To assemble the model, connect the forward ends of the sticks carrying the motors by a piece of reed bent to a half circle, by merely binding the ends firmly together. The sticks should diverge so that the propellers will be about ten inches apart, giving plenty of room for the propellers to turn without striking one another. Next fasten the larger plane in position across the top of the sticks, and about two inches away from the propellers, making the plane serve as a cross piece to hold them firmly in position. The strands of the motor should preferably be carried above the plane. This plan does away with the rear stick of the motor base, thus saving this weight. Adjust the parts very carefully, that the frame will be rigid enough to stand the strain of the motor. [Illustration: An Efficient Three-ounce Model.] The model will require careful adjusting to be brought to an even keel. The forward plane should be attached in such a way that it may be tilted up or down as desired. With care, the weight of the model may be brought within three ounces, although a fraction over will not matter. Models built on these lines have flown in a perfectly straight line for 900 feet. AN ALL-METAL MODEL FRAME. In a previous paper, it was suggested that the motor base be made of tubes of aluminum. The idea has been carried further, and attractive frames are now constructed in which not only the main frame is constructed of metal tubing, but the cross piece supporting the propellers and the braces as well are of the same material. The new metal, "magnalium," has been used successfully for this purpose. It is a trifle heavier than aluminum, but much stronger, and almost as easy to work. In England, the motor base is sometimes made of metal tubing one inch in diameter, and the rubber motor is passed through the tube itself. [Illustration: An All-metal Model Frame.] Such a frame may be made readily by one who has had no experience in tinsmithing or metal work. The metal frames are sometimes constructed by driving wooden blocks into the ends of the tubes and letting them project one-half an inch or more. The plug may be cut off flush, and the cross piece fastened by wire and stout nails through the cross tube into the plug of the main tube. A convenient brace may be constructed by cutting the tubes to the proper size, fasten the ends and pass the rivet through both tubes at the point of intersection, and screw the nut down firmly on the opposite side. Such a frame is practically indestructible. There is one possible drawback, however, in the tendency of the metal to bend if the rubber motor pulls too strongly. Once bent, it is difficult to get back into shape. This tendency may be overcome when twin propellers are used, by winding alternately, giving one propeller one hundred turns and the other propeller one hundred turns, then the first another hundred, and so on until the motor is wound up. The planes, propellers and skids may be of any reliable design.