THE BMW801A FOURTEEN cylindertwin row radial engine powering theDornier Do217 series – and amodification of which powers theFocke_Wulf 190 fighter – represents

the farthest production advance ofGerman design in the aircooledfield. An 18-cylinder model – 802 –developing some 2,000 hp., reportedcoming into production, is the only

Nazi engine to better it.In layout, conception and

compactness the 801 represents abig advance in German design; it isa complete power unit housed inexceptionally close-fitting cowling.Conforming to modern Luftwaffepractice, it is a direct fuel injectionengine.

The 14 cylinders are arranged instaggered positions in a triple splitcast steel crankcase with the bottomcylinder of the front row and topcylinder of the rear row beingvertical. Characteristic ofconstruction throughout the engine,no expense appears to have beenspared to give the most rigid casepossible. The whole case ismachined all over and, for wartimeconstruction, is very finely finished.

The crankshaft is machined fromtwo steel forgings, coupled in thecenter by a serrated Hirth joint, thehalves of which are threaded coarseand fine in each half of the shaft. Tolock the shaft up a solid steel bush,internally splined for the assemblytool, is screwed into the threadsbringing the serrations on thecoupling into close engagement. Theouter circumference of the Hirthcoupling acts a s the journal for acenter bearing for the crankshaft.The bearing itself is a heavy-dutysingle row ball bearing type, whileboth front and rear crankshaftbearings are of the roller type.

The crankshaft has four heavywebs with counterweight integral,the webs being drilled and leadfilled for balancing.

Master connecting rods are

located in the low port cylinder inboth front and rear rows.Connecting rod bearings are steel,lead-bronze lined.

The steel cylinder barrels areclosely finned, and at the base ofeach there is a thick flange drilledcircumferentially for the retainingstuds fixed in the crankcase.Cylinder heads are of aluminumalloy and appear to be screwed andshrunk to the steel cylinder. Eachhead has two large diameter valves– one inlet and one exhaust, thelatter having a hollow stem and issodium cooled.

Valves are operated by push-rodsfrom circular cam rings located atthe front and rear of the engine, eachseries of cams operating the valveson front and rear rows of cylinders.Valve rockers run on needle

bearings and are completelyenclosed and pressure lubricatedclosely following current Americanpractice.

A simple epicyclic gear train fordriving the front valve train camring is carried on the front end of thecrankshaft in front of which is asteel drum containing the epicyclicstar gearing for the propellerreduction gear.

At the front end of the drum is cuta large diameter spur gear driving ashaft which drives a geared sleeveon the crankshaft center line. Thissleeve is flanged forward of the gearteeth and bolted to a correspondingflange on the rear of the cooling flanthus forming a drive for th fan.

From the fan drive gears is takenthe drove for the Twin Bosch typeZ.M.14 magnetos. Both magnetos

are vertical mounted on thealuminum alloy front casing.

Unusual Cooling Fan UsedThe cooling fan is mounted

directly behind the screwed andsplined propeller shaft. Slightly tothe rear of the fan and locatedcircumferentially in the forward partof the cowling is the special oilcooler through which cooling air isforced between the cooling gillsuntil it exits thru a controllableperipheral slot near the cowlingnose.

Between cylinders there is anannular ring forming a center tracingfor the cowl and also acting as acollector ring for cooling air for therear cylinder leads. Air form thefront fan is forced into the ring fromwhich it passes through “scoop-ducts” which are riveted to the ringand which guide the air direct to thecylinder head fins. Front and rearcylinders have these “sc oop-ducts.”

Around the cylinder barrels andsides of the cylinder heads areelaborately shaped one-piececooling baffles, the throats of whichlead into the center annular collectorring. At the front of teach of theseskirt baffles are riveted small fin-shaped deflector baffles for directingthe flow air to the rear of the engine.

The aluminum alloy superchargerdelivery casing is bolted at the rearof the crankcase,in turn having aheavily ribbed magnesium alloyintake case bolted to it. Bolts fixingthe two casings together passthrough into the crankcase andsecure the whole assembly

The supercharger has a two-speedgear train – the drive to both gearrations being made through a maindrive gear with a hydraulic-operatedclutch mechanism. The superchargerimpeller is a little more than 13 in.diameter and has 24 blades. It ismachined fro an aluminum forging.Alternate blades have a curl-overcenter portion to direct the air to theblade tips form the center intake.The rear half of the super chargercasing is a good example of fineGerman magnesium castingtechnique. This cover carriesflanged bosses for the generator,vacuum pump, gasoline deliverypump and the elaborate 14-cylinderinjection pump.

This injection pump is interesting

in that it is the first multi-plungerhigh pressure pump built forproduction in radial form. The pumpis made by Friedrick Deckel and,typical of that firm' s products, is realprecision engineering.

The 14 radially disposed plungersare moved back and forth by a camring with three cams driven from thesupercharger drive at 1/6 enginespeed. Each plunger is moved by aspring loaded roller cam followerwhich is in constant running contactwith the base of the cam ring.

Each pump plunger-sleeve carriesa gear ring at its lower end and inslots in this gear – with its flat-sidedwings – slides the plunger. Rotationof the gear rotates the plungeraltering the cut-off angle of thequantity control which is helicallycut into the head of the plunger. Thewhole set-up is similar in design tothe familiar Bosch diesel pump.

