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Dec 21, 2017, 07:58 AM
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Ianda217's Avatar
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1:12 Scale Gloster Javelin


Well, Iím all good to go. My next build is going to be a 1/12 scale Gloster Javelin and I have decided to try a new building method (for me) and build it from foam. I have got my hot wire cutters built and have done some experimenting so that I will (hopefully) be able to cut everything out without too many screw ups. Plans are all done (obviously) and I have got all the mechanical bits and pieces Ė retracts, servos, esc, etc. I have even managed to tidy up a corner of my shed to do the wire cutting in although I will do the assembly and building down in the workshop.

I am planning to power the model with a single 90mm Wemotec fan which has the potential to provide 3.5 Kg of thrust which is also the estimated weight of the model. I will lose some thrust from the motor since there is a two into one inlet duct and then I have to run the exhaust from a circular shape at the fan to an oval shape at the outlet to match the full size tail end. How much I will lose wonít be known until the model is pretty much put together.

One problem that we have over this side of the pond is getting XPS foam. The building regulations in Scotland demand such high levels of insulation that polystyrene isnít normally good enough so most of the insulation used now is either polyurethane or polyisocyanurate (try saying that after half a dozen beers) so I canít just nip down to the local buildersí merchants and pick up a sheet of foam. The only practical way to get the stuff is via the web and this usually means buying a full bale of 8í x 2í sheets at a cost in excess of £150. However, I did find a web site that sells Dow Styrofoam specifically for modellers in small quantities. There is a premium added (of course) but I got enough to build the model for £50 and this is a lot cheaper than balsa and ply would have cost for the same model.

The templates for the fuselage sections and wing ribs have been laser cut in 1/16Ē birch ply. I went this route because it would give me very accurate templates that can be used more than once. I havenít actually seen the templates yet because my wife decided that they would be my Christmas present from her. This means that real work wonít start until Tuesday next but, in the meantime, I have got all the blocks pre-cut for the fuselage sections. Roll on Monday!
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Dec 21, 2017, 10:44 AM
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jumo004's Avatar
Nice subject !
Will be following, for sure !
Dec 21, 2017, 12:59 PM
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turbonut's Avatar
Go Ian!...You do have good taste inaircraft...And you know looking at it that it will fly great
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Dec 26, 2017, 10:28 AM
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Ianda217's Avatar
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Santa's been and gone and left me some laser cut ply so it's time to get going. By close of play yesterday, I had managed to get all the formers cut out, cleaned up, marked up with datum lines and drilled for pins. All that whilst helping to prepare dinner for 11 and then getting totally blitzed after dinner!

Today, I was allowed out to the shed and started hot wire cutting. It's trickier than I thought and I will need to redo a few of the pieces but I feel that I've made decent progress for the first day with a new process. I'm about a third way along the fuselage so far. I would have done more but it was cold enough that it stopped being fun. The last section I cut today was from former 8 to 9 (out of 26). This was a tricky shape but by the time I got to that one, I was getting the hang of using the hot wire cutting jig. Still lots to learn.
Dec 26, 2017, 12:01 PM
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Very nice work...Heck you could build a balsa Javelin from the formers when the foam is all cut
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Dec 27, 2017, 09:18 AM
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union1's Avatar
Fantastic work!
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Dec 27, 2017, 12:11 PM
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Ianda217's Avatar
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Thanks, guys. However, there's much room for improvement.

I got a good bit more done today before the cold forced me back into the house. Also, I did manage to improve since I'm learning from my mistakes. I got the fuselage sections cut up to former 17 today and there was only one cut that I felt might need to be redone.

There are a lot of lightening holes in the formers as well as the inlet ducts and my arrangement for cutting these is working well. The wire in my cutting jig is simply tensioned by way of the top end being tied to a length of 6 gauge piano wire. There is only a very small notch cut in the top of this so all I need to do is ease the tension on the piano wire and slide the cutting wire off so I can pass it up through a hole drilled in the foam block before re-fitting the cutting wire.
Dec 28, 2017, 12:02 PM
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Practice doesn't necessarily make you perfect but it definitely makes you better. I got the rest of the fuselage sections cut today and the cutting was going much better so I decided to redo the sections that I wasn't happy with. Six of the eight formers I cut on Tuesday were pretty poor so I junked them all and re-cut them.

