L2 TRA 8993, NAR 79813

I finished the update to Rocket Calculator and submitted to Apple last night. It should be approved and available in three to five days. This update contains the new altitude prediction calculator as well as a few usability improvements.

The new calculator displays burnout velocity, burnout altitude, peak altitude, and coast time. The user inputs motor case mass, propellant mass, average thrust, burn time, empty rocket mass, drag coefficient, and frontal area. There is a data assistant screen that can help determine some of the required values based on other known values. For example, you can calculate average thrust if you know the total impulse and burn time. You can calculate the burn time if you have the total impulse and average thrust. You can calculate the area with the body tube diameter.

I plan on adding some kind of system for body tube and motor look-ups to make data entry even easier. For the time being, a good source for motor data is the NAR Certified Motors list. Another great resource is thrustcurve.org.

The calculations used are based on the Fehskens-Malewicki solution to the equations of model rocket motion. These equations are also mathematically identical to the solution determined independently by Randy Culp. Randy Culp’s site is a excellent resource for understanding the equations. Tom Beach’s site is also extremely helpful.

Here is a screen shot of the new calculator. As with the other calculators you can print or email the results.

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