Patent GB-414881-A (GB)
Title: Improvements in and relating to speed, distance and drift angle indicators for aircraft
IPC: G01P3/36
Filed: 1933-06-16
Abstract: 414,881. Speedometers and odometers. COLVIN, C. H., Squanset, Point Pleasant, and COLVIN, H. F., 218, Conway Court, South Orange, both in New Jersey, U.S.A. June 16, 1933, No. 17199. Convention date, July 30, 1932. [Class 106 (iii).] Comprises an instrument for indicating directly and continuously distance travelled by an aircraft relatively to the ground, said instrument incorporating a synchronizer adapted to be observed in relation to the apparent movement of the ground and operated at a speed which is a direct function of the ground speed, and means for indicating distance as the integration of ground speed against time. The ground 14 is viewed by looking through an eyepiece 11 below which is an optical member 12 which allows a simultaneous view by reflection of a synchronizing element comprising a belt 13. The points A, B of the synchronizing element will appear to coincide with the point C, D of the ground when the speed of the element 13 is a direct function of the speed of the aircraft and an inverse function of the altitude. The shaft 15 of the belt 13 is driven directly from a shaft 16 driven through a variable speed transmission 20 from a shaft 17. The transmission is such that the ratio of the speed of the shaft 16 to that of the speed of the shaft 17 is an inverse function of the number indicated on the dial 21. The shaft 17 is also driven through a variable speed transmission 22 from the shaft 18 of a constant speed power unit 24. The ratio of the speed of shaft 17 to that of shaft 18 is directly proportional to the numbers on the dial 23. In Fig. 3, the shaft 37 of a constant speed motor 34 drives through a gear 39 a friction disc 40 in contact with which is a wheel 44 slidable on but rotatable with a shaft 45. The hub of the wheel 44 is grooved to receive a fork 47 of a threaded nut 51 working on a screwed shaft 52 which is rotated by bevel gear 53, 54 and a wide spur wheel 56 in gear with a spur wheel on a shaft 61. When it is desired to shift the wheel 44 along its shaft, the button 62 is first pushed in. This slides the shaft 61 against the influence of the spring 64 and also a second spring 67 moves a pivoted link 63 against which the spindle 41 of the disc 40 bears so as to relieve the pressure between wheel 44 and disc 40. The button 62 is then turned to adjust the wheel 44. In the upper part of the same casing 31 is a similar transmission unit. The shaft 45 is common to both transmissions and carries a friction wheel 74 gearing with a disc 70. In this case the wheel 74 is the driving member and drives a synchronizing member in the casing 151. The shaft 101 drives through bevel gears 153, 154, 156, 157 and a spur gear 161, 162 a cylinder 165 on which is marked a helical line which may be viewed through a slot 172. The shafts 52 and 82 drive through bevel gears 111, 112 and 121, 122 counters 113, 123 which indicate miles per hour and height respectively. The shaft 45 drives through bevel gear 131, 132 a counter 133 which indicates distance. This indication may be transmitted to a distance by a cam 135 which engages two contacts causing an electric circuit to be made once per mile. A fourth counter 143 is driven from the shaft 37 through bevel gear 148, 149 and a shaft 147 which is connected by means not shown to a shaft 147<1>. The gear reduction is such that when the shaft 37 is running at the preselected speed, the hand 145 makes one revolution in one hour and the hand 144 is geared to the hand 145 at a ratio of 12 : 1. In practice the hands of the counter 143 are set to agree with the hands of a good time piece and should keep in agreement therewith if the speed of the shaft 37 is constant. The top part of the casing 151 may be moved relatively to the bottom part about the axis by a handle 159 to cause the lines of the spiral viewed in slot 172 to appear to turn simultaneously with the ground and a scale on the outside of the casing indicates angle of drift. By varying the speed of the shaft 101 the apparent speed of movement of the lines can be made to coincide with the speed of the ground. Fig. 10 shows the optical system. Prisms 184, 185 may be used to offset the vertical line of sight and the objective 181 forms an image at I-I which is observed through the eyepiece 182. The plane glass 183 is at 45‹ to the optical axis of the eye-piece and the surface of the cylinder 164 at the slit is at the same distance from the plane glass as is the image I-I. A prism 186 having a plane section 188 and two or more bridge-shaped sections 189 causes the helix to appear as three or more parallel rows of marks. A lamp 191 illuminates the marks. In a modification two additional counters and a gear shift mechanism are provided to afford a doubling of the range of the instrument both as to altitude and speed, the gear lever also operating a shutter to obscure the pair of counters not in use.