I'm getting interested in amateur rocketry. I'm realistic about it and understand that my skills and technology currently available won't let me construct anything beyond very simple designs, with glued paper hull and improvised nozzles, or at most with a hull from a pipe and water nozzle used fit to it.
What performance can I expect? How large such a rocket should be? Should I ever try build something longer than a couple of decimeters using such a primitive technology?
Try a basic calculation using the Rocket Equation and an Isp of 110 seconds:
$$ \Delta v = I_\text{sp} \cdot g_0 \ln \frac {m_0} {m_f} $$
$\Delta v\ $ is the maximum change of velocity of the vehicle (with no external forces acting).
$m_0$ is the initial total mass, including propellant, also known as wet mass.
$m_f$ is the final total mass without propellant, also known as dry mass.
m0 and mf depend on your design. The formula doesn't take wind resistance and gravity into account so it's optimistic, but it'll give a ballpark figure for the final speed, and from there you can calculate the altitude it'll reach.
