I know drop tanks are used to extend the range on many fighter jets, but how often are they actually detached from the plane once empty? A lot of WWII movies and documentaries show tanks being dropped before entering combat, but I'm curious about more modern planes and non-combat conditions. Does the increased air resistance offset the cost of dropping the tank on say, a standard patrol, or are they landed and recovered with the plane and if so, are they re-used or simply scrapped?
In general, unless it's an emergency or needed for certain flight operations, the tanks are retained and flown back to base.
There are maneuvering limitations for carriage of certain stores on some aircraft. The F-16C/D for example limited maneuvering to +6.5/-3 Gs with stores on the inboard two pylons and/or centerline drop tank installed. If the aircraft was attacked by an offensive flight of enemy fighters, one of the first items prior to commencing ACM with the threat was to jettison stores on these stations. This allowed the aircraft to maneuver up to a maximum of +9 Gs as the fight commences.
Today's external tanks are not exactly cheap, so they are nearly always returned to base with the aircraft.
These tanks have "only" 2 drawbacks :
- They add some weight (slightly increasing fuel consumption and limiting aircraft maneuverability, or how much Gs he can take)
- They add some drag (slightly increasing fuel consumption and slightly decreasing performances like speed recovery, in case of a dogfight)
There are only 2 cases where the aircraft will jettison his external fuel tanks :
- They are engaged by hostile SAMs or aircrafts and have to perform evasive maneuvers / air combat maneuvers, they will get rid of anything they won't need to survive and that affects aircraft performances (drop tanks, air-ground armament ...) to optimize their chances to survive.
- Technical issue that would require clean wing / lighter aircraft (loss of thrust, landing gear issue, fuel leak ...)
Some aircrafts like french interceptor Mirage 2000-C have optimized fuel tanks (center line tank in this case), to affect as little as possible aircraft performances and allow max G once empty so they don't have to jettison it.