Defence

Northrop Grumman hopes to fly the first supersonic oblique flying-wing aircraft by 2010-11 under a US Defense Advanced Research Projects Agency (DARPA) programme. The company has received a $10.3 million, 20-month contract for risk reduction and preliminary design of the unmanned X-plane demonstrator.

© Northrop Grumman

At low speed and sweep (top image) aerodynamic efficiency is high. At high speed and sweep supersonic drag is reduced

DARPA’s Oblique Flying Wing (OFW) programme is being distanced from the US Air Force’s emerging long-range strike requirement, but the tailless variable-sweep aircraft’s combination of high speed, long range and long endurance looks promising for longer-term applications if design and controllability challenges can be overcome.

At low speed, with the wing at low sweep, aerodynamic efficiency is high, and the configuration has good subsonic loiter capability. At high speed and high sweep, supersonic wave drag is reduced compared with a conventional swept wing because the aircraft’s volume and lift are distributed along the length of the oblique wing.

However, the tailless and unstable OFW presents severe flight-control challenges because of the unique coupling between the asymmetric aircraft’s aerodynamic and structural modes. Integration of the propulsion system – mounted in a pod slung under the wing in Northrop’s concept – is also a technical challenge, as is manoeuvring the aircraft on the ground.

GRAHAM WARWICK / WASHINGTON DC