Patent GB-572648-A (GB)
Title: Improvements in or relating to apparatus for controlling the release of bombs or thelike from aircraft
IPC: B64D1/04
Filed: 1943-07-19
Abstract: 572,648. Dropping bombs from aircraft. AUTOMATIC ELECTRIC LABORATORIES, Inc. July 19, 1943, No. 11711. Convention date, July 18, 1942. [Class 9 (ii)] Bombs &c. are dropped from aircraft at timed intervals under the control of an adjustable timing device which includes an electronic tube, the timing device being adjusted by altering the variables of the electronic tube circuit by means of a movable member graduated in ground speed of aircraft, which cooperates with a fixed scale graduated in distance between bomb hits. The number of bombs to be dropped may be pre-set and these may be dropped individually under the control of the bomb-aimer, in which case the electronic tube circuit is inoperative, or serially as a train under the control of the timing device. Provision is made to maintain the space-current through the electronic tube substantially constant irrespective of fluctuations in the anode voltage and a resistance of negative temperature coefficient is incorporated in the electronic tube circuit to compensate for variations in the time-constant of the circuit arising from changes of temperature, these provisions being made to avoid errors in the spacing of bomb hits. When bombs are to be dropped under individual control, a knob 181, Fig. 4, is rotated so that an indicator 181a registers on a fixed scale 403 the number of bombs to be released under such control, this movement causing a contact pin 172, Fig. 1, on a ratchet wheel 174 to be offset through a predetermined angle from a position in which the pin 172 breaks the operation circuit. The ratchet wheel is rotated step-by-step by a pawl 177 actuated by an electromagnet 175 each time a current impulse passes to a known electromagnetic bomb-release mechanism 185, until the pin 172 returns to normal position after the predetermined number of bombs has been dropped, thereby breaking the operating circuit. After pro-setting the bomb counting mechanism the master switch 168a is closed, and the switch 160 operated to " select " position. The control switch 1.67 is then operated by the bomb-aimer each time a bomb is to be released and at each operation a circuit is completed through the contact springs 173 to energize the primary windings of a vibrator 165 and the winding of a locking relay 140. The relay 140 closes a contact 143 and completes a circuit through a signal lamp 137. The output voltage of the vibrator 165 appears across the terminals 165b to energize the pulsing relay 150 in a circuit including the contact 163 and resistor 164. The energization of the pulsing relay 150 closes a contact 151 to actuate the bomb-release mechanism and also closes a contact 154 to energize the magnet 175 to actuate the ratchet pawl of the bomb counting mechanism. These operations are repeated at each closure of the switch 167 until circuits are broken by the pin 172 opening the contact 173 after the pre-set number of bombs has been dropped. When a train of bombs is to be dropped at timed intervals to give a predetermined ground spacing, the counting. mechanism is pre-set as described above, for the required number of bombs, and a knob 133, Fig. 4, is rotated to set a movable scale 405 so that the graduation speed at which the bombing operation is to be carried out, registers with the graduation on a fixed scale 404, indicating the required bombhit spacing. The operation of the knob 133 actuates a wiper to incorporate a corresponding portion of a rheostat 102, Fig. 1, in a circuit which includes the grid 100g of an electronic tube 100, a condenser 134 and a variable resistance 101. The switch 160 is then set to " Train " position and the switch 168a closed, thus completing a circuit through the heater 100h of the electronic tube 100. The switch 167 may then be operated to initiate the release of the train of bombs, by the completion of a circuit through the contact 173 to energize the locking relay 140 which closes the contact 143 and energizes the signal lamp 137. The switch 167 may then be released without interrupting the bombing operation as the primary windings of the vibrator 165 are maintained energized in a circuit which includes the contacts 162, 143 and 173. The output voltage of the vibrator 165 is applied to the screen electrode 100s of the tube 100 over a path including the resistor 139, and the relay 150 is energized by the space current flowing through the tube 100 by reason of the anode 100a being in circuit with the relay through the " Train " switch contact 161. The relay 150 then closes the contact 151 to actuate the bomb-release mechanism 185, and also closes the contact 154 to energize the stepping magnet 175 of the bomb-counting mechanism. At the same time the relay 150 opens the path, short-circuiting the condenser 134 through the contact 153 and the encircuited portion of the rheostat 102 and bridges the condenser 134 across the encircuited portion 101a of the biassing element 101 in series with the encircuited portion of the rheostat 102 by way of the contact 152. The condenser 134 is thereby charged and builds up a voltage which biasses the control grid 100g negatively with respect to the cathode 100c and so reduces the space current flow through the tube 100 to a value such that the relay 150 restores. On release of the relay 150, the contact 151 is opened to terminate the current pulse to the bomb-release mechanism ; the contact 154 is opened to de-energize the stepping magnet 175 and the contact 153 is restored to short the condenser through the encircuited portion of the rheostat 102. As a result of the consequent decrease of bias voltage between the control grid 100g and the cathode 100c, the spacecurrent through the tube increases until the relay 150 is re-operated to release a further bomb and to effect a further actuation of the bomb-counting mechanism, this cycle being repeated until the pin 172 of the counting mechanism opens the contact 173 after the whole pre-set train of bombs has been released, thereby releasing the relay 140 and breaking the primary circuit of the vibrator 165. The switch 160 is then operated to disengage the contacts 161, 162, thereby de-energizing the signal lamp 137. The time interval between successive energizations of the relay 150, and hence the bomb-hit spacing is governed by the value of the encircuited portion 101a of the resistor 101 and the encircuited portion of the rheostat 102, the ratio of the make-to-break periods in the energization of the relay 150 being adjusted by altering the value of the portion 101a, this ratio preferably being unity. The pentode electronic tube 100 has the charac - teristic that by holding the potential of the screen electrode 100s constant, wide fluctuating in the voltage applied to the anode 100a do not appreciably vary the space-current flow through the tube and substantial constancy of screen potential is secured by shunting the output terminals of the vibrator 165 by a gas-filled electric discharge tube 138 e.g. of neon type in series with a resistor 139. According to a modification the gas-filled discharge tube may be connected directly between the screen electrode and the cathode of the electronic tube.