Rolls-Royce Engines: Vulture
Note: This is a sub-section of Rolls-Royce.
Rolls-Royce's Vulture was an X-24 aircraft engine of the World War II era. Originally designed to produce around 1,750 hp, continuing problems with both the Vulture and the underlying Peregrine meant the Vulture was de-rated to around 1,450-1,550 hp in service. Although several aircraft designs had planned on using the Vulture, work on the design ended in 1941 as Rolls concentrated on their more successful Rolls-Royce: Merlin. Another engine produced to the same criteria, the Napier Sabre, would prove more successful after a lengthy shaking-out period.
The Peregrine, a supercharged Kestrel , was a fairly standard design (at first sight) with two cylinder banks arranged in a V form and with a displacement of 22 litres. The Vulture was basically two Peregrines joined at the crankcase, with a common crankshaft, producing an X-engine configuration with a displacement of 44 litres.
Both engines suffered from a far too short pre-service development period and the reliability was very poor. Apart from delivering significantly less than the designed power, the Vulture suffered from frequent failures of the connecting-rod big-end bearings, which was found to be caused by a breakdown in lubrication, and also from other engine heat dissipation problems. One engine suffered catastrophic failure due to overheating. The root cause appeared to be impaired heat transfer from the cylinder liners to the coolant, caused by the presence of oil in the cooling system. Problems on the Merlin also occurred when a 30% ethylene glycol/water misture was used, but not with 100% ethylene glycol, possibly because this dissolved the oil. Flushing of the cooling system with sodium metasilicate cured the Merlin problems, and may have been applied to the Vulture, but other cooling system problems remained. One problem arose due to airlocks in the system. Once identified, it was readily cured by fitting a balance pipe between the two pumps. This also reduced oil temperature problems.[1]
Some engine failures on the Avro Manchester resulted from failures of the aircraft's hydraulic systems.
Rolls-Royce were initially confident that they could solve the problems, however the company's much smaller Merlin had already reached the same power level as the Vulture's original specification, and so production of the Vulture was discontinued.
The Vulture had been intended to go into the Hawker Tornado, but with the cancellation of Vulture development, Hawker abandoned the Tornado and concentrated on the Hawker: Typhoon, which was powered by the Napier Sabre. Likewise, the same cancellation caused the abandonment of the Vulture-engined version of the Vickers Warwick bomber.
The only aircraft type designed for the Vulture to actually go into production was the twin-engined Avro Manchester. When the engine reliability problems became clear, the Avro team (who were designing a four Rolls-Royce Merlin version as a contingency plan) persuaded the Air Ministry that switching to the four-Merlin version of the Manchester was preferable to retooling Avro's factories to make Handley Page Halifaxes. The resulting aircraft was initially called the Manchester Mark III and then renamed Lancaster, going on to great success as the RAF's leading heavy bomber.
For an outstanding detailed account of the Avro Manchester's development, problems and operating history, see 'Avro Manchester' by Robert Kirby [2]. This provides valuable insight into the effects of shortcomings of the engines' performance and reliability on the aircraft. Some of the effects were indirect. For example, at a late stage, some aircraft started to experience severe tail flutter when taking off with a full bomb load. Avro introduced a minor modification to the wing's upper service to improve oil flow through the engine oil coolers. It transpired that this induced a breakdown in the airflow over the wing surface, causing turbulence.
The most fundamental problem centered on the star-rod design, having one master rod to which were connected three slave rods. Failure of the big end or of its bolts resulted in destruction of the engine, and, potentially uncontrollable fire. Further, the propeller feathering line was often severed as a consequence, preventing feathering and causing excessive drag.
Major redesign would have been required to fully overcome the big end problem. In fact an improved design was prepared, but development of the Merlin identified the benefit of other potential improvements, namely in the cylinder blocks and in the adoption of two-speed superchargers. Such changes were not on the cards, given the preference for the four-Merlin application, and the effort being devoted to the development and production of that engine. Various improvements to the connecting rod problem were introduced, but the greatest benefit came from reducing the maximum speed from 3200 to 2850 rpm to reduce the connecting rod bolt load. The reduction in power output was compensated by raising boost pressure to 9 lb.[3]
See Also
Sources of Information
- ↑ 'Avro Manchester - The Legend behind the Lancaster' by Robert Kirby, Revised and enlarged second edition, Fonthill Media, 2015, pp.61-63
- ↑ 'Avro Manchester - The Legend behind the Lancaster' by Robert Kirby. First edition: Midland Publishing Ltd., 1995; Revised and enlarged second edition, Fonthill Media, 2015
- ↑ 'Avro Manchester - The Legend behind the Lancaster' by Robert Kirby. Revised and enlarged second edition, Fonthill Media, 2015, pp.171, 216
- [1] Wikipedia