Studies on Rudders with Flap

Abstract

This paper deals with experimental results of three types of rudders with flap i. e. flap ratio =0.5, 0.25 & 0.165. Their dimensions are 200 mm in chord, 40 mm in thickness and the aspect ratio is unity. They were tested at a speed of 0.69 m/s with a recirculating water channel whose dimensions at the test section are 1.2 m × 0.8 m.The results are as follows;(1) Increment in lift coefficient is almost linear with respect to flap angles.(2) Separation depends only on the angle of the main part and is independent from the flap angle.(3) Change of the centre of pressure is a function of the ratio between main part and flap angles.(4) The twisting moment of the rudder stock of a main part can be decreased by selecting the position of a rudder stock suitably.(5) The moment of the rudder stock of the flap becomes larger according to the area of the flap.(6) Best performance is shown by a rudder of flap ratio =0.25 and of rudder angle ratio (=flap angle/main part angle) =2, which is twice as good as that of an ordinary rudder without flap.