Navy Piston Engine Dash Numbers

[airplane176]

I generally understand the basic Army/Navy piston aircraft engine designation system as applied from the late 1920s. Odd dash numbers 1, 3, 5... were Army ordered or developed engines. Even dash numbers 2, 4, 6... were Navy ordered or developed engines. This is simple enough. The Army engine dash numbers in most all cases proceed in rough chronological order. For example, the R-1340-1, -3, -5... up to the R-1340-61. This all makes sense to me. On the other hand, the Navy R-1340-6 of the NJ-1 and SNJ-1 seems out of place, being later than the -8 and -10 of the F4B. Then there are two different R-1340-48, the 450 hp model of the P3M-1 then the 600 hp version from the HOK-1. I cannot believe that these are the same engine. The experimental Wright R-1510 numbering is another puzzle. There is a single Army version, the XR-1510-1. The Navy versions that I have found are the XR-1510-8, XR-1510-12, R-1510-26, -28, -92, XR-1510-94, and R-1510-98. I understand there were only about 35 R-1510/R-1670 engines built, so why all of the jumping around? I could see a few unbuilt experimental models with assigned designations, maybe XR-1510-2, -4, -6.

It seems to me that the Navy did not use the dash number system until the late 1920s, preferring to use the manufacturers letters such as R-1340-A, B, C..., then arbitrarily starting numbering. Examples are XR-1830-54, R-975-20, R-985-38. These are the lowest even numbers that I have found. Sometimes it appears that numbers were backfilled such as R-985-2, -4, R-1535-2. The systems seem to line up better beginning about 1941, and then the Navy reuses numbers postwar like the aformentioned R-1340-40.

Does anyone have the techhnical orders, or other official paperwork to explain these anomilies? I have also never seen an official document for the beginning of the engine desination system in the mid-1920s.

Thank you.

Roger

 

[Piper106]

As far as i know, the dash numbers were assigned in date order when the government contracts were issued.

In some cases, a contract was issued for a version that was still on the drawing board and which everyone hoped would be the 'next great thing' when the design work and development was completed in 2+ years. A few months later the government ordered an otherwise well extablished version that needed a new 'higher' dash number (for example because it had a slightly different magneto or carburetor than the current dash number) but which would be delivered to the aircraft plants a couple of months.

There are several good examples in Graham White's book on the R-2800. You will see some 'late' C series engines with low dash numbers and some 'earlier' A and B series engines with high dash numbers. For example you have the C series engine with all the late war 'goodies' used in the F4U-4 Corsair has a -18/18W identifier, while there were 'plain Jane' B series engines planned for the Lockheed PV2 patrol plane that had a -26 identifier.

You see similar 'early' engines with high dash numbers in Dan Whitney's book on the Allison V-1710.

There are also examples of contracts assigned dash numbers, then before the engines were delivered the contract was cancelled, or the requested characteristics were modified by the government, and the engines were delivered with the new characteristics and the new dash numbers.

 

[Piper106]

Same thing on the Army side. The R-2800-57 was a C series engine installed in the P-47M and P-47N. The R-2800-75 was a B series engine for the C-46.

I would also suspect that during the cash poor early 1930s, the Navy was only able to get money for a 'new' higher dash number engine. There would be no money for continued development or production of 'last years' dash number. I would start the betting that dash numbers were 'churned' for the slightest change (or maybe even no change) to keep the money flowing.

 

[ohogain]

An interesting site that I found:

ModDesig

lists most of the engines used by the USAAC/USAF up through 1949. It is an interesting read on how minor the change had to be to generate a new dash number, answering one of my questions as to why there were so many dash numbers extant. It is also interesting to note how, as Piper106 points out, newer versions of older models had higher dash numbers than newer models of the same engine.

If someone knows of a similar site for Navy engines, I would love to know about it.

 

[fubar57]

Thanks for the link ohogain.

Geo