10-11: Aft Fuse Bulkeads and J Stiffners - Prep and Priming

It was nice to have a little break from deburring and do some riveting of the aft 3 bulkheads - but enough fun already. Back to deburring.....

The 1407 and 1408 bulkheads were edge deburred and clecod to the skin. The lower J stiffners were also edge deburred and tested for fit. A couple were a little too close to the bulkheads, so i rounded the ends and removed a little material (respecting the required edge distance of course). The battery angles were deburred previously, but i deburred the bellcrank ribs and also the forward bulkhead and test fit everything together.

SB 18-09-17 - Lower Skin Cracking

Van's released a SB related to the lower fuselage skin cracking around the end of the long J stiffners - the fix was to place a strengthening plate on the lower fuselage externally, and to tie the J stiffners into the 1408 bulkhead. Since i had everything clecod together, i elected to test fit these parts now and match drill the clips to the bulkhead:

The parts required for the SB - the countersunk plate goes on the outside skin, and therefore any holes underneath this (including the skin and stiffners, do not get dimpled). The little flat plates go on the inside on top of the J Stiffners where the reinforcement plate is located.

Clips in place ready to be match drilled to the bulkhead.

The reinforcement plate on the outside skin.

At this point, everything was ready to go so far as the lower skin assembly and what is attached to it, so i prepped and primed all these parts.

Back to riveting

I like to prime before i dimple, as it makes it a lot easier to prep the parts when there are not dimples sticking up all over the place. All the bulkhead flanges were dimpled, with the exception of the locations were a longitudinal stringer is located later on, and also where the SB reinforcement plate is located.

Before any parts can be riveted to the lower skin, the 1407 and 1408 bulkheads get riveted together. There are a few rivets that get left out of the top of the 1407 bulkhead (a longitudinal rib on the top skin gets riveted to this later).

The larger 1407 bulkhead is riveted together

The aft 1408 bulkhead and rudder cable guide is also riveted together. 

Once this was done, i dimpled the remaining holes in the flanges of the bellcrank ribs, and also the flanges (and a few on the face) of the forward bulkhead.

Next up was to rivet a bunch of nutplates to the "battery angles" - this is not where the battery is located on the -14, but this is a hangover from the -10, where the battery is located aft of the baggage compartment. I had a little helper with my riveting today which was great fun. He did a good job using the hand squeezer (even if i helped him surreptitiously). In fact there were only 2 rivets that had to be removed, and both of them were mine! Note there are 2 nutplates that have a larger hole and take a bolt instead of a screw later on (the forward 2).

Careful with the nutplate convention - K1000-3 is LARGER than K1000-08 (note, one is "3" and the other is "08" - with a zero. Ones with a zero are for that sized screw, hence K1000-06 and -6 screws, K1000-08 are -8 screws, but K1000-3 is an AN3 bolt!). Least they make it simple).

Using the hand squeezer to set the rivets on the "battery angles"

This one tipped over when the die on the squeezer contacted the body of the nutplate and moved sideways. I find the hand squeezer is a lot more forgiving for these little delicate rivets than the pneumatic one. 

Once the nutplates were on, the "battery angles" are riveted to the bell crank ribs. In hindsight, i think i should not have completed this step here - because the angles cover the lower flanges of the bell crank ribs, you are unable to backrivet these to the skins as we are able to do with all the other bulkhead flanges and stiffners. Next time i would leave them off at this point, and install them with a squeezer later on (there would be ample room once the lower skin assembly was flipped upright).

The battery angles were then riveted to the bell crank ribs. 

 Once the bellcrank ribs were done, a bunch of nutplates were squeezed onto the forward bulkhead, and the forward bulkhead was riveted to the bell crank ribs. All done with the squeezer. Then the bellcrank ribs/bulkhead assembly, was riveted to the 1407 bulkhead (the larger forward one).

Dimpling the Lower Skins

Before anything can be riveted to them, the lower skins were dimpled - i took care not to dimple the area where the SB reinforcement plate is located.

The DRDT2 and my portable dimpling support tables were used. 

A different order to do things! 

I taped over any holes which don't get rivets in this section - this includes the forward bulkhead (step 6 on page 10-13 doesn't specifically say not to rivet this, but it does not ask you to either, and I could see how you could easily make that mistake. These rivets are left out until the 2 fuselage halves are joined later).

Next up was to start riveting all these pieces to the lower skin. I decided from looking at a few blogs of people before me, so go against the order of proceedings in the plans and i completed the riveting steps as follows.

