After I’d laminated 3 pieces of 5mm x 33mm balsa for one of the leading edges, I remembered just how much strength the laminating process can impart to fragile balsa wood. The finished product has bags of strength, and is highly resistant to warps and twists, that non laminated balsa wood can have, which I recalled, has been the ruin of many a poor wing!
I’ve also progressed the canopy mould a little further, in fact it’s ready for its final coat of wood filler, before the finished sanding processes.
Next up, I turned my attention to the first wing, which was fairly straightforward, but with a few tricky moments when attaching the leading edge. It took quite the afternoon, but I wasn’t unduly bothered, as it is important that things are done right, so that undesirable cambers and twists are avoided. After I’d dry assembled the components, which entailed a couple of mods to the ribs themselves, but most of the laser cutting was spot on.
I had the idea to bolt the rear spar to the fuselage former, which will of course be removed when the glue has dried.
Then it was a simple case of sliding the ribs on to the spars, gluing them in as I went, and making sure things were square. It turned out that as the spars were all pre attached, that things went in very nicely.
Next up, I laid out the laminated leading edge, and marked the slots for the spars and ribs, which I cut with my circular saw at 45 degrees, but I’d probably have been better off simply using the dremell, as that’s exactly what I ended up doing to get things to fit together. I’m fairly pleased with the results, I epoxied the spars to the leading edge for a quick grab, but used the PVA for the ribs.
I plan to get the bottom surface covered with the 3/32 balsa sheet, then part the wing tip before adding the R6 rib with dihedral, before gluing it back on at the appropriate angle, then add the wing tip. Then, it’s do it all again on the other side!
I've just ordered up some more 3/16th (5mm) balsa, one sheet for laminating up for the second leading edge, the other for the tail lamination, or 'Stabilator' assembly. I've also started planing down the leading edge I fixed last weekend, and remembered how messy a job it is! Should've done it outside, instead of my loft workshop/bolt-hole/Nirvana/Shangri-la etc, now it's a serious vacuum job. Oh well, such is life, at least my new balsa plane woks well, nice, clean and acurate cuts, a job to be taken very steadily. I won't finish it off until I've sheeted the wings, but I want to get it roughly the right dimensions, so I can part the wing tip(s).
I've also ordered a couple of X-Acto style razor saw blades for the more precision of cuts (the Dremel is great, but one slip and it's toast!), oh, and I've also completed the heat insulation, which I ended up epoxying to the aluminium cone assembly, as it would have been too fiddly to feed it through the former's unfastened. All seems well, and is a pretty good fit.
Not too much progress today, but progress nevertheless! I only found time to glue up the 3 pieces of 3/16” balsa for the leading edge, likewise for one layer of the stabilator assembly, and a little more filling and sanding.
If I maintain this level of activity she’ll be finished by Christmas (2016 that is). ;-)
Half the battle with these things is finding the time, but I managed to find a little more today, and pretty much got done all I’d hoped to do. First off, I prepped the battle scarred plan for the second wing by rubbing a little oil into the plan, making it translucent, so it could be reversed, and laid out flat on the table.
Next up, I dry assembled the wing ribs, making one or two mods (as I made on the first wing). Once I’d satisfied myself that it was going to go together pretty well, I started gluing the ribs up, one by one. I also used my trick of bolting the trailing spar to aid assembly, which worked quite well I thought.
This time, I simply used my newly acquired razor saw to notch out the leading edge. I then applied some epoxy to the spar ends, and pva to the ribs and pulled it all together until the epoxy had set.
It’s all looking nice and square...
I paused for a little weigh-in...14g shy of 1kg so far.
Buoyed up by the apparent success of the fuselage and wings, I thought I’d use up my remaining time by finishing off the canopy mould. I sanded the whole thing a little more, then mixed up some filler for the remaining blemishes, and sanded that all back after it had set. I then spent a little time with the wet & dry, and got it about as good as it was going to get, before applying several coats of dope to seal the whole shebang..
And the finished article!...
