Aeroplane Construction and Operation

by John B. Rathbun

All steel tubing shall be thoroughly cleaned, slushed with mineral oil inside, and plugged at both ends by wood plugs impregnated with mineral oil or paraffine. All steel nuts, bolts, pins and cotter pins shall be protected by heavy nickel plating over copper. All wood members, especially faying surfaces, end grain butts, scarfs and joints, shall be protected against the access of moisture before final assembly by the best grade of varnish, or by impregnation by paraffine. All wood shall be straight grained, well seasoned, of uniform weight, and free of knots, pitch pockets, checks or cracks. Spruce to be of the very highest grade of selected straight, even grained, clear spruce. It shall be air seasoned, preferably for two years. Kiln dried wood is not acceptable.

It is highly desirable to have all bolts, pins, plate fittings and turnbuckle ends made of chrome vanadium steel (S. A. E. Specification 6.130), heat treated to obtain the best physical characteristics. All parts and fittings that must be bent shall be heat treated after all bending operations are completed, and by such a sequence of treatment as will produce the desired grain and toughness, and relieve all stresses due to the bending. This includes sheet and forged steel fittings, turnbuckle ends and bolts and pins. All steel parts and fittings submitted to stress or vibration shall be heat treated in such a manner as to produce the highest possible refinement of grain and give the greatest possible resistance to alternating and vibratory stresses. Where plate fittings are in contact with wooden members, sharp edges next to the wood shall be removed. In making up and connecting steel fittings, welding shall be used wherever possible. If impracticable to weld, and in such cases only, brazing will be used, proper heat treatment to be employed to restore strength and toughness of metal after such welding or brazing. Extreme care should be taken to avoid nicking or kinking any wire, cable or fitting. Fittings, sheet or forged, must be free from sharp corners and supplied with generous fillets.

In general the S.A.E. Standards will be acceptable, and these standards for screw threads shall be used wherever possible. U.S. Standard threads will be accepted where threaded into cast iron, cast aluminum or copper alloys. All nuts and pins must be provided with one or more positive and durable safety devices. In general, where it must be expected that a structural fitting will be disassembled a number of times during the life of the aeroplane, castellated nuts with split pins, in accordance with S.A.E. Standards, shall be used. Wherever this is not the case, pins or bolts shall be riveted in a workmanlike manner.

Seats shall be securely braced against both horizontal and vertical stresses. Arrangement and dimensions of cock-pits shall be as nearly as practicable to that indicated by the drawings (not published in this chapter). In addition, if practicable, the pilot should be provided with quick release arm rests. Sections of best grade of khaki on each side of seats, in which pockets are made, should be fastened to longerons and vertical posts in such a way as to be securely in place and yet readily detachable for inspection of structural wiring and fittings. Safety belts shall be provided for both seats and securely fastened. The belts shall safely support at any point a load of 2,000 pounds applied as in practice. Rubber shock absorbers in the safety belt system are considered to be an advantage. The quick release device shall be as indicated in drawings and shall reliably and quickly function. Seat pads shall be quickly detachable in order that they may be used as life preservers. They will be filled with Kapok or other similar material and covered with real leather to protect it against the action of salt water.

Suitable covers shall be provided over the top of the rear end of the fuselage. These must be easily removed and capable of being securely fastened in place during flight. Space shall be allowed in the body directly in the rear of the observer's seat for the stowage of the sea anchor. When in use, the sea anchor shall be attached by suitable and convenient fastening hooks to the two points along the lower longerons, and at the junction of the two vertical struts in the rear of the front seat. The structure must be such that it will successfully withstand the stresses imposed by the sea anchor. Controls shall be of the standard Deperdussin type, installed in the rear cock-pit only. The tanks for the main supply of gasoline shall be in the fuselage and located so that the longitudinal balance will not be disturbed by the emptying of the tank during flight.

The above data is not in the exact form of the original specifications and is not complete, but gives only the specifications that affect the design of the body. These were picked out part by part from the original.

Army Specification 1003 (Speed Scout). These specifications cover the design of land machines, the extracts given here referring only to the safety factor. Body forward of the cockpit shall be designed for safety factor of 10 over static conditions, with the propeller axis horizontal. Body in rear of cockpit shall be designed to fail under loads not less than those imposed under the following conditions:

(a) Dynamic loading of 5 as the result of quick turns in pulling out of a dive. (b) Superposed on the above dynamic loading shall be the load which it is possible to impose upon the elevators, computed by the following formula: L = 0.005AV², where A is the total area of the stabilizing surface (elevators and fixed surface), and V is the horizontal high speed of the machine. The units are all in the metric system. (c) Superposed on this loading shall be the force in the control cables producing compression in the longerons.

Fuselage Covering. Disregarding the monocoque and veneer constructed types of fuselage, the most common method of covering consists of a metal shell in the forward end, and a doped linen covering for that portion of the body that lies to the rear of the rear seat. The metal sheathing, which may be of sheet steel or sheet aluminum, generally runs from the extreme front end to the rear of the pilot's cockpit. Sheet steel is more common than aluminum because of its stiffness. Military machines are usually protected in the forward portions of the fuselage by a thin armor plate of about 3 millimeters in thickness. This is a protection against rifle bullets and shrapnel fragments, but is of little avail against the heavier projectiles. Armor is nearly always omitted on speed scouts because of its weight. Bombers of the Handley-Page type are very heavily plated and this shell can resist quite large calibers.

The fabric used on the rear portion of the fuselage is of linen similar to the wing covering, and like the wing fabric is well doped with some cellulose compound to resist moisture and to produce shrinkage and tautness. On the sides and bottom the fabric is supported by very thin, light stringers attached to the fuselage struts. On the top, the face is generally curved by supporting a number of closely spaced stringers on curved wooden formers. The formers are generally arranged so that they can be easily removed for the inspection of the wire stay connections and the control leads. On some machines the top of the fuselage consists entirely of sheet metal supported on formers, while in others the metal top only extends from the motor to the rear of the rear cockpit.