NOVEMBER 7, 1940 - WWII Aircraft Performance

1 NOVEMBER 7, 1940 Enemy Aircraft Official view on the port side of the DB 601A. The air intakearrangements and the absence of ejector exhausts indicatethe engine is out of a Heinkel He this view of the starboard side more details of the enginemounting can be seen. This is a magnesium alloy header tank for the cooling fluid will also be noticedat the front of the INVERTED VEE ENGINEThe Mercedes-Benz DB601A : Hydraulic Drive to Supercharger :Clockwork Boost Control : Roller Bearing Big EndsGERMAN military Aircraft engaged upon the opera-tional work of fighting or bombing are nowexclusively equipped with petrol-injection engines,and the carburettor has been discarded.

2 The carburettoris retained on the smaller engines used in trainers and someof the other non-operational types, but the preference forthe injection system is most marked, probably on accountof fuel economy and freedom from icing trouble. In theearly months of the war carburettors were still in use. Thedirect-injection system on the Junkers Jumo 21 iA wasdescribed exclusively in Flight of January 18, Mercedes-Benz or Daimler-Benz may be used asthe name for the DB 601A engine ; they refer to the samedesign made in different inverted-vee type, of which this 12-cylinder engineis an example, is very popular in German design, butradials are also in use, and the Bramo Fafnir, which waspreviously a carburettor engine, now has petrol in-jection and is fitted to Dornier Do 215s.

3 This enginehas not the hydraulic supercharger drive of theDB 601, but has a two-speed DB 601A is basically similar to the DB 600, except(Below) The underhead valve gear is driven by a singlecamshaft, each cam operating one exhaust and one inletvalve, there being four valves per cylinder. Needle rollerbearings are incorporated in the rockers. The three-studattachment of the exhaust stubs will be noticed. (The engineis inverted in this view.)that the single-speed supercharger and pressure carburettorhave been replaced by the very interesting hydraulic driveand the injection pump.

4 (The DB 600 was described, withother German engines, in Flight of NOVEMBER 16, 1939.)German aero-engine design has been influenced byAmerican, this being partly due to the fact that 132 radial was the g-cylinder Pratt and WhitneyHornet built under licence. The influence appears mostlyin the greater specific volume used by the designers of boththese nations when compared to British designing practice.(Left) Roller bearings (three rows of 24) areprovided between the forked connecting rodand the crankpin.

5 The other connecting rodhas a plain bearing to take the relative move-ment between the two big ends. Serratedjoints, with the splines parallel to therollers, ensure perfect alignment of thetwo halves of the split race. Thoughthe forked rod has splined nuts, theother rod has the usual hexagonal type.(Right) The two gear-type pumpswhich deliver oil to the hydrauliccoupling of the supercharger lower one delivers its fullcapacity constantly but the upperis governed by an altitude-con-trolled capsule which is housed inthe right of the body of the 7, 1940A comparison of the take-off power of our Rolls-RoyceMerlin X with its capacity of 27 litres against that of theDB 601A with the considerably larger capacity of is revealing.

6 The merlin rating gives 1,065 forthree minutes at 5! lb. /sq. in. boost and 3,000 TheDB 601A rating is very similar, being 1,050 for oneminute with a boost of in. at 2,400 Thedifference in capacity is, of course, most CouplingWhat is undoubtedly the most interesting feature it isbelieved to be unique is the fluid drive to the super-charger. This hydraulic coupling operates on the principleof the '' fluid flywheel'' well known in automobile en-gineering. Under this system power is transmitted fromdriving to driven member by the continuous circulation ofoil in the curved channels of both the drive of the DB 601 A, oil is pumped along apassage A in the shaft of the driving member (the otherend of which runs in a spigot bearing) and then emergesthrough the radial holes of the shaft B into the radialpassages C of this member.

7 The rotation causes it to flowoutwards, and the shape of the passages is such that theoil is directed into the similar passages D of the drivenmember. As it has a component of tangential velocity itimpinges on the vanes and so drives the member fluid, in going from driving to driven member, mustcross the small gap between them, and a certain loss offluid occurs continuously. Hence the need for pumpingthe oil into the coupling. Slip between driving and drivenmembers is always a characteristic of hydraulic couplings,but this decreases with increase of speed and is also affectedby the amount of oil in the passages of the is this last characteristic which is turned to goodaccount in the adoption of the coupling tosupercharger drive.

8 At the "superchargealtitude" of the engine a "solid" drive is re-quired, and the coupling will give this if theoil passages are keptfilled. (This must bequalified by sayingthat hydraulic drive isnever quite "solid,"the minimum of slipnever being lower than2 or 3 per cent.)Below the super-charge height it isdesired to run thesupercharger at lower / The supercharger of the DB 600 will be seen inthis drawing. The DB 600 was the forerunnerof the DB 601A and has the same dimensions,but lacked the hydraulic coupling.

9 (Left) The "dry " cylinder liner is attached tothe cylinder block by a screwed j oint. At its otherend the liner is retained in the crankcase by aring nut which is tightened by means of one ortwo of the tools shown. When rotated in the holesin the crankcase, the pinion of the tool engageswith the gearing on the ring nut.(Below) The Mercedes-Benz DB 601 A inverted vee-twelve engine is seen here in the upside down positionduring maintenance work at an Air Ministry stationprior to testing. The bank of injection pumps, thevalve gear and the supercharger will be noticedNOVEMBER 7, 1940AN INVERTED VEE ENGINE (CONTINUED speeds in relation to the engine,and this is accomplished by reduc-ing the oil supply to the two-stage pump supplies thecoupling from the main pressureoil filter, each pump stage being ofthe normal gear design.)

10 The firststage has no control on it and sup-plies the whole of its output to thecoupling, so that there is alwayssome oil present in the spaces. Theoutput of the second stage isgoverned by a capsule whichresponds to intake pressure, socontrolling a piston valve whichdivides the oil between thecoupling and the by-pass back tothe engine sump. The second stagecommences delivery to the couplingat a barometric height of 4,900ft.,and full delivery occurs at 11, In this way is thedesired result of a variable-speeddrive between engine and super-charger the Mercedes-Benz thehydraulic coupling is a double-sidedone, the driving member being onthe inside with one driven memberthrust is thereby balanced.