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A head-up display, or heads-up display, also known as a HUD (), is any transparent display that presents data without requiring users to look away from their usual viewpoints. The origin of the name stems from a
pilot An aircraft pilot or aviator is a person who controls the flight of an aircraft by operating its directional flight controls. Some other aircrew members, such as navigators or flight engineers, are also considered aviators, because they a ...
being able to view information with the head positioned "up" and looking forward, instead of angled down looking at lower instruments. A HUD also has the advantage that the pilot's eyes do not need to refocus to view the outside after looking at the optically nearer instruments. Although they were initially developed for military aviation, HUDs are now used in commercial aircraft, automobiles, and other (mostly professional) applications. Head-up displays were a precursor technology to augmented reality (AR), incorporating a subset of the features needed for the full AR experience, but lacking the necessary registration and tracking between the virtual content and the user's real-world environment.


Overview

A typical HUD contains three primary components: a ''projector unit'', a ''combiner'', and a ''video generation computer''. The projection unit in a typical HUD is an optical collimator setup: a
convex lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'') ...
or concave mirror with a cathode-ray tube, light emitting diode display, or liquid crystal display at its focus. This setup (a design that has been around since the invention of the
reflector sight A reflector sight or reflex sight is an optical sight that allows the user to look through a partially reflecting glass element and see an illuminated projection of an aiming point or some other image superimposed on the field of view. These sig ...
in 1900) produces an image where the light is
collimated A collimated beam of light or other electromagnetic radiation has parallel rays, and therefore will spread minimally as it propagates. A perfectly collimated light beam, with no divergence, would not disperse with distance. However, diffraction p ...
, i.e. the focal point is perceived to be at infinity. The combiner is typically an angled flat piece of glass (a beam splitter) located directly in front of the viewer, that redirects the projected image from projector in such a way as to see the field of view and the projected infinity image at the same time. Combiners may have special coatings that reflect the monochromatic light projected onto it from the projector unit while allowing all other
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...
s of light to pass through. In some optical layouts combiners may also have a curved surface to refocus the image from the projector. The computer provides the interface between the HUD (i.e. the projection unit) and the systems/data to be displayed and generates the imagery and symbology to be displayed by the projection unit .


Types

Other than fixed mounted HUD, there are also
head-mounted display A head-mounted display (HMD) is a display device, worn on the head or as part of a helmet (see Helmet-mounted display for aviation applications), that has a small display optic in front of one ( monocular HMD) or each eye ( binocular HMD). An ...
s (HMDs). These include
helmet-mounted display A helmet-mounted display (HMD) is a device used in aircraft to project information to the pilot's eyes. Its scope is similar to that of head-up displays (HUD) on an aircrew's visor or reticle. An HMD provides the pilot with situation awareness, ...
s (both abbreviated HMD), forms of HUD that feature a display element that moves with the orientation of the user's head. Many modern fighters (such as the
F/A-18 The McDonnell Douglas F/A-18 Hornet is an all-weather, twin-engine, supersonic, carrier-capable, multirole combat aircraft, designed as both a fighter and attack aircraft (hence the F/A designation). Designed by McDonnell Douglas (now part ...
, F-16, and
Eurofighter The Eurofighter Typhoon is a European multinational twin-engine, canard delta wing, multirole fighter. The Typhoon was designed originally as an air-superiority fighter and is manufactured by a consortium of Airbus, BAE Systems and Leo ...
) use both a HUD and HMD concurrently. The
F-35 Lightning II The Lockheed Martin F-35 Lightning II is an American family of single-seat, single-engine, all-weather stealth multirole combat aircraft that is intended to perform both air superiority and strike missions. It is also able to provide elect ...
was designed without a HUD, relying solely on the HMD, making it the first modern military fighter not to have a fixed HUD.


Generations

HUDs are split into four generations reflecting the technology used to generate the images. * First Generation—Use a CRT to generate an image on a phosphor screen, having the disadvantage of the phosphor screen coating degrading over time. The majority of HUDs in operation today are of this type. * Second Generation—Use a solid state light source, for example LED, which is modulated by an LCD screen to display an image. These systems do not fade or require the high voltages of first generation systems. These systems are on commercial aircraft. * Third Generation—Use
optical waveguide An optical waveguide is a physical structure that guides electromagnetic waves in the optical spectrum. Common types of optical waveguides include optical fiber waveguides, transparent dielectric waveguides made of plastic and glass, liquid light ...
s to produce images directly in the combiner rather than use a projection system. * Fourth Generation—Use a scanning laser to display images and even video imagery on a clear transparent medium. Newer micro-display imaging technologies are being introduced, including liquid crystal display (LCD),
liquid crystal on silicon Liquid crystal on silicon (LCoS or LCOS) is a miniaturized reflective active-matrix liquid-crystal display or "microdisplay" using a liquid crystal layer on top of a silicon backplane. It is also referred to as a spatial light modulator. LCoS was ...
(LCoS), digital micro-mirrors (DMD), and
organic light-emitting diode An organic light-emitting diode (OLED or organic LED), also known as organic electroluminescent (organic EL) diode, is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compound that emits light i ...
(OLED).


