Engine mount bracket fit - 3 hours

One of the items I notice some have struggled with on other build logs was to get the correct placement and fit between the engine mounts and the longerons. Seems the margin for error here is a bit tight. So as I typically try to do on parts, I marked out edge distance on all of the engine brackets first. Here I used an edge distance of about 0.025". It gives me a bit of a buffer rather than using the Mil-Spec minimum of 0.0219" (The buffer is always a good thing).

After marking things out. I placed the engine mounts to check fit (but not to drill just yet). Initially the fit is ok, its just on the line...



I've used some clamps to get things help in place. When I really look at it, it looks like things can get just a tiny bit better. There is still a small gap between the aft most flanges of the engine mount that I can tighten up. So I dug out another small clamp and clamped the mount vertically as well.

This snugged up the fit just a bit better and allowed for much more edge distance. Looking really good now. Plenty of material to work with on those mounts.

Fitting the firewall - 2 hours

I need to set the firewall in place to begin checking fit and alignment, but I was scratching my head on how exactly I was going to do this. Borrowing an idea I seen on another build-log, I used the ironing board (with some help) to get it to the right height.

At this point I can start checking center, alignment, etc. I still need to trim back the longerons just a bit but I will wait until that becomes critical.

Drilled the longerons fwd of F-704 bulkhead - 6 hours

A big item on my to-do list is to finish drilling the longerons forward of the F-704 bulkhead. I've put this off for a couple of days thinking how best to do this. I want to ensure that the longerons are even on both sides. I fear that if I just go ahead and drill them they may not be exactly aligned, even crooked. I finally decided that I need to temporary install the firewall. I used the ironing board to support the weight and clamped/secured it.

I drew centre lines all down the firewall and down the centre of the bottom skin.

Then I set up the laser level and began checking everything. Some very small adjustments, but I was happy that both longerons where sorted. This was a very tedious process I might add. I began drilling from the F-704 bulkhead forward alternating sides. I finally reached the #30 holes and I marked them with a sharpie to double check edge distances. All good!



I finished drilling the longerons. Now I just need to trim them back 3/4" from the forward edge of the skin. I'll save that for tomorrow.


I need to get the F-904L attach strips cut. Reading other build logs edge distance is a possible concern here so I just used the full 3" lengths that came with the kit. Ill drill them first and then cut after to ensure edge distance is not compromised. I checked the fwd pieces and marked them to be cut at an angle so that they will nest into the longeron.

I started to carefully mark and drill my holes. I also rounded the bottom edges to nest into the radius of the longeron.

As you can they are very long. The aft pieces will allow me to drill an extra cleco at the top.   I will trim them down. The blue line represents 2 1/16" however that is too close to the rivet hole so I scrubbed that line. I'll do some checking on build logs first, but I will likely leave a good amount of edge distance and go a bit longer than the 2 1/16" dimension.

Worked on the firewall - 2 hours

Very small day on the build today. I'm getting to the point where I need to get the firewall riveted so that I can install it on the fuselage. Its been sitting for quite some time now as I accidentally counter sunk a hole I wasn't supposed to back when I was working on it. I ordered the new part, and put the bulkhead aside to continue with the fuse and hadn't needed to look at it until now.
So I took care of it. I match drilled and counter sunk the new angle.

The only thing I need to figure out is do I seal anything with firewall sealant. For example...Do I apply a layer of sealant between the firewall and angles to provide an extra layer of protection? Do I prime the angles? I tried to do some research and basically I figured out that its darn near impossible to get CS 1900 sealant in Canada. I think I may have to drive to the States to pick some up. Aircraft Spruce only sells the 3M fire Barrier 2000+ which is not as good as CS 1900, but given the circumstances. My choice is narrowed down to using a thin layer 3M fire barrier between the angles and the firewall. Guess I need to put in an order.   

Drilled longerons to F-704 Bulkhead - 3 hours

Spent a few hours drilling holes....Lots of holes.

Drilled all of the longerons from where I left off yesterday all the way forward to the F-704 bulkhead. I'm really glad that I have the small drill housing/side which allows me to drill perpendicular to the work. I'd hate to drill these free hand through that thick material. (The blue x indicates a tab with a predrilled hole. In order to not accidentally oblong those holes when drilling, I partially drilled the longeron and will finish drilling when the longeron is taken off the fuselage). 

