14-02: Wing Rib Preparation

Once all the ribs were primed, each rib was fluted then the flanges were straightened.

Fluting

I find the best way to flute is to place the rib down on a flat board on the table (i ended up putting some paper down to protect the rib) and press down in the centre of the rib. You will see where the rib is bowed from the forming process. 

These are all the tools needed for the task

You can see the bow in the rib from the forming process

I start fluting in the area where the most bow is located; the depth of the flutes is proportional to the bow off the table. Eventually the rib lowers and begins to touch the table and you can see the very ends of the rib starts to lift off the table. The whole time i am holding the rib down in the centre with my free hand. Once the ends start to lift, i stop fluting and check the straightness using a long ruler along the rivet holes. This method seems to work perfectly, and removes the frustrating process where you over flute, then flatten it out, but go too far, so flute again etc.

Straightening Flanges

To make sure all the flanges are at 90 degrees, i use the wooden tool that is screwed to the bench in the photos above. This tool allows me to push the flange at every rivet hole 11 degrees past 90, which after spring back, leaves the flanges perfect. I check using a small square in a few locations (especially at the ends, or on small tabs) to make sure they are indeed 90 degrees. 

Here is a link to how the tool is built, and here is a link to how i used it on the HS ribs

Dimpling

Page 14-02 Step 3 asks me to dimple all the BOTTOM flanges of each wing rib (except the tabs under the spar flanges). 

Further on, in the Top Wing Skins section page 16-02, Step 7, it asks you to dimple all the TOP flanges of all the wing ribs, but not the ones under the wing walk doubler. 

As it turns out, these holes will remain undimpled because the wing skin holes will be countersunk at all locations which are common to the wing walk doublers. 

Knowing this, i saw no reason why i couldn't dimple all the TOP flanges at this stage (surely it is easier with them on the bench, not riveted to the spar?), however i would NOT dimple those holes on ribs 1-4 (common with the wing walk doublers). 

EXCEPT! On one rib (the inboard most wing rib on the left side) i had a massive brain fart, and dimpled the TOP flanges of this rib... DOH! 

A solution?

From reading on the forums, it seems that on other Van's designs the wing walk doublers and skins are dimpled, so i decided to do a little test. At the inboard skin / wing walk doubler locations the 'stack up' of materials would be as follows:

The skin stack up at the 4 inboard ribs is:

0.032" Inboard Wing Skin

0.025" Wing Walk Doublers

0.032" Wing Rib (or 0.025" wing rib for ribs 2-4).

So i thought i would do a little test with some scrap as above, and compare what a countersunk versus a dimpled connection would look like:

This left me with 2 options:

• Undimple all the holes on the TOP flange of the one rib where i made the mistake, or
• Dimple all the other ribs and just go with a dimpled connection for all locations!

Before making the decision, i decided to ask the mothership and got the following reply:

Must consider the nutplates

Having been given the go ahead from the mothership to dimple instead of countersink, it got me thinking about the nutplates for the wing root fairing. This part is fitted much much later in the build, however the nutplates are fitted in the top and bottom wing skin chapters. 

If you follow the plans:

• The lower flanges of the ribs are just the inboard wing skin and the rib flange (no doubler) and both these are dimpled. The #19 screw holes are dimpled at the skin and the rib, and a dimpled nutplate (K1100) is used. 
• The upper flanges of the ribs are skin / doubler / rib so are a bit thick to dimple for a #8 screw - these are therefore dimpled at the nutplate attach rivets, but not at the screw locations (a K1000 nutplate is used). Once everything is riveted in place, the #19 holes are countersunk through the wing skin and doublers to accept the dimple of a #8 screw in the wing root fairing. 

So what would happen if i dimpled the TOP flange of the inboard wing rib? 

The answer is basically as follows:

• There is no issue from Van's for the dimpling of the parts, however i can't dimple for a #8 screw dimple (the part stack is too thick where there is skin / doubler / rib), so
• All rivet locations are fine to be dimpled, but the holes where the root fairing screws go, will need to be flattened. 
• Eventually, i will match drill the nutplate rivet holes from the wing skins to the ribs. These holes in the ribs will all then be dimpled. 
• The flattened holes will be updrilled to #19, and countersunk for for a #8 screw dimple in the root fairing - if any of these crack slightly when i flatten them, there should be no issue as i am updrilling and countersinking these holes. 
• For these holes, a normal K1000 nutplate will be used, but i will need to dimple the attach holes in this nutplate to go over the dimples.

I think this plan is a sound one and will hopefully mitigate the risk of a cracked dimple, if i were to try to flatten a whole wing rib worth of dimples. 

As a side note for anyone following me with regard to the bottom flanges on the inboard wing ribs - Van's asks you to dimple these on page 14-02. However, there are a number of these holes which end up being screw holes - and will eventually be updrilled and dimpled for a #8 screw dimple in the wing root fairing. It's interesting they didn't ask you to skip these holes - now i have some that are dimpled for a #40 dimple, but will need to be updrilled and dimpled larger later. No biggie i guess.