THE FIRE CONTROL TECHNICIAN – THE GUN FIRE CONTROL PROBLEM

[Music] a shipboard weapon system comprises four major subsystems or components first the units that detect locate and identify targets second the controlled units that solve the fire control problem that is they compute the data needed to accurately position the third component of the weapons system the delivery devices that launch or propel the system's fourth component the projectile designed to destroy or severely damage the target because the target gun and projectile factors of the fire control problem vary with each situation the solution will be different in each case [Music] however each fire control problem involves three basic functions first positioning the radar director to the designated targets present position point for acquisition second tracking the target so that its rate of movement with respect to own ship can be determined and third computing the proper gun positioning orders for the projectile to be used in this film we shall see how these functions are provided and how the fire control problem is solved let's begin with the basic fire control concept of points and lines planes and coordinate systems point O is the origin that point on the centerline of the ship from which the problem starts the line that connects point O two point one the present position of the target is known as the line of sight point two defines the future target position point three defines the advance position and allowance for interior ballistics and for such exterior ballistics as air resistance and wind the line that connects point O two point four the point at which the gun is aimed so that the projectile will intercept the target is the line of fire this aiming position compensates for projectile drift caused by spin and also for gravity the north-south and east-west lines are Compass Point references for the fire control problem now let's look at the basic reference planes that are used in solving the problem the horizontal plane H passes through the point of origin and is perpendicular to the radius of the earth it is the reference for the fire control problem any plane that is perpendicular to the horizontal plane such as this one through the line of sight is a vertical plane e the Dec plane D passes through the point of origin and is parallel to the ship's deck the deck plane changes with the role and pitch of the ship any plane that is perpendicular to the deck plane such as this one through the line of sight is a normal plane eeep rhyme any plane that is neither perpendicular nor parallel to the horizontal or deck planes such as this one through the line of sight is a slant plane g coordinate systems are used to identify the present position of the target with respect to own ship in the polar coordinate system this is done by means of the bearing angle the elevation angle and the range to the target the system is also known as the spherical coordinate system the Cartesian system is also known as the true coordinate system it is based on true bearings and uses the horizontal range component in the north-south axis the horizontal range component in the east-west axis and the vertical range component this system and the polar system are used by the fire control computer for determination of target position a third system the cylindrical coordinate system employs the bearing angle the horizontal range components and the vertical range component this system is used within the computer for predicting the future target position fire control symbols for angles and liens may appear confusing but there is order the same basic symbols are used for quantities of given types such as bearings ranges and elevations the modifiers are also easy to understand and remember bearings have the basic symbol B alone it represents the relative bearing of the target for true bearing the modifier y is added the relative bearing of the future target position point two is B 2 however we are more interested in the horizontal angular movement between the line of sight and point 2 and this is designated SH similarly the relative gun bearing is BG again we are more interested in the horizontal deflection which is between the line of sight and point for this is L H elevations are represented by E e alone being target elevation e 2 is future target elevation eg is gun elevation range is designated by r r alone being the present range along the line of sight the horizontal range is RH the vertical range or target height is RV the range 2.2 or the future range are two future horizontal range are h2 and future target height are v2 r4 is the aiming range and Rh for its horizontal component linear movements of the target and the projectile are symbolized by M m rh is the linear movement in horizontal range m b is the linear movement in bearing and M V is vertical linear movement upward in this case with the target climbing now let's see how the gunfire control problem is solved through development of the present position of the target with respect to own ship the relative motion of the target and own ship the prediction process and the gun and fuse orders the solution of any fire control problem requires that a reference be established in most systems the horizontal plane is the reference the director is mounted on the deck plane which tilts as the ship rolls and pitches since the director measures the line of sights bearing and elevation with respect to the deck plane this data must be converted to the horizontal reference the corrections are computed by the fire control systems computer and applied to the deck data to determine the horizontal values with the target located with respect to the horizontal plane the next step is to compute the horizontal range RH and the target height RV for use in later calculations RV is found by multiplying are by the sine function of the elevation angle and Rh by multiplying our by the cosine function of e the first step in establishing point to the future target position is to compute the relative motion rates DM RH DMV and DMV which are coordinated to the line of sight we relate ship speed and target speed to the horizontal component of the line of sight by means of vector analysis the speeds are resolved into