Boeing 787 Dreamliner - Mark Wagner [72]
In October 2003 Boeing revealed outline details of the outsize conversion, together with news that the bluff-sided transport had already undergone two major wind tunnel test campaigns. Configured with a hugely extended upper lobe, the original concept was aimed at being able to load 7E7 assemblies without the need for a hinging fuselage. Although the yawning gap of the 136-inch-by-98-inch nose door of the 747 freighter was large enough to swallow big loads, it was nowhere near large enough to take the completed fuselage sections, wings, and other large 7E7 subassemblies. Instead, the cavernous interior was to be accessed via two extremely large cargo doors installed on the left aft fuselage, about midway between the wing and the horizontal stabilizer.
Rising aft from around the Section 41 (nose section) production break line, the extended upper fuselage line ran back at such a height above the standard body that it would have easily accommodated a third deck had it been a passenger aircraft. As it was, the modification increased the interior height by up to ten feet as far back as the middle of Section 46 (aft fuselage), where it tapered into the Section 48 tail area. The extra bulge also increased the girth sufficiently to make the LCF about twenty inches wider than the Airbus A380.
The volume above the main cargo deck was to be increased to about sixty-five thousand cubic feet, or approximately three times that of the 747-400F. The tail also was changed, with a 4.9-foot extension, giving it a distinctively “747SP” appearance, the fin of this shortened variant having been enlarged to compensate for the reduced moment arm. Like the SP, the fin also was to be extended downward.
Concerned about the effect of the bulging fuselage on directional stability, Boeing also studied extending the horizontal stabilizer as well as even putting large end plates on its tips, similar to the Space Shuttle carrier. However, wind tunnel tests showed that none of these changes was needed when lateral stability was augmented with a large dorsal fin and a connecting “strong back” reinforcement beam that extended forward from the leading edge of the fin.
The upper fuselage extension created a wider constant cross section that was big enough to take the “full 7E7 cross section,” said Boeing at the time. Design range was expected to match “747-400 capabilities, but the additional structural weight will reduce payload to between roughly 220,000 and 249,700 pounds,” it added. All the while, the basic aim was to keep the modification simple with a minimum of change, although the company acknowledged that the conversion was inevitably going to involve a “large statement of work,” no matter how final configuration was defined.
SWINGING THE TAIL
By the end of 2003 it had, however, become clear that some changes were needed. The side-loading door, for example, simply would not provide adequate clearance for the loading vehicles, so the decision was made to develop a swing-tail cargo door instead. Various options were considered before Boeing engineers eventually settled on a simple double-hinge design similar to that developed for the Canadair CL-44D4, a Canadian-developed freighter variant of the Bristol Britannia turboprop.
The Canadian design team hit upon the unique swing-tail concept in the late 1950s as a way of meeting a tight sixty-minute turnaround time specified by potential freight customers such as Seaboard World Airlines and Flying Tigers. It also developed the “high loader” scissor-lift loading tool to operate with the CL-44, and which subsequently went on to widespread use at airfields around the world. Boeing would ultimately use distant cousins of both design concepts on the 747, which by early 2004 was known as the large cargo freighter, or LCF.
The dramatic extent of the rebuild required for the Dreamlifter is clearly seen in this December 2005 view of the first conversion underway at Evergreen Aviation Technologies Corporation’s modification facility in Taipei’s Chiang Kai-Shek