Even if Son of a Blackbird’s twin-tail, waverider configuration continues to evolve, is already representative of a feasible hypersonic design
Boeing is planning to develop a hypersonic successor to the legendary SR-71 Blackbird.
As brought to my attention by Manoj Balachandran, a reader of The Aviation Geek Club, Boeing showed its concept for a Mach 5 hypersonic future high-speed strike and reconnaissance aircraft last week at the American Institute of Aeronautics and Astronautics SciTech forum and Guy Norris of Aviation Week has the details.
“Like the outwardly similar SR-72 concept revealed in 2013 by Lockheed Martin, the Boeing design also is aimed at a hypersonic successor late in the 2020s to the long-retired SR-71 Blackbird reconnaissance aircraft,” Norris Said.
Kevin Bowcutt, Boeing chief scientist for hypersonics told Aerospace Daily that the vehicle is based on Boeing’s experience with the X-43 and X-51A (the first vehicle to demonstrate sustained air-breathing hypersonic flight) projects and includes input from the XB-70 program. “It’s a really hard problem to develop an aircraft that takes off and accelerates through Mach 1 all the way to Mach 5 and beyond. The specific impulse of an air breathing engine goes down with increasing velocity, so you have to make the engine bigger to get to Mach 5. But doing that means a bigger inlet and a bigger nozzle, and trying to get that through Mach 1 is harder,” he points out.
“We asked, ‘What is the most affordable way to do a reusable hypersonic demonstrator vehicle?’ And we did our own independent research looking at this question,” says Bowcutt. If the concept is selected for full-scale development, Boeing envisions a two-step process beginning with flight tests of an F-16-sized, single-engine proof-of-concept precursor vehicle leading to a twin-engine, full-scale operational vehicle with about the same dimensions as the 107-ft.-long SR-71.
However even if the the twin-tail, waverider configuration continues to evolve, is already representative of a feasible hypersonic design.
Actually careful integration of the airframe and propulsion system through multidisciplinary design optimization (MDO), a process in which designers incorporate all relevant disciplines simultaneously, has enabled Boeing to develop a working configuration.
Although initially independently funded by Boeing, development of the hypersonic vehicle concept is continuing under Darpa’s Advanced Full Range Engine (AFRE) initiative and a closely-related turbine-based combined cycle (TBCC) flight demonstration concept study run by the U.S. Air Force Research Laboratory.
According to Norris, the vehicle configuration is dominated by the TBCC propulsion system, which combines conventional turbine engines with dual-mode ramjets/scramjets (DMRJ). The turbine engines operate up to a sufficiently high Mach number to enable transition to the DMRJ. The engines will share a common inlet and nozzle, with the turbine cocooned after transition and then restarted once the hypersonic vehicle slows down for return to a runway landing.
The inlets are divided by a prominent septum derived from the XB-70, Bowcutt says, adding that the TBCC is only one of a number of potential propulsion options. The nozzles also are separated by a prominent boat-tail divider.
“The propulsion system determines the length of the vehicle,” says Tom Smith, Boeing Research and Technology chief hypersonic aircraft designer.
As Norris explains, the inward-turning inlets are positioned to capture the initial shockwave from the nose of the vehicle, while the sharply swept forebody chines are contoured into the relatively large-span delta wing to provide waveriding capability at hypersonic speed and sufficient lift for landing and takeoff at subsonic speed.
The term waverider refers to a design in which the vehicle rides the shockwave attached to the leading edge, thus benefiting from lower induced drag. “As the narrow chine transitions to the wing, that produces a good vortex, which you care about at low speed,” Smith concludes.
The SR-71, unofficially known as the “Blackbird,” was a long-range, advanced, strategic reconnaissance aircraft developed in the 1960’s by the U.S. Air Force (USAF).
The first flight of an SR-71 took place on Dec. 22, 1964, and the first SR-71 to enter service was delivered to the 4200th (later 9th) Strategic Reconnaissance Wing at Beale Air Force Base (AFB), Calif., in January 1966.
As we have already explained, throughout its nearly 24-year career, the SR-71 remained the world’s fastest and highest-flying operational aircraft.
Actually its incredible speed enabled it to gather intelligence in a matter of a few seconds while streaking across unfriendly skies. From 80,000 feet, it could survey 100,000 square miles of Earth’s surface per hour. And in the off chance an enemy tried to shoot it down with a missile, all the Blackbird had to do was speed up and outrun it.
Thanks to its astonishing flight characteristics, the aircraft has set numerous speed and altitude records during its career, like those established on Jul. 28, 1976 by an SR-71 that set two world records for its class – an absolute speed record of 2,193.167 mph and an absolute altitude record of 85,068.997 feet.
The U.S. Air Force retired its fleet of SR-71s on Jan. 26, 1990, because of a decreasing defense budget and high costs of operation.
Photo credit: Guy Norris, Boeing and TSgt. Michael Haggerty / U.S. Air Force
Artwork courtesy of AircraftProfilePrints.com