The full-scale air drag of some flying-boat seaplanes

Abstract

An analysis has been made of the full-scale measured drag and lift performance, data available on the Sunderland, Solent, Shetland, Sealand, Saro E.6/44 and Princess boat seaplanes, which all have hulls of fairly orthodox length/beam and fineness ratios but with different degrees of aerodynamic fairing. The drag coefficient and profile drag show progressive decreases from the order of 0.033 to 0.018 and from 1.5 lb to 0.33 lb per 100 lb of all-up weight respectively, the best seaplane being the Princess. The value of the extra-to-induced drag coefficient k, at 1.1 is generally good for all the aircraft and extends up to a C~ of the order of 1.0. This drag reduction is caused by improvement in hull design, reduction of drag with change of propulsion unit from propeller reciprocating to propeller turbine and turbine jet, and also with increase of size. The hull drag is of the order of 0.22 of the total profile drag for all the aircraft but the ratio of the turbulent skin-friction drag of the idealised wing, hull and tail unit to the actual profile drag, increases to 0.73 for the Princess from 0.4 for the Sunderland. Further drag reductions would be possible if full use were made of recent methods of reducing hult air drag still further by detail fairing and increase of length-to-beam ratio.