RAH-66 Comanche

Carrying on the design tradition of American attack helicopters with the tandem cockpit and turreted nose cannon, the RAH-66 Comanche also brings a suite of new technologies shaped to fit the US Army’s 21st century vision. It is a vision often described using terms such as efficiency, economy, flexibility and rapid-deployment. With the reduction of military strength after the cold war and the increasing involvement of the US Army in "Operations Other Than War", it has become evident that future forces need to be of a higher quality. They need to deploy anywhere in the world rapidly and win in combat with the minimum number of casualties.

Combining systems initially developed for the Apache and Light Helicopter Experimental (LHX) program with new high-technology systems, the Boeing Sikorsky RAH-66 Comanche represents the state-of-the-art in attack helicopters.

Visually, the most striking feature is the exterior body shape. Using what is known as low observable (LO) properties, the fuselage is designed to reflect radar energy away from any transmission source. Boeing claims the radar signature is around 1/300th of current aircraft. To maintain a low radar profile, stores can be hidden in IRAMS (Integrated Retractable Munitions System), this is an internal weapons bay capable of holding 6 Hellfire missiles. Mounting stores internally in such a way prevents any radar energy being deflected back off the weapon and thus increasing the helicopter’s radar cross section (RCS). Should the mission profile call for firepower over stealth then additional weapons may be fitted under removable wings. A total of 14 Hellfire missiles can be fitted in this configuration.

The Comanche has an advanced bearingless composite rotor with swept blade tips that reduces its acoustic signature, particularly at the reduced RPM levels of the so-called "quiet" flight mode. The low-noise rotor system, reduced infrared exhaust and small radar cross-section make the Comanche the stealthiest helicopter in the world. While not invisible to radar it is much harder to detect at longer ranges.

Sensors are mounted on the nose and top of the rotor mast in a similar configuration to the AH-64D Longbow Apache. Indeed the RAH-66 boasts the next generation Longbow radar system that is half the size of the previous model fitted to the Apache D model. Mounted on the nose is a second generation FLIR (forward looking infrared), this has double the resolution of the FLIR pod fitted to the Apache. This second generation FLIR permits more reliable target recognition at 40% greater range. With 100% greater resolution and 35% greater field of view, it is much safer for night flying which should give some comfort to the crew.

In populated regions the greatest threat to a helicopter operating at night comes from suspended or overhead cables. Whenever conventional helicopters are lost or damaged it is usually through a cable strike. The improved FLIR can resolve cables that have small currents running through them; electrical currents heat up wire to a point where they begin to "glow" by a small amount in the infrared spectrum. To further reduce the risk of wire strikes, the Comanche is fitted with a wire detector that provides an audible warning should it stray too close to a current carrying cable.

Flying the AH-64 Apache using the PNVS (pilots night vision system – presented via a helmet mounted monocle) has been described as, "trying to fly a helicopter by looking through a drinking straw". The RAH-66 comes with a 53° wide field of vision holographic helmet mounted display system and is biocular. Called HIDSS, the Helmet Integrated Display and Sight System delivers FLIR sensor, flight and targeting symbology to both eyes. As in the Apache, weapon targeting can be slaved to the pilots’ helmet movements. Wherever the pilots look, the helicopter sensors will follow. In addition to this, the chin mounted 20mm GIAT Vulcan-II cannon can also be slaved to follow the pilots’ head movements. When not in use, the cannon is normally stowed in a LO cowling positioned under the chin.

Front and rear cockpit configurations are near identical. The fly-by-wire flight control system is triply redundant, the cyclic side-stick includes a twist action which controls aircraft yaw. When used with flight assist modes the Comanche can be flown with just one hand. This makes the Comanche a remarkably easy aircraft to control.

The cockpit is over-pressurized to prevent any possible crew contamination from NBC - nuclear, biological or chemical agents. Should the cockpit suffer a minor breach after an attack the positive cabin pressure will prevent any contaminant invading the crew area.

On-board computing power is equivalent to four super computers, however only 10% of this power is needed to fly the aircraft; the rest is utilized in a highly advanced mission equipment package. For target acquisition, there is automatic visual and radar target recognition. Depending on the orientation of the target to the sensor, the computer can distinguish not only between wheeled and tracked vehicles, but also determine vehicle type. It has the remarkable ability of recognizing the difference between an M1 Abrams and a T-80.

EO sensors can be set to visually scan a crew-designated sector and automatically classify and track high-priority targets detected within that sector. Target removal is via man-in-the-loop battle damage assessment, if a target has been hit and destroyed, the operator is required to confirm destruction before it is removed from the tactical picture.

