Allison Piston Engines
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With its roots in Indianapolis Motor Speedway racing and Liberty aircraft engine production during WWI, the Indianapolis Speedway Team Company / Allison Speedway Team Company / Allison Experimental Company / Allison Engineering Company / Allison Division of General Motors Corporation / Allison Engine Company of the Rolls-Royce Aerospace Group has produced a huge array of aircraft engines and other aerospace products. Details of the Company's many products and projects appear in John Leonard's Allison Engine Catalog. Historical details are included in his presentation before the 2009 AEHS Convention.
This page is dedicated to Allison Piston Engines |
Allison Serial Numbers
by Dan Whitney
18 Mar 2011
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| Allison V-1710 Data Plate |
Allison V-3420 Data Plate (Blank) |
Serial numbers on Allison engines can be confusing; in truth they are logical, however the logic changed several times between the 1930 and 1950s.
The first Allison was Manuf. No. 1, AAC S/N 25-521, the X-4520, a 12-cylinder air-cooled 4-bank “X” configured engine designed by the Army Air Corps and built by the Allison Engineering Company in 1925. The Air Corps serial identifies the Federal Government Fiscal Year in which the funds that purchased the engine were acquired, followed by the sequential number of the engine in the total number of engines purchased by the Army during that year. 25-521 says that this was the 521th engine purchased with FY 1925 funds.
The very first V-1710 was purchased by the US Navy as their GV-1710-2, and appears to have had an Allison serial of number 1, suggesting that they restarted numbering for the V-1710. The first V-1710 engine purchased by the USAAC was AAC 33-42, Allison SN 2, the XV-1710-1, while SN’s 3, 4, 5 were V-1710-4 engines for USN airships, followed by a batch of 11 Air Corps engines purchased with FY-1934 funds (34-4 thru 34-14) that covered Allison serials 6 through 16. After these the production race was on, totaling over 70,000 V-1710s.
This scheme continued for all engine manufacturers until the beginning of FY 1944, July 1, 1943. Evidently the Air Corps found it difficult to have every engine identified by two very different serial numbers. Beginning in Fiscal Year 1944 the scheme was changed so that the manufacturers sequential production number, or serial number, was used to identify the engine, prefixed by a letter identifying the manufacturer. “A” was for Allison, “R” for Ranger, “P” for Pratt and Whitney, etc. For Allison these numbers began around A-029879, which was a 24-cylinder V-3420-13(A16L) engine.
Allison assigned their serial numbers irrespective of engine type or model. Thus their manufacturer’s number sequence includes the X-4520, V-1710, V-3420, J31 and J33 engines. For example A-074138 is a V-1710-145(G6L) and A-074337 is a J33-10 jet engine.
Included in the list of Allison serials are some 6,000 engines purchased by the British and French as “Commercial” engines. These engines predated “Lend-Lease” and as such never received USAAC serials, or model numbers (such as V-1710-39). They were known as the V-1710-F3R within Allison, and to the British. These engines were assigned both an Allison SN and a British “Air Ministry” number. These numbers can be confusing as they were also prefixed with an “A”, but differed in that there is no “dash” in the number and the numbers are six digits in the range of 199xxx to 208xxx. An example is A207498, Allison SN 7408, a V-1710-F5L purchased for a British P-38 Lightning, however neither the aircraft nor the engine were delivered to the British as they were taken over by the USAAC following Pearl Harbor. The engine was operated and overhauled twice by the USAAC during the war, and never redesignated as a V-1710-51, the corresponding Air Corps model, nor was the serial changed.
Also included are a few Allison serials beginning with "S.E." , which denotes "School Engine". These engines, which are believed to have been built from rejected, surplus or out-of-date parts, were used for training purposes.
With the above knowledge we can interpret a serial such as “AC 41-33305”, which was issued to a V-1710-27(F2R) Allison engine. “AC” means “Air Corps”, which evolved in 1942 to an “AF” prefix, which means “Army Air Forces”. The “41” indicates the engine was purchased with FY 1941 funds, and was the 33,305th aircraft engine purchased by the Army that year. Note that a similar scheme was used by the Army to identify their aircraft, however there was no attempt to match the engine SN to that of the aircraft. The aircraft SN is not shown on the engine data plate. AC 41-33305, accepted by the Air Corps on October 29, 1941 (about six weeks before Pearl Harbor), was one of the last V-1710-27 engines built, as by 41-33357 Allison was delivering V-1710-49(F5R) engines for the P-38F. At this time Allison was delivering about 20 engines per day.
Another number often seen on data plates is the Contract number. Until about 1944 all engines, and almost everything else aviation related purchased by the Army Air Corps/Air Forces, were identified by the prefix W535-ac-, followed by the contract sequence number, which reached into the five digits.
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| Allison X-4520 Restored in 2010 by the Rolls-Royce Heritage Trust Allison Branch |
