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
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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
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
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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
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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
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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
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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
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
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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
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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.
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
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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
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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
Cloud cover or obstacles can block the laser beam so it never makes it to
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
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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
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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
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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
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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
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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
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.
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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
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jammer, which generates infrared energy of varying frequencies to confuse
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.
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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.
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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.
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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 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.
This one is the easiest. Every object on earth has weight (including air).
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).
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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.
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