How about this?
Thanks all for your input and concern on this.
I will agree with all of you, this rollbar attachment IS pretty sad. Before buying the project, I had a tech counselor look at it and, with the exception of the roll bar attachment and the canopy fit, the workmanship is very good (this problem was NOT noted during the tech inspection). I did have to replace a few bad rivets here and there. As I said, the canopy was cracked, so I'm replacing it anyway - I may glue it. Don't worry too much about me, I'm a mechanical engineer and understand structural inegrity and it's importance on a 7A roll bar that I hope to operate off my own grass strip
This WILL be done RIGHT, one way or another.
Unfortunately, the issue is bigger than just the rollbar, because the window is clecoed to the rollbar, and that's clecoed to the skin. So changing the rollbar will mean replacing these items too. To refresh your memories the canopy was cracked on the last rivet hole (I think that's why the guy sold it) and I already have a new canopy, which is still new in the box. The back window from the first canopy is OK, clecoed in place.
Here's what I'm thinking (further comments are appreciated):
1. I can't lower the roll bar the 5/16" that's required per the plans without scrapping the currently clecoed tip-up back window over the baggage compartment (or the adjacent skin), and that is not cracked so I'd prefer to keep it. Question is, what ramifications might exist for the fit of the rest of the currently clecoed together canopy frame that I'll be re-building??? If I can't make that work with the additional height, there's no point trying to save the back window and / or interfacing skin.
2. I think I'd like to make new roll-bar attach brackets that are taller than the originals (2.5" vice 2"). The inner attach brackets are OK, it's just the outer ones where edge distance rules-of-thumb are violated. Because the fuselage skin dictates the locations of the forward holes in these outer brackets, and they're drilled already, those holes can not be moved without redoing the rear window or skin. I am thinking of adding a 1/8" doubler 6 or 8 in. long inside the roll bar riveted in 4 or 5 places above the bolts (Thanks Craig). This would help transfer the load from the brackets to the roll bar despite the edge distance problems on the forward bolts. I would also squeeze the rollbar together at the bottom prior to riveting so that the two halves don't spread out at the bottom as they do currently. I would make brand new AFT holes in the outer brackets and put them 1/2" higher (BETWEEN and ABOVE) the original holes so that edge distance rules are adhered to. Hence the need for a 1/2" taller bracket. Finally, the new external brackets would be WIDER than the originals, but ONLY on the VERTICAL flange. The HORIZONTAL flange UNDER the roll barwould remain the same width. This will allow the fore and aft edge distance to increase. The fore-aft edge distances for these countersunk holes on this bracket are too small IMHO, even with the rollbar halves spreading apart near the bottom, which I'm going to eliminate. So I think I'd make the bracket's vertical flange 1/8" wider - any reason not too, weight excepted?
3. I would move the new external brackets inboard, so that the vertical flange doesn't have to be shaved down to wafer-thin thickness for the side-skin to fit nicely. This would require a slight bit of pre-lead on the roll bar, but less than 20 pounds from my estimation pushing on it and seeing how it flexed. Shaving the vertical flange is really questionable to me, maybe it's not supposed to be shaved as much as mine are but if you look at the picture, its SCARY how little material is left. I'd rather move the bracket inboard, keep it full thickness, and shim with custom-made countersunk washers to the skin. This would be a LOT stronger, and not much more trouble. I could find nothing in the plans / manual where it says to shave it anyway - did I miss it?
4. As far as the S-bend in the roll bar, I don't think I could bend this out of it, and if I could, again I'd have to scrap the window as its already drilled but not riveted to the roll bar. Only question is, would the interface and "fit" to the tip-up frame not work or be ridiculously difficult? Since I haven't done one of these, I'm not clear on the flexibility of adjustment there might or might not be - shimming, fit of seals, etc. I'd estimate that the rollbar might have 3/16 or 1/4" of bow to it maybe, tough to say.
If none of this works, I can always buy a new one, and cut a new rear window from the new canopy which is as-yet untouched!
So, what do you guys think of this approach? What haven't I thought of? Thanks again for your thoughtful comments and assistance.
Noah Forden
RV-7A Finishing
Rhode Island