BurnSim Fields
This is a field-by-field reference for BurnSim 4's main window. For a walkthrough of building your first motor, see Getting Started with a Basic Simulation.
File Menu
- New (Ctrl+N) - start a new, empty motor
- Open... (Ctrl+O) - open a saved .bsx motor file
- Recent Files - the last few motors you've opened
- Save (Ctrl+S) / Save As... - save the current motor to a .bsx file
- Export ENG... - export the burn to a .eng file for use in flight simulators
- Export CSV... - export the full simulation trace (time, Kn, pressure, thrust, mass flux, etc.) to CSV
- Print / Report... (Ctrl+P) - generate a PDF motor report
Action Menu
- Simulate (F5) - run the simulation now. Usually not needed - see Auto-Simulate below.
Settings Menu
- Auto-Simulate on Changes - when on (the default), BurnSim re-runs the simulation automatically as you edit grain, nozzle, or propellant fields
- Log Activity for Bug Reports - writes a per-run activity log; use Open Log Folder... to find it if you need to attach one to a bug report
- Use Eroder for Surface Area - on (default): surface area is computed from the pixel-based grain eroder, which correctly handles complex or irregular cores. Off: use the older analytic geometry formulas instead
- Simulate Erosive Burning (Use Axial Grain Slices) - off by default. When on, each grain is divided into axial slices and burn rate is locally augmented by an erosive burning model reacting to mass flux down the port - see Erosive Burning Overrides below
- Set Slice Count... - how many axial slices each grain is divided into when the above is on. More slices resolve a tapered port or burn-through more finely, at the cost of simulation speed
- Erosive Burning Model - which correlation the sliced simulation uses:
- Lenoir-Robillard - the model motor designers traditionally fit test data with. Needs a per-propellant blowing coefficient (beta) and derives its heat-transfer coefficient from thermochemistry, so the propellant needs its Molar Mass set. Always augments to some degree, with no threshold
- Mukunda-Paul - a universal correlation fit against a broad set of published test data, with no per-propellant constant to characterize - it needs nothing beyond a/n/density plus gas viscosity. Has a hard threshold: below it, there's no augmentation at all
- Set Simulation Timestep... - the simulation's internal time step in seconds (0.01s default). Smaller values are more precise at the cost of simulation speed
- Theme - Dark or Light
- Units - Imperial (in, psi, lbf, lbm) or Metric (mm, kPa, N, g); Always show Total Impulse in N-sec overrides just that one Results line regardless of the Imperial/Metric choice, since motor-class designations ("H128" etc.) are always in Newton-seconds
Help Menu
- Activate... - enter or check your license
- About... - version info and license terms
Grains Grid
One row per grain in the motor, in burn order. Columns are Type, Length, Dia, Core, Offset, Fin len, Pts, Inhib. (number of inhibited ends, 0-2), and Propellant - which fields apply depends on the grain type selected. Click add a grain or use the Grain Editor below to add one; select a row to edit it.
Grain Editor
Below the grid, an editor for the selected grain(s):
- Add - adds a new grain with the fields below
- Remove - deletes the selected grain(s)
- Up / Down - reorders the selected grain within the motor
- Select All - selects every grain, so a field change and Apply updates them all at once
- Apply - writes the Type/Length/Diameter/Core dia/Ends inhib./Propellant fields back to the selected grain(s)
Grid cells can also be edited directly, without going through this editor.
Below the editor, a Cross-Section preview shows the selected grain's end view (left) and the whole motor's longitudinal cutaway (right). The slider and Play button scrub through the burn, animating how the grain erodes over time using the same pixel-based eroder that drives the simulation.
Motor and Nozzle
- Throat dia (in) / Exit dia (in) - nozzle throat and exit diameters
- Efficiency (%) - combustion/nozzle efficiency applied to the theoretical performance
- Ambient (psi) - ambient pressure the motor fires into
- Thrust method - how thrust is derived; Nozzle geometry computes it from the throat/exit dimensions above
Propellant
- Dropdown selects which propellant in your database applies to the currently-selected grain(s); New, Edit, Save As... and Delete manage the database itself
- Two tabs: Properties (the fields below) and Erosive Burning (the override fields further down) - split out so the common case stays uncluttered, since the Erosive Burning tab only matters once axial slicing is turned on
- Name, Density (lb/in^3), C* (ft/sec), Specific heat ratio, a and n (the Saint-Robert's law burn rate coefficient and exponent), and Molar mass (g/mol) are the propellant's characterization numbers - see Propellant Characterization for how to derive them. Fields are read-only until you click New or Edit
Erosive Burning Overrides
On the Propellant panel's Erosive Burning tab. Only relevant when Simulate Erosive Burning is on (see Settings Menu above). Each box is optional - leave it blank and BurnSim derives a value from the propellant's other properties (the small gray text under each box always shows what value is actually in effect, derived or overridden):
- Beta - blowing coefficient (Lenoir-Robillard only)
- Viscosity (mu) - combustion gas viscosity
- Prandtl - Prandtl number of the combustion gas
- Surface temp (R) - propellant surface temperature
- Solid heat capacity (cs) - propellant solid-phase heat capacity
- Combustion temp (R) - adiabatic flame/combustion temperature
Graph
Checkboxes above the graph toggle which traces are plotted against time: Kn, Kn Eff, Pressure, Thrust, Mass Flux, Mass Flow. When test data has been imported and marked "Use in simulation" (see Test Data Tab), three more become available: Imported Pressure, Imported Thrust, and Thrust From Imported Pc (thrust back-calculated from the imported pressure trace via the nozzle) - letting you overlay real test data against the simulated curves.
Results, Test Data and Notes Tabs
- Results - a text summary of the burn: designation, total impulse, burn time, peak pressure/thrust, delivered Isp, Kn max/min, web thickness, propellant mass and length, initial core volume, peak mass flux/flow - plus any warnings BurnSim generated about the design (for example, a core narrower than the nozzle throat). If erosive burning is on, a line also reports whether it actually had any effect on this particular run (peak augmentation over the nominal burn rate), not just that the option was enabled
- Test Data - import, edit and manage real motor-test data; see Test Data Tab
- Notes - free-text notes, saved with the .bsx file