Editing Rolls-Royce Merlin (section)

==Variants==
<!-- Units abbreviated as this is effectively a specification table -->
{{Main|List of Rolls-Royce Merlin variants}}
This is a list of representative Merlin variants, describing some of the mechanical changes made during development of the Merlin. Engines of the same power output were typically assigned different model numbers based on supercharger or propeller gear ratios, differences in cooling system or carburettors, engine block construction, or arrangement of engine controls.<ref>Bridgman 1998, p. 283.</ref> Power ratings quoted are usually maximum "military" power. All but the Merlin 131 and 135 engines were "right-hand tractor", ''i.e.'' the propeller rotated clockwise when viewed from the rear. In addition to the mark numbers, Merlin engines were allocated experimental numbers by the [[Ministry of Supply]] (MoS) – e.g.: RM 8SM for the Merlin 61 and some variants – while under development; these numbers are noted where possible.<ref>Morgan and Shacklady 2000, p. 608.</ref> Merlin engines used in [[Supermarine Spitfire|Spitfires]], apart from the Merlin 61, used a propeller reduction ratio of .477:1. Merlins used in bombers and other fighters used a ratio of .42:1.<ref>Harvey-Bailey, 1995, p. 62.</ref>

''Data from Bridgman (Jane's)<ref>Bridgman 1998, pp. 281–283.</ref> unless otherwise noted:''
{{anchor |Merlin II}}
* '''Merlin II''' ''(RM 1S)''
: {{convert|1,030|hp|kW|abbr=on}} at 3,000&nbsp;rpm at {{convert|5500|ft|m|abbr=on}} using + 6&nbsp;[[pounds per square inch|psi]] boost (41 kPa gauge; or an absolute pressure of 144 kPa or 1.41&nbsp;atm); used 100% glycol coolant. First production Merlin II delivered 10 August 1937.<ref name="MoSh610"/> Merlin II used in the [[Boulton Paul Defiant]], [[Hawker Hurricane|Hawker Hurricane Mk.I]], [[Supermarine Spitfire (early Merlin powered variants)#Mk I (Type 300)|Supermarine Spitfire Mk.I]] fighters, and [[Fairey Battle]] light bomber.<ref name="Bri281">Bridgman 1998, p. 281.</ref>
{{anchor |Merlin III}}
* '''Merlin III''' ''(RM 1S)''
: Merlin III fitted with "universal" propeller shaft able to mount either [[de Havilland Propellers|de Havilland]] or [[Dowty Rotol|Rotol]] propellers.<ref name="Robertson 1973, p. 144.">Robertson 1973, p. 144.</ref> From late 1939, using 100-octane fuel and +12&nbsp;psi boost (83 kPa gauge; or an absolute pressure of 184 kPa or 1.82&nbsp;atm), the Merlin III developed {{convert|1,310|hp|kW|abbr=on}} at 3,000&nbsp;rpm at {{convert|9000|ft|m|abbr=on}};<ref name="Harvey-Bailey 1995, p. 155.">Harvey-Bailey 1995, p. 155.</ref> using 87-octane fuel the power ratings were the same as the Merlin II. Used in the Defiant, Hurricane Mk.I, Spitfire Mk.I fighters, and Battle light bomber.<ref name="Bri281"/> First production Merlin III delivered 1 July 1938.<ref name="MoSh610"/>
{{anchor |Merlin X}}
* '''Merlin X''' ''(RM 1SM)''
: {{convert|1,130|hp|kW|abbr=on}} at 3,000&nbsp;rpm at {{convert|5250|ft|m|abbr=on}}; maximum boost pressure +10&nbsp;psi; this was the first production Merlin to use a two-speed supercharger; Used in [[Handley-Page Halifax|Halifax Mk.I]], [[Vickers Wellington|Wellington Mk.II]], and [[Armstrong-Whitworth Whitley|Whitley Mk.V]] bombers. First production Merlin X, 5 December 1938.<ref name="MoSh610"/>
