blaplante
Well Known Member
Well, here is a conundrum. RV6 build I'm helping with. Kit has bounced around. Builder A finished the fuselage including installing the top front fuselage skin (slider) to the airframe.
Builder B decided it would be a lot easier to install avionics with the skin off. So proceeded to drill out the rivets. And did not do a good job of it, especially on the longerons. Pretty much every hole along the longeron (so the first 2+ feet from the firewall) is oversized. A '4' (1/8") rivet is way loose in those holes.
Builder C now owns it.
The front top skin will be replaced.
Mothership has advised the builder to not use 1097 rivets, and not use #5 rivets. I think there wasn't a clear communication of the problem. And of course the last option was to replace the longerons. A big job. Frankly better to find a replacement fuselage IMO. Being as this is at the upper engine mount (and equally bad on both sides) this is a real ouch.
My thoughts:
(A) Review of https://www.vansaircraft.com/wp-content/uploads/2019/02/MIL-R-47196A_MI.pdf says the edge distance is OK, if the #5 rivets are NOT countersunk. So use universal head #5 rivets... bore the holes out to 5/32 and go. OK will look odd and bit 'ugly' but compared to a longeron swap....
(B) For the not so bad holes - there are the CherryMax oversized rivets (0.140") - so could even use the existing countersunk holes. Not sure how many holes will look good at 0.140".
(C) And lastly another brainstorm: adding a 0.050" shim strip between the forward top skin and the side skin. Why? Because then the top skin can be dimpled, and the 0.050 shim can be machine countersunk. So then no further dimpling or countersinking into the side skin and the longeron. Hence... could actually use #5 flush rivets, and minimize the ugly factor.
(C2) Using a shim strip could be done in conjunction with drilling new holes. The plans call for 1.25" rivet spacing on most of the length and per the MIL doc above, the acceptable inter-rivet spacing is half of that. Could install new #4 rivets on most of the length. The new top skin will hide the old holes. Unfortunately the rivets are close spaced at the engine mount and so another solution needs to happen there (about 4" at the firewall).
(D) And deep into the engineering ditch... splice or doubler on the longeron somewhere. Per https://www.faa.gov/documentlibrary/media/advisory_circular/ac_43.13-1b_w-chg1.pdf page 175 although the details on how to do are beyond me.
Builder B decided it would be a lot easier to install avionics with the skin off. So proceeded to drill out the rivets. And did not do a good job of it, especially on the longerons. Pretty much every hole along the longeron (so the first 2+ feet from the firewall) is oversized. A '4' (1/8") rivet is way loose in those holes.
Builder C now owns it.
The front top skin will be replaced.
Mothership has advised the builder to not use 1097 rivets, and not use #5 rivets. I think there wasn't a clear communication of the problem. And of course the last option was to replace the longerons. A big job. Frankly better to find a replacement fuselage IMO. Being as this is at the upper engine mount (and equally bad on both sides) this is a real ouch.
My thoughts:
(A) Review of https://www.vansaircraft.com/wp-content/uploads/2019/02/MIL-R-47196A_MI.pdf says the edge distance is OK, if the #5 rivets are NOT countersunk. So use universal head #5 rivets... bore the holes out to 5/32 and go. OK will look odd and bit 'ugly' but compared to a longeron swap....
(B) For the not so bad holes - there are the CherryMax oversized rivets (0.140") - so could even use the existing countersunk holes. Not sure how many holes will look good at 0.140".
(C) And lastly another brainstorm: adding a 0.050" shim strip between the forward top skin and the side skin. Why? Because then the top skin can be dimpled, and the 0.050 shim can be machine countersunk. So then no further dimpling or countersinking into the side skin and the longeron. Hence... could actually use #5 flush rivets, and minimize the ugly factor.
(C2) Using a shim strip could be done in conjunction with drilling new holes. The plans call for 1.25" rivet spacing on most of the length and per the MIL doc above, the acceptable inter-rivet spacing is half of that. Could install new #4 rivets on most of the length. The new top skin will hide the old holes. Unfortunately the rivets are close spaced at the engine mount and so another solution needs to happen there (about 4" at the firewall).
(D) And deep into the engineering ditch... splice or doubler on the longeron somewhere. Per https://www.faa.gov/documentlibrary/media/advisory_circular/ac_43.13-1b_w-chg1.pdf page 175 although the details on how to do are beyond me.
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