Fig. 3. Comparison of drag coefficients of cavities and solid projectiles of the same shape.

Comparison of the variation of the drag coefficient C_D with Reynolds number Re for (i) lower data set: gas cavity in 21°C water around superhydrophobic steel spheres of diameter D_S = 15, 20, and 25 mm (solid red squares) and around Leidenfrost steel spheres at T_S = 400°C in 95°C water of diameter D_S = 10, 15, 20, and 25 mm (solid red triangles), and (ii) upper data set: the drag on solid replica projectiles: D_P = 25 mm, L_P/D_P = 4.5 containing different weights in 21°C water (solid blue squares) and 95°C water (solid blue triangles). Side images are snapshots of the falling projectile and sphere-in-cavity from movie S4. Fins on the solid projectiles were added to ensure rectilinear free fall. Their effect on the magnitude of the drag coefficient is estimated to be less than 10%.