With a package of improvements, Cessnahas made the latest version of the world'sbest-selling jet even better
Cessna's latest offering, the Citation XLS, is the enhanced descendant of the world's best-selling business jet, the Citation Excel. Since certificating the Excel in April 1998, the manufacturer has delivered more than 350 to customers worldwide. The aircraft owes its success in part to the niche that Cessna carved out for a light business jet with mid-size cabin, outstanding runway performance and low acquisition and operating costs.
The Excel's combination of size and economics made it a runaway hit, and the XLS is Cessna's bid to continue that success. The aircraft was on the verge of certification when Flight International sampled its upgrades on a flight from Cessna's production and test facility in Wichita.
The XLS shares its fuselage and cabin cross-section with the Citation X and soon- to-be-certificated Citation Sovereign, both mid-size jets. This ovoid profile offers 1.73m (5.7ft) of cabin height, only 20mm lower than that of the more expensive mid-size Hawker 800XP. The 5.69m-long cabin slots neatly between that of Bombardier's Learjet 40 light jet and its longer Learjet 45 - the XLS's direct competitor in the super-light sector. At 1.7m, the cabin is slightly wider than that of the Learjet's, and only 100mm narrower than the Hawker's.
The XLS's baseline interior offers seating for nine passengers: two facing sideways opposite the cabin entry door, four in a club arrangement at mid-cabin, two facing forward at the vanity divider in the rear and one in a belted seat opposite the aft toilet. While the seating arrangement is identical to the Excel's, Cessna has improved the cabin in several ways.
LED lighting
Whereas the Excel has armrests that slide down into the seat cushion area, the XLS has slender armrests that rotate up and away and the seat-bottom cushions are nearly 100mm wider. Cabin lighting has been upgraded to LEDs. Two closets are provided, one forward behind the co-pilot and one aft of the vanity area. An unpressurised 2.55m3 (90ft3) baggage compartment is located aft of the cabin. Its external door features two integral steps, and the relatively low sill height of 1.14m should facilitate loading and unloading from ramp level.
Enhancements have been made in other areas. Brakes have been improved by elimination of the Excel's toe pedal-operated master cylinder system. The pedals now directly control the brake pressure-metering valve. Additionally, the standalone brake hydraulic power-pack has been moved from the nose to a bay aft of the wing, reducing cabin noise as it periodically cycles on to top off brake-accumulator pressure. This has allowed the forward avionics bay to be cleaned up, giving easier access for maintenance tasks.
The trailing-link main landing gear retracts into the wing, but the wheel wells are not covered. To reduce drag, Cessna has installed doughnut-shaped fairings around the wheel-well openings. At the same time thrust is increased, with the XLS's uprated Pratt & Whitney Canada PW545B turbofans producing 3,990lb (17.8kN), a 4.9% improvement made by tweaking fan-blade design and engine control software. At climb and cruise conditions above 37,000ft there is a 2% increase in available thrust.
The basic operating weight of the XLS matches the Excel's at 5,756kg (12,690lb) and maximum useable fuel remains the same at 3,057kg. The most measurable result of the more powerful engines is a 91kg increase in maximum take-off weight. This allows at least one more passenger to be carried with full fuel tanks. With less than full tanks, the XLS's superior payload capability allows it to carry more fuel than the Excel with the same passenger numbers, the extra fuel translating directly into increased range.
For my flight I was accompanied by senior engineering test pilot Donald Alexander. The walk-around was straightforward, with all necessary inspection items readily accessible from ramp level. One notable external feature is the two ventral strakes. They improve stall performance above 30,000ft, and the Excel and XLS are the only Citations to incorporate them. The 17m-span unswept wing has fixed leading edges, with two-piece trailing-edge flaps that span the inside half of each wing. The wing itself is constructed as a single unit, which allows structural loads to be carried underneath the cabin. No wing spar runs through the cabin, and a flat aisle runs the length of the passenger compartment.
Access to the cabin is via a mechanically counterbalanced door with integral steps. The door has a primary pneumatic and secondary mechanical seal. A curtain separates the cockpit from the cabin, while an optional sliding door is available. Ample storage for flight publications is provided behind both the pilot and co-pilot seats.
