The fuselage of a helicopter is strongly affected by the rotor and its wake under hovering and low-speed forward flight conditions. Unsteady loading is observed on the fuselage surface owing to the blade passing effect and periodic collision of the wake vortices. Panel and vortex methods were combined for simulating rotor- fuselage aerodynamic interaction. Although the panel method involves the use of Bernoulli's equation to obtain the surface pressure, it is difficult to consider the increase in stagnation pressure in the vortical flow region under the rotor. In this study, an integral solution of the Poisson equation was adopted to calculate the pressure at the surface of the fuselage. The flow around the Georgia Institute of Technology's rotor-fuselage model was simulated to demonstrate the increase in stagnation pressure along the topline of the fuselage, during which unsteady loading caused by tip vortex impingement was observed. The ROBIN (rotor body interaction) model, which considers a generic helicopter fuselage, was also used to analyze the unsteady pressures at the top and the side of the fuselage. For the models, the Poisson equation was found to accurately predict both unsteady pressure fluctuation and stagnation pressure increase on the fuselage in the presence of the rotor wake without any special treatment.