Don't Dismiss the Supersonic Bizjet: U.S. Has Awarded First R&D Funding

The idea of a supersonic business jet (SBJ) is far from dead: indeed, new U.S. military requirements stemming from the Pentagon's current defense review could boost its development of a supersonic business jet (SBJ). Currently, small teams at the three major US airframe developers-Boeing, Northrop Grumman and Lockheed Martin-are working on the conceptual design of a highly efficient supersonic cruise vehicle which would produce such a small sonic boom that it could operate over land without restrictions.

Lockheed Martin has patented these concepts.

The importance of the current U.S. defense review is that it will likely call for improvements in long-range precision-strike forces. Supersonic-cruise aircraft could be invaluable for intercontinental missions, avoiding the marathon 30-hour sorties which the B-2 flew in the Kosovo campaign. Supersonic aircraft could deliver their first attacks more quickly and fly more missions in the same time span.

The main focus of the supersonic effort is the Quiet Supersonic Platform (QSP) project, launched late last year by the Defense Advanced Research Projects Agency (DARPA). Boeing, Lockheed Martin and Northrop Grumman have been awarded one-year Phase 1 contracts of around $2.5 million to study the QSP design. Under Phase 2, DARPA will pick the most promising technologies for another year of more intensive "technology maturation," with approximately twice as much money available.

Phase 3 plans have not been finalized and funding has not been identified, but the intention is a flight demonstration program, leading to a production-ready design: a demonstrator could fly as early as 2006.

Some designers involved in QSP indicate the results could be as visually shocking as the F-117 and B-2 stealth aircraft. DARPA's goals for efficiency and boom reduction are lofty, and may involve throwing away the rule book: it wants a 100,000 lb craft to carry 20,000 lb for 6,000 nm at Mach 2.4, yet meets Stage 3 noise rules. This is the same size as a large bizjet or-not without some coincidence- a medium bomber, which is why Northrop Grumman is involved (teamed up with Raytheon's bizjet unit). The key to making QSP a working reality, explains Barnaby Wainfan, Northrop Grumman aerodynamicist, "is to explore the possible and the only slightly impossible." As in the case of stealth, he suggests, designers recognize that "we could do it if it looked like this, but it would never fly. So how do we make it fly?" The Northrop Grumman team is looking both at radical approaches-such as braced, slender arrow wings, unswept laminar-flow wings or plasmas-and at refined versions of familiar supersonic designs. As Wainfan points out, even "traditional" supersonic aircraft have respectable aerodynamic efficiency when Mach numbers are taken into account.

NASA, meanwhile, is supporting work on inlets and propulsion, and aims to test a light, efficient supersonic mixed-compression inlet on its SR-71 research aircraft. The agency has also worked with the tiny Reno Aeronautical, whose founder and CEO Richard Tracy holds numerous patents on un- conventional laminar-flow supersonic aircraft. In addition, the U.S. National Academy of Sciences has convened a group of highly experienced experts to look at "breakthrough technology" for supersonic aircraft.

Engine firms are working on much more efficient supersonic jets. One approach is a high-bypass supersonic engine, probably with highly swept fan blades. The supersonic aircraft could also be a candidate for a hybrid engine combining features of a conventional jet with pulse-detonation technology. Perhaps significantly, Pratt & Whitney bought Adroit Systems' Seattle-based propulsion unit-a leader in pulse-detonation technology-in January.

By Bill Sweetman