Boeing 787 Dreamliner - Mark Wagner [18]
Airlines were also by now being shown other new configurations that had emerged from a complex set of trade studies. “In late 1999 we set out with the idea that we could offer a sonic aircraft, and the best-looking configuration that could make that happen is the [aft wing] one we released to the world. However, the only bit of nervousness about it was the CFD codes. Were they really telling us the truth about the drag performance at Mach 1?” Gillette said.
Although transonic wind tunnel tests verified that the canard-configured design “sliced right through Mach 1,” Boeing’s design team continued to explore alternatives. “As always we had to know if we’d been making the best use of the technologies for the mission. We ended up doing dozens of trade studies on wings and engine positions as well as canard locations,” said Gillette. “Clearly this would have been the largest canard aircraft ever to fly [bigger even than the Tupolev Tu-144], and was intended for extremely efficient cruise.”
Canards, or foreplanes, were designed to work with elevators and elevons to allow operation over a wide range of center-of-gravity conditions that would otherwise be virtually impossible to handle on configurations such as the Sonic Cruiser, with large, heavy engines mounted aft. Retractable canards were used on the Tupolev Tu-144 supersonic transport to increase lift at low speeds, countering the pitch-down moment effects of the elevons mounted on the trailing edge of the delta wing. The canards are displayed to good effect on the Tu-144LL, reactivated for high-speed research at Russia’s Gromov Flight Research Institute, Zhukovsky, near Moscow in August 1999. Mark Wagner
One of the basic trade studies involved removing the canards altogether, moving the wing forward, and adding a horizontal tail. “As the wing moves forward and sits near the middle of the aircraft, it needs to be wasp-waisted a bit,” said Gillette, explaining the area-ruling requirements of the transonic design. The canard-configured Cruiser, on the other hand, allowed Boeing to stick with a large aft wing, which in turn enabled a constant-section fuselage. “But canards are an unusual configuration, and you have to find ways of getting it out of the way of jetbridges [articulating covered walkways connecting the gates with the aircraft] and so on.”
Alongside the new midwing design, the original Project Yellowstone not only remained alive but also began to prosper. Although considered a true project in its own right, the Sonic Cruiser team used Yellowstone primarily as a reference configuration against which the airlines could better judge the true benefits of the proposed Sonic Cruiser technology versus a conventional 767. Roundhill recalled that “on the presentation charts we always showed the ‘reference’ aircraft, and there was a lot of debate about whether we should take it off. Of course, we didn’t know about 9/11 then, and with Alan’s approval we decided to leave that data point on there.”
The performance targets for Yellowstone were “a little more aggressive than the 787, and we did that intentionally, but it was a ‘real’ airplane,” said Roundhill, who added, “we made it a fairly big ‘dot,’ but we didn’t want to overpromise. I’m certainly glad we kept that dot on the chart!”.
Slowly but surely, however, the tide was indeed turning. At presentations, the airlines listened patiently to the Sonic Cruiser briefing before asking to see more details about the reference model. Rumors of this unexpected swing in favor of Yellowstone began circulating in about May 2002 but were strongly downplayed by Boeing at the time, saying, “We talk to the airlines about the reference aircraft, but it’s not really what we’re