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Aviation History
1996
1996 - 2313.PDF
Advertisement COVER STORY What Falcon jets don't have.. Not all business jets are crea ted equal, for while all have the same basic aerodynamic features, such as wings, empennage, flaps and ailerons, some carry additional devices like winglets, stick pushers or ventral fins. These appendages amount to an admission that the original design was not as good as it was supposed to be. Engineers then have no choice but to adapt the airflow to the aircraft's design. Lets look at some of these fea tures - none of which can be found on Falcon jets. WINGLETS Winglets help an aircraft fly better at low airspeeds by redu cing drag-inducing vortices at high angles of attack, for example Winglet during take-off and landing. But winglets also create drag during cruise because, unlike landing gear, they cannot be retracted. Dassault designs its Falcon busi ness jets from die start to deliver superior performance throughout die operating envelope without artificial enhancements. The airfield performance of a Falcon is typically better than mat of any competing aircraft, so wing lets are actually unnecessary. VORTEX GENERATORS The air moving over the wing of an aircraft tends to separate pre maturely, reducing aileron autho rity, or it may wander spanwise along the wing instead of parallel to die line of flight. Manufacturers may therefore install a line of vortex generators, or vortilons, near the leading edge or in front of the control Vortex Generators surfaces to energise the airflow and help delay the onset of flow separation. Falcons don't require vorti lons because wing shape, thick ness and tip curvature are optim ised at every point from root to tip using three-dimensional com puter modelling techniques to ensure that the airflow over and under the wing follows precisely the correct route. STALL STRIPS, STICK SHAKERS AND STICK PUSHERS Some business jet designs offer inadequate stall safety margins in certain flight conditions. Engi neers may then add spanwise strips to the leading edge of the wing to ensure that the stall begins there first. This usually has the desired effect, but may affect performance drastically. Stall Strip Occasionally, aircraft whose wings are optimised for speed rather than good handling may not exhibit pre-stall buffet - the shaking motion caused by air tur bulence over the inboard part of the wing when it is about to stall. Such aircraft may require a stick shaker, which causes the control yokes to shake when the angle of attack increases towards the stall, replicating a natural buffet. Some T-tailed aircraft may be susceptible to deep stall, meaning that if flown beyong a certain angle of attack in an aft centre of gravity condition, not only will the wing stall, but the airflow over the elevators may be obstructed, preventing die nose from being lowered. A stick pusher may then be added, which forces the yoke forward to lower the nose while there is still enough elevator authority to recover from die stall. Stall Strip Falcons don't need eidier stick shakers or pushers because they are designed from the start to provide a natural pre-stall buffet warning with built-in immunity to deep stall. As a Falcon approaches the stall, the leading edge slats deploy automatically, improving boundary layer adhe sion to die outboard portion of the wing, enabling the ailerons to continue functioning and preven ting a high, uncommanded angle of attack being reached. VENTRAL HNS Protruding down and out from the tail like an inverted V, ventral fins improve stall protection and directional stability on some smaller business jets by scooping air under the tail, helping to push the nose down if the angle of attack becomes too high. They are simpler than stick shakers or pushers, but impose a significant drag penalty. Falcons don't have diem. YAW DAMPERS Yaw dampers are part of the auto matic control system that pre vents Dutch roll (an uncomfor- Ventral Fins table coupled yawing and rolling motion) on swept-wing aircraft. Yaw dampers are found on all business jets, including Falcons. On Falcons, however, they are not required for dispatch. The aircraft's design ensures mat lon gitudinal stability is adequate to prevent yawing in most condi tions, and in die event that slight yawing does occur, it is damped naturally. PURE FALCON AERODYNAMICS Clean aerodynamic design drives not only efficiency, but reflects the intelligent thinking that went into the design. At Dassault, engi neers design Falcons widi two clear priorities: integrity and safe ty. They can draw on a wealdi of aerodynamic experience accumu lated on business jets and super sonic fighters - something that no other business jet manufacturer can claim. This translates into continuous product improve ments so that, for example, while the Falcon 2000 boasts almost diree times the cabin volume of the Falcon 10, its fuel burn at Mach 0.80 is only around 8% higher. The design is refreshingly simple in every important aspect, which is why you don't need doo dads on a Falcon Jet! • • Dassault Aviation Jean-Claude Bouxin (33 1) 40 83 93 08 • Dassault Falcon Jet John Rosanvallon (201) 967 2746
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