240:, introduced in late 1917, the D.IIIaü was a standardized refinement of the D.III and D.IIIa design and the ü designation was never official. This engine changed the pistons again, this time to a domed profile that further increased the maximum compression – the ü was for "über", meaning "overcompressed". Additionally, a new altitude-compensating carburetor was added, which improved performance at higher altitudes. To support operations at these altitudes, water from the radiator was used to heat the air intake and prevent icing in the carburetor. The aü model, which included upgraded D.III and D.IIIa engine blocks, was the most prolific German fighter engine of 1918 and designed into most fighter designs from late 1917 on. This included most of the entries in the First Fighter Competition at
26:
198:
154:, suitably scaled up for higher power settings. Like most inlines of the era, it used a large aluminium crankcase as the main structural component, with separate cylinders made from steel bolted onto it. The technology for screwing a threaded cylinder of steel into an aluminium crankcase did not exist at that time. Jackets for cooling water covered the top 2/3 of the cylinder, feeding a radiator via connections at the back of the engine. The only obvious design change from the earlier D.II was to use separate cooling jackets for each cylinder, whereas the D.II used one jacket each for a trio of adjacent pairs of cylinders.
345:
still be seen in very large numbers even at the end. At the end of the war the D.IIIaü would still be the numerically predominant German fighter engine. As a result, the Fokker D.VII's (those not equipped with BMW IIIa's) and the Pfalz D.XII's would be engine-limited in performance (as opposed to "airframe-limited") and yet would still be formidable adversaries to their Allied counterparts. The D.IIIaü was considered the optimum engine for the Roland D.VI, Pfalz D.IIIa, and
Albatros D.Va fighters, whose airframes were of an earlier, "all-wood" generation in design.
292:
268:
255:(or avü), introduced mid-October 1918. The av used slightly longer pistons made of aluminium (possibly a first for a production engine), increasing the compression yet again, while at the same time allowing them to move faster due to the reduced weight. The maximum allowable RPM increased from 1,400 in the earlier models to 1,600 in the av, accounting for most of the gains in power. It is unclear if any av's saw service use. The increased use of
228:, which took over on the production lines in June 1917. The main change was to change the piston profile to have a flat head instead of the former concave one, thereby slightly increasing maximum compression to 4.64:1. Other changes were mainly in design details, notably a redesigned crankcase and new carburetor. Many of the accessories were also redesigned or moved around on the engine. This model was produced only briefly, for use on the
402:
287:
positioned directly over the cylinders with the rocker arms exiting through vertical slots, one cut into each of the opposing sides of the boxes, as shown at left. The earlier "side-slot" rocker arm design had also been used for the
Mercedes D.I and D.II engines' valvetrains. In later versions of the
138:. The initial versions were introduced in 1914 at 120 kW (160 hp), but a series of changes improved this to 130 kW (170 hp) in 1917, and 130 kW (180 hp) by mid-1918. These later models were used on almost all late-war German fighters, and its only real competition, the
344:
of 138 kW (185 hp) and then 150 kW (200 hp)(British rated it at 170 kW (230 hp)) in 1918, however, the small number of BMW's produced ensured that the
Mercedes D.III series would be the primary German fighter engine up to the last month or two of the war and it would
279:
All of the D.III series were generally very similar to other models, with the exception of the piston profile, carburetor details and valvetrain details. It appears that upgrades were available for many of the engines, certainly for the III to IIIa, and IIIa to IIIaü. It would seem unlikely that
205:
The original D.III was introduced in 1914. While it saw widespread use in early examples of the C-series of two-seat general-purpose biplanes, the D.III was too large for contemporary fighter designs and did not see use in that role. At the time, fighters were generally powered by lighter rotary
288:
D.III engines, the boxes were relocated rearward on the tubular camshaft housing, and the now easily sealable cylindrical rocker arm shafts protruded forwards through the front surfaces of the boxes, operating the now fully exposed rocker arms with the exposed shaft ends, as shown at right.
