Engine Choice Will Drive Sonic Cruiser's Design

Boeing has already engaged with Rolls-Royce, General Electric, and Pratt & Whitney about the engine needs for its 0.95-0.98 Mach Sonic Cruiser with the results of the deliberations likely to impact the aircraft's shape.

Boeing has already ruled out use of an existing engine, but believes modifications of existing ones could be acceptable. But the airframe maker also is still considering opting for an entirely new design, says John Roundhill, Boeing's VP for new airplane program marketing. A new engine would take a lot longer and would likely extend the development program.

For a 9,000 nmi range aircraft, which the company is currently targeting in its baseline design, the Sonic Cruiser would require two 90,000-pounds-thrust engines. The range may vary though. Boeing is also considering 6,500 nmi range in an initial design which could grow later.

A new engine would take longer to develop, but could lead to a more streamlined design, Roundhill indicated. The Sonic Cruiser's wingspan would likely have to grow if an existing engine is modified, because it would be less efficient.

Boeing's early design work indicates the new aircraft's wingspan will be about 117 feet, approximately the same as the 767-400. The wings will also feature the swept tips found on the 767-400 and 777X.

Operating altitude for the Sonic Cruiser is estimated to be 41,000 feet with a maximum altitude of 50,000 to 51,000 feet. Landing speeds are being projected at 140-145 knots, with take-off possible on a 10,500-foot runway.

The Boeing design, which is expected to evolve continuously over the coming months, has already undergone changes. For instance, the wingspan and tail have grown, and the canard's upward sweep has been increased.

One of the issues the company is still grappling with is how it would grow the aircraft. Because the design is highly integrated, adding extra structure for a larger aircraft would probably require changes to the canards and strake. "We will have to change some of the geometry," Roundhill said.

There is a chance that a gust could take a Sonic Cruiser flying at Mach 0.97 slightly above the speed of sound. However, because the speed would be only slightly higher than Mach 1, a sonic boom would dissipate before being heard on the ground, Roundhill said.

Touting some of the advantages of the Sonic Cruiser, Roundhill said the higher speed might allow airlines to reduce the number of crew required on a long-endurance mission. Furthermore, the high operating altitude would allow more direct routes because of less congested air space.

By Robert Wall