Jim.Thompson's blog View Details
Posted by Jim.Thompson | Jan 07, 2012 @ 03:08 PM | 7,323 Views
Some of the bubbles that occured in more than one of my vac bagged wings has developed into a significant delamination. This one is on my 1.8mtr. homebrew "Endorphin". The bubble had spread to an actual compression ripple due to inflight stress's. There is no spar in this wing.
I repaired it very successfully using vacuum applied under the skin on one end of the ripple. I used a sports inflation needle (used to inflate footballs I think), inserted through a drilled hole. Then in another hole at the other end, I applied low viscosity epoxy using a syringe untill I could visually see the epoxy bubbling out the needle through the clear vinyl tubing.
I have previously tried repairing these by just syringing the epoxy under the skin with very limited success: the epoxy simply will not spread enough to cover the affected area.
This worked very well and emboldened by this success, I went and repaired several other bubbles.
I have since identified what is the cause of this phenomenon. I used to mix "Q" cells with the spackle that I filled slight dings on the foam cores before vac bagging. The "Q" cells caused slight dust which repelled the epoxy slightly, sufficiently so to reduce adhesion. Any offgassing of the foam with heat (during hot box post curing or simply in the hot sun), would then cause a bubble or more.

Posted by Jim.Thompson | Jan 05, 2012 @ 05:25 PM | 7,443 Views
I have completed the fit out and ballance. It took 300 grams of nose weight. And the AUW is 2 kg.! Much heavier than I anticipated, but it will be ok in "big air" conditions. The sort of conditions we get out at Mt. Borah NSW where our annual slope festival is held.

That work out at close to 70 g./sq.Dm wing loading, the highest loaded plane that I have. My Cobra flies very nicely at 65 g./sq.Dm, so this should be fine. I still have the provision for ballast, two cast lead slugs totalling 650 grams, but.......................

Posted by Jim.Thompson | Jan 03, 2012 @ 02:27 AM | 6,552 Views
I have got the paint job done. No clear coat yet, I will wait untill I give it the maiden flight and any necessary trimming before I do that.
I'm quite pleased with the job, the fuse came out with an almost "gloss off the gun" while the wings are a bit flat. No problem though, a wet sand with 600 - 800 grit to level off the masking ridges etc. and then a clear coat will make it look ok.
It seems the trick with acrylic lacquer is to use a high dilution rate, almost 2:1, and apply several coats, preferrably many. But of course, the danger of runs is high, so care must be taken. Any pro's reading this? I would appreciate any tips.
I just need to fit the cast nose lead (200grams), the batteries and final fitting etc. The servos and pushrods are already in, and the tx. program sorted out to suit.
Then ready for that maiden flight out at one of the beach headlands.


p.s. The model now has a name. "Circa" latin for, well, you know what!
Posted by Jim.Thompson | Dec 10, 2011 @ 09:53 PM | 6,755 Views
The wipers are formed with the mylar tucked under the wing skin. Curing as I write. All surfaces are bottom hinged.
Posted by Jim.Thompson | Dec 10, 2011 @ 05:46 PM | 5,319 Views
The wipers are being made using Joe Manor's description on his thread.
I have hung the plane like shown in the picture to ensure the "Q" cells splooge slumps onto the mylar to form the wiper surface but not onto the hinge line.
When the epoxy starts to kick and become jelly like consistency, I will slide the mylar strips under the wing top skin to form the required curve.
Posted by Jim.Thompson | Dec 09, 2011 @ 03:09 PM | 4,842 Views
I have glued in pine servo mounting blocks front and back of the servo position. These also bridge the top and bottom skins, so provide a bit of support for them in a vulnerable area.
The servos will be slid in between these blocks and then hot glued to the blocks. For subsequent removal if necessary, a piece of wire is heated and used to melt the hot glue.
I just need to monitor just how soft the hot glue becomes in when the plane is in the hot summer sun!
This is another reason for painting composite planes light colours. Apart from the HTD (high temperature distortion) concern.

Posted by Jim.Thompson | Dec 08, 2011 @ 06:28 AM | 4,978 Views
I cut a template for the control surface cut outs. This is to minimise mistakes and ensure both wings are cut the same!
Posted by Jim.Thompson | Dec 07, 2011 @ 06:35 PM | 4,779 Views
I fitted the wing/joiner/pin set to a previous fuselage. I used an aluminium root rib as a template to locate and cut the holes in the fuse. It all fits well, especially considering this was "reversed engineered". The original plug and mould was not meant to be for a moulded, two part wing aeroplane.
It started life as the simplest fuselage shape I could imagine to learn how to do fuse moulding with and inflation bladder. It progressed to included fin and fillets. And finally, this moulded version. So the alignment had to be done after the fact, which is not to be recommended for obvious reasons.

Posted by Jim.Thompson | Dec 06, 2011 @ 11:29 PM | 4,757 Views
These are the wings trimmed and fitted together with the joiner and pin. Alignment is correct! I will now make a root alignment rib out of 2 mm aluminium to act as set out guide for cutting the holes in the fuselage. Then I can do a full test assembly!
Posted by Jim.Thompson | Dec 06, 2011 @ 03:50 PM | 4,572 Views
I pulled both wings from the moulds this morning, and they are successful! There is a slight blemish on one in the form of small bubbles too small to show up in the pictures. It will be quite repairable and is only about 10mm or so diameter. I am suspecting that it is my old blue foam offgassing come back to haunt me again! I had many vac bagged wings form bubbles when heated either in the hot box or in the sun when using this same foam. These moulded wings have foam cores aft of the spar.
And the only thing that I had forgotten to install were the servo cover spacers in the top skins! Not a major problem, but will have to be done on the next ones.
The weights are 425gram and 440 grams untrimmed. The joiner will be around 70 grams trimmed. No lightweight, but I was very generous with the resin. No sign of any resin voids!
I will type up a list of process and build sequence, get it laminated and pin it on the wall of my shed before doing any more. Especially for moulded jobs. I often manage to forget some small (or large!) aspect of the job.

