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Adding a quiet spike nose probe (lower right) and boom control tail bump (lower left) helped Comac meet its sonic boom target.
China’s Comac is studying a potential low-boom supersonic airliner for possible mid-century market entry.
A study published in China details the design and the challenges that are still to be overcome.
The study raises the possibly that China could be first to field a supersonic aircraft using boom-reducing technology pioneered in the U.S. A product roadmap released by Comac suggests a supersonic airliner is one option for a proposed C949 planned to enter service in 2049.
The C949 would follow the in-production C909 and C919 narrowbodies, the Boeing 787-class C929 widebody under development for service entry in 2029, and the 777-class C939 planned for 2039. In addition to a supersonic airliner, options identified for the C949 include a double-deck twin-aisle, a three-aisle aircraft, and an unspecified “new layout.”
The ability to reduce sonic boom strength through airframe shaping was first demonstrated by DARPA and Northrop Grumman in 2003. NASA subsequently worked with Boeing and Lockheed Martin to study low-boom supersonic airliner concepts.
This led to Lockheed’s Skunk Works being selected to design and build NASA’s X-59 Quesst low-boom flight demonstrator, now in ground testing and expected to fly this year. But no U.S. manufacturer publicly plans a quiet supersonic airliner, as Boom’s planned Overture is not low boom.
The study by Comac’s Shanghai Aircraft Design and Research Institute, published in Chinese academic journal Acta Aeronautica et Astronautica Sinica, details the evolution of a low-boom concept for a 48-passenger, Mach 1.6-1.7 cruise, 6,000-nm (6,900-mi.)-range airliner.
Comac’s design target is a sonic boom strength of less than 85 PLdB when cruising at Mach 1.6 and 16,000 m (52,500 ft.) altitude. This compares with 110 PLdB for Concorde and 75 PLdB for the X-59. The study provides insight into the challenges of designing a low-boom supersonic airliner.
The concept has a three-surface configuration—with a canard foreplane, 68.8-deg. swept wing, and V-tail—and is powered by a pair of rear-mounted, medium bypass, non-afterburning turbofans with spike inlets. Length is 61.2 m (200 ft.), wingspan 22.5 m and maximum takeoff weight 79,000 kg (174,000 lb.).
Passengers are seated individually on either side of the center aisle, the seats angled toward the windows. The cabin is narrow—2.2 m wide and 1.8 m high, slightly smaller than that of an Embraer ERJ.
In low-boom design, the sonic boom reaching the ground is reduced by shaping the airframe to control the generation of compression and expansion waves. The goal is to prevent them coalescing into strong bow and tail shockwaves as they propagate through the atmosphere to the ground, avoiding the formation of an N-shaped signature that generates the classic “double-bang” sonic boom.
The Comac team used an inverse design method, deriving the desired airframe shape from the target near-field shockwave signature. But the initial design, called Scheme A, produced a sonic boom as high as 105.2 PLdB, well above the target.
This was because a strong compression wave from the wing caught up with the canard compression wave and merged into a bow shock with a high overpressure peak. At the same time, the expansion wave from the tail formed a strong tail shock.
The design was revised to reduce the cross-sectional area of the center fuselage and weaken the compression wave. The lower fuselage volume was reduced, introducing an upward bend that generates lift, reduces the compression wave, and weakens the tail expansion wave. The revised design, Scheme B, reduced sonic boom to 93.5 PLdB, still above the target.
Scheme B still had strong bow and tail shocks, so a third design iteration, Scheme C, introduced a quiet spike nose probe and boom control tail bump as well as increasing the mid-fuselage curvature. The spike, first flown by NASA and Gulfstream in 2003, divides the nose compression wave into two paths to extend the ground pressure-rise time, while the bump freezes the expansion and compression waves from the tail. Scheme C has a sonic boom of 83.8 PLdB.
Having achieved the performance and targets, the Comac team says future development will have to focus on undesirable characteristics, including significant longitudinal aerodynamic nonlinearity, weakened directional static stability at certain angles of attack, and strong inlet distortion at large sideslip angles. The aircraft will require a full-time, full-authority, fly-by-wire flight control system, Comac says.
The Chinese airframer has a way to go in designing a supersonic airliner and has yet to fly a low-boom demonstrator similar to the X-59 or the air-dropped subscale model the Japan Aerospace Exploration Agency plans to test in 2028. Such a step is likely if Comac is to take the path to a supersonic C949.
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