Well, here's how it started, an "initial concept" entry in my journal...
The basic idea being that the booster stage ejection gases would pass through the interior of the booster, cut a "burn string" to deploy the spring-loaded helicopter blades, and then ignite the upper stage motor. Easy. A more detailed view of the spring mechanism looks like this:
With the exception of the protruding spring arm (made of 0.032" music wire) to support the helicopter blades, the whole assembly would slide inside the rocket body. The spring arm pivots on an axel near the top and is held in tension by a spring connected by a Kevlar string. When readied for flight, the blades are folded down along the rocket body, under tension, and tied with a piece of elastic thread passing through the body tube.
The spring arm itself was a piece of work, but hopefully will provide enough "flex" that it will absorb the stresses of blade deployment and not tear itself apart. I included a 3D .stl file of the spring arm itself below.
Now armed with an idea of the size, weight, and locations of the spring mechanism and the upper stage transition, I worked up a draft of the proposed rocket in OR, Slingblade 3.0.ork file also below.
This is tricky also. Weight is a big issue since the maximum lift weight of a C6-0 is 4.0 oz.! (I'd like to avoid using a D booster if I can, but am designing for it anyway.) Also, increasing the fin size of the upper stage for it's stability plays havoc on the booster stage stability. Lots of trade offs. Note in these OR simulations, the weight and configurations of the spring mechanism have been all lumped together as an "internal mass component" using an override. (Same with the transition.)
I'm just now starting on design for the blades themselves, but intend on using BT-55 stock, cutting them to a propeller-like profile, and adhering them to the spring arms. I know, not real stout materials but again: the idea here is for them to flex with the forces, not remain rigid.
That's kinda where I'm at.