The Boeing AH-64 Apache

Helicopter gunships tend to be ugly machines that look like something out of science-fiction movies, projecting menace and firepower instead of grace and elegance. One good example of the style is the Boeing (previously McDonnell Douglas and originally Hughes) "AH-64 Apache" gunship, the mainstay of the US Army's attack helicopter force, also in service with several foreign nations. This document provides a history and description of the Apache.

Origins - "Advanced Attack Helicopter (AAH)"

In the 1960s, the US Army pinned its hopes for a front-line attack helicopter on the advanced Lockheed AH-56 Cheyenne gunship, adopting the less sophisticated Bell AH-1 HueyCobra as an interim solution until the Cheyenne became available. Like many interim solutions, the HueyCobra would remain in service for far longer than originally expected, since in the end the Cheyenne proved to not be quite the machine that the Army really wanted. It was a hefty, powerful "flying tank" that put a premium on raw speed and firepower at the expense of agility and treetop operation, and the Army decided that a somewhat smaller and more maneuverable gunship would be more survivable.

The collapse of the Cheyenne program led the Army to issue a new request for proposals (RFP) for an "Advanced Attack Helicopter (AAH)" in August 1972. Five manufacturers submitted designs, and on 22 June 1973 the Bell "Model 409 /YAH-63" and the Hughes "Model 97 / YAH-64" were selected as finalists, with each contractor to build two flight prototypes and a ground-test machine for evaluation.

Bell believed their YAH-63 was the front-runner because of the company's proven experience with the HueyCobra, and in fact their contender was basically a bigger and badder HueyCobra. The initial YAH-63 prototype performed its first flight on 1 October 1975, with the second machine flying on 21 December.

The Hughes YAH-64 - Apache forerunner

The first Hughes YAH-64 actually beat the first Bell prototype into the air by one day, performing its first flight on 30 September 1975. The second YAH-64 performed its initial flight on 22 November 1975. The Army put all four machines through an intensive test program. A separate competition was conducted for the sensor and targeting suite for the AAH, with Martin Marietta and Northrop submitting proposals in November 1976.

Late in the prototype evaluation, the Army threw Bell and Hughes a curve ball by changing the specification for the primary antitank weapon for the AAH from the proven TOW wire-guided missile to the new Hellfire laser-guided missile, with longer range and greater killing power than TOW. This was risky because Hellfire hadn't even been flown at the time, with the initial development contract with Rockwell International signed in October 1976.

In any case, the Hughes YAH-64 was declared as the winner on 10 December 1976. Both designs were regarded as very good, but the Hughes design seemed to have an edge in survivability. The "Phase 2" development program funded development of three preproduction "AH-64s", as well as bringing the two YAH-64 flight prototypes and the ground test machine up to the same specification.

The Phase 2 program suffered through a number of delays for various reasons and stretched out to over five years. First Phase 2 flight, of an upgraded initial prototype, was on 28 November 1977, with first flight of a new-build preproduction prototype on 31 October 1979. Initial Hellfire launches had already taken place by that time, with first firings in April 1979. A competitive evaluation of preproduction machines, one fitted with the Martin Marietta sensor / targeting suite and the other fitted with the Northrop suite, was performed, with Martin Marietta winning the competition in April 1980.

The Hughes AH-64A "Apache"

An initial production order for 11 "AH-64A Apache" attack helicopters was finally issued on 26 March 1982, with a follow-on order for 48 more machines delayed until the government and Hughes could work out some differences.

The first production machine was formally rolled out at the Hughes factory in Mesa, Arizona, on 30 September 1983. An Apache tribesman, in native dress and on horse with a Winchester rifle, helped honor the occasion, though embarrassingly the Hughes in-house newspaper failed to report his name while listing every other person of importance who attended.

Initial production hand-over to the US Army was on 26 January 1984, with the machine painted in dark green colors that would become standard for the Apache. By that time, the helicopter had become the "McDonnell Douglas (MDD) Apache" since MDD had bought out Hughes Helicopters in December 1983. MDD was bought out in turn by Boeing in the late 1990s, and so the machine is now the "Boeing Apache".

The AH-64A reached formal operational status with the US Army in July 1986, and went into service with the Army National Guard in 1989. The Army initially planned to buy 536 Apaches. Rising costs of the type ended up forcing cutbacks to 436 machines, but additional procurement eventually led to acquisition of 807 machines by 1994, not counting the six prototypes. A number of attrition replacement machines were also ordered, bringing the total of US Army production AH-64As to 821, with final deliveries in 1996.