232:
but there are indications that possibly some early
Albatros (Alb.) made Fokker D.VII's were also equipped but probably had the engines upgraded or replaced as quickly as possible. This engine has been referred to in postwar British analysis as generating 130 kW (180 hp)
379:
An unofficial designation, (ü for über), for D.IIIa engines with domed pistons, operating "over-compressed", (at a higher compression ratio). These engines were not able to operate at full throttle at sea level, utilising a self compensating carburettor. 130–150 kW
322:
Confusingly, the "ü" was not an official part of the name. This leads to a number of problems in various references, which often confuse the IIIa with the IIIaü, listing the former as a 130 kW (180 hp) engine. There are two D.IV engines — from the
303:
The newer arrangement was stated as being interchangeable as a set with the complete camshaft, rocker boxes, rocker arms and valve springs, with the D.III's earlier "side-slot" cam drive system design - the later system seems to have influenced both
220:
standard of roughly 735 watts per PS horsepower, it is probable that this engine would have had a slightly higher rating under
British HP numbers. Fuel consumption was 11.75 gallons per hour. Its compression ratio was 4.5:1.
214:. Production of this version was essentially wound down by May 1917, with only a handful continuing to be delivered until October. British HP ratings being slightly different (with 746 watts = 1 hp) to the German PS or
1035:, volume=XI, Issue 8, No. 530, 20 February 1919, pp. 233–236. (Contemporary technical description of the D.IIIaü with drawings and photographs, issued by the British Ministry of Munitions based on a captured example).
386:
D.IIIa engines with the domed pistons made from
Aluminium alloy giving the higher compression ratio as well as a higher operating rpm and thus more power. 150 kW (200 hp) (149–162 kW (200–217 hp))
206:
engines of power output levels from 60 kW (80 hp) to about 82 kW (110 hp), or by water-cooled inline engines in the 75 kW (100 hp) to 89 kW (120 hp) range such as the earlier
173:
for redundancy. The ignition cables were protected in tubes running down either side of the cylinders. Fuel was fed into the cylinders via pipes on the left side of the engine, supplied from a twin-barrel
210:. By 1916 new designs had grown in size and performance and the D.III became popular on new designs. By 1917 the D.III was being widely used in fighters, most notably on the famous
431:
259:
in German aviation fuel may have helped this final upgrade of power, its higher octane rating being better suited for the higher compression ratio.
1065:
716:
130 kW (174 hp) at 1,400 rpm (rated power at sea level), 152 kW (204 hp) at 1,600 rpm (maximum power at altitude)
251:
A final version attempting to keep the D.III block competitive was the 150 kW (200 hp) (149–162 kW (200–217 hp))
280:
early III's would ever make it to the IIIaü standard, as they would almost certainly have been worn out in service before then.
1139:
1010:
295:
Later pattern SOHC D.III valvetrain, using the relocated rocker box design, with rotary shafts to operate the fully exposed
178:
located just above the crankcase. Both the fuel and oil reservoirs were pressurized by an air compressor run off the crank.
201:
Original 120 kW (160 hp) Mercedes D.III, with "side-slot" rocker-arm design SOHC valvetrain atop the cylinders.
142:, was available only in very limited numbers. Compared to the Allied engines it faced, the D.III was generally outdated.
248:. In British post war evaluation the D.IIIaü demonstrated 150 kW (200 hp) according to the British standards.
1134:
1058:
856:
189:
during this period, but it did not see widespread use. The lengthened crankshaft of the D.IV proved prone to breaking.
846:
987:
972:
312:'s engine designers to adopt a nearly identical "slotless" rocker-box overhead cam valvetrain design feature for the
215:
738:
283:
The valvetrain changes concerned the layout of the rocker arms that operated the valves. Early models had square
1039:
Daimler
Sechszylinder Flugmotoren. Type D III und D IIIa, 1917 (Mercedes D.III and D.IIIa aero engine manual).
158:
1144:
1051:
1038:
1074:
131:
25:
275:
valvetrain for the D.III - the rocker arm emerges from the "rocker box" through a slot in the box's side.
1026:
925:
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197:
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882:
516:
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511:
316:
1085:
48:
8:
628:
124:
876:
571:
224:
Development of the basic design led to the slightly modified 130 kW (170 hp)
161:
operating the single intake and exhaust valves, powered by a shaft running up from the
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34:
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619:
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127:
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577:
441:
426:
340:
The D.III line of engines would find themselves eclipsed in performance by the
334:
229:
182:
1128:
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1098:
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466:
451:
436:
364:
330:
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207:
186:
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100:
88:
68:
1043:
181:
Daimler also used the pistons of the D.III to produce the reduction geared,
1093:
521:
486:
456:
446:
421:
313:
284:
245:
211:
169:, one located on either side of the cylinders, each powered by a separate
967:(Facsimile ed.). London: David & Charles (Publishing) Limited, 1969.
