JART UPDATE

Some before and after photos
the start

the final product.(1st prototype)

The details of the JART control surface hindging and final finishing as part of this build thread, has been moved to the new SA-JARTS Blog (link on the right) as this blog will hopefully reflect all the JART activity in South Africa from now on.

Well its ready to fly,from a lump of blue foam to a sexy soarer,... but time for some reflection , I am sure all scratch builders must get a kick out of admiring their creation prior to that first flight, it is often a long road with pitfalls along the way, but when your beauty takes flight it all seems worthwhile.(especially when it wasnt unpacked out of a box ,but built with your own hands)

I know it gives a deep sense of achievement. Whatever you build and fly ,take pride in your work and enjoy this hobby and all the aspects it has to offer.

The Jart is complete and should fly soon .

Now go build yours I am waiting and impatient.

JART BUILD

Jartists...

Look I said I would not post the wing build , but hey with the interest being shown from overseas as well as Reed Sherman the designer, I might as well . The count down to the maiden flight has already started so I am building at a rate of knots.

Build thread Wings and the rest .

The wings were cut from pink foam offcuts , just a tad short so a piece of blue foam was added in the middle I have changed the airfoil (is that allowed?) I have a set of lazer cut Mh 32 stainless steel templates and was struggling to make accurate templates of formica by hand. Anyway the MH32 is also used in F3B and can perform and is fast, and may be better at altitude.

The leading edge of the cores has 3 x 12 k carbon tows layed on, and allowed to cure.

I cut some mylars, waxed and sprayed them red, to bag the wing in one shot, I joined the mylars in the middle , this helps with the skins conforming to the tapers , if you use a one piece mylar, it sometimes makes a wrinkle on double taper shapes.

The foam core , now with its carbon leading edge was blown free of any dust, and the vacumn bag and glass cloth pieces all cut and ready. Its disaster to start a layup once the epoxy is mixed and find something has been overlooked, carefull preparation is the key.

The layup is 104gr at 45 degrees ( fine cloth less print through) directly against the painted surface, wet out and spread evenly into the cloth with a plastic phone card.

Next was the uni-directional carbon, stringy stuff , this is layed onto the wet out 104gr and I work it down through the plastic backing film , you can see the resin as it starts to wet out,

carefully peel off the backing and add resin to dry areas, by working the card back and forth with the grain ,the little strings holding the ud-carbon in place can be removed.

Finally a layer of 163gr was layed onto the carbon ud at 45 degrees and wet through, add only just enough resin.(This is a strong layup a lighter cloth could be used on the last layer)

The skins are carefully attached to the cores starting from the top surface(in other words you build it upside down) the top surface will be against a flat board while it is bagged.

The mylars are held in place with some masking tape and the end wrapped with some paper towel , this aids in sliding it into the bag and soaks up some of the excess resin which may ooze out.

The bag is sealed ,vacumn pulled and then released , this allows you to check nothing has shifted and smooth out the bag, then the vacumn again applied and left on overnight. The flat board was placed under the bag and two pieces of heavy wood weighted down the cores(I had no outer foam shells into which you would normally align the bagged cores.)

I now have a Jart kit of sorts , next comes putting the pieces together.

It all came out rather well , no time to celebrate just yet . The wings leading and trailing edges were cleaned up and then the whole wing polished, the tailplane was built at the same time and was perfect(I left out the carbon-ud but added a small piece of carbon cloth in the middle ).

The fuselage was carefully cut out, I have taped it extensively to protect the finish, carefull attention to the incedence is required.

Moving right along ,a trail fit of the wing was next, a little sanding was required . I have also marked the centre of the wing and then roughed the areas that are going to be bonded to the fuselage. At this time the control surfaces have been cut out with a modelling knife. The wings are fitted and aligned ,then tacked with some cyano, then I have used the ideal fillet material Sika-dur epoxy paste , its strong and you can smooth it on with your wet finger and contour it, it washes of with water.

The JART is now looking like a glider ,it has a weight of 770 grams excluding radio gear and balancing , looks like it will be at the lighter side (40-50 oz auw).

The canopy lip has 1 layer of glass , this will be sanded to shape and re-inforced , not entirely sure how the canopy will be held on at this stage.

Next thread ... fitting out control surfaces and hindging , radio gear, and final finishing.

cheers for now.

Race what jart race where are the other BERG club JARTS, ???????

JARTS HOT

Well while I have building momentum, and with a some slopes trips comming up shortly I continued with the JART over the weekend. I decided to leave the flying field early on sunday as conditions weren't great and I have missed a few rounds in the postals already.

I decided on a nice crimson red for JART no 1 (there will be more) after waxing the fresh moulds and masking off ,I sprayed about 4 coats of red 2k with an airbrush.

