United States military aircraft designation systems

F-111 Terrain Following Radar Systems circa 1973 US Air Force Training Film

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• published: 16 Feb 2015
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more at more at http://scitech.quickfound.net/aviation_news_and_search.html "In all models of the F-111, terrain following radar not only provides a visual display of approaching terrain, but through the capabilities of a computer, pitch steering commands can be automated to guide the aircraft safely over obstacles in its flight path..." US Air Force Training Film TF-6851 Public domain film from the US Air Force, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied. The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original). There is a broadband hum in the vocal frequencies of this film which I cannot completely remove. http://creativecommons.org/licenses/by-sa/3.0/ http://en.wikipedia.org/wiki/Terrain-following_radar Terrain-following radar (TFR) is an aerospace technology that allows a very-low-flying aircraft to automatically maintain a relatively constant altitude above ground level. It is sometimes referred-to as ground hugging or terrain hugging flight. The term nap-of-the-earth flight may also apply but is more commonly used in relation to low-flying military helicopters, which typically do not use terrain-following radar. The technology was originally developed by Ferranti for use with the TSR-2 aircraft... The system works by transmitting a radar signal towards the ground area in front of the aircraft. The radar returns can then be analysed to see how the terrain ahead varies, which can then be used by the aircraft's autopilot to maintain a reasonably constant height above the earth. This technology is primarily used by military strike aircraft, to enable flight at very low altitudes (sometimes below 100 feet (30 metres)) and high speeds, avoiding detection by enemy radars and interception by anti-aircraft systems. This allows the pilot to focus on other aspects of the flight besides the extremely intensive task of low flying itself. It can also enable low-altitude flight at night and in other low-visibility conditions. Some aircraft such as the Tornado IDS have two separate radars, with the smaller one used for terrain-following. However more modern aircraft such as the Rafale with phased array radars can look forward and at the ground simultaneously. Most aircraft allow the pilot to select the ride "hardness", to choose between how closely the aircraft tries to keep itself close to the ground and the forces exerted on the pilot. The F-111 used a switch to select for a hard, medium or a soft ride. The TFR computer will consider many factors in determining the flight path for the aircraft. These factors include, distance to the forward terrain, aircraft speed and velocity, angle of attack and quality of signal being returned... By flying at very low altitude, the aircraft can take advantage of terrain masking and avoid detection by enemy radar systems. The system is also largely automated and can take some of the workload off the pilot. The radar emissions can be detected by enemy anti-aircraft systems with relative ease once there is no covering terrain, allowing the aircraft to be targeted. The use of terrain-following radar is therefore a compromise... Even an automated system has limitations, and all aircraft with terrain-following radars installed have limits on how low and fast they can fly. Factors such as system response-time, aircraft g-limits and the weather can all limit an aircraft... http://en.wikipedia.org/wiki/General_Dynamics_F-111_Aardvark The General Dynamics F-111 Aardvark was a supersonic, medium-range interdictor and tactical Attack aircraft that also filled the roles of strategic bomber, aerial reconnaissance, and electronic warfare in its various versions. Developed in the 1960s by General Dynamics, it first entered service in 1967 with the United States Air Force. The Royal Australian Air Force (RAAF) also ordered the type and began operating F-111Cs in 1973. The F-111 pioneered several technologies for production aircraft, including variable-sweep wings, afterburning turbofan engines, and automated terrain-following radar for low-level, high-speed flight. Its design influenced later variable-sweep wing aircraft, and some of its advanced features have since become commonplace. The F-111 suffered a variety of problems during initial development and several of its intended roles, such as an aircraft carrier-based naval interceptor with the F-111B, failed to materialize. USAF F-111 variants were retired in the 1990s, with the F-111Fs in 1996 and EF-111s in 1998. The F-111 has been replaced in USAF service by the F-15E Strike Eagle for medium-range precision strike missions, while the supersonic bomber role has been assumed by the B-1B Lancer. The RAAF was the last operator of the F-111, with its aircraft serving until December 2010...