794:
566:
561:
551:
526:
481:
476:
471:
461:
333:
based on the 140 mm bore D.III pistons; and the later, six-cylinder
135:
373:
An up-graded D.III introduced in 1917 rated at 130 kW (170 hp)
671:
655:
556:
309:
175:
162:
491:
241:
784:
411:
341:
329:
aircraft powerplant class designations based on power output — one
236:
A more "radical" upgrade was the 130–150 kW (180–200 hp)
337:
with 160 mm bore cylinders, which was essentially unrelated.
789:
416:
325:
305:
256:
139:
401:
799:
38:
363:
The original production version directly developed from the
676:
272:
120:
150:
The D.III was based on the same pattern as the earlier
262:
906:. Flightglobal Archive. December 3, 1915. p. 948
134:
and used on a wide variety of German aircraft during
165:
at the rear of the engine. Ignition was provided by
932:. Flightglobal Archive. June 20, 1918. p. 683
392:alternative unofficial designation for the D.IIIav
1003:German & Austro-Hungarian Aero Engines of WWI
982:. Cambridge, UK: Patrick Stephens Limited, 1989.
900:"The Mercedes Engines on the Captured Aeroplanes"
1126:
679:rocker operated single inlet and exhaust valves.
119:as it was known internally, was a six-cylinder
1073:
1059:
725:(10.281 kW/L (0.2259 hp/cu in)
576:Germany's giant aircraft of World War I the
367:developing 110–120 kW (150–160 hp)
584:
1066:
1052:
597:
1027:200 h.p. High Compression Mercedes Engine
874:
851:. Bloomsbury Publishing. pp. 21–22.
606:6-cyl. water-cooled in-line piston engine
405:Mercedes D.IIIa mounted in a Fokker D.VII
145:
1005:. Vol. 2. n. p.: Aeronaught Books.
400:
290:
266:
196:
944:
1127:
1000:
844:
697:Pressure system; multiple plunger pump
192:
157:The D.III featured a rather prominent
1047:
749:27 mL/kW/hour (0.0355pt/hp/hour)
633:14.78 L (901.93 cu in)
593:Jane's All the World's Aircraft 1919.
965:Jane's All the World's Aircraft 1919
870:
868:
926:"The 180 H.P. Mercedes Aero Engine"
685:Dual Mercedes twin-jet carburettors
263:External differences between models
244:in January 1918, notably the famed
13:
994:
980:World Encyclopedia of Aero Engines
743:412 mL/kWh (0.541 pt/hp/hour)
14:
1156:
1020:
865:
357:Company designation for the D.III
271:Aft-end details of the original
24:
957:
758:0.492 kW/kg (0.299 hp/lb)
512:Hansa-Brandenburg C.I Series 63
396:
33:DIIIa engine on display at the
918:
892:
838:
829:
707:
1:
1140:1910s aircraft piston engines
817:
764:752 kPa (109.1 psi)
664:
651:1,072 mm (42.20 in)
639:1,650 mm (64.96 in)
881:. Otterbein Press. pp.
878:Airplane Engine Encyclopedia
7:
875:Angle, Glenn; Dale (1921).
768:
645:490 mm (19.29 in)
348:
10:
1161:
950:Grey 1969, pp. 1b to 145b.
624:160 mm (6.30 in)
615:140 mm (5.51 in)
185:160 kW (220 hp)
1135:Mercedes aircraft engines
1084:
845:Miller, James F. (2013).
739:Specific fuel consumption
660:310 kg (683 lb)
123:valvetrain liquid-cooled
32:
23:
18:
1001:Düsing, Michael (2022).
822:
812:List of aircraft engines
585:Specifications (D.IIIaü)
598:General characteristics
167:two sets of spark plugs
517:Hansa-Brandenburg W.12
406:
319:V-12 aviation engine.
300:
276:
202:
146:Design and development
835:Gunston 1989, p. 101.
