An offline flight computer for model rocketry — predict altitude, compare motors side by side, check stability, size recovery, and log your flights to close the loop between prediction and reality.
Select up to 8 motors from the full catalog and Apexline runs the complete flight simulation for each one against your current rocket in one pass. Results rank by predicted apogee, thrust-to-weight, rod-exit speed, or delay match — all in a single sortable table. An optional bar chart shows the spread at a glance. No more switching motors one at a time.
Open the chart icon in the Flight Log toolbar to see your prediction accuracy across all flights with altimeter readings: mean error, mean absolute error percentage, a calibration quality verdict, and a flight-by-flight error trend chart. Colour-coded points show which flights were within 10 % and whether accuracy is improving over time.
"Comparing motors side by side" explains how to get the most out of Motor Compare. "Reading your flight statistics" walks through interpreting the error trend and using Cd Calibration to close the gap between prediction and reality.
Enter your rocket's mass, diameter, and drag coefficient, pick a motor from the built-in catalog, and Apexline simulates the full flight — boost, coast, and climb to apogee. It reports predicted altitude, max speed and acceleration, burnout conditions, and the optimum ejection delay. An altitude-vs-time chart shows the whole arc at a glance. Launch-site altitude and air temperature are factored in because thinner air really does fly higher.
Tap the arrows icon in the Motors tab to open Motor Compare. Pick up to 8 motors from across the catalog and Apexline runs the full trajectory simulation for each one against your current rocket. The results table ranks every motor by apogee, thrust-to-weight ratio, rod-exit speed, or how well its available delays match the calculated optimum — whichever matters most for your flight. An optional bar chart shows the apogee spread instantly.
Find your rocket's center of pressure from nose and fin geometry using the Barrowman equations (NASA, 1966) — the same method every desktop simulator uses. Enter your measured balance point and get an instant verdict: unstable, marginal, stable, or overstable. A live CP/CG diagram shows the margin visually so you can see exactly how much room you have before you fly.
Compute terminal descent rate under any canopy at your launch-site air density. A target-descent slider shows you the diameter you need for a soft landing. The drift calculator estimates how far downwind the rocket will travel so you can judge whether your field is big enough — or whether to use a streamer instead.
Record each flight with the motor used, measured apogee, launch site, and notes. The log shows your prediction error as a percentage so you can see how well your Cd estimate tracks reality over time. Export all entries as a CSV file. The new Stats view summarises your accuracy across all altimeter flights, shows a flight-by-flight error trend chart, and tells you whether your calibration is improving — all colour-coded so the answer is obvious at a glance.
Browse Estes, Quest, AeroTech, Apogee Components, and Klima motors organized by impulse class with total impulse, thrust, burn time, available delays, and masses. Not sure what "C6-5" means? Type any code into the decoder and get a plain-English breakdown of the class, average thrust, and ejection delay.
Twelve illustrated guides cover how a rocket flies, reading motor codes, the impulse ladder, choosing an ejection delay, the Barrowman stability method, altitude estimation, parachute sizing, your first launch checklist, hitting a target altitude, a plain-language summary of the NAR Model Rocket Safety Code, comparing motors side by side, and reading your flight statistics. Plus a 40-term searchable glossary and quick-reference tables for nose cone shapes and recovery devices.
Apexline is an estimation and reference tool. Motor specifications are typical published values for planning — always confirm against the certified data on the motor — and every flight should follow the official Model Rocket Safety Code, the motor instructions, and your local laws.