ENGINE
With a small speed and temperature increase, within the existing certificated limits, the thrust capability of the CF34-3B is up by 7%; this is used in flat rating power to ISA+15¡C.
The take-off distance of the CL-604 in standard conditions has been improved, in a reduction in take-off distance for the same range by nearly 200m for a 5,550-6,500km (3,000-3,500nm) sector; in ISA +15¡C conditions it gives a greater improvement for all ranges. The advantages extend to multi-hop sectors and reduced uplift of fuel on turn-round at high-cost destinations.
Airline maintenance practice is more commonly applied and engine-life cycle costs are claimed to be the same as for the CF34-3A1.
The new "blisk" for the compressor first stage has integral blades. This lighter disc is mainly responsible for increased core airflow. Blade-tip clearances have been reduced and the variable geometry inlet guide vanes redesigned.
Low-pressure stage shrouds, high-pressure turbine stators, inter-stage and turbine internal seals have been given particular attention. The exhaust nozzle and shroud are of new material.
Hot-section inspections have been kept to 3,000h, with intermediate boro-scope inspections. The routine inspection interval is now 400h rather than 300h. Overhauls are scheduled at 6,000h.
The aircraft and engine meet Federal Aviation Regulations Part 36 Stage 3 noise limitations, with a margin of about 8dB within the take-off, sideline and approach limits (with the air-conditioning packs off, but with the APU running on approach).
GEAR AND BRAKES
Ring-retained flanges shorten tyre change times. Larger wheels (slightly more undercarriage bay space has been allowed) with lower-pressure tyres - 12.1bar (175lb/in2) instead of 14.5bar - were specified to reduce the cuts and foreign-object damage associated with high-inflation pressures; the tyre strength is double the maximum possible load.
Electrical harnesses are now steel braided for increased protection. Brake discs are grooved, with 60% more carbon mass in new lighter carbon material giving 100% better heat capacity. It means shorter turnarounds after landings at heavier weights; it also reduces the risk of the fuse-plugs deflating the tyres after a take-off abort from high speed.
FUEL
The fuel system is simple, but fuel distribution is complicated. Two wing tanks and a central tank make up the bulk of the fuel; but over the evolution of the Challenger other tanks have been added - auxiliary tanks for and aft of the centre tank and a tail tank.
Now installing a further forward tank, the large saddle tanks and a small extension to the tail tank has added a final extra 1,243litres.
Fuel use in flight is programmed to maintain its centre of gravity (CG) within limits, as the tail fuel-feed forward is restricted through a valve, but this cannot control CG by fuel transfer in both directions.
A more aft CG can be maintained early in the cruise, with lower trim drag (an average CG at 30%, compared with 25% of mean aerodynamic chord).
The tail tank is fitted with a dumping shute, as on the RJ; dumping is only allowed at the zero flap setting. An automatic jettison system operates independently, to jettison tail fuel if the CG moves out of tolerance.
Source: Flight International
