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Aviation History
1946
1946 - 0166.PDF
FLIGHT JANUARY 24TH, T946 ROLLS-ROYCE MtRLIN 130 SERIES but the intermittent nature of the ejection from the in-dividual exhaust stacks results in a higher thrust than that obtained from a comparable steady stream. As the engines of the 100 Series operate at higher*ratingsthan any previous Merlin engine, a target of ioo hours' continuous running at maximum r.p.m. and plus 181b. boostwas aimed at to ensure 100 per cent, reliability. It is worthy of note that in flight the maximum duration forthese conditions is five minutes! To eliminate the slightest weaknesses that might be revealed, a programme of de-velopment was initiated which culminated in the success- ful completion of the 100 hours' continuous running at theconditions stipulated before "the engines were passed for production. Results of Testing As was to be expected, rigorous testing of this natureindicated points which could usefully be strengthened with- out unduly adding to weight. The crankcase panels sup-porting the main bearings have therefore been thickened, and extended bosses for the cylinder block and main bear-ing studs have been incorporated. Additionally, the cylin- der head has been reinforced, and, by a repositioning ofthe core-plugs, a reduction in stress concentration has also been brought about. By virtue of the higher boost ratings,the differential pressure across the valves at high altitudes is considerably increased, and the valve springs are, there-fore, of increased load capacity. Refinements introduced include a double-flanged outer-luce to the bearing at the forward end of the rotor shaft, secured in position by bolts. This unusual type of bearingproved to be more reliable than the normal bearing, and it permitted an increase in capacity in the space available.A redesigned spring-drive is also incorporated, with an outer member completely independent of crankshaft deflec-tions. The coolant pump has been brought into line with < iriflon practice and has a spindle mounted on ball-bearingslubricated from the low-pressure oil system. Service main- The modified spring-drive shaft with the outer membercompletely independent of crankshaft deflections. having the employment of a carbon ring a packless- on the pump Simpl'City itself. Reverse rotation of the airscrew by introducingan idler wheel <n the reduction-gear casing. tenance is eliminatedgland coolant seal spindle. Supercharger efficiency is raised by moving the rearbearing of the first-stage rotor from the suction side to the delivery side. This leaves the suction side free fromrestriction, and results in a better mass airflow with reduced turbulence. Further improvement is effected by the adop-tion of the S.U. fuel-injection system, this eliminating pressure losses occasioned by the restriction ofventuri tubes as used with suction carburettors. The cumulative effect of these modifications is anincrease in rated altitude of 2,500ft. It was un- doubtedly the continuous progressive improve-ment in supercharging which enabled the Merlin to maintain its superiority over all enemy typesthroughout the war. The fuel-injection system comprises a gear-typepump supplying fuel to a five-plunger pump oper- ated by a swash-plnto, the stroke and the capa-city of the pump being varied by alteration of the angle at which the swash-plate operates ; thelatter assumes a mean position after compensating for all the variables determining fuel demand.Variation in pump capacity, by varying the stroke, is governed by a "Z" shaft and rockinglevers'linked to an oil-operated servo-piston; this shortens the stroke, and a second piston subjectto boost pressure lengthens it, a balance between these two forces being established by a small leak-valve. The sensitive portion of the valve is con- trolled by a capsule subject to boost on the out-side, teinjK-mtuiT on the inside, and exhaust back pressure on the end convolution. As with allpositive displacement pumps, elimination of air is essential, and a de-acrator is therefore inter-posed between th? delivery side of the gear pump and the suction side of the plunger pump. Byi'his means all air is extracted before the fuel enters the plunger pump, and accurate meteringis thus assured. Owing to production commitments during thegreater part of the war it was not possible to incorporate the axial flow system of lubricationan Merlin engines before the introduction of the Concluded at foot of page 96.)
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