A hardpoint, or weapon station, is any part of an airframe designed to carry an external load. This includes a point on the wing or fuselage of military aircraft where external ordnance, countermeasures, gun pods, targeting pods or drop tanks can be mounted.
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Large missiles and rockets are typically mounted on rail-type launchers and are propelled clear of the aircraft under the power of their own rocket engine. The exceptions are aircraft such as the F-4 Phantom II, the F-18, and the Panavia Tornado ADV that have missiles that are semi-recessed into the fuselage to reduce drag, and hence use ejector launchers that first propel the missile clear of the aircraft before igniting the motor.
Free-fall stores and sometimes missiles and rockets are suspended from an ejector rack, which may be an integral part of or mounted on a pylon, which is in turn mounted in the hardpoint. The pylon is designed to position the rack and its stores to keep them clear of control surfaces and position them close to the aircraft's center of gravity. The modular separation of the pylons and racks simplifies maintenance and allows for upgrades and modifications.
The mechanical interface between the rack and various stores is standardized so that a single type of rack can carry different stores. With the aid of a multiple-ejector rack, an aircraft may carry several weapons on one hardpoint, subject to various considerations of clearance, weight, drag, radar signature, and technological limitations.
For NATO-standardized stores, the stores are mounted onto the rack by means of lugs mounted on the store, spaced either 14" apart for lighter stores or 30" apart for heavier items. These lugs are engaged by L-shaped hooks in the rack. The rack is equipped with explosive cartridges to disengage the suspension hooks and propel the store clear of the aircraft in a consistent manner to aid the precision of unguided gravity bombs. Some racks contain an auxiliary cartridge in the event that the primary cartridges fail to fire. The rack will also have accessories such as arming solenoids to pull arming wires from fuzes, and ports for data, video or electrical fuzing. To keep stores from rocking sideways as the aircraft maneuvers, sway braces are provided to steady the stores. These may be automatically or manually adjusted.
Wet hardpoints refers to hardpoints which are plumbed and thus capable of interfacing with drop tanks mounted on it, to feed fuel from these external fuel tanks and provide additional fuel capacity for the aircraft. This extends the aircraft's flight range and duration for extended operations. These drop tanks can then be jettisoned if there is a need to reduce drag or weight during the flight. While wet hardpoints are capable of using drop tanks, they may also mount weapons as with other 'dry' hardpoints. In particular, the Matra JL-100 represents this as a pod that contains a drop tank in the rear and a rocket pack in the front.
Any hardpoints on swing-wings must swivel to minimize drag, such as on the General Dynamics F-111 and the Panavia Tornado. Alternatively, the hardpoints can be placed on a rigid part of the aircraft, such under the fuselage or on fixed wing gloves as on the F-14 Tomcat and Mikoyan MiG-27. On the F-111 not all hardpoints can be used if the plane is to operate with fully swept wings because of the narrowed spacing between pylons.
Hardpoints on aircraft are numbered from left to right. For example, the Boeing F/A-18A/B/C/D family has nine weapons stations:
By extension of the common usage, the word hardpoint is sometimes used to refer to a point on any vehicle where weapons or other accessories can be attached.