Apache Helicopter

APACHE HELICOPTER

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. It can zero in on specific targets, day or

night, even in terrible weather. As you might expect, it is a terrifying machine

to ground forces.

In this topic, we'll look at the Apache's amazing flight systems, weapons

systems, sensor systems and armor systems. Individually, these components are

remarkable pieces of technology. Combined together, they make up an

unbelievable fighting machine -- the most lethal helicopter ever created.

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.

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, McDonnell Douglas purchased

Hughes Helicopters, and in 1997, Boeing merged with McDonnell Douglas.

Today, Boeing manufactures Apache helicopters, and the UK-based GKN

Westland Helicopters manufacturers the English version of the Apache, the

WAH-64.

Central Polytechnic College, Thiruvananthapuram PAGE NO: 1

APACHE HELICOPTER

HELICOPTER BASICS
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. The

pilot has to think in three dimensions and must use both arms and both legs

constantly to keep a helicopter in the air! Piloting a helicopter requires a great

deal of training and skill, as well as continuous attention to the machine.

To understand how helicopters work and also why they are so

complicated to fly, it is helpful to compare the abilities of a helicopter with

those of trains, cars and airplanes. There are only two directions that a train can

travel in -- forward and reverse. A car, of course, can go forward and backward

like a train. While you are traveling in either direction you can also turn left or

right:

A plane can move forward and turn left or right. It also adds the ability

to go up and down. HA helicopter can do three things that an airplane cannot:

 A helicopter can fly backwards.

 The entire aircraft can rotate in the air.

 A helicopter can hover motionless in the air.

In a car or a plane, the vehicle must be moving in order to turn. In a

helicopter, you can move laterally in any direction or you can rotate 360


APACHE HELICOPTER

degrees. These extra degrees of freedom and the skill you must have to master

them is what makes helicopters so exciting, but it also makes them complex.

To control a helicopter, one hand grasps a control called the cyclic, which

controls the lateral direction of the helicopter (including forward, backward,

left and right). The other hand grasps a control called the collective, which

controls the up and down motion of the helicopter (and also controls engine

speed). The pilot's feet rest on pedals that control the tail rotor, which allows

the helicopter to rotate in either direction on its axis. It takes both hands and

both feet to fly a helicopter!

Imagine that we would like to create a machine that can simply fly straight

upward. Let's not even worry about getting back down for the moment -- up is

all that matters. If you are going to provide the upward force with a wing, then

the wing has to be in motion in order to create lift. Wings create lift by

deflecting air downward and benefiting from the equal and opposite reaction

that results straight upward.

A rotary motion is the easiest way to keep a wing in continuous motion. So

you can mount two or more wings on a central shaft and spin the shaft, much

like the blades on a ceiling fan. 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


APACHE HELICOPTER

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 a human being and the

vehicle, you need an engine of some sort. Reciprocating gasoline engines and

gas turbine engines are the most common types. The engine's drive shaft can

connect through a transmission to the main rotor shaft. This arrangement works

really well until the moment the vehicle leaves the ground. At that moment,

there is nothing to keep the engine (and therefore the body of the vehicle) from

spinning just like the main rotor does. So, in the absence of anything to stop it,

the body will spin in an opposite direction to the main rotor. To keep the body

from spinning, you need to apply a force to 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. What you end up with is a vehicle that looks something like this:

A helicopter's main rotor is the most important part of the vehicle. It

provides the lift that allows the helicopter to fly, as well as the control that

allows the helicopter to move laterally, make turns and change altitude. The


APACHE HELICOPTER

adjustability of the tail rotor is straightforward -- what you want is the ability to

change the angle of attack on the tail rotor wings so that you can use the tail

rotor to rotate the helicopter on the drive shaft's axis. To handle all of these

tasks, the rotor must first be incredibly strong. It must also be able to adjust the

angle of the rotor blades with each revolution of the hub. The adjustability is

provided by a device called the swash plate assembly. The main rotor hub,

where the rotor's drive shaft and blades connect, has to be extremely strong as

well as highly adjustable. The swash plate assembly is the component that

provides the adjustability.

The swash plate assembly has two primary roles:

 Under the direction of the collective control, the swash plate assembly

can change the angle of both blades simultaneously. Doing this increases

or decreases the lift that the main rotor supplies to the vehicle, allowing

the helicopter to gain or lose altitude.

