In this paper we investigate the unsteady aeroelastic response of a contrafan stage using nonlinear time-integrated RANS equations and multichorochronic boundary conditions which are able to propagate multiple periodic perturbations with uncorrelated frequencies. The objective is to model a single passage in each blade row to reduce the computational cost and to take into account both unsteady phenomena relative to the blade passage of the neighboring blade row and to the vibration induced by the blade deformations. Numerical comparisons are performed between a full annulus reference computation of a radial slice and the present multichorochronic simulations on a single passage to check the quality of the approximation. The influence of several parameters like the number of harmonics or spinning modes is investigated. Particular attention is finally paid to the approximation of the generalized aerodynamic forces from which the aeroelastic stability can be assessed.