_The carved out propeller_ is the one most generally used and is not only a good exercise in modeling with a knife, but is a good serviceable kind. There are a number of types of propellers, named mostly by men who have designed them. For simplicity in laying out and carving, I like the Langley type. A rectangle is made of wood, say ¾” × 1½” × 6”. Fig. 244. Draw the diagonals, as in Fig. 245. With a radius of ¼”, and center at the intersection of the diagonals, draw a half-inch circle. Connect the diagonal lines and the circumference of the circle, as in Fig. 246, and cut down to the outline as it now appears. The blank is now as shown in Fig. 247. We will now take off two big slices, not all in one cut, but in several. Fig. 248 has the dotted lines showing the depth to be cut, and Fig. 249 shows these same parts cut away. Now cut away _x_ and _x_ until the blade is curved back to edges _z_ and _z_. The cut away portions will be as in Fig. 250. Cut the opposite side the same way, and cut away the back corners a little, giving the result as shown in Fig. 251. Sandpaper well and shellac. Drill hole carefully for the propeller shaft. [Illustration: FIG. 252.] [Illustration: FIG. 253.] [Illustration: FIG. 254.] The principal objection to the metal propeller is the bending that is liable to occur when the model lights, unless there are lighting devices underneath, and they all add weight. The hub propellers may have metal or hardwood veneers for fans. The hub may be round or square; see Figs. 252 and 253. Very good propellers may be made in this way. Extra curvature of the outer ends of the fans is possible, Fig. 254.