A Sample Feature From Aviation News

Blackswift a quantum leap

Above: The exact configuration of Blackswift is still classified and will change from the shape it presently has, but this rendition is a good approximation of the first operational hypersonic combat vehicle to go operational. (All photos via Av News) Below: The legendary X-15 pioneered aerodynamic research into hypersonic flight, the three vehicles making 199 flights between 1959 and 1968, of which 1hr 25min 33sec was spent above Mach 5 and 1min 18sec at Mach 6 or greater. The highest speed achieved was Mach 6.70 by air vehicle #2 on October 3, 1967.

It is now almost 47 years since the experimental North American X-15 became the first manned aircraft to exceed Mach 5, defined as the threshold of hypersonic flight. That event took place on June 21, 1961. Although speeds in excess of Mach 6 were subsequently achieved with the air-launched X-15, no production-line military aircraft has routinely operated above Mach 3. Since the late 1950s, numerous studies have been carried out on hypersonic aircraft, but all have proven elusive. Now, the US Defense Advanced Research Projects Agency (DARPA) and the Arnold Engineering Development Center (AEDC) have teamed industry with US Air Force engineering and technology specialists to develop an operational vehicle that will routinely fly at speeds in excess of 4,000mph (6,436km/h) and an altitude above 100,000ft (30,500m).

It is not an experimental research project but an operational strike aircraft. It is called Blackswift and it will be built by Lockheed Martin’s Skunk Works, utilising a combined-cycle engine developed by Pratt & Whitney. Blackswift is an outgrowth of several precursor research and development projects veiled under shifting codenames grouped under the generic title Falcon, of which the X-51 hypersonic cruise weapon is a part. Its predecessors and unmanned vehicles Aviation News will be outlining in subsequent issues are married to the High-Speed Weapons Program – a keystone in new warfare technologies and war-fighting rationales.
By limiting Blackswift’s speed to Mach 6.5 it avoids the onset of steep penalties paid in materials and engine design. At speeds higher than this, thermal protection enabling the air vehicle to survive sustained hypersonic velocities in heated air becomes exotic and expensive in the extreme, and that is not what the Air Force wants. The purpose of Blackswift is not to be a research vehicle like early rocket-powered X-planes and several subsequent, failed, projects but rather an operational strike and reconnaissance aircraft. In effect a successor to the A-11/SR-71 family of which Lockheed Martin and Pratt & Whitney have much experience – since they built and powered the ubiquitous Blackbird, hence ‘Blackswift.’ We are assured, however, that it will not be designated SR-72!

Instead of playing to the freedom of expensive compound materials capable of protecting aero-structures in the thermal environment of high Mach numbers, Blackswift is a prudent compromise between very high speed and cost-effective operating flexibility. It will operate within the atmosphere and is not a spaceplane. It will be manned and it is to be based in the United States as a new form of surveillance and strike aircraft responding at very short notice, using almost exclusively off-planet data assets and sensors – satellites to you and me. The Air Force wants an operational air vehicle on the ramp and ready to go at very short notice and therefore it has to be rugged, durable and serviceable on line, not in an exotic Skunk Works hangar, and it must be affordable. Elements of the Falcon programme include the ability to launch small satellites at very short notice because these will be vital to Blackswift operations both for off-board sensor input and communications.

Using existing materials, including composites, thermal protection is standard with heat-sink ceramics employed only on hot areas such as the leading edge of lifting surfaces and tail-planes. In fact, all the hot structures are protected by heat-sink materials – that is materials that dissipate thermal energy but are poor conductors and bad radiators. That imperative is why DARPA insists on a combined-cycle engine that achieves Mach 6.5 but nothing greater. Go to just Mach 7 and things get a lot hotter, a great deal more complicated and very expensive. Simpler to devise, with existing and proven materials, the combined cycle engine takes the best of what has been flying already and adapts it to an operational airframe. Burning hydrocarbon fuel and providing power on ascent, throughout cruise and on landing, it is much more flexible and adaptable than exotic scramjet engines favoured in earlier high-Mach concepts using hydrogen or similarly difficult and expensive fuels. NASA wasted a lot of money trying to find an exotic successor to the Shuttle – a hydrogen burning air-breathing scramjet incorporated within a core rocket stage using onboard oxidiser for combustion in the vacuum of space.

