I'm consider building this cluster **** using BP motors. Have the booster stage on (3) E-9-0 when it drops it will come down via parachute, verses tumble drop. Those motors will ignite the next 3 engines E-9-0 which will be tape to E-12-? after they burn out they will drop out the bottom of the rocket and lite the final 3 motors recessed in the air frame. which will continue to apogee and motor ejection coming down on a nice size parachute. Considered using a BT-80 for the air frame design.