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Apache Helicopter Seminar Report
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.
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Apache Helicopter Seminar Report
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.
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Apache Helicopter Seminar Report
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.
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LIFT
WEIGHT
THRUST
DRAG
Apache Helicopter Seminar Report
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.
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Apache Helicopter Seminar Report
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
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Apache Helicopter Seminar Report
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
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Apache Helicopter Seminar Report
long drive shaft that runs from the main rotor’s transmission back through
the tail boom to a small transmission at the tail rotor.
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CHAPTER V
MAIN PARTS OF AN APACHE
Apache works in the same way as any other helicopter. It has two
rotors that spin several blades. A blade is a tilted airfoil, just like an air plane
wing. As it speeds up through the air, each blade generates the lift
The main rotor, attached to the top of the helicopter, spins six
meter blades. As the main rotor spins, it exerts a rotation force on the entire
helicopter. The tail rotor blades work against this force-they push the tail
boom in the opposite direction. An Apache has double tail rotors, each with
two blades.
The pilot maneuvers the helicopter by adjusting a swash plate
mechanism. The swash plate changes each blade’s pitch 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 to the rotation
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Apache Helicopter Seminar Report
cycle creates uneven lift, causing the helicopter to tilt and fly in a particular
direction.
Fig: The rotor assembly on an AH -64A Apache
The swash plate mechanism has two primary roles:
Under the direction of the collective control, the swash plate 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 can change the
angle of both blades individually as they revolve. This allows the
helicopter to move in any direction around a 360 o circle, including
forward, backward, and left and right.
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
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Apache Helicopter Seminar Report
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
5.1 Apache Engine and its Working
The Apache Helicopters use turbo shaft jet engines to power
their rotors. Some older or smaller helicopters use "reciprocating" (Piston)
engines for their power source, but most of the helicopters in use today use
gas-turbine engines. They are light, very powerful and economical. The best
part is that they are very reliable as well. Failure rates for gas-turbine engines
are very low because there are not as many internal moving parts as there are
in a reciprocating engine.
A jet engine works on four very simple principles: "Suck, Squeeze,
Burn and Blow". The picture posted here shows a simple gas-turbine
engine cross section. In the front of the engine is the compressor section
which "Sucks" in air and "Squeezes" it to make it denser and better for
combustion. Air is brought into the compressor by the turning compressor
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Apache Helicopter Seminar Report
blades that are shaped like little airfoils. It works like a big fan to move air
into the engine. In between the moving rows of compressor blades are
stationary blade sets called "stators". The stators change the direction of the
airflow and help in the compression process. The area that the air can occupy
gets smaller as the air travels through the compressor. The air then goes
through the diffuser section which transports the air neatly into the
combustion chambers, which are in the combustion section. There the air is
mixed with fuel and is ignited to create a powerful reaction. (The "Burn"
part) The explosive burned fuel and air mixture then travels into the turbine
section where the force is turned into a combination of drive power and thrust
(or exhaust). If the force is converted mainly into drive power to drive a
transmission, as in most helicopters, then it is referred to as a turbo shaft
engine. If the force is only converted to enough power to drive the
compressor, and the rest is used as thrust, then it is considered to be a turbojet
(or thrust producing) engine. (That is the "Blow" part).
Fig An example of an Apache helicopter turbo shaft engine.
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5.2 How does the power get from the Engine to the Rotors?
The newest Apache sports twin General Electric T700-GE-701C
turbo shaft engines, boasting about 1,700 horsepower each. The power is
transferred from the engine using a main gearbox which changes the power
from the engine and sends it to the transmission. In the transmission RPM is
reduced from thousands of RPM to hundreds of RPM. By doing this the
torque is increased and the rotation is slowed to an acceptable level for the
rotor system. The transmission drives the mast which gives direct rotation to
the rotors. Often another shaft will come out of the transmission to directly
drive the tail rotor as well.
An accessory gearbox mounted on the engine draws little engine
power to drive things like the oil pump, the generator and the fuel control for
the engine itself.
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Apache Helicopter Seminar Report
CHAPTER VI
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 fire power, 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.
Fig Hellfire Missiles attached in rails
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
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Apache Helicopter Seminar Report
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 of acceleration triggers the arming
mechanism. When the missile makes contact with the target, an impact
sensor sets off the warhead.
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 laser light. To change course, the guidance system moves the
missile's flight fins. This is basically the same way an airplane steers.
The laser-guided Hellfire system is highly effective, but it has
some drawbacks:
Cloud cover 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 waves aren't obscured by clouds or obstacles, the missile is more likely
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Apache Helicopter Seminar Report
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.
CHAPTER VII
CONTROLS AND SENSORS
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. 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.
Fig Apache cockpit sections
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
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Apache Helicopter Seminar Report
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.
Fig Inside the Apache cockpit
One of the coolest things about the Apache is its sophisticated
sensor equipment. The Longbow Apache detects surrounding ground forces,
aircraft 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
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each potential target. The computer pinpoints these targets on the pilot's and
gunner's display panels.
Fig Apache Longbow with Radar Dome mounted to its mast
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.
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Apache Helicopter Seminar Report
Fig The sensor array on an Apache helicopter
CHAPTER VIII
EVASION AND ARMOUR
The Apache's first line of defense against attack is keeping out of
range. 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 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 jammer, which generates infrared energy of varying
frequencies to confuse heat-seeking missiles.
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Apache Helicopter Seminar Report
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.
CHAPTER IX
CONCLUSION
Flying an Apache into battle is extremely dangerous, to be sure,
but with all its weapons, armours and sensor equipment, it is a formidable
opponent to almost everything else on the battlefield. It is a deadly
combination of strength, agility and fire power.
The U.S is now developing a new revolutionary helicopter called
‘COMANCHE’, which has several superior techniques. But it is still under
construction. So, at present the APACHE holds the no.1 position among the
revolutionary helicopters.
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CHAPTER X
REFERENCES
1. Kroes, “ Aircraft-Basic Science”.
2. Kroes, Watkins, Delp, “ Aircraft-Gas Turbine Engine Technology”.
3. www.howstuffworks.com
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Apache Helicopter Seminar Report
ABSTRACT
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 look at the Apache’s amazing flight systems,
engines, weapon systems, sensor systems and armour systems. Individually
these components are remarkable pieces of technology. Combined together
they make up an unbelievable fighting machine – the most lethal helicopter
ever created.
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Apache Helicopter Seminar Report
CONTENTS
1. INTRODUCTION 01
2. HISTORY 02
3. AERODYNAMIC FORCES 03
4. WORKING OF A HELICOPTER 05
5. MAIN PARTS OF AN APACHE 07
6. HELLFIRE MISSILES 12
7. CONTROLS AND SENSORS 14
8. EVASION AND ARMOUR 17
9. CONCLUSION 18
10. REFERENCES 19
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