Lead computing optical sight system (LCOSS)
The lead computing optical sight system or short LCOSS, is used to establish a visual sight reference to either air-to-air or air-to-ground weapons delivery. A red reticle is projected on a combining glass. The LCOSS features seven different modes that can be selected via the Sight Mode Knob.
LCOSS Controls
Sight mode knob
The sight mode knob selects the mode of operations which are the following:
| Sight mode knob | Function |
|---|---|
| OFF | De-energizes the sight system. |
| STBY | Energizes the sight system for warmup but does not display any reticle. |
| CAGE | Reticle is displayed and caged at the radar boresight line (RBL). |
| A/G | Selects the air-to-ground mode. The reticle can be depressed from 0 mils to 245 mils below the fuselage reference line (FRL). |
| A/A | Selects the air-to-air lead compute mode. The reticle position is governed by the sight gyro, radar range, the CADC Sensor and the cage button on the throttle. |
| BIT 1 and BIT 2 | Energizes the lead computing amplifier relays so that fixed voltages are applied to the sight system for a self test. Displays self test pictures. |
Reticle depression control
The reticle can be depressed by rotating the reticle depression knob until the readout (in one-mil increments) shows the desired sight setting. The Reticle cannot be positioned manually in azimuth.
Reticle intensity control
Rotating the reticle intensity control knob changes the brightness of the reticle.
Shutter lever control
The shutter control lever is a two position lever with positions of CL (closed) and OPEN. In the CL position a shutter is placed between the optical light source and the combining glass thus preventing damage to the optics from bright sunlight. In the OPEN position the shutter is removed and the reticle will be displayed.
Reticle Image
The reticle image that is projected onto the combining glass is composed of a fixed reticle, roll reference tabs, and a range bar. The fixed reticle consists of 2-mil diameter pipper located in the center of a 25-mil diameter segmented circle, and a 50-mil diameter completed circle.
The roll reference tabs rotate about the 50-mil circle. The roll reference tabs have two separate functions. During the offset bombing mode and the target finding mode the roll tabs provide steering information from the WRCS. The position of the roll tabs, with respect to the fixed index tabs, indicates the angle between the ground track and course to the target. In every other mode of operation the roll tabs indicate the aircraft roll attitude, supplied by the INS.
| Roll tab left roll | Roll tab right roll |
|---|---|
 |  |
| 1 left roll tab, 2 center roll tab, 3 right roll tab | 1 left roll tab, 2 center roll tab, 3 right roll tab |
The range bar is semicircular and appears on the inside of the 50-mil circle only when a target has been acquired by radar lock-on. The instantaneous length of the range bar, and the rate at which the length is changing indicates the actual radar slant range and the range between the aircraft and the target. The minimum length of the range bar (and minimum range indication) exists at the 6 o'clock position. With gun selected the inside tab of the range bar at 6 o'clock, the actual radar range is 1000 ft. At the 5 o'clock position the range bar is 2000ft continuing with 1000ft increments per tab. The maximum range that can be shown is 6667ft with guns selected. When any other mode than GUN is selected the range bar is 3000ft at the 6 o'clock position and 6000ft at the 5 o'clock position, with increments of 3000ft per tab. The maximum displayable range is then 20000ft.
| Range bar with guns | Range bar in any other mode |
|---|---|
 |  |
Reticle Cage Function
The reticle cage function is applied through the CAGE button on the throttle. With the sight operating in the (GUNS) A/A mode and with CAGE pressed (no radar lock-on) the reticle is caged at radar boresight line (RBL). When CAGE is released, a pseudo range of 1000ft is supplied to the computer but the range bar is not displayed. With radar lock-on the stiffening function is applied as long as CAGE is pressed. The range bar continues to indicate the actual radar range or the maximum displayable range. When CAGE is released the reticle moves in azimuth elevation to display the lead required to a maximum of 4000ft. This will only happen with GUNS selected.
Principle
At 0 mils the reticle lines up with the Fuselage Reference Line (FRL) of the aircraft. 35 mils, as for example also used by the CAGE setting, lines the sight up with the Radar Boresight Line (RBL).
The 35 mils depressed reticle, also called the Gun Cross, is the reference point for using the gun, as it represents the point in space where the bullet stream impacts at a distance of 2250ft. This is generally the aiming reference used for Air To Ground Gunnery, as well as Air To Air Gunnery against a stable non-maneuvering target. Targets closer than that will be hit as well, but beyond the harmonization range bullets will generally fall below the target and proper lead has to be given.
In A/A mode with guns selected the sight will provide an automatic lead computation to correct for the targets movements. Without a target lock the system assumes a target distance of 1000ft. With radar lock the actual target distance will be obtained. The lead computer has no knowledge of the targets actual movement vector or its speed, it assumes the own aircraft's parameters instead. Therefore, it is paramount that the pipper is stabilized on the target for at least a full second before shooting. Should the targets speed differ from the own speed or the target initiates a maneuver, the pilot has to account for that and lead the sight accordingly.