# Production Terminology Of WW2 Era Aircraft



## syscom3 (Feb 17, 2010)

Lets collect some info on what constitutes production model terminology and what was decided on to be a block change of WW2 era aircraft. Such as "P38L-5-LO". What did it mean? What were the major changes? And how did different countries assign model and block numbers.



PRODUCTION BLOCKS vs FIELD CHANGES

Robert A. Mann

What is a production block – besides a part of the model number? Irving B. Holley Jr., in Buying Aircraft: Materiel Procurement for the Army Air Forces, defines it as:

“The block system was nothing more than an arbitrary pattern of model identification. Thus a B-24J, after being equipped with a different type of life raft and improved sights on the waist guns, might be designated the B-24J-15 to distinguish it from the B-17J-10, the last production block without those additions”

“The series letter “J” would be changed only when there were modifications affecting major alterations in structure of the primary armament of the aircraft.”

To illustrate the need for what Holley called “.. the closest kind of production control.”, in the case of the B-29, there were 1,174 engineering changes introduced even before the first plane was accepted by the USAAF.

Some 900 of these were last minute modifications growing out of flight testing and training aircraft flights

The five digit jump in block numbers, assigned at the factory, was built into the system to accommodate field modifications not ‘large’ enough to merit a new block number for changes to all planes not incorporated at the factory . Thus a field relocation of antenna attachment points and the installation of a new antenna location is certainly a change of form, fit or function to the –15 production block described above, and so would be described as block –16. The author has seen photographs of B-29’s at an overseas base with the model painted in the Technical Data Block as B-29-16-BW, thus indicating some change(s) had been made to the plane beyond the –15 level.

But let us consider the situation with the early B-29’s sent to the CBI. Two situations for which the author has never seen an explanation are evident: (1) to what block number were the modifications done in the “Battle of Kansas” assigned; and (b) how, and to what block number(s), were the field modifications done in the CBI assigned.?

An aspect not given not widely considered is the relationship of individual aircraft model designation, and in particular the block number, to the activities of the Logistics Command in regards of the delivery of replacement parts.

Let’s examine a hypothetical situation within the fifty airplanes of the B-29-5-BW production block. Field modifications are done to the cowl flaps for improved cooling by the installation of locally manufactured shortened cowl flaps. Ditto the field installation of relocated antenna mounts. Thirdly there was the installation of new locally designed doors for the camera hatch.

Were drawings made of fabrication and installation of these modifications? Were new block numbers assigned? By who? Were drawings entered into the Logistics pipeline? Again, hypothetically, depending on the timing of the changes, these could be block numbers –6, -7 and –8. What happens if two more dash numbers to the –5 block were developed. That would be –9 and ?????

With time to incorporate changes in the production line, said changes can be incorporated in “five digit “ block numbers. There is no upper limit. The B-24J’s produced at the San Diego Convair plant go up to B - 24J - 210 – CO. But a high number of field modifications with the ‘interior’ block numbers


----------



## FLYBOYJ (Feb 17, 2010)

Very Cool Sys - thanks for posting...

Along with this there is usually a document that will list production serial numbers to the changes or mods done along the assembly line. Lockheed used simple 4 digit numbers usually found on the nose of the aircraft. If you were to go to this document it would tell you that (for example) P-38J-5-LO 5273 should have changes 1 - 50 incorporated in a "Production Line Change Document." Production planners will usually issue these changes at a predetermined aircraft number and usually the inspectors will follow up to ensure the line change was followed through. When there is a substantial change to the basic design, the manufacturer and customer will determine whether the letter designator will bump up as well (going from a P-38A to P-38B for example. The article Sys posted goes on to explain further codex's...


----------



## syscom3 (Feb 17, 2010)

Was this common for all the US aircraft assembly plants? Or did different manufacturers have different ways of determining block and line modification criteria?

Any difference between AAF and USN?

Flyboy ..... if an AC was field modified from one block up to another block, did the local command have authority to remove the builders plate and update it?


----------



## FLYBOYJ (Feb 18, 2010)

syscom3 said:


> Was this common for all the US aircraft assembly plants? Or did different manufacturers have different ways of determining block and line modification criteria?
> 
> Any difference between AAF and USN?
> 
> Flyboy ..... if an AC was field modified from one block up to another block, did the local command have authority to remove the builders plate and update it?



As far as I know each manufacturer had a little different system. If I remember right Boeing had a system called "blue lines" and "green lines," all production line modification paperwork was placed on a board and when completed taken down and then placed in a big book.

As far as removing data plates - I don't believe that authority was ever given, however mod status was definitely put in the aircraft logbooks.


----------