their components along the line of sight and across it those along the line of sight are algebraically added to produce DM RH the horizontal range rate the components perpendicular to the line of sight are similarly added to produce DMV the rate of linear movement in bearing to determine target motion in the vertical plane we use the targets linear movement in the horizontal range DM RH and it's vertical rate of climb DMV these are resolved into components along the line of sight and across it components along the line of sight are added algebraically to produce DM are the present range rate components perpendicular to the line of sight are added to determine DM e the rate of linear movement in elevation the systems computer also resolves true wind wh into components along the horizontal component of the line of sight w RHS and across it WV s now let's see how the system computes a line of fire that is oriented to the line of sight and the horizontal plane the future target position is determined by first multiplying the relative motion rates DM rh d mb and DMV by an assumed value 42 time-of-flight the resulting values are the linear quantities mr h mb and MV these are then combined with RH and RV the present target position values to determine future target position the line of fire which is directed to the aiming point is found by means of its vertical component its horizontal component its deflection angle and its elevation angle to see how these elements are determined let's begin with the horizontal aspects of the line of fire the value of LH the horizontal deflection is obtained by combining the horizontal angular motion SH with WB qlh the total deflection angle due to wind drift and corrective input or spot now let's look at the vertical elements relating to the line of fire the gun elevation angle eg is the sum of the elevation aiming position angle E 4 and the super elevation angle V 4 V 4 is determined by solving the triangle whose vertical side is H 4 which is the sum of RV the target height and M V the target's vertical linear movement rh 4 the horizontal range to the aiming point is the adjacent side the solution yields the value efore the value of v4 is computed from the values of R for the adjacent side of the triangle and the height of the vertical forming the opposite side this is the sum of the various superelevations used to overcome the effects of gravity initial velocity air density and apparent wind the sum of V 4 & E 4 then gives the value of eg the gun elevation the values of R 4 and E 4 are now used to compute the time of flight T 2 if it does not agree with a value assumed for a trial solution a new assumed value of T 2 is selected and the problem resolved a closed loop is used and the computation process is repeated again and again until the correct value of T 2 is found two computations remain gun orders and fuse orders because the guns are mounted on trunnion axes that tilt when the guns are trained or elevated while the deck plane is not horizontal eg & LH values must be modified when they are converted to gun trained and elevation orders fuse orders are designated as T 5 a time value it is equal to the sum of T G the time needed to set the fuse mechanism just prior to firing + T 2 the time of flight one additional factor must be taken into account parallax error parallax is the distance between the origin the director that is and the gun which is lower than the director and either forward or aft of it parallax is treated as vertical and horizontal displacements let's first consider the effect of the horizontal displacement if the gun elevation order EDG prime which is computed from point O data were applied to the gun without incorporating parallax correction the line of fire would not be elevated to the aiming point a correction must therefore be computed and applied to EDG Prime it is designated P EDG prime H the P and H signifying parallax horizontal and the parentheses indicating a correction to EDG Prime the correction varies with the elevation if EDG prime is zero the correction angle is zero as elevation increases the correction increases becoming maximum at 90 degrees the correction varies as the sine function of the elevation angle EDG Prime the correction is also affected by the bearing of the aiming point if the aiming point bears either 180 or zero degrees the correction is maximum as the bearing angle changes the correction value decreases becoming zero when the aiming point is a beam here the guns elevation angle equals the computed EDG Prime the correction to EDG prime then also varies as the cosine function of B D G Prime the gun train order bearing also modifies the effect of horizontal parallax on gun train if B D G Prime were applied to the gun without parallax correction the line of fire would not be trained to the aiming point the correction is P B D G Prime H if the aiming point bears either 100 or zero degrees the correction is zero as the bearing changes the correction value increases becoming maximum when the aiming point is a beam the correction to B D G prime varies as the sine function of B D G Prime gun elevation also modifies the effect of horizontal parallax on B D G Prime at a given bearing and increase in the height of the aiming point which calls for increased gun elevation results in an increase in P E D G prime H in this type of angular increase the correction varies as the secant function of e D G prime range also modifies the effect of parallax as range increases the parallax errors and thus their necessary Corrections become proportionately smaller the reciprocal of R for the aiming range is used to compensate for this factor now let's look at the vertical displacement the difference in the height of the director and that of the gun it is considered as a portion of H for the advance position height as such it affects the computations of efore and of EDG Prime the gun elevation order a fixed value of 10 yards is used by the computer for all guns in the system in this film we have seen the gunfire control problem defined the gunfire control concepts of points and lines claims coordinate systems the various symbols and how the problem is solved including the handling of gun and fuse orders and parallax [Music]