Lockheed Martin’s famed Skunk Works has finally unveiled the long-awaited successor to the SR-71 Blackbird. Aviation Week and Space Technology’s Guy Norris pulled the covers off the project that Lockheed Martin is simply calling the SR-72. The new airplane will be roughly the same size as the record-setting Blackbird, but will be able to fly twice as fast as the jet that still holds the speed records.
The new spy plane will be capable of Mach 6 cruise speeds, making it the first hypersonic aircraft to enter service should it be produced. Only the rocket-powered North American X-15 was able to regularly fly those speeds, and the three examples built were used for research. The SR-71 Blackbird is legendary in aviation circles for its Mach 3 capabilities, and different iterations served as a spy plane for 35 years until its retirement in 1998. It still holds several records, including a flight from Los Angeles to Washington D.C. in 64 minutes, 20 seconds.
The new SR-72 has long been rumored and debated, and is part of the U.S. Air Force’s plan for hypersonic capabilities that will allow fast reaction for gathering intelligence around the world. A Mach 6 airplane fills the gap between current surveillance aircraft that can loiter for long periods of time, but don’t have the ability to transit to a new area quickly. The SR-72 is also expected to have optional strike capabilities, according to Aviation Week.
The key to the new airplane, as it was with the SR-71, will be the engines. Lockheed Martin told Aviation Week the company has been working with Aerojet Rocketdyne to build an air breathing engine that combines both a traditional turbine and a scramjet to deliver the Mach 6 performance.
Normal turbine jet engines have problems operating at speeds beyond Mach 2. The original SR-71 used a complicated system of a movable nose cone on the engine, along with vents that prevented shockwaves from interfering with the flow, and slowed the air down enough so that it could be ingested by the engine. Though “unstarts” were a regular problem for Blackbird pilots, and caused problems throughout the life of the airplane.
The new SR-72 will use a turbine-based combined cycle (TBCC) that will employ the turbine engine at lower speeds, and use a scramjet at higher speeds. A scramjet engine is designed to operate at hypersonic velocities by compressing the air through a carefully designed inlet, but needs to be traveling supersonic before it is practical to begin with. So far research projects from NASA, the Air Force and other Pentagon entities have not been able to solve the problem of transitioning from the subsonic flight regime, through hypersonic flight with a single aircraft.
Lockheed Martin told Aviation Week it has found a way to use existing turbine engines, and by lowering the operating speed of the scramjet, make a transition to hypersonic speeds possible.
The aerospace company says it may have a scaled demonstrator of the SR-72 technology flying by 2023. That airplane would be smaller, about the size of the current F-22 fighter and would be optionally piloted. The SR-72 could enter service by 2030.
Skunk Works Reveals SR-71 Successor Plan
“It is time to acknowledge the existence of the SR-72 because of the HSSW going forward,” says Leland. Together with the strategic “pivot to the Pacific,” the concept of high-speed ISR is “starting to gain traction,” he notes. “According to the hypersonic road map, the path to the aircraft is through the missile, so now it is time to get the critical demonstration going.” These would test individual elements of the propulsion system, which would then be integrated for the full-scale FRV evaluation.
“We have been continuing to invest company funds, and we are kind of at a point where the next steps would require large-scale testing, which would significantly increase the level of investment we've had to make to-date. Between Darpa and the Air Force, it would be highly likely they'd have to fund the next steps,” Leland says. The FRV will also give the Skunk Works a better idea on overall development costs, he adds.
As for rumors of an existing high-speed ISR aircraft, Leland is dismissive. “It's been almost 20 years since the SR-71 was retired. If there was a replacement, they've been hiding it pretty well,” he says.
Quellen: WIRED, USAF, AVIATIONWEEK,
Opinion: High Speed Could Be The Next Stealth
Lockheed Martin has labeled the hypersonic technology to be used in the proposed SR-72 Mach 6 aircraft as the “new stealth.” It is really the old stealth, and it points to a classic example of how almost every military and political leader in Western defense fell in line behind a technical miscalculation.
