Airframe
While it doesn't possess the long and slender profile typical of many missiles in production, the AGM-114 Hellfire is nonetheless a very aerodynamic design capable of supersonic flight.  At 5.3 feet in length and 7 inches in diameter, the Hellfire is a compact design capable of a range of approximately 8 km. Weighing just over 100 pounds at launch, the missile is capable of Mach 1.4 in level flight.
The various systems of the missile are housed in a metal airframe featuring two sets of cruciform wings. The entire fuselage is made up of five separate modules, each containing systems dedicated to a particular task crucial to the objective of the missile. From fore to aft these components consist of laser seeker, warhead, guidance section, propulsion, and control section.
Laser Seeker
The laser seeker resides in the extreme forward part of the missile, occupying the space between the nose-cap an the forward set of stabilizing fins. A clear glass dome caps the nose of the missile, providing the laser seeker with an unobstructed field of view in order to find and track the designated target. The seeker itself consists of the seeker array, the drive motors which steer the array, and the computer that interprets the information and transfers the data to the guidance computer.
Warhead
Sitting behind the seeker section, the warhead is made up of an 8kg HEAT (High Explosive Anti-Tank) shaped-charge with a copper liner. Such a warhead is cone-shaped, with the widest portion facing forward. With shaped-charge warheads, detonation collapses the cone into an armour-piercing jet of molten metal, which upon penetration, incinerates the interior of the vehicle. Rather than defeating armour with sheer blunt force, the shaped-charge warhead concentrates all of its energy into a tight focal point roughly the size of a human fist.
The warhead is designed to arm itself once it has undergone 10 Gs of forward thrust, a force generated by the missile when the motor ignites during launch. The warhead is detonated when impact trips a collision sensor which sends electrical impulses to the fusing mechanism.
The AGM-114K Hellfire II features a redesigned warhead. The copper liner of the shaped-charge warhead has been replaced by molybdenum (a silvery metallic chemical element) steel liner. This improvement increases both the potency of the warhead as well as the missile's effectiveness against new armour technologies.
In addition, the Hellfire II system features a tandem warhead. The tandem warhead emerged in response to the development of "reactive" armour. The concept behind reactive armour is relatively simple. Blocks of plastic explosive sandwiched between two metal plates cover the armour of the vehicle. When a shaped charge warhead comes into contact with this armour the missile's explosion sets off the block of plastique, which in turn propels the outer metal plate towards the warhead, the resulting kinetic energy dissipating the effectiveness of the shaped-charge. The exterior metal plate bears the brunt of the energy from the molten jet, allowing the armoured hull of the tank to receive minimal or no damage.
The tandem warhead defeats this counter-measure with two explosive charges: a minor initial explosion followed by the main shaped-charge warhead. The initial charge sets off the reactive armour, causing the metal plate to be blasted outward prematurely. By the time the primary shaped-charge warhead detonates, the energy of the reactive plate has been dissipated while the plate itself is fractured and weakened. The main explosive force simply punches through the remnants of the reactive armour and penetrates the tank's actual armour.
Guidance
Just aft of the fuse lies the guidance section. The guidance computer performs two tasks simultaneously, both crucial to the weapon's mission. First, it interprets signals from the laser seeker and translates them into steering cues to be sent to the control section. Second, it records pitch, roll, and yaw rates - ensuring that all three are within the limits of controlled flight. Data is sent to the control section should any of these variables begin to stray outside the flight envelope.
Propulsion
The AGM-114 is powered by the Thiokol TX-657 solid-fuel rocket motor. The propellant starts about where the aft wings start and run down approximately 2/3 the length of those fins. Once ignited, the fuel provides about 2-3 seconds of burn-time, the number varying due to the air temperature at launch. The motor is designed to generate 10 Gs of initial thrust - enough to arm the missile's warhead - as well as to produce enough momentum to provide approximately 8 km of range.  Maximum velocity for the Hellfire is Mach 1.4, approximately 950 mph.
Starting from the development of the B-model Hellfire, the powerplant has been altered in order to provide a reduced smoke signature, thus decreasing the visibility of the AGM-114 when launched. This reduction has two benefits. First, ground forces have little warning that they are under attack. Second, the missile is less likely to give away the attacking force's position. This is particularly important to a helicopter that depends on stealth to avoid attack itself.
Control Section
Surrounding the motor outlet tube are the actuators, which provide steering authority to the four aft fins. Pneumatic actuators convert electrical signals from the guidance section into actual mechanical movement, which in turn interacts with the airstream in order to providing steering forces to both stabilize and guide the missile in flight.
Stabilizing and Control Fins
Protruding from the airframe are two sets of cruciform wings, with the first set located within the first quarter of the missile's fuselage, and the second set mounted at the tail end. They give the Hellfire a wingspan of 12.8 inches. The forward fins are fixed and are designed to provide stability in flight while the aft wings are tasked with providing directional control. While the aft wings are quite long, only a small portion at the extreme tail-end of each wing move. The moving surfaces are very much like tiny ailerons, their movements corresponding with signals fed to the control section from the guidance computer.
|
