Published in the July/August 2020 Issue – Tracing the development of high tech flying helmets for frontline pilots.
Flying wearing a helmet mounted sight, a pilot only has to look at the target to cue the onboard weapons, while the data displayed in front of the pilot’s eyes frees the need to constantly look down at the cockpit displays, or even to look ahead through the Head Up Display (HUD).
The simple leather helmets worn by the earliest military aviators provided warmth in an open cockpit, but afforded little protection, and no extra functionality. Most aircrew also wore separate goggles, and sometimes a silk scarf over the unprotected lower part of the face. By the Second World War, helmets had gained oxygen masks and integral headphones. The arrival of the jet age saw the widespread introduction of ejection seats, and a hard outer shell was worn on the head, creating the first ‘bone dome’ or ‘brain bucket’. Goggles gave way to a visor, which was soon made integral with the helmet itself, but helmets themselves then changed very little until the 1970s and 1980s, though efforts were made to reduce their weight, to improve their comfort, and to provide better protection.
The development of night vision goggles in the 1960s and 1970s initially led to no major changes to helmet design. NVGs were typically mounted on the front of a helmet (usually replacing the visor) on a simple mount that allowed them to be swung down into the pilot’s sightline when required. Heavy batteries were sometimes Velcro’d to the back of the helmet to compensate for the additional weight at the front.
The next major change came with the development of missile cueing systems, which were designed to allow a fighter pilot to ‘point’ the seeker head of a missile at its target, rather than having to ‘boresight’ the enemy aircraft – manoeuvring to place the enemy aircraft centrally in the head up display where the missile seeker would ‘see’ it.
The first useable helmet mounted missile sight was probably the Honeywell Visual Target Acquisition System (VTAS) produced for the US Navy, with a ‘granny glass’ monocular eyepiece providing an aiming reticle, and comprehensive head trackers to allow the weapons system to work out exactly where the pilot was looking. The system could direct the radar where to point, which in turn cued the missile seeker, and there was a mode that allowed the helmet to directly cue the seeker. The system could also provide simple up/down left/right cues to direct the pilot’s eye onto a target.
The system was fielded on about 500 Navy and Marine Corps F-4 Phantom fighters from 1973 to about 1979, but was then abandoned, though it did influence work on similar systems being developed in South Africa and the Soviet Union. The South African Cat’s Eye HMS programme resulted in the first operationally deployed helmet sight, initially teamed with the indigenous Armscor V3A Kukri AAM on the Mirage F1. Soviet HMS studies started in 1969 at the Kiev Arsenal plant, resulting in the development of the Schel-3U, which was ordered into production in 1977 to equip the new MiG-29 and Su-27 fighters.
The combination of the Schel helmet sight and the new thrust vectoring R-73 (AA-11 ‘Archer’) gave the new fighters a formidable ‘off boresight’ capability, and kick started the development of a new generation of helmet-mounted sights and display systems in the West.
A very similar Marconi/Honeywell Helmet Mounted Sighting System was used by Royal Air Force Jaguars (and later Tornados) primarily for sensor cueing, slaving the TIALD laser designator pod to the pilot’s sightline, demonstrating that helmet sights are not only useful in the air-to-air environment. It could also be used to update the aircraft’s navigation system, and, of course, for off-boresight missile aiming.
Attack helicopters provided the first application for more complex helmets. The Boeing AH-64 Apache’s Integrated Helmet & Display Sighting System (IHADSS) allows the pilot or gunner to slave the helicopter’s 30mm M230 Chain Gun to their helmet, so that the gun points where they are looking. The helmet can also be used to steer the slewable thermal camera system and sighting system mounted on the nose of the aircraft. The helmet’s monocular display had a 40° by 30° field of view, presenting video and raster symbology.
Israel’s Elbit Systems produced the first modern Western HMD to enter operational service. Like the older South African system, the company’s DASH (Display and sight helmet) used a CRT to project symbology onto the spherical visor to provide a collimated image to the pilot. Produced in a succession of progressively improved versions, the original DASH provided the basis of a digital variant with advanced video and colour capabilities and also led to a number of derivatives, including the US Joint Helmet-Mounted Cueing System (JHMCS)
JHMCS (pronounced juh-hamicks) was a derivative of the DASH III and the Kaiser Agile Eye, and was developed by a joint venture company formed by Elbit Vision Systems International (VSI) and Rockwell Collins (who bought out Kaiser Electronics). JHMCS presented collimated cursive symbology and raster scanned imagery to the pilot in monochrome, displaying FLIR/IRST pictures for night operations and allowing standard night-vision goggles to be used. The Digital JHMCS (D-JHMCS) is an upgrade to the existing system, and added advanced video and colour capabilities. It provides NVCD (night symbology) and offers improved comfort and a better optimised centre of gravity.
The newer JHMCS II system is designed for new applications and provides a new optical-inertial head tracker which does not require cockpit mapping. It also uses a new lightweight Aircraft Interface Unit (ACIU) which does not require a mounting tray or additional cooling and has support for virtual training.
Both D-JHMCS and JHMCS II can be integrated with Elbit’s Canary system, which can provide advance warning of hypoxia and can trigger automatic aircraft recovery if the pilot loses consciousness.
Integration on US frontline fighter types and adoption by the US armed forces has given the JHMCS a tremendous competitive advantage, but there are other options, some of them more capable.
The latest derivative of the DASH is Elbit’s TARGO 2 which was originally marketed as a low-cost, low-integration solution for light attack, airlift, and trainer aircraft. Interestingly, the TARGO 2 has been selected by a number of recent Dassault Rafale export customers, while the Swedish Defence Material Administration (FMV) has ordered an unspecified number of Targo helmet-mounted display and sight (HMD/S) systems for the new JAS-39E/F Gripen.
