Aeroplane Construction and Operation

by John B. Rathbun

Pusher Type Fuselage (Nacelle). Compared with the tractor biplane and the monoplane fuselage, the body of the pusher is very short and light. The latter body simply acts as a support for the motor and personnel since the tail loads are carried by the outriggers or tail booms. The motor is located at the rear end of the body and may be either of the air or water-cooled type. The accompanying figure shows a typical pusher type body, or "Nacelle" as it is sometimes called.

The advantages of the pusher type for military service are obvious. The observer or gunner can be placed immediately in the front where his vision is unobstructed, and where the angle of fire is at a maximum.

Typical Pusher Body Showing Wings, and Outrigger to Tail Surfaces.

Twin Motored Fuselage. Twin motored aeroplanes generally have the power plants mounted at a point about midway between the fuselage and tips of the wings. In almost every case, the power plants are of unit construction, that is to say, consist of the motor, radiator and propeller complete on one support, only the fuel and oil tanks being mounted in the fuselage. The fuselage of the twin may be similar in length and general construction to that of the tractor biplane, or it may be a short "nacelle" similar to that used in the pusher type. In any case, the observer can be located in the extreme front of the body.

An interesting and unusual construction is the body of the Caproni Biplane (1916). A center nacelle carries the passengers, a pusher screw being located at the rear of the central body as in the case of the pusher biplane. On either side of the center are the motors driving the tractor screws, each motor being encased in a long tractor type fuselage that also supports the tail surfaces. The latter fuselage serves to streamline the motors and takes the place of the usual outrigger construction. There are three bodies, two tractor screws, and one pusher screw. Somewhat similar in design is the famous German "Billy Two-Tails," this machine being equipped with two tractor type bodies. A motor is located in the front of each body. Each fuselage is provided with accommodations for passengers, and is long enough to support the tail surfaces. The Caproni and the German machine are both very large machine and heavily powered.

U.S.A. Sea-Plane Specifications (1916). These government specifications cover a twin motored sea-plane with a central nacelle. The body is arranged so that the forward man (observer) can operate the forward machine gun through a horizontal arc of at least 150°, and through a vertical arc of at least 270°, with the gun at an angle of about 75° with the center line of the body. The muzzle must be forward of the propeller plane. The rear man (pilot) operates a machine gun through a vertical arc of at least 150° to the rear, and through a vertical arc of at least 180°, with the gun at an angle of about 105° with the fuselage center line. The muzzle must be to the rear of the plane of propeller rotation.

The number of stays and other important connections which extend across the plane of propeller rotation shall be reduced to a minimum. It is considered advisable to incorporate in the design of the body such a structure (in the plane and 8 inches forward of propeller plane) as will prevent a broken propeller blade from severing the main body. The system used in the construction of the cage masts used on battleships is suggested, with a number of spruce compression members in place of stay-wires. The clearance of the propeller tips from the sides of the central body shall be from 5 to 12 inches. No part of the gas tanks shall lie in the plane of propeller rotation, nor within a space 6 inches ahead of this plane.

A space extending at least 9 inches back from the rear of the observer's seat, and entirely across the body, must be left open and unoccupied in order that any desired instruments can be installed therein. In the center line of the body, a circular hole 9 inches in diameter shall be cut in the floor of the observer's cock-pit, the rear of the hole being 5 inches forward of the forward edge of the observer's seat. The flooring of the pilot's and observer's cockpits shall consist of spruce strips 1/2" x 1/2 " spaced at 1/2" intervals along the longerons. No flooring is to be placed under the seats.

The safety factor of the body and tail structure shall not be less than 2.5, the air speed being taken at 100 miles per hour with the elevator at an angle of 20° and the fixed stabilizer surface at 6°. All wire tension members not readily accessible for inspection and adjustment are to be single strand high tensile steel wire. All tension stays that are easily accessible shall be of non-flexible stranded steel cable. For turnbuckle safetying No. 20 semi-hard copper wire shall be used. All cable shall be well stretched before making up the connections. A load equal to 20 or 30 per cent of the breaking load shall be applied for a period of from two to three hours. The hard wire must undergo a bending test by bending at a right angle turn over a radius equal to the diameter of the wire, back and forth four times each way. No more than four sizes of turnbuckles shall be used on the entire aeroplane structure. The strengths and size numbers of the turnbuckles will be as follows: No. 1 = 8,000 lbs. No. 2 = 4,600 lbs. No. 3 = 2,100 lbs. No. 4 = 1,100 lbs. Controls and fittings in the vicinity of the compasses shall, as much as possible, be of non-magnetic material. All steel plate and forged fittings shall be protected against the action of salt water by baking enamel, the best standard three coat process being used. All covered wiring and turnbuckles shall be coated by at least two coats of Flexible Compound.