Slowly but surely I finished up to the bulkhead.

Removed skin ripple and started drilling the longeons - 8 hours

So I started in again on trying to fit these side skins. Not much helpful information on the forums on how to solve this issue. I just decided to spend the hours figuring it out. What I did learn was everyone seems to cleco the F-704 and F-705 bulkheads first. So that's what I did.
I then spent the next few hours trying to get the aft end of the skins sorted. Firstly I decided to try to get the left conical bend a tad tighter. Comparing the two skins side by side, I see the left didn't quite match the right side...Maybe that will remove some ripple. Still no crack so we are good!

I finally was able to get the side skins on!!!I'll spare you the long winded story but what solved it for me was that I used a 4th sawhorse placed under the F-705 (rear spar bulkhead). This is something I did on the first skin fitment, and that's why it went so easy. However on subsequent fitting.....I took the sawhorse away to allow me to access the baggage floors. When I took it away, It seemed like it was unnecessary and it certainly didn't fit with the Vans instructions or pictures. As I found out today....Placing that 4th sawhorse made all the difference in the world. It makes lining up the aft holes in the skin sooo much easier.

We are just about there.

Just a bit of pressure with one hand pressing down on the aft fuse, I can get cleco's into the holes. I started clecoing the left side first, the right side. This time, that mysterious ripple in the side skin had nearly disappeared.

Once the fit looked good. I then removed the 4th saw horse to see what that would then do. Yup, the fit is still good. I have a good fit both sides.Next step I doubled checked the longeron fit and alignment. Looks really good. Nice and even on both sides for length. Spot on for the alignment with the top of the skin/angle (Well. bottom in the picture). Small footnote....I purposely left the longerons long on purpose. I would rather have too much material to work with than not enough. That's why I have more material than most build log pics.



Now to address the items that I skipped over in my haste to get those conical bends done. I fluted and drilled the arm rests.


After double checking all the fit again.....I began drilling the longerons starting at the aft end working forward. I alternated sides every few cleco's.

Second Conical Bend, Left side - 7 hours

Setting up for the left side conical bend was quite quick now that I have the back rivet plate edge radius'd. As mentioned earlier, I very carefully prep'd the edges and polished the relief hole prior to bending.

Much less stress bending the second time.


I then cleco'd the skin onto the fuse on the left side of the fuse. Looking good!




But then I noticed a bit of a fit issue where the left F-770 side skin meets the left F-623 rib. There is a bit of a ripple there.


Pressing on the side skin where it lays against the Left F-715 seat rib tends to accentuate the ripple. The right side isn't like this...maybe a slight ripple, but very slight. The fit is tighter on the right than the left, which doesn't sit well with me. I pondered leaving it and moving on...but it really bothered me. So I spent the next number of hours messing with the fuse trying to get the ripple out. I clecoed/installed the baggage floors to see if that would pull it tight. But it had little effect. I tried to move the tail cone up, down, left, right. I tried shimming the front, shimming the back. I then decided to try to remove the side skins and take a second crack at it. This time I started with the left skin, and then moving to the right. I clecoed the side skin on the F-704 and F-705 bulkheads first and then tried to cleco the conical bends and ends of the skin to the F-706 bulkhead. Well holy heck....If that wasn't the most impossible fit ever. I dunno why I am having such and issue with the fit now. The holes are a solid 3/4" mis-aligned. What the heck!?!. I removed all the clecos and started with installing the side skins at the aft end and conical bend first and then worked forward. Now getting it clecoed to the F-704 bulkhead was impossible. I just don't get it....It went together relatively easily the first try, but now I just can't get it.  By the end of the night I threw in the towel....I had enough.

Trimming the F-623 ribs for the side steps - 2 hours

Small day in the garage today. I need to finish trimming the F-623 rib for the side step on the left side of the plane. Process was the same as the right side. Went slow, checked, checked and rechecked. I'm really happy with the fit.

