*Equations for finding your rocket's peak altitude and motor delay. *

**Definition of Terms **

- m = rocket mass in kg (see below)
- g = acceleration of gravity = 9.81 m/s
^{2} - A = rocket cross-sectional area in m
^{2} - C
_{d}= drag coefficient = 0.75 for average rocket - r (rho) = air density = 1.22 kg/m
^{3} - t = motor burn time in seconds (NOTE: little t)
- T = motor thrust in Newtons (NOTE: big T)
- I = motor impulse in Newton-seconds
- v = burnout velocity in m/s
- y
_{1}= altitude at burnout - y
_{c}= coasting distance - Note that the peak altitude is y
_{1}+ y_{c} - t
_{a}= coasting time => delay time for motor

Note on the rocket mass: you usually know the empty (no motor)
mass of your rocket m_{r}. You can usually find the
loaded mass of your motor, m_{e}, and the mass of the
propellant, m_{p}. Both Estes and
Aerotech
provide these numbers in their spec sheets and with the motors.
Then

- average mass during boost is m
_{r}+ m_{e}- m_{p}/2

use this value for all but the y_{c}, q_{a}, and q_{b}calculations.

- mass during coast is m
_{r}+ m_{e}- m_{p}

use this value for the y_{c}, q_{a}, and q_{b}calculations.

Back to Rocket Equations

*Your questions and comments regarding this page are welcome.
You can e-mail Randy Culp
(Tripoli #6926) for inquiries, suggestions, new ideas or just to chat.
Updated 24 August 2008*