Graham Warwick/WASHINGTON
A new US Government research programme to develop technology for a quiet supersonic aircraft falls short of the funding required to build a flying demonstrator that could form the basis of a supersonic business jet (SSBJ), as had been hoped by Gulfstream and partner Lockheed Martin.
The US Defense Advanced Research Projects Agency (DARPA) has launched the Quiet Supersonic Platform (QSP) programme with $35 million of funding provided by Congress after lobbying by Gulfstream and Lockheed Martin, which are co-operating on the design of a supersonic business jet. The two year programme aims to develop technology for low-boom, long-range supersonic military aircraft similar in size and performance to an SSBJ. Many of the technologies will be applicable to SSBJs.
A leading candidate for QSP funding is a supersonic laminar flow design developed by Reno Aeronautical. The Carson City, Nevada-based company is working on a Mach 1.5 business jet with a range of almost 11,000km (6,000nm). As conceived, the 50,000kg (110,000lb) gross-weight aircraft is powered by two Pratt & Whitney JT8D-219 turbofans.
Conventional supersonic transports have highly swept delta wings, which lower shockwave drag at the expense of higher friction drag because the airflow is turbulent. Reno's design has low sweep and a sharp leading edge to maintain laminar flow over most of the wing, reducing friction drag. To offset the increase in wave drag, the wing is extremely thin.
Reno calculates its design can reduce wing drag at supersonic speeds by 50% or more, and can improve lift-to-drag ratio by 30% or more. This results in range performance which is competitive with subsonic transports, says president Richard Tracy. "The most fundamental challenge is to get the range up and the cost down. We think we've got the answer."
Tracy says Reno is "95% of the way towards developing a supersonic business jet, entirely off the shelf". An M1.5 cruise speed avoids the need for high-temperature materials and allows use of existing engines. Work with P&W shows the JT8D-219 can operate continuously at M1.5 "without reducing the overhaul life", he says.
With DARPA funding, Reno has flown a subscale model of its wing under a NASA Boeing F-15 at speeds approaching M2 and confirmed that natural laminar flow can be maintained over more than 80% of the wing. The test article has a leading-edge sweep of 15%, but Tracy believes it should be possible to maintain laminar flow up to 20% sweep. Tests with a larger model are planned.
Source: Flight International
