Getting Started with a Basic Simulation
This walks through building a simple two-grain 54mm 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), leave Type as BATES and pick a propellant from the Propellant dropdown - this example uses "Viper". Enter:
- Length (in): 12.5
- Diameter (in): 1.825
- Core dia (in): 0.625
- Ends inhib.: 0
Click Add. A grain appears in the grid above. Click Add again with the same values to add a second, identical grain - this motor uses two 12.5" BATES grains stacked end to end, 25" of propellant overall.
Set the Nozzle
In Motor & Nozzle, enter:
- Throat dia (in): 0.75
- Exit dia (in): 3.5
- 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 - designation, total impulse, burn time, peak pressure/thrust, delivered Isp, and more.
This particular motor also shows a warning:
[Warning] The bottom grain's core is narrower than the nozzle throat (port/throat area ratio 0.69), so the core diameter is being used as the effective throat area instead of the nozzle's - this will continue until burning widens the core past the nozzle's throat diameter.
BurnSim surfaces warnings like this rather than silently simulating a physically questionable design - 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