Intercontinental business jets
A look at current business aircraft development shows large-cabin long-range transonic jets will lead the way.
Among the strategies to suppress sonic booms being considered are the following.
• Gulfstream Aerospace and NASA's Dryden Flight Research Center are collaborating in investigations, using a spike made of composite materials to create 3 small shock waves traveling in parallel, producing less noise than typical shock waves that build up at the nose of supersonic jets.
• Supersonic Aerospace Intl's design increases the ratio of length to wingspan, using canards, and ensures that individual pressure waves generated by each part of the aircraft structure reinforce each other less significantly, producing a longer but less objectionable boom.
• One key technology, demonstrated using a Northrop F5E, has been to reshape the boom so that it sounds more like distant thunder than the booms that annoy the public.
• The Aerion SSBJ design does not incorporate boom suppression but relies on the Mach cutoff principle that the speed of sound increases with temperature, and is therefore lower at cruise altitude than on the ground. By adjusting cruise speed based on temperature data, the sonic shock wave can be kept from hitting the ground, dissipating instead at a selected altitude, eg, 5000 ft.
It is also imperative to ensure that NOX, H2O, and CO2 emissions, primarily at high altitude, are minimized to limit their impact on the ozone layer.
There is a performance challenge. The "low boom, high drag" paradox holds that aircraft configurations that tend to reduce sonic booms tend to increase drag. The lift/drag ratio of a supersonic jet is much lower than that of a subsonic aircraft.
Supersonic Aerospace Intl (SAI) hired Lockheed Martin to complete a feasibility study of an aircraft which could potentially fly at supersonic speeds over land. The study verified the M1.8, low-sonic-boom design concept but further development of the Quiet Supersonic Transport (QSST) is currently pending.
Reducing aircraft weight, by using new lightweight materials, will reduce drag and the fuel needed per passenger mile. Another drag-reducing approach is to employ natural laminar flow (NLF) wings.
Supersonic cruise efficiency needs to be combined with efficient performance in the transonic and takeoff/landing regimes. A variable cycle engine (VCE) system will change the bypass ratio (fan airflow to core airflow) from the higher levels during takeoff/landing to the lower levels best suited for supersonic cruise conditions.
Industry forecasts predict that, as the global recession eases, the return to a brighter commercial future will be led by large-cabin intercontinental business jets. Our natural instinct to push the boundaries further will bring the SSBJ to reality in relatively quick succession.
Don Van Dyke is an 18,000-hr TT pilot and instructor with extensive experience in charter, business and airline operations. A former IATA ops director, he has served on several ICAO expert panels and is a Fellow of the Royal Aeronautical Society.