Unknown Aircraft Part (Emerson Electric Manufacturing?)

Hey Carlsberg1883 again,

Having thought about it a little more, if it is an Emerson part, the EM402 might be the inspector's stamp. The first 3 digits of the S.N. would indicate the electric drive system, generator set, or some other assembly?

Wow thank you ThomasP
Emerson Electric Manufacturing seems to be a perfect fit for the manufacturers stamp E.E.M.
Having no luck finding any info on the SN, I thought the first few digits of the SN was modelnumber.
So I might be looking for an American aircraft after all. Or any ww2 aircraft that had parts from Emerson Electric Manufacturing installed.
B17, B24, B29 had Emerson turrets, what other aircraft could have Emerson turrets fitted?

ThomasP said:

Hey Carlsberg1883,

I am wondering if the markings could be for an Emerson Electric Manufacturing (i.e. E.E.M.) product. The 7 digit S.N. (i.e. 8148348) stamp is consistent with WWII production or shortly thereafter. Exactly what the hatch might be for I have no real idea, but if it is from a WWII vintage aircraft it could be for anything from an Emerson aircraft gun turret, the turret drive system, an engine mounted electric generator, etc. I believe some Bendix products (including aircraft gun turrets) and some US & UK mixed heritage aircraft gun turrets used Emerson motors also. If it is from Emerson the EM402 on the access plate would be the product the part is associated with (i.e. something like an EM402 electric drive system, EM402 generator set, etc.). It could be later but if memory serves me correctly the S.N. system changed significantly shortly after WWII.

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Hi Thomas.
I had not thought of Emerson and yes that may be a valid response. However I have only been physically working on aircraft since 1962 and but I have been involved with many restorations. The type of QR fastener on that panel was never used on any American aircraft that I have ever seen. Only on British aircraft so, to me, Emerson is unlikely unless they were producing that part for a British aircraft.

Next 8148348 is a PART number not a serial. There is NEVER a serial on small parts on mass produced aircraft unless it is put there later by the operator.

A serial is ALWAYS proceeded by a prefix such as Serial or S/N or Ser No or Ser..

Part numbers do have a pattern but every manufacturer has their own pattern or patterns (Boeing numbers in the 40s have no apparent pattern but there must be one)

EM402 is an INSPECTION stamp and has absolutely no relation to the particular product that the stamp is affixed to. EM indicates the maker, 402 indicates inspector number 402. There may have been more than one inspector 402 but there is always a period between each person using one stamp so that it is easy to determine who was using that stamp when the part was produced.

Under your scenario every one of the thousand odd inspectors at the B-24 plant at Willow Run would have the identical stamp saying something like (FWR B-24) and that is not true. It would also be dangerous because when a defective part was found how do you determine which Inspector passed it if they all have the same stamp?
Two actual Willow Run stamps are shown below and I provided samples of various Curtiss stamps above.

Airframes said:

My mistake in not being clear - I meant that EE did not build their own design aircraft.

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Oh, my apologies, I thought that might be it Terry, not like you to go there. and, yes, of course you are right. Their indigenous types to WW2 were a few flying boats and the Wren (really) light aircraft.

Hey MiTasol,

re:"Under your scenario every one of the thousand odd inspectors a..."??

I am pretty sure nothing in either of my posts would indicate that I thought more than one inspector would use the same inspection stamp. If you can point out the wording that seems to imply that please let me know so I can be more careful in my wording in the future. (seriously)

re: "A serial is ALWAYS proceeded by a prefix such as Serial or S/N or Ser No or Ser.."

In today's world of more meticulous record keeping and regulation, you are correct where aircraft parts are concerned.

Before WWII, during WWII, and sometimes still today, however, the serial number may be stamped (whether by punch, rubber/ink, laser etch, etc.) onto the part without a SN in front of it. How it was done in WWII was upto the manufacturer and/or the purchaser. You may be right that it is just a part number, but some assemblies (and the part pictured above would be considered an assembly) that were cheap and easy to make were sometimes stamped with an assembly serial number to identify them, and no separate part number was stamped on the part. But if you looked in an actual catalog of parts there would be separate part numbers for each of the parts in the assembly.

If it matters, the computer I am using right now has a long string of letters and numbers to ID it, but there is no SN or PN in front of it. The number serves as both the assembly number (i.e. the computer) and the serial number (the production sequence number).

As far as the QR fastener goes, while the UK did buy many Emerson products during the war I do not know for sure if Emerson produced assemblies with that type of fastener or not. As with many other pieces of equipment built to UK specifications by US manufacturers, however, it would not be unreasonable to assume so.

