A mass flow sensor for bulk flow measurements is designed. The sensor consists of a curved chute and the force executed by the flow on the chute is a measure for the force. By properly selecting the projection angle of the force, i.e. the direction in which the force is measured, the sensor can be made almost independent of the friction coefficient of the bulk. The selection of the projection angle involves an optimisation problem. To carry out the optimisation, a physical model of the differential force is derived. The differential force is the force executed on the chute by an infinitesimal mass. Based on the model of the differential force, a starting value for the optimisation process is computed. After the optimisation the influence of friction on the measurement is less than 0.5% per 0.1 change of the friction coefficient. For some installation conditions, the effect of friction on the force measurement can be completely eliminated. (C) 2003 Silsoe Research Institute. All rights reserved.