The quantity control mechanismfor the 14 plungers is ingenious. Asstated, each plunger sleeve has agear at the inner end; this gear andother plunger gears are inter-meshedby a circular gear ring which rotateseach plunger. Control to the pilot ismade by a short shaft geared at oneend and meshing with the topplunger sleeve bear.

Gasoline is fed to the injectionpump plungers through acircumferential core in the pumpcasting from the supply pumplocated close-by on the rearsupercharger case. Provision ismade for any air accumulation in theliquid to be diverted trough a seriesof cored passages to an air collectorlocated in the injection pump bodywithin the circumference of the ringof plungers.

Plunger design closely followsstandard diesel practice. Eachplunger head is helically cut andgrooved to provide a suitable angleface to the intake and cutoff ports inthe sleeve to allow of varyingthrottle condition. Every pumpingelement is provided with a sliding-type non-return valve on the deliverside. This is in no way similar to thefamous Bosch-Atlas valve but nodoubt fulfills the same purpose asfar as is necessary on a lowerpressure injection system.

The injector which is locatedbetween the valves in the cylinderhead is of interesting design. Incontrast to Mercedes-Benz design,

the injector orifice is of the opentype and the head of the needleclosely resembles the Bosch pintletype injector. Diameter of the pintleinjector needle is .050 in.

Directly inside the injector bodyat the injection end the needlediameter is increased and a three-start sharp-cut thread is used both asa fuel passage and also to impart aswirling action to the gasoline whenentering the cylinder. The remainderof the injector design followsstandard practice. A small circularfilter is incorporated within the bodyof the screw-in gasoline inlet pluglocated at the top of the injector.

The lubrication system in theBMW motor is interesting in viewof its complexity and thoroughness.No fewer than six pumps are used –two pressure and four scavengerpumps.

Reference to the accompanyingdiagram showing this lubricatingsystem lay-out readily shows the oilflow.

The pump A in the drawingdelivers at 175 lb. psi, and a specialcheck valve is provided between theoutlet and the inlet side of the pumpto prevent excessive build-up in theaircooling system. The pump Bdelivers through a rotating vane typefilter driven by gearing from thepump. Pumps A and B are coupledon the delivery side and the commonoutlet is fitted with an automaticpressure control valve whichmaintains a constant oil deliverywhen hot at a little in excess of 100psi. This valve also serves toprovide excessive oil pressure whenthe motor is cold.

There is a lead-off through apressure-reducing valve to the valvegearing which is lubricated at muchlower pressure. The valve gear isscavenged by the pump B.

Drainage and scavenging from thewhole of the front of the engineincluding the fan drive gear,propeller reduction gear and frontcam epicyclic gearing are scavengedby the two pumps E and F. Drainagefrom the lower half center crankcaseand the accessory drives located onthe rear supercharger casing are alldrained and scavenged throughpump C.

Very thorough arrangements havebeen made for de-icing and heating,

all of which are taken from theexhaust system. in the Dornier 217Ethe effectiveness of this heatingsetup is shown by a plate on theinstrument panel giving the pilotinstructions as to what to do whenthe cabin and other parts get too hot.Air is led across the finned exhaustpipes to such places as the wingleading edges,the front bombcompartment and the cabin. Aspecial multi-drilled tube runs roundthe transparent cockpit coverthrough which hot air is distributedover the wind shield.

Specifications are as follows:International power rating – 1,460 bhp. @2,400 rpm. @ 16,250 ft. @ 3.6 psi manifoldpressure.Maximum cruising power (continuous) – 1,280bhp. @ 2,300 rpm. @ 18,500 ft. @ 2.2 psimanifold pressure.Maximum power (emergency) – 1.585 bhp. @2,550 rpm. @ 15,750 ft. @ 4.5 psi manifoldpressure.Normal cruise (economy) – 1,150 bhp. @ 2,100rpm. @ 19,500 ft. @ psi. manifold pressure.Maximum power for takeoff for 3 min. -- 1,580bhp. @ 2,700 rpm. @ 4.7 psi. manifoldpressure.

Bore – 6.15 in.Stroke -- 6.15 in.Volume – 2,520 cu. in.Overall diameter of engine – 50 in.Overall diameter of cowling – 52 in.Length – 58 in.Propeller reduction gear – 0.54 crankshaftspeed.Supercharger twin speed. low ratio – 5.07 x crankshaft speed. high ratio – 7.46 x crankshaft speed.Forward cooling fan – 1.72 x crankshaft speed.Three blade constant speed propeller – 13 ft.diameter.Spinner diameter – 19-1/2 in.

Illustrations courtesy “Flight”

Editor’s Note:

This article originally appeared in the November and December, 1942, (Volume 41, Numbers 11 and 12) issues of Aviation magazine, published by McGraw- Hill Publishing Company of New York, NY, USA

It was reconstructed from microfilm by J.L. McClellan. The microfilm was taken from a tightly bound volume, so that there is some distortion of the images, especially near the binding. It has not been practical to remove or compensate for all the distortions, so none of the illustrations in this reconstruction should be considered reliable sources as to fine details of shape, proportion or spatial relationship. The distortions are, in general, small, and should not detract from a general appreciation of arrangement and relationship. Mr. McClellan has attempted to represent the original layout of the article, but there are some exceptions. Limitations in the compositing tools cause a difference in the text flow relative to the illustrations, compared to the original, so that some changes have been made, to compensate partially for that effect, and the tabular data have been removed from the flow of text and brought together on a single page after the text, partly to make them more accessible, and partly to sidestep problems with page layout.