There are four kinds of propellers:
1. Propellers carved out of solid and laminated blocks.
2. Metal propellers with curved or twisted surfaces.
3. Built up propellers. In this type a small block is used as a hub, and the wood or metal fans are projected out from this. The fans are attached on the diagonal.
4. Propellers made of pressed wood veneer. These are excellent, but require more skill and more apparatus to make.
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 3/4"x1 1/2"x6", Fig. 244. Draw the diagonals, as in Fig. 245. With a radius of 1/4", 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.
The principal objection to the metal propellor 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.
The veneer propeller must be steamed and pressed. This is by far the most difficult to make. The 1/16" hardwood veneer is the best. The propeller is not reinforced to make up for the extra thickness of the carved propeller, but is of uniform thickness thruout. The veneer is first cut to shape in outline and then is steamed and twisted to shape. Fig. 255 shows a pattern for a propeller blade. The veneer should be steamed or soaked in hot water until the wood is very pliable and soft. A form should be ready so as to get both wings with equal twist from the central portion. I will suggest one, others can be devised. A clamp is necessary for the center, which may be made as follows: take a one-inch piece of wood about 1 1/4" wide and any length. Set it up edgewise. Make a cut 1/16" deep and one inch long across the upper edge, Fig. 256, and screw a small piece over top as a clamp. After thoroly steaming the propeller blade until it is very pliable, insert it into the clamp at the center and twist from the straight side, one fan up, the other down. It is not easy to get the two sides just alike, so I recommend the bending of one side at a time, and when that is dry, remove, and reverse the ends, being sure to keep the straight edge to the front, or the same as before. To be accurate, there must be a guide block to bend to. For a nine-inch propeller, a block like Fig. 257 would be about right. Place guide in position, press blank down to the oblique surface and secure there until dry. Repeat for the other end. It will be seen that the guide block and clamp are both secured to a board for a base; they may be secured to a table or bench-top. A clamp might be devised also that would hold the propeller in a vertical position with guide blocks on either side of center so as to bend and secure both ends at the same time.
Figs. 255, 256, 257, 258.
Another way to bend propellers is to clamp the center of the blank in a vertical position, and with two clamps made by sawing into the ends of two pieces of wood, Fig. 258, a cut wide enough to take the thickness of the blank, and deep enough for the width, bend one blade forward and the other back, Fig. 259. The small clamps on the propeller blades should be placed at equal distances from the center, and should be given an equal amount of twist. The small clamps on the blades will not be forced over until they touch the base, so blocks of equal size should be used as stops in the operation of twisting. The clamps should be secured in the last position by means of cord to the base until the propeller is dry.
Still another way to attain the twist in veneer propellers, would be to have two blocks gouged out to the proper shape, one just fitting in the other. After the propeller is shaped in outline and steamed, it is placed between the two blocks, which are in turn clamped firmly together until propeller is dry.