RCM&E Atom Build

I woke up to thick fog and freezing conditions this morning, so no flying this week.

I really need to get on with building the RCM&E Atom as I haven’t touched it since before Christmas, despite the required spruce and plywood supplies turning up from SLEC the week before. Their mail order service was certainly very prompt as I was worried about getting caught up in the Christmas mail order chaos, but it arrived in a couple of days.

My main reason for writing this article, though, is to prevent other people from making the same stupid mistake that I made. Now, I’ve built a couple of dozen aircraft from ARTF through to scratch built own designs, so I’m not a complete novice, but I must be getting out of practice. I could try and blame the lack of 3D construction diagrams with the ATOM plans, but the truth is I measure the wood wrong. The photo below shows the problem:

Looking from the back at the sandwich of B1, B3 and B4, plus sides

Looking from the back at the sandwich of B1, B3 and B4, plus sides

Back view of the fuselage with the sides removed

Back view of the fuselage with the sides removed

The base piece, B1 is 5mm balsa, along with B3 which sits on top. Then the top piece, B4 is 3mm. In the photo you can see B1+B3+B4 in the centre with the pencil drawn vertical datum lines visible going up along the end of all three pieces for alignment when glueing. The two sides aren’t glued at this stage and you can see the doublers, D1, left and right sitting on top of B3 and forming a nice square box. It wasn’t always like this though.

My mistake was that B1 and B3 are from the same stock, which isn’t exactly 5mm deep. Either my eyesight is going, or I didn’t measure it properly, as it’s about 0.75mm thicker than it should be, so 2×0.75mm is 1.5mm and the extra height meant that with the doublers, D1, glued to fuselage sides, the sides didn’t reach the bottom. Without any construction drawings on the plan, it took me a long time to work out what was wrong and how everything was supposed to fit together, but then that’s half the fun anyway. I like the idea of the plans being a bit “open ended” as I always like to tinker with things, so this isn’t a criticism, just a bit of advice for anyone else building it – measure B1+B3 together!

Anyway, my solution was to place the base on the flat building board and offer up one of the sides. Then I drew a very fine pencil line along D1 using the top of B3 as a guide. Placing the fuselage side flat on the worktop, I cut very carefully just inside the thickness of my line to remove about 1.5mm from the bottom of D1 so it now fits as in the photograph above. Then I repeated the process for the other fuselage side.

OK, so everything now fits together and I think I understand where all the remaining pieces go, so the everything should just fall into place. I won’t forget to double check all the angles, though, as the modified D1 might have some consequences for the former and mast angles. And the hole is obviously slightly bigger than my 5mm square spruce strip.

IMG_20150104_162719 IMG_20150104_162746

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