabin pressurisation, and a pressurised inner seal provides extra acoustic silencing.

Dominating the cockpit's forward instrument panel, the four 200 x 250mm (8 x 10in) liquid-crystal displays of the Honeywell Primus Epic integrated avionics suite provide each pilot with a primary flight display (PFD). One centre display is used for the engine indication and crew alerting system (EICAS) and the other as a multifunction display (MFD).

The flight-guidance panel is located centrally beneath the glareshield, and system control panels are at the base of the instrument panel. In another first for Cessna, lighted pushbutton switches are used throughout the cockpit, with blue signifying normal operations. The centre pedestal has two multifunction control display units (MCDU) forward of the thrust levers and two cursor control devices (CCD) aft. The parking-brake T-handle is located at the aft end of the pedestal, within easy reach of both pilots.

The Honeywell RE100(CS) APU was fired-up in preparation for engine start. Unlike those in larger business aircraft, the Sovereign's engines are started by electrical starter/generators, not bleed air. As well as keeping the aircraft battery charged during engine start, the APU provides bleed air to cool the cabin. Each engine was started individually, with full-authority digital engine control (FADEC) metering fuel for a cool start.

Idle power was sufficient to keep the aircraft moving once out of the chocks. Nosewheel steering (NWS) control via the sidewall-mounted tiller was direct and allowed accurate tracking of taxiway centrelines. Rudder pedals alone, which gave a limited amount of NWS displacement, were used on the straight portions of the taxi. The toe-actuated hydraulic wheel brakes were easy to modulate and allowed taxi speed to be kept at a reasonable level. During taxi, the emergency stow feature of the thrust reversers was checked, while the electrically actuated flaps were set to 15° for take-off.

Once on the runway, the thrust levers were advanced to the take-off detent, and the engines stabilised at 99.6% N1. After brake release, the 10,966kg aircraft, including 2,595kg of fuel, accelerated briskly down the runway. On this 27°C day, the computed balanced field length was 1,038m, and Bodlak called "rotate" at 103kt (190km/h) indicated airspeed. The aircraft lifted off in a 10° nose-high attitude just 15s after brake release.

Previewing

The initial portion of the climbout was at 140kt, while the gear and flaps were retracted. The electrical pitch trim was fast enough to zero out forces as the aircraft accelerated to 250kt. Flight director guidance was followed as air traffic control (ATC) cleared us directly to our first waypoint.

As we passed 8,000ft, the autopilot was engaged and thrust levers retarded to the maximum continuous detent for the climb. During the climb I familiarised myself with the flight-management system (FMS). Although selecting a "direct" course to a waypoint was easily accomplished, the system did not allow for previewing the proposed route change before execution.

During the climb, ATC issued traffic avoidance vectors, and the autopilot's heading mode was used to navigate the aircraft. Passing 30,000ft, a climb Mach number of 0.64 was captured and maintained. The aircraft levelled off at 43,000ft 16min after brake release and with a fuel burn of 390kg. At the 13,608kg MTOW and standard day conditions from sea level, Cessna projects the aircraft will take 26min to reach 43,000ft with a fuel burn of 500kg.

Five minutes after levelling off, the thrust levers were retarded to the cruise detent and the aircraft's speed allowed to stabilise. The 10,505kg aircraft maintained 219kt indicated (441kt true airspeed for the ISA -5°C conditions). Indicated Mach number was 0.778 and total fuel flow was 653kg/h (1,440lb/h). For these conditions on a standard day, Cessna publishes 425kt true airspeed as the high-speed cruise.

With the autopilot still engaged, I left the cockpit to sample the cabin, where the 0.64bar (9.3lb/in2) pressurisation system was maintaining an altitude of just 6,000ft. The deck angle was about level, making it easy to walk through the 1.73m-high cabin. Overall the environment was quite quiet, and the entry door's acoustic seal appeared to do a good job as the noise level did not vary appreciably throughout the cabin's length.

After returning to the left seat, I slowed the aircraft to 175kt indicated, which yielded a long-range cruise speed of 360kt true for current conditions. Indicated Mach number was 0.634 and total fuel flow was only 454kg/h.

Still level at 43,000ft, the autopilot was disengaged for a series of steep turns, and the thrust levers advanced to accelerate to M0.77. During the acceleration, I found the aircraft rather pitch-sensitive. While the stabiliser trim nulled out forces, it was not as precise as I would have liked to fine-tune the pitch attitude. Roll and pitch forces were well harmonised during several level 60° banked turns. The nose tracked smoothly across the horizon and no buffet was felt at 224kt.

Emergency descent

Before descending to medium altitude, Bodlak explained the autopilot's emergency descent feature. At altitudes above 30,000ft, with the autopilot engaged, a rise in cabin altitude to 13,500ft will trigger the emergency descent mode. Once triggered, the autopilot will turn the aircraft 90° to the left and lower the nose to maintain MMO/VMO. Without pilot intervention, the autopilot will level the aircraft at 15,000ft. With the autopilot disengaged, I initiated a simulated emergency descent from 43,000ft.

During the descent, the MMO of 0.8 was held with the speedbrakes stowed. Sharp control inputs in all three axes showed the aircraft to be quite stable. The speedbrakes - five panels on each wing - were then extended, and a descent rate of 9,500ft/min (48m/s) maintained. The Sovereign is equipped with emergency oxygen, but its ability to get down to low altitude quickly after loss of cabin pressurisation is a useful capability.

