Here is a simplified drawing of the Avro Lancaster wing spar structure: two beams top & bottom joined by a sheet. Generally in the Avro engineering drawings it is referred to as the ‘web’. A better interpretation for ‘web’ is the sheet itself with its vertical top hat stiffeners (not shown) joining the two beams.
Avro drawing O.2362 gives the general arrangement of the joint between the wing spar web and the undercarriage support beam. Here is a front view photo of the port & starboard inner UC support beams attached to the front web. The inner support beams are mirrored each by a corresponding outer support beam whose location is given by the red outlines.
Here is a segment of Avro drawing O.2362. I have not shown more of this drawing as I believe the whole drawing is far too big to allow detail to be read if the image is reduced in size to fit normal screen sizes.
Showing a plan view section of the join between the bottom beam of the web spar and one of the four UC support beams, the reference here is to a shim 13/E.4560 between the two surfaces and the comment which I read to be “Not reqd when 7G web is used”. The last amended date of O.2362 is 23-2-45. So the design modification to the spar webs referred to as “7G” occurred on or before this date.
The drawing of the shim not required is given by Avro drawing 13/F.4560. Note, it is “F.”, not “E”. The “E” identity code refers to “Cowlings and Fireproof Bulkheads” whereas the “F” identity code refers to “Wing Structure”. The shim is 20G Alclad, i.e. has a thickness of 0.032 inches.
In my original interpretation of ‘7G’ I forgot about the standard sheet metal rhickness gauge and thought that it referred to the maximum acceleration limit for the structure; the intention being to strengthen the wing structure against violent combat evasion manoeuvres such as the corkscrew.
So, simply, the most probable interpretation of ‘7G’ is the standard gauge thickness of the web sheet as being 0.1443 inches.
Sorry, but it was fun!
Mike
By: Piston - 25th September 2015 at 21:24
Yes John, it’s a simplistic term used when SWG (standard wire gauge) doesn’t seem apt for sheet materials.
By: John Green - 25th September 2015 at 21:08
Is ‘g’ a common abbreviation for ‘swg’ ?
By: MikeHoulder - 25th September 2015 at 18:20
Mike, here’s the point, it was my mistake:
I forgot about the standard sheet metal rhickness gauge and thought that it referred to the maximum acceleration limit for the structure
I had on my mind the stresses/accelerations of violent manoeuvres and so interpreted it in accordance …
Also I was including the beams as well as the sheet as part of the ‘web’. To which swg would not apply
Stupid, but it happens.
Mike
By: Bluebird Mike - 25th September 2015 at 17:27
Am I missing the point to all this? The drawing clearly means 7swg, i.e the gauge of the required material. So?
By: Vega ECM - 25th September 2015 at 16:22
Sorry, but it was fun!
Mike
7g is that ultimate or limit or proof?
7g as an ulitimate (on set of rupture) feels about right -what does Avp970-00 require?
Then Limit ie no permanent distortion would be 5g and proof ie cleared operational envelope is 4.5g
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September 25, 2015 at 4:06 pm