 Under the direction of the cyclic control, the swash plate assembly can

change the angle of the blades individually as they revolve. This allows


APACHE HELICOPTER

the helicopter to move in any direction around a 360-degree circle,

including forward, backward, left and right.

POWER AND FLIGHT

At its core, an Apache works pretty much the same way as any other

helicopter. It has two rotors that spin several blades. A blade is a tilted airfoil,

just like an airplane wing. As it speeds through the air, each blade generates

lift.

The main rotor, attached to the top of the helicopter, spins four 20-foot

(6-meter) blades. The pilot maneuvers the helicopter by adjusting a swash plate

mechanism. The swash plate changes each blade's pitch (tilt) to increase lift.

Adjusting the pitch equally for all blades lifts the helicopter straight up and

down. Changing the pitch as the blades make their way around the rotation


APACHE HELICOPTER

cycle creates uneven lift, causing the helicopter to tilt and fly in a particular

direction. As the main rotor spins, it exerts a rotation force on the entire

helicopter. The rear rotor blades work against this force -- they push the tail

boom in the opposite direction. By changing the pitch of the rear blades, the

pilot can rotate the helicopter in either direction or keep it from turning at all.

An Apache has double tail rotors, each with two blades.

The newest Apache sports twin General Electric T700-GE-701C

turboshaft engines, boasting about 1,700 horsepower each. Each engine turns a

drive shaft, which is connected to a simple gearbox. The gearbox shifts the

angle of rotation about 90 degrees and passes the power on to the transmission.

The transmission transmits the power to the main rotor assembly and a long

shaft leading to the tail rotor. The rotor is optimized to provide much greater

agility than you find in a typical helicopter.

The core structure of each blade consists of five stainless steel arms,

called spars, which are surrounded by a fiberglass skeleton. The trailing edge of

each blade is covered with a sturdy graphite composite material, while the

leading edge is made of titanium. The titanium is strong enough to withstand

brushes with trees and other minor obstacles, which is helpful in "nap-of-the-

earth" flying (zipping along just above the contours of the ground). Apaches

need to fly this way to sneak up on targets and to avoid attack. The rear tail

wing helps stabilize the helicopter during nap-of-the-earth flight as well as

during hovering.


APACHE HELICOPTER

You could say, based on all this information, that the Apache is just a

high-end helicopter. But that would be like calling James Bond's Aston Martin

just a high-end car. As we'll see in the next few sections, the Apache's

advanced weaponry puts it in an entirely different class.

HELLFIRE MISSILES

The Apache's chief function is to take out heavily armored ground

targets, such as tanks and bunkers. To inflict this kind of damage, you need

some heavy firepower, and to do it from a helicopter, you need an extremely

sophisticated targeting system.

The Apache's primary weapon, the Hellfire missile, meets these

demands. Each missile is a miniature aircraft, complete with its own guidance

computer, steering control and propulsion system. The payload is a high-

explosive, copper-lined-charge warhead powerful enough to burn through the

heaviest tank armor in existence.

The Apache carries the missiles on four firing rails attached to pylons

mounted to its wings. There are two pylons on each wing, and each pylon can

support four missiles, so the Apache can carry as many as 16 missiles at a time.

Before launching, each missile receives instructions directly from the

helicopter's computer. When the computer transmits the fire signal, the missile

sets off the propellant. Once the burning propellant generates about 500 pounds

of force, the missile breaks free of the rail. As the missile speeds up, the force


APACHE HELICOPTER

of acceleration triggers the arming mechanism. When the missile makes

contact with the target, an impact sensor sets off the warhead.

Fires two Hellfire missiles in a training exercise

The original Hellfire design uses a laser guidance system to hit its mark.

In this system, the Apache gunner aims a high-intensity laser beam at the target

(in some situations, ground forces might operate the laser instead). The laser

pulses on and off in a particular coded pattern.

Before giving the firing signal, the Apache computer tells the missile's

control system the specific pulse pattern of the laser. The missile has a laser

seeker on its nose that detects the laser light reflecting off the target. In this

way, the missile can see where the target is. The guidance system calculates

which way the missile needs to turn in order to head straight for the reflected


APACHE HELICOPTER

laser light. To change course, the guidance system moves the missile's flight

fins. This is basically the same way an airplane steers.

