Harry Hopkins/WICHITA
THE CANADAIR CHALLENGER series of corporate jets has evolved over 15 years in a series of small steps which have not detracted from the success of the original formula - to marry the widest-bodied fuselage of the day for the first time with a super-critical wing and with turbofan power.
The RJ regional jetliner later evolved as a branch of this tree; the fuselage was extended and the avionics were substantially improved with the adoption of the Rockwell-Collins Proline 4 integrated suite.
The improved avionics have now been fed back into the Challenger, with the latest version, the 7,400km (4,000nm)-range CL-604 (certificated in September), which benefits from an engine upgrade, too. This more revolutionary step in the corporate market brings an advanced engine-indicating and crew-alerting system (EICAS), and easier maintenance of both engine and avionics (see box).
LIGHTER AND STRONGER
Through satisfying more demanding damage-tolerance requirements, Canadair has been able to reduce some inspection requirements. Greater maximum take-off and zero fuel weights have required undercarriage strengthening and an increase in braking capacity.
The avionics take up less space than before, and hydraulic-pump reliability has been improved, as has that of the proximity switches, which signal the positions of doors and landing gear.
Canadair claims that the 604 is, in fact, better than it estimated: the empty weight is 90kg under estimate, take-off and landing distances are about 50m (165ft) less, and fuel consumption is 1.5% below that of the original target.
The increased core flow, of the General Electric CF34-3B engine, results in a 7% power uplift. It is used to raise the flat-rating temperature, rather than increasing maximum thrust, which is unaltered for automatic performance reserve (APR) operation on engine failure.
Climb and cruise specific-fuel-consumption criteria, are 3% better than those of the earlier CL-601-3R, with improved hot-and-high field performance.
As on any other performance of the wing is generally outstanding. This quality handling was reviewed in an evaluation flight at Bombardier's recently centralised test site at Wichita, for Canadair, de Havilland Canada and Lear aircraft.
Senior Canadair test pilot Doug Adkins walked me round the second test aircraft, C-FTBZ. With a body clearance of less than 1m, Challengers have always seemed to hug the ground. Among generally subtle visual changes, the most obvious are that the undercarriage is noticeably more chunky, and that a third angle-of-attack sensor (a turning-cone type on the right side) is dedicated to the Collins avionics - the two Canadair units are vanes.
The central refueling-panel ensures that, no matter how rapid the uplift, the flow to the many subsidiary tanks is apportioned to remain in balance.
In the rear bay, the new "saddle" fuel tanks are closely tailored to the fuselage shape, while still leaving ample space for access to equipment. The triple hydraulic lines in this space are now spaced vertically instead of laterally and the previous hydraulic heat exchanger has been deemed unnecessary.
Although glass outer-windscreens and wipers are fitted on the RJ, the Challenger still has no wipers. Its acrylic screens are deemed to be self-clearing in rain.
This aircraft sported a nose-pilot boom, carrying flight-test vanes for measuring angle of attack and sideslip. The cabin was stacked with orange-painted test equipment and water-ballast tanks to the rear. An extra airspeed indicator (ASI), speed-rate meter and gauges showing control loads in all three axes and at the brake pedals, made up a suite of test equipment.
Challengers are delivered green, so interior decor is the customer's choice.
SMOOTH CONTOURS
The cockpit's centre console remains unique. Its rear half slopes down strongly, to ease feet-first entry to the seats. Access is hindered slightly by the low sweep of the roof and the cockpit bulkhead, which limits aft-seat travel.
The windscreen-to-fuselage contour is a continuous sweep, free of angular joins. The instrument panel is now more highly raked, as in the RJ, so that the electronic flight-instrument system (EFIS) panels face directly to the pilot's eyes.
Avionics include two digital air-data computers, three inertial-reference systems (IRS), and dual radio-tuning units, as on the RJ. There are dual options to the single weather radar and radio altimeter.
The pedestal-mounted and overhead individual systems-panels have been reshuffled, but test switches are still dotted about. The initial warning-systems design was structured, as on those of the McDonnell Douglas DC-10 and Lockheed L-1011, with warning and test functions distributed around the systems panels. The full audio-test cycle takes a long time to complete, and intrudes on the cockpit checks.
The six 180mm-square EFIS/EICAS displays, which allow even more space for data than the RJ's 150 x 175mm units, abut edge-to-edge across the cockpit. The wider pilot's main panels overlap the edges of the centre console by about 30mm.
