Info Required On Parts Drawing Alterations/Mods

Adding to what PowerandPassion wrote. What he describes is how the Airspeed Horsa drawings are and I assume it’s a standard engineering practice.

Bottom left of the drawing is a box listing modifications starting with Airspeeds own and then the numbered service modifications. Therefore the drawing you are looking at has all those modifications already included into it and acts as the production version of the drawing. If you manufacture the part as per the drawing you’re doing up to that “mod level”.

Modification drawings for the Horsa (and I assume other aircraft) only detail the work that has to be done to existing parts/components to bring them up to that modification spec. Once complete you’d find the data plate on the part/sub assembly and stamp it to add the modification number to show it had been incorporated into the aircraft.

Many thanks for your replies.

The alterations/mods appear to be ones that have been made on the original drawings, and tend to give the dates they were made. A new issue number was then added to the original drawing, and in some cases, the date of the new issue number is also included.
One drawing I am currently looking at, was drawn in 1928, and the last mod is dated 1933 “mod 336”.
Sopwith’s on the other hand, seem to both alter the original drawings, as well as issue new ones-
eg- D2420. D2420/1. D2420/4, are different issues of the same drawing/part number. The original drawing being replaced by the latest issue.
Whilst say drawing D2400/1 has issue numbers 1-25 on it, in other words the original drawing was modified many times, then re-issued after each alteration.

P&P-
The Bombay is only planned to be the various panels, or possibly a cockpit section if enough info can be acquired.
The Heyford was one of my first choices regarding cockpit sections, unfortunately I was unable to find enough drawings…

Bob T.

My memory is stirring – way back in early 60’s in the Weybridge D.O. drawings would have a side column where drawing changes were listed in a shorthand note, say ‘Dim 1.23 was …’ and the drawing issue would be raised – some times the issue would be a superscript P followed by a letter. At some defined time the drawings would be frozen & issues would change to numeric & any further changes would be the subject of a Modification committee & if agreed would be assigned a number. This number would then be listed in the change column & the drawing changed to reflect the mod. The committee would also agree as to which aircraft would be affected on the production line. The modification would be described & noted for reference, but back then not sure how that was done before the aircraft entered service, probably in the Committee meeting minutes, although there should be a register listing the mods somewhere.
In service mods would again be analysed by a mods committee & a Modification leaflet created, it would also be decided if it was to be incorporated by Service, manufacturer, or working party. If still in production then assigned aircraft would carry that mod.
Thats my memory – could be faulty at my age!

My understanding, subject to illumination from more knowledgeable folk, is that a drawing with a mod listed in the title block would incorporate the mod within the new drawing. In other words, if you had an Issue 1 drawing, and Frank from the floor came back and told you that something within it was nonsense, and you modified the drawing accordingly, you would print an Issue 2 drawing, with a mod reference in the title block. The context of this is a drawing used for manufacture, not for subsequent maintenance, when Biggles would land and say that the wing tips had flutter, and the Service end user, in conjunction with the manufacturer would resolve a fix and document it in an Amendment Leaflet to a Vol II Maintenance AP.

I say this in context of digitising thousands of vintage AGS drawings ( www.silverbiplanes.com ) which were found in a stack, where earlier revisions were piled under later revisions. AGS are manufacturing drawings, sometimes revised up to 18 times. So the same AGS Issue 1 part for 1932 is not the same as the Issue 13 part for 1952. By comparing the 1932 with the 1952, you can see the modifications. No doubt there would be a separate manufacturing record detailing the nature and reasons for the mods. The point is that a 1952 AGS XXX may not be suitable for application within a 1932 design, unless the logic of the mod is understood. Upon this I anchor the contention that a drawing with mods in the title block incorporates all the latest revisions. It seems that the drawing office was kept busy re-drawing the same drawing over and over again, with changes. I cannot see it as being acceptable that an Issue 1 manufacturing drawing would be lazily issued onto the floor, with only a title block reference to a mod, with a requirement for a fitter to consult a second modification record to ensure that the part being made was correct. You can’t find too many Issue 1 drawings, because they went into the incinerator.

