F-796 Reinforcement Angle Edge Distance

[tgmillso]

Hi All,

I guess this is a bit of a heads up regarding the edge distances on this angle. I had originally pre drilled the top hole on the F-796 reinforcement angle to full size per the plans as I pre-fabricated most of my components so that I could prime before the weather got cold. I later found out in the instructions that you shouldn't drill the top hole to full size until it was aligned between the fuselage longeron angles, or better still, don't drill it at all until clamped to the structure.
Once I'd modified the angle to fit (the stock dimensions were close but not perfect) I noticed that the pre-drilled hole from the F-770 forward side skin would be off center, and that the edge distance was going to be compromised. I decided that the best bet would to start again from scratch (because I just love grinding metal ) but I would not match drill them at all until they were properly nested in place. I thus made two of the most perfect aeroplane parts I have built to date, with nesting radii so perfect that it provided almost an airtight fit (ok, not that perfect but pretty close - it took me HOURS). I then clamped them in position against the F-902, which were fully clecoed in position against the side skin, longerons and F-7101. Sure enough, when I went to mark the top and bottom holes through the F-770 fwd side skin, there was still only 9/32" edge distance on both holes. I called Van's, and spoke with Joe, who seemed not too concerned. He said that because the loads on this component were mainly in compressing due to the bolt loads and not bending or tension, unlike the longerons, then the edge distance would not be a problem. Subsequently when looking at photos on other build sites, this is not an uncommon issue, so it's not just specific to my longeron geometry. Thus out of all of this, I would recommend that if you fabricate these F-796 angles, you do not drill them at all until they are clamped in position. Don't sweat the 9/32" (1.5xD for a 3/16" hole) edge distance, as there is little you can do about it regardless of how accurately you fabricate things and that assembly is predominantly in compression anyway so it is less of an issue according to Van's. Here is a page from Mike Bullock's build site that also discusses the issue.
http://rvplane.com/?categoryid=4&dayid=418
I hope this is of value to future builders.
Cheers,
Tom.

[wirejock]

Tom
Would you post this to the "Gotchas" page as well for future builders. Please.

[JurgenRoeland]

For what it's worth. I can confirm the story. I had similar concerns on my tank attach bracket. I remade them twice and either ended up with poor edge distance on the tank bracket, or bad edge distance on the F713 longeron.
I ended up with 0.202" on the F796B top AN3 hole (from edge to edge of hole) and 0.163" on the longeron for the AN3.

Here's Sterling Langrell's response: "Given the thickness of the parts and the loads involved I don’t see any cause for concern with what you have."