Patent GB-906777-A (GB)
Title: Improvements in or relating to landing indicators
IPC: G01C5/06
Filed: 1960-07-05
Abstract: 906,777. Indicating-apparatus; calculating-apparatus. LITTLE, D. S., MELCHIOR, F. C., and PIKE, E. W. July 5, 1960 [July 20, 1959], No. 23483/60. Classes 106 (1) and 106 (4). Indicating-apparatus comprises a servo drive shaft 201 rotatable linearly with pressure and coupled, within a portion only of its operating range, to the input shat 216 of a computor 230, 236, 232, whose output shaft 234 is rotatable in accordance with a logarithmic function of rotation of its input shaft 216, and pins 244, 246 for coupling the output shaft 234, at an adjustable predetermined angular position, to a single revolution indicator 108. In a barometric altimeter the servo drives a logarithmically graduated scale band 102 to indicate altitude over a range of say 0 to 50,000 feet above sea level and a single revolution pointer 108 turns uniformly anticlockwise over say the last thousand feet above the landing ground enabling the pilot to judge his height from the scale 110, whose graduations are not numbered. The pointer 108 has an opaque arrowhead 110 which may be covered with phosphorescent paint and the pointer is also illuminated by the edge lighting lamps of the instrument. The servo is coupled to the computor over a range of say 0 to 15,000 feet to allow for the heights above sea level of various landing grounds and the angular position of the pin 246 at which it is to be engaged by the pin 244 is manually set by knob 114 in accordance with the altitude of the airfield at which it is intended to land, shown in terms of height by indicator 286 and in terms of pressure by indicator 291 which indicators are interconnected by the same type of logarithmic computor 296, 298, 297. An alternative computor is described with reference to Figs. 5, 6 and 7 (not shown). Coupling. The servo shaft 201 is secured to a gear 202 meshing with a gear 203 fast on a threaded shaft 204 which works in a hole 206 in a stationary plate 205 and on descent draws the pin 224 to the left as shown in Fig. 2 until the pin 224 engages a pin 236 on a gear 208 loose on the shaft 204. This can be arranged to happen at 15,000 feet and upon further descent the gear 208 carries its pin 220 away from a stationary stop 222 and by meshing with a gear 212 turns the computor input shaft 216 against the action of a return spring 214. Computor. The computor comprises two reels 228, 232 mounted on shafts 216, 234 and interconnected by a tape 236 fixed to their hubs. The tape has a predetermined thickness and in winding from one hub on to the other will increase the effective hub diameter of one reel and correspondingly decrease that of the other thus continuously varying the speed ratio therebetween in accordance with a hyperbolic function. This function can be made to approximate a logarithmic function over a predetermined short range as disclosed with reference to Figs. 3, 4 (not shown). Setting of airfield data. The computor output shaft 234 is coupled to the pointer 108 through the pins 244, 246 and through a differential gear comprising spur gears 252, 254 interconnected by a spider gear 256 carried by a gear 276 which can be driven from the knob 114 to set the relative angular position of the pins 244, 246 in accordance with the height of the airfield. Specification 774,844 is referred to.