NACA-TN-3615

Abstract

An experimental investigation was made to determine the scale effects of the forces from water spray generated by a flat rectangular planing surface and impinging on a collector plate representative of an aerodynamic surface or other part of a water-based airplane. Lift and drag forces on the flat rectangular planing surface and on the spray-collector plate were measured. Underwater photographs of the wetted planning area and photographs of the spray generated by the planing surface were made. Two sizes of models were tested. The small model consisted of a flat rectangular planing surface with a 2-inch beam and a flat rectangular spray-collector plate 16 inches long and 10.67 inches wide. The large model was geometrically similar to the small model and was five times its linear dimensions. Tests were made with the collector plate in two vertical locations, 1.0 and 1.5 generator beams above the free water surface. The trim of the planing surface was set at 9^o, 15^o, and 20^o, and wetted-length-beam ratios of 1.0, 1.5, 2.0, and 2.5 were tested at towing speeds from 10 to 80 feet per second. <br>The results of the investigation show that impinging-spray lift forces can be scaled by the conventional Froude relations. The small-model-spray drag forces, however, were found to be higher than those of the large model when scaled by the conventional Froude relations; thus, a Reynolds number effect on spray drag was indicated. By using an empirical method for correcting the spray friction drag coefficients on a Reynolds number basis, reasonable agreement with the Schoenherr line was generally obtained.