There has been a thread on Chad's site relating to the construction of keel fins. I have posted this here so that I can attach a couple of drawings of the way I make my fins and rudders. I have used both NACA 63A010 and NACA 64008a, data from the Seelig site, plotted using the Profile software from the Aveox site. The profile produced is so close to the design that you need a micrometer to measure the variations - more deviations can occur during the sanding/glassing than occur from the forming of the ply skins!

The latest fin is for an 'M' and is about 600mm (24in) long. You can bend it if you really try, but it is quite stiff and resistant to twisting. Weight is about 160 grams (6oz) painted, ready for the bulb. The construction procedure is as follows:

Fin:

• Cut out two skins from 1.5mm gaboon mahogany ply (use what you prefer).
  
• Glue leading edge filler to inside of one skin.
  
• Chamfer inner faces of leading and trailing edges to suit.
  
• Assemble the spine:
  - Cut carbon kite spar to length.
  - Sand lightly.
  - Glue together with epoxy.
  
• Note: taper created by setting the spars in a slight 'X' arrangement.
  
• When cured, trim off the 'overlap' as drawn.
  
• Tack the spine to the inner face of one skin with super glue.
  
• Coat complete inner faces of both skins with epoxy (cloth laminating grade).
  
• Assemble in pre-prepared jig.
  
• Clamp down using T-section aluminum to 'ensure straight and true'.
  
• When cured:
  - Trim trailing edge as required (knife-edge or flat).
  - Shape leading edge using appropriate templates.
  - Close-off open ends.
  
• Apply two layers of 0.7oz glass cloth/epoxy.
  - One layer with weave along the fin.
  - One layer with weave at 45 degrees to the fin.
  
• Fill and paint to suit.
  

Rudder:

• Cut out two skins from 0.8mm air-ply (use what you prefer).
  
• Glue leading edge filler to inside of one skin.
  
• Chamfer inner faces of leading and trailing edges to suit.
  
• Cut the spine from 0.8mm ply.
  
• Tack the spine to the inner face of one skin with super glue.
  
• Coat complete inner faces of both skins with epoxy (cloth laminating grade).
  
• Assemble in pre-prepared jig.
  
• Clamp down using T-section aluminum to 'ensure straight and true'.
  
• When cured:
  - Trim trailing edge as required (knife-edge or flat).
  - Shape leading edge using appropriate templates.
  - Close-off open end.
  
• Apply one coat of laminating epoxy.
  
• Insert rudder post - fiberglass arrow shaft (your choice).
  
• Fill and paint to suit.
  

Attached are two construction drawings (yes, I was a design draftsman in an earlier life. I hope that they may be of some use to someone. Happy building!