Patent GB-125468-A (GB)
Title: Bomb Dropping Sight for Aircraft.
Inventor: POLLEN ARTHUR HUNGERFORD
IPC: F41G3/24
Filed: 1916-08-17
Abstract: 125,468. Pollen, A. H., and Landstad, H. F. Aug. 17, 1916. Speed indicators operating by sighting terrestrial objects.-Consists in a bomb-dropping sight having means for ascertaining the velocity and the direction of the wind by forming a vector triangle, the sides of which represent respectively the speed through the air, the speed overland, and the velocity of the wind. The speed through the air is known from the propeller revolutions, and the speed overland is measured by providing a vertical line of sight and a line of sight making a fixed angle therewith or intercepting a fixed distance on the ground, and timing the interval between the instant at which an object on the ground cuts these lines of sight. In the construction shown in plan in Fig. 1 and in elevation in Fig. 2, the sight is carried on a framework 1, 2 at the side of the aeroplane body, and consists essentially of a backsight 6, adjustable for windage, and a foresight x adjustable along an arm 13 set in the direction of the overland travel. The speed-through-the-air vector is set up parallel to the fore-and-aft line of the aeroplane by adjusting a slide 28 along a guide 29 provided with a scale 30 representing 10 miles per hour to the inch. The slide 28 has pivoted to it a graduated horizontal arm 12, shown folded up out of use in Fig. 2, which forms the velocity-ofthe-wind vector. The speed-overland vector comprises an horizontal arm 13 pivoted to turn about a point z<1> arranged vertically beneath the backsight 6. The arm carries a fixed longitudinal wire y, a fixed cross-wire z vertically beneath the backsight 6 and an adjustable cross-wire or pointer x which constitutes the foresight. In using the device to measure the overland speed, the foresight x is adjusted at the line 26 marked " full time in which position the line of sight through x makes an angle of 30 degrees with the vertical line through z. The time in seconds taken by an object on the ground to travel from x to z is then observed, and the wind vector arm 12 is set to cut the' central wire y at the corresponding graduation on the left of the arm. A number of scales, each relating to a particular height of flight, are provided, means being provided for removably securing the scale to the arm 13. In Fig. 5, the scale for 4000 feet is shown separately. The speed overland is indicated at the left hand side of the scale, in terms of seconds of observation, and on the right of the scale is a second set 20 of the same numerical graduations used in setting the foresight for bomb-dropping. This second scale can be moved as a whole to adjust for different types of bomb. The backsight 6 is carried by a radial arm 10 on a ring 11 which can be rotated on a frame ring 8 to set the arm 10 parallel to the vector arm 12, and the sight is set eccentric to the ring 11 by a rotary knob 9 an amount corresponding to the wind velocity. In a modification, shown in Fig. 6, the scale on the speed-overland vector 13 is in terms of miles per hour and does not require to be changed. The bomb-dropping scale is graduated both in seconds of observation and in miles per hour, and a separate scale is necessary for each height. This is attained by making a series of scales on a band 91, Fig. 8, wound on rollers 87 and adjusted by a knob 86. In the modification shown in Figs. 10 and 11, the overland speed is measured by timing the flight over a definite distance on the ground, say one-third, of a mile, this distance corresponding to a definite angle at a known height. The sight is not directly on the vector triangle but the vector arm 13 and the whole of the rest of the sight pivot around the axis z. The backsight 6 is mounted on a ring frame 8 which has a depending arm 39 carrying at its lower end the foresight 41. The ring 8 carrying the two sights is adapted to swing in trunnions 40 about an horizontal axis perpendicular to the overland vector 13. The ring and a scale drum 53 are both geared to a crank shaft 44 in such a way that a definite angular position of the drum corresponds to a definite angular position of the sight. The overland speed is first measured either in terms of seconds of observation or, by a stop watch suitably graduated as shown in Fig. 14, directly in miles per hour; a pointer 55 is then moved along a scale 54 to the height of flight, in which position the pointer registers with the corresponding scale of speeds on the drum 53, shown developed in Fig. 13, and the drum is then rotated by means of a crank 43 to bring the observed speed opposite the pointer, the sight being turned by the same crank to the correct setting for bomb-dropping.