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 article, 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.

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.)

We'll learn more about the rotors and blades next.

Apache Rotors and Blades

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.

Apache 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.

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.

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.

We'll look at the Apache's rockets next.

Apache 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.

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.