Blade tip clearance is one of the most critical factors affecting the flight safety of coaxial rigid rotor helicopters. To achieve high-precision calculations of blade tip clearance in forward flight, this study establishes a rotor/body coupling aeroelastic model based on 15-degree-of-freedom (15-DOF) medium-deformable beam and free wake model. Validation against the rotor natural frequency of XH-59A demonstrates a computational error that less than 5%, confirmed the accuracy of the forward-flight blade tip clearance prediction method. This study analyzes the influence of lateral differential control, pitch angle, and sideslip angle on blade tip clearance during forward flight. The results indicate that lateral differential control can effectively control rotor rolling moment, and lateral differential control serve as a reliable means to ensure safe blade tip clearance during forward flight. Additionally, a decrease in fuselage pitch angle during forward flight leads to more critical blade tip clearance conditions. An increase in sideslip angle affects the rotor lift offset and reduce blade tip clearance.