History

HUDs evolved from the
reflector sight A reflector sight or reflex sight is an optical sight that allows the user to look through a partially reflecting glass element and see an illuminated projection of an aiming point or some other image superimposed on the field of view. These sig ...
, a pre-World War II parallax-free optical sight technology for
military A military, also known collectively as armed forces, is a heavily armed, highly organized force primarily intended for warfare. It is typically authorized and maintained by a sovereign state, with its members identifiable by their distinct ...
fighter aircraft. The
gyro gunsight A gyro gunsight (G.G.S.) is a modification of the non-magnifying reflector sight in which target lead (the amount of aim-off in front of a moving target) and bullet drop are calculated automatically. The first examples were developed in Britain ...
added a
reticle A reticle, or reticule also known as a graticule, is a pattern of fine lines or markings built into the eyepiece of an optical device such as a telescopic sight, spotting scope, theodolite, optical microscope or the screen of an oscilloscop ...
that moved based on the speed and turn rate to solve for the amount of
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
needed to hit a target while maneuvering. During the early 1940s, the
Telecommunications Research Establishment The Telecommunications Research Establishment (TRE) was the main United Kingdom research and development organization for radio navigation, radar, infra-red detection for heat seeking missiles, and related work for the Royal Air Force (RAF) ...
(TRE), in charge of UK
radar Radar is a detection system that uses radio waves to determine the distance ('' ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, we ...
development, found that
Royal Air Force The Royal Air Force (RAF) is the United Kingdom's air and space force. It was formed towards the end of the First World War on 1 April 1918, becoming the first independent air force in the world, by regrouping the Royal Flying Corps (RFC) an ...
(RAF)
night fighter A night fighter (also known as all-weather fighter or all-weather interceptor for a period of time after the Second World War) is a fighter aircraft adapted for use at night or in other times of bad visibility. Night fighters began to be used i ...
pilots were having a hard time reacting to the verbal instruction of the radar operator as they approached their targets. They experimented with the addition of a second radar display for the pilot, but found they had trouble looking up from the lit screen into the dark sky in order to find the target. In October 1942 they had successfully combined the image from the radar tube with a projection from their standard GGS Mk. II
gyro gunsight A gyro gunsight (G.G.S.) is a modification of the non-magnifying reflector sight in which target lead (the amount of aim-off in front of a moving target) and bullet drop are calculated automatically. The first examples were developed in Britain ...
on a flat area of the windscreen, and later in the gunsight itself. A key upgrade was the move from the original AI Mk. IV radar to the microwave-frequency
AI Mk. VIII radar Radar, Airborne Interception, Mark VIII, or AI Mk. VIII for short, was the first operational microwave-frequency air-to-air radar. It was used by Royal Air Force night fighters from late 1941 until the end of World War II. The basic concept, u ...
found on the de Havilland Mosquito
night fighter A night fighter (also known as all-weather fighter or all-weather interceptor for a period of time after the Second World War) is a fighter aircraft adapted for use at night or in other times of bad visibility. Night fighters began to be used i ...
. This set produced an
artificial horizon The attitude indicator (AI), formerly known as the gyro horizon or artificial horizon, is a flight instrument that informs the pilot of the aircraft orientation relative to Earth's horizon, and gives an immediate indication of the smallest or ...
that further eased head-up flying. In 1955 the
US Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...
's Office of Naval Research and Development did some research with a mockup HUD concept unit along with a sidestick controller in an attempt to ease the pilot's burden flying modern jet aircraft and make the instrumentation less complicated during flight. While their research was never incorporated in any aircraft of that time, the crude HUD mockup they built had all the features of today's modern HUD units. HUD technology was next advanced by the
Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against ...
in the
Buccaneer Buccaneers were a kind of privateers or free sailors particular to the Caribbean Sea during the 17th and 18th centuries. First established on northern Hispaniola as early as 1625, their heyday was from the Restoration in 1660 until about 168 ...
