Thursday, December 16, 2010

helmet-mounted display systems (HMDS)

By manipulating sensor fusion technologies, avionics manufacturers have since the last decade developed a wide array of helmet-mounted display systems (HMDS) for both fixed-wing combat aircraft and attack helicopters, and which are now being offered the Indian Air Force (IAF).

The present-day HMDS has become a virtual HUD with superimposed imagery when the pilot looks forward, or in the boresight direction. HMDS options today promise breakthrough abilities for night-fighting in the areas of head comfort and safety, cockpit resources organisation/management and situational awareness. Off-boresight, the HMDS provides HUD-like aircraft performance details, threat information and targeting cues in addition to mid-wave and near-infra-red (IR) imagery from a suite of six aircraft-mounted IR sensors and a helmet-mounted night vision sensor. Such HMDS’ provide spherical coverage around the aircraft, even allowing pilots to look sideways and down through the floor. For the Eurofighter EF-2000 Typhoon, BAE Systems is designing a head equipment assembly (HEA) that will present night vision and off-axis targeting and cueing information all via the helmet. The helmet is designed to use image intensification technology to amplify light from external sources, as well as an advanced laser head tracking system. The HEA does not, however, replace the HUD. In both designs visual information provided by sensors--either embedded in the helmet or located elsewhere on the aircraft--will be projected on to a see-through visor patch located on the inside of the visor. This allows for a more compact design with an improved centre of gravity relative to a traditional helmet-mounted night vision goggle (NVG) system. But in order for the pilot to see the imagery correctly, the head gear--an inner lining and a hard outer shell--will require a more precise fit than ever before, hence the introduction of laser scans to measure the exact dimensions of each user's head.
For the F-16IN Super Viper and F/A-18E/F Super Hornet, Vision Systems Int’l, a joint venture company formed by Elbit Systems and Kaiser Electronics, is offering to the IAF the Joint Helmet-Mounted Cueing System (JHMCS), designed to provides pilots with ‘dirst look, first shot’ high off-boresight weapons engagement capabilities. JHMCS enables the pilot to accurately direct (cue) onboard weapons against enemy aircraft while performing high-G aircraft manoeuvres. The pilot needs only to point his/her head at the target and the air combat missiles will be directed to where the pilot is looking. The system can also be employed to accurately cue the pilot to ground targets. As a cueing system, JHMCS is a two-way interface in that sensors on board the aircraft can cue the pilot to potential targets or, conversely, the pilot can cue weapons and sensor systems to areas of interest. Critical information and symbology such as targeting cues and aircraft performance parameters are graphically displayed directly on the pilot’s visor.

For the Tejas LCA, Vision Systems Int’l will be supplying the Dash 3 HMDS, which is customised to individual pilot head shapes and sizes using either poured foam or thermal plastic liners. Once the helmet is fitted to the pilot, the optronics are adjusted to provide the proper exit pupil size for the pilot, since individual pilot’s eyes will differ slightly. The Dash 3 can also accommodate pilots who must wear corrective spectacles. Its all-up weight is 1.65kg for the larger helmet size. An umbilical cable carries power and video drive signals to the internal helmet electronics, and position-sensing signals from the helmet to the signal processor box. The umbilical is provided with a quick disconnect connector to provide for safe ejection. The 8.5kV high-voltage supply for the helmet’s CRT display is embedded within the helmet, so that no high voltages are present on the umbilical. The tube and supply are embedded in the back of the helmet. The Dash 3 projects the CRT image via a folded optical path directly on to the spherical section visor. It provides a solid angle field-of-view (FoV) of 20 degrees, with a 15mm exist pupil for the optics. All symbology is calligraphic, produced by a programmable stroke generator, and a green phosphor is employed. Integration of HMDS modes, HOTAS controls, and weapons system modes have been done in the Tejas LCA’s mission computer operational flight programme and are specific to the IAF’s requirements.

For the Indian Navy’s MiG-29K/KUB carrier-based MRCA, THALES Avionics is supplying its TopSight-F HMDS, which weighs only 1.45kg and provides a 20-degree FoV for the pilot’s right eye, and calligraphic symbology generated from target and aircraft parameters. Electromagnetic position sensing is employed. The TopSight-F, which is also being offered to the IAF along with the Dassault Aviation Rafale F-3 M-MRCA, is primarily employed for display of critical mission information, visual target designation by transmitting the target’s line of sight to the navigation/attack system, performing wide off-boresight target designation for within-visual-range air combat missiles, visual target acquisition via the reverse cueing mode in which the display’s symbology guides the pilot’s eyes to the target tracked by the aircraft sensors, generating concise display of vital tactical, navigation and flight safety data, and providing physiological protection of the pilot (against impact/penetration, windblast, acoustic interference, laser pointing, fire, and loss of oxygen). The TopNight HMDS for attack helicopters is a raster and calligraphic binocular HMDS, designed specifically for adverse weather and nighttime air-to-ground operations. While in general appearance it resembles the TopSight-F, it is heavier at 1.8kg and employs more complex optics to project collimated imagery overlaid with symbology, providing a 30-degree by 40-degree FoV.
As part of its offer for the JAS-39N Gripen NG M-MRCA, Gripen International is offering the Cobra HMDS, which has been co-developed by Saab Aerosystems and BAE Systems. The HMDS displays data directly onto the helmet visor, allowing the pilot to stay ‘heads-up’ at crucial points in the mission. The Cobra is a binocular system that displays both air-to-air and air-to-ground weapons symbology, as well as basic flight data. The helmet and display systems have been developed by BAE Systems, the mask by G4, the helmet tracking system by Denel Optronics of South Africa and the display symbology by Saab. BAE Systems has also developed the Striker HMDS for the EF-2000 Typhoon, another M-MRCA being offered for the IAF. The Striker includes laser head tracking system for target cueing. It incorporates twin image intensifier tubes on the sides of the helmet, providing a binocular 40-degree horizontal by 30-degree vertical FoV with fully overlapped images. The helmet employs a dual-visor configuration--a clear blast/display visor for night and a glare/laser eye protective visor that swivels down for day operations. Analogue symbology information is delivered from aircraft avionics to a CRT display on the helmet via wires. The information is then transferred by a series of lenses and/or mirrors to the visor. The HEA’s optical path, however, includes a ‘brow’ mirror that allows minimised centre-of-gravity (CG) offsets, and hence g-effects on the pilot’s head. The Striker displays ‘virtual heads-up display’ symbology and video imagery from the aircraft’s sensors and from a helmet-mounted, image- intensified night vision system. It is an integral part of the EF-2000’s avionics suite, providing night vision equipment and forward-looking infra-red sensor displays, combined with full navigation and weapons-aiming symbology. The HMDS also provides for interface between the pilot and the EF-2000’s direct voice input system.

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