Kind of Material RequiredThere are three all-important features in fying machine construction,viz.: lightness, strength and extreme rigidity. Spruce is the wood generallyused for glider frames. Oak, ash and hickory are all stronger, but they arealso considerably heavier, and where the saving of weight is essential, thedifference is largely in favor of spruce. This will be seen in the followingtableWeigTensileCompressiveper cubic ft. StrengthStrength Woodlbs. per sq. in. Ibs. per sq in. Hickory12,0008,500oak5012,0009.000 Ash12,0006.000Walnut8,0006,000 Spruce5.000 Pine4.500Considering the marked saving in weight spruce has a greaterpercentage of tensile strength than any of the other woods. It is also easierto find in long, straight- grained pieces free from knots, and it is this kindnly that should be used in flying machine construction.You will next need some spools or hanks of No 6 linen shoe threadmetal sockets, a supply of strong piano wire, a quantity of closely-woversilk or cotton cloth, glue, turnbuckles, vamish, etcNames of the various partsThe long strips, four in number, which form the front and rear edges ofthe upper and lower frames, are called the horizontal beams. These areeach 20 feet in length. These horizontal beams are connected by uprightthe front edge, and six on the rear. They serve to hold the upper planeaway from the lower one. Next comes the ribs. These are 4 feet in length(projecting for a foot over the rear beam), and while intended principallyas a support to the cloth covering of the planes, also tend to hold the frametogether in a horizontal position just as the stanchions do in the verticalThere are forty- one of these ribs, twenty-one on the upper and twenty onthe lower plane. Then come the struts, the main pieces which join thehorizontal beams. All of these parts are shown in the illustrationsreference to which will make the meaning of the various names clear
Quantity and Cost of materialFor the horizontal beams four pieces of spruce, 20 feet long, 11/2nches wide and 3/4 inch thick are necessary. These pieces must bestraight-grain, and absolutely free from knots. If it is impossible to obtainclear pieces of this length, shorter ones may be spliced, but this is notadvised as it adds materially to the weight The twelve stanchions shobe 4 feet long and 7/8 inch in diameter and rounded in form so as to offeras little resistance as possible to the wind. The struts, there are twelve ofthem, are 3 feet long by 11/4 x 12 inch. For a 20-foot biplane about 20yards of stout silk or unbleached muslin, of standard one yard width, willbe needed. The forty-one ribs are each 4 feet long, and 1/2 inch square. Aroll of No. 12 piano wire, twenty-four sockets, a package of small coppertacks, a pot of glue, and similar accessories will be required. The entirecost of this material should not exceed s20. The wood and cloth will bethe two largest items. and these should not cost more than $10. This leavesS10 for the vamish wire, tacks, glue, and other incidentals. This estimateis made for cost of materials only. it being taken for granted that theexperimenter will construct his own glider. Should the services of acarpenter be required the total cost will probably approximate $60 or $70Application of the RuddersThe figures given also include theof rudders. but the detailsof these have not been included as this really complete withoutthem. Some of the best flights the writer ever saw were made by Mr. A Mrudder, properly proportioned and placed, especially a rear rudder, is ofgreat value to the aviator as it keeps the machine with its head to the windwhich is the only safe position for a novice. For intial educationalpurposes, however, a rudder is not essential as the glides will, or shouldbe made on level ground, in moderate, steady wind currents, and at amodest elevation. The addition of a rudder. therefore. may well be leftuntil the aviator has become reasonably expert in the management of his
Putting the Machine TogetherHaving obtained the necessary material, the first move is to have therib pieces steamed and curved. This curve may be slight, about 2 inchesfor the 4 feet. While this is being done the other parts should be carefullyrounded so the square edges will be taken off. This may be done with sandpaper Next apply a coat of shellac, and when dry rub it down thoroughlywith fine sand paper. When the ribs are curved treat them in the same wayLay two of the long horizontal frame pieces on the floor 3 feet apart.Between these place six of the strut pieces. Put one at each end, and each 41/2 feet put another, leaving a 2-foot space in the center. This will give youfour struts 4 1/2 feet apart, and two in the center 2 feet apart, as shown inthe illustration. This makes five rectangles. Be sure that the points ofcontact are perfect, and that the struts are exactly at right angles with thehorizontal frames. This is a most important feature because if your frameskews"or twists you cannot keep it straight in the air. Now glue the endof the struts to the frame pieces, using plenty of glue, and nail on stripsthat will hold the frame in place while the glue is drying. The next daylash the joints together firmly with the shoe thread, winding it as youwould to mend a broken gun stock, and over each layer put a coating ofglue. This done, the other frame pieces and struts may be treated in theame way, and you will thus get the foundations for the two planeAnother Way of Placing StrutsIn the machines built for professional use a stronger and more certainform of construction is desired. This is secured by the placing the struts fori allowing them in each instance to come out flush with the outer edgesof the frame pieces. They are then securely fastened with a tie plate orclamp which passes over the end of the strut and is bound firmly againstthe surface of the frame piece by the eye bolts of the stanchion sockets