Military aircraft utilize air-to-surface and air-to-air weapons to attack enemy targets. In the case of air-to-surface ballistic weapons, these typically consist of bombs, dispensers and missiles. These weapons tend to be large, approximately 8 to 15 feet long, and heavy, between 500 and 2500 pounds. Their size and weight can be determinative of aircraft design. For small aircraft, internal carriage of large numbers of these weapons is impractical. These aircraft normally carry their weapons or stores externally on hardpoints located on the wings or fuselage.
Generally, these weapons are designed for good aerodynamic characteristics when externally carried. The design considerations of many of these weapons, however, did not emphasize the reduction of the weapon radar signature or observability, as defined by the radar-cross-section of the weapon. For example, the radar-cross-section of these weapons can exceed the levels of the latest generation of fighter/attack aircraft (e.g., F-117, F-22, and JSF) and modified modern fighter/attack aircraft (e.g., F-14, F-16, and F/A-18E/F).
In addition to the surface texture and material of these weapons, other elements of these weapons increase the radar-cross-section. For example, many of these weapons are characterized by a nose tip or nose plug which is adapted to receive a large wrench in order to screw off the nose tip of the weapon to gain access to the interior payload. Due to this wrenching, sharp angles and flat surfaces are located at the nose tip which increase the radar-cross-section. In addition, these weapons typically have rear fins, which may be movable for aerodynamic control. These fin edges greatly increase the radar-cross-section of the weapon.
Accordingly, the carriage of these weapons significantly increases the overall radar-cross-section of the aircraft, and, therefore, the observability of the aircraft. Typically, aircraft radar observability impacts the mission success rate and survivability.
Large numbers of these weapons are currently held in inventory. While utilization of these weapons with their poor radar observability characteristics is undesirable, retro-fitting or modifying these weapons is a desirable option.
In addition to weapons, air vehicles may be required to externally carry other stores. These include, but are not limited to, fuel stores, sensor suites, communications stores (e.g., data link electronics, antenna, and the like), targeting pods, bivets, and counter-measures stores (e.g., chaff, flares, and the like). These other stores are subject to the same undesirable radar-cross-section characteristics as the above-described weapons.
Prior attempts to modify the radar-cross-section of these stores include the application of radar absorptive coatings or material. This approach is expensive, not only in terms of initial coating application costs, but costs due to inspection and maintenance in controlled conditions and associated extensive training.
Other approaches to reducing the radar-cross-section of externally mounted stores include significant alterations to the external shape of the store. Radar observability is a function of the radar signal which is reflected back to a radar detecting sensor which is usually located concurrent with the radar signal source (i.e., back scatter). The external shape of the store directly impacts the radar signal which is reflected back to the radar detecting sensor. Thus, the objective of shape alterations is to reflect a radar signal to desired direction (i.e., away from the radar detecting sensor which is usually located concurrent with the radar signal source). This approach is undesirable, however, due to the drastic change in the shape of the store. Significant alteration in the shape of a store, such as a weapon, triggers the Governmental requirement for a flight re-certification program for both the weapon and the aircraft. Such re-certification programs are undesirable due to cost limitations. Another approach used to reduce radar-cross-section of externally carried stores is to encase them in a pod, shell or shroud. These solutions have proven to be undesirable due to the weight and mechanical complexity associated with a pod which is permanently affixed to a wing or fuselage.
Additionally, launched stores, such as ballistic weapons, often employ aerodynamic control surfaces which are used to provide a desired flight performance characteristic. These aerodynamic control surfaces include strakes and wings. Radar-cross-section reduction approaches which utilize rigid pods or shells are additionally undesirable due to the potential interference with these aerodynamic control surfaces.
Accordingly, there is a need in the art for a system which is able to achieve the reduction of externally mounted store radar observability, is relatively low cost, does not interfere with the utilization of aerodynamic control surfaces mounted on the store, and does not significantly alter the shape of the store and aircraft, thereby requiring governmental fight re-certification.