Now I need to summon up the courage to get it all in the oven and try my hand at plastic moulding...Can’t wait!
Wow! those birds are amazingly detailed aren't they? certainly in another world, and that location?! Oh well back down to mother earth...
Well, I had a little half-hearted attempt to get some kind of cockpit canopy formed a couple of days ago (whilst my wife was safely out of the house ;-)) by heating the oven up to about 150 degrees C. I placed the mould in the oven for about 10 minutes first off, to get it up to temperature, then carefully laid the perspex sheet over the mould. I judged it to be about ready after aprox five minutes, as the sheet started to curl downwards. I'm totally new to this process, so could only go by Ralph's sketchy advice: "five to ten minutes may be necessary to soften the plastic depending on a number of unpredictable conditions", and: "You must act fast! In fact the first sheet may melt before you realise it is ready!".
The problem I had with mine, is that it simply wasn't big enough, I had mis-calculated the amount of material I would need with some surplus around the edge to work with, so it curled downwards and prevented the female part from being pushed down. Also, the mould making process had made the female part too tight over the mould, all in all, the adage 'fail to prepare, prepare to fail' springs to mind here. :-(
It was a tad disappointing to say the least, particularly as the rest of the build had gone so well. As I say, this was a few days ago, and I have since re evaluated the situation, and decided to use our vac forming machine at work. It had occurred to me to use it before, as it is designed for this very purpose, but I simply wanted to follow Ralph's methods at home, and I'm sure that it could be done this way by anybody wanting a try it, you just need to purchase the correct size of sheet. I used an A4 sheet, which really had little chance of success, I have now ordered up a sheet of 1.5mm thick perspex 500 x 300, which covers the aperture of our forming machine nicely. I have also modified the mould as advised by our design guru, by sloping the rear of the mould ( to aid the release) and also need to drill a series of holes around the base of the mould aprox 1mm dia, to assist in the draw of air over the mould.
I'll post some video of the 'event' when the material arrives! Watch this space. :-)
God managed without machinery, but most of us need a little help
Well, maybe sometime later today, I may get a crack at the vac forming machine, in all its glory. I have now reduced the mould to it's minimal state, and added some 3mm holes all around the perimeter, to aid in the draw of the hot perspex material.
It's not easy to photograph clear perspex, but here it is anyway!
I hope to be able to video the draw process in all it's glory, so lets hope it's a first time take!
Well, there is some good news, and some not so good news..:-) Yes, I have successfully managed to pull a decent canopy from my mould, but alas, only with a 'test' piece of thin material. So buoyed up was I with this success, that I rashly decided to go ahead with the 1.5mm perspex sheet on my tod, as opposed to awaiting the good council of my main man & design guru Nathan. Basically, he had explained to me that the timer corresponded to some guide times for different materials and their thicknesses, and had erroneously supposed my material had been 2mm instead of 1.5, so the time of 200 seconds had been way out. I had perhaps taken these guide times a little too literally, when the process really relies on the skill and experience of the operator, to know exactly when the material is at the correct temperature. This is a 'learned' process utilising both observation, and touch, but as the first had been so easy (20 seconds then bang!) I had no reason to suspect the second would be any different. I let it get way too hot, until the perspex sheet started to sag right down, this caused the material to stretch, leaving thin areas, but the disaster was the fact that the material pulled out of the frame and up underneath it, so all in all not good! That'll teach me to be so impatient.
So, moving on rapidly, (and If you recall, Ralph had prophetically warned that the first piece/attempt would likely get too hot!) at least I have managed to get a test canopy to check it's size against the fuselage cockpit area, and low and behold, it is looking to be a good potential fit, which is at least reassuring to me.
However, I'm pleased with the general quality of the moulding itself. Any blemishes on the tester are mainly due to the imperfections present in the plastic sheet before it was moulded to shape, as it was simply a used off-cut. It appears to follow the desired curve from front to back and is looking good overall size wise, so it is indeed promising. I have ordered up another sheet of 1.5mm, so fingers crossed for next time!
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