Patent GB-763121-A (GB)
Title: Improvements in or relating to navigational instruments
Inventor: MAJENDIE ALASTAIR MICHAEL ADAI
Filed: 1954-07-16
Abstract: 763,121. Aircraft navigation instruments. SMITH & SONS, (ENGLAND), Ltd., S. July 14, 1955 [July 16, 1954], No. 20851/54. Class 4. [Also in Group XL(c)]. A navigation instrument comprises a first pointer 9 rotatable in a plane about an axis 1, a scale 4 having a first datum, centred and settable about said axis, means to rotate said first pointer so that its angular displacement from the first datum is equal to the compass heading of the craft, a second linear pointer 15 adjacent and substantially parallel to said plane, and displaceable in a direction at right angles to itself and parallel to said plane, and means to displace the second pointer from a second linear datum 53 passing through the axis, in accordance with the displacement of the craft from a track laid down by a radio beacon or the like, whereby when the known heading of the track as indicated on the scale is aligned with the second datum, the position of the axis and the first pointer relative to the second pointer indicate the position and heading of the craft relative to the track. In Fig. 2, the instrument comprises a fixed mask 2, having a slot 3 for an arm 14 carrying the pointer 15, which is displaceable laterally by a milliameter 13 responsive to a radio beacon receiver 51, so that pointer 15 is displaced from the datum 53, 54 in accordance with separation of an aircraft from the beacon track. The first pointer 9 with ring 10 and bar 11, bears a representation of an aircraft 12, and is rotatable about axis 1 by a gear ring 8. The scale 4 is rotatable by a gear ring 5. In Fig. 3 is shown epicyclic gearing comprising planet gears 25 and 26, mounted on a stub shaft 24 attached to a gear wheel 23, and sun gears 27 and 29. Gear 23 is entrained with ring gear 5, and scale 4, through pinions 20 and 22. Gear 27 is entrained with ring gear 8 and pointer 9 by gears 30, 31, 32 and 34. Gear 29 is integral with gear 35, which is connected to a servomotor 36 by a gear train 37. The motor 36 is fed by an amplifier 40, having inputs from a gyro-compass 39 and a transmitter 38, Fig. 4, controlled by gear 35, so that gear 35 is positioned in accordance with the aircraft heading as indicated by the gyro compass 39. Ring gear 5 also engages a frictionally braked idler 17, which can be rotated by gear 18 secured to the shaft of a knob 19. The gear ratios of the epicyclic system and transmission gears are chosen so that rotation of ring gear 5 by knob 19 rotates ring gear 8 equally in the same sense, so the rotation of knob 19 rotates the scale 4 and pointer 9 together, if the signal from gyro compass 39 does not change. If gear 35 is rotated by motor 36 due to a change in heading, ring gear 5 is held stationary by the frictionally braked idler 17, and the pointer 9 is thus rotated to indicate the new heading against scale 4. By pulling out knob 19, gear 50 engages an idler 49 meshing with a ring gear 6. Knob 19 then rotates a marker 7, Fig. 2, reading against scale 4 to indicate a desired heading. This rotation is transmitted through gears 48, 46, 45 and 44, Fig. 4, to a potentiometer winding 42. The wiper arm 41 is positioned by the shaft 28 of gear 29, and thus derives an analogue signal corresponding to deviation from a desired heading. In operation, knob 19 is pushed in, and turned until the known heading of the track appears on scale 4 opposite datum 53. Knob 5 is pulled out, and turned to offset marker 7 in accordance with the traverse wind velocity to compensate for drift. The representation 12 and the pointer 15 will then represent in plan view the relative positions of the aircraft and track ; and the pilot endeavours to maintain the bar 15 centred on axis 1, and the pointer 9 on the mark 7. Specification 669,471 [Group XXXV] is referred to.