The inspiration, the philosophy, and the story behind the Jart can be found on the Jart World Web page. Well worth a visit!

Monday, December 31, 2007

Jart's Maiden flights at Volksrust -Trevor & co.

Kobus, Wesley and Trevor, went down to Volksrust just after Christmas to maiden their Jarts. I was there and took a few photos of the action. Very impressive when a scratch built model is launched and flies beautifully straight off the building board. Not to mention how great these models look in the air and how well they fly. And the paint jobs on theses three Jarts are very striking. Well done to them all on a great project.

Both Trevor and Kobus flew their Jarts, but unfortunately Wesley's did not get to fly because of a problem with the ailerons movement. The photos below can tell the rest of the story.

Trevor's first with Kobus helping with the pre-flight checks and Lionel doing the launching.

Then it was Kobus' turn with Trevor lending a hand!

Sunday, December 30, 2007

Joining the wings by Trevor & Co

Hi Jarters

After crossing the hurdle of preparing the fuzz, it is now ready to add the wing joiner for the wings onto the fuzz.

We took the same size hollow carbon tube as we put in the wings, and aligned the wings up on the fuselage and inserted this tube across the fuselage. The wing joiner was made out of carbon toes pulled through an aluminium tube the same side as the carbon tube used in the wings. We used caustic soda to remove the aluminum from the rod.

Once we had aligned the wings, we found imperfections in our wing-lets and had to remould and form them all over.

After much sanding and finally getting the wings lined up with the fuzz, we needed to set the incidence on the wings and the stabilizer. Using the plan as a guide line,we used and incident meter to set everything up.

As we went along, things got easier, by the time we did the 3rd plane.

Once Kobus's Jart had been set, it was now time to mask off the stab and paint the fuzzes.

(At least some progress seemed to be taking place)

Finally we started the painting.

After struggling with Kobus's painting we finally had finished the three Jarts.
We now had to finish the cutting and making the hinges on the ailerons and stab.
We cut out on the bottom of the wings for the HS125mg wing servos and put the pushrod in for the HS85mg elevator survo mounted in the front of the fuzz. We checked out the CG and had to add 160G of lead to the nose and they are all ready to fly. All three Jarts weighed between 1.5kg and 1.55kg.

When the winds picked up at about 2pm on Friday at Volksrust we Maidened our Jarts.
I was amazed at how well they moved in the sky and only trimmed out the elevator about 2 clicks of up trim and she flew straight and fast. Kobus also added a little up trim when he flew the yellow Jart. After the two flights we discussed the performance of the two planes and came to a mutual agreement that they are great in the sky and all the hard work really was worth it.
We will maiden Wesley's next time and I am convinced that his (the blue Jart) will also fly great.

Evan has some photos of the Jart in action on the slope and said he will post them soon.(can't wait)
This has been a great project and we have enjoyed learning new ways of creating and building planes using carbon and fiberglass. We look forward to another project like this one.
Trevor, Kobus & Wsley

The Fuzz (cont) by Trevor and co

Hi Jarters

The last time we spoke we were getting our fuzz's ready for undercoating and the removing of the foam, wow preparing the fuzz is a lot of hard work and sanding, but eventually got it right.

We sprayed the fuzz in mc primer, only once we had sprayed the primer on, did we realise how many holes and defects there really was, so we sprayed and patched and sprayed over and over......

I don't recommend that the wing-lets be put on while preparing the fuzz as we have, because getting everything straight and aligned is a mission. Doing this type of building for the first time really made it time consuming getting it all straight, but in the end after all that hard work we decided to cut them off of Kobus and Wesley's fuzzes.

Finally we got all the fuzzes sprayed and undercoated and decided to create the canopy now before opening up the fuzz and removing the foam from the inside.
To create our canopy, we were privileged to have Kobus in our team to make a plastic mould from one of his moulds from another plane.
We took this mould and polished the inside of the plastic and laid up some fibreglass and resin to create a canopy.
This canopy was our dummy canopy to cut out on the fuzzes.

Once we had tested and made sure that this canopy fitted snug on the fuzz, we then used the same mould and laid up 3 canopies with 2 layers carbon(96g cloth).

