TheWright R-2600 Cyclone 14 (also calledTwin Cyclone) is an Americanradial engine developed byCurtiss-Wright, and widely used in aircraft in the 1930s and 1940s.
In 1935, Curtiss-Wright began work on a more powerful version of their successfulR-1820 Cyclone 9. The result was the R-2600 Twin Cyclone, with 14 cylinders arranged in two rows. The 1,600 hp (1,200 kW; 1,600 PS) R-2600-3 was originally intended for theC-46 Commando (being fitted to the prototype CW-20A). It was also the original engine choice for theF6F Hellcat; a running change (one which would not stop production) for the CW-20A, and one in late April 1942 for the second XF6F-1, led to the adoption of the 2,000 hp (1,500 kW; 2,000 PS)Pratt & Whitney R-2800 Double Wasp in the R-2600's place for both designs.
The following is a list of known R-2600 models. Engines would receive a three-part designation fromCurtiss-Wright. For example, "R-2600-1;" the "R" indicating a "radial engine," "2600" indicating anengine displacement of 2,600 cu in (43 L), and "1" indicating the internal model number, usually assigned chronologically. Engines accepted by the U.S. government were assigned a separate, three-partgovernmental designation. For example, the "R-2600-13" was accepted into service as the "GR-2600-B655;" the "GR" indicating a "(geared) radial engine," the "2600" indicating an engine displacement of 2,600 cu in (43 L), and "B655" indicating the governmental model number. The Curtiss-Wright designation is usually utilized more often than the governmental designation, and the U.S. government utilized both designations interchangeably and often together.
The Curtiss-Wright designation will be listed first, followed by the — when known — governmental designation in parentheses (the lack of a governmental designation does not indicate that the model was not accepted into governmental service). Engines known only by their governmental designation will be listed at the bottom.
R-2600-1 - 1,600 hp (1,194 kW)
R-2600-2 - 1,500 hp (1,118 kW); Prototype variant; Few were made.[2]
R-2600-8[4] - 1,700 hp (1,268 kW); Utilized, among other uses, by theNational Advisory Committee for Aeronautics (NACA) to testwater injection generally and in-regards to the R-2600 series, specifically. Without water injection, the R-2600-8 was capable of producing 1,700 hp (1,268 kW) at 2400 rpm for limited periods at take-off power. With water injection, testing was able to achieve 1,943 hp (1,449 kW) (maintaining the standard 2400 rpm), a 14.3% increase in power, with a fuel efficiency increase of 5%. By increasing to 2600 rpm, testing was able to achieve 2,060 hp (1,536 kW), a 21% increase in power, while providing a 4% boost in fuel efficiency. Water injection would feature heavily in mid- to late-WWII U.S. engines, including some earlyjet engines[5]
R-2600-9 - 1,700 hp (1,268 kW); Powered the initial production run of theB-25 Mitchell, the B-25 (24 built), B-25A (40 built), and the B-25B (designated the "Mitchell Mk.I" by theRoyal Air Force; 23 built). The B-25C (1,625 built) would see the -9 replaced with the R-2600-13[7]
R-2600-10 (GR-2600-B676) - 1,700 hp (1,268 kW); Experimental high-altitude R-2600 variant with an "advanced" two-stage mechanicalsupercharger, vice the usual single-stage supercharger. The 2600-10 also served as a testbed forturbo-supercharging the 2600 series (which would come to fruition with the R-2600-16). Very few were produced.[8][9] The R-2600-10 poweredGrumman's prototypeF6F Hellcat, the XF6F-1. The XF6F-2 would be powered by the developmentally similar R-2600-16. Grumman and the U.S. Navy were not happy with the R-2600's performance, which led to the 2,000 hp (1,491 kW)Pratt & Whitney R-2800 engine replacing the R-2600 on the XF6F-3 and F6F production models.[10]
XR-2600-10 - 1,900 hp (1,420 kW); Experimental version of the R-2600-10 uprated to 1,900 hp (1,420 kW), a 12% increase over the 1,700 hp (1,268 kW) R-2600-10. The XR-2600-10 powered two examples of theGrumman TBF Avenger, the XTBF-2 (1 built) and the TBM-2 (1 built). Neither the XTBF-2, TBM-2, nor the XR-2600-10 would enter serial production
R-2600-14 - 1,700 hp (1,268 kW); Powered at least one of the prototypes of theGrumman F7F Tigercat (a twin-enginedheavy fighter-interceptor), the XF7F-1. The R-2600-14 was a development of the R-2600-10 and featured "advancedsupercharging" for high-altitude performance. The R-2600-14 was developed specifically for the Tigercat project. The engines were replaced in initial production versions by the 2,100 hp (1,566 kW)R-2800-22, ultimately trading superior high-altitude performance for the R-2800-22's significantly improved low- and medium-altitude performance.[14]