Cockpit layout
Cockpit layout is logical with all system controls on the instrument panel or centre pedestal. The Honeywell Primus 1000 avionics suite is essentially unchanged from the Excel, with the exception of the displays. The XLS has three 200 x 255mm (8 x 10in) liquid-crystal displays that provide more useable area than the Excel's smaller cathode-ray tubes. Each pilot has a primary flight display (PFD) and shares a centre-mounted multifunction display (MFD). The two forward-panel engine displays and two radio-tuning units are now active-matrix LCDs, providing enhanced legibility and reliability over the previous CRTs.
Each pilot has a guidance-mode selection panel above the PFD, but course selection and altitude select knobs, as well as autopilot and yaw-damper engagement buttons, are located on the aft portion of the centre pedestal. The XLS lacks an engine indication and crew alerting system, and the glareshield is occupied by a central master caution and warning panel. This is prime real estate that would be better devoted to a flight guidance and control panel.
While the test aircraft was being towed out of the hanger, Alexander loaded the route of our flight into the Universal Avionics UNS-1Esp flight management system (FMS). While the XLS comes standard with one FMS, our aircraft had the optional second system. The FMS has a take-off and landing computation capability that allows it to determine required field length as well as "V" speeds. With two pilots and two passengers our aircraft had a zero-fuel weight of 6,079kg, and 2,318kg of fuel gave a take-off gross weight of 8,397kg. With a wet runway and 5kt (9km/h) headwind, the FMS computed a required field length of 3,220ft for a 15° flap setting on the cold -1°C (30¡F) day.
While engines can be started solely on battery power, Alexander started the Honeywell auxiliary power unit to provide electrical power for the avionics during engine start. After engaging the starter on the right engine, light off was nearly immediate when the throttle was taken out of the cutoff position at 8% N1.
Inter-turbine temperature (ITT) peaked at 400°C, and an idle RPM of 50% N2 was reached in 35s. Left engine start mirrored the right, ITT peaking well below the 760°C limit at 389°C.
Idle power was sufficient to start theaircraft rolling after the parking brake was released. Rudder pedal-actuated nosewheel steering give +/-20° of control and was extremely precise, allowing easy tracking of the taxiway centreline. The toe-actuated wheel brakes were easy to modulate, allowing smooth control of taxi speed. During the taxi the flaps were set to 15°in preparation for take-off.
Before taking the active runway, each throttle was advanced individually to test the operation of the rudder bias system. This compares relative engine thrust levels, and displaces the rudder in the direction of the high-thrust engine to prevent excessive yaw build-up. As the rudder is a conventional cable-actuated surface, the pedals moved as the rudder was displaced. According to Alexander, the bias system alone would not entirely counteract a thrust asymmetry, but would provide a good tactile cue as to which direction to move the rudder.
Straight-wing climber
On the runway, I released the toe brakes and advanced the throttles to the take-off detent. Single-channel electronic engine controls (EEC) stabilised each PW545B at an N1 setting of 86.4%. With a thrust-to-weight ratio of 0.431, acceleration was brisk. Even at maximum take-off weight the XLS has a thrust-to-weight ratio of 0.395, roughly 15% greater than that of the smaller and faster Learjet 40.
Passing 85kt indicated airspeed Alexander called V1 and I took my right hand off of the throttles. At the rotation speed of 103kt about a 10kg pull was required to move the yoke about one-third of the way aft to attain the take-off attitude. The aircraft lifted off the runway at the V2 speed of 116kt in a 10° nose-high attitude. Landing-gear retraction caused negligible change in pitch forces as the nose was lowered and the aircraft accelerated to the initial climb speed of 250kt.
As the flaps were retracted, the hydraulically actuated two-position horizontal stabiliser rotated from its 2° nose-down setting to its up and away setting of 1° nose up. Operation of the moveable stabiliser, required for extreme forward centre-of-gravity conditions, was signalled by a light on the caution panel. Resultant yoke forces for the cable-actuated elevator were as expected, with nose-down trim required as the aircraft accelerated and cleaned up.
Passing 3,000ft above mean sea level (about 1,700ft above ground level) I retarded the throttles to the climb detent, allowing the EECs to maintain optimum power for the climb. During the climb to FL430 (43,000ft) I was able to get a feel for the XLS's control harmony with a series of gentle bank turns. The relative pitch and roll forces are well harmonised.