The Boeing AH-64 Apache description

The Apache is of conventional configuration for a modern attack helicopter. It has a main-tail rotor arrangement, a tandem-seat cockpit, nose-mounted sight, and two stub wings with a total of four pylons for underwing stores. The airframe is made mostly of aircraft aluminum alloys, but is designed to withstand 12.7 (0.50 caliber) millimeter projectile hits from all quarters, and can tolerate 23 millimeter projectile hits. A "wire strike protection system (WSPS)" is fitted, with six cutters and eleven deflectors protecting the machine from collisions with telephone lines and power cables.

The gunner sits in the forward seat and the pilot in the rear seat, which is raised 49 centimeters (19 inches) to give the pilot a view over the gunner's head. The gunner's position actually has simple backup flight controls, and the gunner is formally referred to as the "Co-Pilot / Gunner (CPG)". Both crew are protected by boron armor shields lining the cockpit, and their Kevlar seats are designed to help absorb the shock of a crash landing.

The AH-64A has fixed taildragger landing gear, with the main gear on heavy-duty shock mounts for survivability in hard landings; on really hard landings the main gear struts will collapse in a controlled fashion to further soften the impact. The landing gear can "kneel" to ease transport of the helicopter. The seats and the landing gear provide a surprising amount of crew protection, as demonstrated by one of the prototype machines that suffered a catastrophic engine failure at an altitude of about 90 meters (300 feet). The crew walked away from the crash, banged up but otherwise unharmed.

The crew gets into and out of the cockpit through upward-hinging canopy panels. Various handholds and steps are fitted to the machine to ease entrance and exit. Detonation cord rings the canopy panels on both sides to blow off the windows in an emergency for a faster exit.

The AH-64A is powered by twin General Electric T700-GE-701 turboshaft engines with 1,265 kW (1,696 SHP) each. Prototypes and test machines had used the less powerful T700-GE-700. while AH-64As from the 604th production item on were fitted with uprated T700-GE-701C engines, with 1,342 kW (1,800 SHP) each.

The engines are mounted in pods alongside the fuselage to permit easy maintenance. The wide separation of the pods also helps reduce the chance that both engines will be knocked out by ground fire. The engine exhausts are shielded to protect the helicopter from heat-seeking missiles using a three-nozzle "black hole" exhaust suppressor for each engine. The transmission system can run for an hour after complete loss of lubricating oil. There is a Garrett GTCP 36 auxiliary power unit with 93 kW (125 HP) in the fuselage between the engine pods for main engine start and ground power.

The main and tail rotors are both four-bladed. The main rotor has wide-chord blades, with swept tips to reduce noise and improve rotor aerodynamic efficiency. The tail rotor has a "scissors" configuration, with the blades arranged at alternating 55 and 125 degree intervals, also to reduce rotor noise. There is a moving tailplane at the base of the tailfin. Incidentally, the tailplane was mounted on top of the tailfin in the YAH-64s.

Each main rotor blade has five stainless steel spars to allow it to resist projectile strikes and stainless steel skinning on the outer part of the rotors, with the rest of the blade structure consisting of synthetic Nomex honeycomb and fiberglass skin. The main rotor can be removed for air transport on cargolifter aircraft. The main rotor head design is based on that of the earlier Hughes OH-6 scout helicopter. An air data sensor is prominently mounted on top of the rotor head.

The Apache is very agile, and in fact in its early days it was regarded as one of the most maneuverable helicopters in the world. It can tolerate gee limits from +3 to -2 gees, has pitch limits of 30 degrees, and roll limits of 60 degrees. It apparently can actually perform a barrel roll, but it's not something that pilots who have done it want the brass to find out about, and nobody says much about it.

The default armament of the Apache is a McDonnell Douglas M230 30 millimeter "Chain Gun" (a trademark, incidentally), which is a mechanically operated automatic weapon driven by a bicycle-style chain looped around the firing mechanism box. The scheme is simple -- in fact, so simple that in hindsight it is puzzling that it hadn't been invented a hundred years ago -- as well as lightweight and reliable.

The cannon is supplied with 1,200 rounds of ammunition and has a maximum rate of fire of 650 rounds per minute. Its 30 millimeter ammunition is compatible with the British Aden and French DEFA 30 millimeter cannon. The usual ammunition is the "M789 High-Explosive Dual Purpose (HEDP)" round, which features an armor-piercing hollow charge with a fragmenting case. The HEDP round can penetrate 5 centimeters (2 inches) of rolled steel armor.

