Chrysalis-Lite Build - RC Groups
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Jul 16, 2017, 10:01 PM
ˇʇsol
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Build Log

Chrysalis-Lite Build


Before laminating the ply doublers to the balsa sides I set things out as they should be first. I'll inevitably do something really boneheaded if I'm not careful, so this kind of thing keeps me from making two left sides.



I also tend toward using slow glues where it makes sense so I at least have a little time to align things (thin CA wicked into an assembly already dry-fit is an obvious exception, if that technique is appropriate for the situation). For the doublers I opted for slow-setting CA. During previous projects I've found this type of CA also tends to flow out nicely when the parts are clamped, giving a really solid bond across a large area - and it doesn't take a whole lot of glue to do it.

Working quickly I glued up the ply, lined everything up using a board with a jig on it that kept the ends of the doubler/balsa assembly flush while keeping the bottom edges aligned by pressing the edges down on the board together. Quickly clamping the assembly between two planks assures a good bond between the parts and keeps everything flat in the process. Even though it's CA I give the slow stuff several minutes to completely set up before moving on.



For those that haven't seen the instructions, plans, or kit, it may be helpful to know how everything is designed to go together - at least up the "pod" stage (presumably the rest will be equally well thought out). It's well designed to be self-jigging, the parts all line themselves up with minimum effort while resulting in good fitting, well aligned joints. The design and cutting of the formers and plywood have given tight, almost "snap together" precision - which is how it should be. Gluing up the formers is a good example:

Gluing the formers to the pod's bottom, the instructions first call for fitting F2 to the pod sides to use the sides as a "locating tool". The procedure does more than just "locate" the former. It precisely aligns it to the pod. No cutting, sanding, trimming, or fitting needed (except to remove the holding tabs left over from laser cutting, a few swipes of a sanding block with 800-grit paper worked for me). This is F2 'snapped' onto one of the pod sides - no glue:

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The pod's sides and bottom also have interlocking tabs, so when everything is put together it jigs itself into perfect alignment:
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After test-fitting the former is glued to the pod bottom with one bead of glue along the bottom of the former, everything is held together in it's self-forming jig until dry then the sides are removed. Formers F3 & F4 are added the same way:

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The wing hold-down plates are installed using the same technique. Everything aligns itself and results in nice tight joints. The two wing hold-down plates are designed with tabs that fit inside their two associated formers, as well as into slots in the ply doublers. The result is what appears to be a simple and strong structure without the need for additional gussets, triangles, etc.

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At this point it's kind of like assembling a 3D puzzle. No need to worry about using jigs, triangles, clamps, etc - the parts jig themselves:

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I've kind of gone out of my way to describe this for those that are used to the more traditional builds, or are new builders. The instructions suggest this isn't a beginners kit, but the engineering behind it (so far, anyway) eliminates a lot of the places where new or lazy builders start to pick up problems.
Latest blog entry: Sagitta 600 build 2018
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Jul 16, 2017, 10:02 PM
ˇʇsol
vulturetec's Avatar
More details to point out to future kit builders: tail-boom alignment is pretty simple. All the major parts have center-lines engraved by laser so there's no guesswork there. The kit has a template (former) that slips on the tail-boom that has a centerline and also acts to align the part vertically. The instructions call for lining it up on the plans, but if the template is located correctly a straight-line will work on a flat surface too:

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I was also stuck pondering the battery issue without going to a LiPo and a BEC/regulator. A stacked 2x2 AAA NiMh ((flat, 2 cells tall, 2 cells wide) pack will fit ok without any modifications (I didn't try it but the dimensions seem to be fine). A 2-Cell LiFe pack also looked to be an alternative but the one I had was just too thick. Ultimately I decided to try a Spektrum 2-cell 900mah LiFe RX pack - turned out to be an almost perfect fit (more on the battery later). The longerons have to be trimmed away vertically for the battery to fit; I ended up beveling the bottoms of the longerons before installing them.

