As I mentioned last week, I have been working on helicopter model rockets for teeny 1/4A3-3T model rocket engines. I test flew my first model last week. The blades deployed before landing, but just barely. I'm now working on a shorter model that I hope to test before the contest this weekend. Here is the model I tested with blades folded before launch.
Just barely visible is the white elastic thread that keeps the blue and yellow rubber bands from spreading the blades.
After the ejection charge blows through the little hole just above the fins and burns through the elastic thread, the blades spring out like this.
I'm holding the model sideways/top down in the picture.
Now, for a close-up of the open blade/spinner hub assembly.
You can see the rod that passes through the spinner hub. The wooden nose cone is glued to the rod and nothing else. Everything below the nose cone spins freely on the black rod. Notice the wedges of balsa wood at the base of the blades where they are attached to the hinges. That is to give the blades an incline so they will spin around the hub. The black blobs are rubber containing flexible super glue.