The Chain Gun is on a hydraulically-driven swiveling mount between the forward landing gear legs. It can be pointed 11 degrees up, 60 degrees down, and 100 degrees to either side. If hydraulics are lost, the cannon pops to its stowage position, with the barrel forward and up. There is a void in the nose above the cannon into which the weapon collapses in a crash, reducing the likelihood of injury to the crew.

The stub wings can pivot up and down to provide some lift control and to aim stores, and automatically level themselves on landing to make life easier for armorers. The wings do interfere somewhat with hovering flight and, more significantly, can interfere with "autorotation", in which a helicopter that has lost power "flutters" to the ground as its rotor keeps on spinning. The wings generate lift that can work against the tendency to sink, with the result of a harder impact in the end.

The Apache's primary external armament is the laser-guided AGM-114 Hellfire antitank missile, with a stated range of 8 kilometers (5 miles). The initial Army variant of the missile, the AGM-114A, soon gave way to the improved AGM-114C model. The Apache can carry a rack for four Hellfires on each stores pylon, giving a maximum warload of 16 Hellfires.

Another common load are 19-round 70 millimeter (2.75 inch) "Hydra 70" unguided rocket pods. The rockets can be fitted with armor-piercing, general-purpose blast-fragmentation, flechette anti-personnel, smoke, illumination, or training warheads. Although unguided, the gunner can set fuzing options for the rocket warheads to provide a range of options for attacking different classes of targets -- contact detonation for targets in the open, delayed detonation for targets under cover, and timed detonation for "enfilade" attacks on targets hidden by terrain or other obstacles.

A mix of Hellfires, Hydra-70s, or other stores can be carried. The AH-64A can also be fitted with four 772 liter (204 US gallon) external tanks for ferry flights, giving the machine a range of 1,850 kilometers (1,150 MI / 1,000 NMI), impressive for a helicopter.

The Apache's primary sensor suite is the "TADS/PNVS", where "TADS" stands for "Target Acquisition & Designation System" and "PNVS" stands for "Pilot's Night Vision System". It is a somewhat complicated multi-turret system fitted on a horizontal ring mount on the nose:

The AN/ASQ-170 TADS is the gunner's targeting system, and is fitted under the ring mount. It resembles a barrel set on its side. It features four subsystems, including:

• A "direct view optic (DVO)" sensor, really just an optical telescope.
• A "Daylight TV (DT)" camera.
• A forward looking infrared (FLIR) imager.
• A laser rangefinder / spot tracker / target designator.

The TADS turret can be turned 120 degrees to either side, and can be rotated 30 degrees up and 60 degrees down. The FLIR is on the right ("night") side of the barrel. The other four subsystems are on the left ("day") side, with the DVO on top, the DT on bottom, and the much smaller lens for the laser subsystem offset to the left below the DT. The day and night sides can be rotated up and down independently, though of course they move as a unit from side to side. TADS was upgraded in service with optical filters to protect it from laser illumination.

The DVO telescope can be set to a wide-angle field of view (FOV) of 18 degrees or a narrow-angle FOV of 4 degrees; the DT camera has a 4 degree wide FOV and a 0.9 degree narrow FOV; and the FLIR has zoom capability, allowing it to be set to 50, 10, 3.1, or 1.6 degrees. The laser target designator uses a powerful neodymium-YAG solid-state laser and isnot eye-safe, which imposes restrictions on its use in training. The TADS system has a "auto-tracking" capability to allow it to keep the crosshairs on a moving target automatically.

The AN/AAQ-11 PNVS is, as its name suggests, used by the pilot to fly the machine. It is fitted on top of the ring mount, with the sensor lens assembly mounted on top of a flat rotating drum. PNVS consists solely of a wide-angle FLIR imager with no zoom capability, allowing the pilot to fly the machine day or night, in all but the worst weather. The FLIR has a FOV of 40 by 30 degrees (horizontal and vertical respectively), and can be turned 90 degrees to either side, 20 degrees upward, and 45 degrees downward. It can be reversed to protect the optics when not in use.

TADS/PNVS imagery can be backed up on a videotape recorder system for after-action / post-strike analysis, and for training purposes. The videotape system is now way out of date and not compatible with any modern standard videotape player, and work has been done in recent years to fit a modern high-resolution 8-millimeter video recorder in its place.

TADS/PNVS has a stabilization system, as well as fine and coarse aiming mechanisms. The sensor systems are somewhat maintenance-intensive, particularly because flight vibration can misalign them, undermining targeting accuracy. Ground crews spend a fair amount of effort making sure the systems are properly boresighted.

