Fighter Combat

12 HGHTER WEAPONSoften bars of light on each side of the sight image, which could be movedtoward or away from the center of the sight to represent the wingspan ofvarious targets at maximum or optimum ranges. The center of these sightswas usually shown as a spot or a cross of light called the "pipper."Optical sights of this type represented only a very small advance overthe original ring-and-bead variety. The fighter pilot needed more help,particularly with lead estimation for high-deflection shots. For some,this help arrived during World War II in the form of the gyroscopic leadcomputingoptical sight (LCOS). There are many variations of the LCOS,both in sight picture and sophistication, so a general discussion iscalled for.The three basic components of the LCOS are a sight display unit, agyroscopic sensing unit, and a computer. The attacking pilot tracks thetarget by attempting to hold the pipper steady on the center or somevulnerable portion of the target. Simultaneously, he constantly adjusts thesight picture to the wingspan of the target, often by turning an adjustablethrottle grip, which, when the type of target or its wingspan has beenselected prior to the attack, allows the computer to calculate target range.Any turning required by the attacking aircraft in order to track the target issensed by the gyroscopes and is also sent to the computer. Once theangular rate of the target LOS and target range are known, the computercan calculate the required lead angle. The gyros can also sense the shooter'sattitude and enable the computer to calculate the direction and magnitudeof the gravity drop for the target's range.All these corrections are displayed to the pilot by the sight unit, whichcauses the sight picture to move opposite to the direction of the LOSmovement. In order to continue tracking the target, the pilot must adjusthis aim in the proper direction for the lead correction. For example, if thecomputer determines that more lead is required, the pipper slides towardthe target's tail, requiring the pilot to adjust his aim farther forward,thereby providing the necessary lead correction.Such a sight system attempts to predict the future LOS to the targetbased on the present LOS and its angular rate of change. The time forwhich this future LOS position is predicted is the TOF of a bullet fired atthe present time. The TOF, in turn, is dependent on the firing conditions(essentially shooter speed and altitude) and the distance the bullet musttravel to reach the target. This distance must also be predicted, based onrange at firing and the range rate of change (closure).Obviously, there is a lot of predicting going on here. The fire-controlcomputer must make these calculations based only on the quality of theinformation available to it. Since not only current values of various parameters(LOS, range, etc.), but also the rates of change in these parameters,may be used in the calculations, smoothness of the input information (i.e.,smooth, steady tracking and smoothly changing range input) is essential toavoid large errors caused by false rate information. Each computer alsorequires a finite amount of time, known as "settling time," to makecalculations based on new data inputs. Rapid changes in these inputs can