The story of the SR-72's predecessor, the A-12 Oxcart, is endlessly fascinating. One of its most important and long-concealed aspects was the critical role of stealth. The Skunk Works' Texas rival, Bob Widmer's team at General Dynamics, came close to beating Lockheed for the CIA's business with their stealthy Kingfish, which looked weirdly like the much later F-117. Skunk Works head Kelly Johnson, who had been a staunch skeptic when it came to “radar camouflage,” hurriedly reshaped the Lockheed contender with chines, canted tails and radar-absorbing structures.
Behind both designs was a theory that reduced radar cross-section (RCS) and high speed would combine to defeat surface-to-air missile (SAM) systems. North American was even looking at ways of reducing the head-on RCS of the B-70 Valkyrie heavy bomber.
None of this cut any ice with Robert McNamara, Kennedy's defense secretary. His “whiz-kid” operations analysts believed the Soviet Union would quickly develop bigger SAMs and radars that would wipe out the advantages of height and speed. The B-70 was canceled, and a nuclear-strike version of the A-12 was tolerated only when it was turned into the experimental YF-12 and unarmed SR-71. McNamara's favorite combat aircraft, the F-111, was designed around the ability to fly at Mach 1.2 at low altitude, and that was the only Pentagon-approved formula for a follow-on bomber study that would lead to the B-1.
The problem with McNamara's orthodoxy was that it was wrong. The S-200 SAM and MiG-25 interceptor that the Soviets designed to shoot down the A-12 could not alter the laws of physics. At high altitude, it takes wing area to intercept even a not-very-agile target, and it takes a lot of propellant to loft that big, draggy kill vehicle before the Mach 3 intruder turns the intercept into a tail-chase that the rocket loses.
Johnson's successor, Ben Rich, estimated the S-200 could down an SR-71 only if the warhead was of the instant-sunshine variety. In practice, nobody ever hit a Blackbird, while McNamara's low-fast penetrators proved vulnerable to guns, pelicans and attempts to tie the record for minimum altitude.
The U.S. Air Force dusted off the “high-fast sanctuary” in 1982 in defining the Advanced Tactical Fighter, the program that led to the Lockheed Martin F-22. ATF was intended to cruise at Mach 1.6 and pull 6g at supersonic speed in burner, all at 60-65,000 ft.
The original ATF requirements balanced stealth against speed, height and agility. All-aspect stealth was added to the menu after Lockheed and Northrop promised the Pentagon that the price in weight, money or risk would be small. The USAF would be in better shape today if they had been right. If you want to see the original requirements in action, look at the Chengdu J-20 and Sukhoi T-50.
High-fast made another brief return to the limelight in the early 2000s. Northrop Grumman's bomber studies focused on sortie generation over long distances. A supersonic aircraft cost more than a subsonic design, but could fly more sorties in the same period and deliver the first strike more rapidly. If the goal was to threaten fleeting targets over a wide area, each supersonic aircraft could hold a greater area at risk. One engineer argued, “You need fewer systems, because the question is 'Where can I be in 10 minutes?'”
Is high-fast worth reconsideration now? There are challenges. Speed makes it harder to search for and hit targets on the ground. It's costly, but whether it need be much more costly than a high degree of stealth is an open question. It means reviving investment in forgotten technologies.
The SR-72's Mach 6 goal will be hard to reach. But do we really need to go that fast? Mach 3-4, high altitude, situational awareness, reduced front-sector RCS and good electronic attack might be enough, and we could get there without resorting to ramjets.
But today's bomber studies are focused on stealth, and even the value of the F-22's speed and agility in dodging SAMs is not stressed today because awkward questions might follow concerning the survivability of slower, less maneuverable aircraft with a similar or slightly larger RCS. That is today's orthodoxy, more deeply entrenched than McNamara's faith in hedge-hopping.
As the 19th century humorist Josh Billings put it: “It ain't what a man don't know that makes him a fool. It's all the things he does know that just ain't so.”