The Drag of Streamline Bodies: The Relative Importance of Skin Friction and Pressure in Relation to Full‐Scale Design Available to Purchase

THE drag of a streamline body, such as an airship hull or an aeroplane fuselage, with its axis in the direction of the relative wind, is almost entirely due to skin friction. The drag component clue to surface pressure is, in general, small and relatively unimportant. Unfortunately, in the range of Reynolds numbers obtainable in most wind tunnels, the drag due to skin friction is abnormally sensitive to the degree of initial turbulence in the wind tunnel stream and to the shape of the model, particularly near the bow. Wind tunnel tests on models of airship hulls at a Reynolds number RL= U0L/v (where L is the length of the model and Uo the velocity in the free stream) of the order of 10° show wide variations in the values obtained for the drag coefficients of the same model in different wind tunnels or for different models in the same tunnel. At Reynolds numbers of about 4 × 108, appropriate to a full‐scale airship, it is impossible to carry out a reliable series of tests, but there is reason to believe that careful streamlining is not important and that a shape which is usually considered a “poor” streamline will have as low a resistance on the full scale as the shapes adopted for “R100” and “R101,” which, in the wind tunnel, appeared to be the best obtainable. From the structural point of view the “good” streamline shape proved to be a distinct disadvantage owing to the restricted gas volume in the bow and stem and the consequent lack of lift to balance the weights of fins and mooring gear, which produced increased bending moments throughout the ship.