Standby instruments are relocated along the top, instead of between the two EICAS screens. They are 50mm lower above a shallower forward up-slope of the console ahead of the power levers, which house two control and display units (CDUs) for the flight-management system (FMS). A third is optional as a "hot spare".
The audio-control panels are placed vertically where there is room - outboard of the instrument panels, at arm's stretch.
On the left-hand EICAS, primary engine-data displays are shown on "dials", and secondary engine data are shown as numerals. Gear and flaps indicators are simple bars, above a clear trio of trim-setting indicators. A free area at the top right is for warnings and cautions.
Status and advisory messages are shown on the right-hand EICAS, which is also used to display four pages of systems synoptics.
The navigation displays (NDs) on the multi-function displays can show individual positions as crosses: in weather-radar mode, lightning locations are indicated by "strike" symbols, not dots, and the solid-state radar incorporates turbulence detection.
There is room to show three route legs above an ND (or eight on a full flight-plan progress page), which is better for head-up flight- plan visualisation than are the FMS CDU pages.
The flight director and autopilot, are controlled by four, flight control computers. One pair is in active command, while the other pair act as monitors. The autopilot is cleared for engagement down to 80ft, but only for Category II operations for now.
Two IRS replace attitude/heading reference systems (AHRS) and there is an option for a third - as for FMS and digital air-data computers. The AHRS could run for just 11min on battery power, whereas the IRS runs for 50min.
The Collins FMS-6000 has a large keyboard and user-friendly pages, but all FMS equipment needs careful relearning. The pilot has flight-plan options, including "what-if" viewing and the setting of a particular fuel burn rate.
STARTING ENGINES
Each automatic engine start took 40-45s, after fuel was selected on at 20% N2; ITT peaked at 660-680°C, well within the 900°C limit. The start cycle was completed at 55%N2 (high-pressure spool speed), and speed then increased to idle at 66% - with 27%N1 (fan speed), inter-stage turbine temperature (ITT) 530°C and fuel-flow in each engine at 190kg/h.
During the taxi, I tested the new digital anti-skid system, which has a higher cycling-frequency and so is more effective. It must, however, be tested at low speed - under 5kt (9km/h) compared with the 20kt used with the previous analogue equipment.
The electric-hydraulic pumps begin running automatically as soon as the flap lever is moved. In flight, the centre system remains powered exclusively by electric pumps. The take-off configuration warning is extensive and includes a warning for autopilot engagement.
Our take-off weight was light - 18,330kg with a fuel load of 4,290kg. (The maximum take-off weight is 21,590kg, with a certificated option of 21,865kg.) . The centre of gravity (CG) was well forward, at 22.8%: since the addition of the new tail fuel-tank, the fore and aft CG limits against zero fuel weight have been modified.
As we positioned for take-off, a bug was set for 92.4% N1, derived from the FMS. Before full power was applied, N1 was checked above 79% - the point at which hydro-mechanical control of N2 is replaced by ECU control of N1. Take-off reference speeds, with 20¡ flap, were, decision speed (V1) 122kt; rotate speed (Vr) 128kt; and flight safety speed (V2) 137kt. (V2 at maximum weight is 146kt and the one-engine-out climb-rate after a maximum weight sea-level take-off is 1,100ft/min (5.58m/s) at 190kt, flap retracted.)
On brake-release, the 604 accelerated rapidly by the time "gear-up" was selected 5s after lift-off, our rate of climb had reached 1,200ft/min. There was a noticeable drop in noise as pressurisation commenced. Airspeed was maintained at 160-170kt, with 20° flap, for a formation photo-shoot with a Cessna 412, during which the picture on the traffic-alert-and-collision avoidance system (TCAS) was extremely useful for the rendezvous.
The auxiliary power unit (APU) is still only certificated for operation in flight up to 20,000ft - 1,000ft below the engine-relight ceiling. Bleed air cannot be drawn at the same time as electrical power, nor can it be drawn at altitudes above 14,500ft.
The aircraft ceiling remains 41,000ft. Raising this to 45,000ft has been considered by Canadair, but bulkhead modifications would be needed under current certification. At most cruise weights, anyway, a higher ceiling would not be achievable. In the near future, reduced vertical separation of 1,000ft on trans-oceanic crossings will probably obviate the need for many operations at very high altitudes.
