The Leishman-Beddoes (L-B) unsteady and dynamic stall model is applicable to the medium Mach numbers(Ma>0.3)

and some inconsistent problems for predicting airfoil airload when comparing with airfoil airload test data at low Mach numbers (Ma<0.3)

so firstly the unsteady and dynamic stall aerodynamic behavior of airfoil at low Mach numbers was investigated

secondly the modified L-B model was set from the viewpoint of the variation of the flow on the airfoil surface

finally the comparisons between the modified L-B and airfoil airload test data at low Mach numbers show that the modified L-B model with state space formulation is accurate and can be used to predict the airfoil airload at low Mach numbers

and also it can be easily incorporated into a helicopter comprehensive code.