Helmet-mounted display

A helmet-mounted display (HMD) is a device used in some modern aircraft, especially combat aircraft. HMDs project information similar to that of head-up displays (HUD) on an aircrew's visor or reticle, thereby allowing them to obtain situation awareness and/or cue weapons systems to the direction his head is pointing. Applications which allow cuing of weapon systems are referred to as helmet-mounted sight and display (HMSD) or helmet-mounted sights (HMS). These devices were created first by South Africa, then the Soviet Union and followed by the United States.

Aviation HMD designs serve these purposes:

HMD systems, combined with High Off-Boresight (HOBS) weapons, results in the ability for aircrew to attack and destroy nearly any target seen by the pilot. These systems allow targets to be designated with minimal aircraft maneuvering, minimizing the time spent in the threat environment, and allowing greater lethality, survivability, and pilot situational awareness.

In 1962, Hughes Aircraft Company revealed the Electrocular, a compact CRT, head-mounted monocular display that reflected a TV signal onto a transparent eyepiece.

The first aircraft with simple HMD devices appeared for experimental purpose in the mid-1970s to aid in targeting heat seeking missiles. These rudimentary devices were better described as Helmet-Mounted Sights. Mirage F1AZ of the SAAF (South African Air Force) used a locally developed helmet-mounted sight. This enables the pilot to make bore attacks, without having to maneuver to the optimum firing position. South Africa subsequently emerged as one of the pioneers and leaders in helmet-mounted sight technology. The SAAF was also the first air force to fly the helmet sight operationally. The US Navy's Visual Target Acquisition System (VTAS), made by Honeywell Corporation was a simple mechanical "ring and bead"–style sight fitted to the front of the pilot's helmet that was flown in the 1974–78 ACEVAL/AIMVAL on U.S. F-14 and F-15 fighters

VTAS received praise[by whom?] for its effectiveness in targeting off-boresight missiles, but the U.S. did not pursue fielding it except for integration into late-model Navy F-4 Phantoms equipped with the AIM-9 Sidewinder. HMDs were also introduced in helicopters during this time.[citation needed] were fielded by the South African Air Force. After the South African system had been proven in combat, playing a role in downing Soviet aircraft over Angola, the Soviets embarked on a crash program to counter the technology. As a result, the MiG-29 was fielded in 1985 with an HMD and a high off-boresight weapon (R-73), giving them an advantage in close in maneuvering engagements.

Several nations[which?] responded with programs to counter the MiG-29/HMD/R-73 (and later Su-27) combination once its effectiveness was known, principally through access to former East German MiG-29s that were operated by the unified German Air Force.

One successful HMD was the Israeli Air Force Elbit DASH series, fielded in conjunction with the Python 4, in the early 1990s. The U.S., UK, and Germany pursued a HMD combined with ASRAAM systems. Technical difficulties led to the U.S. abandoning ASRAAM, instead funding development of the AIM-9X and the Joint Helmet-Mounted Cueing System in 1990. American and European fighter HMDs became widely used in the late 1990s and early 2000s.

While conceptually simple, implementation of aircraft HMDs is quite complex. There are many variables:

HMD designs must sense the elevation, azimuth and tilt of the pilot's head relative to the airframe with sufficient precision even under high "g" and during rapid head movement. Three basic methods are used in current HMD technology – optical, electromagnetic and sonic.

Hybrid inertial tracking systems employs a sensitive Inertial Measurement Unit (IMU) and an optical sensor to provide reference to the aircraft. The optical sensor also constrains IMU drift. Hybrid trackers feature low latency and high accuracy. The * Scorpion HMCS utilizes a tracker called the Hybrid Optical-based Inertial Tracker (HObIT).

Optical systems employ infrared emitters on the helmet (or flightdeck) infrared detectors in the flightdeck (or helmet), to measure the pilot's head position. The main limitations are restricted fields of regard and sensitivity to sunlight or other heat sources. The MiG-29/AA-11 Archer system uses this technology. The Cobra HMD as used on both the Eurofighter Typhoon and the JAS39 Gripen both employ the optical helmet tracker developed by Denel Optronics (now part of Zeiss Optronics ).

Electromagnetic sensing designs use coils (in the helmet) placed in an alternating field (generated in the flightdeck) to produce alternating electrical voltages based on the movement of the helmet in multiple axes. This technique requires precise magnetic mapping of the flightdeck to account for ferrous and conductive materials in the seat, flightdeck sills and canopy to reduce angular errors in the measurement.

