Sunday, February 25, 2007

How to build rudder blades and centerboards

I was generously sent some material from an interested F-22 builder in my area yesterday.

How to build rudder blades and centerboards

The article makes me think about the question of material for the daggerboard. Should I use shaped foam or edge glued red cedar? I'm imagining the flow around the aft edge of the board at 15 knots.

Here is a section from the link that I find very interesting about the trailing edge.

Here is a technique for fiberglass covering that has proved over the years to provide a long lasting trailing edge. When rebuilding an existing blade or before applying fiberglass cloth to a new blade, plane a flat on the trailing edge about 1/8"-wide (wider for large rudders and centerboards). When applying the fiberglass cloth, position the rudder or centerboard horizontally so the leading edge is up. Drape the fiberglass over the foil and trim so that it extends 1/2" past the trailing edge. If you make a full-scale drawing of the trailing edge of your board or rudder, you will get a better idea of exactly how much fiberglass cloth to leave.
After the fabric is wet out, use an #807 syringe to apply epoxy thickened to a non-sag mix with 406 Colloidal Silica to fill the gap between the two layers of fiberglass cloth. Squeegee out excess epoxy and align the trailing edge so that it is straight. If necessary, clamp a plastic covered straight edge in place to make the fabric conform to the shape of the trailing edge. After the epoxy cures, do the final shaping with a sander or sandpaper and a block of wood. Use caution, the edge can be very sharp!


MartinF said...

Hi Grant

I done some foils in my time and i got a exel spreadsheet for calculating Naca profiles for naca 4 digit (ex. 0010), 64 series and 65 series. The two last is for higher constant speeds and is not so foregiving as the 4 digit. But I have done a 505 dinghy High aspect centerboard in naca 64 doing well. If interested please email me. See my F82R blog

Grant said...

Hello Martin,
I was planning to use the profiles supplied with the plans. My thoughts now are more oriented towards the question, how to build a light but durable daggerboard. Your blog site is impressive. I'll be adding your site to mine as a link soon.

MartinF said...

The profiles are proberly naca 4 digit, like the F82 foil. The easy way out is to have the core CNC routed, if you know of someone that got the knowhow and the machine. First you need a drawning in a cad version the cutting machine can read. The nice thing is that you know that both sides are completly alike. The spreadsheet can be used for such a drawning or for hand building as well. tell me if you want a copy by email.

I don't know if Ian has not provided you drawing of the daggerboard yet, but in my planbook there is a full how-to-do-it plan using normal foam and hi den. foam in the middle.

My site was started because i saw yours and other F22 builders using this blog form instead of a home page. This is very easy and it looks good too.