Patent GB-1277251-A (GB)
Title: Ballistic computer
Inventor: MCADAM WILLIAM ERNEST JR
IPC: F41G3/08
Filed: 1969-07-24
Abstract: 1277251 Gun fire control HUGHES AIRCRAFT CO 24 July 1969 [21 Aug 1968] 37302/69 Heading G4G A ballistic computer comprises a first multiplier to multiply the range signal by a term relating to a particular projectile and particular conditions to produce a normalized range signal, second multipliers to apply non-linear functions related to time-of-flight and elevation, further means to produce time-of-flight and superelevation signals related to selected projectiles and specific conditions and additional multipliers to multiply the time-of-flight and superelevation signals by respective constants to correct for ballistic deviations related to different ballistic and environmental conditions. The range signal R is just normalized by applying a standard condition term 1/R no  in multiplier 954 (ballistic term multiplier) which is adjustable for each ammunition. A non-standard temperature-pressure coefficient signal B is produced by master multiplier 964 in response to air temperature and pressure sensor inputs #T/T 0  and #P/P 0 . The signal BR/R n0  is produced in multiplier 966 and fed together with signal R/R n0  to the amplifier 968 which produces the signal R/R n =R/R n0 (1-B) where R/R n  is a normalized range signal for non- standard T, P conditions and K being a temperature coefficient. The signal R/R n  is then fed to function generators 956, 958 which produce non-linear ballistic function signals f # (R/R n ) and f t (R/R n ) and these are further multiplied in multipliers 960, 962 by standard condition ballistic terms # n0  and t n0  Consequently, the output signal # 1  = # n0 f # (R/R n ) constitutes a superelevation signal for the particular projectile at the particular range R in accordance with ballistic laws (given in the Specification) partially corrected for non- standard T, P conditions. The signal is the corresponding time-of-flight signal (ballistic law also given in the Specification). A master multiplier 970 receives grain temperature and effective full-charge sensor input signals K g #T g /T g  and f(EFC). K e  for producing a muzzle velocity coefficient H, which together with the T, P coefficient B is applied to correct the signals # 1  and t f1 . In detail (Fig. 1B), signals B and H are respectively fed to slave multipliers 972, 980 and 976, 984, these being associated respectively with amplifiers 974, 982 and 978, 986. These circuits operate upon inputs # 1  and t f1  to produce a superelevation signal and a time-of-flight signal which are corrected for non-standard conditions. The signal H is generated by circuitry 942, 944, 946, 948 (Fig. 1A) and is given by where f(EFC) A  is a function of effective fullcharge for a selected ammunition, Tg is standard condition propellant grain temperature and K gA  is an ammunition temperature coefficient. A parallax correction signal p is generated -in the break-point function generator 990, 992, 994. It is obtained as p=D p (1/R-1/R c ) where D p  is the offset between line of sight and gun line, and R c  is a cross-over range where the l.o.s. crosses the gun line.  Details.-The ballistic term multiplier 954 consists of n series combinations of a FET and a resistor arranged in parallel between input and output, each resistor having a value corresponding to one of n projectile types. One of the series circuits is selected by applying a +ve gating voltage to the respective FET and a -ve gating voltage is applied to the rest (Fig. 2, not shown). The output circuit comprises an operational amplifier of unit gain. The master and slave multipliers 964, 966 are of the time-division type in which the output is a train of pulses of which the duty cycle is the ratio of two variables and the amplitude is controlled by another variable (Fig. 3, not shown). In such multipliers, one variable is fed to an integrator the input of which is switched between positive and negative values of the other variable, the integrator being arranged to trigger the switches. The switch driver of the master multiplier 964 is arranged to drive the switches of the slave multiplier 966. The function generators 956, 958 are of the type in which a non-linear characteristic is synthesized as a series of linear segments, each linear segment being realized by the gain of an operational amplifier controlled by a selected input resistance. The input resistance is selected according to the magnitude of the input variable by means of a parallel array of amplitude-sensitive selector circuits each controlling a FET connected in series between the input of the generator and one of the input resistances of the amplifier. The elevation control signal E and deflection control signal D are generated from the signals # and t f  which are corrected for ballistic drift angle # d , wind deflection angle # w , angular turret rate # k , parallax p, jump D j , E j  and droop E d , D d . The drift angle # d  is developed in multiplier 1160 which applies a multiplier K d  for each selected ammunition to the signal #. A cross-wind signal V w  is modified in multipliers 1164 and 1166 for ammunition type and temperature-pressure and a signal V w K w (1-B) developed in amplifier 1168. Thereafter it is multiplied in circuit 1170 by a time-of-flight signal T to produce winddeflection signal # w . Angular rate signals in azimuth and elevation, # 1  and # e  respectively, are fed to follow-and-clamp circuits 1172, 1262 and stored as D.C. signals when the right-leadlock signal RtLL is received. Thereafter, they are fed through multipliers 1174, 1264 which develop the kinematic lead angle signals # 1 T and # e T. In a one-gyro system the lead-angle signal # 1 T is fed as a single-gyro lead angle signal # k  to amplifier 1162. The output signal # of amplifier 1162 in a one-gyro system is #=# d +# w +# k . In a two-gyro system switch 1178 is operated to feed lead-angle signal # 1 T to amplifier 1180 and the signal # becomes # d +# w . The signal # is also fed to amplifier 1252 which produces an output α=# 1 . The signals α, # are fed either directly, or through cant-resolver 1256 to analogue switches 1254a, 1254b depending upon whether the cant-resolver is switched on or off. The resolver comprises a pendulum-actuated transformer and produces signals where C is a signal representing the angle of the turret to the horizontal. The signal C activates the analogue switches 1254a, 1254b. The signals D<SP>1</SP> and E<SP>1</SP> are corrected for jump, droop and parallax in amplifiers 1180, 1257. In a two-gyro system the kinematic lead-angle signal # e T is also fed to the amplifier 1257. Finally the corrected signals E<SP>1</SP> and D<SP>1</SP> are fed through analogue switches 1278a, 1278b, which respond to the command COMPUTE, to amplifiers 1280, 1282 which apply boresight correction signals D f , E f . The follow-and-clamp circuits 1172, 1262 are of conventional design and a typical circuit is shown in Fig. 8.