Spar centerline on mylar drawing

[OfTheWolf]

Can anyone tell me if centerline(s) marked on the Mylar drawing indicating the spar locations correspond to the web? or the centerline of the spars c channel in cross section? I interpret it as the web. Just want to verify before I make any more ribs……thanks.

[Frank]

My thinking is the C-channel IS the web. So the answer is yes to both questions?

[OfTheWolf]

Frank
I guess this is what I am getting at. Is the alignment A or B?
David

[OfTheWolf]

[Frank]

Definitely A.

[Frank]

Also drawing no. 3 indicates 31 in. front to rear spar, same as the Mylar.
Once I made a master template then everything was based off that.
Several builders here suggested leaving the ribs long rather than trim to final lengths when forming the ribs.
When assembling there will be trimming for cap strip stack thickness, and I think other fiddling.
I now try to take that advice generally: don't be in a hurry to cut to final dimensions.

[Frank]

Regarding "other fiddling" I'm finding it necessary to "cut the corners" of the ribs where they fit into the C-channel and meet the inside radius of the spar web flange.

[nborer]

I believe that is is "A" in your post above. Specifically, I think the lines are the centerlines of the spar webs - that is, the webs themselves are 0.032" wide, so the vertical portion of the webs will extend 0.016" from either side of the line on the Mylar drawing. Of course, there are other features on the webs as well - cap strips, flanges, attach angles, etc. - that are not represented on this drawing.

At least, that's how I made my form blocks and cut my ribs. Looking at the plan view drawing of the wing structure as well as the sheet with the ribs, and scaling them as noted, more or less confirms this interpretation (though the Mylar is the "controlling" drawing here). Granted, I have a 4-place Model B, so it may be worth a quick check with a ruler on the wing structure plan view and the rib drawings, and I think it'll be close enough to make a determination.

[OfTheWolf]

The “As” have it. Thanks for the reassurance! I made it all like the “A” drawling and they do match the 31 inch drawing on #3 (just slightly long) so I should be good after final fitting/trimming. I was mostly worried that an incorrect assumption about where the centerline was could lead some alignment problems to the wing attach points down the line…