Two-dimensional control characteristics

Abstract

The design of lifting surfaces for aeroplanes depends fundamentally on two-dimensional data for the aerofoil sections, with flaps where necessary for control. Data of this kind are required for the use of designers, and for the development of methods of calculating control characteristics and stability derivatives for finite wings. Researches on the lift, pitching moments, and hinge moments of aerofoils with plain flaps have been carried out at the National Physical Laboratory at a Reynolds number of about 10 6. The results of the experiments have been presented in a generalised form, which shows promise of being applicable over a wide field. The generalised curves have been tested as far as possible from other sources, including some tests made on one of the National Physical Laboratory sections in a Royal Aircraft Establishment Tunnel at Reynolds numbers up to nearly 10 7. It appears that a suggestion due to Preston that the ratio of experimental lift slope to the theoretical value, corresponding to the Joukowsky condition of flow past the trailing edge, provides a criterion giving the combined effects of Reynolds number, transition points, and aerofoil shape, and is a very usefnl starting point for the estimation of control characteristics. The generalised charts in this report are intended for the estimation of hinge-moment and pitching-moment derivatives from the flap/chord ratio, E after al/(a~)T has been determined from a special figure. The latter figure (Fig. 14) is a key to the whole process, and it would appear to be very desirable to improve its accuracy and usefulness by further experiments on two-dimensional lift slopes of thin wings at high Reynolds numbers.