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Monday, November 12, 2007



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, ???????

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