Thorn Project

Hi All,

After hearing about the Thorn from a mate whom first saw it on RCGroups, I had to have one. I literally got him to order one for me too before I had even seen it. I trust his judgement. After a little while he dropped around the box with my Thorn. A piece of art I must say.

Opening the Box.

On openning the box here is what you see. 2 beautifully milled wing halves with servo and lead cutouts ordered to fit a choice of servos. In this case the Hitec HS125mg Thin wing servos. A Baseball bat fuse, tail section and a bag of bits. And, Of course a detailed instruction manual. The instruction manual was actually downloaded around a month ago. I am a strong beleiver in building a model in your head from start to finnish before even opening the box. I read the instructions front to back and back to front and sourced all possible information from fellow modellers and of course RCGroups. You could say I have built heaps of Thorns allready, about 30 in my head so far :)

Checking for Warps

Been a solid timber plane there was talk of possible warping with such a long trip from colorado to Australia and the difference in humidity on its long voyage around the world, so, a close inspection was carried out. All parts were free of warp except for the starboard wing. A very slight warp from route to tip, which proved no problem to get back to straight with a few weights left for a few nights. I did enconter another warp. This took a little thought to make things right again and a deviation from the instruction manual was required. The warp was from LE to TE at the route which revealed a 3mm droop on the starboard leading edge when matching the routes together. An email to Andreas saw a prompt reply with the measurements required to glue the wing halves together laying the wing right side up (this been the deviation from the instructions). I will be clamping the starboard route so that the flat spot, to mate with the wing saddle, is flat on the granite bench top and not bowed upward as was the case. (I like my granite bench top for building on a truely flat surface).

Wing Preperation

Following the instructions and been a bit anal, I sanded the wings with 240 then 400 then 600 to make sure I have a good surface for finnishing in a true gloss. I also sanded the 3 joiners to a snug fit and trial fit the wing havles together. I did this for about 2 days making sure I am able to get the warp out from LE to TE, as previously mentioned. I also did a bit more research to find the absolute strongest bonding glue I could get. I think I have found it in the trusty Selly's Super Strenght Araldite. 1 hour working time, 6-8 hours cure and 3 days to full strength.

Tail Section

Horizontal and elevator Stab.

Following the instruction, I sanded back the tail section with 240 then 400 then 600 (the anal bit :)). I decided to Hinge my elevator first, before priming and painting, using the goop method. (Goop is not available in Australia so we use ShoeGoo.) It is the first time I have used this method but have helped a friend set his composite model up with silicon hinges.

So I begin taping the sanded horizontal stab and elevator on the topside together with a 1mm gap. I also tape off the area either side of the hinge line on the bottom surfaces. I then apply goo or goop in the hinge line. I know the instruction say to use a small amount but to make sure I would have a nice hinge I used too much :). This resulted in a very tight hinge. (It took over 200grams to deflect up and a bit more on down). I decided to try another Idea to loosen the hinge to get minimal resistance and still maintain maximum strength. After letting the goop cure fully I went beyond full up throw. Basically bent the elevator up and around 120 degrees or there abouts. I then sanded the goop hinge down till resistance measured less than 30gm for up and 50gm for down. The result was a perfect elevator hinge with minimal resistance and maximum strength (I have tried to pull them appart with no luck. probably around 10kg for force). (See picture for a thousand words). I then shaped the elevator tips to match the horizontal stab tips perfectly. I think the instructions say to do it the other way, but it is easier to match the 2 surfaces perfectly this way.

Prime Time

Main Wing

After Glueing the wing halves I have sanded the overflow of all epoxy (aryldite) back to a 600 grade finnish. I will sink the HS125Mg servos and leads in and using wood fill to ensure an absolute smooth finnish after more sanding. (Poor Andreas, I only just feel what he feels in the knee deep saw dust.) Please see the next section to get the rest of the Thorn upto Priming stage.

Tail Plane

With a little more sanding to take out imperfections due to little bits of sand, grit and the like; left on the granite top bench. I was ready for priming.

Masking

I intend to have wood to wood surface for joining essential parts, such as, Horizontal stab to vertical stab, complete tail to fuse. I also intend on putting the kevlar DS Mod in place after the first coat of primer filler. I intend on doing at least 2 X (prime/fill and sand) sequences, if not 3.

Prime and Sand Prime and Sand.

I tried 3 different ways of aplying the primer/fill. Brush, Roller and Foam. Foam is by far the best aplicator as it has a lot less work when sanding back to flush, smooth (as close to mirror as possible). I have so far done around three coats to the top, 2 on the bottom of the wing and sanded back to 1200 and 1600 finnish.

Fuse

After sanding the fuse smooth with 600 dry. I applied 2 coats of prime and sanded back to a 1200 wet finnish. Dead smooth for a dead smooth finnish.

Painting.

Afer playing around a little with spraying tecniques. I found the best finnish i believe possible. using auto acrylic spray. My choice of colours was Black Metalic Fuse and Yellow Glo for the canopy and all wing and tail surfaces.

First coat.

A light spray keeping the nossle about 20 cm away from the target. Room Temp between 20 and 25 celcius for all spraying. The first coat is a mist coat with a very rough surface finnish like 180 wet and dry sand paper, by doing this, it allows the final coat to be spray to a thick gel coat spray with minimal or no runs. A run on the fuse and canopy can will be taken out with a light sand back and recoat. The wing surfaces result in a mirror finnish when enough paint is applied. Any less and you get orange peel effect. This with a lot of buffing can be taken out. but a light polish on an already gloss finnish will go alot further. Especially on the top of the wing. After all this is where everyong looks first.

 WHATS LEFT

Install elevator servo and linkages, glue tail assempbly together and do all hinges. Install charged battery program and test fly. This along with pics of the complete model will be forth coming as I have now got the majority of the work done and am begining to be impatient to see My Thorn in action.

 Photos,

I have included a group of detailed photo's in no particular order. Not that hard to figure out what is what if you read the above. After all, anyone considering the Thorn would have to be an intelligent person no wouldn't They :)

Beno