I was reading through the crew chief notes for one of the aircraft that I work on and it had the noise (dB(A)) profiles at various distances from the aircraft at various engine settings.
The curious (to me) thing was that the highest noise spike came out at about 35-40 degrees (horizontally - these are ground measurements) from the aircraft centreline. I usually do the pointy end of the aircraft (cockpits, mission data etc) so the nearest I usually get to the engines is the throttle box. In my ignorance, I would have expected the loudest noise to be directly behind the engines.
I've asked around the office, but the ones who would know have been in management for too long to remember anything useful, and the intern (who would remember) is out at the moment.
It has been suggested that the loudest noise comes from the largest area of turbulence, which would be where there is the largest speed differece (and, therefore, pressure difference) between air pockets. This would mean that the highest pressure difference would be between the stationary air at the side of the exhaust nozzles and the exhaust gas itself.
So, is the sound all generated at this point and continues outwards (I would have expected more of a hemisphere effect); or does it travel with the moving air (which is being blown backwards); or does the noise continue to be generated along the line of the dissipating exhaust flow; or have I got it badly wrong and there is something else at work here?
The aircraft is a twin-engined 'multi-role' fighter built by a European consortium. Can you guess what it is?