Boeing last month quietly booked a single order for a 747-8 “Intercontinental” jet– its first for a passenger 747 in several years and thought to be a VIP variant for Qatar Airways. Boeing believes it can sell 450 examples of the newly stretched 747-8. That represents half the perceived 20-year market for airliners with 400-plus seats and around 5.5 percent of the dollar value for all commercial-aircraft sales in the period, according to sales, marketing and in-service support vice president Randy Tinseth.

Having studied many possible developments of the 40-year-old basic design, Tinseth cited engine advances and available technology from the 787 twin-jet as major enabling factors supporting this latest 747 variant. The company plans the 747-8 “Intercontinental” (or -8I) will seat 450 passengers in typical three-class configuration and offer an 8,000-nm range. Compared with today’s 747-400, Boeing aims to provide 21 percent greater cargo volume and 9-percent lower seat-mile costs.

Its 747-8 “Freighter” brother should fly 4,475 nm with a payload capacity of around 140 metric tons. Contrasted with the current model, this represents 16 percent more revenue cargo volume and slightly greater range, according to Boeing, which claims the -8F will offer “equivalent” trip costs and 15 percent lower metric-ton-mile costs.

Launch customer Cargolux is scheduled to receive the first 747-8, a freighter, in September 2009 with initial deliveries of passenger variants beginning about six months later. The European cargo operator has ordered ten 747-8Fs and has purchase rights for another 10, while Japan’s Nippon Cargo Airlines has ordered eight 747-8Fs and taken options on a further six.

Boeing expects to freeze the 747-8F design as a firm configuration late this year, and the 747-8I design in “early to mid-2007.” Among outstanding decisions is the location of stairs to the upper deck. Boeing is still evaluating which 747-8 features could be offered for 747-400 retrofit.

Firm propulsion configuration for the 66,500-pound-thrust General Electric GEnx engine was achieved in May. The GEnx, selected over the Rolls-Royce Trent 1000, has been optimized for the 747-8 in terms of both size and power, the former resulting in a smaller fan than that on the twin-engine Model 787.

“We found the 111-inch fan diameter impacted [wing] aerodynamics, especially in the outboard position,” Tinseth told Aviation International News. “The 104.7-inch fan diameter [permits] a new, smaller nacelle, reduces weight and provides the lowest operating costs and best economics.”

Discussing the selection of new technologies for this latest variant of a mature design, Tinseth said the key lies in adopting improvements that provide the most customer value for the least cost: “We have been able to apply new [engine, wing and other] technologies to a well-developed and proven structure and system architecture.” Changes from the 747-400 include the introduction of fly-by-wire control for spoilers and possibly outboard ailerons as well to reduce weight once Boeing has received more wind-tunnel test information.

Tinseth said that high Reynolds number testing at NASA Ames has confirmed computational fluid dynamics and the wing shape. Qinetiq is conducting low-speed tests to confirm takeoff and landing performance at its wind tunnel in the UK.

Boeing’s insistence that all changes must be justified economically might have been expected to produce a common airframe, so why have different fuselage lengths been adopted for the two variants? “Customer input is a main driver. They wanted a new higher capacity 747 that offers the lowest operating cost and best economics of any large passenger or freighter airplane,” explained Tinseth. “Differences in the range, payload and economic requirements for passenger and cargo airlines led to the differences in body length.”

Boeing’s intention has been that the 747-8I will be stretched 11.7 feet to accommodate 34 additional seats, while the -8F will be 18.3 feet longer than the 747-400 freighter. However, recent reports suggest that Boeing has been revisiting this aspect of the design and that the differential may not be maintained.

The manufacturer has made several wing changes that give the 747-8 additional fuel volume, increased efficiency and better low-speed handling. The thicker wing provides greater fuel capacity, while its new double-slotted inboard and single-slotted outboard flaps and drooped ailerons are designed to improve low-speed performance and reduce noise. Raked wingtips improve cruise performance and increase span by 13 feet to reduce drag.

Redesigned flap tracks and better rigging of the related “canoe” fairings, which will be mounted closer to the flap underside, improve low-speed drag and noise. Redesigned inboard Krueger slats, which introduce a gap in front of the leading edge, are designed to increase takeoff and landing lift; the equivalent 747-400 panel is sealed against the wing. Despite these wing changes, Tinseth said Boeing expects to be able to use the existing basic 747 tooling, infrastructure and production processes.

One factor in the increased capacity of the -8I is the relocation of the galley from the main deck to the crown-area, which releases space for 12 seats. The crown also could be used as bunk, lounge or business center space, said Tinseth.