, the prototype of which first flew on 1958. The aircraft was designed to fly at very low altitudes at very high speeds and drop bombs in engagements lasting seconds. As such, there was no time for the pilot to look up from the instruments to a bombsight. This led to the concept of a "Strike Sight" that would combine altitude, airspeed and the gun/bombsight into a single gunsight-like display. There was fierce competition between supporters of the new HUD design and supporters of the old electro-mechanical gunsight, with the HUD being described as a radical, even foolhardy option. The Air Arm branch of the
UK Ministry of Defence The Ministry of Defence (MOD or MoD) is the department responsible for implementing the defence policy set by His Majesty's Government, and is the headquarters of the British Armed Forces. The MOD states that its principal objectives are to ...
sponsored the development of a Strike Sight. The Royal Aircraft Establishment (RAE) designed the equipment and the earliest usage of the term "head-up-display" can be traced to this time. Production units were built by Rank Cintel, and the system was first integrated in 1958. The Cintel HUD business was taken over by Elliott Flight Automation and the Buccaneer HUD was manufactured and further developed, continuing up to a Mark III version with a total of 375 systems made; it was given a 'fit and forget' title by the Royal Navy and it was still in service nearly 25 years later. BAE Systems, as the successor to Elliotts via GEC-Marconi Avionics, thus has a claim to the world's first head-up display in operational service. A similar version that replaced the bombing modes with missile-attack modes was part of the
AIRPASS AIRPASS was a British airborne interception radar and fire-control radar system developed by Ferranti. It was the world's first airborne monopulse radar system and fed data to the world's first head-up display. The name is an acronym for "Air ...
HUD fitted to the
English Electric Lightning The English Electric Lightning is a British fighter aircraft that served as an interceptor during the 1960s, the 1970s and into the late 1980s. It was capable of a top speed of above Mach 2. The Lightning was designed, developed, and manufa ...
from 1959. In the United Kingdom, it was soon noted that pilots flying with the new gunsights were becoming better at piloting their aircraft. At this point, the HUD expanded its purpose beyond weapon aiming to general piloting. In the 1960s, French test-pilot Gilbert Klopfstein created the first modern HUD and a standardized system of HUD symbols so that pilots would only have to learn one system and could more easily transition between aircraft. The modern HUD used in
instrument flight rules In aviation, instrument flight rules (IFR) is one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other is visual flight rules (VFR). The U.S. Federal Aviation Administration's (FAA) ''Instrument Fly ...
approaches to landing was developed in 1975.Spitzer, Cary R., ed. "Digital Avionics Handbook". Head-Up Displays. Boca Raton, FL: CRC Press, 2001 Klopfstein pioneered HUD technology in military
fighter jet Fighter aircraft are fixed-wing military aircraft designed primarily for air-to-air combat. In military conflict, the role of fighter aircraft is to establish air superiority of the battlespace. Domination of the airspace above a battlefield ...
s and
helicopter A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...
s, aiming to centralize critical flight data within the pilot's field of vision. This approach sought to increase the pilot's scan efficiency and reduce "task saturation" and information overload. Use of HUDs then expanded beyond military aircraft. In the 1970s, the HUD was introduced to commercial aviation, and in 1988, the
Oldsmobile Cutlass Supreme The Oldsmobile Cutlass Supreme is a mid-size car produced by Oldsmobile between 1966 and 1997. It was positioned as a premium offering at the top of the Cutlass range. It began as a trim package, developed its own roofline, and rose during the mi ...
became the first production car with a head-up display. Until a few years ago, the Embraer 190, Saab 2000, Boeing 727, and
Boeing 737 The Boeing 737 is a narrow-body aircraft produced by Boeing at its Boeing Renton Factory, Renton Factory in Washington (state), Washington. Developed to supplement the Boeing 727 on short and thin routes, the twinjet retains the Boeing 707, 7 ...
Classic A classic is an outstanding example of a particular style; something of lasting worth or with a timeless quality; of the first or highest quality, class, or rank – something that exemplifies its class. The word can be an adjective (a ''c ...
(737-300/400/500) and Next Generation aircraft (737-600/700/800/900 series) were the only commercial passenger aircraft available with HUDs. However, the technology is becoming more common with aircraft such as the Canadair RJ, Airbus A318 and several business jets featuring the displays. HUDs have become standard equipment on the Boeing 787. Furthermore, the Airbus A320, A330, A340 and A380 families are currently undergoing the certification process for a HUD. HUDs were also added to the
Space Shuttle The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program ...
orbiter.


