No nose weight needed (the 1/8" balsa supplies a LOT of weight up front just by itself)
Parts:
Poster Paper nose-pyramid (not really a cone)
Duct tape and dental floss hinges (light, incredibly strong, not difficult to do but you do need a sewing needle)
1/8 inch balsa (need the stiffness)
Rotor Fins are 18 inches long. Front 2 inches are used to make a "hub" Angle of attack is 15 degrees.
Fin parts are 7 inches long,-- 2 inches wide) they stick out perpendicular to the rotors. They are actually attached at a 45 degree "joint"
Rotor stops are double ply 1/16 inch balsa, one piece cut with the grain, the second across the grain. When these are attached, they are very strong in any direction of stress. The are set to position the rotors at a 15 degree dihedral nose-down.
On the tips of the rotor stops are short segments of coffee stirrer straw, 1/2 diameter. This makes a "trough" to hold the pull strings away from the body of the rocket.
4 triangles are cut out of plastic "hotel key cards" (could use card stock. Cannot use balsa as needs to be strong in all directions) These are 3 7/8 on each edge, to fit just INSIDE the fins.
Two of these attach the motor mount, a 1 1/2 inch BT-20 segment, plugged at the nose end to force rear ejection. One triangle each is placed on the other two fins, they are "staggered" below the opening of the motor mount tube. Small balsa strips are used to "brace" the triangles against the fins. The central holes are just big enough to pass the BT-20.
Pull strings made of kevlar (just cuz I have a huge spindle of it) are attached to the front of the balsa hub at the base of the nose-pyramid . These run about 1/2 way down the length of the body. Small dental floss loops are attached about 1 inch up from the tail end of the rotors to hold the rubber bands. Tiny S-hooks made of paper clip wire are used to attach the rubber bands to the pull strings. These are easily released when the rocket is stored.
Two other models you might get a kick out of:
https://www.rocketreviews.com/umm-me-uranus-explorer-2-scratch-by-tom-markel.html
https://forums.rocketshoppe.com/showthread.php?t=9824