Dassault Unveils Falcon 5X

By Fred George fred_george@aviationweek.com
Source: Business & Commercial Aviation

The digital flight control system, designed and built by Dassault, is based upon the Falcon 7X architecture, but it will integrate more functions. In addition to carefree handling, flight path stability and envelope protection, the fly-by-wire (FBW) system will host control of mid-span flaperons that can function as ailerons, flaps and/or spoilers.

The cockpit will have left and right sidestick controls; three main or primary, dual-channel flight control computers that host normal, alternate and direct law functions; plus three backup, or secondary, single-channel flight control computers that only host direct law functions, including yaw damper. Unlike the Falcon 7X, the Falcon 5X won't be fitted with an analog emergency computer used for temporary control to be used only in the event that all six main and backup flight control computers fail. But the aircraft can be dispatched after any single electronics failure.

Most primary and secondary flight control surfaces will be hydraulically powered. But in a departure from the Falcon 7X, the trailing edge flaps will be electrically powered rather than hydraulically actuated. Use of flaperons is a first aboard a business jet. When the crew selects speed brakes 1, for instance, the outboard ailerons will deflect up while the mid-span flaperons will move down, thereby increasing drag while minimizing wing bending moment. The flight control surface geometry also virtually eliminates turbulence over the horizontal tail that's felt as airframe buffet. The new function especially will be appreciated by passengers when the aircraft is descending with bleed air anti-ice on. Engine power must be increased for adequate bleed air supply. During descents, the speed brakes on older Falcons had to be used to control speed with anti-ice on. That should no longer be necessary with the split aileron/flaperon function.

The 5X has conventional air brake panels, but they only begin to deploy when speed brakes 2 is selected.

The split aileron/flaperon geometry, along with the aircraft's full-span leading edge slats, will be key to enabling Dassault to earn steep approach certification for the 5X, enabling it to use London City Airport.

Bleed air will be used for wing leading edge and engine inlet anti-ice heating. Unlike previous Falcon Jets, pilots will be able to select wing anti-ice while on the ground. It automatically will activate with weight off wheels. UTC Hamilton Sundstrand in San Diego will furnish the ground-use-only APU.

Balancing Act

Falcon Jets are known for their class leading fuel efficiency and the Falcon 5X will be no exception. No other large-cabin aircraft, except for Dassault's own Falcon 2000S and 2000LXS, should squeeze more miles out of a pound of jet fuel on equal length trips.

One reason is the Falcon 5X's Mach 0.80 design cruise speed, which is relatively placid by current standards. Some large-cabin business aircraft makers now tout cruise speeds of 0.85 to 0.90 Mach, shaving as much as an hour off of longer trips.

The Falcon 5X easily can speed up to 0.85 Mach, but doing so increases fuel consumption by close to 9% and shortens max range by 450 mi. Dassault's market research, though, indicates that the most likely Falcon 5X buyers will value cabin comfort, range and price above the need for speed.

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