FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1942
1942 - 0457.PDF
"LIGHT, February 26th, 1942. A BRITISH MASTERPIECE horse-power—the prodigious figure of over 100 b.h.p. per cylinder! And yet remarkable as those figures may seem, we have the even more amazing figures of the " R " racing type Buzzard engine to reflect upon. That engine specially developed by Rolls-Royce for the Schneider Trophy, which it won outright, gave 2,300 b.h.p. at 3,200 r.p.m. and scaled 1,630 lb. = n oz. per b.h.p. It was a masterpiece of precision engineering in 1931 and remains a symbol of British efficiency ten years later. Aluminium Largely Used The cylinder block of the Merlin is a single ^atoinium casting comprising the head and the coolant jacket. '' Wet'' cylinder liners of steel are provided which start life as a 26 lb. forging and finish up weighing 7 lb. only. The liners have shoulders which fit against the crankcase and the cylinder block at opposite ends. A coolant joint is effected around the base of each liner by means of two rubber rings fitting grooves in the liner. A joint ring of aluminium alloy is arranged between the upper shoulders of each liner and the cylinder block. The resulting joints are maintained by means of 14 long studs which extend from the crankcase through to the tops of the cylinders Except for the four end studs, the remaining ten pass through corrosion- resisting tubes which form oil return ways and make coolant joints at either end by means of rubber rings held in annular recesses in the block casting. Two main coolant pipes extend from the centrifugal pump to the rear connections of each cylinder block. Two inlet and two exhaust valves are provided for each cylinder operated by an overhead cam shaft through the medium of rockers having aluminium bush bearings. All valves are placed parallel with the centre line of the cylinders. Sodium-cooled exhaust valves are utilised operat ing in phosphor-bronze guides. The seatings, which are screwed into the head, are of high silicon chro mium steel, and the engaging face and crown of the valves are surfaced with " Brightray." The stem tips are of Stellite. Inlet valves work in cast-iron guides and also have high-silicon chromium steel seatings. Each valve has two concentric valve springs retained by a collar and split wedge. Adjustment is effected by means of a tappet screw ed lock-nut. * V»^The camshafts are driven by inclined shafts and bevel gears from the wheelcase at the rear of the engine, and each camshaft has additional gear wheels for driving various auxiliaries. Forged aluminium pistons are employed, having three pressure rings and two drilled scraper rings, and a hardened- steel floating gudgeon pin. Forked H-section connecting rods scale 8£ lb. and 7J lb. respectively in the raw state ; when machined all over 2f lb. and i\ lb. They are pro vided with lead bronze bearings for the crank-pin, and a floating phosphor-bronze bush is fitted in the small end. Hollow Steel Crankshaft The hollow crankshaft compels admiration as a supreme example of design and perfect finish. It is a one-piece forging reduced during machining from 280 lb. to a finished weight of 180 lb. At the front end there is a flange bolted to it which transmits the drive through an internally t( ¥thed annulus to a short floating roller quill shaft which drives the reduction gear pinion through internal splines *t the front end. Thus the crankshaft end-bearing is insulated from loads due to the gearing. The airscrew shaft, which has a reduction of 0 = 420 to r, is carried in roller bearings and a ball thrust is provided. It scales .ut 34j lb. of its original 108 lb. as a forging. Lubrica tion is of the dry-sump system, and there are two gear- type scavenge pumps working in parallel to drain the front ••- Section through No. 5 cylinder looking towards rear of engine. and rear of the lower half crankcase. The supply system comprises a main and low-pressure circuit served by a single pressure-pump. Two screened magnetos are spigoted to the wheelcase, and each is arranged to fire all twelve cylinders inde pendently. Lodge special type sparking plugs are arranged on opposite sides of the combustion chambers. Dual gear- type fuel pumps are driven in tandem from the L.H. side of the wheelcase and deliver fuel direct to the float chambers. Twin Choke Updraught Carburettor An improved type of S.U. carburettor is employed having increased diameter of chokes, and two independent float chambers with two saddle-type cork floats—one around each main diffuser well—and control the fuel inlets by needle valves. The effect of banking on fuel level has thus been reduced. The automatic boost-regulator controls the supercharger delivery pressure by an automatic servo mechanism work ing through a differential linkage to limit the throttle opening and to protect the engine from damage resulting from overboosting. It is of the progressive type with the boost pressure determined by the degree of throttle opening and maintained automatically within a range determined by the altitude, this range increasing as the throttle opening is increased. Until the rated boost pressure is reached, the boost pressure is not maintained over the whole throttle range. The regulator consists of an aneroid (balance flexible metallic bellows) which is exposed to the boost pressure. The aneroid is coupled to a piston-valve to admit boost pressure to one side or other of a relay piston which is interconnected with the throttle control. Thus the open ing of the throttle is controlled to suit the intake pressure.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
