Northrop Grumman and Raytheon have unveiled "preferred" strike and business aircraft concepts based on the "dual relevant", braced-wing design revealed in January as part of the US Defense Advanced Research Projects Agency's (DARPA) Quiet Super-sonic Platform (QSP) project.

The concepts emerge as Northrop Grumman prepares to flight test an F-5E Sonic Boom Demonstrator (SBD) for DARPA's QSP Phase 2. The F-5E is at Northrop Grumman's St Augustine, Florida, site awaiting modification with a "low boom" composite nose section.

"We hope to do the first flight clearances in December, maybe spilling into January," says Northrop Grumman future strike systems programme manager Charles Boccadoro. Initial subsonic tests will be in Florida before theF-5E moves to Edwards AFB, California, early next year for supersonic testing.

During testing, an unmodified F-5 will create a normal sonic boom at Mach 1.5 and 30,000ft (9,000m). The modified F-5 will follow moments later, allowing the differences in boom signature to be recorded. The new nose is designed to modify pressure distribution around the aircraft, preventing the shock waves from coalescing into a classic "N-wave", instead producing a "flat-top" low intensity boom.

High-speed windtunnel tests of the revised F-5, with a reshaped lower fuselage, are due to begin this week at the Arnold Engineering Development Center, Tennessee, as part of preparations for a flight readiness review due in late November. Previous windtunnel tests validated the near-field (two body lengths) pressure wave shaping and in-flight measurements of sonic boom characteristics made earlier this year by a NASA Boeing F-15 flying supersonically in formation with a unmodified F-5.

F-5E flight test and windtunnel tests of the preferred concepts will be fed into a planned QSP Phase 3, which is expected to begin next year. "We're hoping this could include definition of a full demonstration programme leading to an X-plane," says Boccadoro.

The X-plane would focus on long range, low-observable characteristics for a supersonic strike aircraft, and possibly low boom for a supersonic business aircraft.

Source: Flight International