In addition to manual ailerons, the Sovereign has three roll spoilers on each wing. The roll spoilers are the middle three speedbrake panels and are hydraulically actuated. Spoiler deployment is proportional to control wheel movement, with the first spoiler motion occurring at 12° of displacement. At 10,000ft and airspeeds from 200-290kt, I did a series of half-deflection aileron rolls. With feet on the floor and yaw damper engaged, time to roll from 60° bank to 60° opposite bank at all speeds was about 11s.

During these manoeuvres, I found roll control forces moderate and desired bank angles easy to capture and hold. But during the half-deflection rolls, there was noticeable aerodynamic buffet on the ailerons. While the buffet was less than that experienced when flying Cessna's Citation XLS, there are several other aircraft in this class that also have manual ailerons and do not display this mildly annoying trait.

The last event flown before returning to Wichita was a stall series in each of three configurations, which highlighted one nice feature of the PFD - the ability to display an angle-of-attack (AoA) indicator just below the airspeed tape. The first stall was in a clean configuration at idle power. The 10,131kg Sovereign was slowed at 1kt/s in a wings-level attitude. At 97kt and 0.80 AoA in a 13° nose-high attitude, the dual stick-shakers fired. Light buffet at 93kt preceded a slow dropping of the right wing, which was easily countered by left rudder. Recovery to normal flight was effected by lowering the nose and advancing the thrust levers.

The second stall was in a take-off configuration, gear up and flaps 15°. In a 20° banked turn, the aircraft was again slowed at idle power. The stick shakers fired at 91kt, again at 0.8 AoA, and further slowing the aircraft to 87kt caused the onset of light buffet. A slight wing drop wascountered with rudder, and lowering the nose accelerated the aircraft to normal flight conditions.

The third and final stall was in a landing configuration, gear down and flaps set to full (35°). With the engines set to 50% N1 in level flight, the stick shakers fired at 81kt. Slowing a further 5kt was accompanied by buffet and the left wing dropping. Once again I found the rudder quite effective in keeping the wings level, and recovery to normal flight was accomplished by relaxing yoke back-pressure to lower the nose.

Once the aircraft was cleaned up, ATC provided vectors to the instrument landing system (ILS) final approach course to runway 19R. Using the MCDU, I installed and activated the approach. The FMS automatically tuned the navigation radio to the ILS frequency - a nice feature. Approaching the field, with the autopilot engaged, I used the CCD to change ranges on the MFD's map display and closely monitor traffic with the TCAS. I found the CCD fairly intuitive to use, similar in execution to that in Dassault's EASy flight-deck.

Because of gusty high winds, approach target speed for the 10,056kg aircraft with flaps full was 120kt, with a VREF of 100kt. Before capturing the localiser, I disengaged the autopilot and followed the flight director's guidance. The gear was extended and flaps set to full before glideslope capture. Once on glideslope, I found the flight director's commands allowed me to track both course and descent path despite the gusty wind conditions.

Approaching 60ft above ground level, I retarded the thrust levers to idle and initiated the flare manoeuvre at 20ft. At MTOW, the Sovereign has a wing loading of only 284kg/m2, and at our lower weight the aircraft floated down the runway. It gently touched down at 95kt and the flaps were set to 15° in preparation for the "go" portion of the touch and go.

With the thrust levers in the take-off detent, Bodlak called "rotate" at 102kt. Once airborne, he rapidly pulled the right thrust lever to idle to simulate an engine failure. Like the Citation XLS, the Sovereign has a rudder bias system. If this detects a difference of more than 15% in N2 speed between the engines, it automatically puts in rudder to reduce the yawing motion caused by the asymmetric thrust. The bias system is required for dispatch, and can put in up to 100kg of force to counter asymmetric thrust.

With the left engine at 99.5% N1 in the 140kt climbout (flaps 15°), less than 15kg rudder force was required to maintain co-ordinated flight. Once level on downwind, less than a quarter of the available rudder trim was needed to maintain co-ordinated flight. ATC vectors were followed to another hand-flown ILS approach to runway 19R. Final approach was flown with flaps at 15° and, once on the glideslope, 65% N1 on the left engine held 120kt. With the rudder trim set to neutral, less than 5kg of force was required to keep the "ball" centred on final.

Once landing was assured, the flaps were extended to full. This time I delayed the flare manoeuvre and the aircraft touched down on centreline just past my aimpoint. With the main gear on the runway, I deployed the speedbrakes, causing the five panels on each wing to dump lift and keep the aircraft firmly planted on the runway. Then the flaps were set to 15°, speedbrakes retracted and power advanced for take-off.

Maximum breaking

The last pattern flown was a visual approach and landing with maximum-effort braking. Flaps were again set to full and 120kt held on final. The power was retarded to idle passing 60ft, and flare initiated so as to touch down within 150m of the runway threshold at 100kt. Once on the runway, I extended the speedbrakes and stepped on the brakes. The aircraft had slowed to less than 50kt before the thrust reversers were fully unstowed, so was stopped with wheel brakes alone. With a 18kt headwind, the 9,850kg aircraft was brought to a halt about 850m from the threshold.

Taxi back to the ramp was accomplished with the control gust lock installed, the NWS now controlled by the tiller alone. Post-flight and shutdown procedures were accomplished easily.

Developed as a replacement for the Citation VII, Cessna's Sovereign is the newest entry into the mid-size business jet segment. It offers the largest cabin in its class, along with a huge baggage compartment. While the Sovereign offers US coast-to-coast range at high-speed cruise, it can operate out of fields too short for its competitors. MSG-3 design guidelines mean the Sovereign should be less expensive to maintain than its predecessor and provide more up-time to its operators.

The Sovereign is not the most passionate business jet on the market, but dollar-for-dollar, it may be the best mid-size value available.

MICHAEL GERZANICS / WICHITA, KANSAS

 

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