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Wednesday, February 07, 2007


The last posts of the tailplane covered the material preparation and the lay up to vacumn
bag stage, normally I bag overnight and can remove the vacumn the next morning, its good practice to leave the parts in the moulds for at least a day in summer and maybe longer in winter, to totally cure.
This series of photos cover the joining of the halves and the finishing off.

The joiner tube be it carbon, or aluminium for the main joiner is put in place slightly ahead of the centre of lift this keeps the forces nicely balanced and if no slop exists will not induce flutter(the situation where airflow forces create an oscillation around a neutral point or axis).
This should also ideally be between the tows.

I have made a balsa shear web not end grain, but have wrapped the tube in with some carbon tows, this is all tacked in place with cyano, and later painted lightly with resin.
The rear tube is thinner and for this I prefer brass , this thin joiner goes through the belcrank that the servo is going to actuate. The STILLETO design also has a small joiner in front of the tailfin leading edge to reduce twisting and help alignment between the tailplane halves.
Once the sheer webs are in place with the joiner tubes( important to have them all parallel)
we prepare the joining mixture.

Here I have mixed about 10 grams of resin /harderner with about half a teaspoon of cotton flocks(a fine form of shredded fibre glass still providing strength) a teaspoon of micro balloons
which adds volumne and is light but does not add much strength.

The mixture is well stirred and must be ever so slightly runny but not like paste, add micro balloons if required. This is then placed in small plastic bag and the very tip cut off, you now use this to squeeze a thin bead of mixture on the surfaces to be joined.

The moulds are now left overnight to cure , the next move once cured ,is to gently twist the moulds, a distinctive cracking will be heard as the part is released, normally one half will pop off , carefully twist the rest of the mould and the tailplane will come free.

It looks good , lightly sand the flash(excess) off the edges and race to the scale to see what it weighs (90 grams on the dot) it could be slightly better but still beats the 1st one at 120 grams ,
I am pleased ,its in the design weights.

Pretty colour scheme, remember to spray your stripes in the correct order ie outside in.
next post will be more detail on the wing tip mould which is currently curing.

Any comments are welcome as I am fairly new to composites / moulding and learning and teaching at the same time, trying to combine art with science.
So your input is welcome , please post a comment._

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