Patent GB-586271-A (GB)
Title: Improvements in aircraft sights for use in aiming bombs during a dive
IPC: B64D43/00
Filed: 1940-08-01
Abstract: 586,271. Bomb - dropping sights. HENDERSON, SIR J. B., THOMPSON, D. V., and HENDERSON, J. G. Aug. 1, 1940, No. 12454. [Class 92 (ii)] Sighting apparatus for use on aircraft to facilitate the aiming of bombs during a dive, comprises means for indicating on the craft during a free parabolic, dive the line of sight to the target which a bomb would strike if released, and the diving angle required to hit the target. Further, the apparatus includes means for gyroscopically stabilizing a telescopic or other line of sight in a vertical plane and orienting said plane to suit the ground track and to measure the drift and ground speed. The apparatus enables the dropping angle for horizontal flight to be continuously set up, the sight line being automatically deflected when the dive is entered, and the pilot's indicator then showing the necessary changes in the angle of dive to maintain a free parabolic trajectory for the aircraft during the dive. The -apparatus enables bombs to be released at several points throughout the dive. The apparatus shown is based on the known laws for bodies falling in a parabolic trajectory, the release angle #o for horizontal flight being given by the equation tan#o = gT/2V, where T is the time of fall corresponding to the known height and V the velocity of the aircraft. If T<1> is the time of fall to reach an average velocity V, then tan #o = T/T<1> in which the times T, T <1> correspond to the height and speed respectively. Assuming a parabolic dive, the release angle # is given by the equation tan #o = T+t/T<1> which, if T<1> is previously set up, involves a uniform increase in tan # during the time t after entering the dive. The apparatus shown comprises a telescope 10 for viewing the target through a window 11, mirror 12, objective 26, reflector 27 and graticule 28. The telescope and mirror are stabilized in the vertical plane by a gyroscope 3 driven as described in Specification 166,570, [Class 97 (iii)]; the effects of roll and pitch and changes in course and speed are thus avoided. The mirror 12 is gimbal-mounted in a frame 13 fixed to the gyro gimbal-ring 5 and having pivots 15, 16 for the inner and outer rings. The mirror is fixed to a slotted lever 17 on the pivots 15, the slot 18 engaging a pin 19 on an arm 20 fixed to the gyro gimbal-ring 4. The mirror is thus tilted through half the angle of ring movement. The telescope 10 is carried' by arms 23 on the inner ring and is connected to the gyro. ring 5 by a universal joint. The stabilized sighting system which is that described in Specification 586,273 is connected to a frame 7, Fig. 2, movable round a horizontal trunnion 8 which permits of moving the sight line in the vertical plane of sight by the setting- bar system housed in the side cover 2 of a box 1. This box carries the eyepiece 29 and is mounted on trunnions 30 on a frame 31 which can be moved by the observer about a universal joint 33, 35. The observer can thus keep the eyepiece 29 on the graticule 28 and, after releasing a detent device, move the instrument round the pivot 35 until the target is seen moving parallel to a cross-wire in the graticule. The detent is then restored and the angle of drift measured on a scale 43. The dropping angle for horizontal flight is obtained by moving two right-angle bars 45, 46, Fig. 5, in accordance with height and ground speed respectively, the combined movement of the bars being conveyed to the support 7 by a coupling of the Oldham type comprising sliding right-angle rods 57. The bars 45, 46 are moved by flexible bands wound round pulleys 47, 48 connected to drums 51, 52, Fig. 2, graduated for height and speed or for times T, T<1> respectively. The pulleys 47, 48 may be driven by operating the drums or by a constant speed spring motor 63 through a change speed disc 62 driving friction wheels 64, 65. The wheel 64 driving the pulley 48 by a gear 68 is moved radially on the disc 62 to vary the speed by a rack 75 gearing with a sector 78 driven from a knob 76 and, when the target remains fixed in the graticule, the setting of the sector 78 or the dropping angle is indicated by a pointer 80, Fig. 2. To set the sight to the dropping angle #o, after operating an arm 91 to declutch the gears 68, 69, the drum 52 is turned by hand to register with the pointer 80, a mark on a scale 81 moving' with the frame 7. The ground speed is then indicated on tlrum 52. For dive bombing, on entering the dive, the clutch arm 91 is operated to bring the gear 70 driven by the friction roller 65 into mesh with the gear driving the pulley 47 and height drum 51. The roller 65 is adjusted to a fixed radial position with respect to the disc 62 so that the drum 51 is turned at a constant speed to suit the term T+t in the formula tan #= T+t/T<1>, the drum 52 having already being adjusted for T'. A pointer connected to the sight mechanism by a suitable transmission is provided in the pilot's artificial horizon to indicate the required change in the diving angle #, the pointer being moved at the tangent rate given by the formula tan Ï = gt/V = 2t/T<1>, that is at double the tangent rate of the line of sight. The pilot is also provided with an inertia-controlled indicator formed by a weight supported by a cantilever spring which shows no deflection when the trajectory is free.