When these two braces are in position the next matter that calls for the attention of the constructor is the matter of getting into position at the two outer extremities of the propeller brace bearings for the propellers. For this purpose two pieces of ³⁄₃₂nd inch brass tubing, each ³⁄₄th of an inch long, should be used, and should be fastened to the underside of the propeller brace, at each extremity of that brace, by the use of thread and glue. Sometimes greater efficiency is secured by putting these pieces of bronze tubing about ¹⁄₄″ from the end. Some model constructors make a very neat jointure here by soldering the piece of tubing to a strip of thin brass, which is bent over the end of the propeller brace and bound and glued thereon. In fastening the bronze tubing to the propeller brace it should be soadjusted that it will run parallel to the side members of the frame and will therefore offer the least possible resistance to the shaft of the propeller when the rubber strands have been attached.
When the frame has been completed a coat of shellac should be applied to the entire structure to render it damp-proof.
Theproper assembling of the parts of the model is as essential to good results as is the designing and making. Parts, although properly made, if improperly placed in relation to each other will very often lead to trouble. Therefore very great care must be exercised in the assembling process.
When all the parts have been prepared and are ready to be assembled the first thing that should be done is to mount the propellers in position. This must be done very carefully on account of the fact that the propeller shafts are easily bent and if bent the result is considerabletrouble, for such a bend in the propeller shaft will cause the propeller to revolve irregularly with a consequent loss of thrust. Before inserting the propeller shafts in the tubing 4 washers each ¹⁄₄″ in diameter should be cut from hard metal, and a hole large enough for the propeller shaft to pass through should be bored in the center of each washer. The metal washers should be passed over the straight ends of the shafts which extend from the rear of the tubing, after they have been inserted in the tubing, and in this manner the cutting into the hubs of the propellers which would follow is avoided. The propellers are now to be mounted and this is accomplished by allowing the ends of the shafts, which extend out from the rear of the tubing, to pass through the hole in the hub of each propeller. In mounting the propellers it is absolutely necessary to have the straight edge of the propellers to face the point or front end of the model. The propeller shown inFig. 4 of diagram 1, should be mounted on the left side of the frame to revolveto the left, while the propeller shown inFig. 1should be mounted on the right side of the frame to revolve to the right. When the propellers have thus been mounted the one-half inch of shafting which extends out from the hubs of the propellers should be bent over to grip the propeller hub and thereby prevent the shaft from slipping during the unwinding of the rubber strands. For the reception of the rubber strands to provide motive power a hook must be formed in each shaft and this can be done by holding securely that portion of the shaft which extends toward the point of the model, while the end is being formed into a hook as illustrated indiagram 7.