The 3 DOF Helicopter system is a simplified helicopter model that is well-suited for teaching intermediate to advanced flight dynamics and control concepts relevant to tandem rotor helicopters. It models three degrees of freedom - pitch, yaw, and roll - through differential equations. A PI controller was designed for the yaw axis to command a desired roll angle and travel rate. The 3 DOF Helicopter can be used for research in areas like adaptive control and nonlinear control.