At 16,500ft in a 250kt climb, a simulated engine cut was made by Adkins; with the slow run-down of the fan and core engine at this airspeed, direction and flight path could be adjusted slowly. The minimum control speed in the air (Vmca) is 116kt (commendably low for such a short aircraft), too slow to demonstrate. That on the ground (Vmcg) is 108kt.
I next tried a simulated go-around: when the flaps were set to 30°, there was a slight airflow rumble, then the gear was selected down and a rapid go-around was made to a 1,700ft/min climb. Engine acceleration from flight idle to full power took under 3s; slam accelerations, retardations and rapid reversals of power lever were accommodated easily.
As ECU control of N1 takes over from the N2 hydro-mechanical control, the power lever must be pulled back slightly if the ECU fails to avoid a high ITT.
The feel in manoeuvres is of a highly coordinated aircraft. The CL-604 took up bank smoothly as turns were made on rudder alone - whether the yaw damper was in or out. A roll reversal from 30° bank left to 30° right, took less than 3s, even without the spoilerons, which are fitted to the RJ. Lateral feel in level flight is not at all nervous.
STALLING MANOEUVRES
Stalls were made at 17,000kg, with the CG well forward at 21.6%. Stalling speeds are fairly high, as there are no leading-edge devices.
I let speed rise clearly before attempting recovery, as there are no whiskers on the PFD attitude display to indicate stall-warning pitch angle.
The Challenger has a stick-shaker and a stick-pusher, as might be expected in a T-tailed design. The attitudes and speeds at which the pusher and shaker come into operation with varying degrees of flap are as follows:
Shaker Alpha Pusher Alpha height loss
0° 49kt 11.3° 138kt 14.0° 900ft
20° 133kt 10.3° 124kt 13° 900ft
land 121kt 7.5° 112kt 11.1° 1,200ft
Stick-pusher operation can be inhibited by, pressing and holding the autopilot cancel button. I wondered if push operation with the autopilot engaged might cause some confusion.
A stick-shaker attitude marker is not included, although there is an aural warning and a caption on the pilot's flight display (PFD) for windshear. This is a pity, as such angle-of-attack information is useful also for stall recovery and an angle-of-attack gauge is not fitted (although two large gauges are fitted for testing the stick-pusher on the ground!)
Pitch attitude changes by about 3° nose down as each of the three stages of flap extension is applied, leaving the aircraft in a level attitude on the approach path. There is no pitch correction for flap, as on the RJ, but the need to trim is less noticeable than on earlier Challengers.
The pitch-trim schedule has been slightly adjusted, but it does not change for speed or altitude. Still, trim rate at lower speeds is well graded and it is not at all touchy at high altitude and speed.
The speed-brake was extended in a run to 350kt IAS at 15,000ft: the effect was progressive, giving a sturdy but not disturbing buffet, with a not-sharp effect, but very obvious deceleration.
There is a warning to guard against application of power against extended speed brake, but there is no such warning for mere air-brake extension. It is allowable in all configurations in flight, but the manual recommends that the speed brake is retracted before, altitude drops below 300ft during landing.
As on the RJ, there is no auto-throttle, and speed targets are set manually; vertical-performance mode was not yet available from the FMS. The "level-change" autopilot mode is used for controlling climb and descent. Airspeed changes steadily, making best use of energy trade to reach any new airspeed - with speed changing at under 0.3kt/s, climb rates ranged from 2,500-3,500 ft/min.
We continued the climb at 250kt until Mach 0.78 was reached, thus staying well within the complex Vmo/Mmo profile followed by the upper limit on the PFD speed scale (300kt to 8,000ft; 350kt to 22,000ft; M0.78 to 26,500ft; 320kt to 31,000ft and, finally, M0.85). This profile is determined by gust alleviation and wing-strength requirements resulting from the addition of winglets and weight growth.
As is typical of fan engines, N1 increased by 2% during the climb, while the N2 reduced by a similar amount. ITTs remain steady at around 840°C in ISA + 15°C conditions, as thrust was kept to maximum climb value. Maximum continuous thrust is delivered at an ITT of 900°C.
The fuel flows of 860kg/h each at 20,000ft, reduced to 715kg/h by 27,500ft, when climb rate was still 1,600ft/min. During this portion of the climb, the nose-up attitude slowly decreased from 7° to 4°.
In level high-speed cruise at 31,000ft, fuel flow was 730kg/h per engine, for a true airspeed (TAS) of 501kt: at 35,000ft it had reduced to 625kg/h and TAS was 490kt. Cruise attitude is 1.5° nose up. At 15,600kg, we easily reached 37,000ft on a hot day, and an operator might expect to use this as initial cruising level in cooler conditions from a maximum-weight take-off.
