Dassault touts ‘green’ Falcons

NBAA Convention News » 2008
October 1, 2008, 11:00 AM

As more business jet buyers worry about the damage their airplanes are potentially causing the environment, French business jet maker Dassault is seeking ways to make future Falcons greener.

“Owners want to be able to say their business jet is quite environmentally friendly,” said Bruno Stoufflet, the company’s vice president for scientific strategy, research and development and advanced business. To address such concerns, Dassault engineers say they have ushered in the era of “eco-design,” whereby renewable materials and improved end-of-life recycling are incorporated into designs for new airplanes. Moreover, they are working on further lengthening structural life and studying a range of performance enhancements designed to reduce noise, boost efficiency and save weight.

To address noise, for example, 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. Newly developed engines for commercial airliners have bypass ratios closer to 10:1. Besides making engines quieter, the higher bypass ratio also lowers specific fuel consumption.

The challenge for integrating a high-bypass-ratio engine is its comparatively large diameter and the accompanying drag it creates. Stoufflet claims nacelle shape optimization can help in this area. Airflow separation can be dramatically reduced, thus cutting drag, he said.

Another possibility is to design the empennage so that there is a special screen below the engine’s exhaust shielding the ground below. The horizontal empennage could be used in this role, Stoufflet said, in an attempt to reduce downward noise radiation.
Dassault is also exploring much closer engine integration, where the nacelles are almost blended into the aft fuselage. This enhancement is intended to cut drag and thereby increase fuel efficiency. The manufacturer claims the level of engine integration is already exceptional on Falcon business jets, thus providing a 15- to 35-percent fuel burn advantage over the competition for a given range.

The novel empennage configurations under study would be challenging to certify, however. An uncontained engine failure could have disastrous consequences, meaning getting the engineering right is crucial. Nevertheless, Dassault anticipates entry into service of a completely new empennage design between 2015 and 2020.

The wing, too, can certainly help the aircraft be greener. Stoufflet mentioned a new generation of control surfaces intended to improve efficiency. Also, flow and load control could be enhanced by active and passive means, and the wing’s aspect ratio could be further increased. In addition, one day camber could become variable.

A significant amount of engineering work will be needed to avoid designing a wing that is larger than those of earlier Falcons. For example, new high-lift devices (such as flaps) could help retain short-field performance while actually reducing the size of the wing. “Five hundred feet of better field performance normally equates to 20 percent more wing surface,” Stoufflet asserted, adding that improved wing design could obviate the need for such size increases.

Dassault, however, has all but ruled out using a blended wing. The weight advantage would not offset the engineering complications of such a design, according to Stoufflet.

Further use of digital (fly-by-wire) flight controls is expected to reduce drag as well because computer-aided flight controls can cope with more instability than the human pilot can. Dassault is planning for entry into service of such a “smarter” flight control system in the 2015 to 2020 time frame.

Another way to make aircraft more efficient is to replace hydraulic systems with electric types. Electric systems have been lacking in terms of power-to-weight ratio but this is changing so they now can be seriously considered.

Aircraft manufacturers insist that efforts aimed at improving the environment should not be solely their domain, and point at air traffic management (ATM) initiatives as vital to such endeavors. Dassault is working on compatibility with future ATM requirements. One focus is continuous descent approaches, which cut fuel burn. Another area of interest is reduced aircraft separation.

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