Blackbird to Blackswift – via Falcon?

DARPA’s annual tech-fest has caused a stir in the blogosphere with the first appearance of a model of the HTV-3X demonstrator being designed by Lockheed Martin’s Skunk Works under the Falcon hypersonic technology programme.

Bill Sweetman broke the story on AvWeek’s Ares blog, and Sharon Weinberger weighed in on Wired’s Danger Room. Hopefully Bill won’t mind me stealing his picture…

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But what’s this about the Blackswift?Flight was first to reveal that the orginal rocket-boosted, scramjet-powered HTV-3 had morphed into the combined-cycle HTV-3X, which would take off from a runway on turbine engines and accelerate to Mach 4, where dual-mode ramjet/scramjets would take over and power the unmanned vehicle to a Mach 6 cruise before returning to a runway landing.

Bill is correct in saying the HTV-3X would be fighter-sized – about the size of an F-18 judging by a doctored photograph spied on the programme manager’s desk. Sugar-scoop inlets under the forebody feed both the high-Mach turbines and the “inward-turning” scramjets and are key to what makes this different to other hypersonic demonstrators.

Scramjet demonstrators like the X-43 and X-51 have two-dimensional, or rectangular, inlets that compress the air flowing into the engine using an angled ramp. An inward-turning scramjet has an axisymmetric, or round, inlet that compresses the air on all sides. This is more efficient and allows easier integration of the turbine and scramjet flowpaths.

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The Falcon programme has changed significantly since it began in 2003. Originally standing for Force Application and Launch from the Continental US, the plan was to build a series of increasingly advanced unmanned, unpowered test vehicles to by launched by rocket to demonstrate sustain hypersonic cruise.

The first in the series, the HTV-1, was abandoned when it proved to difficult to build. DARPA and the Skunk Works are now focusing on the more-producible HTV-2. The last of the series, HTV-3, was intended to be reusable, and still unpowered, but that changed after NASA cancelled plans for an X-43 combined-cycle flight demonstrator.

DARPA saw the opportunity to morph the HTV-3 into turbine/scramjet-powered hypersonic demonstrator, resulting in the HTV-3X now in concept design at Lockheed. It is quite a stretch from the original idea – and nothing has even flown yet – but DARPA seems confident the Skunk Works can deliver the goods. If it does, it will have a worthy successor to the famed SR-71 Blackbird.

Which leads us to the Blackswift. While there is one reference suggesting Blackswift is the name for the HTV-3X, DARPA’s official response is: “We’re currently holding preliminary discussions regarding a possible program called Blackswift, but no decisions have been made.” I will leave it to you to read Bill’s and Sharon’s blogs and decide for yourself whether Blackswift is the HTV-3X…or the SR-72.

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