Well my first rib test was a success - it survived in tact loaded up to 8g (71.8Lbs / 32.6kg) without failing... though the middle brace was bowing a little at full load.

You can find three photos of the rib and test stand in my photos folder - (Root-Rib-1 to Root-Rib-3) - groups.yahoo.com/group/Carbondragonbuild.../1647894528/pic/list

The rib was constructed from 5mm thick closed cell PVC foam sandwiched between two single layers of 195gsm (3K) carbon twill cloth. The internal braces and rib perimiter are all 25mm (1 inch) wide by 5mm thick. The rib was laid up over a 12mm thick male mold (made of varnished MDF) which allowed a 12mm wide flange (comprising two layers of carbon cloth) to be be formed all around the outer perimiter of the rib. This flange adds significant stiffness to the rib and prevents it from buckeling under high load. Once the rib was post cured in an electric fan oven at 140F for 24hrs, the rib was demolded and trimmed using a Dremmel-style tool (a fine carbide disc) to its final configuration.

The finished rib weighed approximately 90grams (of which the foam core weighed 25grams). The rib was given a peel-ply finish all over. A small saving of weight could be achieved by only putting the peel-ply finish on the flanges where the rib will be bonded to other components - every little helps!

Load was applied evenly along the rib aft of the central diagonal brace (which was mounted upside down on the test pillar to simulate positive g-loading) by adding water to a large plastic barrel hanging from broad nylon straps.

My next step is to construct another, similar rib, but this time with internal braces and perimiters of just 12mm (half an inch) wide rather than 25mm. If this survives testing then it will represent a significant weight saving on the first rib and should also be lighter than a rib constructed of spruce (approx 60grams).

Phil.