Acoustic sensing designs use ultrasonic sensors to monitor the pilot's head position while being updated by computer software in multiple axes. Typical operating frequencies are in the 50 to 100 kHz range and can be made to carry audio sound information directly to the pilot's ears via subcarrier modulation of the sensong ultrasonic sensing signals.

Older HMDs typically employ a compact CRT embedded in the helmet, and suitable optics to display symbology on to the pilot's visor or reticle, focused at infinity. Modern HMDs have dispensed with the CRT in favor of micro-displays such as liquid crystal on silicon (LCOS) or liquid crystal display (LCD) along with a LED illuminator to generate the displayed image. Advanced HMDs can also project FLIR or NVG imagery. A recent improvement is the capability to display color symbols and video.

Systems are presented in rough chronological order of initial operating capability.

In 1985, the U.S. Army fielded the AH-64 Apache and with it the Integrated Helmet and Display Sighting System (IHADSS), a new helmet concept in which the role of the helmet was expanded to provide a visually coupled interface between the aviator and the aircraft. The Honeywell M142 IHADSS is fitted with a 40° by 30° field of view, video-with-symbology monocular display. IR emitters allow a slewable thermographic camera sensor, mounted on the nose of the aircraft, to be slaved to the aviator's head movements. The display also enables Nap-of-the-earth night navigation. IHADSS is also used on the Italian Agusta A129 Mangusta.

The Russian designed Shchel-3UM HMD design is fit to the ZSh-5 series helmet, and is used on the MiG-29 and Su-27 in conjunction with the R-73 (missile). The HMD/Archer combination gave the MiG-29 and Su-27 a significantly improved close combat capability and quickly became the most widely deployed HMD in the world.

The Elbit Systems DASH III was the first modern Western HMD to achieve operational service. Development of the DASH began during the mid-1980s, when the IAF issued a requirement for F-15 and F-16 aircraft. The first design entered production around 1986, and the current GEN III helmet entered production during the early to mid-1990s. The current production variant is deployed on IDF F-15, and F-16 aircraft. Additionally, it has been certified on the F/A-18 and F-5. The DASH III has been exported and integrated into various legacy aircraft, including the MiG-21. It also forms the baseline technology for the US JHMCS.

The DASH GEN III is a wholly embedded design, where the complete optical and position sensing coil package is built within the helmet (either USAF standard HGU-55/P or the Israeli standard HGU-22/P) using a spherical visor to provide a collimated image to the pilot. A quick-disconnect wire powers the display and carries video drive signals to the helmet's Cathode Ray Tube (CRT). DASH is closely integrated with the aircraft's weapon system, via a MIL-STD-1553B bus.

After the U.S. withdrawal from ASRAAM, the U.S. pursued and fielded JHMCS in conjunction with the Raytheon AIM-9X, in November 2003 with the 12th and 19th Fighter Squadrons at Elmendorf AFB, Alaska. The Navy conducted RDT&E on the F/A-18C as lead platform for JHMCS, but fielded it first on the F/A-18 Super Hornet E and F aircraft in 2003. The USAF is also integrating JHMCS into its F-15E, F-16, and F-22 aircraft.

JHMCS is a derivative of the DASH III and the Kaiser Agile Eye HMDs, and was developed by Vision Systems International (VSI), a joint venture company formed by Rockwell Collins and Elbit (Kaiser Electronics is now owned by Rockwell Collins). Boeing integrated the system into the F/A-18 and began low-rate initial production delivery in fiscal year 2002. JHMCS is employed in the F/A-18A++/C/D/E/F, F-15C/D/E, and F-16 Block 40/50 with a design that is 95% common to all platforms.

Unlike the DASH, which is integrated into the helmet itself, JHMCS assemblies attach to modified HGU-55/P, HGU-56/P or HGU-68/P helmets. JHMCS employs a newer, faster digital processing package, but retains the same type of electromagnetic position sensing as the DASH. The CRT package is more capable, but remains limited to monochrome presentation of cursive symbology. JHMCS provides support for raster scanned imagery to display FLIR/IRST pictures for night operations and provides collimated symbology and imagery to the pilot. The integration of the night-vision goggles with the JHMCS was a key requirement of the program.

When combined with the AIM-9X, an advanced short-range dogfight weapon that employs a Focal Plane Array seeker and a thrust vectoring tail control package, JHMCS allows effective target designation up to 80 degrees either side of the aircraft's nose. In March 2009, a successfully 'Lock on After Launch' firing of an ASRAAM at a target located behind the wing-line of the ‘shooter' aircraft, was demonstrated by a Royal Australian Air Force (RAAF) F/A-18 using JHMCS.

