APPEARANCES CAN be deceiving, and the GV's outward similarity to the GIV belies the changes wrought to achieve an almost-60% increase in range.
The wing is all-new, sized to house the fuel required for a 12,000km (6,500nm) range, but shaped by the desire to maintain the GIV's low-speed handling qualities while enabling the GV to cruise at M0.85.
The GV's aerodynamic design is the result of about ten man-years of computation fluid-dynamics (CFD) work, using Gulfstream's own Convex supercomputer, says Dr Bob Mills, staff scientist, aerodynamics. CFD predictions were validated by some 1,450h of wind tunnel tests, he says.
Major factors driving the wing design were the range requirement and the decision to move the engine nacelles back, Mills says. Range dictated the wing area, aspect ratio, taper and thickness. Moving the engines back created a problem. On the GIV, the nacelle helps keep the shock wave in position over the inboard wing. Moving the GV nacelle back moved the shock back and required re-contouring of the root with a larger leading-edge radius to reposition the shock.
The outboard wing was designed to control the position and strength of the shock across the GV's cruise regime, from 41,000ft (12,500m) to 51,000ft. "Towards the end of a [M0.8] flight...the wing is effectively shock-free," says Mills.
Gulfstream designed its own aerofoil section, for the GV. "It's not supercritical and it's not peaky," says Mills, referring to the two best-known transonic-aerofoil designs. "Inverse" aerofoil-design techniques were used, in which the desired pressure-distribution was specified and used to derive the best section.
A supercritical aerofoil was rejected, he says, because the associated aft loading produces pitching moments, which increase trim drag, and non-linear control-surface hinge-moments, which affect handling. In addition, Gulfstream tradition calls for all flap hardware to be enclosed within the aerofoil, for a clean design, and there was not enough room in the highly cambered trailing edge of a supercritical aerofoil, Miller says.
The aerofoil developed has a modified "peaky" section, which reduces shock strength while minimising the aft loading and is thick enough at the trailing edge to house the flap mechanism. The new winglet has a super critical section and was redesigned with an increased blend radius and longer span, after the GIV winglet, was found to be unsuitable.
CFD was used to design the high-lift devices, which are simple Fowler flaps, as used on the GIV, but substantially larger. The engine nacelle and pylon were designed using CFD. Initially, there was a strong shock between the nacelle and the fuselage.
Now the airflow is "barely sonic", Mills says. CFD was also used to design the fintop and wing/fuselage fairings and to reshape the forward fuselage to reduce interior noise.
Computers were used extensively in the design of the GV, with the IBM/Dassault CATIA three-dimensional computer-aided design system being used to create an electronic mock-up of the aircraft. The mock-up has allowed more than 1,800 interferences between components to be detected before assembly.
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Source: Flight International
