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Apache Helicopter
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CHAPTER I
INTRODUCTION
The Apache Helicopter is a revolutionary development in the history of war. It is essentially a flying tank – a helicopter designed to survive heavy attack and inflict massive damage. As a whole, it is a terrifying machine to ground forces.
The Apache is the primary attack helicopter in the U.S.Arsenal. Other countries, including the United Kingdom, Israel and Saudi Arabia, have also added Apaches to their fleet.
In this topic, we’ll look at the Apache’s amazing flight systems, weapon systems, engines, sensor systems and amour systems. Individually, these components are remarkable pieces of technology. Combined together, they make up an unbelievable fighting machine – the most lethal helicopter ever created.
CHAPTER II
HISTORY
The first series of Apaches, developed by Hughes Helicopters in the 1970s, went into active service in 1985. The U.S military is gradually replacing this original design, known as the AH-64A Apache, with the more advanced AH-64D Apache Longbow. In 1984, Mc Donnell Douglas purchased Hughes Helicopters, and in 1997, Boeing manufactures Apache helicopters, and the UK-based GKN Westland helicopters manufacturers the English versions of the Apache, the WAH-64.
CHAPTER III
AERODYNAMIC FORCES
The four basic aerodynamic forces are Drag, Thrust, Weight and Lift.
DRAG: Drag is an aerodynamic force that resists the motion of an object moving through a fluid. The amount of drag depends on a few factors, such as the size of the object, the speed of the car and the density of the air.
THRUST: Thrust is an aerodynamic force that must be created by an airplane in order to overcome the drag. Airplanes create thrust using propellers, jet engines or rockets.
WEIGHT: This is the force acting downwards or the gravitational force.
LIFT: Lift is the aerodynamic force that holds an airplane in the air, and is probably the important of the four aerodynamic forces. Lift is created by the wings of the airplane.
Lift is a force on a wing immersed in a moving fluid, and it acts perpendicular to the flow of the fluid but drag is the same thing, but acts parallel to the direction of the fluid flow.
1. Air approaching the top surface of the wing is compressed into the air above it as it moves upward. Then, as the top surface curves downward and away from the air stream, a low pressure area is developed and the air above is pulled downward toward the back of the wing.
2. Air approaching the bottom surface of the wing is slowed, compressed and redirected in a downward path. As the air nears the rear of the wing, its sped and pressure gradually match that of the air coming over the top. The overall pressure effects encountered on the bottom of the wing are generally less pronounced than those on the top of the wing.
3.1 FOR STRAIGHT AND LEVEL FLIGHT
The following relationships must be true:
THRUST = DRAG
WEIGHT = LIFT
If for any reason, the amount of drag becomes larger then the amount of thrust, the plane will slow down. If the thrust is increased so that it is greater than drag, the plane will speed up.
If the amount of lift drops below the weight of the airplane, the plane will descend. By increasing the lift, the pilot can make the airplane climb.
CHAPTER IV
WORKING OF A HELICOPTER
Helicopters are the most versatile flying machines in existence today. This versatility gives the pilot complete access to three dimensional space in a way that no airplane can.
The amazing flexibility of helicopters means that they can fly almost anywhere. However, it also means that flying the machines is complicated.
A plane can move forward and turn left or right. It also adds the ability to go up and down. The helicopter can do three things that an airplane cannot:
a. A helicopter can fly backwards.
b. The entire aircraft can rotate in the air.
c. A helicopter can hover motionless in the air.
A rotary motion is the easiest way to keep a wing in continuous motion. The rotating wings of a helicopter are shaped just like the airfoils of an airplane wing, but generally the wings on a helicopter’s rotor are narrow and thin because they must spin so quickly. The helicopter’s rotating wing assembly is normally called the Main Rotor. If you give the main rotor wings a slight angle of attack on the shaft and spin the shaft, the wings start to develop lift.
In order to spin the shaft with enough force to lift the vehicle, engine of great power is required. Reciprocating gasoline engines and gas turbine engines are the most common types. The engine’s driveshaft can connect through a transmission to the main rotor shaft. The arrangement works really well until the moment the vehicle leaves the ground. At that moment, there is nothing to keep the engine from spinning just like the main rotor does. So, in the absence of anything to stop it, the body will spin in the direction opposite to the main rotor. To keep the body from spinning, a force is needed to apply on it. The usual way to provide a force to the body of the vehicle is to attach another set of rotating wings to a long boom. These wings are known as the Tail Rotor. The tail rotor produces thrust just like an airplane’s propeller does. By producing thrust in a sideways direction, counteracting the engine’s desire to spin the body, the tail rotor keeps the body of the helicopter from spinning. Normally, the tail rotor is driven by a long drive shaft that runs from the main rotor’s transmission back through the tail boom to a small transmission at the tail rotor.