ThomasP
Yes on modern computers and stuff the reference number or whatever the particular manufacturer wants to call it often contains the specification of the unit as well as the unit serial.
Aircraft have never operated that way.

Regarding your claim that each part has an assembly serial number I suggest you look at these Technical Drawings (blueprints) and title boxes from a number of manufacturers relating to a small number of the aircraft types I have personally worked on. Not one calls a part a serial. Every single one refers Part numbers. And yes Boeing and Airbus call them Illustrated Parts Catalogs and the standards specifying how they are laid out is commonly called ATA 100. It also specifies the name for each manual
AMM = Aircraft Maintenance Manual
CMM = Component Maintenance Manual
SRM = Structural Repair Manual
IPC = Illustrated Parts Catalog.

If you look in the manuals sections on this forum you will also find a large number of parts lists and parts catalogues - but never a serials catalog.

I would also suggest you read the attached pretty vague PDF which was all I could find quickly or find a copy of a real textbook on the subject like Aircraft Layout and Detail design OR Aircraft sheet metal blueprint reading both of which can be found on the internet.

Hey MiTasol,

Sorry, but I am not getting what you are saying.

Yes, I realize that all parts have a part number, and that part number is recorded on a blueprint and usually in a parts catalog. And sometimes the parts are shown in an assembly, such as the first blue print you posted above, with the assembly part number in the lower right corner.

I did not say that every part has an assembly number. I said that sometimes manufacturers stamp the assembly with a serial number, said serial number identifying the individual assembly just like a serial number can be used to identify an individual part. Often the assembly serial number includes a sequence of numbers that also identify the assembly part number. For the hatch(?) that is the focus of this thread the number may indicate the assembly part number and be a serial number. Or the entire number could be a serial number. Or the entire number could be a part number.

Before WWII, for the most part, aircraft manufacturers were not required to keep track of individual parts, and often did not mark the individual parts with serial numbers. But some manufacturers did so anyway, on their own initiative. The idea behind marking with a serial number is to track potential problems (such as breakage, wear rates, corrosion, etc.). If the problem with the part/assembly is in the design or manufacture, and you do not know what manufacturer the part/assembly came from and the batch the part/assembly was included in, you cannot know how many other parts/assemblies are a potential problem, or where they are (they could be installed in the aircraft, on the way to the maintenance depot, or sitting in a warehouse). When dealing with large scale production, without the serial numbers you would have no way of knowing what manufacturer or batch it came from. The problems with quality control in WWII were the impetus for the modern system of quality control (which includes tracking parts).

Today, just about every part on an airplane has a serial number marked on it, if the part has a large enough area to do so. Usually the only parts that do not have a serial number marked on them are things like common fasteners (i.e. standard screws, rivets, etc.), parts that have no possibility of failing in some way that matters (i.e. the cloth on the seats), and parts where the marking itself would potentially cause a problem. As far as I know, some parts have a part number marked on them, some do not.

I read the PDF on aircraft blue print drawing you linked above and it is well laid out, though very basic. It also says nothing about the proper method of marking an actual aircraft part, whether using the part number or a serial number.

I feel it is only fair that I should mention that I am a qualified engineer (mechanical/automotive/systems/manufacturing), fabricator (machinist/sheet metal), and draftsman, with about 40 years in the field.

If it matters, the following quote is from the US FAA's 'Production and Airworthiness Approvals, Part Marking, and Miscellaneous Amendments' regulations passed in 2009, taking effect in 2010. (For anyone not familiar with the acronym TSO, it stands for 'Technical Standard Order', in effect a minimum performance standard for specified materials, parts, and pretty much anything used on civil aircraft that could cause a safety problem - to anyone on the plane or on the ground, with the plane in the air or on the ground, to anything in the air or on the ground, ... (well, you get the idea).)

"Unless otherwise specified in the applicable TSO, § 45.15 now requires manufacturers of TSO articles to permanently and legibly mark the article with the TSO number and letter of designation, all markings specifically required by the applicable TSO, and the serial number or the date of manufacture of the article, or both. Likewise, each person who manufactures a part or component for which a replacement time, inspection interval, or related procedure is specified in the Airworthiness Limitations section of a manufacturer's maintenance manual or Instructions for Continued Airworthiness must permanently and legibly mark that part or component with a serial number (or equivalent)."

This is a link to the total document: (Federal Register :: Production and Airworthiness Approvals, Part Marking, and Miscellaneous Amendments)