[Ill.u.s.tration: FIG. 47.--How the Motors are Connected to Winder for Winding.]

Of course the rubber motors must be twisted an equal number of turns, in order to make the propellers work the same, and this is usually done with an ingenious winder made from an egg-beater, which winds both motors simultaneously.

=The Home-made Motor-winder= shown in Fig. 45 is made from a Dover egg-beater (Fig. 46). To convert the egg-beater into a winder, it is necessary to cut off the loop ends and the center pivot wires on which the loops turn. Then bend the cut-off ends of the loops into hooks, and punch them to fit over the pivot wire ends, as before (Fig. 45). The ends of the pivot wires must be riveted to keep the hooks in position.

Figure 47 shows

=How the Egg-beater Winds the Motors=. While an a.s.sistant supports the model by the propeller end, you remove the motor rings from the hooks on the bow of the fuselage, and slip them on to the hooks of the egg-beater. Then you turn the crank of the winder, counting the turns as you do so, and when you have wound the motors as far as you wish, slip off the motor rings, and slip them back on to the bow hooks of the model aeroplane. Motors of models like that shown in this chapter are wound one-thousand turns or more for each flight.

=Wind the Motors Slowly=, especially after the first row of knots begin, as it puts the rubber to the least amount of strain by doing this. Quick winding not only strains the rubber but makes the knots form in bunches, and uneven winding, of course, produces an uneven unwinding.

The propellers must be held after the motors have been wound, to keep them in check. Figure 34 shows

=The Position to Take for Launching a Model= from the hand. The machine should not be thrown forward, as the movement would cause too great a disturbance of the air, resulting in the machine losing its stability, and probably upsetting. The best method is to give the model a slight push that will start it off at a speed a trifle under that produced by its propellers.

CHAPTER IV

A HOME-MADE TOY MOTOR-BOAT

The toy motor-boat shown in Figs. 48 and 49 is propelled by a tin propeller run by a rubber-band motor. A handful of rubber-bands will cost only a few cents, and the rest of the working material can be picked up at home.

[Ill.u.s.tration: FIG. 49.--The Completed Motor-boat.]

[Ill.u.s.tration: FIG. 50.--Stern, with Motor in Place.]

=Prepare the Bottom of the Hull= out of a piece of wood 1 inch thick, making it of the shape and dimensions shown in Fig. 51. Be careful to curve the side edges the same. Use a saw for cutting out the piece, then smooth up the edges with a plane and sandpaper. The stern should be sawed off on a bevel as shown in Fig. 52.

[Ill.u.s.tration: FIG. 51.--Diagram of Hull.]

=The Sides= of the hull (_B_, Figs. 52 and 53) are thin strips 2-1/2 inches wide. Nail one to one edge of the bottom block, then saw off the bow end on a line with the bow of the bottom block, and the stern end on the same slant as the bevel cut on the stern of the bottom block. With one piece in position, nail on the second side and trim off its ends. If you have any difficulty in making a neat joint between the bow ends of sides _B_, take a piece of tin from a can, bend it around the bow, and tack it in place as shown in Fig. 48. The stern piece (_C_, Figs. 53 and 54) should be cut next, to fit the slanted ends of the sides.

[Ill.u.s.tration: FIGS. 52 and 53.--How the Hull, Sides, Stern and Deck Pieces are a.s.sembled.]

=The Deck= (_D_) extends from the bow almost to the center of the boat.

Its top surface should taper in its length and curve from side to side.

The piece may be whittled or planed to this shape. Fasten it with brads to the top edges of the sides of the boat.

[Ill.u.s.tration: FIG. 48.--LAUNCHING THE TOY MOTOR-BOAT.]

=To Complete the Boat=, go over the work carefully, trim off all projecting edges, drive nail heads beneath the surfaces, putty nail holes and cracks, and give the wood two coats of paint of whatever color you want to have the motor-boat.

=The Propeller= (_E_, Fig. 54) is cut from the side of a tin can. Cut a piece 3 inches long and 3/4 inch wide, round its ends, and with the point of a nail pierce a hole through it each side of the center of the length of the piece (Fig. 55). To finish the propeller, it is only necessary to take hold of the two ends and twist the piece into the shape shown in Fig. 56.

=The Propeller-shaft= requires a short piece of wire with one end bent into a hook (_F_, Fig. 56). Stick the straight end of this shaft through one hole in the propeller, and the hooked end through the other hole, then twist the hooked end over on to the main part of the shaft, as shown in Fig. 57. Make a tight twist so the propeller will be held perfectly rigid on the shaft.

