BurnSim 4 is currently in beta. See the Download page for the latest builds. Please email greg@blastzone.org with bug reports or feedback.

Version 4.0.0.12 - released 8/5/2026

• Added a Custom grain type: draw or import your own grain cross-section instead of picking a parametric shape. Import from an ASCII DXF, SVG, or raster image (PNG/JPEG/BMP), or build one from scratch in the new shape editor - an outer boundary plus repeatable holes and slots you can drag directly in the preview - and export back to DXF when you're done. This feature is brand new - see the caveats on the Download page
• Added an axial (side-on) motor cross-section next to the radial preview, showing the grain stack, case, and nozzle for any grain type, with the same erosion slider animating both. Case/nozzle dimensions beyond throat and exit are estimated rather than modeled
• Fixed a rasterization bug inflating a D grain's reported peak Kn by roughly 11% - other grain types were unaffected
• Removed the Pie Segment grain type (it's no longer offered when adding a grain); a motor file that already has one still opens and explains what happened, instead of failing with an unrecognized-type error
• Grain geometry the simulator can't actually represent (e.g. an oversized finocyl fin) is now flagged directly in the grid instead of silently simulating something else
• Grains left with no burning surface (e.g. an end burner with both ends inhibited) are now reported instead of crashing the simulation
• Sped up simulations where several grains share the same shape by eroding each distinct shape once instead of once per grain
• Fixed New, Open, and Recent Files immediately discarding an unsaved motor instead of asking whether to save it first, the way closing the program already did
• Fixed an imported custom grain shape occasionally being silently discarded instead of applied to the grain
• Fixed the grain editor's toolbar overlapping the grain grid when the window was narrow

Version 4.0.0.11 - released 7/30/2026

• The grain grid is now a full in-place editor - every grain parameter has its own editable column (including Offset, Fin length and Points), so a motor can be built end to end in the grid without using the fields below it. Ambiguous column headers carry tooltips explaining what they mean for each grain type, and parameters a grain type doesn't use are left blank instead of showing 0
• Grain Type and Propellant are now single-click dropdowns in the grid - no more double-clicking to reach the list
• Typing on a selected cell now starts an edit, the way a spreadsheet does. Previously the only ways in were F2 or a double-click, so the grid looked like it wasn't editable at all
• Added a "click to add a grain" row at the bottom of the grid, and an "Add the first grain" prompt on an empty grid, so grains can be added without knowing about the Insert key. Pressing Enter or Space on that row adds a grain too
• Insert, Delete and Move Up/Down are now available on a right-click context menu in the grid, and Delete can remove several selected grains at once
• Fixed arrow keys silently rewriting a grain's Type or Propellant while moving through the grid - arrowing down a column could change every grain's type without the dropdown ever opening. Arrow keys now move between rows, and Alt+Down, Alt+Up or F4 open the dropdown
• Fixed an unescapable dialog loop: closing the program with a throat diameter of 0 stacked the "Simulation Problem" alert on top of the unsaved-changes prompt, and the two traded focus so neither could be dismissed. More generally, automatic re-simulation no longer raises error popups or moves the cursor - only the Simulate button does
• Added Save As to the propellant editor - saves what's currently shown as a new propellant under a different name, leaving the original untouched. Useful for deriving a new batch from a characterized one, since the copy keeps the notes and pressure-varying data the editor has no fields for
• Added Delivered Isp to the Results tab
• On the graph, Thrust From Imported Pc is now genuinely calculated from the imported chamber pressure, so it can be compared against the measured thrust trace. Previously the two series drew the same line whenever the imported file supplied a thrust column
• Fixed values derived from imported test data continuing to compute from the last measured pressure after the imported data ended, which drew phantom thrust in a region where the measured pressure read zero. This also corrects the test impulse for any run that outlasts its test data
• Imported test data columns are back in File > Export CSV - they had been silently dropped from every export. Measured thrust and thrust calculated from imported pressure now export as two separate columns, and the imported pressure/thrust columns follow the Imperial/Metric setting with the unit shown in the header
• Fixed importing test data from a CSV with a header row, a units row or a trailing note - those lines became a bogus 0,0,0 sample at t=0. Quoted fields are now handled as well
• Every dialog now has Alt-key shortcuts on its buttons and puts the cursor where you'd expect on open, so text-entry dialogs can be typed into without clicking first
• The divider between the grain grid and the graph now keeps its position between launches

Version 4.0.0.10 - released 7/27/2026

• Grains can now be multi-selected in the grain grid (ctrl-click, shift-click, or the new Select All button); editing the fields below the grid and clicking Apply updates every selected grain at once, instead of one at a time
• Added Web thickness to the Results panel
• Peak mass flux and peak mass flow now show their units and follow the Imperial/Metric setting - lb/in²-sec and lb/sec in imperial, kg/m²-sec and kg/sec in metric. Previously both were shown as unlabeled numbers that stayed in imperial units regardless of the setting. This applies in the Results panel, on the graph, and in the PDF motor report
• On the graph, Mass Flux and Mass Flow each get their own scale on the right-hand side, with units shown in the legend, so neither curve flattens the other

Version 4.0.0.9 - released 7/22/2026

• Cross-platform release: BurnSim 4 is now available for Windows, Linux, and macOS (previously Windows-only), with a native Windows installer and Linux desktop-entry packaging
• Added win-arm64, linux-arm64, and macOS (Apple Silicon) builds
• Replaced the graphics engine with SkiaSharp for consistent rendering across platforms
• Added an editable data grid to the Test Data tab; decluttered the tab (dropped Molar Mass from the Propellant UI, hid imported-series checkboxes when not in use)
• Added a separate Imported Thrust trace, distinct from the calculated one
• Added light and dark theme
• Fixed the "Use in simulation" checkbox only re-plotting stale data instead of re-simulating
• Fixed long thrust tailoff not resolving correctly (thrust coefficient floor issue)
• Fixed the burn loop not stopping once thrust had genuinely ended
• Added a warning in the Results text when nozzle efficiency is below 75%
• Added Print/Report: a one-page PDF motor report, with direct printing support
• Added a play/stop button to loop the grain erosion visualizer
• Numeric fields are now rounded to 4 decimals when saving .bsx files and the propellant database
• Added a per-field unit override to lock Total Impulse to Newton-seconds
• Fixed cored Tablet grains simulating identically to BATES grains, fixed the Tablet erosion preview, and fixed a crash simulating a solid (uncored) Tablet grain
• Fixed a graph rendering glitch causing runaway padding/overflow at the end of a burn
• Made the Grains/Graph panes vertically resizable, added a scrollbar to the grain grid
• Moved the motor Notes field to its own tab, alongside Results/Test Data
• Fixed simulation results silently going stale when a field was edited mid-run
• Fixed several usability gaps when starting a new motor from scratch
• Added a per-run activity log to help diagnose bug reports
• Fixed the installer defaulting to Program Files (x86)
• Added right-click pickers on the throat diameter field (1/64" increments and Loki Research nozzle sizes), working regardless of unit mode