Basic Contraction of Aircraft

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  • Topic: Fixed-wing aircraft, Aircraft, Helicopter rotor
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CHAPTER 4

AIRCRAFT BASIC CONSTRUCTION
INTRODUCTION Naval aircraft are built to meet certain specified requirements. These requirements must be selected so they can be built into one aircraft. It is not possible for one aircraft to possess all characteristics; just as it isn't possible for an aircraft to have the comfort of a passenger transport and the maneuverability of a fighter. The type and class of the aircraft determine how strong it must be built. A Navy fighter must be fast, maneuverable, and equipped for attack and defense. To meet these requirements, the aircraft is highly powered and has a very strong structure. The airframe of a fixed-wing aircraft consists of the following five major units: 1. Fuselage 2. Wings 3. Stabilizers 4. Flight controls surfaces 5. Landing gear A rotary-wing aircraft consists of the following four major units: 1. Fuselage 2. Landing gear 3. Main rotor assembly 4. Tail rotor assembly You need to be familiar with the terms used for aircraft construction to work in an aviation rating. STRUCTURAL STRESS LEARNING OBJECTIVE: Identify the five basic stresses acting on an aircraft. The primary factors to consider in aircraft structures are strength, weight, and reliability. These factors determine the requirements to be met by any material used to construct or repair the aircraft. Airframes must be strong and light in weight. An aircraft built so heavy that it couldn't support more than a few hundred pounds of additional weight would be Tension (fig. 4-1, view A) is defined as pull. It is the stress of stretching an object or pulling at its ends. Tension is the resistance to pulling apart or stretching produced by two forces pulling in opposite directions along the same straight line. For example, an elevator control cable is in additional tension when the pilot moves the control column. COMPRESSION If forces acting on an aircraft move toward each other to squeeze the material, the stress is called compression. Compression (fig. 4-1, view B) is the opposite of tension. Tension is pull, and compression is push. Compression is the resistance to crushing produced by two forces pushing toward each other in the same straight line. For example, when an airplane is on the ground, the landing gear struts are under a constant compression stress. useless. All materials used to construct an aircraft must be reliable. Reliability minimizes the possibility of dangerous and unexpected failures. Many forces and structural stresses act on an aircraft when it is flying and when it is static. When it is static, the force of gravity produces weight, which is supported by the landing gear. The landing gear absorbs the forces imposed on the aircraft by takeoffs and landings. During flight, any maneuver that causes acceleration or deceleration increases the forces and stresses on the wings and fuselage. Stresses on the wings, fuselage, and landing gear of aircraft are tension, compression, shear, bending, and torsion. These stresses are absorbed by each component of the wing structure and transmitted to the fuselage structure. The empennage (tail section) absorbs the same stresses and transmits them to the fuselage. These stresses are known as loads, and the study of loads is called a stress analysis. Stresses are analyzed and considered when an aircraft is designed. The stresses acting on an aircraft are shown in figure 4-1. TENSION

4-1

Figure 4-1.—Five stresses acting on an aircraft.

SHEAR Cutting a piece of paper with scissors is an example of a shearing action. In an aircraft structure, shear (fig. 4-1, view D) is a stress exerted when two pieces of fastened material tend to separate. Shear stress is the outcome of sliding one part over the other in opposite directions. The rivets and bolts of an aircraft experience both shear and tension stresses. BENDING Bending (fig. 4-1, view E) is a combination of tension and compression. For example, when bending a piece of tubing, the upper portion stretches...
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