R-2600-15 - 1,800 hp (1,342 kW); Planned to power the XB-33A, a prototype model of theB-33 Super Marauder (itself a high-altitude version of theB-26 Marauder). The project was cancelled, and neither the prototype XB-33A or production B-33A were ever built.[15]
R-2600-16 - 1,700 hp (1,268 kW); Similar to the R-2600-10 & -14, the -16 was tuned for high-altitude performance; The -16 was designed to be mounted alongside aturbo-supercharger system. The -16 would power the secondGrumman F6F, the initial XF6F-2.[16] The XF6F-1 and XF6F-2 was found to be lacking in performance; The XF6F-2 designation was re-used on a third prototype, anR-2800-powered XF6F-2. The R-2800 would carry-over into the final prototype, the XF6F-3, as well as production models.[17]
R-2600-17 - 1,700 hp (1,268 kW); May have powered aVultee A-31 Vengeance (or A-35) variant. May have also powered one of the C-55 prototypes, a derivative of theC-46 Commando[18]
R-2600-17A - 1,750 hp (1,305 kW); Uprated R-2600-17
R-2600-19 (GR-2600-A5B) - 1,600 hp (1,194 kW), 1,660 hp (1,237 kW)
R-2600-20[4] - 1,700 hp (1,268 kW), 1,900 hp (1,420 kW)[19]
R-2600-21 (GR-2600-A5B) - 1,500 hp (1,118 kW), 1,600 hp (1,194 kW), 1,700 hp (1,268 kW); Experimental R-2600-19 engines modified with new carburetors and cylinder baffles. -21s were "converted" back into -19s and retained their governmental GR-2600-A5B designation
R-2600-23 (GR-2600-A5B-0) - 1,600 hp (1,194 kW), 1,675 hp (1,250 kW); The R-2600-23 required 91octane fuel (other R-2600 models accepted higher-octane fuel).[26] The -23 was normally rated at 1,600 hp (1,194 kW) atsea level while at take-off power, but could be "uprated" to 1,675 hp (1,250 kW). These "uprated" -23s were utilized in theDouglas A-20G Havoc, the most-produced (2,850 built) A-20 model[27]
R-2600-28 - No known information; Occasionally the 2,100 hp (1,566 kW)R-2600-22 is referred to as the R-2600-28
R-2600-29[4] - 1,700 hp (1,268 kW),[30] 1,850 hp (1,380 kW);[31][32] Likely the most-produced R-2600 variant, with at least 17,848 produced. The R-2600-29 powered theB-25C and -25D as well as theA-20G and -H. AnR-2600-29A is also referenced in various manuals and reports as the powerplant of the twin-engineTB-25N medium bomber trainer aircraft. The R-2600-29A is referenced interchangeably with theR-2600-35.[33]
R-2600-31[4] - 1,700 hp (1,268 kW); TheLockheed B-34 Ventura, originally powered by theR-2800, was chosen to be converted into a large, armed reconnaissance and observation aircraft, designated as the "O-56." This was later changed to "RB-34B," then to "B-37," and finally to "RB-37." 500 RB-37s were ordered, but the contract was cancelled after 18 were delivered. As the RB-37 was not expected to carry bomb loads, it was felt a lower-powered engine would suffice; The 2,000 hp (1,491 kW) R-2800 was replaced by either the 1,700 hp (1,268 kW) R-2600-31 or, with early models, the R-2600-13
R-2600-34 - 2,100 hp (1,566 kW); Two R-2600-34s served as the powerplants of the early versions of thePBM-5 Mariner, before the switch-over to theR-2800[35]
R-2600-35 - 1,700 hp (1,268 kW),[36] 1,850 hp (1,380 kW);[37][38] AnR-2600-29 orR-2600-29A modified with a Bendix Stromberg PR48A4carburetor. The -29, -29A, and -35 may have been considered interchangeable to a degree.[39]
GR-2600-A71 - 1,350 hp (1,007 kW); May have been a simplified name of theGR-2600-A71-3[40]
GR-2600-A71-3 - 1,600 hp (1,193 kW); Early R-2600 model, developed in late 1938 or very early 1939. Powered theNorth American NA-40B, a twin-enginemedium bomber of which only one was built. The NA-40 would lead the toB-25 Mitchell. May also be referred to as theGR-2600-A71[40]
^"Teesside Aviation News"(PDF) (Press release). Teesside, UK: Teesside Aviation Society. 1982-11-01. Retrieved2021-04-06.... for the RAF, 19 were experimentally fitted with R-2600-4-53 Cyclones ... engines of 1650 hp.
^abcdefghParts Catalog; Models R-2600-8, 8A, 12, 13, 20, 22, 29, 31; T.O. 2R-R2600-4 (Formerly AN 02A-35H-4) (Report). Marion, Indiana, USA: Secretary of the Air Force and the Chief of the Bureau of Aeronautics via Central Press, Inc. 1951-09-13.
^Thomas, Cleaver (19 Oct 2017). "The Pacific Theater".Pacific Thunder The US Navy's Central Pacific Campaign, August 1943–October 1944 (1 ed.). Bloomsbury Publishing. p. 45.ISBN9781472821867.The XF6F-1 was powered by the Wright R-2600 14- cylinder Twin Cyclone radial engine. After meeting O'Hare, Grumman suggested a power increase which ... put the super new Pratt & Whitney R-2800 ... in the second prototype.