Design factors

There are several factors that interplay in the design of a HUD: * Field of View – also "FOV", indicates the angle(s), vertically as well as horizontally, subtended at the pilot's eye, at which the combiner displays symbology in relation to the outside view. A narrow FOV means that the view (of a runway, for example) through the combiner might include little additional information beyond the perimeters of the runway environment; whereas a wide FOV would allow a 'broader' view. For aviation applications, the major benefit of a wide FOV is that an aircraft approaching the runway in a crosswind might still have the runway in view through the combiner, even though the aircraft is pointed well away from the runway threshold; whereas with a narrow FOV the runway would be 'off the edge' of the combiner, out of the HUD's view. Because human eyes are separated, each eye receives a different image. The HUD image is viewable by one or both eyes, depending on technical and budget limitations in the design process. Modern expectations are that both eyes view the same image, in other words a "binocular Field of View (FOV)". * Collimation – The projected image is
collimated A collimated beam of light or other electromagnetic radiation has parallel rays, and therefore will spread minimally as it propagates. A perfectly collimated light beam, with no divergence, would not disperse with distance. However, diffraction p ...
which makes the light rays parallel. Because the light rays are parallel the lens of the human eye focuses on infinity to get a clear image. Collimated images on the HUD combiner are perceived as existing at or near optical infinity. This means that the pilot's eyes do not need to refocus to view the outside world and the HUD display – the image appears to be "out there", overlaying the outside world. This feature is critical for effective HUDs: not having to refocus between HUD-displayed symbolic information and the outside world onto which that information is overlaid is one of the main advantages of collimated HUDs. It gives HUDs special consideration in safety-critical and time-critical manoeuvres, when the few seconds a pilot needs in order to re-focus inside the cockpit, and then back outside, are very critical: for example, in the final stages of landing. Collimation is therefore a primary distinguishing feature of high-performance HUDs and differentiates them from consumer-quality systems that, for example, simply reflect uncollimated information off a car's windshield (causing drivers to refocus and shift attention from the road ahead). * Eyebox – The optical collimator produces a cylinder of parallel light so the display can only be viewed while the viewer's eyes are somewhere within that cylinder, a three-dimensional area called the ''head motion box'' or ''eyebox''. Modern HUD eyeboxes are usually about 5 lateral by 3 vertical by 6 longitudinal inches (13x8x15 cm). This allows the viewer some freedom of head movement but movement too far up/down or left/right will cause the display to vanish off the edge of the collimator and movement too far back will cause it to crop off around the edge (
vignette Vignette may refer to: * Vignette (entertainment), a sketch in a sketch comedy * Vignette (graphic design), decorative designs in books (originally in the form of leaves and vines) to separate sections or chapters * Vignette (literature), short, i ...
). The pilot is able to view the entire display as long as one of the eyes is inside the eyebox. * Luminance/contrast – Displays have adjustments in luminance and contrast to account for ambient lighting, which can vary widely (e.g. from the glare of bright clouds to moonless night approaches to minimally lit fields). * Boresight – Aircraft HUD components are very accurately aligned with the aircraft's three axes – a process called '' boresighting'' – so that displayed data conforms to reality typically with an accuracy of ±7.0 
milliradian A milliradian ( SI-symbol mrad, sometimes also abbreviated mil) is an SI derived unit for angular measurement which is defined as a thousandth of a radian (0.001 radian). Milliradians are used in adjustment of firearm sights by adjusting t ...
s (±24 
minutes of arc A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The n ...
), and may vary across the HUD's FOV. In this case the word "conform" means, "when an object is projected on the combiner and the actual object is visible, they will be aligned". This allows the display to show the pilot exactly where the artificial horizon is, as well as the aircraft's projected path with great accuracy. When Enhanced Vision is used, for example, the display of runway lights is aligned with the actual runway lights when the real lights become visible. Boresighting is done during the aircraft's building process and can also be performed in the field on many aircraft. * Scaling – The displayed image (flight path, pitch and yaw scaling, etc.), is scaled to present to the pilot a picture that overlays the outside world in an exact 1:1 relationship. For example, objects (such as a runway threshold) that are 3 degrees below the horizon as viewed from the cockpit must appear at the −3 degree index on the HUD display. * Compatibility – HUD components are designed to be compatible with other avionics, displays, etc.


Aircraft

On aircraft avionics systems, HUDs typically operate from dual independent redundant computer systems. They receive input directly from the sensors ( pitot-static,
gyroscopic A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rot ...
, navigation, etc.) aboard the aircraft and perform their own computations rather than receiving previously computed data from the flight computers. On other aircraft (the Boeing 787, for example) the HUD guidance computation for Low Visibility Take-off (LVTO) and low visibility approach comes from the same flight guidance computer that drives the autopilot. Computers are integrated with the aircraft's systems and allow connectivity onto several different data buses such as the
ARINC 429 ARINC 429, "Mark33 Digital Information Transfer System (DITS)," is also known as the Aeronautical Radio INC. (ARINC) technical standard for the predominant avionics data bus used on most higher-end commercial and transport aircraft. It defines the ...
, ARINC 629, and
MIL-STD-1553 MIL-STD-1553 is a military standard published by the United States Department of Defense that defines the mechanical, electrical, and functional characteristics of a serial data bus. It was originally designed as an avionic data bus for use with ...
.