The first layer of cloth is a 104 gr which drapes well, you can press it into the mould and smooth it out prior to wetting it out. I have also cut a piece of 163 gr and some carbon before mixing 50gr of resin.

Two carbon tows 12k run the length of the fuselage as well as the leading and trailind edges of the fin, the carbon cloth 96gr is layed in the area were the wing will go through and the tail plane attaches , some small carbon off cuts beef up the pointy nose(I expected the nose to be difficult to wet out without a bubble so I made a cut from the nose down the fuse about 2cm long)this allowed the glass to conform to the shape ,ok. Next I layed up a second layer of 163 gr but this I cut slightly inside the mould and wet out.

After about 3hrs the resin had become semi cured (the so called green stage) and using a new blade the cloth is cut down flush with the mould. At this stage I join the halves a little different to the standard method , I cut strips about 2cm wide and wet them out in the mould , one strip on the bottom egde of mould 1 and the other on the top of mould 2 ( the photo above shows the joining strip on the near side sticks up about 1 cm). This is allowed to go to the green stage at which time I mix up 10gr resin with some flox to a syrup and using a syringe or plastic bag you "ice" a bead along the outer edge of the joining strip. The verticle fin has NO strip so relies only on the bead of goop to bond it. The two halves are accurately bolted together make sure the joining layer has slid into the other half, and leave to cure.
This morning was like a prelude to Christmas , I could not wait to see the results.

The mould was flexed and I could hear the cracking sound as the part released, first half popped off, and all looked good, a little more flexing and out it came.The white flashing is the joining mix that squeezed out and will be trimmed of.

The completed fuselage... perfect I am thrilled, it is a little waxy as I decided for the first one I would rather the part released ok. The paint will now be buffed with P1 polish back to a gleam.

For the record it weighs 185 grams and feels more than rigid enough.

Next we start with tailplane and wings but I am not posting these.I may however cover the canopy mould.

PS I am sure the designer Reed has been keeping an eye on my build as there is some info on JART WORLD .

Mike

JART

For all the JART fans busy building out there, here is the next part of my build thread. Part 4 and 5. (For more posting on my Jart Build, click on the "Jart" label at the bottom of this post)This is quite detailed and lengthy as I know there are others going the moulded route .

The photos are from my cellphone so not the best but if you have any questions please ask on the TAG board

The final coat of 2k was good (sanded and sprayed 4 times in total).

This was water papered with 800 grit wet paper on my fingers not a block.

The fuselage was surported on two blocks of foam sponge and polished with a sponge mop shown left, water and premier P1 polishing cream. (Not rubbing or burnishing compound. It is white in colour). Use plenty of water and keep it on the move so as not allow heat build up (very important if you have a foam plug.)

It must gleam as the finish will be reproduced in your mould. (I wear gloves so no fingerprints)

The Jart outline is marked onto a suitable piece of chipboard (this piece was part of a previous mould). I drill holes where the jigsaw blade needs to change direction and then cut it out (select a jigsaw blade that cuts on the down stroke. It gives a smoother edge.)

The Jart plug is test fitted. It must fit in to the centre line. The chipboard may need to be spaced on some blocks, be carefull not to touch the finish of the plug which protrudes underneath.
The gaps are now carefully filled with fast setting body filler. I use a product called featherlite. The type that uses a blue or red paste as a catalyst, not MEK liquid catalyst.

Tip: Mix small amounts (teaspoon) at a time and scrape it into the gap with a mixing stick and flatten it as you go. The filler soon becomes rubbery and then it is scraped flush with the splitter board and 90 degress to the plug.

It is easier to do than to descibe. Promise!

Once the plug is seated in the splitter board and gaps sealed and flush, you wax. Plenty of release wax. An hour or so later you buff off the plug, but not the splitter board. I have also made two little rounded bumps which will help locate the two halves later.

The gelcoat is painted on with a soft brush and allowed to go tacky but not cured. At this point I lay on the glass cloth and resin.

I lay carbon tows into the edges as shown. (A little extravegant but it makes this mould a little stiffer) You can also use a mix of flox and resin. The first layer of cloth is the finest, 49 gr then 86 gr then, 104gr and finally some realy thick bi-axial cloth to give thickness. Finish off with some fine cloth as this is easier on your hands later when working on the moulds.

The layup was allowed to cure properly and now the splitter board comes off. The mould is trimmed using a grinder with a thin cutting disc (Inox stainless steel 1.6 mm or thinner if you can). A Dremal cutting disc also works but is small and tedious.

