Page 25 - January 2006

Fig. 5. Aircraft maneuver for F-18 generation of low overpressure N waves. (Courtesy NASA Dryden Flight Research Center.)
would be very useful to know how people react to such low amplitude sonic booms. Such tests are not yet planned, but they likely will be very useful in assessing the acceptability of the low-boom designs that industry would like to build.
Ongoing work by the PARTNER Center of Excellence
Since no aircraft designed for low-boom currently exists, substantial research is underway using artificially reproduced sonic booms. There is much research being conducted in this area in Project 8 (sonic boom mitigation) of the FAA/NASA/Transport Canada Center of Excellence (CoE) PARTNER15 (Partnership for AiR Transportation Noise and Emissions Reduction). PARTNER was established in September 2003, but funding for the sonic boom mitigation aspect was received by the participating universities in April 2005. Since Project 8 was funded much later than the other projects in PARTNER, the work is still in its infancy at the time of this writing.
One of the major purposes of Project 8 is to determine the acceptability of low-boom sonic boom noise to the gen- eral population. What signatures will be acceptable to the public for overland supersonic flight?
Project 8 consists of a number of research tasks that are interconnected. Potential aircraft manufacturers are supply- ing baseline supersonic signatures at the ground from their designs, but rarely will individuals actually hear these signa- tures. During supersonic cruise people most often will instead hear the signatures after they have been distorted by propa-
gating through the atmosphere. During other portions of the flight when the air- craft is climbing, turning, or descend- ing, the aircraft will produce other signa- tures on the ground, and these waveforms also will be needed. Hence some of the tasks in Project 8 are to take the baseline signatures and pro- duce synthesized sig- natures, similar to the ones that will be actually heard by the public. It is these sig- natures that will be jury tested for accept- ability. After subjec- tive testing, recom- mendations then can be made for use by the FAA and NASA.
There are three tasks initially funded in Project 8. Task 8.1 is to incorporate
pulls out of the dive at a safe altitude. This interesting aircraft maneuver necessary for this supersonic dive was shown to the ISBF attendees via playback of a cockpit video.
The work so far has been successful, with all of the meas- urements producing low boom N waves in the desired geo- graphical area. Example low-overpressure N waves are shown in Fig. 6. Haering reported that the resulting waves had rise times which greatly increased with decreasing maximum pressure amplitude.
The importance of this work cannot be overstated. Given the ability to place low amplitude sonic booms in a specific geographic area should allow for future performance of sub- jective testing of these waves both indoors and outdoors. It
Fig. 6. Example low overpressure N waves. (Courtesy NASA Dryden Flight Research Center.)
Lowering the Boom 23