How to Prove Quiet Supersonics Can Work
4:44 PM on May 27, 2011
Concept: Lockheed Martin
Boeing and Lockheed Martin are working on designs for low-boom supersonic airliners under NASA contracts that include windtunnel tests to validate they can in fact meet both sonic-boom and performance goals.
For those of you familiar with the swoopily gorgeous design that Lockheed's Skunk Works produced for NASA's three-generations-from-now "N+3" supersonic airliner study in 2009, the slightly
ugly-duckling looks of its two-generations-distant N+2 trijet (above) will come as a bit of a shock. Boeing's N+2 twinjet (below) definitely has the edge in the style stakes.
The goal of NASA's "system-level experimental validation" project is to prove out the technologies and tools that would be used to create a full-scale low-boom supersonic airliner by designing and windtunnel-testing an configuration meeting NASA's targets for an aircraft that could be ready to enter development by 2020. Those "N+2" targets include a sonic boom intensity of 65-70PLdB (Concorde was almost 110PLdB) and a range of 4,000nm carrying 35-70 passengers at Mach 1.6-1.8.
Meeting those targets requires shaping of both the fore and aft shockwave signatures to soften the boom, and results in some rather racy stretching and shaping of the aircraft to prevent the various shockwaves coalescing into the N-wave signature of a classic "double-bang" sonic boom - as Boeing's low-boom windtunnel model (below) clearly illustrates.
The sonic-boom threshold set for Phase 1 of the study is 85PLdB. Windtunnel testing has still to be completed, but Boeing says that, at Mach 1.6, its design has a boom of 84PLdB and a lift-to-drag ratio that beats the range goals. At Mach 1.8, the L/D not as good but the boom is lower (81PLdB) and Boeing says the design has the potential to get down to 70-75PLdB in the N+2 timeframe.
Graphic: Lockheed Martin
Lockheed, meanwhile, is refining its N+2 configuration (which seats 81 passengers) to reduce boom loudness off-track, and not just below the flightpath. This is not a small aircraft - it's 230ft long and has a cruise weight of 271,000lb (longer but lighter than Concorde's 202ft and 310,000lb). Cruise is Mach 1.6, starting at 45,500ft and climbing to 52,800ft. General Electric and Rolls-Royce Liberty Works are working with Lockheed on variable-cycle engine concepts.
Concept: Lockheed Martin
PS. If, like me, you were brought up with the designs of Gerry Anderson, and you feel there is something vaguely familiar about Lockheed's design, check out the "Shadair hypersonic transport" from the TV series UFO.
awt, supersonics, NASA