CHAPTER 3 PRINCIPLES OF FLIGHT

CHAPTER 3 PRINCIPLES OF FLIGHT INTRODUCTION Man has always wanted to fly. Legends from the very earliest times bear witness to this wish. Perhaps the most famous of these legends is the Greek myth about a father and son who flew with wings made of wax and feathers. It was not, however, until the successful flight by the Wright bothers at Kitty Hawk, North Carolina, that the dream of flying became a reality. Since the flight at Kitty Hawk, aircraft designers have spent much time and effort in developing that first crude flying machine into the modern aircraft of today. To understand the principles of flight, you must first become familiar with the physical laws affecting aerodynamics. PHYSICAL LAWS AFFECTING AERODYNAMICS LEARNING OBJECTIVE: Identify the physical laws of aerodynamics to include Newton's laws of motion and the Bernoulli principle. Aerodynamics is the study of the forces that let an aircraft fly. You should carefully study the principles covered here. Whether your job is to fly the aircraft and/or to maintain it, you should know why and how an aircraft flies. Knowing why and how lets you carry out your duties more effectively. LAWS OF MOTION Motion is the act or process of changing place or position. Simply put, motion is movement. An object may be in motion in relation to one object and motionless in relation to another. For example, a person sitting in an aircraft flying at 200 mph is at rest or motionless in relation to the aircraft. However, the person is in motion in relation to the air or the earth. Air has no force or power other than pressure when it's motionless. When air is moving, its force becomes apparent. A moving object in motionless air has a force exerted on it as a result of its own motion. It makes no difference in the effect whether an object is moving in relation to the air or the air is moving in relation to the object. The following information explains some basic laws of motion. Newton's First Law of Motion According to Newton's first law of motion (inertia), an object at rest will remain at rest, or an object in motion will continue in motion at the same speed and in the same direction, until an outside force acts on it. For an aircraft to taxi or fly, a force must be applied to it. It would remain at rest without an outside force. Once the aircraft is moving, another force must act on it to bring it to a stop. It would continue in motion without an outside force. This willingness of an object to remain at rest or to continue in motion is referred to as inertia. Newton's Second Law of Motion The second law of motion (force) states that if a object moving with uniform speed is acted upon by an external force, the change of motion (acceleration) will be directly proportional to the amount of force and inversely proportional to the mass of the object being moved. The motion will take place in the direction in which the force acts. Simply stated, this means that an object being pushed by 10 pounds of force will travel faster than it would if it were pushed by 5 pounds of force. A heavier object will accelerate more slowly than a lighter object when an equal force is applied. Newton's Third Law of Motion The third law of motion (action and reaction) states that for every action (force) there is an equal and opposite reaction (force). This law can be demonstrated with a balloon. If you inflate a balloon with air and release it without securing the neck, as the air is expelled the balloon moves in the opposite direction of the air rushing out of it. Figure 3-1 shows this law of motion. 3-1 Figure 3-1.—Newton's third law of motion.