{{anchor |Merlin XII}}
* '''Merlin XII''' ''(RM 3S)''
: {{convert|1,150|hp|kW|abbr=on}}; fitted with [[Coffman engine starter]]; first version to use 70/30% water/glycol coolant rather than 100% glycol. Reinforced construction, able to use constant boost pressure of up to +12&nbsp;psi using 100-octane fuel; Used in [[Supermarine Spitfire (early Merlin powered variants)#Mk II (Type 329)|Spitfire Mk.II]].<ref name="Robertson 1973, p. 144."/> First production Merlin XII, 2 September 1939.<ref name="MoSh610"/>
[[File:Rolls Royce Merlin XX.jpg|thumb|alt=A left side view of a gloss grey -painted aircraft piston engine on static display|Preserved Merlin XX at the [[Royal Air Force Museum London]]]]
{{anchor |Merlin XX}}
* '''Merlin XX''' ''(RM 3SM)''
: {{convert|1,480|hp|kW|abbr=on}} at 3,000&nbsp;rpm at {{convert|6000|ft|m|abbr=on}}; two-speed supercharger; boost pressure of up to +14&nbsp;psi; Used in Hurricane Mk.II, [[Bristol Beaufighter|Beaufighter Mk.II]], Halifax Mk.II and [[Avro Lancaster|Lancaster Mk.I]] bombers, and in the [[Supermarine Spitfire (early Merlin powered variants)#Mk III (Type 330)|Spitfire Mk.III prototypes (''N3297'' & ''W3237'')]].<ref>Morgan and Shacklady 2000, p. 129.</ref> First production Merlin XX, 4 July 1940.<ref name="MoSh610"/>{{#tag:ref|In August 1940 drawings of the Merlin XX were sent to the [[Packard Motor Car Company]] and used as the basis for the [[Packard V-1650 Merlin|Packard Merlin 28]].<ref name="MoSh610"/>|group=nb}}
{{anchor |Merlin 32}}
* '''Merlin 32''' ''(RM 5M)''
: {{convert|1,645|hp|kW|abbr=on}} at 3,000&nbsp;rpm at {{convert|2500|ft|m|abbr=on}}; a "low altitude" version of Merlin with cropped supercharger impellers for increased power at lower altitudes and a maximum boost pressure of +18&nbsp;psi; fitted with Coffman engine starter; used mainly in [[Fleet Air Arm]] aircraft, mainly the [[Fairey Barracuda|Fairey Barracuda Mk.II]] torpedo bomber and [[Supermarine Seafire|Supermarine Seafire F. Mk.IIc]] fighters. Also [[Hawker Hurricane variants#Hurricane Mk V|Hurricane Mk.V]] and [[Supermarine Spitfire (early Merlin powered variants)#PR Mk XIII (Type 367)|Spitfire P.R. Mk.XIII]].<ref name="Robertson 1973, p. 144."/> First production Merlin 32, 17 June 1942.<ref name="MoSh610"/>
{{anchor |Merlin 45}}
* '''Merlin 45''' ''(RM 5S)''
: {{convert|1,515|hp|kW|abbr=on}} at 3,000&nbsp;rpm at {{convert|11000|ft|m|abbr=on}}; used in [[Supermarine Spitfire (early Merlin powered variants)#Mk V (Types 331, 349 & 352)|Spitfire Mk.V]], PR.Mk.IV and PR.Mk.VII, Seafire Ib and IIc. Maximum boost pressure of +16&nbsp;psi. First production Merlin 45, 13 January 1941.<ref name="MoSh610"/>
{{anchor |Merlin 47}}
* '''Merlin 47''' ''(RM 6S)''
: {{convert|1,415|hp|kW|abbr=on}} at 3,000&nbsp;rpm at {{convert|14000|ft|m|abbr=on}}; high-altitude version used in [[Supermarine Spitfire (early Merlin powered variants)#Mk VI (Type 350)|Spitfire H.F.Mk.VI]]. Adapted with a [[Marshall Aerospace and Defence Group|Marshall]] compressor (often called a "blower") to pressurise the cockpit. First production Merlin 47, 2 December 1941.<ref name="MoSh610"/>
{{anchor |Merlin 50}}
* '''Merlin 50.M''' ''(RM 5S)''
