NASA is to test a 57%-scale fan for a turbofan combined cycle engine. This follows work that has continued progress made with the cancelled NASA Next Generation Launch Technology programme's Revolutionary Turbine Accelerator (RTA) project.

The fan test will evaluate the tools used to develop it. The fan would act as part of a turbine engine for take-off and acceleration to hypersonic transition speeds before the vehicle is switched to using a supersonic combustion ramjet engine. Turbofan combined cycle work in Europe and Japan has focused on turbojets.

The turbofan combined cycle engine with a fan would be part of a 9.15m (30ft)-long "over, under" propulsion system with the turbofan on top of a scramjet, with both engines fed by a 3m-wide dual inlet. In a flight's early stages the fan would operate conventionally. At hypersonic speeds it would windmill.

"The transonic thrust margin, the transition from low thrust to high speed, is the most important issue [for reusable hypersonic vehicles]. To get through the transonic we need tons of thrust," NASA Glenn Research Center aerospace engineer Kenneth Suder said at the American Institute of Aeronautics and Astronautics' space planes, hypersonic systems and technologies conference in Dayton, Ohio.

He added that the US Defense Advanced Research Project Agency's Blackswift project is addressing all these key transition issues. The RTA programme attempted to modify an existing engine core, including removing some elements to meet its mass target, to achieve the thrust increase needed for the transonic regime.

Source: Flight International