Displayed data

Typical aircraft HUDs display
airspeed In aviation, airspeed is the speed of an aircraft relative to the air. Among the common conventions for qualifying airspeed are: * Indicated airspeed ("IAS"), what is read on an airspeed gauge connected to a Pitot-static system; * Calibrated ...
,
altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...
, a horizon line,
heading Heading can refer to: * Heading (metalworking), a process which incorporates the extruding and upsetting processes * Headline, text at the top of a newspaper article * Heading (navigation), the direction a person or vehicle is facing, usually s ...
, turn/bank and slip/skid indicators. These instruments are the minimum required by 14 CFR Part 91. Other symbols and data are also available in some HUDs: * ''boresight'' or ''waterline'' symbol — is fixed on the display and shows where the nose of the aircraft is actually pointing. * ''flight path vector (FPV)'' or ''velocity vector'' symbol — shows where the aircraft is actually going, as opposed to merely where it is pointed as with the boresight. For example, if the aircraft is pitched up but descending as may occur in high angle of attack flight or in flight through descending air, then the FPV symbol will be below the horizon even though the boresight symbol is above the horizon. During approach and landing, a pilot can fly the approach by keeping the FPV symbol at the desired descent angle and touchdown point on the runway. * ''acceleration indicator'' or ''energy cue'' — typically to the left of the FPV symbol, it is above it if the aircraft is accelerating, and below the FPV symbol if decelerating. * '' angle of attack indicator'' — shows the wing's angle relative to the airflow, often displayed as ''"α"''. * navigation data and symbols — for approaches and landings, the flight guidance systems can provide visual cues based on navigation aids such as an
Instrument Landing System In aviation, the instrument landing system (ILS) is a precision radio navigation system that provides short-range guidance to aircraft to allow them to approach a runway at night or in bad weather. In its original form, it allows an aircraft to ...
or augmented
Global Positioning System The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite sy ...
such as the
Wide Area Augmentation System The Wide Area Augmentation System (WAAS) is an air navigation aid developed by the Federal Aviation Administration to augment the Global Positioning System (GPS), with the goal of improving its accuracy, integrity, and availability. Essentia ...
. Typically this is a circle which fits inside the flight path vector symbol. Pilots can fly along the correct flight path by "flying to" the guidance cue. Since being introduced on HUDs, both the FPV and acceleration symbols are becoming standard on head-down displays (HDD). The actual form of the FPV symbol on an HDD is not standardized but is usually a simple aircraft drawing, such as a circle with two short angled lines, (180 ± 30 degrees) and "wings" on the ends of the descending line. Keeping the FPV on the horizon allows the pilot to fly level turns in various angles of bank.


Military aircraft specific applications

In addition to the generic information described above, military applications include weapons system and sensor data such as: * ''target designation (TD)'' indicator — places a cue over an air or ground target (which is typically derived from
radar Radar is a detection system that uses radio waves to determine the distance ('' ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, we ...
or
inertial navigation system An inertial navigation system (INS) is a navigation device that uses motion sensors (accelerometers), rotation sensors ( gyroscopes) and a computer to continuously calculate by dead reckoning the position, the orientation, and the velocity (dir ...
data). * ''Vc'' — closing velocity with target. * ''Range'' — to target, waypoint, etc. * ''weapon seeker'' or sensor line of sight — shows where a seeker or sensor is pointing. * ''weapon status'' — includes type and number of weapons selected, available, arming, etc.


VTOL/STOL approaches and landings

During the 1980s, the military tested the use of HUDs in vertical take off and landing (VTOL) and short take off and landing (STOL) aircraft. A HUD format was developed at
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...
Ames Research Center The Ames Research Center (ARC), also known as NASA Ames, is a major NASA research center at Moffett Federal Airfield in California's Silicon Valley. It was founded in 1939 as the second National Advisory Committee for Aeronautics (NACA) labo ...
to provide pilots of V/STOL aircraft with complete flight guidance and control information for Category III C terminal-area flight operations. This includes a large variety of flight operations, from STOL flights on land-based runways to VTOL operations on aircraft carriers. The principal features of this display format are the integration of the flightpath and pursuit guidance information into a narrow field of view, easily assimilated by the pilot with a single glance, and the superposition of vertical and horizontal situation information. The display is a derivative of a successful design developed for conventional transport aircraft.


