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Aviation History
1951
1951 - 0852.PDF
FLIGHT, 4 May 1951 Evolution of the Guided Missile out at the Guided-Weapons Establishments both in this country and Australia, the actual production of missiles will be in the hands of aircraft firms and associated manufacturers. In time of emergency, all manner of ordinary commercial firms can then be brought into the scheme around this nucleus. The absence of a dependable guidance system was Germany's chief handicap in the development of her war-time missiles, and several ingenious suggestions were made for side-stepping the long and arduous research that would otherwise have been required to provide a foolproof system of remote control. One of the ideas originated in 1944 to combat our high-flying bombers, for example, was that the intercepting missile should be piloted, which resulted in the development of the Ba 349 Natter (Fig. 1). The design of this unique intercepter was centred in a vertical take-off and an exceptionally high rate of climb. To satisfy these requirements, it was decided to concentrate on the climb factor and to effect no compromise such as maintainir^ a reasonable wing-loading for the usual flight manoeuvres and landing. The design, in fact, was such that landing by normal means was impossible and it was at first planned to sacrifice the complete aircraft. The latter problem was overcome by arranging that the pilot abandoned the machine after pressing home the attack and descended by parachute the after-section of the fuselage (contain- ing the propulsion unit) following him down in similar fashion. Powered by a Walter 109-509 A-i rocket motor, the Ba 349A version was capable of climbing at the phenomenal rate of 35,8ooft/min to reach its ceiling at nearly 50,000ft. The radius of action after a height of 37,000ft had been reached was estimated at 25 miles. The armament envisaged consisted of 33 R4M-type rockets carried in the nose; after firing, the Natter became unstable because of the displaced e.g., and, as the machine fell back to a safe altitude, the nose section was discarded and the pilot para- chuted away. At least, that was the intended method, for although many tests were made under the control of an autopilot, the war ended before the weapon could be used operationally. Another interim scheme was demonstrated by the air-to-air X-4 missile, which was "wire-controlled" : command impulses were transmitted directly from the launching aircraft through fine wires which unwound from bobbins on the missile. An original idea for the guidance of rocket missiles was con- ceived as long ago as 1925, when it was suggested that a rocket could be made to climb along a searchlight beam by means of a control system worked by four selenium cells. A cell would be fitted to the tip of each fin so that, if the missile deviated from the centre of the beam, each cell would react to a different intensity and a simple transmission device, acting on the rudders, would re-stabilize the missile. Thus, having once been picked up, the missile would remain captive in a pencil of light. This was obviously one scheme that looked well on paper but offered little in practice, and in the form described it was never developed. Nevertheless, it has a striking parallel with the present-day Beam-Rider system which employs exactly the same principle except that ultra short-wave antennae are used instead of selenium cells and the rocket climbs along a radar beam. Fig. 5. The Fairchild Lark, here seen rising with the assistance of two Aerojet booster rockets, is a subsonic missile developed to a U.S. Navy specification. 535 Fig. 4. One of Germany's most successful rockets, the Wasserfall was a super- sonic missile designed to attack at altitudes between three and nine miles. It pos- sessed astonishing stability. A beam transmitter for guiding rocket missiles consists of a parabolic reflector with a rotating dipole. This is the accepted method of producing intensity variation in the beam with decreased value at its centre. The type of rocket normally envisaged for this system has cruciform wings and fins, and an antenna is located in the trailing edge of each of the four wings. These antenna; are linked in an oscillatory circuit in which the currents are amplified, rectified and, through relays, are made to actuate the control surfaces. Such a missile will, of course, only travel on a direct course when all its antenna: are influenced to the same degree. Should it deviate from the centre of the beam, the antenna: will be influenced disproportionately, those farthest from the centre having more intense reception and causing the function of appropriate controls to re-centralize the rocket. This technique is shown diagram- matically in Fig. 2. It is usually considered in conjunction with a self-homing device which monitors the gyropilot so that in the final stage of an attack, the missile is self-directing. The Beam-Rider system, however, has a great deal to condemn it in practice. To provide a usable intensity difference in the cross-section, the controlling beam must be reasonably narrow; to obtain the necessary variation, a wide beam would be imprac- ticably strong in the fringe. Tracking is a delicate operation made especially acute when the target aircraft suddenly alters course and the missile is not yet sufficiently close to fly on its homing device. To have the beam too narrow will make it easy for the missile to escape from its controlling influence for, once the point of maxi- mum intensity is passed, it will not re-centralize and will be difficult to pick up again. The sole remedy, therefore, is to effect a compromise by slightly widening the beam and relying on a smaller difference in intensity. This naturally involves corres- pondingly sensitive controls in the missile. The better of the two directing systems is Command Guidance, which employs two tracking radars, one for the target aircraft and the other for the missile (Fig. 3). The technique was developed by the Germans during the war, when a two-man optical system (using telescopic sights and range-finders) was employed, com- mands being transmitted to the missile according to the impulses generated by moving a control stick. An adjacent transmitter, linked to the control box, relayed the initial impulses as radio signals on predetermined frequencies. In the missile, these radio commands are translated, through a time-modulated system, into movements of the control surfaces by servo-motors. The greater the stick movement, the stronger is the modulation. Control in the pitching and rolling planes depends on the relative durations of individual tones in pairs of audio-frequencies. When the stick is centralized, the tones in each pair are of equal duration and the servo-motors hold the controls neutral. If the stick is moved, the equi-period timing is disturbed and a sensitive polarized relay brings the servo-motors into operation to deflect the control surfaces. To be fully effective, the interception of an out-of-sight target requires a command system which transcribes on a single cathode- ray tube the directional and distance plots fronvfwo radar sets, one representing the target bomber, the otherSshe missile: the luminous "blips" are followed by the aimer, whoManipulates the control stick to make them finally coincide. If the*plots are fed into a computer, it is possible for steering orders tib^ reach the missile automatically. The Command Posts which direct guided missiles need not, of course, be restricted to the ground but may be carried in anips and
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