Aircraft Construction

operate the flight instruments, essential systems, such as anti-icing, and passenger services, such as cabin lighting. Engine The flight controls are the devices and systems that govern the attitude of an aircraft and, as a result, the flight path Propeller followed by the aircraft. In the case of many conventional airplanes, the primary flight controls utilize hinged, trailing- edge surfaces called elevators for pitch, ailerons for roll, and the rudder for yaw. These surfaces are operated by the pilot in the flight deck or by an automatic pilot. In the case of most modern airplanes, airplane brakes consist of multiple pads (called caliper pads) that are hydraulically squeezed toward each other with a rotating disk (called a rotor) between them. The pads place pressure on the rotor Cowling which is turning with the wheels. As a result of the increased friction on the rotor, the wheels inherently slow down and stop turning. The disks and brake pads are made either from steel, like those in a car, or from a carbon material that weighs Figure 3-13. Engine compartment. less and can absorb more energy. Because airplane brakes are used principally during landings and must absorb enormous propeller blade, as measured against the hub of the propeller, amounts of energy, their life is measured in landings rather keeps the angle of attack (AOA) (See definition in Glossary) than miles. relatively constant along the span of the propeller blade, reducing or eliminating the possibility of a stall. The amount Types of Aircraft Construction of lift being produced by the propeller is directly related to The construction of aircraft fuselages evolved from the early the AOA, which is the angle at which the relative wind meets wood truss structural arrangements to monocoque shell the blade. The AOA continuously changes during the flight structures to the current semimonocoque shell structures. depending upon the direction of the aircraft. Truss Structure The pitch is defined as the distance a propeller would travel in The main drawback of truss structure is its lack of a one revolution if it were turning in a solid. These two factors streamlined shape. In this construction method, lengths of combine to allow a measurement of the propeller’s efficiency. tubing, called longerons, are welded in place to form a well- Propellers are usually matched to a specific aircraft/ braced framework. Vertical and horizontal struts are welded powerplant combination to achieve the best efficiency at a to the longerons and give the structure a square or rectangular particular power setting, and they pull or push depending on shape when viewed from the end. Additional struts are needed how the engine is mounted. to resist stress that can come from any direction. Stringers Subcomponents and bulkheads, or formers, are added to shape the fuselage and support the covering. The subcomponents of an airplane include the airframe, electrical system, flight controls, and brakes. As technology progressed, aircraft designers began to enclose the truss members to streamline the airplane and improve The airframe is the basic structure of an aircraft and is performance. This was originally accomplished with cloth designed to withstand all aerodynamic forces, as well as the fabric, which eventually gave way to lightweight metals such stresses imposed by the weight of the fuel, crew, and payload. as aluminum. In some cases, the outside skin can support all or a major portion of the flight loads. Most modern aircraft The primary function of an aircraft electrical system is to use a form of this stressed skin structure known as monocoque generate, regulate, and distribute electrical power throughout or semimonocoque construction. [Figure 3-14] the aircraft. There are several different power sources on aircraft to power the aircraft electrical systems. These Monocoque power sources include: engine-driven alternating current Monocoque construction uses stressed skin to support almost (AC) generators, auxiliary power units (APUs), and external all loads much like an aluminum beverage can. Although power. The aircraft’s electrical power system is used to very strong, monocoque construction is not highly tolerant 3-8