Civil aircraft specific applications

The use of head-up displays allows commercial aircraft substantial flexibility in their operations. Systems have been approved which allow reduced-visibility takeoffs, and landings, as well as full manual Category III A landings and roll-outs. Initially expensive and physically large, these systems were only installed on larger aircraft able to support them. Unfortunately these tended to be the same aircraft that as standard supported autoland (with the exception of certain turbo-propp types that had HUD as an option) making the head-up display unnecessary for Cat III landings - this delayed the adoption of HUD in commercial aircraft. At the same time, studies have shown that the use of a HUD during landings decreases the lateral deviation from centerline in all landing conditions, although the touchdown point along the centerline is not changed. For
general aviation General aviation (GA) is defined by the International Civil Aviation Organization (ICAO) as all civil aviation aircraft operations with the exception of commercial air transport or aerial work, which is defined as specialized aviation services ...
, MyGoFlight expects to receive a STC and to retail its SkyDisplay HUD for $25,000 without installation for a single piston-engine as the
Cirrus SR22 The Cirrus SR22 is a single-engine four- or five-seat composite aircraft built from 2001 by Cirrus Aircraft of Duluth, Minnesota. It is a development of the Cirrus SR20, with a larger wing, higher fuel capacity, and a more powerful, 310-horsepo ...
s and more for
Cessna Caravan The Cessna 208 Caravan is a utility aircraft produced by Cessna. The project was commenced on November 20, 1981, and the prototype first flew on December 9, 1982. The production model was certified by the FAA in October 1984 and its Cargoma ...
s or Pilatus PC-12s single-engine turboprops: 5 to 10% of a traditional HUD cost albeit it is non- conformal, not matching exactly the outside terrain. Flight data from a
tablet computer A tablet computer, commonly shortened to tablet, is a mobile device, typically with a mobile operating system and touchscreen display processing circuitry, and a rechargeable battery in a single, thin and flat package. Tablets, being com ...
can be projected on the $1,800 Epic Optix Eagle 1 HUD.


Enhanced flight vision systems

In more advanced systems, such as the US
Federal Aviation Administration The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic ...
(FAA)-labeled 'Enhanced Flight Vision System',U.S. DOT/FAA – Final Rule: Enhanced Flight Vision Systems
www.regulations.gov
a real-world visual image can be overlaid onto the combiner. Typically an
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
camera (either single or multi-band) is installed in the nose of the aircraft to display a conformed image to the pilot. 'EVS Enhanced Vision System' is an industry accepted term which the FAA decided not to use because "the FAA believes tcould be confused with the system definition and operational concept found in 91.175(l) and (m)" In one EVS installation, the camera is actually installed at the top of the vertical stabilizer rather than "as close as practical to the pilots eye position". When used with a HUD however, the camera must be mounted as close as possible to the pilots eye point as the image is expected to "overlay" the real world as the pilot looks through the combiner. "Registration," or the accurate overlay of the EVS image with the real world image, is one feature closely examined by authorities prior to approval of a HUD based EVS. This is because of the importance of the HUD matching the real world. While the EVS display can greatly help, the FAA has only relaxed operating regulations so an aircraft with EVS can perform a CATEGORY I approach to CATEGORY II minimums. In all other cases the flight crew must comply with all "unaided" visual restrictions. (For example, if the runway visibility is restricted because of fog, even though EVS may provide a clear visual image it is not appropriate (or legal) to maneuver the aircraft using only the EVS below 100 feet above ground level.)


Synthetic vision systems

HUD systems are also being designed to display a
synthetic vision system A synthetic vision system (SVS) is a computer-mediated reality system for aerial vehicles, that uses 3D to provide pilots with clear and intuitive means of understanding their flying environment. Functionality Synthetic vision provides situati ...
(SVS) graphic image, which uses high precision navigation, attitude, altitude and terrain databases to create realistic and intuitive views of the outside world. In the 1st SVS head down image shown on the right, immediately visible indicators include the airspeed tape on the left, altitude tape on the right, and turn/bank/slip/skid displays at the top center. The boresight symbol (-v-) is in the center and directly below that is the flight path vector (FPV) symbol (the circle with short wings and a vertical stabilizer). The horizon line is visible running across the display with a break at the center, and directly to the left are numbers at ±10 degrees with a short line at ±5 degrees (the +5 degree line is easier to see) which, along with the horizon line, show the pitch of the aircraft. Unlike this color depiction of SVS on a head down primary flight display, the SVS displayed on a HUD is monochrome – that is, typically, in shades of green. The image indicates a wings level aircraft (i.e. the flight path vector symbol is flat relative to the horizon line and there is zero roll on the turn/bank indicator). Airspeed is 140 knots, altitude is 9,450 feet, heading is 343 degrees (the number below the turn/bank indicator). Close inspection of the image shows a small purple circle which is displaced from the flight path vector slightly to the lower right. This is the guidance cue coming from the Flight Guidance System. When stabilized on the approach, this purple symbol should be centered ''within'' the FPV. The terrain is entirely computer generated from a high resolution terrain database. In some systems, the SVS will calculate the aircraft's current flight path, or possible flight path (based on an aircraft performance model, the aircraft's current energy, and surrounding terrain) and then turn any obstructions red to alert the flight crew. Such a system might have helped prevent the crash of
American Airlines Flight 965 American Airlines Flight 965 was a regularly scheduled flight from Miami International Airport in Miami, Florida, to Alfonso Bonilla Aragón International Airport in Cali, Colombia. On December 20, 1995, the Boeing 757-200 flying this route ( r ...
into a mountain in December 1995. On the left side of the display is an SVS-unique symbol, with the appearance of a purple, diminishing sideways ladder, and which continues on the right of the display. The two lines define a "tunnel in the sky". This symbol defines the desired trajectory of the aircraft in three dimensions. For example, if the pilot had selected an airport to the left, then this symbol would curve off to the left and down. If the pilot keeps the flight path vector alongside the trajectory symbol, the craft will fly the optimum path. This path would be based on information stored in the Flight Management System's database and would show the FAA-approved approach for that airport. The tunnel in the sky can also greatly assist the pilot when more precise four-dimensional flying is required, such as the decreased vertical or horizontal clearance requirements of
Required Navigation Performance Required navigation performance (RNP) is a type of performance-based navigation (PBN) that allows an aircraft to fly a specific path between two 3D-defined points in space. Navigation precision Area navigation (RNAV) and RNP systems are fund ...
(RNP). Under such conditions the pilot is given a graphical depiction of where the aircraft should be and where it should be going rather than the pilot having to mentally integrate altitude, airspeed, heading, energy and longitude and latitude to correctly fly the aircraft.


