Modern aircraft Helmet Mounted Displays
(HMD) project information similar to that of heads up displays
(HUD) on an aircrew’s visor or reticle, thereby allowing him to obtain situational awareness and/or cue weapons systems to the direction his head is pointing. Some aplications refer to these devices as Helmet Mounted Sight and Display (HMSD) or Helmet Mounted Sights (HMS). For non-aviation applications, see Head mounted displays
Aviation HMD designs serve two basic purposes:
- using the pilot's eye (actually head angle) as a pointing device to direct air-to-air and air-to-ground weapons seekers or other sensors (e.g., radar, FLIR) to a target merely by pointing his head at the target and actuating a switch via HOTAS controls. In close combat prior to HMDs, the pilot had to align the aircraft to shoot at a target. HMDs allow the pilot to simply point his head at a target, designate it to weapon and shoot.
- displaying targeting and aircraft performance information (such as airspeed, altitude, target range, weapon seeker status, "G", etc.) to the pilot while "heads-up", eliminating the need to look inside the cockpit.
HMD systems, combined with High Off Bore Site (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.
The first aircraft HMD devices appeared in the mid seventies to aid in targeting heat seeking missiles. These rudimentary devices were better described as Helmet Mounted Sights. The first of these to see wide use was the US Navy
's Visual Target Acquisition System (VTAS), made by Honeywell
Corporation. VTAS 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
VTAS received praise 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.
The Soviet Union observed the ACEVAL/AIMVAL and embarked on a crash program to counter the technology. As a result, the MiG-29 was fielded in 1985 with an HMS and a high off-boresight weapon (AA-11 Archer/R-73), giving them the advantage in close in maneuvering engagements.
Several nations responded with programs to counter the MiG-29/HMS/AA-11 (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.
The first successful Western HMD was the Israeli Air Force Elbit DASH series, fielded in conjunction with the Python 4, in the early 1990s. American and European fighter HMDs lagged behind, not becoming widely used until the late 1990s and early 2000s. The US-UK-Germany responded initially with a combined ASRAAM effort. Technical difficulties led to the US abandon ASRAAM and embark on AIM-9X and the Joint Helmet Mounted Cueing System in 1990.
While conceptually simple, implementation of aircraft HMDs is quite complex. Many considerations must be taken into account:
- precision - the angular error between the line-of-sight and the derived cue. The position of the helmet is what is used to point the missile, it thus must be calibrated and fit securely on the pilot's head. The line between the pilot's eye and the reticle on the visor is known as the line of sight (LOS) between the aircraft and the intended target. The user's eye must stay aligned with the sight – in other words, current HMDs cannot sense where the eye is looking, but can place a "pipper" between the eye and the target.
- latency or slew rate - how much lag there is between the helmet and the cue.
- field of regard - the angular range over which the sight can still produce a suitably accurate measurement.
- weight and balance - total helmet weight and its center of gravity, which are particularly important under high "g" maneuvers. Weight is the largest problem faced by fighter aircraft HMD designers. This is much less a concern for helicopter applications, making elaborate helicopter HMDs common.
- safety and cockpit compatibility, including ejection seat compatibility.
- optical characteristics – calibration, sharpness, distant focus (or 'Collimation', a technique used to present the images at a distant focus, which improves the readability of images), monocular vs. binocular imagery, eye dominance, and binocular rivalry.
- durability and ability to handle day to day wear and tear.
- cost, including integration and training.
- fit and interfacing the aviator's head to the aircraft – head anthropometry and facial anatomy make helmet fitting a crucial factor in the aviator's ability to interface with the aircraft systems. Misalignment or helmet shift can cause an inaccurate picture.
Head Position Sensing
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. Two basic methods are used in current HMD technology - optical and electromagnetic.
systems employ infrared
emitters on the helmet (or cockpit
) and infrared detectors in the cockpit (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.
sensing designs use coils (in the helmet) placed in an alternating field (generated in the cockpit) to produce alternating electrical voltages
based on the movement of the helmet in multiple axes. This technique requires precise magnetic mapping of the cockpit to account for ferrous
materials in the seat, cockpit sills and canopy to reduce angular errors in the measurement.
Modern 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
. Advanced HMDs can also project FLIR or NVG
Systems are presented in rough chronological order of initial operating capability
Integrated Helmet And Display Sight System (IHADSS)
In 1984, 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 provided 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 IR imaging 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 A-129.
ZSh-5 / Shchel-3UM
The Russian designed Shchel-3UM HMD design is fit to the ZSh-5 series helmet, and is used on the MiG-29
in conjunction with the AA-11 Archer
. 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.
Display And Sight Helmet (DASH)
The Elbit Systems
DASH III was the first modern Western HMD to achieve operational service. Evolution 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
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.
Joint Helmet Mounted Cueing System (JHMCS)
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-16 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, Elbit and Kaiser Electronics. 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-18C/D/E/F, F-15C/D, and F-16 Block 40/50 with a design that is 95% common to all three 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 calligraphic 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.
ASELSAN of Turkey has developed a similar system to the US made JHMCS called the AVCI Helmet Integrated Cueing System. It is envisaged that the ASELSAN JHMCS will be incorporated with Turkey's F-16 CCIP modernization program. The system will also be utilized into the T-129
Turkish Attack Helicopter
The French thrust vectoring Matra MBDA MICA
missile for its 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 calligraphic 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.
Eurofighter Helmet Mounted Symbology System
utilizes the Helmet Mounted Symbology System (HMSS) developed by British Aerospace
and Pilkington Optronics. It is capable of displaying both raster imagery and calligraphic symbology, with provisions for embedded NVGs
Helmet Mounted Display System
Vision Systems International
(VSI), along with Elbit Systems, Rockwell Collins
, and 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. As a result, the F-35 is the first tactical fighter jet in 50 years to fly without a HUD.
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.
- VSI is developing the QuadEyeTM Night Vision Cueing & Display (NVCD) for the US Navy and US Air Force, and is also producing the DASH Generation IV HMD.
- Eye Tracking - Eye trackers measure the point of gaze relative to the direction of the head, allowing a computer to sense where the user is looking. These systems are not currently used in aircraft.
- Direct retinal projection - Systems that project information directly onto the wearer’s retina with a low-powered laser (virtual retinal display) are also in experimentation.
Head Mounted Displays: Designing for the user; Melzer and Moffitt; McGraw Hill, 1997