Holds four Hellfire missiles.

The laser-guided Hellfire system is highly effective, but it has some significant

drawbacks:

 Cloud cover or obstacles can block the laser beam so it never makes it to

the target.

 If the missile passes through a cloud, it can lose sight of the target.

 The helicopter (or a ground targeting crew) has to keep the laser fixed

on the target until the missile makes contact. This means the helicopter

has to be out in the open, vulnerable to attack.

The Hellfire II, used in Apache Longbow helicopters, corrects these flaws.

Instead of a laser-seeking system, the missile has a radar seeker. The

helicopter's radar locates the target, and the missiles zero in on it. Since radio


APACHE HELICOPTER

waves aren't obscured by clouds or obstacles, the missile is more likely to find

its target. Since it doesn't have to keep the laser focused on the target, the

helicopter can fire the missile and immediately find cover.

ROCKETS & CHAIN GUNS

Apaches usually fly with two Hydra rocket launchers in place of two of

the Hellfire missile sets. Each rocket launcher carries 19 folding-fin 2.75-inch

aerial rockets, secured in launching tubes. To fire the rockets, the launcher

triggers an igniter at the rear end of the tube. The Apache gunner can fire one

rocket at a time or launch them in groups. The flight fins unfold to stabilize the

rocket once it leaves the launcher.

The Hydra rocket launcher (right) and Hellfire missile rails (left) on an AH-64A Apache
helicopter


APACHE HELICOPTER

The rockets work with a variety of warhead designs. For example, they

might be armed with high-power explosives or just smoke-producing materials.

In one configuration, the warhead delivers several sub munitions, small bombs

that separate from the rocket in the air and fall on targets below.

The gunner engages close-range targets with an M230 30-mm automatic

cannon attached to a turret under the helicopter's nose. The gunner aims the

gun using a sophisticated computer system in the cockpit. The computer

controls hydraulics that swings the turret from side to side and up and down.

The M-230A1 30-mm automatic cannon on an AH-64A Apache

The automatic cannon is a chain gun design, powered by an electric

motor. The motor rotates the chain, which slides the bolt assembly back and

forth to load, fire, extract and eject cartridges. This is different from an


APACHE HELICOPTER

ordinary machine gun, which uses the force of the cartridge explosion or flying

bullet to move the bolt.

The cartridges travel from a magazine above the gun down a feed chute to the

chamber. The magazine holds a maximum of 1,200 rounds, and the gun can

fire 600 to 650 rounds a minute. The cannon fires high-explosive rounds

designed to pierce light armor.

CONTROLS & SENSERS

The Apache cockpit is divided into two sections, one directly behind the

other. The pilot sits in the rear section, and the co-pilot/gunner sits in the front

section. As you might expect, the pilot maneuvers the helicopter and the gunner

aims and fires the weapons. Both sections of the cockpit include flight and

firing controls in case one pilot needs to take over full operation.

The Apache has two cockpit sections: The pilot sits in the rear and the gunner sits
in the front. The rear section is raised above the front section so the pilot can see
clearly.


APACHE HELICOPTER

The pilot flies the Apache using collective and cyclic controls, similar to

ones you would find in any other helicopter. The controls manipulate the rotors

using both a mechanical hydraulic system and a digital stabilization system.

The digital stabilization system fine-tunes the powerful hydraulic system to

keep the helicopter flying smoothly. The stabilization system can also keep the

helicopter in an automatic hovering position for short periods of time.

On the Longbow Apache, three display panels provide the pilot with

most navigation and flight information. These digital displays are much easier

to read than traditional instrument dials. The pilot simply presses buttons on the

side of the display to find the information he or she needs.

Inside the Apache Longbow cockpit

One of the coolest things about the Apache is its sophisticated sensor

equipment. The Longbow Apache detects surrounding ground forces, aircraft


APACHE HELICOPTER

and buildings using a radar dome mounted to the mast. The radar dome uses

millimeter radio waves that can make out the shape of anything in range. The

radar signal processor compares these shapes to a database of tanks, trucks,

other aircraft and equipment to identify the general class of each potential

target. The computer pinpoints these targets on the pilot's and gunner's display

panels.