Tanks

In mid-2017, the Israel Defense Forces will begin trials of Elbit's Iron Vision, the world's first helmet-mounted head-up display for tanks. Israel's Elbit, which developed the helmet-mounted display system for the
F-35 The Lockheed Martin F-35 Lightning II is an American family of single-seat, single-engine, all-weather stealth multirole combat aircraft that is intended to perform both air superiority and strike missions. It is also able to provide elect ...
, plans Iron Vision to use a number of externally mounted cameras to project the 360° view of a tank's surroundings onto the helmet-mounted visors of its crew members. This allows the crew members to stay inside the tank, without having to open the hatches to see outside.IDF to trial Elbit's IronVision in Merkava MBT
Peter Felstead, Tel Aviv - IHS Jane's Defence Weekly, 27 March 2017


Automobiles

These displays are becoming increasingly available in production cars, and usually offer speedometer,
tachometer A tachometer (revolution-counter, tach, rev-counter, RPM gauge) is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute (RPM) on a calibrated analo ...
, and
navigation system A navigation system is a computing system that aids in navigation. Navigation systems may be entirely on board the vehicle or vessel that the system is controlling (for example, on the ship's bridge) or located elsewhere, making use of radio or othe ...
displays. Night vision information is also displayed via HUD on certain automobiles. In contrast to most HUDs found in aircraft, automotive head-up displays are not parallax-free. The display may not be visible to a driver wearing sunglasses with polarised lenses. Add-on HUD systems also exist, projecting the display onto a glass combiner mounted above or below the windshield, or using the windshield itself as the combiner. In 2012,
Pioneer Corporation commonly referred to as Pioneer, is a Japanese multinational corporation based in Tokyo, that specializes in digital entertainment products. The company was founded by Nozomu Matsumoto in January 1, 1938 in Tokyo as a radio and speaker repair ...
introduced a HUD navigation system that replaces the driver-side sun visor and visually overlays animations of conditions ahead, a form of augmented reality (AR). Developed by Pioneer Corporation, AR-HUD became the first aftermarket automotive Head-Up Display to use a direct-to-eye laser beam scanning method, also known as
virtual retinal display A virtual retinal display (VRD), also known as a retinal scan display (RSD) or retinal projector (RP), is a display technology that draws a raster display (like a television) directly onto the retina of the eye. History In the past similar s ...
(VRD). AR-HUD's core technology involves a miniature laser beam scanning display developed by MicroVision, Inc.
Motorcycle helmet A motorcycle helmet is a type of helmet used by motorcycle riders. Motorcycle helmets contribute to motorcycle safety by protecting the rider's head in the event of an impact. They reduce the risk of head injury by 69% and the risk of death by 42% ...
HUDs are also commercially available.
Uniti The Fiumi Uniti is a river in the province of Ravenna in the Emilia-Romagna region of Italy. The source of the river is the confluence of the rivers Montone and Ronco south of Ravenna. The river flows east 12 kilometers before entering the Adri ...
electric city car will replace the
dashboard For business applications, see Dashboard (business). A dashboard (also called dash, instrument panel (IP), or fascia) is a control panel set within the central console of a vehicle or small aircraft. Usually located directly ahead of the drive ...
with a large HUD to display information directly on the
windscreen The windshield (North American English) or windscreen (Commonwealth English) of an aircraft, car, bus, motorbike, truck, train, boat or streetcar is the front window, which provides visibility while protecting occupants from the elements. Mo ...
. The purpose is to increase safety as the driver will not have to move his eyes out from the road to look at the speed or the GPS screen. In recent years, it has been argued that conventional HUDs will be replaced by holographic AR technologies, such as the ones developed by
WayRay WayRay is a deep-tech company with offices in Switzerland, United States, China, Hong Kong, and Germany. It develops holographic AR technologies for connected cars. WayRay's in-house R&D center and prototyping facilities create holographic ...
that use
holographic optical element Holographic optical element (HOE) is an optical component (mirror, lens, directional diffuser, etc.) that produces holographic images using principles of diffraction. HOE is most commonly used in transparent displays, 3D imaging, and certain scannin ...
s (HOE). The HOE allows for a wider field of view while reducing the size of the device and making the solution customizable for any car model. Mercedes Benz introduced an Augmented Reality based Head Up Display while Faurecia invested in an eye gaze and finger controlled head up display.


