‘Dual relevant’ concept could lead to an SSBJ

 - May 7, 2008, 11:15 AM

A supersonic business jet (SSBJ), which many in the industry see as inevitable but just not in the near future, may have taken another step forward when Raytheon Aircraft partner Northrop Grumman unveiled its latest design for a supersonic military strike aircraft.

Northrop Grumman and Raytheon are working on what is called a “dual relevant” concept, meaning a design that could be turned into a strike aircraft or a business jet. The effort is being backed by the Defense Advanced Research Projects Agency (DARPA) and is supposed to investigate possible synergies with the private sector.

Referred to as the quiet supersonic platform (QSP) program, Northrop Grumman’s project includes the planned test of an F-5E “sonic-boom demonstrator” at the NASA Dryden Flight Research Center at Edwards Air Force Base in California early next year. During the testing, the sonic boom from an unmodified F-5E will be measured against that of the demonstrator.

The demonstrator will have a shaped sonic boom, which engineers claim will be less noisy. That aircraft is to be modified at Northrop Grumman’s facility in St. Augustine, Fla., and will undergo some subsonic testing there before being shipped to Dryden.

DARPA’s goals are speeds exceeding Mach 2.0 and a range of 6,000 nm. The basic design is 156 ft long and has a 58-ft wingspan. It incorporates wings with a computer-changeable leading edge. A special air inlet modifies the airflow into the engine, which is mounted atop the fuselage, reducing air turbulence before it reaches the engine inlet. It also features extensive laminar flow across the entire airframe.

Phase II To Begin

In late April DARPA selected Lockheed Martin Advanced Development of Palmdale, Calif., and Northrop Grumman of El Segundo, Calif., to head Phase II of its
QSP program. They will continue to work in the systems studies segment of the QSP program, updating their aircraft designs and technology assessments based on revised program goals. Meanwhile, Raytheon Aircraft will remain as a subcontractor to Northrop.

While Lockheed and Northrop are working on competing designs, Arizona State University is demonstrating distributed roughness to inhibit crossflow instabilities for natural laminar flow on swept wings, and General Electric of Cincinnati is studying advanced propulsion systems.

Northrop’s test of the F-5E demon- strator is a separate program, where the aircraft is outfitted with a specially designed nose glove to produce a shaped sonic-boom signature on the ground. It is being tested in
a wind tunnel at the Arnold Engineering Development Center in Tullahoma, Tenn.

A key finding of Phase I, according to DARPA, was that no single breakthrough technology would enable a QSP-type vehicle. A range of technologies has to be properly integrated to approach the stringent sonic boom and performance goals. Business-aviation leaders agree that a muted sonic boom is needed to permit supersonic operation across land for an SSBJ to make economic sense.

In addition to its work with Northrop Grumman, Raytheon Aircraft has won a separate award from NASA to continue to work on a supersonic civil aircraft. Meanwhile, Gulfstream is continuing with some DARPA-funded studies of the different technology issues that need to be solved before anything is even close to being marketable and operational.