What is a Heads Up Display?

The head-up display refers to a display device that projects the main pilot instrument attitude guidance indicator and main flight parameters onto the front of the pilot's helmet or on the windshield. This allows the pilot to see the main driving instruments and their important flight parameters at the same time when looking forward to the front vision outside the aircraft. This was developed by military aircraft, which generally use a helmet-type head-up display, which is convenient for piloting the aircraft while searching for targets. Civil aviation aircraft have also begun to use, generally using a head-up display on the projection windshield, mainly for approach and landing. ^[1]

The head-up display can project flight parameters, targeting attacks, self-detection and other information in the form of images and characters through optical components onto the optical / electrical display device on the front glass of the cabin. When pilots observe the exterior of the cabin through the combined glass, they can simultaneously see information such as characters and images superimposed on the exterior. And the projection focal length is located at the front of the imaging combination glass, so that the pilot can easily view the flight parameters at any time without changing the eye focal length, and the visibility will not be affected by sunlight. In the past, pilots had to observe the out-of-vehicle targets and in-cabin instruments alternately during air combat, which was prone to instantaneous visual interruption, which would result in slow response, operational errors, and possibly fighter aircraft. The head-up display can overcome this shortcoming. Today, head-up display systems are developing rapidly and have been used in high-end cars. ^[2]

HUD uses the principle of optical reflection to project important flight-related information on a piece of glass. This piece of glass is located at the front of the cockpit, and its height is roughly level with the pilot's eyes. The projected text and image are adjusted at an infinite distance from the focal length.

The predecessor of HUD was used on fighter aircraft

The basic structure of HUD includes two parts: data processing and image display.

The data processing unit integrates and processes the data of the various systems on the aircraft and converts them into pre-set symbols according to the selected mode. The graphics are output in the form of text or numbers. Some products divide the signal processing and image output into two devices, but they are generally similar in operation.

The upper image display device is installed in the front of the cockpit in the space between the pilot and the cockpit cover. The image display device receives information from the data processing device and projects it on the glass. The display device is also equipped with a control panel, which can adjust or change the output image.

HUD-future development

Improvements in the image display of the new generation of HUD include the use of holographic display methods to expand the range of displayed images, especially to increase the horizontal field of view angle, reduce the limitation and influence of the thickness of the bracket on the field of view, and enhance different luminosity It can adjust the display with the external environment, enhance the sharpness of the image, and cooperate with other optical image output. For example, it can directly project the image of the front of the aircraft generated by the infrared image camera onto the HUD, and display it in conjunction with other data.

The HUD projects images on a fixed device in front of the cockpit. When the pilot turns his head, these images temporarily leave his field of vision. Therefore, it has been suggested that the image be transmitted directly in front of the pilot's helmet and coincide with the pilot's field of view at any time.

The United States was one of the earliest countries to study helmet displays. The helmet sight, code-named VTAS, was briefly tested on F-4 fighters in the 1960s, but it has not entered mass production. It has been used only for the aiming of attack helicopter weapons. The Soviet Union was the first country to officially use a helmet sight on fighter aircraft. For example, the MiG-29 used a helmet sight with R73 (NATO number AA-11) air-to-air missiles.

However, the helmet sight is only a derivative of the optical sight, and it must cooperate closely with the HUD in both the amount of data displayed and the function. For example, the Soviet helmet sight was mainly used as the firing command of the R73 missile. It does not provide other flight facilities. Required information. A further enhanced version is called Helmet Display. After integrating the HUD with other related functions, it is projected directly in front of the pilot's helmet. The Joint Helmet Mounted Cueing System (JHMCS), which has just been in service in the United States, can replace the display function of the HUD, and can assist crews in projecting various air-to-ground and ground-to-ground weapons. It is not limited to specific missile systems. When the field of view overlaps with the existing HUD on the aircraft, the JHMCS image will automatically disappear to avoid confusion. ^[3]