Rocket Experiment: Why Calculations Were Off

[jnimagine]

we fired off a rocket in physics class and we have to write a report about it.
I found out that the height of the rocket calculated using formulas was very off from the real height of the rocket figured out by calculating the tangent of the angle of altitude. (there was an altitude person who measured the angle to the height of the rocket when it was fired off) That angle was 40degrees. The height I got using formulas ( first figuring out max kinetic energy then gravitational energy, then total energy, then the height) was 1127 while the one using distance measured from the rocket's highest point to where the altitude was measured and tan of 40 was 82 yah i know the two numbers aren't close at all.
So we have to discuss why the result is so off. Reasons other than things like human errors... what i have thought of so far are friction, wind, and energy losses...but i just can't seem to be able to explain those reasons very well... and could you also explain the energy losses during the flight that might have caused the calculations to be wrong?

Thank you for your help

 

[berkeman]

First of all, it's good to get in the habit of including units with each number. As to reasons for potential disagreements between the expected height and actual height...

-- How are you calculating the expected max height? Do you know the thrust of the rocket versus time (like from a stationary test of the rocket motor against a spring balance)? Do you know the weight of the rocket versus time as the propellant burns off? If you know those things, all that is left is air resistance and wind effects, which you can add into your calculations with some approximations.