During the climb, I used the centre MFD's map display to track our progress and monitor the standard traffic collision avoidance system (TCAS). This information can also be displayed on the horizontal situation portion of the PFD. Passing FL250 a climb Mach of 0.62 was held until levelling off at FL430, 2,000ft below the XLS's certificated ceiling. From brake release the climb to 43,000ft had required only 18min and used 320kg of fuel. Our climb, however, was hindered by air-traffic vectors and abnormally hot temperatures of ISA +8°C above FL300. At maximum take-off weight (9,163kg) and standard-day conditions, Cessna projects a fuel burn of 348kg and a time to climb of 23min.
Once level at FL430 I engaged the autopilot, with throttles still in the climb detent. After 6min I retarded the throttles to the cruise detent and the 8,090kg aircraft accelerated to and stabilised at M0.726. At 203kt indicated airspeed, a total fuel flow of 517kg/h gave a true airspeed of 424kt. At standard-day conditions Cessna projects a cruise speed of 431kt for a 7,710kg aircraft.
The XLS's cruise performance, while slower than its competitors, is a marked improvement over the Excel's. Due primarily to the wheel-well fairings and slight thrust increase, the aircraft's FL430 cruise speed of 431kt is a full 20kt faster than the Excel's. Slowing the aircraft to M0.7 yielded a 407kt cruise speed, while total fuel flow decreased slightly to 494kg/h.
Quiet cabin
While Alexander took control of the aircraft, I left the cockpit to sample the cabin in cruise conditions. The deck angle was nearly level and ambient noise was low, even near the entry door. The cabin pressurisation system is essentially automatic and can maintain a sea-level altitude up to 25,230ft. At 45,000ft, the 0.642bar (9.3lb/in2) pressure differential will give a comfortable cabin altitude of 6,800ft.
Returning to the cockpit, I took control of the aircraft for several 45° bank-angle steep turns at FL430 and M0.7. Roll response was fairly crisp and the target bank angle was easy to maintain. During the turns the nose tracked smoothly across the horizon and no airframe buffet was felt as the aircraft held 190kt indicated.
Next the aircraft was accelerated to M0.73 and the yaw damper disengaged. I exited the Dutch-roll mode with a symmetrical one-third displacement rudder doublet. The resulting motion was lightly damped as the wing remained nearly level and the nose snaked repeatedly across the horizon. Turning the yaw damper on immediately stopped the decreasing-amplitude oscillations.
Throttles were then advanced and a descent started to sample the XLS at its maximum operating Mach number of 0.75. The PFD's airspeed tape turned yellow at M0.75 and a "beep beep" sounded. At M0.755 the airspeed tape turned red. I stabilised the XLS at M0.76, where aircraft responses to a series of sharp control inputs in each axis were well damped.
Satisfied with the stability at high Mach, I retarded the throttles to idle to simulate an emergency descent. At M0.73 with the speedbrakes retracted a descent rate of over 4,500ft/min (22.9m/s) was maintained. Extending the speedbrakes using the throttle quadrant-mounted toggle switch caused slight airframe buffet as the rate of descent increased to 6,500ft/min. As in the Citation X, the XLS's autopilot has an emergency descent mode. In the unlikely event of cabin altitude exceeding 14,000ft when the aircraft is at or above 31,000ft, the autopilot will turn the aircraft 90° off heading and initiate a descent at just below MMO/VMO. While the autopilot cannot retard the throttles to expedite the descent, it will level the aircraft off at 15,000ft above mean sea level and give the crew a chance to regain control.
I retracted the speedbrakes and levelled the aircraft off at 14,000ft to further investigate the XLS's handling characteristics. With the yaw damper off a rudder doublet at 200kt excited a Dutch-roll response that was well damped. A series of 45° to 45° bank-angle rolls at airspeeds from 200kt to 280kt at half and full yoke deflections showed the XLS to be quite responsive in the roll axis. Yoke forces were fairly low.
Next I slowed the XLS for a series of stalls in clean, take-off and landing configurations. With 1,592kg of fuel remaining, I first slowed the clean aircraft at a rate of 1kt/s with idle power set. At 103kt the dual stick-shakers activated. Aircraft response to elevator and aileron inputs at this low speed was quite good. The rudder was effective at yawing the aircraft, but generated little roll motion.
