| MadSci Network: Engineering |
Greetings: The head up display (HUD) was originally developed for use in the 1960s for combat aircraft. Today HUDs are also available in commercial aircraft, in automobiles such as GM’s Eye Cue(TM) system and they are also being used in a variety of applications including virtual reality and surgery. Cockpit displays (and automobile displays) were traditionally head down displays (HDD). These displays are mounted on an instrument panel below the level of the wind screen (wind shield) and pilots have to take their eyes off the outside environment and lower and refocus their vision to read the meters, dials and indicators. As aircraft became more sophisticated and electronic instrument landing systems (ILS) were developed in the 1930s and 1940s, it was necessary while landing in poor weather for one pilot to monitor the instruments to keep the aircraft aligned with radio beams while a second pilot watched out side of the windows to quickly take control of the aircraft as soon as the runway appeared through the weather. This is still the standard practice used for passenger carrying aircraft in commercial service while making ILS landings. As single piloted aircraft became more complex, it became very difficult for pilots to monitor the external warfighting and all-weather flying world while also monitoring a large array of navigation and/or warfighting instruments at the same time. To overcome this problem the head up display (HUD) was developed in the 1960s by a number of companies. HUDs enable a pilot to monitor the external environment while simultaneously being able to monitor key instruments and information presented in their field of vision (FOV). The HUD information is also focused at infinity so that the pilots need not refocus their eyes while monitoring both the external world and the instruments. Early HUDs presented only a few key instruments readings such as airspeed, heading direction, altitude and attitude relative to the horizon (gyrohorizon) and also gun sites for the warfighters. Typical HUDs project information from a bright cathode ray tube (CRT) mounted vertically in the insturment panel. These CRTs project light upward onto the surface of a nearly transparent glass plate through which the pilot also continues to see the outside world. Most often this transparent glass plate is placed in between the pilot and the wind screen and is tilted toward the pilot at about a 45 degree angle. In some HUD systems, such as General Motors Eye Cue ™ system for automobiles, the instrument projection is reflected off a reflective patch coated directly on the inside surface of the wind screen. Several types of HUD displays for aircraft are presented on the Kaiser Aerospace Company web pages at: http:// www.kaiseraerospace.com/products.htm More recently helmet integrated displays (HID) have been developed so that the users can read instruments while turning their heads to view the world. In these systems one or two miniature CRTs are usually mounted inside of the helmet over the pilot’s ears and project forward to reflect off the inner surface of the helmet face plate back into the pilot’s eyes. Two CRT or liquid crystal display (LCD) systems (one for each eye) are being developed to provide 3D stereoscopic display of information to the pilot. A miniature display of this type of display is now being tested for medical applications such as surgery. This new design with light weight LCD displays are mounted on eyeglasses (the helmets with CRTs are heavy and cumbersome). This new lightweight design of HID can be seen at the Johns Hopkins University Hospital web site: http:// pediatricsurgery.gen.com/Art_gal/hud.htm For military aircraft, helicopters and commercial aircraft for warfighting navigation and ILS applications, new HUDs are being developed that present microwave and infrared red (night vision) images to the pilot. These wavelengths penetrate fog and rain and can present images of objects such as runways in very severe weather. However, a pilot must still make the final visual landing. This requires that the projected HUD images viewed by the pilot exactly match the field of view of the real world that the pilot will see through the HUD. To date this has been very difficult to do and a number of military helicopters have crashed because of the poor field of view of current night vision equipment. Best regards, Your Mad Scientist Adrian Popa
Try the links in the MadSci Library for more information on Engineering.