Aerospace Manufacturing Processes

Pradip K. Saha

• Éditeur: CRC Press
• Année: 2016
• ISBN:
  9781315350936
• Édition: 1
• Sujet: Tecnologia e ingegneria
• Sous-sujet: Scienza dei materiali

Manufacturing processes for aircraft components include broad activities consisting of multiple materials processing technologies. This book focuses on presenting manufacturing process technologies exclusively for fabricating major aircraft components. Topics covered in a total of twenty chapters are presented with a balanced perspective on the relevant fundamentals and various examples and case studies. An individual chapter is aimed at discussing the scope and direction of research and development in producing high strength lighter aircraft materials, and cost effective manufacturing processes are also included.

1

Fundamentals of Aerospace Vehicles

1.1 Introduction

The term aerospace is derived from the words aeronautics and spaceflight. An aircraft is a vehicle which is able to fly through the earth’s atmosphere. The vehicles connected with or driven by rockets are not aircraft because they are not supported in flight by the surrounding air. All the activity including the design, development, production, and the operation of an aircraft is called aviation. Aircraft can either be heavier than air or lighter than air. Lighter than air vehicles include balloons and airships whereas heavier than air vehicles are powered aircraft, gliders, helicopters, and space craft. The first form of an aircraft was the kite, designed in the fifth century BC. Later on in the thirteenth century, Roger Bacon, an English monk, performed studies which later gave him the idea that air could support a craft just like water supports boats. In the sixteenth century, Leonardo da Vinci studied birds’ flight, and later produced the airscrew and the parachute. The airscrew, leading to the propeller later on, and the parachute were tremendously important contributions to aviation.

In the early 1900s, two American brothers, Orville and Wilbur Wright from Dayton, Ohio began to experiment with gliders. The gliders were built using data from Otto Lilienthal in Europe. Most of these flights turned out to be failures. In 1901, the Wright brothers decided to gather their own wing data by conducting systematic experiments on different type of wing configurations. In 1902, their Glider had a wingtip to wingtip measurement of 32 ft. and wing width of 5 ft. This was the first aircraft with three-axis control, the aircraft could go up or down, left or right, and could also roll about its longitudinal axis. At Kitty Hawk, they performed over 800 flights and resolved early problems of the aircraft (Figure 1.1).

From 1903 to today there have been remarkable developments in the aviation technology. The technology development in various areas, including aerospace structure and propulsion systems, during the last few generations has brought the aerospace industry to a very solid foundation. The aerospace industry has reached a much matured stage capable of designing and manufacturing very large capacity, fuel efficient commercial vehicles, global positioning system/laser-guided bombers, high-technology fighter jets as well as a wide variety of satellites and space vehicles. The aerospace vehicles are mainly classified in the following three categories based on the purpose of each vehicle:

• Commercial airplanes—airplanes used for flying passengers/freight goods in the air from one point to another point in any part of the world and also taking business executives for business meetings using business jets.

• Military aircraft—aircraft used as a bomber, fighter jet, refueling tanker or to transport armies and military vehicles and equipment, gunship helicopters, and many more type of military hardware.

• Spacecraft—spacecraft used for space research and most useful space communication satellite systems. A satellite is an object that moves around, or orbits, a larger object, such as a planet.

FIGURE 1.1
Wright brother’s first flight.

This chapter introduces the essential parts of an aircraft, along with their function, underlying aerodynamic principles, and basic structural features.

1.2 Aircraft Basics

To provide a wide-scale overview of an aircraft, the fundamental information about the forces acting on aircraft is presented, followed by brief discussion the aerodynamic principles allowing the aircraft to fly [1].

1.2.1 Forces Acting on Aircraft

Figure 1.2 shows the schematic representation of an aircraft with its major functional components for providing high lift and the flight control system. Three axes with four major forces act on the aircraft. Each axis is perpendicular to other two axes. All three axes intersect at the center of gravity (CG) of the aircraft. The axis which extends lengthwise through the fuselage shown in Figure 1.2 from the nose to the tail is called the longitudinal axis. The axis transverse to the longitudinal from the left to the right wing of the aircraft represents lateral axis. The axis which passes through the fuselage at the CG perpendicular to the longitudinal plane is called the vertical axis. The rotation of aircraft about its longitudinal axis is called roll, rotation about its lateral axis is pitch, and finally rotation about its vertical axis is yaw. Those three terms are always precisely handled by the pilot to control the flight at any flying stage.

FIGURE 1.2
Aircraft terminology and four major forces.

The four major forces acting on an aircraft during the flight through the air as shown in Figure 1.2 are identified as

1. Weight or gravity force

2. Lift

3. Thrust

4. Drag

Weight or gravity force is directed toward the center of the earth. The magnitude of the total takeoff weight of the aircraft, W_T, is the summation of the following components:

${\text{W}}_{\text{T}}={\text{W}}_{\text{G}}+{\text{W}}_{\text{F}}+{\text{W}}_{\text{P}}$

(1.1)

where W_G is the gross weight of the aircraft, W_F the weight of fuel at the takeoff, and W_P the weight of payload on board (passenger, baggage, freight, etc.).

The weight is actually distributed throughout the aircraft. But it could be considered that W_T is acting through a single point which is the CG of the aircraft. In flight, the aircraft has three axes of rotation as shown in Figure 1.2 about the CG. During the flight, the weight of an aircraft decreases due to fuel burned. As a result, the distribution of weight and the CG also changes; it is required to adjust the flight control devices to keep the aircraft balanced.

Lift and drag discussed in the next section are considered as aerodynamic forces, since the forces are generated due to the movement of the airfoil-shaped wing and stabilizers of an aircraft with the air flow. Thrust is the mechanical force generated by the engines attached normally to the wing (Figure 1.2) to move the aircraft through the air. Thrust opposes drag caused by air resistance to the airplane. During takeoff, thrust must be greater than drag and lift must be greater than weight so that the airplane can become airborne.

1.2.2 Aerodynamic Principles

An aircraft flies in accordance with the aerodynamic principles. In this section, the fundamentals of aerodynamic principles are discussed. Aero is derived from a Greek word meaning air whereas dynamics come from another Greek word meaning power. Air currents are movement of the air with respect to the object. Aircraft wings, horizontal, and vertical stabilizers are built with airfoil-shaped cross sections as shown in Figure 1.3.

Figure 1.4 shows the type of airfoil and its terminology. The wing with an airfoil-shaped cross section used to produce lift force to lift the aircraft from the ground and also to balance the aircraft in flight.

Angle of attack is the acute angle measured between the chord of an airfoil and the relative wind flow as shown in Figure 1.5.

FIGURE 1.3
Airfoil-shaped wing and stabilizer.

FIGURE 1.4
Type of airfoil and its terminology: (a) symmetric, (b) non-symmetric.

FIGURE 1.5
Angle of attack.

The lift of an aircraft is produced by the differential pressure between the lower pressure created on the upper surface and the higher pressure at the lower surface of the wing. The lift has to be sufficient to overcome the gravity force (total weight of the aircraft) before it leaves the ground during takeoff (Figure 1.6). The special geometry of the aircraft wing (airfoil) is required for...