Remember DARPA’s Quiet Supersonic Platform programme? It’s best known for proving that an aircraft can be shaped to modify its sonic boom. But the industry teams involved also completed substantial conceptual design work on low-boom supersonic strike aircraft – and business jets.
Now Hawker Beechcraft, which as Raytheon Aircraft was part of Northrop Grumman’s QSP team, has received a patent as a result of the work. The patent is for a method of developing an aircraft configuration by first defining a target sonic boom signature.
And designing an aircraft to eliminate the characteristic “double bang” sonic boom produced by a traditional N-wave shockwave signature produces some interesting results:
Supersonic wave drag is a function of the area distribution of an aircraft. The “coke bottle” fuselage of the Northrop F-5 is a result of area ruling – the waisting of the fuselage offsets the additional cross-sectional area of the wing. The trick of low-boom design is shape the aircraft to both control the shockwave pattern and minimise supersonic drag.
Pick a target sonic signature
According to the patent, Hawker Beechcraft’s design method begins by defining a target sonic boom signature, then determining a total area distribution based on that target. The total area distribution is made up of the cross-sectional area of the airframe plus the equivalent area due to wing lift. This in turn determines the area distribution of the aircraft body.
Determine the area distribution
Defining the location of an internal aircraft component then determines whether there is sufficient cross-sectional area available at that location. If not, then the aircraft configuration is revised to provide additional area at that location while still providing the total area distribution that produces the target sonic boom signature. Iterate a few a times, et voila!
And work out if everything fits
Well, it’s probably a bit more complicated than that…