First up, i backriveted the 1486D and 1486E J stiffners (the aft most centre fuselage ones). There is no issue with fitting the 1408 (aft, smaller) bulkhead into place with these stiffners in place. The SB reinforcement plate straddles 2 holes on each stiffner (and the 1408 bulkhead as well) so i backriveted the J stiffners to the skins, and skipped the holes common with the reinforcement plate. I then backriveted the plate, the stiffners and the tiny support plates (on top of the stiffners).

My large backriveting plate flush with my workbench carpet. Not the tapes - they are to assist me in not riveting unless the plate is underneath!

Here you can see the SB parts in their place:

The smaller aft 1408 bulkhead goes between these 2 stiffners. On the outside, underneath the skin, is where the reinforcement plate is. (hence the undimpled holes). 

Obviously backriveting these is a lot easier than laying on your back to do it with a partner, but the main reason is that I felt the most forward rivet in the aft J stiffner (1486E) would have been very hard to get to, since the 1408 bulkhead leans backwards and has the rudder cable support bracket attached to it:

The top most rivet on the J Stiffner / SB support plate would have been very hard to get to with the 1408 bulkhead in place. Backriveting these alleviated this issue. 

Next up was to move the skins into the back room and begin to attach the rest of the components. Again, i deviated a little from the plans. If you look at the lower flange of the 1407 bulkhead (the larger one attached to the bellcrank ribs etc), you will notice a cutout in the lower part of the bulkhead, where the J stiffner is slid into place. Once this is in place, the J stiffner (1486C-R and 1486C-L) effectively covers over the rivet, making it impossible to get to except by using a bucking bar and mushroom set on the outside). We therefore installed the 1407 bulkhead and the bellcrank ribs etc with clecos, but before sliding the J stiffners into place, we set these 2 rivets (one on each side). These 2 rivets are shown circled in red below:

Here is an example of the rivet being hidden under the 1486C J stiffner

For the remaining sections, i had my dad come over to help with the riveting - this was a great help, and we used the homemade backriveting bucking bar he made up on his lathe (which worked great). I ended up laying on the ground backriveting upward, and he held the bar on the outside of the skin.

SB Shear Clip Troubles

The only major issue i had in this section was the riveting of the SB clips to the 1408 bulkheads. Because this bulkhead is angled, and because there is a J stiffner on one side, it was very hard to get access to this location for squeezing a rivet. I initially tried to set the AD4 rivets with a gun and bar, but because the material is so thin (and they are AD4 rivets), this really didn't work to well and the rivet tipped over (and the clips and bulkhead deformed a little). In the end i used a hand squeezer and just barely managed acceptable rivets. In hindsight, there would be no reason not to rivet these clips to the 1408 bulkheads before they are even installed. This way you could use the pneumatic squeezer and get them easily.

My first go using the gun and bar. You can see how the gun deformed the material. 

This one has got to go! You can see here how the gun has deformed the material. 

To fix the above, i removed the rivet (had to drill out using a 12" #40 bit initially, then took the head off with a 12" #30). I then flattened the deformation out with a flat set in the hand squeezer. I finally used the hand squeezer to set all 4 rivets - would have been a lot easier to do before the bulkhead was installed.

Suggested Order of Operations

As a summary of this section for anyone after me, i can recommend following this "order of operations":
1. Don't rivet the battery angles to the bellcrank ribs on page 10-12
2. Backrivet the 1486D and 1486E stiffners to the skins before flipping the whole thing upside down on page 10-12 (backrivet also the SB reinforcement plate and the support plates on top of the 1486D and 1486E stiffners).
3. Rivet the SB clips to the 1408 bulkhead.
4. Flip the bottom skin and cleco on the 1407 bulkhead / bellcrank rib / forward bulkhead assembly.
5. Set the 2 rivets as indicated above, that would be hidden under the 1486C-R and 1486C-L J Stiffners.
6. Slide the 1486C-R and 1486C-L stiffners into place, and celco on.
7. Cleco on the 1408 (smaller) bulkhead with the SB clips already riveted to it.
8. Rivet it all together!
9. Flip it upright, and use the squeezer to rivet the battery angles onto the bellcrank ribs

When riveting all this together, we did the flanges of the 2 bulkheads first, working from the centre outwards. Then i did the long J stiffners. I had to use a mushroom set and bucking bar to get to the rivets on the flanges of the bellcrank ribs, but using the method above, i think you would be able to backrivet these also.

Here are some  images of the assembly all riveted together (except for the bellcrank ribs, these were yet to be done when the photos were taken).

Next up, back to deburring and priming the side skins and side longerons.