Measurement of the Aerodynamic Forces on Oscillating Aerofoils: A Survey of Techniques Used for the Experimental Determination of Aerodynamic Derivatives for Flutter Calculations

AT the present time it is a general practice to make extensive investigations of the flutter and oscillatory stability characteristics of all prototype aircraft at an early stage in the design. So far as theoretical investigations of these characteristics are concerned there is often considerable uncertainty as to the values of the aerodynamic coefficients to be used, for there is evidence that measured and theoretical coefficients may differ considerably. Measured values of the coefficients are therefore required both for direct use in calculations and as a check on the theoretical coefficients, and also to provide a guide in the development of more precise theories. Unfortunately the wide variations in wing plan forms and the rapid increase in flight speeds which have occurred in recent years have meant that experimental work in this particular field has not kept pace with development and the designer is faced with the problem of ensuring the safety and operational efficiency of his aircraft using theoretical coefficients whose values may be unreliable.