Thales Introduced the Scorpion Helmet-Mounted Cueing System to the military aviation market in 2008. Scorpion was the winner of the Helmet Mounted Integrated Targeting (HMIT) program in 2010. Scorpion has the distinction of being the first color HMD introduced. It was developed for targeting pod best steel water bottle, gimbaled sensor or high off-boresight missile cueing mission scenarios. Unlike most HMDs aluminium drink bottle, which require custom helmets, Scorpion was designed to be installed on standard issue HGU-55/P and HGU-68/P helmets and is fully compatible with standard issue U.S. Pilot Flight Equipment without special fitting waterproof camera case. It is also fully compatible with standard unmodified AN/AVS-9 Night Vision Goggles (NVG) and Panoramic Night Vision Goggles (PNVG).

Scorpion uses a novel optical system featuring a light-guide optical element (LOE) which provides a compact color collimated image to the pilot. This allows the display to be positioned between the pilot's eyes and NVGs. The display can be positioned as the pilot wishes. Sophisticated software correction accommodates the display position, providing an accurate image to the pilot and allowing the Scorpion HMCS to be installed onto a pilot's existing helmet with no special fitting. A visor can be deployed in front of the display providing protection during ejection. The visor can be clear, glare, high contrast, gradient, or laser protective. An NVG mount can be installed in place of the visor during flight. Once installed, NVGs can be placed in front of the display, thus allowing the pilot to view both the display symbols as well as the NVG image simultaneously.

Scorpion has been deployed on the U.S. A-10C and F-16 Block 30 and F-22 aircraft. The first squadron to deploy into Afghanistan in early 2013 with the HMIT (Scorpion) system was the 74th Fighter Squadron.

The U.S. Army Common Helmet Mounted Display (CHMD) program was awarded to Raytheon in early 2013 and will implement a new display from Thales for the integration effort. CHMD is part of the Air Warrior program. The Thales CHMD features an upgraded LOE display with a larger field of view than the HMIT version. CHMD is designed to mount to a standard HGU-56/P Rotary Wing helmet.

Aselsan of Turkey is working to develop a similar system to the French TopOwl Helmet, called the AVCI Helmet Integrated Cueing System. The system will also be utilized into the T-129 Turkish Attack Helicopter.

The French thrust vectoring Matra MICA (missile) for its Dassault Rafale and late-model Mirage 2000 fighters was accompanied by the Topsight HMD by Sextant Avionique. TopSight provides a 20 degree FoV for the pilot's right eye, and cursive symbology generated from target and aircraft parameters. Electromagnetic position sensing is employed. The Topsight helmet uses an integral embedded design, and its contoured shape is designed to provide the pilot with a wholly unobstructed field of view.

TopNight, a Topsight derivative, is designed specifically for adverse weather and night air to ground operations, employing more complex optics to project infrared imagery overlaid with symbology. The most recent version the Topsight has been designated TopOwl-F, and is qualified on the Mirage-2000-5 Mk2 and Mig-29K.

The Eurofighter Typhoon utilizes the Helmet-Mounted Symbology System (HMSS) developed by BAE Systems and Pilkington Optronics. It is capable of displaying both raster imagery and cursive symbology, with provisions for embedded NVGs. As with the DASH helmet, the system employs integrated position sensing to ensure that symbols representing outside-world entities move in line with the pilot's head movements.

Vision Systems International (VSI; the Elbit Systems/Rockwell Collins joint venture) along with Helmet Integrated Systems, Ltd. developed the Helmet-Mounted Display System (HMDS) for the F-35 Joint Strike Fighter aircraft. In addition to standard HMD capabilities offered by other systems, HMDS fully utilizes the advanced avionics architecture of the F-35 and provides the pilot video with imagery in day or night conditions. Consequently, the F-35 is the first tactical fighter jet in 50 years to fly without a HUD. A BAE Systems helmet was considered when HMDS development was experiencing significant problems, but these issues were eventually worked out. The Helmet-Mounted Display System was fully operational and ready for delivery in July 2014.

JedEyes TM is a new system recently introduced by Elbit Systems especially to meet Apache and other rotary wing platform requirements. The system is designed for day, night and brownout flight environments. JedEyes TM has a 70 x 40 degree FOV and 2250x1200 pixels resolution.

Sweden's JAS 39 Gripen fighter utilizes the Cobra HMD, developed by BAE Systems, Denel Optronics of South Africa, and Saab. It has been exported to the South African Air Force.