A New de Havilland
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184 b.h.p. Engine
A Description of the Gipsy Six, A Six-cylindered Version of the Gipsy Major Inverted Air-cooled Unit
pROBABLY the most widely used engines for civil flying in the past few years have been the Gipsy engines made by the de Havilland Aircraft Co., Ltd., at Stag Lane, Edgware. The Gipsy 1, an upright engine, was designed in 1928, but the latest models have been of the inverted air-cooled type with the cylinders in line. The Gipsy Major, widely used in British ai,r transport, develops 120 b.h.p..at 2,100 r.P.m. and 132 b.h.p. at 2,350 r.p.m.
Now the company announces the Gipsy Six, which has the same bore, stroke and compression ratio as the Major, but with two extra cylinders. COntidence in it may be expected in that the Major and earlier models have, on long ocean flights, like those made by Mr. J. A. Mollison, proved them klves wonderfully reliable. • The cylinders, cylinder heads, valves, valve gear, pistons, connecting rods, big-end bearings, impulse starters, carburetters and many small parts of the Gipsy Six are interchangeable with those of the Gipsy Major. • The cylinder barrels are machined all over from carbon-steel torgings and carry detachable beads cast in aluminium bronze and held by long hightensile steel studs extending from the crankcase. The use of this metal enables the two valVes for each cylinder, vertically arranged, to have their B36 seatings machined directly in the head.
The slipperetype pistons, in beattreated aluminium alloy (specification D.T.D.131), are designed so that the thrust is taken from the crown direct to the gudgeon-pin bosses. The connecting rods are machined from forgings of D.T.D.130 alloy, and each big-end is clamped by four bolts and has a bronze-shell bearing lined with white metal.
The crankshaft runs in eight steelhacked white-metal beatings and has a hall thrust race. The airacrew boss is fitted on a tapered crankshaft extension and driven by two keys, and the front flange plate is positively driven. The crankcase and cover are Elekiron castings and the main bearings lie well below the joint face. There is no separate timing case and the cover serves as a mounting for the magnetos, distributors, etc.'
The camshaft, on the port side, has seven bearings and operates directly on hard steel tappets. Duralumin tubular push-rods and steel rockers are used, the whole gear being enclosed and lubricated by splash from the rockers which dip into the oil baths provided by their covers.
The camshaft and all auxiliaries are
driven from a gearwheel at the front of the crankshaft between the. ban thrust bearing • and the first; crank throw. This is the steadiest-point in the system.
• A train of hardened gears extends downward to the camshaft and upward to a longitudinal shaft within the top cover, which runs at 1.5 crankshaft speed and, at its rear end, meshes with gears driving the two magnetos and their. distributors. A bevel gear at the rear of the camshaft drives a vertical oil-pump shaft. The camshaft also provides drives for the dual petrol pumps and tachometer connections.
The oil pumps and filters form a detachable unit at the rear. A gear-type pump draws oil from a separate tank and delivers it to an Autoklean filter, whence it is divided into two streams ; the main stream flows upwards to a. cast-in gallery connected by drillings to the main bearings and big-ends, the latier having holes to spray the cylin der walls. Oil is cooled by contact
with the top cover... The second stream -passes through a balanced piston mechanism, reducing the pres• sure to about 15 lb., and lubricates the camshafts, etc.
After passing through the engine the oil collects 'around the cylinder extensions and. is. drained by two scavenger pipes. These are arranged in tandem with the pressure pump, and each has a detachable suction filter. As -the two filters are connected by internal passages, drainage is definite no matter
the attitudeof the engine. Apart." from connections to the separate. oil tank there is no internal or external pipework.
Ignition is by two B.T.H. magnetos with -Siinms flexible vernier couplings and impulse starters, and there are two Claudel Hobson A1/4813 downdraught carburetters with an ti-freezing a re l flame-trap devices. A Rotax six-volt electric starter can be arranged to engage with a dog on the rear end of the crankshaft.