I wonder.... how many souls on here have a spifire? i would reccomend the build to most anyone. as a sheet metal worker i can appreciate the math involved on the round offsets. I built a C powered version of my own design while waiting for the real one to arrive. It looks cool but is underpowered, mostly because my version is heavy. i iused thick cardboard stock for my tube which i would not do again... this overweight situation has led to the thought of a first stage..... would be easier on my version because mine had a flat bottom and no engine hook.