Patent GB-1347462-A (GB)
Title: Homing torpedoes
IPC: F41G7/00
Filed: 1963-01-04
Abstract: 1347462 Torpedoes PLESSEY CO (UK) Ltd 3 Jan 1964 [4 Jan 1963] 585/63 Heading B7A [Also in Divisions G3 and H4] A homing torpedo for attacking submarines sinks vertically through the water while searching with an omnidirectional sonar beam a shallow horizontal zone centred on the torpedo's position, and on receiving a sonar echo it pulls out of its dive in the direction of the target and commences actively homing on it by means of a narrow forward looking sonar beam. Torpedo construction (Fig. 1).-The torpedo is propelled by two contra-rotating propellors driven by electric motors powered by a seawater activated battery. An empennage 17 provides large stabilizing surfaces during full descent, and is jettisoned (e.g. by a pyrotechnic device) when the torpedo has commenced active homing. If necessary, provision may be made for correcting verticallity by using the control surfaces in response to signals from a reference pendulum. From bow to stern, the torpedo comprises the forward looking sonar assembly 11, warhead 12 (or dummy), the sideways looking sonar search assembly 13, a control section 15, and propulsion and control surface activator section 16. Opposed pairs of control vanes normally work in unison, although they may be used differentially to roll the torpedo on its axis. The auxiliary empennage fins are mechanically linked to the normal fins. In order to reduce turbulence over the control surfaces during free sinking, the propellers are fitted with freewheel devices. Control system (Fig. 4).-Guidance is effected through four independent controls 30. A three gyro system provides rate information relative to the roll, yaw and pitch axes, and positioned information is provided by integrating amplifiers 34. Information is also fed to the logic unit by a programme unit 36 which stores a pre-set programme which can be amended manually prior to launching the weapon and/or it can be amended by information derived during the torpedo's operation. A servo followed transducer 37 feeds depth information to the logic unit, and records the target acquisition depth. Sideways looking sonar.-Eight rectangular magnetostrictive transducers (see also Fig. 1) are pulsed simultaneously from separate transmitters with narrow band pulses of 60 kc. of 5 millisec. duration. On receipt of an echo, the information received will provide details of target sector and range. Timing pulses are sent from the logic unit to the transmitters. The polar diagram is in the form of a very thin horizontal disc. The receiving system (Fig. 7) includes an oscillator 51 in each transducer line, each operating on a different frequency, so that a single amplifier 53 may be used. Filters 56 separate the received echo pulse and feed it to the logic unit so that the latter may associate it with the correct transducer. Homing sonar system (Fig. 10).-Two transducer arrays 59a, 59b are used, each comprising eighteen half-wave magnetostrictive elements; they are arranged one above the other, pointing 4 degrees to port and starboard respectively. The arrays are energized by two separate transmitters for simultaneous transmission. The outputs of amplitude and phase comparators 61, 62, respectively give indications of target position in azimuth and elevation; only one amplitude and one phase output is present at any instant. Operation.-The torpedo will normally be dropped by parachute from an aircraft, although it may be ship launched, the parachute being released when the torpedo enters the water. Primary underwater descent is retarded by a drogue which is released at about 50 feet, by which depth the batteries have been activated. From this point the sideways sonar search is commenced. When an echo is received, the depth is stored by transducer 37, the motors are started, and the torpedo rolls on its axis and pulls out of the dive in the target direction, levelling off when target depth is again reached. The forward looking sonar is now energized, and the torpedo is caused to weave through about 15 degrees in azimuth until the target is again located. Any signal indicating an error to port or starboard, or up or down, causes the guidance system to make a fixed incremental correction which may be repeated or reversed according to the next signal received. Active homing ceases at a range of 50 feet and passive homing continues on the target noise. The possibility of a near miss is obviated by switching on the sideways looking sonar during the passive homing stage, and arranging for this to activate the warhead on receipt of constant very strong signals.