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Aviation History
1953
1953 - 0068.PDF
66 FLIGHT, 16 January 1953 RADAR GUNSIGHT A Partial Lifting of the Security Veil from American Fighter Equipment AT the present time the armament of fighter aircraft is in the throes of a major upheaval. We say "throes" L advisedly, for valuable time has been lost in more than one country by failure to appreciate the probable require ments; and discussion is still sometimes heated when the relative merits of small- or large-calibre guns or air-to-air rockets or guided missiles are the topic. In any such discussion, only one fact is really certain : it is that, no matter what the armament, it will be all but useless unless the aircraft which carries it is equipped with a good radar gunsight. Recent Korean fighting appears to have converted all who have taken part to this way of thinking. Even now, however, very little can be disclosed about radar gunsights; their applications to turreted weapons are many, and we may recall the radar gun-laying tail-turret carried by the Lincoln for upwards of six years and the completely automatic tail turret to be fitted to several American bombers, including the B-47B, the RB-66A and the A2J. Radar sighting on fighters is usually less obvious, and for this reason we welcome the appearance of a brief note on such devices which appeared in a recent issue of the American journal Air Trails. The account opens by quoting two of the people best fitted to speak on the subject. The former, an armament officer of F.E.A.F., said : "If any one factor accounts for our combat score against the Mig-15, it is the radar gunsight." And the other speaker, a pilot from the 27th Fighter Escort Wing—the first unit to use the A-i sight in combat—was equally emphatic : "Our outfit and other fighter-bomber units have been making some remarkable hits with rockets and bombs as well as our gun armament. The sight has more to do with this than any single factor, including skill or luck." The standard American fighter sight consists essentially of two parts : the AN/APG-30 radar ranging unit coupled with the A-1 CM gun, bomb and rocket sight. The basic design is credited to Dr. Charles S. Draper, head of the department of aeronautical engineering at the Massachusetts Institute of Technology. Production of the equipment was turned over to the Sperry Gyroscope Company and it has since been built in very large numbers. The Thunderjet was the aircraft selected for the sight's service trials, the F-84E-25 series being the first production-line aircraft in which it was fitted. Unfortunately, little can be said of the method of operation of the equipment, notwithstanding the fact that many F-84S and F-86s have fallen, more or less destroyed, into Com munist hands. The best that can be done is to present the accompanying drawings—prepared from Air Trails illus trations—which reveal something of the nature of the installation. The sight can be switched to air-to-air or air-to-ground work at will, and can be used for any normal airborne weapon. Search radar is, presumably, not fitted—so the pilot still has to find his target and then track it by centering the spot of light (see the smaller illustration) on the target circle. But the sight does everything else. For air-to-air work, it determines range, deflection, and any other factor necessary for good shooting. For ground attack, range along the weapon's trajectory, windage, drift, and any peculiar charac teristics of the missile, are all accounted for. In most day-fighter installations the aircraft remains under the control of the pilot, who follows the target in the classical manner. And if the range, proximity of the ground, or destruction of the target so require, range control can be effected by hand. But in some versions—our contemporary quotes the A-iC—the sight flies the fighter, by coupling with the normal autopilot installation. In Korea, pilots are reported to have achieved results which would be considered impossible with a conventional gyro sight. Hits, and even kills, have been made at ranges of 2,000 yards—well over a mile—and all this at speeds and altitudes roughly double those of the late war. Moreover, by providing equipment capable of detecting enemy aircraft at night, in bad weather, or beyond the limit of human vision when the sky is clear, the A-i and J-i radar sights have conferred upon the standard single-seat fighter much of the all-weather and night-flying capability of the bigger and more costly two-seater. This is reflected in the recent decision to cut back heavily upon production of the Douglas Skynight, Lockheed Starfire and Northrop Scorpion, and boost pro duction of several American single-seaters. The pilot (/eft) lines up the fighter in order to centre the radar "pip", or target image, in the gunsight circle. As the fighter banks, two gyros tilt a mirror device in the sight head; then, when the pilot corrects for mirror tilt by turning to centre the "pip" a computor supplies correct deflection. The "pip" glows very brightly as the target comes within shooting range at 2,000 yards. The three switches seen are, from the left: bomb-target- wind scale; weapons selector; and rocket-setting unit. The complete installation (right) weighs some 80 lb. The APG-30 radar range unit acts as the "eye" for the computers 4 and 11. These three units comprise separate, but /inked, assemblies for sensing deflection, elevation and g-loading; the first two are gyroscopic and the third a gravity-drop device for bombing. 1. Horn antenna. 1. Voltage regulator. 3. Waveguide assembly. 4. Range computer power supply. 5. Static convertor. 6. Amplifier. 7. BTW (bomb-tar get-wind) drive chain. 8. Sight head. 9. Sight inverter. 10. Range servo unit. 11. Computor. 12. Radar T-R (tar get-range) unit. 13. Range servo.
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