US aeronautics agency NASA managed to capture the Boom Supersonic XB-1 research aircraft as it broke the sound barrier during its final flight on 10 February.
The flight – the XB-1’s second in excess of Mach 1 – was the last in a series of test sorties by the aircraft, conducted to support Boom’s development of the proposed Overture airliner.
One of the aims of the flight over the Mojave desert was to acquire a Schlieren photograph of the jet at supersonic speed.
Schlieren photography involves imaging light which has been refracted by changes in the air temperature or pressure.
Such techniques enable the shockwaves generated by the aircraft to be visualised, but the process required NASA to capture the XB-1 passing in front of the sun, using ground telescopes fitted with filters.
“This image makes the invisible visible – the first American-made civil supersonic jet breaking the sound barrier,” says Boom Supersonic chief Blake Scholl.
NASA also obtained acoustic data from the aircraft which demonstrated the ‘boomless cruise’ principle, whereby the sonic boom, under certain speed and atmospheric conditions, can refract away from the ground.
Scholl claims the data confirms XB-1, which had also flown supersonically on 28 January, “made no audible sonic boom”.
This phenomenon, known as Mach cut-off, is intended to provide an avenue for Overture to achieve overland supersonic flight – currently banned by the US FAA owing to sonic boom disturbance.
