With its critical design review complete, the US Air Force Research Laboratory has begun fabrication and assembly of itsX-51A supersonic combustion ramjet engine demonstrator flight unit.
The first of four planned flight tests is expected in August 2009. Next month, the programme's Pratt & Whitney Rocketdyne SJX61-2 engine will be tested. Its predecessor, the SJX61-1 engine, was tested in July last year.
The X-51A consists of two parts, the cruiser and the booster. Designed by Boeing Transformational Space Systems the 1,030kg (2,275lb) booster is a modified US Army tactical missile system with a 760kg interstage. With a dry weight of 550kg, the 4.26m (14ft)-long cruiser is the waverider scramjet vehicle and it has a 228mm (9in)-wide flowpath. The cruiser-booster stack uses a tungsten nosecap, inconel engine and cruiser fins, a titanium interstage, aluminium cruiser and interstage skin, and the stack has 362 sensors.
"It uses a Boeing thermal protection system for acreage [but] will grow by [19mm] as it heats up [during flight]," says AFRL propulsion directorate's X-51A chief engineer Richard Mutzman. He described the X-51A as a medium scramjet. That means it has a mass flow in the order of 45kg/s (100lb/s), compared to a small scramjet that has 4.5kg/s or a combined cycle engine that would have a 450kg/s mass flow.
The first flight's readiness review will be in April next year. Flown off the southern coast of California its notional mission sees a flight time of 800s. That consists of 240s of scramjet-powered flight and 500s of unpowered flight.
Carried under a Boeing B-52 using a port wing JDAM interface from Edwards AFB, the X-51A is released at around 50,000ft (15,250m) altitude, its booster will ignite to accelerate the vehicle for 38s to Mach 4.5, at which point the booster motor cuts off, it separates, and the full authority digital engine controlled scramjet ignition will begin using ethylene to ignite its 123kg of JP-7 to reach a top speed of M6.5.
Source: Flight International