An update for Rocket Calculator is available. This update contains the new altitude prediction calculator, based on the Fehskens-Malewicki equations. There are also some usability improvements, and a couple bug fixes. As with all the other calculators, the unit preferences are very granular and can be changed from the app settings screen.
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.
In the near future I plan to add a 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.
To help promote the new update, I'm selling the app at a reduced price through the end of this month.
Here's a pic of the new calculator: