This book chapter is a discussion of the very fundamental topic of how a fan sucks air from its leading edge when rotated in the correct direction. The explanation is based on the fundamentals of the velocity triangle. The flow pattern established over the airfoil or blade at a given angle of attack creates Lift and Drag. The argument is that, from the relative frame of reference, the flow behavior on the fan’s blade is analogous to conventional flow over a wing. The angle of attack in the relative frame will govern the forces acting on the fan’s rotor. It is shown with the help of experimental data that air will try to enter the fan from the side, which offers lesser resistance, which, under normal operation, is from the leading edge of the fan. For completeness, this study also covers different configurations of the blade stager angle and the direction of the blade velocity.