Patent GB-1185205-A (GB)
Title: Aircraft command altitude guidance apparatus
Inventor: CONE HOWARD MAURICE
IPC: G01S13/91
Filed: 1967-09-30
Abstract: 1,185,205. Radio navigation. PAN AMERICAN WORLD AIRWAYS Inc. 30 Sept., 1967, No. 44616/67. Heading H4D. The Specification describes apparatus for indicating to a pilot the altitude necessary for his aircraft to remain on a chosen landing or take-off path, given the range of the aircraft to a DME responder station and the location of the responder with respect to the take-off or landing point. Both electrical and electromechanical embodiments are described. (a) Electrical, Figs. 1, 8.-A DME set 10 determines the range R of the responder and converts this via a rotation of servo shaft 11, to the position of contact 12 of a potentiometer 13, energized-with switch 39 in the " ON " position and switch 21 in the " NORMAL " position -by source 34. Resistor 40 is adjusted such that the potential of contact 12 represents the basic altitude H = R Sin α where α is the slope of the flight path. This altitude, however, is only correct if (a) the DME station is at sea level, (b) the DME station is situated at the touch down (or take-off) point. Otherwise, as in Figs. 3, 4, 5 a positive or negative reference altitude has to be algebraically added to said basic altitude. Bridge 45 performs the algebraic addition. The basic altitude potential is applied to contact 43 of potentiometer 50 positioned according to the reference altitude. A source 5 engages potentiometer 50 and a calibrating potentiometer 48 which is adjusted such that with contact 43 positioned on the zero reference altitude mark, the potential at contact 49 is the same as that of contact 43. Resistor 53 is adjusted so that the volts/unit altitude of potentiometers 50 and 13 are identical. The corrected altitude output from contact 49 is applied to an indicator 61 via overload protection diodes 69, 70 and resistors 67 and 68 for 0 to 40,000 feet, or resistor 66 for 0 to 4000 feet. With switch 21 in the " TEST " position a potential representing a given basic altitude is applied to contact 43. If as in Fig. 5, part of the flight path is beyond the DME station, such that corrected altitude will be decreasing with increasing range R polarity reversing switch 19 is charged to the " FROM " position. For take off paths angle α must be variable. A continuously variable, Fig. 6 (not shown) or switched discretely variable, Fig. 7 (not shown), α calibrated resistor is therefore provided in series with resistor 40. (b) Electro/mechanical, Figs. 10, 12.-The output of DME set 10 is converted via reversing TO/FROM switch 85 and servo amp 86, to rotation of one input shaft of differential gear 93 representing the basic altitude. The other input shaft is controlled according to the reference altitude as set by knob 94 and displayed at 96. The rotation output of the gear representing the corrected altitude is displayed at 98. The indicator panel is shown in Fig. 9 (not shown). To enable comparison to be made between the corrected altitude and the actual altitude of the aircraft, the output of the gear may control the position of contact 99 of resistor 100, which is a parallel with resistor 101 having its contact position controlled by the output of differential gear 103 having a rotation representing the aircraft's altitude based on a barometric pressure of 29À92 inches Hg at one input and a rotation representing the actual pressure at the other input. The potential between contacts 99 and 102 thus represents the altitude error, and is displayed at 113 and 114 or fed as a correcting signal to an auto pilot.