^"Wright Cyclone R-2600-13 (GR-2600-B655), 2-Row, Radial 14 Engine". National Air and Space Museum. Archived fromthe original on 2024-08-16.R-2600-13 powered the: Brewster SB2A-4; Curtiss P-37; Douglas A-24A/B/C; Martin A-30A/B; North American XB-25E/F/G, B-25C/D/G/H/J, CB-25J, TB-25J, and F-10; Northrop A-35; Lockheed B-37; Short Brothers Stirling; Vega O-56; and Vultee A-31A, Vultee XA-35A, A-35A/B. A total of 13,494 R-2600-13 engines were built between April 1941 and January 1944... Power rating: 1,268 kW (1,700 hp) at 2,600 rpm...
^Hal Andrews (1998)."Naval Aircraft; F7F Tigercat"(PDF).Naval Aircraft. Archived fromthe original(PDF) on 2023-11-29.Both the Army and Navy planned to use Wright R-2600 engines with advanced supercharging... XF7F-1 engineering design began in late spring 1942, with mockup inspection in September. By summer 1943, production was being negotiated and a major engine change from Wright's R-2600 to the Pratt and Whitney R-2800 eliminated supporting an engine model unique to the F7F...
^White, Graham (2001).R-2800: Pratt & Whitney's Dependable Masterpiece. Warrendale, Pennsylvania, United States: Society of Automotive Engineers. p. 508.ISBN9780768002720. Archived fromthe original on 2025-04-01.XF6F-2*... This designation was used twice... Intended to be powered by turbocharged version of Wright R-2600-16, instead re-engined with R-2800.
^The Illustrated Encyclopedia of Aviation. Vol. 20. United States: Marshall Cavendish Corporation. 1979. p. 2304. Archived fromthe original on 2025-04-01....clean design was maintained in the Vengeance, though the cranked wing panton made some observers think (wrongly) that the aircraft's centre of gravity had given problems. Power was provided by a 1,600hp Cyclone R-2600-9 or 1,700hp R-2600-17.
^Dorr, Robert F. (1997). "Variant Briefing: Martin Flying Boats: Mariner, Mars and Marlin".Wings of Fame.7. London: Aerospace Publishing: 125.ISBN1-874023-97-2.
^Aircraft Listing: July 1, 1949 (Report). United States: U.S. Department of Commerce, Civil Aeronautics Administration. 1949-07-01. p. 68. Archived fromthe original on 2025-03-30.R-2600-23... 91 Octane... Sea level... 1600 hp...
^Johnson, E.R. (2012).American Attack Aircraft Since 1926. United States: McFarland, Incorporated, Publishers. p. 67.ISBN9780786471621. Archived fromthe original on 2025-03-30.The A-20G was the most widely produced version of the series, a total of 2,850 being built at Douglas's Santa Monica plant in 1943 and 1944. Influenced largely by Pacific-based A-20As and Cs, the G model introduced a solid nose equipped initially with four fixed 20-mm and two .50-caliber machine guns, along with R-2600-23 engines uprated to 1,675-hp.
^Griffiths, Harold (1944).Mathematics for Aircraft Engine Mechanics. United Kingdom: McGraw-Hill. p. 317.R-2600-25 has a 100 per cent normal rated hp. of 1,350 at 2,300 r.p.m. with a manifold pressure of 37.0 "Hg at 5,800' altitude...
^Aircraft Engine Listing, May 15, 1950 (Report). United States: U.S. Department of Commerce, Civil Aeronautics Administration. 1950-05-15. p. 42.R-2600-29... Take-off... HP... 1700...
^Wilson, Stewart (1998).Aircraft of WWII. United Kingdom: Aerospace Publications. p. 116.ISBN9781875671359.PBM-5 — two 2100hp (1566kW) R-2600-34; four-bladed propellors.
^Aircraft Engine Listing, May 15, 1950 (Report). United States: U.S. Department of Commerce, Civil Aeronautics Administration. 1950-05-15. p. 42.R-2600-29... Take-off... HP... 1700...
^Wilson, Stewart (1998).Aircraft of WWII. United Kingdom: Aerospace Publications. p. 116.ISBN9781875671359.PBM-5 — two 2100hp (1566kW) R-2600-34; four-bladed propellors.
Andrade, John (1979).U.S.Military Aircraft Designations and Serials since 1909. Midland Counties Publications.ISBN0-904597-22-9.
Bridgman, Leonard, ed. (1998).Jane's Fighting Aircraft of World War II. London: Studio Editions Ltd.ISBN0-517-67964-7.
Gunston, Bill (2006).World Encyclopedia of Aero Engines: From the Pioneers to the Present Day (5th ed.). Stroud, UK: Sutton.ISBN0-7509-4479-X.
Thruelsen, Richard (1976).The Grumman Story. New York: Praeger Publishers.ISBN0-275-54260-2.
White, Graham (1995).Allied Aircraft Piston Engines of World War II: History and Development of Frontline Aircraft Piston Engines Produced by Great Britain and the United States During World War II. Warrendale, Pennsylvania: SAE International.ISBN1-56091-655-9.
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