Looking forward to any related developments on this. Once upon a time built a tractor parallel staged model, powered by Estes 24mm D12-0s and an E15-8. Streamer recovery on the booster pods. Flew great, including staging.
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Its design was inspired by an example that you may have seen in Stine's
Handbook of Model Rocketry (pardon the coarsely-scanned image).
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Before building the model at top, I built an intermediate-sized 18mm motor model with two T-fins like the
HMR example, powered by B6-0s and a C6-7. My "that looks about right" friction fit on the booster attachment was too loose, so things disassembled themselves at liftoff and flew in at least two different directions. Good learning experience on the friction fit though. Also learned to make the igniter lead wires as long and as lightweight as I could given the electrical current draw and to suspend the wires on stanchions, to give the igniters as much of a chance to do their work as possible between when the first one and the last one cooked off.