Getting Started with a Basic Simulation

This walks through building a simple three-grain finocyl motor from scratch. For what each field on screen does, see BurnSim Fields.

Start a New Motor

Open BurnSim and choose File > New (or just start with the window BurnSim opens with). You'll see an empty Grains grid, a Motor & Nozzle panel with zeroed fields, and an empty graph:

A new, empty motor

Add the Grains

In the Grain Editor (below the grid), set Type to Finocyl and pick a propellant from the Propellant dropdown - this example uses "Viper". Enter:

• Length (in): 4
• Diameter (in): 2
• Core dia (in): 0.6
• Fin width (in): 0.15
• Fin length (in): 0.3
• # fins: 6
• Ends inhib.: 0

Click Add three times to add three identical grains, stacked end to end - 12" of propellant overall. The Cross-Section preview updates to show the finned core and the longitudinal cutaway of all three grains.

Set the Nozzle

In Motor & Nozzle, enter:

• Throat dia (in): 0.5
• Exit dia (in): 1
• Efficiency (%): 85
• Ambient (psi): 14.7
• Thrust method: Nozzle geometry

As soon as a valid throat diameter is set, BurnSim simulates automatically (this is the Auto-Simulate on Changes setting, on by default - see Settings Menu). You don't need to click anything to run it.

Read the Results

The simulated motor - grains, cross-section, graph and results

The graph (bottom left) plots Kn, pressure and thrust against time. The Results tab (bottom right) summarizes the burn - for this motor, a K-class designation, roughly 1680 N-sec total impulse, a 1.5 second burn, peak chamber pressure around 1480 psi, peak thrust around 380 lbf, and a delivered Isp around 209 seconds - plus designation, Kn max/min, web thickness, propellant mass and length, and initial core volume.

If a design has a physical issue worth flagging - for example a grain core narrower than the effective nozzle throat - BurnSim adds a warning above the results explaining it, rather than silently simulating something questionable. Worth reading whenever one appears.

From Here

• Add more grains, change grain types (see Grain Types), or try different propellants and nozzle sizes, watching the results update live
• Toggle which traces are plotted with the checkboxes above the graph
• File > Save (Ctrl+S) to keep the motor as a .bsx file
• Once you have real test data for this motor, see Test Data Tab to bring it in and compare against the simulation