Patent GB-1072926-A (GB)
Title: Improvements in or relating to aircraft bombsights
Inventor: SMERDON WILLIAM STUART
IPC: G02B27/64
Filed: 1963-11-09
Abstract: 1,072,926. Bomb sights. FERRANTI Ltd. Nov. 4, 1964 [Nov. 9, 1963], No. 44322/63. Heading F3C. [Also in Division G1] In an aircraft bomb sight for facilitating low level attack at high speed an aiming mark defining a sight line is automatically and continuously precessed as the craft approaches the target to rotate the sight line with respect to the flight line of the craft so as to stabilize the mark on the target. The sighting head, Fig. 3, includes a gyro wheel 11 and a spherical aluminium dome 12 secured to a spindle 13 carried by a Hookes joint 14. The dome passes through magnetic air gaps defining elevation and azimuth planes associated, respectively, with coils 17, 18. Thus by differentially energizing coils 17 an eddy current drag is applied to cause the spin axis 16 to rotate in the plane of elevation. Similarly, differential energization of coils 18 causes rotation of the axis 16 in the azimuth plane. To derive elevation and azimuth signals proportional to the angles between datum line 15 and the components of axis 16 in the elevation and azimuth planes, elevation and azimuth pick-offs 21, 22 are provided. The face of gyro wheel 11 has a mirror 23 forming part of an optical display system including a fixed mirror 24, lens 25, and a transmitting reflector 26 whereby the pilot is provided with a head-up display at infinity of an image of a graticule 27 illuminated by a lamp 31. This image 27<SP>1</SP> constitutes the aiming mark and defines the line of sight 32 from the pilot to the ground ahead at an angle of depression from the flight line 33. In order to stabilize the mark 27<SP>1</SP> at a position on the ground ahead, the coils 17, 18 are fed with appropriate signals derived from the pick-offs 21, 22, these signals including a rate-control term K which is constant for a given speed and height of the aircraft and is manually adjustable by the pilot at a stage 41. Resolver 35 corrects the signals # a , # e  from the pick-offs to take account of the aircraft roll. The signal # v  from the resolver 35 is fed to a vertical plane computer 34 together with the rate term K and a term T representative of the gyro time constant, the signal # v  from the computer passing to the elevation coils 17 through a roll resolution stage 46. The signal applied to the azimuth coils 18 is composed of a signal # h  derived from a horizontal plane Sc computer 42 together with a signal - allowing S for wind drift. In operation, the pilot stabilizes the aiming mark 27<SP>1</SP> on any conveniently identifiable object on the ground ahead by adjustment of the rate control stage 41 and then continues to fly towards the target whilst maintaining his height and speed constant. When the target comes into view the pilot raises the mark 27<SP>1</SP> to coincide with the target by a manually operable stage 45 supplying a signal #<SP>1</SP> v , the mark then remaining stabilized in the target. A ballistic computer 44 supplies a signal to an equipment 49 so that the bomb is released to hit the target. The Specification explains the mathematical propositions underlying the stabilization of the mark 27<SP>1</SP> but briefly the gyro processes the mark to rotate the sight line 32 with respect to the flight line 33 so that in each of the horizontal and vertical planes which contain the flight line the ratio of the angular velocity of the component of the sight line resolved in that plane to the square of the sine of the angle between that component and the flight line is controlled, viz. by the stage 41.