The copter is first seen in "The Cleveland-Loretta Quagmire" after Peter calms his friend Cleveland Brown by placing a plastic bag over his head then exclaiming, "To the Petercopter!". The blades cut the leaves from the tree and the copter falls into Joe Swanson's front yard causing a mess.
In "Inside Family Guy", James Woods showed us the Petercopter as one of the famous props in Family Guy. It was even explained that SEAL Team Six used the Petercopter on their mission to kill Osama bin Laden.
Cleveland reveals that he gets first dibs on the items that Peter loses interest in and acquires the Petercopter in "Nanny Goats", turning it into the "Clevelandcopter." Unfortunately, he crashes it into a nearby house when he can't see through the mustache.