USA(A)F GUNSIGHTS – THE K- SERIES OF GUNSIGHTS
Most of the K- series of gunsights were designed for flexible gunnery and were of two types : compensating sights or computing sights.
A compensating sight offsets the line of sight only to compensate for the speed of the firing aircraft. The earliest ones were the so-called wind-vane sights of World War I. The most popular AAF compensating sights were the K-10, K-11 and K-13. These sights do not take into account target range, but base their calculation on the angle between the gun line and the aircraft axis, using either two dimensional cams (K-10, K-11) or a mechanical analog (K-13). In these sights the full compensation for own speed is only applied when set to the STRAFE position. In all other situations only a fraction (about 65%) of the full compensation is applied, because in a pursuit curve the attacking aircraft’s speed has a component in the direction of the target’s flight.
Computing sights, on the other hand, calculate the lead angle based on the angular velocity of the target multiplied by the time of flight. The angular velocity of the target is assumed to match the angular velocity of the sight when tracking smoothly. The angular velocity of the sight is measured either by feeding the turret azimuth and elevation drives into integrators in the sight (as in the K-3, K-4 et al. series) or by a two-degree-of-freedom gyro restrained by an electromagnetic force inversely proportional to the range (in the K-14 series). In the flexible gunnery computing sights (K-15, K-17, Mk-18) additional computing circuitry also compensates for one’s own airspeed, gravity drop and the bullet’s time of flight, based on range and air density (altitude).
K-1 Gunsight (experimental only)
Expenditure Order created in June 1929 for intended use in flexible gunnery. It was service tested in March 1932. Nothing further known at present.
K-2 Gunsight (experimental only)
Developed by Sperry who started to work on computing sights for aircrafts as early as 1938. To be mounted directly on top of gun in a flexible gunnery position (waist and tail positions only). Tested on the waist position of a B-17C in July 1940 . Classified as obsolete in November 1941. Nothing further known at present.
K-3, K-4, K-5 and K-9 Computing Gunsights
K-6 Gunsight (experimental only)
Expenditure Order created in October 1941. Developed by Pioneer (???) for use in flexible mounted machine gun positions only. Classified as obsolete in October 1945. Nothing further known at present.
K-7 Gunsight (experimental only)
Expenditure Order created in October 1941. Developed by General electric for use in upper turrets. Classified as obsolete in October 1942. Nothing further known at present.
K-10 & K-11 Compensating Gunsights
K-13 Compensating Gunsight
K-14 Computing Gunsight
K-15 Computing Gunsight
K-18 Computing Gunsight