The splitter is carefully cut in two weak points. Not right through as you don't want to scar the mould. Then it is easily broken away. The plug and face of mould are cleaned of any debris and waxed. Again only the plug is buffed off. Gel coat and glass layup as before. After this has cured I should have one JART fuselage mould.

The next post will probably show the final product getting ready to fly. I am not doing a build thread of the wings as we have done bagged wings on this blog before.

So far so good one side off.


Some of the paint has stayed behind. This happens from time to time. I will waterpaper with 1000 grit and polish the moulds with polishing cream. (The gel-coat is polishable)
Should I make it hot red, or clean white , or vibrant yellow, or evil black hmmmmm.

JARTS

To all the JARTISTS out there including Glen who has a sensitive side and flies a pinkish epp jart(check out the springfield gliders blog). Only kidding you Glen, later this week it is back to JART building, final polishing and splitter board preparation ,as well as moulding ,will be posted.

I am not sure what has happened to Piets Jart and Evans Jart and Lionals Jart and Roberts Jart and Gerts Jart and so on and so on .I know Reed the designer ,has mentioned on Rc groups that many plans have recently been requested from South Africa.

JART race is on

Not wanting to be left behind by Piet Perseverance in the highly charged JART construction

race I am forging ahead with my own JART.
I am happy with the shape so now starts the filling/ sanding cycles to achieve a moldable plug,

The resin I use at this stage is ZAP finishing resin as this sands easily and gives excellent results with water paper , for a finish you can spray on.


I make a mixture like thick syryp of resin/ 20 aerosil/cabasil (thickerner)and 80 microballoons ,it must just be able to flow like toffee , I then screed this onto the plug using different thickness pieces of acetate or mylar (off cuts lying around) the thinner ones you use to scrape across the curved parts, being carefull to only smooth and spread the mix not scrape it off, the end result is a smooth finish with the hollows filled , after some sanding I may spray or fill again until it looks right.
As it turns out a little filling and then to the water paper prior to spraying.

I have skipped the spray filler step completely, as I use a polyester spray filler and any hint of it near the blue foam and you have melt down.

I will water paper 400grit to flattern and then final spray before mould making.

Regards
Mike

Arother Smart Jart hits the BLOG Chart

Not be be outdone, Piet has forged ahead in the JART race and finished his fuselage. When Piet came around to my place to help me with the knuckles on my Shongololo, he brought it along to show me. We dissolved the foam out with petrol and shed around 100grams.Now the other Jarters must play catch-up because I have it under good authority that Piet is already busy with the wings.

Who will be the first to have their Jarts flying???????

Is it a bird ? Is it a plane? Is it superman?

No its a JART.........

I had my pdf plans printed out full size and being a patient sort of chap decided only to start the next day, here is the build thread thus far.




I marked out a traced template and glued together some scraps of blue foam , I no longer have big pieces so this will have to do.




Using P/U glue from alcolin I glued the pieces after wiping them with a damp cloth, the P/U glue needs moisture to cure, it tends to foam up and this is great as it fills gaps, once dry I roughly cut to shape with a hot wire bow.

AS usual I work on the floor with basic hand tools , the belt sander if used wisely, sorry that should read gently, sands the blue foam quickly, nice to radius edges.

Here I have started hand sanding with a block and trying to reproduce the Jart shape, they weren't kidding with that PNF pointy nose fetish thing, it looks possitively evil.

It does have an appealing jet shape.....
I have shaped the tail fin and attached it, at this time I have decided to layup some thin cloth/epoxy and filler and finish off to a sparkle before pulling off a mould.

How is yours getting along???? Evan , Piet , Robert and many others whose names escape me, right now.

JART FEVER

It looks like someone in our midst has been infected by JART FEVER this is serious, as it is highly contageous and already seems to be spreading. I know ,as I also seem to be showing the early symptoms , I phoned my Docter and he recommends going to a windy slope and throwing your Jart away into the strong wind currents , evidently after an hour the fever will subside,
this is the only known remedy.

JART FEVER dont say you were not warned.

More on the JART

For some more info and some interesting photos go and check out the JART blog.

http://www.jartworld.com/jartworld_pgs/blog_07.html

Be sure to go through the archives, especially August 2007 where you will see and some really cool photos of a Sea Eagle formatting on a Jart.


Also more on this balsa and ply built-up Jart. You don't need composite skills to build a Jart. It looks just as good as any other.

Also, (for Piet's sake) check out the name above the door in the "Jartworld in the UK" post. (Aug 2007)

February 2007 has an interesting piece on the copyright of the Jart.

The more I read about the Jart the more I want to build one. There is just something special about the whole concept and uniqueness of these beautiful looking slope soarers. It is not just the looks, it's the idea of being part of this "Jart International" family that appeals to me.