Keeping the wings level at very slow speeds was a task best left to the highly effective ailerons. Excessive rudder deflections at speeds below the shaker were more likely to cause a wing to drop than level it. To recover the aircraft I relaxed yoke backpressure and advanced the throttles; the increased thrust from the high-mounted engines helping the recovery by pushing the nose down.
Normal recovery
With the flaps set to 15° and gear up, I again slowed the aircraft straight-ahead at 1kt/s. The stick shaker activated at 97kt, 1.1xVstall. I continued to slow the aircraft in idle power to 88kt where the right wing dropped, indicating the stall. Flying airspeed was again attained by relaxing back pressure and advancing the throttles. The gear was lowered and flaps extended to 35° for a landing-configuration stall.
A slight descent was required to maintain the 1kt/s deceleration rate in idle power. The shaker activated at 93kt, where the aircraft was responsive to pitch roll and yaw inputs. As the aircraft slowed through 85kt a slight airframe buffet was felt just before the right wing dropped to indicate the full stall. Recovery to normal flight was again effected by relaxing backpressure and advancing the throttles.
While still at 11,000ft, Alexander suggested we simulate an engine failure after lift-off to evaluate the XLS's single-engine flight characteristics. The landing gear was left down and flaps set to 15°. A V2 of 116kt indicated was set for the 7,370kg aircraft. Alexander advanced the power on both engines to the take-off detent of 95.9% N1. While holding 116kt in a climb he rapidly retarded the right throttle to idle. Initially about 20kg of force and two-thirds available rudder displacement was required to counteract the asymmetric thrust in a wings-level attitude.
As the rudder bias system kicked in, less than 8kg of force was required on the left pedal to keep the desired two-thirds rudder displacement. Approximately one quarter of the available left rudder trim was sufficient to zero out rudder forces and maintain co-ordinated flight. In addition to reducing the pedal forces required, the rudder bias system had provided a cue as to which rudder pedal to push in the event of an engine failure.
After retracting the gear and flaps I engaged the autopilot for the return to Wichita's Mid-Continent airport. Both throttles were retarded to idle and speedbrakes deployed to expedite the descent to the radar traffic pattern altitude of 3,000ft. ATC provided vectors to intercept the localiser for a Category II instrument landing system approach to runway 01L. Level at 3,000ft, I retracted the speedbrakes and armed the autopilot approach mode.
After the autopilot captured the localiser course, I slowed the aircraft to 150kt. As the glideslope indicator came into view on the PFD, the landing gear was lowered and flaps set to 15. Just before glideslope intercept the flaps were moved to their final setting of 35° and the aircraft slowed to the target speed of 116kt. The autopilot accurately tracked both the localiser and glideslope, while a manual power setting of about 52% N1 kept the aircraft on speed.
Descending through an 800ft overcast layer, the runway came into view, with the aircraft aligned nicely with the centreline. I disengaged the autopilot and hand-flew the final portion of the approach. The aircraft was in a near-level pitch attitude as it descended at 600ft/min toward the aim point. About 10ft above the runway I slowly retarded the throttles to idle and started the flare manoeuvre.
I initially rounded out several feet high, but was then easily able to milk it down to the runway. The aircraft touched down softly, about 750m from the threshold. Once on the runway I deployed the thrust reversers and Alexander extended the speedbrakes. As the aircraft rapidly slowed through 60kt I stowed the thrust reversers and applied light pressure on the brake pedals. The aircraft was brought to a halt after a ground run of less than 600m.
Taxi back to Cessna's ramp, engine shutdown and post-flight procedures were easily accomplished. During the 2h 7min flight I was able to sample the extremes of the XLS's flight envelope, where the aircraft displayed docile and predictable handling characteristics. Increased-thrust engines combine with a large straight wing to give the XLS great runway performance.
Standard, not options
While the cockpit of the XLS will never be mistaken for that of some more expensive business jets, it does provide all the required tools to fly safely and efficiently and navigate today's congested airways. In a move to reduce production costs and increase customer value, Cessna has made standard on the XLS a large number of the options popular on the Excel. At $9.9 million, a standard XLS is nearly $188,000 cheaper than its predecessor.
While there are business jets that can fly further or faster, what makes the XLS unique is its combination of a midsize cabin, 3,580km range and low acquisition and operating costs. With deliveries of the new Citation XLS scheduled to begin in June, Cessna has made the world's most-popular business jet even better.
Source: Flight International
