Evaluation of an Internal Balance-Supporting Bracket Simulating Lug Suspension for Captive Stores in Wind Tunnel Tests

Wind tunnel measurements of the aerodynamic loads acting on two store configurations supported in the external captive position on a 120-scale model of the F-4C aircraft have been made. The store models represented stable and unstable pylon-mounted configurations. Six components of forces and moments were measured using an internal strain-gage balance supported by a bracket extending through the upper surface of the store and attached firmly to the left inboard pylon of the aircraft. Two designs of bracket were used, one a solid blade with the appearance of an extension of the pylon, and the other fabricated to the same dimensions but ventilated by cutting a slot through the solid blade so that the remaining bracket material simulated suspension lugs. Measurable differences in forces and moments acting in the longitudinal plane of the store were detected for both stable and unstable stores. From an analysis of the force and moment measurements, it is probable that the pressure distribution over the after portion of a store is altered when using the ventilated bracket.