Abstract: Based on the analysis of the difference between small scale unmanned helicopters and normal scale helicopters, the small scale helicopter was modeled as two rigid bodies: fuselage and main tail rotor. The dynamical model was deduced by Kane method, and another model considering the helicopter as one rigid body was also deduced for comparison. It shows that the kinematics and translational dynamics are the same, but they have different rotational dynamics. The response of the dynamics modeled as two rigid body is cosine while the response of the dynamics modeled as one rigid body is linear. The real flight experiments verify the validity of the model.