My interpretation of thousands of Hawker , deHavilland and Bristol manufacturing drawings is that a mod in a title block is incorporated within that drawing. It always pays to find the ‘latest’ drawing, as much as it pays to find an earlier drawing to unpick the logic. It’s not a single drawing that gives you what you need.

Recently I had to look at a humble shim for the DH Mosquito for which there was a UK drawing (1940), a Canadian drawing (1942) and an Australian drawing (1944) for the same part. By 1944 there are a lot of mods listed, and the same part is different to the 1940 version. Are you building a 1940 design or a 1944 design ? Will other 1940 parts match your 1944 shim ? How many folk died to show the 1940 version was no good ? Is the 1944 material different to the 1940 material ?

A further feature of Manufacturing drawings and documentation are Concessions, that is changes allowed on the shop floor by Works Inspection or AID.

I think you need five fingers to hold a beer :

1.Memoirs from designers, builders, operators, showing insight into design and build issues – eg the fatal flaws exposed in test flights.
2.As many original drawings/manufacturing documents/AP970 -design factors as possible, understanding that these are only part of the resolution of a puzzle.
3.Original parts as templates, understanding where they came from – is it a 1940 shim or a 1944 shim?
4.Materials knowledge – analysis of original parts, original material specs, context of use and modern substitutions.
5.Maintenance docs – for Service aircraft APs VolI-II/Amendment Leaflets

A lot of info to get a Bombay flying again, although I would prefer you did a Handley Page Heyford, Bob T !

From my own experience with Airspeed drawings with the Horsa.

The aircraft AP comes in several parts and Volume II contained an index of leaflets for modifications and some of the modification leaflets themselves. The leaflet either covers the embodiment of the modification itself including small drawings or if necessary a list of required parts, parts to be removed and the references for any additional drawings and reference sheets needed to put the modification in place.

So it may be that if you can find the full AP for your particular aircraft the mod leaflets might at least give you the necessary details. I actually found the PRO at Kew to be useful as the APs they hold are pretty complete.

https://www.rafmuseum.org.uk/research/default/archive-collection/supermarine-drawings.aspx

http://www.supermarine.net/

Presumably at some point mod and revision systems were fairly simple, but here is a general run-down. You will have a drawing office register. Revisions to a drawing that do not have a ‘form, fit, function’ change, such as correcting drafting errors that don’t cause parts to be made incorrectly, then the revision explanation may only appear in the drawing office register. Some revisions do have explanations on the drawings regardless of the extent of the change. For a minor change there may well be other records because, for example, the production office may generate engineering requests for drafting corrections or alternative materials, etc, that are sent to the drafting office.

Form, fit, function changes may be made by mod or part-number change. There are production mods and service mods. Production mods and service mods may have the same number and may have a manufacturer’s number and an RAF number. On the Vampire for example, the DH mod numbers start with a V, and if the mod is the same for production and service aircraft, the V number is the same (although the instructions on how to implement may be different). The DH issuance of the mods are through the Technical News Sheets. I’m not sure if RAF mod instructions (in the 1950s, this was Vol.2 of the AP) cross-reference to the manufacture’s number (if different), but I know that the RAAF APs of the time do list both. Mods generally are much better documented. Mods are coordinated between the manufacturer and the air force by a ‘mod committee’. And air force notes on review and planned incorporation of mods wind up in the national archives.

In the case of the Vampire, both DH and air force style of mod numbers may appear on the mod plates on the aircraft.

Apart from Vampire, I’m aware that you can find mod folders for aircraft such as the Beaufighter (Bristol and DAP, though for the former coverage is probably limited to what is relevant to the marks used by the RAAF aircraft) through the on-line search at the National Archives of Australia website. Some documents are already digitised and can be down-loaded. For earlier types, I do not know what is available, but worth searching!
https://recordsearch.naa.gov.au/SearchNRetrieve/Interface/SearchScreens/BasicSearch.aspx

Cheers.

I’m sure that they all did, but I have seen a reproduction of a page from Supermarine’s book on the Spitfire. Unfortunately the person who posted this on the internet has since died, so I cannot give you any direct reference, but I’m fairly sure that he found it whilst researching in the NA.