Penguin Swimming. I. Hydrodynamics

Drag forces acting on the body (parasite drag) of a Humboldt penguin (Spheniscus humboldti) were determined by towing a cast of a wingless carcass. On the surface Dₚ₋ₛᵤᵣ = 2.27 Uₒ2.55 (Dₚ₋ₛᵤᵣ = parasite drag on the surface, N; Uₒ = towing speed, m s⁻¹) and submerged Dpm-sub = 1.48 Uₒ2.0 (Dpm-sub = parasite drag for submerged model). The minimum drag coefficient, 1.1 x 10⁻², approximates that of a live macaroni penguin (Eudyptes chrysolophus) but is higher than that of a streamlined form with the same diameter:length ratio. The wingbeat was analyzed using high-speed film of submerged swimming Humboldt penguins. Wing data and parasite-drag data were used to compute the lift, thrust, and drag forces of a swimming penguin. Wingbeat thrust was computed using both blade element analysis (which required wind tunnel tests on penguin wing models) and lifting surface theory. Blade element analysis gave remarkably more reasonable results, which were used for subsequent computations. Total thrust (TT) from the wings is equivalent to total drag (DT) of a Humboldt swimming submerged and has the estimated relationship to swimming speed (Ub) Of DT = TT = 2.68 Ub2.0