Development of 3-component force-moment balance for low speed water tunnel.

Abstract

An effort is made to develop a new 3-component force-moment balance, which is capable of measuring lift force, drag force and pitching moment of a model mounted in the water tunnel. The concept used in the balance design is the bending- beam principle. The forces acting on the spring element cause strains on its surface, which are measured by strain gauges. Since strain yielded by the axial force is usually very small, therefore it is not practical to measure axial force using strain gauge directly to sense the strain in axial direction. The main idea of the new balance design is to translate all desired forces (lift and drag) in such a way that they yield bending strain at selected strain-gauge station. This is done by using a bending balance geometry. Under this apparatus, the model wing is mounted at one of its end to the bending balance. The corresponding Lift, Drag forces and Pitching moment are translated into moments at the other end of the balance, and can be measured from sets of strain gauges in bending mode (twisting mode for pitching moment). Example readings are presented in this paper.