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 edition of HowStuffWorks,
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.
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. (See How Airplanes
Work to find out how lift is generated.)
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 cycle creates uneven lift, causing the helicopter
to tilt and fly in a particular direction. (See How
Helicopters Work for a full explanation.)
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 gear box. The gear box 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.
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.
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Who uses the Apache, and
who makes it?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.
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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.
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 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.
Photo courtesy U.S.
Army
Each rail set holds
four Hellfire
missiles.
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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 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 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 and Chain Gun
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.
Photo courtesy U.S. Department of
Defense
The Hydra rocket
launcher (right) and Hellfire missile rails (left) on an
AH-64A Apache
helicopter
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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 submunitions, 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 swing the turret from side to side
and up and down.
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 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.
In the next section, we'll look at the targeting system for
the cannon, as well as the other major Apache controls.
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. 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.
Photo courtesy U.S. Department of
Defense
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.
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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.
Photo courtesy U.S.
Army
Inside the Apache
Longbow
cockpit
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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 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. (See How Night
Vision Works for more information.)
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.
Photo courtesy U.S.
Army
The sensor array on
an Apache
helicopter
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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. (See this
page for more information on the helmet targeting system.)
The helmet targeting system in an Apache
helicopter
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In the next section, we'll look at a few of the systems
that protect the pilot and gunner during battle.
Evasion and Armor
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
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.
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 fire power.
For more information about Apache helicopters and other
weapons, check out the links on the next page.
Lots More Information!
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