Title:
ROLLS ROYCE merlins

Description:
raf aircraft In 1936, the Air Ministry had a requirement for a new fighter aircraft with airspeeds that would eventually have to be over 300 mph (480 km/h). Fortunately, two designs had been developed entirely as private venture exercises: the Hawker Hurricane and Supermarine Spitfire. Both were designed around the PV-12 instead of the Kestrel, and were the only British modern fighters to have been so developed. Production contracts for both aircraft were let in 1936. The PV-12 was instantly catapulted to the top of the supply chain and became the Merlin. Early Merlins were considered to be rather unreliable, but Rolls soon introduced a superb reliability-improvement programme to improve matters. This consisted of taking random engines from the end of assembly line and running them continuously at full power until they failed. Each was then dismantled to find out which part had failed, and that part was redesigned to be stronger. After two years of this, the Merlin had matured into one of the most reliable aero engines in the world, and could be run at full power for eight-hour bombing missions with no problems. As it turned out, the Peregrine saw use in only two aircraft, the Westland Whirlwind and the Gloster F9/37. Although the Peregrine appeared to be a satisfactory design, it was never allowed to mature; Rolls-Royce's priority was troubleshooting the Merlin. The Vulture was fitted to the Hawker Tornado and Avro Manchester, but proved unreliable owing to big-end failures caused by lubrication problems. With the Merlin itself soon pushing into the 1,500 hp (1,100 kW) range, the Peregrine and Vulture were both cancelled in 1943. upgrades to the Merlin were the result of ever-increasing octane ratings in the aviation fuel available from the US, and ever more efficient supercharger designs. At the start of the war the engine ran on the then-standard 87 octane aviation spirit and The next major version was the XX which ran on 100 octane fuel. This allowed it to be run at higher manifold pressures, which were achieved by increasing the "boost" from the centrifugal type supercharger. The result was that the otherwise similar engine delivered 1,300 hp (970 kW). The process continued, with later versions running on further-increased octane ratings, delivering higher and higher power ratings. By the end of the war the "little" engine was delivering over 1,600 hp (1,200 kW) in common versions, and as much as 2,070 hp (1,544 kW) in the Merlin 130/131 versions used on the de Havilland Hornet. The Merlin was running on 150 Octane fuel by the time it was used in the Lancaster bomber. This high octane rating was achieved by large quantities of lead anti-knocking agent, so much in fact, that the engine cowlings around the exhaust outlets were usually heavily stained with it. It had to be regularly removed for aerodynamic, not to mention weight, reasons. The Merlin's lack of direct fuel injection meant that both Spitfires and Hurricanes were, unlike the contemporary Bf-109E, unable to nose down into a deep dive. This meant the Luftwaffe fighters could 'bunt' into a high-power dive to escape attack, leaving the Spitfire spluttering behind as its fuel was forced by negative 'g' out of the carburettor. RAF fighter pilots soon learned to 'half-roll' their aircraft before diving to pursue their opponents. The use of uninjected carburettors was calculated to give a higher specific power output, due to the lower temperature, and hence the greater density, of the fuel/air mixture, compared to injected systems. "Miss Shilling's orifice" (invented in March 1941 by a female engineer named Shilling), a holed diaphragm fitted across the float chambers, went some way towards curing the fuel starvation in a dive. Further improvements were introduced throughout the Merlins, with injection introduced in 1943.

Author:
spineyExtra

Tags:
aircraft, lancaster, merlin, mosquito, p51, packard, raf, rolls, royce, spitfire,