: 1,585&nbsp;hp (1,182&nbsp;kW) at 3,000&nbsp;rpm at {{convert|3800|ft|m|abbr=on}}; low-altitude version with supercharger impeller "cropped" to {{convert|9.5|in|mm|0|abbr=on}} in diameter. Permitted boost was +18&nbsp;psi (125 kPa gauge; or an absolute pressure of 225 kPa or 2.2&nbsp;atm) instead of +16&nbsp;psi (110 kPa gauge; or an absolute pressure of 210 kPa or 2.08&nbsp;atm) on a normal Merlin 50 engine.<ref name="Robertson 1973, p. 145.">Robertson 1973, p. 145.</ref><ref>Price 1982, p. 145.</ref> Merlin 50 series was first to use the Bendix-Stromberg "negative-g" carburettor.<ref>Matusiak 2004, p. 10.</ref>
{{anchor |Merlin 61}}
* '''Merlin 61''' ''(RM 8SM)''
: {{convert|1,565|hp|kW|abbr=on}} at 3,000&nbsp;rpm at {{convert|12250|ft|m|abbr=on}}, {{convert|1,390|hp|kW|abbr=on}} at 3,000&nbsp;rpm at {{convert|23500|ft|m|0|abbr=on}}; fitted with a new two-speed two-stage supercharger providing increased power at medium to high altitudes; +15&nbsp;psi boost; used in [[Supermarine Spitfire (late Merlin powered variants)#Mk IX (Type 361)|Spitfire F Mk.IX]], and [[Supermarine Spitfire (late Merlin powered variants)#PR Mk XI (Type 374) and FR Mk XI|P.R Mk.XI]].<ref>Smith 1942, pp. 655–659.</ref> First British production variant to incorporate two-piece cylinder blocks designed by Rolls-Royce for the [[Packard Merlin]].<ref name="Smith 1942, p. 656">Smith 1942, p. 656.</ref> Reduction gear ratio .42:1, with gears for pressurisation pump.<ref>Harvey-Bailey 1995, pp. 62, 169.</ref> First production Merlin 61, 2 March 1942.<ref name="MoSh610"/>
{{anchor |Merlin 63|Merlin 63A}}
* '''Merlin 63 and 63A''' ''(RM 8SM)''
: {{convert|1,710|hp|kW|abbr=on}} at 3,000&nbsp;rpm at {{convert|8500|ft|m|abbr=on}}, {{convert|1,505|hp|kW|abbr=on}} at 3,000&nbsp;rpm at {{convert|21000|ft|m|abbr=on}}; strengthened two-speed two-stage development of Merlin 61; +18&nbsp;psi boost; Reduction gear ratio .477:1; Merlin 63A did not have extra gears for pressurisation and incorporated a strengthened supercharger drive [[quill shaft]].<ref>Harvey-Bailey 1995, p. 170</ref> Used in [[Supermarine Spitfire (late Merlin powered variants)#Mk VIII (Type 360)|Spitfire F Mk.VIII]] and F. Mk. IX.<ref name="Robertson 1973, p. 145."/>
[[File:RR Merlin 66-266.ogg|thumb|Audio of RR Merlin 66/266 starting]]
{{anchor |Merlin 66}}
* '''Merlin 66''' ''(RM 10SM)''
: {{convert|1,720|hp|kW|abbr=on}} at {{convert|5790|ft|m|abbr=on}} using +18&nbsp;psi boost (124 kPa gauge; or an absolute pressure of 225 kPa or 2.2&nbsp;atm); low-altitude version of Merlin 63A. Fitted with a Bendix-Stromberg anti-g carburettor;<ref>Air Ministry 1943, p. 6.</ref> intercooler used a separate header tank.<ref>Harvey-Bailey 195, p. 172.</ref> Used in [[Supermarine Spitfire (late Merlin powered variants)#Mk VIII (Type 360)|Spitfire L.F. Mk.VIII]] and L.F. Mk.IX.<ref name="Robertson 1973, p. 145."/>
{{anchor |Merlin 76|Merlin 77}}
* '''Merlin 76/77''' ''(RM 11SM)''
: {{convert|1,233|hp|kW|abbr=on}} at {{convert|35000|ft|m|abbr=on}};<ref name="Lo219"/> Fitted with a two-speed, two-stage supercharger and a Bendix-Stromberg carburettor. Dedicated "high altitude" version used in the [[Westland Welkin]] high-altitude fighter and some later Spitfire and [[de Havilland Mosquito]] variants. The odd-numbered mark drove a [[Marshall supercharger|Marshall]] [[Roots-type supercharger|Roots-type]] blower for [[Cabin pressurization|cockpit pressurising]].
