#8 Tank Attach Countersinks (Main Spar)

[Daniel S.]

Morning All-

I'm Getting some differing opinions on this topic and wanted to see what the gereral VAF community opinion is.

Heres the deal. I’ve been avoiding countersinking the main spar for the #8 Tank attach screws till I had some primer mixed up to spot prime. I’m a little confused as to the depth of these counter sinks. Normally, they’d be cut to accept the skin dimple. But the excerpt from the plans (below) makes this sound like they should match a #8 screw head (flush to the spar flange) and not the dimple. What is the proper proceedure here?


"Machine countersink (trying to dimple the 0.063 thick spar flange will result in severe distortion!) the platenut attach holes in the W-706A spar flange. See Section 5E. Use a microstop countersink with a #30 pilot to countersink the (screw holes in the spar to the proper depth for the #8 screw. The pilot will center in the countersunk platenut well enough to keep the hole round and concentric. (Tip: cut a #8 screw short so that it enters the K1100 nutplate easily and use it to gage the depth.)"

Thanks All!

 

[Lemmingman]

I remember getting slowed down on this too, Daniel. Check out this thread by Rudi Greyling not so much for the procedure, which I am sure is great, but for the dimensions of the holes that he observes. I used his measurements and just finished my second wing leading edge/tank and these numbers are spot on. Its a good thread for those getting ready for the exciting and mentally stimulating task of countersinking the holes in the spar.

http://www.vansairforce.com/community/showthread.php?t=2740

 

[rapid_ascent]

I used Rudi's method and it worked like a charm. It takes some time since there are so many holes, but it worked out great. As far as the priming I tried to dab the holes initially and finally decided to mask the flange off and spray the whole edge. Much faster and it looks better too.

 

[Daniel S.]

My only issue with using this method is that I already have all of the Plate nuts installed, as I was following the plans step by step. I'll need to used the van's method (using the plate nuts as the pilot hole). I guess I should have researched this step a little better. IMHO... Someone should just revamp the Van's -7 plans & incorporate all the awesome tips & tricks listed out here in VAF land! This thread definately answered how deep to CS. I'll match to the #8 screw head + a notch or two on the micro stop & shoot the whole flange with primer. I really like the idea of masking off the mating surfaces (spar & doublers). Wish I had thought about that one earlier when I counter sank the plate nut rivet holes!! Thanks guys & thanks VAF!!!

 

[Hornet2008]

In the RVator book that comes with the kit there is a distance across the counter sink. I set up on scrap and used this method. From memory 0.178" but my memory ain't that great.