W

WSBuilder

Well Known Member
Need some advice. I'm about to finish building my spars, with only the rib attach angles yet to go. Bruce at Van's says to fine tune the position of the brackets using the pre-punched skins as a guide to ensure good rivet position on the ribs. Anyone have some advice how to go about doing this? I don't have my wing jig built yet, so I assume I'll lay it out on the work table.
 
Draw centerlines on the ribs and line them up with the prepunched holes.

I would not do this until it was in the jig to prevent skewing of the structure.
 
careful....

I have an older kit. So FWIW. The pre-drilled holes in the spar did not line up well with the pre-punched skins. This was most noticable at the re-enforcing angles. If I lined up the angle with the pre-drilled holes, it shifted the rib over so that the pre-punched skin missed the rib.

Van suggested grinding the bolt heads that attach the angle brackets to give more adjustment.

You can lay the spar up on a bench. Place an angle over the hole location and then but a rib up to the angle. Mark (on the spar) the centerline of the rib. Then lay out the prepunched skin per the plans and make sure that the line of pre punched holes is lined up with your rib centerline mark on the spar.
If so, you're good to go. I was not :-(

Boy is that hard to describe in words :). I hope that makes some sense.

John
 
John_RV4 said:
Van suggested grinding the bolt heads that attach the angle brackets to give more adjustment.

You'd have thought they'd advise using 1" angle so there was more room for error?

You can lay the spar up on a bench. Place an angle over the hole location and then but a rib up to the angle. Mark (on the spar) the centerline of the rib. Then lay out the prepunched skin per the plans and make sure that the line of pre punched holes is lined up with your rib centerline mark on the spar.
If so, you're good to go. I was not :-(

Boy is that hard to describe in words :). I hope that makes some sense.

John
Click to expand...

Good description. I have yet to see how to index the skins so that I have the holes in the right location?
 
build it backwards

Try this- attach the angles to the ribs first, either by clecos or rivets. Then, when you line up the holes in the skin with the ribs, the bracket will more or less align itself.

There is about 5/16" in the middle of the rib flange where you can locate the rivet hole and still be OK for edge distance. Mark this wide centerline with a marker. When you put the rib in place under the skin, you've got that 5/16 to play with to move the rib in and out to get the best position of the bolt holes in the angle, and still have good edge distance on the rib.

Did that make any sense?

I was not aware that the 4 ever shipped with pre-punched skins. My late 90s 6 had them. This is not the current matched hole, which is often mistakenly called "pre-punched." I never liked the pre-punched skins. They made it much harder to allign the ribs, as you are finding out. At least on the fuse there are no pre-drilled holes to worry about.
 
pre punched...

The 4 has had pre punched WING skins for some years now. Unfortunately, Phlogiston builds the spars and Van punches the skins. The two weren't quite on the same page. The odd thing was that the spar holes seemed to be consistently off on both the 4 and the 6 (at that time). Should have been an easy setup change but.....

I actually had a phone converstion with Phlogiston some years ago about this topic. It's an annoying issue but not the end of the world.

John
 
Good Help - Thanks

Your descriptions and approaches are great - thanks! Lastly, am I correct that the main skins index off the inboard spar flanges? What do you use for the leading edge skin?
 
Not sure what you mean by that. IIRC the spar flange stuck out inboard of the skins by 1/4 inch or so. I'd say get the first few ribs in place with the skin on them with proper edge distance and not worry about how the skin alligns with the spar flange.

John- did the Phlogiston spar come with the skin holes prepunched as well? I was too cheap to spring for the Phlogiston at the time, but the standard spar was not pre-drilled.
 
No.. not the skin holes

No, I built my own spars also. The skin holes were not pre-punched (thank God !!). Just the rivet holes for assembling the spar, attaching ribs etc.
Brings back memories.. Some good. Some not so good :).

John
 
sprucemoose said:
Not sure what you mean by that. QUOTE]

I mean, what establishes the skin position span-wise? Attach the inboard-most rib per the drawing and then position the skin from that, then position subsequent ribs per the skin holes? What's the starting point?
Click to expand...
 
Skins

I have built several spars for RV-4 and -6's. When the skins are pre punched you have to get creative to match up the ribs. I first laid out the punched holes at each rib station by laying the spar on top of the skins ( I had one piece skins) and marked the centerline of the holes. The skin and the spar have to match up so this is your constant. Once you have the hole centerline on both sides of the spar yo can start matching up ribs to the center. to get the ribs center on the skin holes you have to push some ribs in and others come out. Ones that have to be pulled away from the 3/16 spar holes I used 1" angles instead of 3/4". This gave me a little more wiggle room to move the ribs over and still have edge clearance. Ribs that have to move in and come awful close the inside of the attach angles I used nutplates riveted to the angles. This would allow me to use a standard bolt on the leading edge skin side going through the spar and into the nutplate on the wing rib attach angles. Ones that are really close I used high tensile strength bolts with phillips heads on them to get me as close to the rib as possible. Once this is all done the skins should lay down in the center of the ribs. Some ribs that I just couldn't get perfect I would flex them in a bit when drilling the skin to grab more meat of the rib flange. The pre punch line is straight but the rib underneath is a little bowed. Since the wing is a constant chord you can cheat on this and get away with it. The RV-4 and RV-6 are what I can bash to fit, paint to match airplane. You just have to do whatever it takes to make it work. No one will ever see you ribs once the skins are on. Just make sure you have good edge clearances on the attach angles and grab lots of rib flanges when drilling them. Hope this helps. Aden Rich
 
Sometimes it takes an idiot...I mean, a village

Thanks for your help, guys! My confidence grows little by little. Just don't stray too far!!!
 
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