{{anchor |Merlin 130|Merlin 131}}
* '''Merlin 130/131''' ''(RM 14SM)''
: {{convert|2,060|hp|kW|abbr=on}}; redesigned "slimline" versions for the [[de Havilland Hornet]]. Engine design modified to decrease frontal area to a minimum and was the first Merlin series to use down-draught induction systems. Coolant pump moved from the bottom of the engine to the [[starboard]] side. Two-speed, two-stage supercharger and S.U. injection carburettor. Maximum boost was {{convert|25|psi|kPa|abbr=on}} gauge; or an absolute pressure of 270 kPa or 2.7&nbsp;atm). On the Hornet the Merlin 130 was fitted in the port [[nacelle]]: the Merlin 131, fitted in the starboard nacelle, was converted to a "reverse" or left-hand tractor engine using an additional idler gear in the [[Propeller speed reduction unit|reduction gear casing]].<ref>{{cite web|url=https://www.flightglobal.com/pdfarchive/view/1946/1946%20-%200165.html|title=Flight 1946, pp. 92–94.|website=flightglobal.com|access-date=22 June 2017|url-status=live|archive-url=https://web.archive.org/web/20170729061838/https://www.flightglobal.com/pdfarchive/view/1946/1946%20-%200165.html|archive-date=29 July 2017}}</ref>
{{anchor |Merlin 134|Merlin 135}}
* '''Merlin 134/135''' ''(RM 14SM)''
: {{convert|2,030|hp|kW|abbr=on}}; derated for use at low altitude 130/131 variants used in [[de Havilland Hornet|Sea Hornet]] F. Mk. 20, N.F. Mk. 21 and P.R. Mk. 22. Maximum boost was lowered to +18&nbsp;psi gauge (230&nbsp;kPa or 2.2&nbsp;atm absolute).  [[George Henry Corliss|Corliss]] throttle.<ref>Harvey-Bailey and Piggott, 1993, pp. 145, 177, 199.</ref> The Merlin 135 was left-hand tractor.
* '''Merlin 266''' ''(RM 10SM)''
: The prefix "2" indicates engines built by Packard, otherwise as Merlin 66, optimised for low-altitude operation. Fitted to the [[Supermarine Spitfire (late Merlin powered variants)#Mk XVI (Type 361)|Spitfire Mk.XVI]].<ref name="Robertson 1973, p. 145."/>
{{anchor |Merlin 620}}
* '''Merlin 620'''
: {{convert|1,175|hp|kW|abbr=on}} continuous cruising using 2,650&nbsp;rpm at +9&nbsp;psi boost (62 kPa gauge; or an absolute pressure of 165 kPa or 1.6&nbsp;atm); capable of emergency rating of {{convert|1,795|hp|kW|abbr=on}} at 3,000&nbsp;rpm using +20&nbsp;psi boost (138 kPa gauge; or an absolute pressure of 241 kPa or 2.4&nbsp;atm); civilian engine developed from Merlin 102; two-stage supercharger optimised for medium altitudes, and used an S.U. injection carburettor. "Universal Power Plant" (UPP) standardised annular radiator installation development of that used on Lancaster VI and [[Avro Lincoln]]. The Merlin 620–621 series was designed to operate in the severe climatic conditions encountered on Canadian and long-range North Atlantic air routes. Used in [[Avro Tudor]], [[Avro York]], and the [[Canadair North Star]].<ref>Flight July 1946, p. 99.</ref>