US agency sets out plan to develop Switchblade, a supersonic, tailless, variable-geometry flying wing demonstrator
Citing the potential to combine high speed, long range and long endurance, the US Defense Advanced Research Projects Agency (DARPA) has requested proposals to develop an oblique flying wing (OFW) technology demonstrator. The supersonic, tailless unmanned X-plane could fly in 2010.
The goal of DARPA’s Switchblade programme is to demonstrate the feasibility of a variable-sweep flying wing so the concept can be considered for an intelligence, surveillance and reconnaissance (ISR) aircraft or bomber in the 2020 timeframe, requiring a combination of high speed and long range and endurance.
The supersonic tailless OFW concept poses daunting aerodynamic control, aerostructural design and propulsion integration challenges, says the agency. Although there have been conceptual studies and small subsonic demonstrations of the oblique-wing concept over the years, DARPA says there is insufficient data to assess the feasibility and controllability of an operational supersonic aircraft.
The X-plane demonstrator is intended to validate the design methods and control approaches. Under Phase 1 of the Switchblade programme, one or more contractor teams will complete the conceptual design of a operational vehicle and derive from it the preliminary design of a subscale unmanned demonstrator. The teams will also conduct risk-reduction activities, including modelling, simulation and windtunnel testing. These could include ground tests of technologies not in the X-plane, such as a fully embedded engine/airframe integration demonstration.
In the absence of a specific mission for an operational OFW, DARPA has two requirements for the conceptual 2020-timeframe vehicle: an ISR mission with a 4,600km (2,500nm) radius and 15h subsonic loiter at 60,000ft (18,300m), carrying an 1,800kg (4,000lb) payload; and a bomber mission with a 4,600km radius, maximum speed of Mach 2, cruise of M1.6 and 6,800kg payload.
The smaller-scale X-plane demonstrator is required to be a “non-expendable” aircraft with air-breathing propulsion capable of conventional take-off and landing and a speed of at least M1.2.
The vehicle must be tailless in supersonic cruise and subsonic loiter conditions and be capable of varying sweep in flight from a minimum of 30° or less to a maximum of 60° or more.
At minimum sweep the aspect ratio must be 7 or more and have a wingspan of 12.2m or more.
Because of the technical challenges, DARPA has not set the funding or timescale for Phase 1. Instead, bidders will propose a baseline programme to mature the OFW to a technology readiness level (TRL) of 4 or 5 by the end of Phase 1.
DARPA then plans to select one team to build and fly the demonstrator, with the goal of reaching a TRL of 7 by the end of Phase 2, enabling the OFW concept to be an option for future operational vehicles.
GRAHAM WARWICK/WASHINGTON DC
Source: Flight International
