Design Methods to Create Frozen Sonic Booms via Lobe Balancing using Aircraft Components

摘要

This study explores how to freeze a sonic boom. A frozen sonic boom is denned as one that does not develop into an N-wave because its shape has stopped changing. First, atmospheric freezing is discussed. As a sonic boom propagates to the ground the age variable which quantifies the nonlinear distortion approaches an asymptotic limit. If it reaches this limit, the sonic boom will stop distorting and be frozen in its current shape. Data is presented that shows for an aircraft cruising at 51,000 feet at Mach 1.7, the age variable is still 24% away from this limit. Thus, the sonic boom continues to distort all the way to the ground and is not frozen by the atmosphere. A second way to freeze a sonic boom is through balancing lobes in the Whitham F-function. This technique is investigated by using software based on modified linear theory. A design is sent to the software where it is transformed into an F-function, which is then propagated to the ground using geometric acoustics. Key performance parameters, such as lift, drag, and static margin are also calculated. This computer code is used to design a lobe balanced supersonic business jet using aircraft components. The lobe balanced aircraft produces a 24% reduction in the overpressure at the price of 13% reduction in the lift-to-drag ratio. Although the reduction in this ratio is undesirable, this study demonstrates that lobe balancing can reduce the maximum over pressure using aircraft components and warrants further detailed investigation.