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report on apache helicopters.
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CONTENTS
1. INTRODUCTION
2. HELICOPTER BASICS
3. POWER AND FLIGHT
4. HELLFIRE MISSILES
5. ROCKET AND CHAIN GUNS
6. CONTROL AND SENSORS
7. EVASION AND ARMOR
8. AERODYNAMIC FORCES
9. CONCLUSION
10. REFERENCES
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. PAGE NO: 1
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 PAGE NO: 2
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
PAGE NO: 3
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 PAGE NO: 4
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
PAGE NO: 5
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 PAGE NO: 6
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. PAGE NO: 7
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
highexplosive, 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
PAGE NO: 8
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
PAGE NO: 9
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
PAGE NO: 10
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
PAGE NO: 11
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 PAGE NO: 12
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. PAGE NO: 13
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 PAGE NO: 14
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.
PAGE NO: 15
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 PAGE NO: 16
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.
PAGE NO: 17
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 PAGE NO: 18
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. PAGE NO: 19
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). PAGE NO: 20
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.
PAGE NO: 21