But I am really pleased, quite excited actually!


Posted by Jim.Thompson | Dec 05, 2011 @ 05:22 PM | 4,461 Views
The wings are glued and closed up in the moulds and in the hot box!

Is there anyone reading this blog?

Posted by Jim.Thompson | Dec 05, 2011 @ 03:58 AM | 4,367 Views
I have closure!
The first wing has been glued up and closed! The picture shows the servo wires in place and some small wooden blocks to act as cheek blocks to mount the servos.
I will glue up the second one tomorrow.

Posted by Jim.Thompson | Dec 04, 2011 @ 02:48 PM | 4,447 Views
The Drag spars are being glued into the bottom skins along with the control surface LE spars.
The drag spars were pre made by winding 30mm wide strips of 100gsm glass on plastic covered carbon rod for a mandrel. Then wrapped with more plastic and allowed to cure. The spiral wound plastic pulled out of the cured tube easily.
The LE spar was made using the drinking straw method. The straws were threaded onto a mandrel and taped together. Then they were spiral wound with glass as above. Wet out, slipped off the mandrel and cut to length before gluing into the lower skins.
Drop sheet plastic was placed on top and the top skins and moulds where then clamped onto them for curing.

Posted by Jim.Thompson | Dec 04, 2011 @ 01:30 AM | 4,236 Views
The main spar has been glued into the lower skins and sanded to clearance fit under the top skin.
I'm now working on the drag spar and the LE of the control surface spar.
I have made up some 7mm dia glass tube which I will use for the drag spar. That is ready to glue into a dremelled trench. Why the trench? Because I mistakenly continued the foam core right past the hinge line etc. in my relative inexperience! I'll leave and appropriate space next wing.
The LE surface spar will be formed on drinking straws, glued in while still green and some drop sheet plastic placed over them before closing the moulds overnight for them to cure into correct depth. If I was more experienced and confident, I could do them last before gluing and closing the wing skins, but I want to see just how much they compact out of round on the first wings.

I've also created joining "lands" or shelves at the LE and tips. I used two rows of 50k tow and formed them up by clamping a waxed strip along the mould flange and pushing the tow into the LE. This will give me good surfaces to glue together.

Posted by Jim.Thompson | Nov 29, 2011 @ 09:16 PM | 4,595 Views
I now have the moulds all prepared, waxed PVA and primed. The first (bottom) skins layup is under vacuum. One layer of 100gsm plain weave glass and balsa core in front of the spar and 2 mm foam core behind the spar. I will install the spar cap tow tomorrow and the internal layer of 100 gsm glass and vac bag again.

Posted by Jim.Thompson | Nov 25, 2011 @ 11:51 PM | 6,622 Views
I am now setting up the two lower wing mould halves so that the joiner will be alligned correctly. The parting plane was not on the chord line due to a mistake of mine, so I put the wing plugs in the moulds and set everything up parrallel and level. Then I set the joiner in place level and filled the space in the moulds to fit the joiner. The alighnment pin/rod can be seen in the picture as well.
There was more slight voids to fill in the root ends. When all this cures I will layup some wing skins. Probably some time next week.

Posted by Jim.Thompson | Nov 21, 2011 @ 10:32 PM | 3,776 Views
I have now made the moulds and split them. I used a fairly light epoxy/glass layup of around 4 mm thick only and stiffened them up with 30 mm RHS section steel tubing. The tubing is only glued along the LE and the TE, but will keep them nice and straight and prevent twisting.
the moulds split ok with only a bit of TE breakout where I failed to fill the join between the TE spacer and the TE. As a result, some resin mix soaked between the spacer and the parting board. No great problem though and I have already started to repair the slight gaps.
I have now made a more reasonably sized joiner - 40 x 14 and with a foam core and ply shear web. It has only 40 lengths of 50k carbon tow and is 85 grams. But I have yet to trim it. Very strong. Today I started the joiner box(s) and began by wrapping the joiner with drop sheet plastic after I had lightly lubricated it with vaseline. Then I spiral wound strips of 100gsm glass about 30mm wide around the plastic covered assembly in both directions. I then wet it out with resin. When it was still green, I made sure it would move on the joiner.
Next step is to spiral wind it with carbon tow in both directions.

I hope to be laying up wings next week!
Posted by Jim.Thompson | Oct 13, 2011 @ 12:54 AM | 4,135 Views
The wing plugs were primed and surfaced adequately so I ventured to spray them with black 2 pack paint. This was my first attempt at using this kind of paint. All was going well when about half way through, I had a power failure!

So I cleaned the gun as best I could without air and put the mixed paint remaining in the mix vessel and took a break. The power came on again about and hour and a half or so later, so I used it and sprayed the rest on the plugs. They came out very rough with severe stippling or "orange peel" finish.
I'm now wet sanding them down again and will most likely have to spray them again.

Posted by Jim.Thompson | Oct 05, 2011 @ 07:50 PM | 4,001 Views
The wing joiner mould is now made and is curing. I plan to make a joiner with carbon tow and a foam core.

Posted by Jim.Thompson | Sep 17, 2011 @ 07:25 PM | 4,656 Views
I have now modified the parting boards to suit the steel framed/epoxy sand filled sandwich construction. The pictures shows how I employed Larrikin Dave's idea of using cling wrap on the plug to mould the LE and TE infill shape.
It will of course be block sanded down to the parting board after curing.