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Aviation History
1943
1943 - 2103.PDF
AUGUST 26TH, 1943 FLIGHT 229 Jumo 211. The oil cooler and coolant radiators are built asfront of the engine in the Ju 88A.1 installation. The air flow is JUNKERS JUMO 2HA ENGINE an annulus at thecontrolled by gills. Cooling No. of cylinders Disposition of cylinders Bore 150 mmCompression ratio Swept volumn (total)Direction of rotation, crankshaft Direction of rotation, airscrewAirscrew reduction gear type Airscrew reduction gear ratioSupercharger type Supercharger drive ... Supercharger gear ratios •Weights, Engine and main engine parts. Engine, oily before strip-ping, with fuel pump, magnetos and airscrew shaft and sparking plugs ...Weight of engine mounting, com- prising two magnesium forgings,tubular struts, ball ends and attach- ment plates for engine liquid 40 per cent. Glysantin, 60per cent, water. 12Inverted 60 deg. Vee; 6 cylinders in line.Stroke 165 mm. 6.57 to 1.35.1 litres (2140 cu. ins.). Left hand.Right hand. Spur gear.SI to 20. Centrifugal.Bevel gear from crankshaft and Ortlinghaus clutch two speed gear.1 to 7.95 and 1 to 11.375. 14531b. 96 Jb. usual feature of this unit is the transverse mounting of the supercharger, which is located by two dowels and fixed with a single ring nut. The impeller is of the usual Junkers spout type of construction, and the diffuser is without vanes. The shaft is carried on hardened-steel bushes which rotate in self-aligning aluminium-alloy bearings. Unusual Scraper Rings The two-speed gear is housed in the auxiliaries gear box and is driven by a bevel gear, which is coupled by a splined shaft to the crankshaft. Examination of the pistons reveal that they are of aluminium alloy, with slightly dished crowns ribbed on the inside. Three gas rings and two scraper rings are fitted, one of the latter being above the gudgeon pin ; oil return holes are drilled behind and below these rings. As mentioned, the scraper rings are of unusual design, being chamtered on the combustion-chamber side to approximately half-ring thickness. On the crankcase side the ring is undercut with a vee groove arranged so that a knife-edge is presented to the oil film on the outward stroke (towards crankshaft) of the piston. Both inlet and exhaust valves are of normal design and slightly recessed on the upper faces. Exhaust valves are sodium cooled in the stem and have " Stellited " laces, and are made of austenitic steel. Inlet valves have 30 deg. seat, whilst exhaust valves have seats at 45 deg. „- Two springs are fitted to each valve, and calculation indicates maximum stresses in the inner and outer springs of 64,000 and 68,000 lb./sq. in. respectively. The unusual feature of the taper cone cotters is that they are made in one piece, split at one side and grooved down the other. The probable advantage of this designis that the spring load on the stem is more evenly distributed with thesecotters than with the normal split cotter. A further unusual feature is to befound in the design of the crankshaft, in which all webs are in the lonn offlat plates and are extended to form balance weights, the shape of the pairof webs on each side of each main bearing being similar. The crank- .shaft receives a supply of lubricating oil through a sleeve at the front end,and all bearings are lubricated through holes drilled in the journals and crank-pins. Short tubes are fitted in each oil hole, which, in addition to prevent •ing sludge entering the bearing, may be intended to act as bushes to reducethe stresses in the shaft around the holes. Apart from the items mentioned,the design follows more or less estab- lished practice; the castings are olhigh quality throughout, several being of magnesium alloy, and all parts are well made and highly finished. The weightof the engine is low in proportion to the swept volume, 1,450 lb. and 35 litres respectively, but on account of therelatively low maximum engine speed the power output per litre is also low. Fuel oil, coolant, hydraulic and ahpipes are individually marked in accordance with a colou; code, and bulkhead connections are numbered to assistinstallation. Forged Engine Mounting The engine mounting, of typical German design, con-sists of two single-piece magnesium alloy forgings attached to the engine at two points on each side and supportedby a steel tubular strut under each rear point of attach- ment. Bearer plates are bolted and dowelled to the sides of theengine crankcase, and connected to the cantilever mounting through flexible rubber bushes The mounting is attached to the nacelle by four " union "type nuts, thus rendering removal of the engine, complete with mounting, extremely easy. The engine and oil cooling systems do not call for anyspecial comment, and in view of the full description already given in a previous issue of Flight relating to the directfuel-injection system this need not be referred to again here. The description so lar relates to an examination olthe Jumo 211A as installed in the Heinkel He IIIH aircraft Following the strip examination of the above enginesuperficial examinations of the Jumo 211A (3) and 211D (1) engines have been made and, in addition, the Jumo211B (1) type, as installed in the Junkers JU88A.I aircraft. Certain modifications have been embodied in the later series which are summarised in the table, with corre-sponding details of the original 211A (1) engine. Such. JUMO 211A SUPERCHARGER Data at maximum engine speed of 2300 r.p.m.—Impeller tip speed in high gear (11.375 x crankshaft speed) 1080 ft./sec.Impeller tip speed in low gear (7.95 x crankshaft speed) ... 746 ft./sec. Number of impeller spouts . 14Total flow area at impeller tip . 13.02 sq. in. Total flow area at impeller eye ... .. ... 18.8 sq. in.Impeller tip diameter ... .. 9.45 ins. Entry guide blade tip diameter . .. 5:79 ins.Entry guide blade root diameter 2.86 ins. Under take-off conditions (1200 b.h.p., 2300 r.p.m.):—Axial velocity at eye 176 ft./scc. Velocity of entry guide blades at mean diameter ... • ... 322 ft./sec.Angle of entry guide blades to tangential direction at me an diameter:—Theoretical . .. ... . .. 29 deg. Measured 81 deg. ± 3 deg.Estimated maximum pressure ratio at ground level, 2300 r.p.m. in high gear is between 2.0 to 1 and 2.1 to 1.Area of mouth of air intake (gross) .. . - ... S2.0 sq. in.
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