First Conical Bend, Right side - 5 hours

I am finally on holidays from work....Yeehaww. But the stress has not subsided yet. I have to get these conical bends on the F-770 side skins done first. I've been reading lots on how best to do this and avoid cracks. Really at the end of the day...The opinions are all over the place so pinning the exact best procedure down is not easy.

Two items that have really stood out in my mind as being critical are:

1. Polish up that relief hole before you bend. As I learned on dimpling the fuel tank skins...It is absolutely critical for success to get those holes clear of all deburring marks and tooling marks. Those cause stress risers which caused cracks to form when dimpling for the screws. Best method I have found was 800 grid sand paper on the shank of the dremmel. Then some maroon scotch brite (1" square) on the dremmel to polish the edges of the hole. 
2. From working on Mike's S-51 mustang I learned that you must have bend radius when bending aluminum. The thicker the aluminum, the larger the radius. So seeing guys bending the conical bends on the sharp edges of their back riveting plate caused me some concern. I was going to use a bend radius.
3. I think everyone's opinion of get the bend done in one fluid motion is key. Don't bend, relax, bend relax.  

 Its fairly easy to put a radius on my back riveting plate. My back rivet plate is huge (I bought scrap 3/8" flat bar from the steel yard and made my own). So it doesn't matter if the bottom side has a rounded side. I pulled out the angle grinder and slowly worked the side edge of the back plate down to a small radius fillet. Using 100 grid sandpaper on the palm sander, I rounded the edge. Took some time....But I'm happy with the result. I have a nice solid edge with a small bending radius.

Next I needed to figure out the bend line. That took a bit of research to sort out but in the end, its not entirely critical where the aft line ends up....The front must align with the relief hole.


Next I fabricated the aluminum angle (0.125x 3/4" x 3/4" x ~12 to 14") that I was going to use to bend the skin.


I learned some things here that nobody really talks about. I fabricated the angle to fit right down to the relief hole and then trimmed the top of the angle flange back to clear the bend line plus ~3/8" thinking I need space to clear the back plate when riveting. I rounded all the edges and made it perfect. Then I looked over the pictures that Van's provides at the back of the instructions. It was very curious that n the Van's pictures, that bending angle is actually set one rivet hole back from the relief hole. After thinking on it for a while....I too moved the angle back one hole (as you will see in my bending pics). It turns out that it gives you proper clearance and it doesn't not affect the bend...It still get pretty tight at the relief hole.

Before bending....I broke all edges with a file, cleaned up the shear marks and then smoothed it all out with the 3M wheel. The relieve hole was opened up slightly with a fine small diameter chainsaw file enough to get my dremmel with the 800 grit sandpaper in there. I then polished all edges up.

I set up...Ready to bend. Notice how my angle is set aft one rivet hole from previous pictures....

I started the bend, ensuring it was done in one fluid motion. I did stop halfway through as I need to change the position of the vice grip but I held pressure on the bend with my hip until I could change vice grip position. I then finished the bend. I used my thumb to put pressure on the tight bend while twisting the vise grip at the other end. It turned out extremely well. Side point - The 1 1/2" hole for the side steps look just fine...Did not have an adverse effect on the bend at all.


I then made adjustments to the large bend to fit the curve of the aft fuselage. When it looked right, I used the edge forming tool on the aft ends of the skin and conical bend. Next I clecoed the side skin on.

Trimming the F-623 ribs for the side steps - 3 hours

Tonight was a lot of head scratching on how to fit the side step tubes and scallop the F-623 ribs.  I wanted to make sure that the F-776 floor skin was sitting flush with the top of the F-770 side skin. I used a toothpick in the relief hole to hold it up.

At first I started to eye ball it and sketch the scallop. Lots of un-clecoing and re-clecoing, checking and re-checking. The plans have the best suggestion using a straight edge to mark the edges of the holes....then you just work out the scallop depth from there. Not easy, but just work slowly at it.
I used a sharpie marker in the scallop, and then would fit the step. I'd rotate the step a number of times which would remove the sharpie from the high points on the rib. I'd know exactly where to trim the material down.


I managed to get the scalloping perfect for the right side step.

In the end, an excellent fit.

I just need to trim the 1 1/2" tube down but I'll save all that adjustment work for later.