Above: Previous attempts to achieve hypersonic flight were split among reusable aerospace vehicles such as the X-33, seen here in an artist’s visualisation, intended as a precursor to a full-scale trans-atmospheric vehicle spending, by definition, the greater part of its trajectory in the upper atmosphere. Below: A more direct approach to propulsion systems capable of operating above Mach 5 has included wedge-shaped test vehicles that provide optimum shape for high temperatures and underbody lift.

Lessons learned
Blackswift does away with exotic and super hi-tech concepts to simplify the objectives and focus on the mission, no matter how retro the means to achieve it. It is an approach that underpins a shift in the way future aircraft are viewed. Not as exotic, high-technology super-weapons with the objective being on the sophisticated nature of the physics, chemistry and technology going in to them, but rather on the mission objective itself. In other words, by shifting the mission back on to the task the vehicle is designed to perform, rather than making the objective the development of the vehicle itself. This approach underpins a broad spectrum of weapons across a wide platform of applications. It is the only redeeming legacy of the Rumsfeld years when that now discredited Defense Secretary attempted to buy high tech solutions at the cost of foot soldiers. It failed to work with ground forces but it is the only way to transition from Cold War technology to the clear advantages on this new generation of weapons and systems now in development.

It is a shift in design rationale that is set to propagate throughout the US defence infrastructure for land, sea and air forces and it has already been pioneered elsewhere. When NASA faced a major decision over sustained operations with the reusable, winged Shuttle, it had to decide whether to put several billions of dollars into upgrades, refurbishment and stockpiling spares to keep it flying, or develop a successor. It chose to do neither. For a while, a replacement to the Shuttle had been sought through even more sophisticated, winged vehicles such as the Lockheed Martin X-33 space-plane or designs like the Crew Recovery Vehicle, shaped like a mini-shuttle but limited in capability. They languished in the backwaters of acceptability and efficiency, and while soaking up several hundred million dollars in failed concepts did nothing to satisfy the objective – which was to get a working vehicle operational.

When conceived in the late 1960s and built in the 1970s, the Shuttle had been a highly advanced vehicle, pushing technology beyond extant capabilities. As such, it was both research vehicle and operational space truck. Even in the former role it was not cost effective; a Mach 25 research vehicle could have been built and flown for less if that alone had been the objective. Instead, using many new technologies it could never be the operational and safe flying vehicle everyone hoped it could become. As first-of-a-kind, it had no precedent upon which to base its design and development and as one-of-a-kind there was no parallel against which to measure its success or failure. As it was, totally different from anything that had gone before, scientists, engineers, industry chiefs and politicians accepted it for what it was – the birth of a new era in space transportation and swallowed the cost as a price to pay for advancement. Now, as successor to the Shuttle, NASA has shifted the objective for human space flight from the vehicle itself back to its objective – which is exactly how the engineering of the Apollo spacecraft and associated launch vehicles proceeded back in the 1960s – with a different mission goal and not by way of a sophisticated replacement vehicle in itself.

No blue skies
The lesson has been learned and Blackswift is neither exotic nor ground-breaking. While its projected performance is stunning and impressive, it utilises proven technologies displayed elsewhere. Just as NASA is picking up existing, proven technologies to build a set of vehicles for developing scientific research stations on the moon, much like there are in Antarctica, so is DARPA dumping far-end, blue-sky concepts for an efficient and rugged platform, no less remarkable for all that. But there is more to the new approach – dumping high-end exotica for rugged operability – because Blackswift will be far from stealthy. It has no need to be. Other air vehicles will push the envelope on that frontier. It is almost impossible to make Blackswift stealthy because it will produce heat through kinetic friction with the atmosphere at the intake and at the exhaust. For the foreseeable future there will be nothing that can catch it, but when there is, the technologies that have been going into missile defence systems will converge to shoot down attacks on Blackswift by hostile forces. Some in the Pentagon say it matters not that the enemy know it is on its way – because the target will still be warm when it arrives, be that a Scud missile, deeply buried bunker or a factory.

Above: The X-43A hypersonic vehicle was optimised around a scramjet engine, essentially a hypersonic ramjet that could not have provided power for take-off and landing, unlike the combined cycle engine that will power Blackswift. Below: Test vehicles like this X-34 that were never deployed operationally provided sound engineering experience in packaging systems and equipment within a hot-soak structure where temperature differences between inner and outer surfaces would exceed 500ºF.

For the rest of this feature please see the February 2008 issue.