A proposed apparatus for measuring oscillatory aerodynamic derivatives

Abstract

This Report describes the principles to be used in designing an apparatus, including half-model of an aircraft, for measuring longitudinal oscillatory aerodynamic derivatives in the R.A.E. High Speed Tunnel. The model is to be oscillated inexorably in pitch about two axes, one near the leading edge and one near the trailing edge. The scheme has the following novel features: (i) The 'fixed parts' of the oscillating mechanism are to be carried on a floating 'raft', the alternating aerodynamic force on the model being deduced from the force required to hold the 'raft' in position. (ii) The in-phase and quadrature components of the force on the 'raft' will be found by measuring the d.c. output of a strain-gauge bridge powered by an a.c. supply synchronous with the inexorable oscillation.