Boeing 747-8 - Design

Design

The 747-8 is a development of the Boeing 747 that takes advantage of improvements in technology and aerodynamics. The two 747-8 variants feature a fuselage stretch of 18.3 ft (5.6 m) over the 747-400, bringing the total length to 250 ft 2 in (76.25 m). The 747-8 is the world's longest passenger airliner, surpassing the Airbus A340-600 by approximately 3 ft (0.91 m). With a maximum take-off weight of 975,000 lb (442,000 kg), the 747-8 is the heaviest aircraft, commercial or military, manufactured in the United States.

Compared to the 747-400, the main changes have been on the wings, which have undergone a complete design overhaul. The sweep and basic structure has been kept to contain costs, but the wing is thicker and deeper, with the aerodynamics recalculated. The pressure distribution and bending moments are different, with the new wing for the passenger version holding 64,225 US gal (243,120 L) of jet fuel, and the cargo aircraft 60,925 US gal (230,630 L). The increased wing span requires airports in Category F rather than E, similar to the Airbus A380. The new wing features single-slotted outboard flaps and double-slotted inboard flaps.

Raked wingtips, similar to the ones used on the 777-200LR, 777-300ER, and 787 aircraft, are used on the new 747 variant instead of winglets used on the 747-400. These wingtip structures help reduce the wingtip vortices at the lateral edges of the wings, decreasing wake turbulence and drag, and thereby increasing fuel efficiency. Another effort to reduce weight is the introduction of fly-by-wire technology for the majority of the lateral controls.

The extra fuel capacity in the redesigned wing compared to the 747-400 eliminates the need to significantly change the horizontal tail unit to accommodate auxiliary tanks, further saving costs. The 747-8's vertical tail unit is largely unchanged with a height of 63 feet 6 inches (19.35 m). The lower rudder has changed from single-jointed to double-jointed in order to increase its effect in the event of 2 engines failing on the same side. Some carbon fiber-reinforced plastic is part of the 747-8's airframe to reduce weight. However, structural changes are mostly evolutionary, rather than revolutionary with respect to the 747-400.

The General Electric GEnx is the only engine available for the 747-8. It is one of the two powerplant choices offered for the Boeing 787. The 747 engine variant has been adapted to provide bleed air for conventional airplane systems and feature a smaller diameter to fit on the 747 wing. The flight tests of the GEnx 2b engine fitted to a Boeing 747-100 aircraft at the left inner engine began in March 2009.