The results of theoretical analysis and experiment have validated that the axially induced velocity distribution at the upper and lower discs of the coaxial twin rotor system is similar to that of the single rotor in hovering and forward flights. In this paper

by introducing an interaction factor and extending the first harmonic nonuniform inflow Pitt-Peters model for the single rotor helicopter to the coaxial helicopter

a simplified and practical mathematical model for coaxial twin rotor loads is formulated. This model avoids the complicated analysis and numerical calculations of the vortex models or CFD methods for obtaining the axially induced velocity at the upper and lower discs. Moreover

it can be employed for coaxial helicopter flight dynamics numeral simulation. The forces and moments on the sample coaxial twin rotor hub are calculated with the help of the math model. The computational results are in good coincidence with those from Russian model.