IMPROVEMENT PLATE FOR SEMIBALANCED RUDDER

The semi-balanced rudder has its fixed portion in the upper part of the leading edge and incorporates a balance area without introducing a vertical gap when the rudder is laid over. However, it necessarily incorporates a horizontal break between the top of the balance area and the lower edge of the fixed portion, which has an undesirable influence on its characteristics. An experiment has been carried out using a small plate to seal off the horizontal gap on rudder section shape NACA 0015, which was then tested in a low-speed wind tunnel with a test section of 30 x 30 cm. Surface pressures on the rudder for various degrees of deflection angle were measured. It was found that, at a large deflection angle, the improvement in normal force by sealing off the horizontal gap is approximately 6% and the steamline pattern is improved, added to which the large variation of the centre of pressure of the semi-balanced rudder may also be reduced.