The "stock" hatch hold-down (a wood tongue on the hatch that slips under the forward hatch block) looked like it might be a tight squeeze on the battery. As an alternative I recessed a hard wood "tongue" and made a pocket in the front hatch block that mates with the tongue. It worked pretty well:

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Back to the battery...I forgot to take pictures of it before gluing on the front hatch block - but this will give a sense of the size/shape of it:
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To finish off the hatch I made two matching wood mounts for the two magnets. There should be a wood piece on the underside of the hatch to keep it from moving from side-to-side anyway (which is described on the plans), this accomplishes that too:

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The hatch is tight-fitting with no wiggling on either end. Should work out well.
Latest blog entry: Sagitta 600 build 2018
Aug 14, 2017, 04:24 PM
ˇʇsol
vulturetec's Avatar
After getting the hatch sorted I moved on to getting the nose-block on. This is somewhat reverse of what the instructions suggest. My idea was to glue the front hatch piece to the fuselage with the hatch intact so they mate correctly. By keeping the front hatch piece oversized I could sand everything flush along the front face of F1 then install the nose block pieces.

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...then sanded the sides of the front-hatch balsa flush with the sides before moving on to the hatch itself:

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Now to start shaping. I've got it >75% finished but haven't taken any pictures yet.

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The instructions also call for installing the top-rear and shaping the rear of the fuselage-pod. I think I'm going to wait until the wing center-section is done so I can fit the top-rear pod balsa to the wing without guessing. Probably not a big deal either way but there's no real need to rush it either.

Now to start some assembly of the wing-tip sections. Four tip-ribs have doublers for the carbon rod that joins the center and tip sections. The doublers line up with the holes for the carbon rod and the rear of the web. To make real sure I don't make two right or left sets I marked each piece ahead of time:

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Not a critical assembly, but to make it easier I used some scrap 1/8" balsa to line the doubler up on, while centering it using the carbon rod.
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Just to make sure I'm not doing it crooked I checked the alignment of the rod then clamped it together. The instructions suggest tacking the doubler in place with medium/thick CA. I opted to use a couple of drops of thin CA around the assembly to finish it off while it was already clamped. I tested this technique with some scrap ahead of time and couldn't break the joint.

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The webs are capped with carbon fiber strips and need to be partially pre-assembled before building the wing. The method in the instructions sounded fine: tape the carbon strip down on a flat surface, then hold it and the web straight (and vertical) using a block 90° to the work surface (the instructions word it better than I do). I used an extruded aluminum T-bar with a tight 90° joint lined with waxed paper with a hard crease for the 90° joint area.

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Seemed a perfect solution, unfortunately I completely loused up my first attempt. What looked "perfect" ended up with a horribly misaligned CF strip.

Instead of salvaging the part (which may have been doable) I cut a new web and started over. Fortunately this was the center-web and relatively easy to duplicate - but with four more to go I really wasn't too confidant about using that technique again.

As an alternative (also mentioned in the instructions) I used 30-minute epoxy, a straight-edge, and lots of tape. This is how I built the spar and sheeting on my Sagitta and it worked well. The straight-edge is a heavy T-square taped to a heavy piece of glass. With everything glued and taped tightly I pressed everything flush to the glass with a large sanding block and left it there to hold things in place while it dried.

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That worked really well but since the T-square straight-edge is relatively thin I found too much clamping pressure from the tape tended to cant the CF strip slightly. I ended up putting a ~1/2" wide piece of 1/8" balsa between the straight-edge and the CF/web assembly to support it (no pictures). The end result is pretty good with the CF/balsa edges perfectly flush. It's just important to use a straight piece of wood as the buffer piece or you'll build a bend into the web.
Latest blog entry: Sagitta 600 build 2018
Aug 14, 2017, 04:40 PM
ˇʇsol
vulturetec's Avatar
Working on the wing: Joe points out that the notches in the ribs should be level with the sheer web so the carbon fiber cap lays flush. I checked the notches before I glued them in, but also found that the edge of the carbon fiber strip is sharp enough to act like a razor plane and levels the notches pretty easily.

The CF strip on the tip needs to be cut to fit against the tip gusset. I'm still really inexperienced working with the CF strips so I've been playing with different ways of cutting it. I resorted to taping the strip to a piece of hardwood, marked the corrected sweep angle on the tape, then cut through the CF/wood with a band saw. Worked pretty well.

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The instructions suggest using pins to hold the forward sections of the ribs when installing the leading edge dowel. I usually keep a can with small balsa blocks to hold pieces like these in place. Only one side of the ribs needed to be held in place. I used slow CA on these joints, working slowly from the tip to the root in sections.

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Latest blog entry: Sagitta 600 build 2018


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