Once we had the canopies done,we put them on the fuzz in the correct position and drew a line around the canopy on the fuzz as our cut line.

Trevor's fuzz was the dummy run and the cut out was the same size as the canopy, but Kobus decided to cut his out smaller and allow his canopy to overlap the fuzz (This turned out to be the better option).

After removing the cut out it was time to clean out the fuzz with petrol. We were all looking forward to this because at this stage all our fuzzes were quite heavy.

To our amazement only about 30g, if that, was taken off the overall weight. It was now starting to take shape because we could start attaching the necessaries for the wings.

On our next postings we will follow up on joining the wings.

Trevor, Kobus & Wesley

Wednesday, December 26, 2007

All I want for Xmas is a RED HOT Jart.

Well after not falling for the reindeer food that I set out for Santa on Christmas eve, I manage to contact the overworked guy to stop in on Boxing day before his long flight back north. He showed me his empty reindeer food bag (as you can see in the picture below).

However I quickly re-fueled it for him (hoping to score some brownie points) and hoping that he just might have one more Jart left amongst all his empty Christmas bags. But alas there was nothing.

There was one bag though, that looked quite full and rounded in the right places. He said that I can gladly keep this although it might not fly to well.

So I offered to look after it (hoping to score some more brownie points). He also gave me his Shotgun and some cartridges and said that I might need it in the process, as nobody is going to Hi Jack a Santa with a empty sledge on his way home.

Not wanting to disappoint the dear old fellow, I agreed to all his terms and conditions and soon he was on his Sledge and with afterburners glowing Red Hot (sounds familiar) he disappeared into late night sky. A happy fellow with his work done for the year.

Obviously I was disappointed at not getting my Jart for Xmas but I could not wait to see what he did given me for Christmas. So I rushed inside and this is what jumped out the bag!!!

Anyway, I am quite happy with this present. Don’t get any ideas guys. Remember the Shotgun!!!.

I will just have to compete my Jart in the New Year seeing as how Santa couldn't help!

Wishing all Jartists a Happy New Year.


Monday, December 24, 2007

email from Julian Kent (aka minifly on RCGroups)

Just to let you know, I think I was the first person to complete a Jart in SA. My Jart flew at Hermanus 2006, and despite its extreme nose-heaviness and me pulling the spoilerons a moment early, managed to get a decent shot at the spot landing. Aragon got some video...I'm quite sure it's on RCGroups somewhere. It is now a very ugly, beat up Jart (I built it by layering wide-weave FG over EPS, with a balsa sheated EPS wing), so I'll probably give it a complete makeover one of these days.

Wednesday, December 19, 2007

Journey to JARTdom - Part 2

Making a plug
During one of the many mold making courses that I attended, I learnt that the first step towards JARTdom was to constructing a fuselage mold – a relatively easy, but somewhat painstaking task. I learnt that one approach was to use a medium grade wood for the plug (& I just happened to have some blocks of local Maranti handy - a medium hardness wood with a relatively close grain) from which a “female” plug is made. Later I decided that this wood grain was too course, & would rather recommend something with finer grain & somewhat softer density. After some research I found the correct version of the freeware Adobe Reader 6.x and printed the plans out using the Tiling feature (this feature is only available in the commercial version of later releases) onto A4 sheets & stuck these together. Soon this was transferred to the wood blocks that had been joined with a PVA wood glue (Lesson: this was a bad choice – as the water used during fine sanding wicks eats into this join & it creates a small mark along the plug – if you are thinking of doing this, use a waterproof glue).
I used a powered jigsaw and a plane to rough shape the blocks, after cutting templates from cardboard. The side profile looked awesome, but the plan view just did not “feel” right, so I modified it a little such that the nose was slightly narrower than the original 8020 shape. Then I applied lots, LOTS, actually HUGE AMOUNTS, of sandpaper until I had something that resembled a relatively smooth block of wood, which had even started to look like a JART fuselage amongst the copious quantities of wood shaving & dust. Did I mention that I used a small warehouse of sandpaper? I now understand why molded aircraft cost so much – it is all the sandpaper that is used.