The pilot and the gunner both use night vision sensors for night

operations. The night vision sensors work on the forward-looking infrared

(FLIR) system, which detects the infrared light released by heated objects. The

pilot's night vision sensor is attached to a rotating turret on top of the Apache's

nose. The gunner's night vision sensor is attached to a separate turret on the

underside of the nose. The lower turret also supports a normal video camera

and a telescope, which the gunner uses during the day.

The computer transmits the night vision or video picture to a small

display unit in each pilot's helmet. The video display projects the image onto a

monocular lens in front of the pilot's right eye. Infrared sensors in the cockpit

track how the pilot positions the helmet and relay this information to the turret

control system. Each pilot can aim the sensors by simply moving his or her

head! Manual controls are also available, of course.


APACHE HELICOPTER

The sensor array on an Apache helicopter

EVASION & ARMOUR

The Apache's first line of defense against attack is keeping out of range.

As we saw earlier, the helicopter is specifically designed to fly low to the

ground, hiding behind cover whenever possible. The Apache is also designed

to evade enemy radar scanning. If the pilots pick up radar signals with the

onboard scanner, they can activate a radar jammer to confuse the enemy.

The Apache is also designed to evade heat-seeking missiles by reducing

its infrared signature (the heat energy it releases). The Black Hole infrared

suppression system dissipates the heat of the engine exhaust by mixing it with

air flowing around the helicopter. The cooled exhaust then passes through a

special filter, which absorbs more heat. The Longbow also has an infrared


APACHE HELICOPTER

jammer, which generates infrared energy of varying frequencies to confuse

heat-seeking missiles.

The Apache is heavily armored on all sides. Some areas are also

surrounded by Kevlar soft armor for extra protection. The cockpit is protected

by layers of reinforced armor and bulletproof glass. According to Boeing,

every part of the helicopter can survive 12.7-mm rounds, and vital engine and

rotor components can withstand 23-mm fire.

The area surrounding the cockpit is designed to deform during collision,

but the cockpit canopy is extremely rigid. In a crash, the deformation areas

work like the crumple zones in a car -- they absorb a lot of the impact force, so

the collision isn't as hard on the crew. The pilot and gunner seats are outfitted

with heavy Kevlar armor, which also absorbs the force of impact. With these

advanced systems, the crew has an excellent chance of surviving a crash.


APACHE HELICOPTER

Flying an Apache into battle is extremely dangerous, to be sure, but with

all its weapons, armor and sensor equipment, it is a formidable opponent to

almost everything else on the battlefield. It is a deadly combination of strength,

agility and firepower.

APACHE HELICOPTER


APACHE HELICOPTER

AERODYNAMIC FORCES

We take a look at four basic aerodynamic forces: lift, weight, thrust and drag.

Straight and Level Flight

In order for an airplane to fly straight and level, the following relationships

must be true:

 Thrust = Drag

 Lift = Weight

If, for any reason, the amount of drag becomes larger than the amount of thrust,

the plane will slow down. If the thrust is increased so that it is greater than the

drag, the plane will speed up. Similarly, 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.


APACHE HELICOPTER

THRUST

Thrust is an aerodynamic force that must be created by an airplane in

order to overcome the drag (notice that thrust and drag act in opposite

directions in the figure above). Airplanes create thrust using propellers, jet

engines or rockets. In the figure above, the thrust is being created with a

propeller, which acts like a very powerful version of a household fan, pulling

air past the blades.

DRAG

Drag is an aerodynamic force that resists the motion of an object moving

through a fluid (air and water are both fluids). It acts opposite to thrust.

WEIGHT

This one is the easiest. Every object on earth has weight (including air).

LIFT

Lift is the aerodynamic force that holds an airplane in the air, and is

probably the trickiest of the four aerodynamic forces to explain without using a

lot of math. On airplanes, most of the lift required to keep the plane aloft is

created by the wings (although some is created by other parts of the structure).


APACHE HELICOPTER

CONCLUSION

With the design of the apache the very concept of helicopter itself has

changed all over the world. Many countries like Russia, Germany etc. have

rolled over their versions of attack helicopters. They replaced the main

drawbacks of apache. But it can be surely emphasized that the Apache is the

pioneer in the attack helicopter family. In this seminar I’ve tried to put forward

some of the design features of the same.


APACHE HELICOPTER

REFERENCE

www.howstuffworks.com

www.answers.com

www.google.com

www.wikiepedia.org

www.helicopters.com

www.apachehelicopters.com


Apache Helicopter

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