Patent GB-988017-A (GB)
Title: Pitch and roll corrector for use in a doppler radar navigation system
IPC: G01S13/60
Filed: 1962-10-25
Abstract: 988,017. Radar. BENDIX CORPORATION. Oct. 25, 1962 [Nov. 2, 1961], No. 40455/62. Heading H4D. In a Doppler radar navigation system utilizing means for radiating and receiving energy beams in fixed angular relation to an aircraft and means responsive to ensuing Doppler data for producing a quantity representative of the speed of the aircraft relative to ground, there are provided first modifying means for modifying that speed by a factor proportional to the cosine of the angle of pitch of the aircraft, first computing means for computing a second quantity proportional to the ratio of transverse to longitudinal components of the velocity of the aircraft relative to ground, second computing means for computing a third quantity proportional to the ratio of normal to longitudinal components of the velocity of the aircraft, second modifying means for modifying the second quantity by a factor equal to the cosine of the roll angle of the aircraft, third modifying means for modifying the third quantity by a factor equal to the sine of the roll angle, and means responsive to the difference between the second and third modified quantities for determining the drift angle of the aircraft. The embodiment relates to a navigation system as described in Specification 949,681 in which Doppler frequency trackers 12, Fig. 1, are associated with a combiner 13 and computers 14, 15, the arrangement also incorporating an oscillator 16 providing an output at a frequency F GS  representative of the aircraft's ground speed. An input representing pitch angle P is fed at terminal 23 to a servo-system and a cosine potentiometer 22 is linked electrically with potentiometer 21. Hence a correction is introduced to compensate for errors due to the vertical velocity component during aircraft climb. It is arranged that for small angles of climb, no correction is given and the " cosine P " correction is restricted to angles below the stalling condition. Fig. 2 illustrates a part of Fig. 10f of the above Specification as modified in accordance with the present invention. The " ground speed " oscillator (16, Fig. 1) is controlled in frequency by a voltage on line 20 derived from a potentiometer 21 in series with a resistance network which includes a potentiometer 22 such as to provide the required " cosine P " factor to potentiometer 21. A clutch 56 with stops on the driveto control transformer 24 corresponding to predetermined angles at which pitch angle no longer approximates to climb angle, is provided. The voltage supply to the potentiometers is derived from a servo loop comprising oscillators 46, 47, discriminator 48, D.C.-integrator 49 and emitterfollower 51; the voltage change at point 52 compensates for temperature changes in the " ground speed " oscillator. The circuit of Fig. 2 is set up by placing pitch angle transducer 23 to zero degrees, adjusting the tap on potentiometer 22 for a frequency minimum in the ground speed oscillator, and then adjusting the ground speed oscillator frequency to that corresponding to maximum indicated ground speed with the tap on potentiometer 21 set at the top end of the winding. Drift angle computation, Fig. 1. In addition to the setting-in of sine (roll angle) to computer 14, cosine (roll angle) is set-in. The detailed arrangement, Fig. 3 (not shown), otherwise closely follows that disclosed in the above Specification.