First steps, the wood blocks are joined, rough shaped,…
... and liberal sanding is applied to create a smooth surface
Then came the interesting task of creating a smooth surface that would yield a polished “glass finish” type model – the stuff you see on all those fancy imported models. I started with common garden variety sanding sealer – boy this stuff smells just like the dope we used with tissue paper on those small free flight models we built as kids. It gives you the same headache too if you paint in a closed area.
After the first coat, the wood was all hairy again, and it was back to sanding until a silky “soft” finish is achieved (round about 400 grade paper). I then switched to water paper (600 grade) and had a “soapy” smooth finish after some effort. At this point I started to think that the building group would have to sponsor pay my medical bills for my tennis elbow! Around this time I also learnt the error of my ways when I elected to use a non-waterproof glue to join the smaller wood blocks, since the water used during sanding seeped into the join & created a small ridge, no matter what. Only dry sanding & later sealing eventually cured this.
After repeating the sealer & sanding most of it off again process for the third time, I sprayed (from a spray can) the first application grey primer paint & again removed 99% of this in the sanding process too. After I had used the entire can of primer (which equated to approximately 3 full coats sprayed on & subsequently sanded off). Just before the final sanding sealer coat & primer was painted, I “added” the 12mm thick balsa fin & had this smooth in no time at all. Unfortunately, I must have gained considerable upper body strength in the previous fuselage sanding process & proceeded to over sand the fin – which was now also a little sleeker than the original section, so I thought “why not?” and stuck it in place. I then applied a fillet of SikaDur epoxy between the fuselage & fin, and with a wet finger smoothed this until it also “looked right”. Sanding time….
I was struggling to remove the grain effect – the wood I chose was a little too course grained & water paper sanding down to the wood layer resulted in fine holes appearing. At the suggestion of an experienced friend, I mixed 10%-20% talcum powder into some sanding sealer & applied this as a surface sealer, before sanding it all smooth with 600 grade water paper. I also learnt the trick of adding a little dishwashing liquid to the water as this prevents instant clogging of the sandpaper. Finally I learnt that you have to wait until the sanding/sealer/talc combination is 100% dry – as tiny little bits are created otherwise which create long grooves in a nearly smooth surface. Oh well, nothing that more sealer & sanding could not cure.
My friend Evan (of F3B - Shongololo building group fame) advised me to use an automotive 2 part paint to create the best surface finish on the plug. So, Marcel, who had planted the orginal seedf, and who had sprayed 2K onto his aerobatic F3A models before, was lured over to the house with the promise of beer. He was soon set the task of spraying the plug (I looked after the beer part of the deal). The only mistake I made was to choose white paint only. If I ever do this again, I would spray layers with alternate colours (like white & black), as it really speed up identifying small holes/bumps during subsequent sanding processes. When it was my turn I learnt all about overspray, pinholes, orange peal & various other interesting “effects” that are achieved when spraying. Fortunately, and once again, it was nothing that a little sanding could not cure. In fact I have come to learn that sandpaper is your friend – my local sandpaper wholesaler provided me with a great wall calendar & even the recommended retail price list for 2008!
The 2 part automotive paint used to achieve the final surface finish
Around 3 days after spraying the frist coat of 2K, I started using 800 grade water paper, and admit that the water & dishwasher liquid approach resulted in a serious saving of the rain forest as I was now only using a few parts of sheet per layer (dunno what the carbon footprint of dishwashing liquid is, but being glider guider, I reckoned I already had to have some positive eco-points stored up already).

Post 800 grade waterpaper sanding – a smooth sheen is starting to emerge

After two more coats of the 2K paint I had almost eliminated all the grain marks & join lines completely. I finally switched to a 1000 grade water paper & managed to get a “buffed” surface finish – if you wipe a wet cloth over it, it shines. I thought that the time for polishing had arrived. Using a sponge polishing pad borrowed from Evan, and some G3 polishing compound, that matt surface was quickly changed into a shiny “new car” finish & at last I had a plug that I was proud of.

I took it along to the BERG club (current home of the F3B Shongololo building group) for a show & tell were we fooled around a little for the photo’s. The list of aspirant building group members has started to grow (note to self: I will have to create a formal list once the molds are ready).

Next stage: building the mold