Patent GB-812038-A (GB)
Title: Improvements in and relating to the testing of anti-aircraft guns
IPC: F41G3/26
Filed: 1957-04-09
Abstract: 812,038. Checking accuracy of aiming of anti-aircraft guns. CONTRAVES A. G. April 9, 1957 [April 26, 1956], No. 11530/57. Classes 92 and 119 Relates to apparatus for checking the hitting accuracy of anti-aircraft guns firing luminous tracer ammunition and by which the target is photographed when it has arrived at the theoretical hitting point after the time of flight of the projectile has elapsed. According to the invention the apparatus comprises a gun laying device constantly aiming at the target and feeding measured co-ordinates of the latter into a computer which calculates the flight time of the projectile fired from the gun to a target point, the output of the computer controlling an impulse storage device in which impulses derived from the firing of the gun are stored for the duration of the computed flight time and are then passed by the device as shutter release impulses to a camera aimed at the target point. The gun laying device comprises a platform 02, Fig. 2, mounted rotatably about a vertical axis on a tripod base O and having supporting columns for a horizontal carrier shaft O3 which is rotatable about its own axis. On the carrier shaft 03 are mounted an azimuth laying telescope Oα, a ranger finder Or, an elevation laying telescope O# and an electrically operated camera OB. Handwheels OHα, OH# and OHr are provided for maintaining the target in the cross wires of the telescope and for operating the rangfinder Or. The co-ordinate values # and r as given by the rotational position of the corresponding control shafts are transmitted to a flight time computer FR which in computing the flight time t takes into consideration the ballistic properties of the gun and projectile. The output shaft Wt of the flight time computer adjusts itself to a rotational angle proportional to the computed flight time t and is directly coupled to a rotatably journalled threaded spindle JS of the impulse storage device J which is in mesh with the internal screw thread of a carriage JT so that this carriage is moved forward or back in accordance with the flight time t. A motor JM drives an endless sound carrier band JC at a constant linear speed over rollers JA fixedly mounted on the apparatus and rollers JB mounted on the carriage JT. Along the path of the band JC are located an effacer head JE, an impulse recording head JF and an impulse reproducing head JG. The recording head JF and the reproducing head JG are arranged at both sides of a series of three deflector rollers JA fixed on the apparatus which together with the two rollers JB mounted on the carriage JT produce an arrangement of two loops of the band, the length of which is determined by the position of the carriage JT on the spindle JS, i.e. proportional to the flight time t. On the opposite side a similar loop arrangement is provided. The length of the band between the recording head JF and reproducing head JG varies in proportion to the flight time t and thus a storage time results for each impulse recorded and reproduced which is proportional to the flight time t. A microphone J4 converts each firing bang of the gun into a current impulse which is fed to the recording head JF and recorded on the band JC. After the lapse of the computed flight time this impulse is reproduced by the reproducing head JG and is supplied as a release impulse for operating the camera OB. The image of the aircraft appears in the centre of the photographs taken, e.g. k1-k4, Fig. 1, and from there the errors of aiming can be directly read off as shown by the position of the projectiles g1-g3, Fig. 1. In a modification, Figs. 3-5 (not shown), the apparatus is arranged for shooting at the mirror image of the target, the gun layer aiming by means of a sight GV at the image in a mirror GS suspended on an articulated rod structure. The arrangement provides a radar gun laying device O for ascertaining the values α, # and r and the value α is transformed into a mirror image value -α by a computer S, this being fed together with the value # as central values into the photo gun laying device O having a camera OB, while the values r and # are fed as control values into a flight time computer FR. While the radar gun laying device O follows the target, the camera OB of the photo gun laying device follow the minror image of the target.