Wind-tunnel tests on seaplane hulls in the R.A.E. 5-ft diameter open jet tunnel and the N.P.L. compressed air tunnel

Abstract

Results of research work done in this country and the subject matter of Refs. 1 to 4 on the measurement and analysis of the air drag of seaplane hulls are collected together in this report. The data consist of the results of systematic tests made in the 5-ft Diameter Open Jet Tunnel of the Royal Aircraft Establishment and in the Compressed Air Tunnel of the National Physical Laboratory. These tests were conducted to find out the origin and order of the component drags of a hull and to determine in what way the hull drag differed from that of an equivalent body of revolution. Tests were made over Reynolds numbers ranging from the order of 2 to 60 x 10power6 in order to examine scale effect as far as possible, and a few tests were made to determine the possible effect of controlling boundary-layer transition. Otherwise all tests were made transition free. Subsequent to the systematic tests, tests were made on a specific hull form to investigate the form of step fairing designed for the Princess flying-boat, which form may be regarded as the best so far applied to hulls of contemporary fineness ratio and beam loading. The results show that the air drag of the hull form need not exceed 1.05 to 1.10 times that of the body of revolution which corresponds to it in length and surface area, if the drag of the body of revolution is estimated to consist only of skin friction with fully turbulent boundary layer and the pressure drag corresponding to its fineness ratio. This hull drag should be obtainable at all Reynolds numbers likely to be achieved full scale. Further work should be done in the Compressed Air Tunnel to measure the effect of using higher fineness-ratio hulls and new forms of main-step and afterbody shape.