The Gyron Junior was a two-fifths flow scale version of the existing Gyron engine. It started as Project Study number 43 in 1954 and the first prototype ran in August 1955. It powered the Blackburn Buccaneer S.1 twin-engined Naval strike aircraft. The engine was rather unreliable and considered short of thrust. The later Buccaneer S.2 used the more powerful Rolls-Royce Spey engine. The engine had variable inlet guide vanes, as used on many other engines, necessary for accelerating from idle to high thrust. However, on the Gyron Junior, positioning of the vanes was not reliable and could cause surging which, in turn, could prevent accelerating to higher thrust levels. A possibly unique feature on this engine was valve-controlled cooling air to the turbine blades. The engine had to supply air for the aircraft's boundary layer control system and the resulting thrust loss was unacceptable. To regain the thrust the turbine temperature limit was raised by using turbine blade cooling, selected only with blowing on. In December 1970 a Buccaneer was lost after one engine surged and failed to accelerate on an overshoot and a week later another aircraft was lost after an uncontained engine failure. This last accident brought Gyron Junior flying to a halt forever. Two Gyron Juniors, with afterburners, were also used on the Bristol 188 Mach 2 supersonic research aircraft. The 188 was originally intended to have the Rolls-Royce Avon but the half ton lighter Gyron Junior was substituted in June 1957.This engine was one of the first in the world to have infinite variation of thrust right up to full reheat. Other manufacturers using thrust increase in discrete steps. The program was terminated early without achieving the high-speed high-temperature trials that had been intended. Limitations included poor fuel consumption of the Gyron Junior and engine surging. Fuel limitations restricted the time spent at its maximum speed, Mach 1.95, to a few minutes. This was not long enough to achieve the required stabilized temperatures in "thermal soaking" tests.
Variants
Ref: ;Gyron Junior DGJ.1: ;Gyron Junior DGJ.2: Interim production stage, used on Buccaneer S. Mk.1. Variable inlet and guide vane, annular manifold for flap blowing, long overall ;Gyron Junior DGJ.10:Exhibited in 1958 at Farnborough, longer than the DJG.1 ;Gyron Junior DGJ.10R: highly augmented afterburning version for the Bristol 188, dry thrust 10,000 lb, wet thrust 14,000 lb. Added zero stage and two rows of variable stators. Variable nozzle with convergent, convergent/parallel or convergent/divergent configuration depending on reheat selection and aircraft speed. Overall length ;Gyron Junior DGJ.20:
