‘Greener’ Falcons coming from Dassault

 - May 30, 2008, 6:02 AM

Dassault Falcon salespeople are starting to hear customers voicing concerns about their airplane’s effect on the environment. “Owners want to be able to say their business jet is quite environmentally friendly,” said Bruno Stoufflet, the company’s v-p for scientific strategy, research and development and advanced business, at a seminar in Paris recently. In response to such comments, Dassault is studying ways to make future Falcons greener.

To address noise, Dassault engineers are working on integrating higher-bypass-ratio engines. The Falcon 2000EX’s Pratt & Whitney Canada PW308C has a bypass ratio of 4:1, but the company expects to be able to improve that, as newly developed engines for airliners have bypass ratios approaching 10. An added benefit of a higher bypass ratio is lower specific fuel consumption.

The challenge of integrating a high-bypass-ratio engine is its large diameter and accompanying drag. Stoufflet claims that careful shaping of the nacelle can dramatically reduce airflow separation, thus cutting drag.

Another possibility is to design the empennage so that there is a screen–such as the horizontal empennage–between the engine’s exhaust and the ground. This would block a large amount of radiated noise.

The company also envisions more integration of the engines, to the point that the nacelles are almost blended into the aft fuselage. This too would reduce drag. Dassault claims its current Falcons score well on engine integration, providing a 15- to 35-percent fuel-burn advantage over the competition for a given range.
These novel aft-fuselage designs would present some certification hurdles because an un- contained engine failure in such a configuration would present new safety challenges. Dassault sees such a new empennage entering service between 2015 and 2020.

The wing, too, could be changed to make the airplane greener. Changes could include a new generation of control surfaces, enhanced flow and load control and a higher aspect ratio. In addition, camber could be made variable by methods more advanced than today’s flaps and slats.

Wing Changes Only Part of Eco Design
A lot of work is anticipated to optimize wing size. For example, new high-lift devices could help a smaller wing retain good short-field performance. According to Stoufflet, “Five hundred feet of better field performance equates to 20 percent more wing surface.”

However, Dassault rules out a blended wing body business jet, asserting that the weight savings would not justify such radical change, according to Stoufflet.

The company hopes further use of digital controls (fly-by-wire) will reduce trim drag because computer-aided flight controls can cope with more instability than a human pilot can. Dassault estimates entry into service of such a “smarter” flight control system between 2015 and 2020.

Another way to make the aircraft more efficient is to replace hydraulics with electric systems, which thus far have long lagged in terms of power-to-weight ratio. But this is changing, making their use possible. Using electric systems has the added benefit of eliminating polluting hydraulic fluids.

Of course, the company will also try to reduce weight by using lighter equipment, including seats. The company also plans to “optimize” its use of composites and fasteners.

Most manufacturers argue that air traffic management (ATM) should shoulder some of the burden for ensuring greener operations, and Dassault is working on compatibility with future ATM requirements. One focus is continuous descent approaches, which reduce fuel burn. Another area of interest is reduced aircraft separation.

Finally, Dassault engineers are ushering in the era of “eco-design,” the idea being to use renewable materials, lengthen structural life and improve end-of-life recycling.