Aft bottom skin frustration

I'm having issues getting the aft most bottom skin (F-828-1 for the RV-8, but I assume all models have a similar part) in place. So far I have spent about 8 hours messing with this thing. It's been the most frustrating part of the build for me so far.

Basically, if I cleco the two aft most bulkheads onto the bottom skin and then slide the skin/bulkhead assembly onto the lower longerons, as called for in the instructions, then I can't get the holes on the bottom skin to line up with the holes in the side skins and lower longerons. If I cleco in the bottom skin first, then I can't get the second aft most bulkhead in place without putting a lot of pressure on the longeron and bulkhead, which I'm really trying to avoid.

The problem is that the skin is made of pretty thick aluminum, so it doesn't want to be shaped. I already tried massaging it with my hands and rolling it like the leading edges of the elevators. The fit has improved but I still can't get it to fit right.

Did any of you have the same problem? What did you do to get these parts to fit without having to stress the parts?

My memory was that this piece was a real bear to deal with, and after digging through my build log, that memory seems to have been confirmed. Unfortunately, there's not a lot there in terms of detail as to what I did, but it sounds like it mostly boiled down to massaging the skin a bit to tighten up its curve and provide a better fit to the bulkheads.

Also, the fun doesn't end there - getting the larger bottom skin in place is a royal PITA as well. And of course you get to do both of these things twice.

https://rv.squawk1200.net/2015/08/17/more-tailcone-fitting/

N546RV said:

My memory was that this piece was a real bear to deal with, and after digging through my build log, that memory seems to have been confirmed. Unfortunately, there's not a lot there in terms of detail as to what I did, but it sounds like it mostly boiled down to massaging the skin a bit to tighten up its curve and provide a better fit to the bulkheads.

Also, the fun doesn't end there - getting the larger bottom skin in place is a royal PITA as well. And of course you get to do both of these things twice.

https://rv.squawk1200.net/2015/08/17/more-tailcone-fitting/

Click to expand...

Thanks for your response and your detailed build log. I have looked at it many times over the course of this build!

Today I decided to try to fit the larger bottom skin and was surprised that I was able to install it myself with out much trouble.

I’m going to keep massaging that small aft bottom skin a bit more to see if I can get everything to fit right. Looking at my second to last bulkhead—if I could just get the bulkhead to sit an 1/8-3/16” deeper then everything would fit perfectly.

The problem is that the bulkhead flanges, including where they connect to the web, are already sitting against the skin and lining up with the holes. So I’m not sure how more reshaping of the skin is going to do much.

I’m starting to wonder if my bulkhead was mis-formed, because everything else fits without coercing the parts in place. I’m toying with the idea of filing off 3/16” of the bulkhead web where I have indicated with an arrow in this attached pic. It would just enlarge the existing cutout and would not affect any hole distances. That would make it fit with all holes aligned and with no pressure on the longeron. Does anyone see why this would be a bad idea?

Bulkheads

If it's at all similar to the 7, I had a bear with mine.
I remember working the thick skin as close to shape as possible. The two aft bulkheads also had to be adjusted because the flanges were perpendicular to the web but they actually need to be at acute and obtuse angles fore and aft.
Once everything was adjusted, it went together easy.

My first aft bottom skin is now a rain diverter for a storm gutter at my old hangar.

I literally spent several days of hours on that one. Then threw it away and started over and spent at least that many more hours on the 2nd one.

Then, to boot, after disassembling to deburr and prime, I spent a whole bunch more time getting everything to line up as I riveted it together.

Then, I was told that's all perfectly normal; to just follow the plans, keep massaging it and "carry on".

But, I'm sure now with the internet being what it is, someone will be along shortly to tell you that it shouldn't be that hard.