Sensor information can be shared with other elements of the combined arms team via a "tactical internet". Command & Control (C2), ground forces, JSTARS, AWACS, indeed any compatible system can exchange correlate and share tactical information with the Comanche systems. Supported protocol stacks include; AFTDS, AFAPD, TACFIRE, VMF, and MTS. Other tactical information distribution systems can be easily incorporated.

For communications, an existing system known as Air Force Integrated Communications Navigation Identification Avionics, is used for interoperability. In addition there are two VHF-FM single channel ground and airborne radio systems, a VHF-AM radio set and a HF (high frequency) radio for non-line of sight communications. An IDM or Improved Data Modem is used for communicating with the tactical internet.

Mission planning and rehearsal can be done completely in-cockpit using the advanced "Tactical Mode". Digital terrain maps provide elevation and feature data, which are optionally overlaid with a tactical situation display then rendered in plan or a real-time 3D perspective view. The map can be overlaid with threat forces, friendly positions, waypoint information and calculate intervisibilities. It can be used for threat avoidance or enroute mission planning. Positional information comes from a composite GPS/Doppler/Inertial navigation system that is constantly cross-checking and updating itself.

Each processor is an easily replaceable module common to the Air Force and Navy. If a module should fail, the systems reconfigure themselves allowing the Comanche to remain in battle and continue its mission despite malfunctions or battle damage.

Analysis of conducted exercises have shown that maneuverability, rate of climb, tandem (instead of side-by-side) cockpit configuration and a turreted gun are winning combinations in head to head helicopter engagements.

Development History

Back in 1981, a plan was drawn up for a single basic utility helicopter called LHX (Light Helicopter Experimental). The intention was to replace the aging UH-1, OH-58 and AH-1 fleets with a production run of 5,000 LHXs. To fulfil the diverse mission roles currently undertaken by the existing fleet, different LHX models were to be equipped with a large variety of new technologies and mission equipment packages. While it was considered to be an expensive program, military spending was generous under the current administration. Six years later in 1987 these mission roles were substantially reduced to scout and attack only. The projected LHX requirement then fell to around 2,000.

The upgrade/replacement program needed a rethink and quite possibly a different helicopter better suited to the narrower mission profile. In 1988 the Department Of Defense issued a "Request for Proposals", the request received a rapid response from Boeing Helicopters in collaboration with Sikorsky Aircraft.

In 1990, the projected number of new helicopters required was further reduced to 1,292 with an option of a further order of some 400. A year later, the Boeing Sikorsky partnership was awarded a contract to build 4 prototypes, designated the RAH-66 (RAH being an acronym of Reconnaissance Attack Helicopter).

Modernisation programs for the Apache and Kiowa were started with a view to enhance real-time intelligence gathering and distribution capabilities. These programs helped shape Army XXI’s view of the electronic battlefield and have in-turn influenced Comanche systems specification.

A combination of cost reviews and specification changes initially resulted in patchy development. At present, the Boeing Sikorsky team manages some 1,100 major subcontractors and suppliers across the United States, quite a feat of co-ordination. Recent successes with two flying prototype Comanches have been good news for the program. The U.S Defense Department has approved an early operational capability program, which will provide six additional aircraft to the U.S Army so they can begin operational testing. These new aircraft will be manufactured in 2001.

Meanwhile, digitization programs of OH-58 Kiowa and AH-64D Apache continue, results suggest both platforms can be integrated more closely with ground forces than previously thought. They will integrate well with the Comanche when it becomes operational and eventually the older OH-58 will be finally phased out.

Initial operating capability (IOC) for the U.S Army’s Comanche is set for 2006. While the Comanche has its critics in the Senate and Pentagon, in the Army there is no doubt that the RAH-66 will be an indispensable asset in the early 21st century battlefield.

Specifications

Armament

Featured in Comanche Hokum

• 20mm three-barrel Gatling gun
• Longbow Hellfire missile
• AIM-92 Stinger missile
• Hydra 70 rocket

  NATO export options - not featured in Comanche Hokum

• Army Counter Air Weapon System
• TOW II missile
• Starstreak
• Matra Mistral
• Euromissile HOT II
• Sura D-81mm rocket
• Oerlikon Snora 81-mm rocket

Features

• Five-bladed bearingless main rotor
• Fantail anti-torque system
• Triply redundant fly-by-wire control system
• Low-workload crew cockpit
• 4 x large flat panel colour multifunction displays
• Wide field-of-view biocular helmet mounted display
• Low observable properties throughout
• Self-healing electronics
• Onboard electronic technical manual
• Simple plug-and-remove modular maintenance
• Internal missile bay
• Stowable three-barrel 20-mm Gattling gun