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:
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 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