A method for estimating the parameters of a linearized model of the fluidelastic forces in an array of cylinders is described. The behaviour of a tube on a flexible mount in the third row of an otherwise rigid 5 row normal triangular array, with pitch-to-diamter ratio of 1.58, has been investigated. The fluid stiffness and damping over a range of flow velocities has been estimated from experimental data. The results are then used to predict a stability threshold which is in agreement with previously published data for critical velocities. The damping in the flexible mount has been varied and shown not to effect the estimated fluid parameters.