Hey now. Heard many references to engines being 'out of sync' and indeed I'm very familiar with the sensation from sitting at the back of many MD80s and hearing that weird throbbing sound.
What does 'sync' mean, how is it achieved, any info or observations please. Including an answer to the question, "Can engines not being in sync cause damage to the airframe, at least in as much as pop a few weakened rivets?" Is it important to the operation of the aircraft, or is it just a crowd pleaser for the back rows?