I went and looked at my CC Express, and I did move the sustainer thrust ring forward to accommodate an E motor, but since they didn't have an E booster motor at that time, mine uses the D12-0 for the booster. I considered making the booster a little longer, but with the fincan in my hands, I noticed that every one of the four fins on that booster had cracks at the base. Even with a D motor, that booster is too heavy for tumble recovery. If you put an E motor in it, you will constantly be repairing it unless you design some sort of recovery system that will slow it's descent. My rocket with a D12-0/E9-8 motor combination will fly out of sight in a clear sky, the only reason I have recovered it is the excellent launch area we have in Rainbow Valley, AZ. I probably will fly it with an E12-8, but I'm gonna watch it with my binoculars when I do!
NAR 92675 L-2 Superstition Spacemodeling Society
I may be getting older, but I refuse to grow up.