754:Power-to-weight ratio
404:
294:
270:
200:
1145:Straight-six engines
49:Inline piston engine
193:Production variants
774:Comparable engines
407:
331:the straight-eight
301:
277:
203:
1122:
1121:
1012:978-1-953201-52-2
848:Albatros D.I-D.II
730:Compression ratio
502:Halberstadt CL.IV
497:Halberstadt CL.II
447:Albatros D.V/D.Va
432:Albatros C.XIII N
380:(180–200 hp)
109:
108:
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1078:aircraft engines
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836:
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780:Austro-Daimler 6
747:Oil consumption:
572:Schütte-Lanz G.I
97:
85:
57:
35:MTU Aero Engines
28:
16:
15:
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995:Further reading
978:Gunston, Bill.
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701:Cooling system:
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547:LFG Roland D.XV
542:LFG Roland D.VI
537:LFG Roland D.II
532:LFG Roland C.II
507:Hannover CL.III
399:
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128:aircraft engine
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56:National origin
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335:Mercedes D.IVa
264:
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230:Albatros D.III
194:
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183:eight-cylinder
147:
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113:Mercedes D.III
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104:Mercedes D.VI
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96:Developed into
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84:Developed from
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988:1-85260-163-9
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973:0-7153-4647-4
970:
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887:mercedes e6f.
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806:Related lists
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437:Albatros D.II
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365:Mercedes D.II
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187:Mercedes D.IV
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152:Mercedes D.II
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101:Mercedes D.IV
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958:Bibliography
946:
934:. Retrieved
929:
920:
910:February 14,
908:. Retrieved
903:
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703:Water-cooled
700:
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683:Fuel system:
682:
670:
654:
648:
642:
636:
629:Displacement
627:
618:
609:
603:
592:
589:
588:
522:Junkers CL.I
487:Fokker D.VII
457:Albatros W.4
422:Albatros C.I
397:Applications
339:
324:
321:
314:Liberty L-12
302:
285:rocker boxes
282:
278:
252:
250:
246:Fokker D.VII
237:
235:
225:
223:
217:Pferdestärke
216:
212:Albatros D.I
204:
180:
159:overhead cam
156:
149:
116:
112:
110:
103:
963:Grey, C.G.
795:Liberty L-6
708:Performance
695:Oil system:
567:Pfalz D.XII
562:Pfalz D.III
552:Rumpler C.I
527:Junkers D.I
482:Fokker D.IV
477:Daimler L14
472:Daimler L11
462:Aviatik C.I
136:World War I
1129:Categories
818:References
689:Fuel type:
672:Valvetrain
665:Components
656:Dry weight
557:Rumpler 6B
310:Hall-Scott
176:carburetor
163:crankshaft
75:First run
590:Data from
492:Gotha G.I
242:Adlershof
130:built by
1075:Mercedes
936:March 2,
785:BMW IIIa
769:See also
691:Gasoline
412:AEG C.IV
389:D.IIIavü
349:Variants
342:BMW IIIa
69:Mercedes
60:Germany
37:museum,
885:, 346.
790:Hiero 6
649:Height:
637:Length:
417:AGO C.I
383:D.IIIav
376:D.IIIaü
326:IdFlieg
308:'s and
306:Packard
253:D.IIIav
238:D.IIIaü
171:magneto
140:BMW III
132:Daimler
1032:Flight
1009:
986:
971:
855:
800:SPA 6A
734:4.64:1
643:Width:
620:Stroke
370:D.IIIa
317:Allied
257:Benzol
226:D.IIIa
125:inline
39:Munich
19:D.III
1114:D.IVa
1104:D.III
823:Notes
762:BMEP:
604:Type:
360:D.III
299:arms.
117:F1466
115:, or
78:1914
45:Type
1109:D.IV
1099:D.II
1007:ISBN
984:ISBN
969:ISBN
938:2015
912:2014
853:ISBN
677:SOHC
611:Bore
273:SOHC
121:SOHC
111:The
1094:D.I
883:341
1131::
1029:,
928:.
902:.
867:^
1067:e
1060:t
1053:v
1015:.
990:.
975:.
940:.
914:.
861:.
756::
741::
732::
723::
674::
658::
631::
622::
613::
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