{{Use dmy dates|date=February 2017}} {{Use British English|date=February 2017}} {{infobox aero engine |name = Cirrus Minor |image = BlackburnCirrusMinor.JPG |caption = Blackburn Cirrus Minor 2A |engine_type=Air-cooled 4-cylinder inline piston engine |manufacturer=Blackburn Aircraft |national_origin=United Kingdom |first_run=1937 |major_applications= |number_built = |developed_from = |developed_into = |variants_with_their_own_articles = }}

The '''Blackburn Cirrus Minor''' is a British four-cylinder, inverted, in-line air-cooled aero-engine that was designed and built by the Cirrus Engine Section of Blackburn Aircraft Limited in the late 1930s.

==Design and development== The '''Cirrus Minor''' started life as a clean-sheet replacement for the original Cirrus and Hermes series of light aircraft engines. Design was led by Technical Director C. S. Napier, son of Montague Napier, and was already under way when in 1934 Cirrus-Hermes Engineering was taken over by the Blackburn Aeroplane & Motor Company and moved to Brough in Yorkshire.<ref name="flight1935-1">"A New Small Engine", ''Flight'', 28 February 1935, pp.218-9.</ref><ref name="flight1935-2">"The 'Cirrus Major'", ''Flight'', 13 June 1935. Supplement.</ref>

Napier remained Technical Director and, while he completed the development and initial sales of the Cirrus Minor and its larger stablemate the Cirrus Major, Blackburn kept Cirrus Hermes Engineering as a separate company (though without the hyphen in its name).<ref name="flight1935-2"/>

Although completely new designs, they were of generally similar layout to the previous inverted engines, being air-cooled inverted four-cylinder inline designs. Like the others the Minor had a robust steel five-bearing crankshaft, but unlike them the long studs bolting the cylinder heads to the crank housing were replaced by short studs and flanges at each end of the cylinder barrels. Light alloy was used for the cylinder heads and con rods, while the valve gear was adopted with little change from the Hermes IV. The Claudel-Hobson down-draught carburetter featured independent altitude control, and the dual-redundant magnetos were of B.T.H. S.G.4/2 type.<ref name="flight1935-1"/>

The Cirrus Minor was introduced in 1935. Two years later, Cirrus Hermes Engineering lost its identity as a separate company and was adopted as an operating division of its parent company, which by then had become Blackburn Aircraft.

The Minor was known for excellent reliability, and had a major "win" when it was selected to power the RAF's Taylorcraft Auster observation aircraft. The RAF's version had several modifications, known as the '''Series I'''. Although externally identical, the '''Series II''' engine was redesigned to operate on 77 octane fuel, as opposed to the original's 70, increasing power to 100&nbsp;hp (75&nbsp;kW).

==Applications== {{Columns-list|colwidth=30em| *Arpin A-1 Mk.2 *Auster J-1 Autocrat *Auster J-4 *British Aircraft Swallow *Deekay Knight *Elliotts of Newbury Eon *General Aircraft Cagnet *Hillson Helvellyn *Marendaz Trainer *Miles M.68 *Miles Gemini *Mulot AM-20 *RWD 21 *SAI KZ III *Taylorcraft Auster I *Taylorcraft Plus C2 *Taylorcraft Plus D *VEF I-12 }}

==Engines on display== *A preserved Blackburn Cirrus Minor II is on public display at the Royal Air Force Museum Cosford.<ref>[http://www.rafmuseum.org.uk/research/collections/engine-blackburn-cirrus-ii/ RAF Museum Cosford - Blackburn Cirrus II] www.rafmuseum.org.uk Retrieved:1 January 2014</ref>

==Specifications (Cirrus Minor I)== {{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 are missing, leave the parameter blank (do not delete it). For additional lines, end your alt units with </li> and start a new, fully formatted line with <li> --> |type=Inline air-cooled inverted 4-cylinder |ref=''Lumsden'' <ref>Lumsden 2003, p. 90.</ref> |bore=3.94 in (100 mm) |stroke=5.00 in (127 mm) |displacement=243 cu in (4 L) |length=39.9 in (1,013 mm) |diameter= |width=17.9 in (455 mm) |height=25.6 in (650 mm) |weight=200 lb (91 kg) |valvetrain=1 inlet and 1 exhaust valve per cylinder |supercharger= |turbocharger= |fuelsystem=1 Claudel carburettor |fueltype=70 octane |oilsystem= |coolingsystem=Air-cooled |power=90 hp (67 kW) at 2,600 rpm |specpower= |compression=5.8:1 |fuelcon= |specfuelcon= |oilcon= |power/weight= 0.45 hp/lb (0.73 kW/kg) |designer= |reduction_gear=

|general_other= |components_other= |performance_other=

}}

==See also== {{aircontent <!-- other related articles that have not already linked: --> |see also=

<!-- designs which were developed into or from this aircraft: --> |related= *Blackburn Cirrus Major <!-- aircraft that are of similar role, era, and capability this design: --> |similar aircraft=

<!-- relevant lists that this aircraft appears in: --> |lists= *List of aircraft engines <!-- For aircraft engine articles. Engines that are of similar to this design: --> |similar engines= *Argus As 8 *ADC Cirrus *Alfa Romeo 110 *Hirth HM 504 *Menasco C4 <!-- See WP:Air/PC for more explanation of these fields. --> }}

==References==

===Notes=== {{reflist}}

===Bibliography=== {{refbegin}} *[http://www.oldengine.org/members/diesel/Duxford/data01.htm Oldengine.org] {{Webarchive|url=https://web.archive.org/web/20070314003852/http://www.oldengine.org/members/diesel/Duxford/data01.htm |date=14 March 2007 }} * {{cite book |last= Gunston |first= Bill |title=World Encyclopedia of Aero Engines |year=1986 |publisher=Patrick Stephens |location= Wellingborough |pages=40 }} * Lumsden, Alec. ''British Piston Engines and their Aircraft''. Marlborough, Wiltshire: Airlife Publishing, 2003. {{ISBN|1-85310-294-6}}. {{refend}}

==External links== {{Commons category|Blackburn Cirrus Minor}} {{Cirrus aeroengines}}

Category:Aircraft air-cooled inline piston engines Category:Blackburn aircraft engines Category:1930s aircraft piston engines Category:Inverted aircraft piston engines Category:Straight-four engines