Patent GB-696519-A (GB)
Title: Improvements in or relating to aircraft navigation-aid systems
IPC: G05D1/06
Filed: 1951-05-24
Abstract: 696,519. Radio navigation. SPERRY GYROSCOPE CO., Ltd., and DOVE, F. May 2, 1952 [May 24, 1951], No. 12172/51. Class 40 (vii). The invention relates to radio navigational aids enabling aircraft to be steered to approach asymptotically and follow a ground track defined by means external to the craft although initially at a considerable distance from the track and in such a case to follow an initial course towards the track, making an angle of the order of 90 degrees therewith. According to the invention in such a navigational aid a resultant control signal is obtained by combining a displacement signal which is a measure of the displacement of the craft from the track and a heading signal which is a measure of the deviation of the heading of the aircraft from a direction corresponding generally with that of the track, but, if desired, compensated for wind drift, limiting means being provided to limit the magnitude of the displacement signal so that the limited displacement signal is greater than the heading signal for heading deviations less than a characteristic angle in the vicinity of 90 degrees and is thereafter smaller than the heading signal through a zone extending considerably beyond the characteristic angle. A localizer signal receiver 1 gives a D.C. output which is a measure of the displacement from a given track and this is fed to control the A.C. output of modulator 2. After amplification at 3 the A.C. displacement signal is limited by means described later and mixed at 4 with the heading signal derived in winding 7 of goniometer 5 fed with signals from a signal transmitter 32 associated with a gyro-magnetic compass. The combined signal is amplified and limited at 10 and 11 and combined with an angle of bank signal at 12 before being applied to a left-right indicator 17 or to control an auto pilot. The limiter. Point 18 is connected to the mid-point 19 of two rectifiers 20, 21 connected between a point 22 of constant potential on potentiometer 23, 24 and a point 27 of variable potential. Coil 6 of goniometer 5 has an output proportional to the cosine of the heading deviation angle and this is applied to transformer secondary winding 29 in opposition to the potential due to the primary winding 31 fed from the same generator as supplies the compass transmitter 32. The maximum signal fed from coil 6 is made equal to the signal induced by the primary in winding 29 and thus for a heading deviation angle of zero, zero signal is applied to rectifier and smoothing circuit 32<SP>1</SP>, for a heading deviation of 90 degrees, the output of coil 6 is zero and the induced voltage is applied to circuit 32<SP>1</SP>, and for a heading deviation of 180 degrees double the induced voltage is applied to circuit 321. Therefore as the heading deviation increases from 0 to 180 degrees the potential at point 27 increases from zero to a maximum value. The maximum value attainable is adjusted to be equal to the potential at point 22 and as the rectifier arrangement 20, 21 serves to limit the amplitude of the A.C. signal fed to mixer 4 to half the difference between the potential at point 22 and that at point 27, the limiting value of this displacement signal has a falling characteristic with respect to heading deviation, reaching zero for 180 degrees heading error. It is arranged that the maximum limited displacement signal is equal to the heading signal at a characteristic angle of 90 to 120 degrees. In a variation units 20, 21, 23 and 24 may be dispensed with and the voltage at point 27 used to progressively decrease the amplification factor of amplifier 3 to zero as the heading angle increases beyond, say, 90 degrees. It is suggested that in a different embodiment a simple limiter limiting the deviation signal to a value equal to the heading signal at the characteristic angle could be used in conjunction with a special heading deviation signal generator providing an increasing output potential as the heading deviation increases from 0 degrees to an angle in the vicinity of 180 degrees. Specifications 646,702 and 691,017 are referred to.