Patent GB-646640-A (GB)
Title: Improvements in or relating to radio navigating systems
IPC: G06G7/22
Filed: 1946-11-12
Abstract: 646,640. Automatic control systems for aircraft. SPERRY GYROSCOPE CO., Inc. Nov. 12, 1946, No. 33592. Convention date, Aug. 4, 1943. [Class 38 (iv)] [Also in Groups XXXVI, XXXVII and XL (c)]. In a radio-navigation system the position of a mobile craft is determined by measurement of differences of the transit-times of radio signals along two pairs of channels between the craft and three fixed points and by a computer operated by forces derived from two comparators continuously comparing these transittimes. Three stations, O, A, B, Fig. 1, transmit different carrier waves, each amplitude-modulated with two common frequencies, f and mf, providing coarse and fine adjustment of the comparators. On an aircraft P, apparatus, Fig. 9, comprises: wireless receivers and null comparators 42, Fig. 10; a computer 47, Fig. 11, for the direction of P from O; a computer 57, Fig. 12, for the great circle distance of P from O and the latitude and longitude of P; a computer 74, Fig. 13, for the deviation of P from a predetermined course S and its distance from an objective T; a controller 84, Fig. 14, for the rudder and ailerons and a device 93, Fig. 15, controlling the throttle, or indicating speed and releasing bombs, or indicating when a given point is reached. Comparator.-The carrier waves are collected at 41, detected at 107, 108, 109 and the two modulations of each carrier are separated by band-pass filters 111-116. The monoperiodic modulations (f) from 111, 113 are amplified at 119, 124 and applied to a phase meter 122, phase-shift being introduced at 117. This phase meter is similar to that described in Specification 609,298, [Group XXXVI], and provides a direct voltage proportional to the phase difference between inputs. This voltage, after amplification at 135, is combined in a summing amplifier 137 with a voltage similarly derived from the polyperiodic modulations (mf) and subjected to a limiter 136. The direct voltage output from 137 is applied through a balanced modulator 138 and a phase-sensitive amplifier 139 to control a motor 141 which rotates a shaft 44 by an amount proportional to the transit-time difference of the radio waves received. The shaft 44 drives phase-shifter 117 to eliminate the phase difference detected at 122 and also drives, through m : 1 gearing, a phase-shifter 125 to eliminate the phasedifference detected at 132, the latter being unable, due to the limiter 136, to take control until the coarse adjustment has been effected. Shaft 43 is similarly operated and indicators 46, 45 show the distance difference KB, KA of P from O, B and from O, A. Computer for #a (POA).-In the computer 47, great circle distances a (OA), b (OB) and the angle # (BOA) are preset at 48, 49, 51 and extensions of the shafts 44, 43 supply the variables to enable the equation to be solved for #a and rotate a shaft 55 and indicator 56 in accordance therewith. Mechanical differentials 178, 179 and 183, 184, 208 sum and differentiate pairs of values. Multiplication is performed by cosine, sine or compound functions in potential dividers 155-159, 161-165. The outputs therefrom pass through buffer amplifiers 166-169, 171-175 to avoid drawing current through the sliding contacts. Assuming amplifier 176 causes a phasesensitive motor 177, acting as a servo device, to generate #a, an alternative equation may be solved by throwing the five switches 221-225. The computers depend upon a null result and are therefore independent of supply voltages injected at 226, 231. Computer for latitude and longitude of P.- Electrical quantities from the computer 47 are applied at 58, 59 to potential divider 259 and difference amplifier 263, to operate a motor 265 through a phase-sensitive amplifier 264 and solve an equation for the value of r (great circle distance OP), which is then indicated at 61. When switches 321-225 in computer 47 are thrown to the left, r is obtained from the equation Shafts 63, 69, 64 are preset to represent the latitude Lo and longitude #o of O and the bearing # of OA. The equations are then solved for the latitude LP and longitude #P of P, using mechanical differentials 276, 286, 302, voltage dividers 268, 278, 273, 292, 288, buffer amplifiers 272, 291, sum amplifiers 277, 295, phase-sensitive amplifiers 283, 297 and servo motors 284, 292. The divider 273 provides cosine and sine factors of angle (#+#), having contact arms 274, 275 separated by 90 degrees. Computer for determining deviation from ground track S and distance from target T.-The latitude LT and longitude #T of the target T are preset at 75, 76 and electro-mechanical computing means . similar to that previously described is used to provide balanced outputs from a buffer amplifier 321 proportional to and similar outputs from 323 proportional to These balanced outputs are applied to voltage dividers 324, 325, the contact arms being set by 77 to one angle r representing the bearing of S at T, so that a sum amplifier 331, yields an output at 85 proportional to perpendicular deviation from track S, indicated at 82. The outputs from 321, 323 are also applied to four 60 degree sectors 336, 338, 335, 337, at least one of which is in contact with at least one of two brushes 333, 334 set on shaft 77 at 45 degrees. The brushes 333, 334 are connected to a voltage divider 342 having a resistance wound for about 192 degrees of its length, from 341 to 339 according to <SP>2</SP>/ 3  of a secant function having values which vary from - 1 to +1 over this range. A fixed resistor 343 is chosen so that the voltage impressed at 341, 339 drops <SP>1</SP>/ 3  of its value in 342. A snap-action switch 349, driven with 180 degree-spaced arms 344, 345 at twice speed of shaft 77, ensures that s (distance from T) is evaluated according to the value of # from equation A phase detector 353 actuates an indicator 83 to indicate s. Rudder and ailerons control.-The rudder is controlled by a torque motor 377 energized by a phase-sensitive amplifier 374 fed by an amplifier 372 which sums the error signal from computer 74 applied at 85 through amplifier 389 and limiter 393 and the signal applied by a magnetically-slaved gyroscope 361 through polyphase windings, 363, 367, the latter being preset by shafts 86, 88 according to the bearing # and wind drift. The wind drift correction is continuously adjusted by the error signal through a phase-sensitive amplifier 391 and a motor 394. Aileron control is effected partly through a bank correction circuit 403, as described in Specification 611,607, [Group XII], partly by a gyroscope 382 and partly in accordance with rate-of-change of the error signal by obtaining a direct voltage from a phase detector 399 and passing the signal through a differentiator and limiter 401 to a balanced modulator 402. When the craft is following a homing course to O, switch 80 may be closed on 300, Fig. 12. Ground speed computer.-With a speed indicator 99 coupled through shaft 429, pinion 409 and rack 411 to a ball carriage 407, a constant speed motor 405 drives a friction disc 406 and cylinder 408 so that a dial 95 indicates the assumed distance s<SP>1</SP> and a corresponding voltage is applied to a sum amplifier 418. In 418, s<SP>1</SP> is compared with the computed value s, and any difference is indicated at 97 and is applied through motor 420 and worm-drive 422 to adjust 99. Alternatively, electromagnetic clutches 427, 428 may be de-energized and energized respectively, so that the desired speed can be preset at 99 and deviations therefrom effect throttle control at 101. Bomb release &c.-A contact 437 is carried by a rack 435 which is preset so that at a given value of s<SP>1</SP> a second contact engages it and completes a circuit causing release of bombs or warning the pilot of the position reached. When the objective is O, a switch 90 may be closed on contact 270, Fig. 12. The Specification states that the computing may be carried out by purely mechanical means in place of the electromechanical method described.