Elbit Systems used DASH technology as the basis of the new Jedeye helmet mounted system developed for rotary wing applications. The system has an unusually wide 70 by 40 degree field of view, and can present dual-vision 3D imagery, useful for augmented reality applications, including brownout mitigation systems.
Sextant Avionique (now part of Thales) has developed a family of Helmet Mounted Display systems, initially producing the futuristic-looking TopSight for the Rafale and late model Mirage 2000. The helmet uses a contoured external face guard which covers the oxygen mask, with no impairment of the pilot’s peripheral vision. Topsight provides a 20 degree field of view for the pilot’s right eye, and employs electromagnetic head tracking.
The heavier TopNight and TopOwl use more advanced optics and project collimated imagery overlaid with symbology, providing a 30 x 40 degree binocular field of view, optimised for adverse weather and night air to ground operations. TopOwl provides integrated night vision using light intensifiers placed on both sides of the helmet, removing the need for separate NVGs. Turkey’s Aselsan is developing a similar system, known as the AVCI Helmet Integrated Cueing System for the T-129 ATAK helicopter.
Thales developed the Scorpion Head/Helmet-Mounted Display System to meet a USAF/ANG/AFRes requirement. A full-colour monocular, the Scorpion Helmet Mounted Integrated Targeting system uses a Hybrid Optical based Inertial Tracker (HObIT) requiring no mapping of the aircraft cockpit, and can be installed on a standard issue USAF flight helmet without special fitting. It is fully compatible with standard and panoramic Night Vision Goggles, and can be worn behind a standard clear, glare, high contrast, gradient, or laser protective helmet visor.
Originally known simply as the HEA (head equipment assembly) or HMSS (Helmet-Mounted Symbology System) the Striker helmet developed by BAE Systems for the Eurofighter Typhoon is platform agnostic, and a derivative, the Cobra, is in use on the Saab JAS39 Gripen. The original Striker was distinguished by a rash of bumps over much of the surface. These bumps were infra-red LEDs used in association with three sensors in the cockpit for accurate head tracking, in order to accurately calculate exactly where the pilot is looking with no lag or latency.
An advanced derivative the Striker II, is lighter and more comfortable to wear and incorporates an integral night vision camera inside the helmet, allowing it to be used at night. Striker II is claimed to be the world’s only helmet-mounted display that combines a daylight readable colour display, a 40⁰ field of view, and integrated night vision.
The Striker II supports the display of imagery from high resolution sensor systems including distributed aperture systems like that fitted to the F-35, and which effectively allows a pilot to ‘see’ through the body of the aircraft.
One feature of the Striker II that is claimed to be unique is its 3D audio capability, which is coupled with intelligent active noise reduction (ANR). The 3D audio system provides 360-degree directional audio, allowing the pilot to hear threat warnings from the appropriate direction, and to tailor the direction from which specific communications are heard, so that ground communications appear to sound as though they originate from below the aircraft. The ANR system greatly improves audio clarity by significantly reducing environmental noise, even on board the noisiest platforms.
The Striker II is very light, with better balance and a lower centre of gravity than most of today’s current HMD/NVG solutions. This improves pilot comfort during high g manoeuvres, reduces neck loads, and decreases fatigue during long endurance missions. The inner liner is manufactured to the exact shape of the wearer’s head, using laser scanning, and is finished with Italian leather. Helmet fit is carefully tailored to ensure optimum weight distribution for every individual pilot.
The closely related Cobra HMD used by South African and Swedish Gripens combines a helmet and display system developed by BAE Systems, display symbology by Saab, and a helmet tracking system provided by Denel Optronics of South Africa.
The Lockheed F-35 Joint Strike Fighter was designed without a head up display, meaning that the pilot relies completely on his Helmet Mounted Display System (HMDS) for critical flight and weapons aiming information, which effectively provides a virtual Head-Up Display. The F-35 HMDS was developed by RCEVS ‒ a joint venture between Rockwell Collins and Elbit Systems’ Vision Systems International.
The F-35 HMDS provides the usual off-axis targeting and cueing capabilities and comprehensive symbology, but can also present video imagery in day or night conditions, including video from the aircraft’s Distributed Aperture System. This allows the pilot to virtually ‘look through’ the cockpit floor (for example). The HMDS also provides fully integrated visor projected night vision capabilities.
The HMDS suffered from severe night-vision, latency and jitter problems during development, and in September 2014, Lockheed Martin awarded a contract to BAE Systems to develop an alternative ‘low risk’ helmet design BAE proposed a hybrid helmet that combined the two-part inner and outer shell design of its Striker helmet with a clip-on Q-Sight holographic monocular display, an optical head tracking system and conventional ‘swing down’ binocular NVGs.
The BAE helmet achieved every milestone and promised to offer a reliable, dependable and affordable alternative to the RCEVS design, but would have required some changes to the cockpit. It was originally planned that both helmets would take part in a competitive fly-off, but the competition was cancelled on cost grounds when problems affecting the original helmet started to be solved. One of the final issues to be solved was inadequate helmet line-of-sight accuracy for strafing. This was eventually sorted by replacing the original head tracker with a new hybrid optical-magnetic tracker.
The HMDS is the first aircraft primary flight display to be worn by the pilot, and is claimed to be a third-generation HMD system. Rockwell Collins is hoping to find other applications for the F-35 HMDS, but with a quoted price tag of $400,000, the market may be limited.
by Jon Lake