A "ramp" (in US aviation jargon) is where aircraft are loaded and prepared for flight. The official term is "apron" and a common layman's term for this area of an airfield is "tarmac." Guessing this is the main source of confusion.
"Tramp" here probably means harlot (consider the cheesecake pinup nose-art common on WWII-era US bombers, as alluded to in the article.)
I'm guessing it's actually akin to "hangar queen," an aircraft that's grounded for maintenance to an unusual extent [1].
EDIT: Or, it might be an analog to a tramp steamer, i.e., a merchant ship that goes from port to port to port carrying whatever cargoes the ship's officers can scare up as they go. [2]
"Tramp" here probably means harlot (consider the cheesecake pinup nose-art common on WWII-era US bombers, as alluded to in the article.)