=The Bearing Plate= _G_ (Figs. 54 and 58) supports the propeller. Cut it out of a piece of tin 1-1/2 inches wide by 3 inches long, bend it in half crosswise to give it stiffness, and then bend it lengthwise to the angle shown so it will fit over the slanted stern of the boat. Punch two holes through the upper end for nailing the plate to the stern, and a hole at the lower end for the propeller-shaft to run through.

=For a Thrust Bearing=, slip a couple of beads over the propeller-shaft, between the propeller and bearing plate _G_. Probably you can find gla.s.s beads in your mother's b.u.t.ton bag.

[Ill.u.s.tration: FIG. 54.--Longitudinal Section of a.s.sembled Motor-boat.]

[Ill.u.s.tration: FIGS. 55-59.--Details of Propeller.]

[Ill.u.s.tration: FIG. 60.--Rubber-band Motor.]

After slipping the beads on to the shaft, and sticking the shaft through the hole in bearing plate _G_, bend the end of the shaft into a hook; then screw a small screw-hook into the bottom of the hull, at the bow end (_I_, Fig. 54), and you will be ready for

=The Rubber-band Motor.= Rubber-bands about 1-1/2 inches in length are best for the purpose. Loop these together end to end (Fig. 60) to form a strand that will reach from hook _I_ to the hook on the propeller-shaft; then form three more strands of this same length, and slip the end loops of all four strands over the hooks.

=To Wind the Motor=, give the propeller about one hundred turns with your finger; then, keep hold of the propeller until you launch the boat.

There are many ways of elaborating upon the design and construction of this toy motor-boat, but, having given the necessary instructions for building a simple model, I am going to leave further development for you to work out. Here is an opportunity for you to use your ingenuity.

Devise an adjustable rudder, add a keel, finish off the c.o.c.kpit with a coaming, install a headlight made from a pocket flashlight--in fact, see just how complete a motor-boat model you can build.

CHAPTER V

HOME-MADE TOY WATER-MOTORS

You can own a water-motor like the one shown in Fig. 61, because its construction requires nothing but easily obtained materials.

[Ill.u.s.tration: FIG. 61.--A Varnish-can Water-motor in Operation.]

=The Case= of this water-motor is made of an empty varnish can--preferably one of gallon capacity. Nothing better could be desired.

The tin can makes a light-weight compact case; the spout in the top is in just the right place and of the right size to receive the water power from a faucet; and as the water connections can be made tight there is no possibility of water splashing on to the floor--a big argument in your favor when seeking permission to use the motor in the bath-tub, wash-basin, or kitchen sink.

You can get an empty varnish can from any painter, or at a paint store.

The first step in converting the can into the motor case consists in removing the bottom. You will find this soldered in place, in all probability, and it can be removed quickly by holding the can over the flame of a gas burner until the solder melts, when a few taps upon the edges will cause the piece of tin to drop off.

[Ill.u.s.tration: FIG. 62.--The Completed Varnish-can Water-motor.]

=The Water-motor Wheel= is shown in the cross-sections of the water-motor (Figs. 63 and 64), and Figs. 65 to 67 show its details. The diameter of the wheel should be about 1/2 inch less than the inside width of the can. In the model from which the drawings were made, this measurement is 5-1/2 inches. Cut the two side pieces of the wheel out of a piece of cigar-box wood, and bore a 1/4-inch hole through the center of each for the wheel axle. Fasten a spool to the center of one side piece for a pulley-wheel (Fig. 66).

[Ill.u.s.tration: FIGS. 63 and 64.--Sections through Water-motor Case.]

=Prepare Eight Paddles= 1-3/4 inches wide and 2-1/2 inches long, out of cigar-box wood. Locate the positions for the ends of the paddles, upon the side pieces, by drawing a horizontal line, a vertical line, and two diagonal lines at angles of 45 degrees, through their centers. This will simplify the matter of s.p.a.cing the paddles equidistant from one another (Fig. 67). Use brads for fastening the side pieces to the paddle ends. Those removed from the cigar boxes will do.

=The Wheel Shaft= should be a trifle shorter than the inside width of the can, and enough smaller than the 1/4-inch hole in the wheel side pieces so the wheel will turn freely. Locate the centers for the axle upon the two sides of the can, in the proper position so there will be the same margin above and at the ends of the wheel. Drive a nail through each side of the can into the axle end.

[Ill.u.s.tration: FIG. 65.--The Completed Water-motor Wheel.]