Helmet-mounted display
An HMD provides the pilot with situation awareness, an enhanced image of the scene, and in military applications cue weapons systems, to the direction their head is pointing.
In 1962, Hughes Aircraft Company revealed the Electrocular, a compact CRT, head-mounted monocular display that reflected a TV signal onto a transparent eyepiece.
[4][5][6][7] One of the first aircraft with simple HMD devices appeared for experimental purpose in the mid-1960s to aid in targeting heat seeking missiles.
The US Navy's Visual Target Acquisition System (VTAS), made by Honeywell Corporation that was flown in early 1970s in F-4J and 1974–78 ACEVAL/AIMVAL on U.S. F-14 and F-15 fighters.
VTAS received praise[8] 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 from 1969.
[9] HMDs were also introduced in helicopters during this time – examples include the Boeing AH-64 Apache with the Integrated Helmet and Display Sighting System (IHADSiSy) demonstrated in 1985.
One successful HMD was the Israeli Air Force Elbit DASH series, fielded in conjunction with the Python 4, in the early 1990s.
[16] Hybrid trackers use a combination of sensors such as inertial and optical to improve tracking accuracy, update rate, and latency.
MEMS based IMUs benefit from high update rates such as 1,000 Hz but suffer from precession and drift over time, so they cannot be used alone.
[23] 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 ultrasonic sensing signals.
[23][failed verification] 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.
IR emitters allow a slewable thermographic camera sensor, mounted on the nose of the aircraft, to be slaved to the aviator's head movements.
A quick-disconnect wire powers the display and carries video drive signals to the helmet's cathode-ray tube (CRT).
[30] 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.
JHMCS employs a newer, faster digital processing package, but retains the same type of electromagnetic position sensing as the DASH.
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 successful '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.
[53] 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.
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.
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.
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.
[55][56] A BAE Systems helmet was considered when HMDS development was experiencing significant problems, but these issues were eventually worked out.
