RGClark
Mathematician
Change the empty weight of the second stage from 3 lbs to 6 lbs, and then to 10 lbs, make equivalent changes to the first stage empty weight, and believe me, you will see a radical change in the altitude of the rocket. Rockets of this class fly like sounding rockets, the higher the propellant fraction, the greater the burnout velocity, and the higher the coast. These rocket are also very sensitive to changes in CD, more drag in the lower atmosphere, lower velocity when you get to the thinner upper atmosphere, the lower the coast distance.
You really need to nail down accurate empty weight estimates for the first and second stages. As I posted, take a look at the Loki Dart booster and other sounding rockets. But remember, almost all high power/amateur rocketeers have not demonstrated those levels of empty weights/propellant fractions.
Chuck Rogers
Sounding rockets or orbital rockets don’t use airframes or body tubes. These take up a significant fraction of the dry mass of amateur rockets. Without this, you just have the weight of the fins for a stage not intended to be recovered, which for space rockets is almost always the case. The fins make a small proportion of the dry weight of the rocket.
Bob Clark