7X mods mean more range for operators

 - September 20, 2006, 9:50 AM

Dassault is about to flight-test production-conforming modifications that should boost the range of its new Falcon 7X. Officials at the French manufacturer last month revealed that the average customer is choosing options and cabin equipment that are raising aircraft weight beyond earlier expectations. On many aircraft the weight gain is cutting range to just short of the promised 5,700 nm. Dassault therefore decided to increase the basic range to regain margin. The new target, announced at the NBAA Convention last November, is 6,000 nm. Certification was pegged for late this year but is now anticipated “early in 2007.”

“We have sold an unprecedented number of aircraft at this stage of a program–80 aircraft,” a Dassault spokesman explained. “Our customers have started choosing options, equipment and cabin layout, and we are seeing that their average choice is heavier than we anticipated. The aircraft’s range is therefore slightly less than the promised figure of 5,700 nautical miles at Mach 0.80. Some charter operators do want to offer the advertised range–Paris to Los Angeles, for example–to their customers, in spite of the heavier cabin.” Boosting the basic range to a target 6,000 nm gives heavier aircraft some margin to reach the initially advertised range.

Dassault engineers are tackling the task on three fronts:

• Winglets. The company has added 4.6-foot-tall winglets to reduce fuel consumption by “a small percentage” thanks to less drag during cruise flight. The winglets add 75 pounds to the aircraft’s empty weight. The aircraft first flew with the winglets in October and Dassault decided two months later to adopt them as standard.

• Secondary rudder. Located under the horizontal tailplane, the lower part of the rudder has been made unmovable. “With Dutch roll in mind, we had deliberately taken some margin on the rudder’s size. Flight tests showed that we could downsize the rudder,” the spokesman told AIN. Immobilizing the rudder has allowed designers to stretch it, which suppresses turbulence in this area. In addition, eliminating a servo control reduces weight and complexity. Prototypes of this modified surface flew last fall, and all three test aircraft are now being fitted with the finalized shape.

• Fuel. Dassault designers added an 1,800-pound-capacity fuel tank in the forward fuselage. The first conforming aircraft with production winglets, vertical tail and fuel tanks should fly this month.

More Modifications
Another major modification, although not related to the range, is in the bleed-air system. According to Dassault, a new and unanticipated FAA rule limits to 200 degrees C the temperature of bleed-air inside the airframe.

In-service Falcons’ bleed air is hotter, at 330 degrees C. According to Dassault, the FAA does not want any hot system to coexist with the fuel plumbing.

Dassault engineers therefore had to redesign the bleed-air system, adding pre-coolers, valves and pipes. With a cooler temperature limit, engineers had to increase the airflow to retain the system’s efficiency. Bleed air is used mainly for airframe de-icing and cabin air conditioning. “The modified system is working,”
the spokesman told AIN.

These changes have extended the certification process and will affect next year’s deliveries, but Dassault expects to be back on track in 2008.

A second consequence is that the mtow has increased. Engine thrust has therefore been uprated from 6,100 to 6,400 pounds at ISA +18 degrees C (the PW307 was already certified for this level of thrust). The approach speed will remain unchanged, at 104 knots. Landing distances will be shorter than originally promised. Finally, full-fuel payload has increased by 50 percent, to 2,850 pounds. Dassault does not expect the changes to affect the price of the 7X.

Meanwhile, the airframe dedicated to fatigue and static testing has undergone 20,000 cycles–two aircraft lives. Loads applied in static tests have reached 70 percent of the airframe’s design limit. These tests are taking place in Toulouse, at the CEAT aeronautical test center.

As of February 10, the fleet of three test aircraft had logged a combined 450 hours on 150 flights, the spokesman told AIN. The entire flight envelope has been opened. The most recent tests included high speed (Mach 0.92, above the Mach 0.90 Mmo), low speed (85 knots), high altitude (51,000 feet, the aircraft’s intended ceiling) and stall. All three modes of the fly-by-wire (FBW) controls have been assessed: normal, alternate and direct laws.

According to the spokesman, during a presentation to customers in January, test pilots emphasized “the perfect stability, accuracy and intuitiveness” of the Falcon 7X. They also praised the FBW’s elimination of a trim system, lauded the efficiency of the brakes and said they were happy with the trijet’s Pratt & Whitney Canada PW307s. Fifteen pilots– 14 from the manufacturer and one from the European Aviation Safety Agency (EASA)–have flown the aircraft so far.

No crosswind testing has been conducted so far because of the lack of suitable weather conditions. The company will test the anti-icing system in icing conditions late this month or early next. The certification flight program will begin simultaneously.