As mentioned before, I'm basing my full scale quad design around a 4m rotor diameter. That makes each rotor blade 2 m long. I've decided on a NACA0012 airfoil which is commonly used for full scale helo's. This is a symmetrical airfoil with a glide ratio of about 60:1. I'm planning to build the rotors of composites with E-glass fiberglass cloth, epoxy resin and extruded polystyrene foam core. My budget is a meer trickle so I am selecting lower cost (and lower performance) materials than might be desired if my budget were larger. For example, I might use urethane foam and carbon fiber cloth for the rotors. However, I believe I can meet the needs using these lower performing materials. The symmetrical airfoil will allow me to build all 8 rotor blades essentially the same which should simplify things a bit. I have purchased some 6 oz/yd standard weave fiberglass cloth, and Series 2000 epoxy resin with 2 hour working time hardener from http://www.fiberglast.com/ . I am currently experimenting with the fiberglass layup process as this is a new area for me. The 2 hour cure hardener requires elevated temperatures to cure, so I glued up a small part and put it under a work lamp to cure. (suggested temperature is 120-130 Deg F for 12-14 hours. I guess I put it a bit close to the lamp because it melted a crater into the polystyrene foam. In hindsight, I learned the working temp of the Owens Corning Foamular 150 polystyrene board is 165 F. I exceeded that.
I'm working towards building a small section (12" long) of rotor spar comprised of a foam core, 5/16" diam fiberglass rod leading edge (for impact durability and rotor CG management) wrapped in two layers of 6 oz glass at +- 45 deg to hopefully give it strength against shear as the web of the rotor "beam" formed by the upper and lower skins.
The chord of the airfoil is 20 cm, and this spar is the front 30% of that chord, or 6 cm. In my research I've seen this approach (a wrapped leading edge acting as a rotor spar) used for rotor blade construction. After building this small section, I will test how much bending moment it can withstand before breaking or kinking.