The wing can take high loads without evident distress in the airflow about it. Load was increased to 1.6g at 45° bank, with no hint of disturbed airflow at M0.81. Indicated airspeed was then reduced from 280kt to 260kt, the minimum speed for acceleration with the power available at this weight and altitude.
A pull-up at M0.65 through 5° in pitch in just 1s did create a low-speed buffet shock. About the only thing against which, the flight manual counsels is very high sideslip at high altitude and low speed.
Roll-reversal time increased only by 1s, when descending at 1,000ft/min under power, as speed reached M0.87 and a steep drag rise is not met till M0.88. There was little effect on handling or reaction to high speed by the wing, which has been taken to M0.94 in flight trials, and 440kt in flutter tests. The shock wave at M0.93 does slightly blank the ailerons.
Back at Wichita, the temperature had climbed to 32°C; Vref at 15,150kg was 124kt. At an approach airspeed of 130kt,with 62% N1, the flat attitude was obvious. It gives a great view down over the nose, but I over-flared and allowed the aircraft to float. I had to push the wheels on, and the automatic spoilers came into effect for a full-stop landing.
The take-off speeds at this weight were V1 108kt, Vr 121kt and V2 125kt - with 91.4% target N1. Adkins cut the left-engine spot on V1, so 2-3s of acceleration along the runway were completed before rotation, covering the speeds between Vmcg (108kt) and the required margin over Vmca. The flight-display attitude target came down from 15° to 10° up, as we settled in a 1,000ft/min climb at 140kt, with flap 20°.
A simulated single-engine approach was made at Vref + 14 (138kt) - for a flap 20° landing. I turned on to final approach still at 170kt, and was glad to be free to kill excess speed with the spoiler.
REVERSE THRUST
Reverse thrust was "felt" in triggers on the "piggyback". Selector levers are unlocked by a light finger tip spring, but the reversers start to deploy, only when the selectors are raised to a stop. Such positive selection usefully discourages frequent lever movements, often made when taxiing propeller-driven aircraft.
It was difficult to feel the point at which the brakes would bite, but then retardation was progressive and easy to keep balanced on each side. When taxiing, the brakes feel powerful, but progressive.
At our lightweight idle reverse was left on one engine for taxiing; then one engine was shut down with no loss of manoeuvrability for parking. Minimum taxiway width for turnabout, is a mere 12.2m using maximum 55°, nose wheel steering angle.
A common pilot type rating with other models might not be easy to introduce on the CL-604, but there is little call for this in corporate operations. Commonality is intended for the RJX; yet, even though having the same avionics fitted, it will have a new wing and leading edge device, a new engine, and provision for head-up display.
Over 15 years and six variants, the Challenger series evolution has been gradual. A good formula does not need major changes. Range has been the constant driver, with progressive boosting of power, increases in fuel, and refinements (see box).
The CL-604 achieves 10-15% more range, than that of the 4 CL-601-3R, which itself, can be operated on intercontinental sectors. Flight testing, has shown a range of 7,450km in ISA + 10°C conditions, carrying five passengers. The Challenger 604 can be seen also as a one-stop 14,800km-range aircraft.
With a shutdown ratio for the CF-34 of 1:114,000h, the engine-reliability requirement for 180min ETOPS is met by more than a factor of two.
Some necessary systems redundancy is implicit in three hydraulic systems and an air-driven emergency generator (limited to 250kt), but the certificated capability of the APU would doubtless have to be expanded considerably.
The CL-604 will be entering service as FANS-1 procedures begin to come into effect. Satellite navigation and communications are already common in the long-range corporate aircraft, and Collins "Avsat" equipment can be integrated into the CL-604'd FMS.
From the pilot's point of view, the Challengers have excellent cockpit space, easy handling, and the CL-604 avionics support a satisfying operation. The considerable improvements do perhaps unfairly highlight some few shortcomings of the original design.
The CL-604 is due for certification, in October and the first four customers will have delivery, before the end of the year.
High power-to-weight ratio, economy in cruise, shorter climb, and better field performance for the same range are bonus enough.
The Challenger is always likely to impress among the larger corporate jets because of its wide cabin. In particular, it impresses not only as a long-range means of transport, but as a quiet and spacious mobile workplace.
Source: Flight International