I won't get anything done tomorrow but on Saturday, I might try gluing up some of the sections.
Dec 28, 2017, 01:00 PM
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turbonut's Avatar
They sure look good form here..I see a bit of sanding in your future.
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Dec 29, 2017, 07:53 AM
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well done for starting this - looking forward to seeing it develop
Dec 29, 2017, 11:39 AM
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fuelsguy's Avatar
I will just have to follow this build. My Dad was a mechanic on the first Javelin and would come home with tales of the flight test program, which probably why I'm a retired engineer building RC models of Canberras and similar.
The ability to cut intricate fuselage sections is impressive, and as of a week ago I have access to a laser cutter.
I did have a question. How you align each section to prevent twist as you glue the sections together?

Ivor
Dec 29, 2017, 12:12 PM
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Ianda217's Avatar
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Ivor,

This is my first ever foam model so the true answer is that I don't know. What I intend to do is glue the sections of each half together over the plan which should keep things aligned and then glue the two halves together.

The fuselage is divided into twenty six slices. Depending on how I fit all the mechanicals, I might break it down into 3 sections. I plan to work on the area around the fan first to sort out the wiring runs from motor to esc to battery. I'm keeping my fingers crossed.

How did you get from Moreton Valence to Seattle?

Don't answer - I just looked at your profile - B Ae and Boeing. Enuff said.
Last edited by Ianda217; Dec 29, 2017 at 01:28 PM.
Dec 29, 2017, 02:04 PM
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fuelsguy's Avatar
Landa, Thanks for the prompt reply.
Your GA-5 looks very doable, butwatch the fan and battery location to get CG close from the start.
I have done the cut foam from two cross sections myself but generally to get an inlet shape, not a full airplane.
I'll watch progress with interest.
Ivor
Dec 30, 2017, 09:40 AM
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fuelsguy's Avatar
Another question, it looks as if you are cutting sections with a vertical hot wire. Are you cutting vertically with one pattern, or do you have a front and back pattern and handle tapers etc. by holding the foam to keep the wire touching both patterns. I do this on long sections but I have to watch carefully where I am on both patterns. Your 2" wide sections would make it a lot easier.
Ivor
Dec 30, 2017, 11:44 AM
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Ianda217's Avatar
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Ivor,

I have a template on both sides of the foam. Even at 2" wide, I had problems with some sections that had steep tapers - especially with pins in the wrong place catching the cutting wire. Also, in some places (for example - where the jet inlets start at former F7) i needed two separate templates for the one former as the shape from F6 to F7 was radically different from the shape from F7 to F8.

I'm afraid that progress on the fuselage has now come to a sudden halt, thanks to my glue.

Having read as many posts as I could find about building with foam, it appeared that the go-to glue for styrofoam is Uhu por, which is readily available over here. I also read that the most economical way to get it is to buy the large 570 gram tin and use naphtha as thinners. Large tin duly bought along with a couple of tins of lighter fluid and this morning, I started gluing up the fuselage sections. I had decanted some of the glue into a jar but it seemed pretty thick on the first couple of pieces that I glued so I added a decent amount of naphtha to it and stirred it up. It didn't get thinner - it actually seemed to get thicker and it became impossible to apply to the foam. Bummer!

So, in the hope that the tubes of Uhu por are a better glue, I've just ordered some from Amazon but I'll be lucky if they're here within the week. Until they arrive, I can fiddle about and sort out where my wiring runs are going to go.

Total weight of all the fuselage sections is 458 grams. When I was drawing up the plans, I had calculated the weight at 435 grams using a notional 2.1 lbs per cubic foot for the foam so I am pretty happy about that.

Since the fuselage was no go, I decided to start on the flying surfaces. After a couple of false starts, I got the fin and elevators cut out but that will be the lot this year as I'm away tomorrow to celebrate the new year.

And a happy New year to you all!!
Last edited by Ianda217; Dec 30, 2017 at 01:50 PM.


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