This is my rebuilt Heli-roc. The thread on the fins holds the blades down, and at ejection the fin unit should separate letting the blades deploy. The plastic nose cone is filled with clay. I used an old Apogee B2-5 motor casing for the tube coupler, and some Kevlar® line for the shock cord. The two motors in the picture are Apogee B2-5 and 1/4A2-2.