Two simple steps transform a standard engine into a D size. Insert a standard engine into the adapter, and insert the adapter into a rocket. 3 adapters per pack. Reusable.
SO MUCH FUN having a rocket that launches SO HIGH on mini engines!
Booster engines push this rocket over 900 feet and is a pretty simple build.
Iris Ultra 36" HP Compact Parachute - 7lb @ 20fps; 3.9lb @ 15fps