Hi
The Gyro Gunsight Mk I - Pt I
The gyro gunsight at last solved the most difficult problem faced by pilots and air gunners, that of finding the correct angle of deflection or 'lead' needed to hit the target when it was moving across the line of fire. Even experienced fighter pilots had great difficulty in overcoming the problem. Indeed, the world's top-scoring fighter ace, Eric Hartmann, revealed that his secret was 'Get in close - down to 25 m - then you don't need to worry about deflection shooting!'
When the gyro sight was perfected, no quesswork was needed. The sight presented an aiming mark which automatically allowed for range, deflection and gravity drop of the projectiles. As early as 1917 the basic theory of using a gyroscope as an aid to deflection shooting was propounded by W/Cdr L.J. Wackett, RFC. With him on the same station was Capt. (later Prof. Sir) Melville Jones, who was to be a leading member of the Farnborough gyro team 25 years later. The idea was later suggested by Dr L.B.C Cunningham of the RAF Education Branch. In 1936 he pointed out that mathematics could be used to solve any problem of dynamics; as an example he put forward the theory that even the complicated problem of air-to-air deflection shooting could be solved mathematically 'by using a gyroscope to offset the sight line from the gun line through an angle determined by the rate of turn of the sight line'. Although his pupils could not understand the implications of his theory (most of them had no idea what the angle of deflection was anyway), his observations did not go unnoticed.
In 1938, with the international situation worsening, the Air Staff arranged an exercise at Northolt in which all aspects of fighter combat were to be assessed. The Committee for the Scientific Survey of Air Defence, headed by Henry Tizard, appointed observers from Farnborough to advise on points of scientific importance which might be otherwise be overlooked.
Camera guns were fitted to many of the aircraft, and a squadron of Gladiators had just been fitted with some of the first batch of Mk II reflector sights. When exposed films from the camera guns were examined, it was found that although the pilots often got into positions to despatch their victims, very few had any idea of the amount of deflection needed.
A report on the findings was duly presented to Tizard, stating:
Although the new Spitfire and Hurricane fighters performed well, their effectiveness would be vastly improved if some means could be found to predict the amount of lead required to hit the target accurately. Many of the gun camera films proved that if the combats had been in earnest the enemy would have escaped unscathed.
The Air Staff were deeply concerned, and the Director of Farnborough was instructed to investigate the possibility of a predictor gunsight suitable for use in fighters and the gun turrets of bombers. The problem was to be given priority over all other work, no expense was to be spared and the utmost secrecy was to observed.
Dr Cunningham's theory depended on the fact that a gyroscope will resist any rotation of its axis. If a gyro is clamped onto a rod on which is fixed a ring and bead sight, any attempt to follow a crossing target will depend on the target's crossing speed. A gyro sight would have to present the marksman with a sight line held back by the gyro, whilst the line of flight and guns would be in front of this sight line. In other words, if the pilot kept to the sight line indicated by the gyro, his guns would automatically point correctly, in direct relation to the rate of turn.
By October 1939 two experimental sights of slightly different design had been fitted to a Hurricane and in the Frazer-Nash FN 25 under turret of the Wellington. The results of the trials were promising, although the sights were rather primitive. By the summer of 1940 the RAE Dircetor was able to report to the Air Staff that a potentially operational sight, the Mk I GGS (gyro gunsight) was ready for testing. It was given the code name Type 6 mechanism.
The Type 6 contained an electric motor driving a rotor mounted on a stem, the end of which actuated a linkage. Also fitted to the stem was a saucer-shaped aluminium dome surrounded by four electro magnets. The motor ran at a speed of 4,000 rpm, so the gyro resisted any angular movement of the housing. Such a movement tilted the axis of the stem and the linkage moved a celluloid strip in the optics of a GI primatic sight. A black ring was engraved on the end of the strip, so that the gunner saw two graticule rings, one fixed, the other on the celluloid.
In principle, the Mk I GGS was very similar to a rate-of-turn indicator which also used a gyro. In this, as the aircraft turned, the gyro held back the needle of the instrument, this deflection indicating, the force of the turn with a needle on a dial. In the GGS the gyro resistance was used to deflect the ring on the celluloid. The electro magnets allowed for host aircraft speed and height: the thinner the atmosphere, the less the bullets drop.
The above text and photos were taken from "British Aiorcraft Armament Vol.2: Guns and Gunsights", by R Wallace Clarke.
Regards
Bob