The crew's primary interface to these sensor and targeting systems is the "Integrated Helmet And Display Sight System (IHADSS)", an early and somewhat bulky "smart helmet" with radio, laser-protective visor, and a "Helmet Display Unit (HDU)" known informally as the "hoodoo". TADS and PNVS can be "slaved" to the helmets, meaning the sensor (and, for TADS the laser target designator) follows the movement of the helmets. The Chain Gun can track TADS as well, which is logical since TADS is a sighting system.

The gunner also has a joystick to control TADs and can direct TADS imagery to a small monochrome (green-black) display designated the "Optical Relay Tube (ORT)" instead of the hoodoo. The pilot has a similar but larger "Video Display Unit (VDU)" for PNVS imagery. It would seem logical as well that the pilot has a joystick for PNVS, but if so this is not clear from sources.

The primary piece of countermeasures gear originally fitted to the AH-64A was the AN/APR-39(V)1 radar warning receiver (RWR), with antennas on the left side of the TADS/PNVS turret assembly and on the rear of the tailfin.

The AN/APR-39(V)1 was linked to a small circular display in the pilot's cockpit that gave the bearing of the threat. The RWR also activated an alert lamp and produced an audio alarm in the crew's earphones if the helicopter was being illuminated by a radar. Incidentally, there were a set of different audio alarms for a wide range of problems, such as "engine out", "IFF activation", and so on. The AN/APR-39(V)1 could be set to respond to specific emitters, or to any emitter it detected.

The AH-64A was later fitted with the improved AN/APR-39A(V)1 RWR, which features a "threat library" that can identify a wider range of specific emitters. It can also produce audio warnings that describe the specific threat and give its direction. The AH-64A also carries an AN/AVR-2A(V) laser detector to determine when the gunship is being "marked" by a laser designator, with this piece of gear also proving useful as a training tool to detect "fire" from laser-equipped adversary forces.

The Apache can be optionally fitted with M130 chaff dispensers on each side of the rear tailboom, with each containing 30 chaff cartridges. The M130s can also carry flares to distract heat-seeking missiles, but Apache crews rely on ground cover and not flares for protection since flares can hit the tail rotor and can set ground vegetation on fire. However, the AH-64A does have an AN/ALQ-144 "disco light" heat-seeker jammer mounted just behind the rotor head.

Other avionics includes secure radios, "identification friend or foe (IFF)" systems, and a Doppler-radar based "Heading & Attitude Reference System (HARS)" for navigation. HARS is something of a weak point in the AH-64A's design, since it requires at least six minutes to align itself before the start of a mission.

During the early days of the program, McDonnell Douglas offered versions of the Apache to the US Marine Corps and the US Navy. Both versions would have had corrosion protection for seaborne operation, main rotor blade folding, more tiedown points, and improved electromagnetic interference protection. The Marines were very interested and conducted a two-week evaluation of the Apache in September 1981, including shipboard operation tests.

The Marine version would have not had the Chain Gun, but it would have been able to carry TOW antitank missiles, pods for Zuni 12.7 centimeter (5 inch) heavy unguided rockets (a favored USMC store), and AIM-9 Sidewinders air-to-air missiles (AAMs) or Sidewinder anti-radar missiles (SideARMs), with the Sidewinders fitted to wingtip launch rails. Sidewinder qualifications were performed with the Apache in 1987 and SideARM qualifications were performed in 1988. The Marines really liked the Apache, but the Corps always tends to be the last in line for funding and the money simply wasn't there.

Incidentally, the US Army had some interest in the Sidewinder and SideARM trials, and also performed test firings of the "AIM-28 Air-To-Air Stinger (ATAS)" heat-seeking AAM in 1989. The ATAS was carried in a two-round pod, allowing carriage of four missiles. It lacked the range of the Sidewinder, but the Sidewinder also produced excessive smoke and flame when launched that announced the location of the gunship launch platform. Further firings were performed with the British laser-guided Shorts Starstreak / Helstreak AAM in 1991, which was also carried in a two-round pod.

The Navy "Sea Apache" version would have had a folding tail for shipboard storage; an AN/APG-65 maritime search and targeting radar replacing the TADS/PNVS turret and Chain Gun; a retractable in-flight refueling probe; and the capability to carry four Harpoon, Penguin, or other antiship missiles. The Navy didn't buy off on the concept.

Author: Greg Goebel