Developmental / experimental uses

HUDs have been proposed or are being experimentally developed for a number of other applications. In the military, a HUD can be used to overlay tactical information such as the output of a laser
rangefinder A rangefinder (also rangefinding telemeter, depending on the context) is a device used to measure distances to remote objects. Originally optical devices used in surveying, they soon found applications in other fields, such as photography an ...
or squadmate locations to
infantry Infantry is a military specialization which engages in ground combat on foot. Infantry generally consists of light infantry, mountain infantry, motorized infantry & mechanized infantry, airborne infantry, air assault infantry, and mar ...
men. A prototype HUD has also been developed that displays information on the inside of a swimmer's goggles or of a scuba diver's mask. HUD systems that project information directly onto the wearer's
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
with a low-powered
laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fi ...
(
virtual retinal display A virtual retinal display (VRD), also known as a retinal scan display (RSD) or retinal projector (RP), is a display technology that draws a raster display (like a television) directly onto the retina of the eye. History In the past similar s ...
) are also in experimentation. Head-up displays can perform real-time language translation.Borghino, Dari
Augmented reality glasses perform real-time language translation
''gizmag'', 29 July 2012.


See also

*
Acronyms and abbreviations in avionics Below are abbreviations used in aviation, avionics, aerospace and aeronautics. A B C D E F G H I J K L M N N numbers (turbines) O P Q R S T U V V speeds W X Y Z See also * List of avia ...
* Augmented reality *
Eyes-on-the-Road-Benefit An automotive head-up display or automotive heads-up display —also known as a auto-HUD— is any transparent display that presents data in the automobile without requiring users to look away from their usual viewpoints. The origin of the name st ...
*
EyeTap An EyeTap is a concept for a wearable computing device that is worn in front of the eye that acts as a camera to record the scene available to the eye as well as a display to superimpose computer-generated imagery on the original scene availabl ...
*
HUD (video gaming) In video gaming, the HUD (heads-up display) or status bar is the method by which information is visually relayed to the player as part of a game's user interface. It takes its name from the head-up displays used in modern aircraft. The HUD is fr ...
* Optical head-mounted display *
Smartglasses Smartglasses or smart glasses are eye or head-worn wearable computers that offer useful capabilities to the user. Many smartglasses include displays that add information alongside or to what the wearer sees. Alternatively, smartglasses are som ...
*
Virtual retinal display A virtual retinal display (VRD), also known as a retinal scan display (RSD) or retinal projector (RP), is a display technology that draws a raster display (like a television) directly onto the retina of the eye. History In the past similar s ...
*
VR positional tracking In virtual reality (VR) and augmented reality (AR), a pose tracking system detects the precise pose of head-mounted displays, controllers, other objects or body parts within Euclidean space. Pose tracking is often referred to as 6DOF tracking, for ...
*
Wearable computer A wearable computer, also known as a body-borne computer, is a computing device worn on the body. The definition of 'wearable computer' may be narrow or broad, extending to smartphones or even ordinary wristwatches. Wearables may be for general ...


References


External links


Rochester Archives Article—'Buccaneer HUD PDU'

BBC Article—'Pacman comes to life virtually'

'Clinical evaluation of the 'head-up' display of anesthesia data'



'Elliott Brothers to BAE SYSTEMS' – a short history of Elliott Brothers


– a 1964 ''
Flight International ''Flight International'' is a monthly magazine focused on aerospace. Published in the United Kingdom and founded in 1909 as "A Journal devoted to the Interests, Practice, and Progress of Aerial Locomotion and Transport", it is the world's old ...
'' article on flying using an early Specto head-up display
Jaguar Unveils 'Virtual Widescreen' Technology to Assist Drivers – Latin Post
{{emerging technologies, displays=yes Vehicle technology Avionics Aircraft instruments Automotive technologies Optical devices Multimodal interaction Mixed reality British inventions Emerging technologies