{{Refimprove|date=April 2018}} <!-- This article is a part of Wikipedia:WikiProject Aircraft. Please see Wikipedia:WikiProject Aircraft/page content for recommended layout. --> {{infobox aero engine |name=BMW VIIa |image= |size= |alt= |caption= |engine_type = V12 water-cooled piston engine <!-- The type of engine, eg: Air-cooled rotary, High-bypass turbofan --> |national_origin =Germany <!-- The country where the engine was first manufactured. Use the main nation (ie. UK), not constituent country (England); don't use "EU". List collaborative programs of only 2 or 3 nations; for more than 3, use "Multi-national --> |manufacturer =Bayerische Motorenwerke <!-- The firm which manufactured the engine. --> |designer = <!-- The person or persons who designed the engine. Only appropriate for single designers, not project leaders --> |first_run = 1928 <!-- The date that the engine was first run. If this hasn't happened, skip this field - don't speculate. --> |major_applications = <!-- aircraft (or other vehicles) that were powered by this engine --> |produced = <!-- Years in production (eg. 1970-1999) if still in active use but no longer built --> |number_built = <!-- Total program cost --> <!-- Incremental or flyaway cost for military or retail price for commercial aircraft --> |developed_from =BMW VI <!-- The engine which formed the basis for this engine --> |variants_with_their_own_articles =BMW IX <!-- Variants OF this engine --> }}__NOTOC__
The '''BMW VII''' was a water-cooled twelve-cylinder engine derived from the successful BMW VI. The engine was not as popular as the VI, due in no small part to the Great Depression, and only a small number were built. Experiments with supercharging led to the related BMW IX.
==Design and development== The main change from the VI to the VII was the addition of a 0.62 ratio propeller reduction gearing system, allowing the engine to run at higher RPM, and thus higher power settings, while still efficiently driving the same propellers. A more minor change was the movement of the magnetos from the back of the cylinder banks to the front, which allowed easier access for maintenance (similar changes to the original six-cylinder BMW V led to the BMW VIII) {{cn|reason=Japanese Aircraft 1910-1941 describes the VIII as a V12 p.157|date=November 2020}}. The crankcase was offered in aluminum alloy or Elektron.
==Operational history== The engine was first built in 1928 and passed its acceptance tests in June 1930. Only a few examples of the BMW VII went into operation, in the single-engined version of the Junkers Ju 52, for example, and in the Dornier Wal which Wolfgang von Gronau flew around the world in 1932. The VII was also used for forced-aspiration experiments with a "mixture blower" (a radial fan located behind the carburetor); this led in due course to the development of the BMW IX aircraft engine.
==Variants== ;Low compression: A low compression variant ran at 5.5:1 compression ratio, delivering {{convert|600|hp|abbr=on|disp=flip}} at 1,565 rpm ;Medium compression: A medium compression variant ran at 6:1 compression ratio, delivering {{convert|750|hp|abbr=on|disp=flip}} at 1,650 rpm ;BMW VIIaU:A high compression variant running at 7.3:1 compression ratio, delivering {{convert|750|hp|abbr=on|disp=flip}} for take-off. <!-- ==Applications== --> <!-- ==Survivors== --> <!-- ==Engines on display== --> ==Specifications (variant) == {{pistonspecs| <!-- If you do not understand how to use this template, please ask at Wikipedia talk:WikiProject Aircraft --> <!-- Please include units where appropriate (main comes first, alt in parentheses). If data is missing, leave the parameters blank (do not delete them). For additional lines, end your alt units with )</li> and start a new, fully formatted line with <li> --> |ref=<ref name=Jakobs>{{cite book|last1=Jakobs|first1=Fred|last2=Kroeschel|first2=Robert R.|last3=Pierer|first3=Christian |title=BMW aero engines: Milestones in aviation from the beginnings to the present|date=June 2009|publisher=Heel Verlag Gmbh|location=Königswinter|isbn=978-3868522143}}</ref> |type= V12 water-cooled piston engine |bore={{convert|160|mm|abbr=on|2}} |stroke={{convert|190|/|199|mm|abbr=on|2}} (nominal: master/slave connecting rods resulted in different stroke for each cylinder bank) |displacement={{convert|46.93|L|cuin|abbr=on}} |length={{convert|2025|mm|abbr=on|2}} |diameter= |width={{convert|864|mm|abbr=on|2}} |height={{convert|1045|mm|abbr=on|2}} |weight={{convert|525|kg|abbr=on}} |valvetrain= |supercharger= |turbocharger= |fuelsystem= |fueltype=Aviation gasoline |oilsystem=pressure fed |coolingsystem=water-cooled |power={{convert|600|or|750|hp|abbr=on|disp=flip}} |specpower= |compression=5.5 / 6 / 7.3 |fuelcon= |specfuelcon= |oilcon= |power/weight=
|designer= |reduction_gear=0.62:1
|general_other= |components_other= |performance_other= }} <!-- ==See also== --> {{aircontent <!-- include as many lines are appropriate. additional lines/entries with carriage return. --> |see also= |related=<!-- related developments --> |similar aircraft=<!-- similar or comparable aircraft --> |lists= }}
==References== {{Reflist}} <!-- ==Further reading== --> <!-- ==External links== --> {{BMW aeroengines}}
Category:BMW aircraft engines Category:1920s aircraft piston engines Category:V12 aircraft engines Category:Liquid-cooled aircraft piston engines