Uni-directional carbon fiber in the rudder blade (updated)

There are a number of steps involved in getting the basic foam core re-inforced properly.  After the wrapped high density core is inserted,  some unidirectional carbon fiber tape has to be laid down on top of it.

Here are the pieces of tape cut to length and ready for application.  I used a 9 oz. weight carbon fiber  tape.  I can never get the tape trimmed as perfect as the plans show it.   You can also see the rebate around the high density core.  I tried to tailor the depth of the rebate down the length of the blade but I am sure some fairing putty will be required to get the profile shape back.  I'm always slightly phobic about making the rebate deep enough (is the high density core too thick?, is it mounted properly?), but I just stick to the dimensions indicated in the plans.

First I filled up the gaps around the rounded corners of the high density core with some high density putty.

And while still wet applied the layers of carbon tape.  The epoxy saturated  carbon uni-directional material really needs to be compressed and using a plastic sheet to squeeze out the excess resin really does minimize the overall thickness, which I think is what you really want.  

Everthing looks good and when it's cured I will apply the fairing putty to the trailing edge of the blade and recover the profile shape over all this carbon fiber.  Then turn the blade over and do the other side.

Updated December 23rd

Work has slowed a bit with Christmas and other projects but I have made a bit of progress in finishing off the one side of the rudder blade.

The above picture shows the trailing edge cut away to the centre and is ready for the lightweight putty fill.  The original layer of 6 oz fiberglass cloth really helps here to cut away one side of the blade at a time.

Here is the blade (port side) with the putty applied and sanded down close to a point that is almost ready for carbon fiber cloth sheathing.  I will now turn the blade over and finish the other side but  I have run low on carbon fiber and will have to visit Noah's or Canada Composites soon. ( A trip to the other side of Toronto).   I want to make sure I have enough material to finish the blade and rudder case.  This will be my last post of the year so merry Christmas and a happy new year to all.  2009 should be interesting. 

Inserting the final high density core into the rudder blade

The final high density insert has to be wrapped in carbon fiber (F-22R option) and helps to create the longitudinal rigidity required in a modern lightweight foam rudder.  The high density foam is tailored in thickness so that further uni-directional carbon can be added on top of each side without adding thickness to the rudder blade.

I wrapped the upper and lower halves seperately so that it could be held for wrapping.  You can see the plastic stretch wrap which really helps to hold the carbon cloth in place.  It also allows all the excess resin to be squeezed out to either end.  

For some reason I decided to shape the foam before glueing in this core.  It probably would have been easier to insert the tailored wrapped core into the original rectangular block of foam, and then do the shaping.  Inserting the core after shaping required the use of some simple jigs, spacers and clamps to make sure there was no twisting or mis-alignment in the blade while the epoxy glue was hardening.

The offcuts from the original blade block of foam were put to good use.  The operation was successful and I am now putting in the rebates for the uni-directional re-inforcements.

Rudder blade foam shaping

Fellow builder Menno had a idea that he shared on the builders group.  He wrote

"My idea is to draw lines on the blank lengthwise, combining all points where the rudder/centerboard has the same thickness. Then use a router to make grooves with the correct depth and use those grooves as a guide..."

Something about this idea stuck with me and the thought of again artistically shaping the blade through the use of the templates seemed like a lot of work.  I know,  I shaped the daggerboard that way last winter.  So I decided to give the router approach a try.

Above is the block of foam with the high density inserts in place.  The block is thicker than required but I wanted to glue the foam  so that the centre had a glue joint.  I also applied a light fiberglass cloth in this centre joint (as I did on the daggerboard)  so that this thin blade might hold together a bit better.  Using the full size plan I transferred the lines.  All the arrows are to remind me to keep the cutter to the outside. 

I've used this mini-router before to create rebates where needed.  This time it is being put to very good use.
Removing the extra block thickness.

I used the oribital sander to get the shape close and then finally some hand sanding. 

And viola, here it is,  close enough to start work on getting the high density foam core inserted down the middle.   I wish I had made the daggerboard this way, this approach is much easier for me.