Fireflash -Britains first air-to-air missile.
Another early British guided missile project was Fireflash (Rainbow code Blue Sky). This was an air-to-air beam rider of unusual configuration; because of the British obsession over the blocking effects of the rocket motor’s exhaust it had a pair of boost motors attached either side of the front of the missile. These burnt for 1·5 seconds and accelerated the missile up to Mach 2. The nozzles were canted to make the missile roll about its axis in order to even out any asymmetric thrust. When the motors had burnt out an explosive release unit fired causing them to separate, and the missile’s control surfaces were unlocked. The free coasting missile then cancelled its stabilisation roll and gathered itself into the guiding beam which it followed to the target; it had an effective range of 3,500 yards.
The guidance radar was based on the existing Ekco Radio Ranging Unit; this was already fitted to the Hunters and Swifts and it simply provided range data to the fighter’s gyro gunsight. The Mk2 version which was used for Fireflash was modified to perform conical scanning to generate the control beam, and also provided target velocity data for the firing aircraft's computer to select either a 65ms or 80ms delay for the missile’s fuze. It did not, however, track the target but relied on the pilot keeping his gunsight on the target; in ‘missile mode’ the sight did not lead the target but stayed locked to the axis of the beam. One curious aspect of this radar was the way in which it accommodated multiple aircraft working together. Rather than having a separate frequency for each aircraft they all used the same frequency (9375MHz); discrimination was done by selecting one of 12 different Pulse Repetition Frequencies.
Fireflash was intended to be used to attack heavy bombers from behind, outside the range of their defensive armament. It would have struggled to engage supersonic targets and although 300 were made, they were only used by the RAF for trials purposes until the introduction three years later of a longer ranged Infra Red homing missile from DH Propellers –Firestreak.
The fuze was a metal detector and consisted of an oscillator driving a tank circuit aerial constructed of a metal loop divided into two halves by a polythene sheet which provided the necessary capacitance. The fuze was designed to detect a bomber's tail from a distance of up to 50 feet; the delay (referred to above) gave time for the missile to coast forward 'to the more vulnerable area near the cockpit'.
The missile could be used between 15,000 feet and 35,000 feet although it was expected to be capable of use at higher altitudes, and needed to be launched within a 15° cone of the target's rear. The pilot had to keep his gunsight on the target for the missile's 6‐8 seconds of flight.
Unlike every other beam riding air-to-air missile system the Ekco radar was gyro stabilised, enabling the firing aircraft to follow its target's manoeuvres without any risk of the missile dropping out of the beam.
There is a very intriguing paragraph in a letter in one of the files in the National Archives:
"Although we do not regard Blue Sky seriously as an operational weapon because of its limitations on altitude and visual observation of the target, it would have a considerable deterrent value because our enemies would not know what stocks we held and would probably be inclined to believe it to be a better weapon than it actually is."
The missile cost £4,800 for an operational round, and £900 for a training round.
Sources: TNA AIR8/2036 & 10/7376, AVIA10/7382.
This page copyright SR Jenkins February 2015; reproduction without prior approval is prohibited.
Page last updated: 10th January 2021.
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