Cyril was born in Esher, Surrey, on 15 January 1895. He competed obsessively against his classmate Reginald Mann and his Aero Club teacher Robert Grimmer, both of whom would later form their own aircraft company. In June 1910 on Wimbledon Common, his monoplane glider took third place in a youth flight competition and won him a bronze medal and five shillings. The following August at Greenford Bridge, his Ridleyplane No. 60, a twin-screw monoplane, won the Gamage Silver Challenge Cup with a flight of 1,681 feet. In 1912 he competed against Charles Richard Fairey, who would go on to found the great Fairey Aviation Company. After school Ridley joined Sopwith Aviation, building the planes that would soon take him into a war he could not have imagined when he was sketching wings in a schoolroom.

Ridley joined the Royal Naval Air Service and was posted to No. 1 Squadron in northern France, flying a Sopwith Triplane. On 29 April 1917 he shared his first aerial victory, driving down an Albatros D.III alongside Flight Sub-Lieutenant Herbert Rowley. The squadron re-equipped with Sopwith Camels, and on 6 December 1917, north of Passchendaele, he scored his fifth victory and became an ace. He destroyed two enemy observation balloons in the spring of 1918. He drove down a Pfalz D.III, destroyed a Fokker triplane, and on 4 July 1918 forced down a Fokker D.VII near Foucaucourt. That was his eleventh and final combat victory. The pilots who survived the Western Front had survived odds that killed most of their peers. Ridley flew through it.

After the war Ridley accepted a short-service commission in the new Royal Air Force, holding the rank of flight lieutenant, and was posted to No. 12 Squadron with the British Army of the Rhine, the occupation force stationed in Cologne. On 17 May 1920 he took off from Cologne in a Bristol F.2 Fighter, registration D8059. In another Bristol Fighter, registration H1566, Flying Officer John Dartnell de Pencier was also airborne. The two aircraft collided over Lindenthal, a leafy suburb on the western edge of Cologne, and fell together from a height of 450 feet. According to the Berliner Lokal-Anzeiger, both pilots were killed instantly. Their two crewmen survived with slight injuries. Ridley was twenty-five. De Pencier was twenty-three.

The two men were buried beside one another in the Commonwealth War Graves section of Cologne's Sudfriedhof, the Southern Cemetery. It is a quiet place, organized in long lines of uniform pale stones, shaded by trees that have grown tall in the century since. The cemetery sits about three kilometers south of the city center. Walking past the British plot today, the visitor sees graves of men killed in two different wars, and a small number, like Ridley and de Pencier, killed in the strange interval between them. He had built a glider at fifteen, beaten his school friend by thirty-four seconds in a re-fly at Crystal Palace in 1911, become an ace in 1917, survived to see the Armistice, and died in a routine flight in peacetime occupation duty. The model aircraft he made are gone. The records of his competitions survive in old issues of Flight magazine. His grave is in Cologne.

Ridley's youth coincided exactly with the birth of practical aviation. The aero clubs that proliferated in pre-war Britain produced a generation of pilots and engineers who shaped the industry for decades: his rival Charles Fairey, his old schoolmates Mann and Grimmer, the dozens of competitors at Wimbledon Common and Mitcham Common and Greenford Bridge. The Aerodrome model competitions where Ridley won his bronze medals were the visible early surface of a much deeper transformation. He was killed before he could see what aviation became. The fact that he flew at all is remarkable. The fact that he died, finally, not in combat but in a training flight over a defeated city is one of the quieter sorrows of a violent century.