Solid motors · version 2.0
Solid rocket motor design
Enter a total impulse, burn time and peak chamber pressure, and the app proposes a grain and nozzle and solves the burn. You can also define the grain yourself. The Review page and the PDF report compare the solved motor with each target.
Windows 11 (64-bit) and Apple silicon Macs (macOS 14 or later), version 2.0.1. The Mac app is signed and notarized; the Windows installer is not code-signed.
What it computes
- Sizing
- From total impulse, burn time, maximum chamber pressure and grain outer diameter, the app proposes the grain segments, throat and expansion ratio for the chosen propellant, solves the motor, and compares the result with each target.
- Burnback
- The burning surface is traced by distance from the surface through the web, for BATES, tubular, star, finocyl, moon, C-slot and slotted grains, and for custom ports drawn or imported from a DXF outline. Each segment's end faces burn or are inhibited as you set them.
- Chamber and thrust
- Quasi-steady chamber pressure at each web step from the burn-rate law and the throat; thrust in vacuum and at your ambient pressure; Kn and burn rate.
- Ignition and tail-off
- 0-D filling to steady pressure at ignition and emptying after burnout.
- Erosive burning
- Screening with the Mukunda and Paul correlation when the propellant gives a gas viscosity. Without one, erosive burning is left out and the result says so.
- Case wall
- Strength check of the case at peak chamber pressure against the material data you enter.
What you enter
- Targets or a grain. Total impulse, burn time, maximum chamber pressure and grain diameter for the sizing; or the segments themselves: outer and core diameter, length, count, and which faces burn.
- Propellant. Density, ratio of specific heats, c*, flame temperature, molecular mass, an optional gas viscosity, and the burn-rate law r = a·pn in pressure ranges with the units of a. Every value carries its source. KNSB and KNDX are built in from Nakka's published measurements; your own entries are used exactly as entered.
- Port shape. A shape from the list with its dimensions, a custom port drawn in the app, or an outline imported from DXF. Grain files in the .ric format can be imported.
- Nozzle and conditions. Throat diameter, expansion ratio, ambient pressure, and efficiencies.
What you get
The Review page shows the thrust and chamber pressure curves, a burn summary (motor class, burn time, ignition and tail-off times, total impulse in vacuum and at ambient), the instant of peak chamber pressure (time, pressure, burn rate, Kn, thrust), and every warning. The PDF report carries the same values with the inputs and their sources.
Files
.eng- Thrust curve in the RASP format that flight simulators read, with the grain's diameter, length and masses.
.csv- Thrust, chamber pressure and the other burn variables against time.
.dxf- Motor section and port drawings for CAD.
.pdf- Report: inputs with their sources, the solved motor against its targets, curves and warnings.
.png- The page's charts and drawings.
.mp4- Burn video: the grain burning back with the flow in the port (licensed plans).
- Imports
.ricgrain files, DXF port outlines, and projects (.rplproj).
Limits
- Quasi-steady ballistics: chamber pressure is solved at each web step; ignition and tail-off are 0-D models.
- Erosive burning uses a screening correlation; the port flow is not solved for it.
- Results depend on the burn-rate data. The built-in laws are published measurements for those formulations; measure your own propellant before relying on a result.
- Not modelled: grain structural loads, combustion instability, nozzle erosion, and heat transfer to the case.
- The propellant data are ballistic parameters. The application contains no formulations or manufacturing steps.
Trial and licenses
The 30-day trial runs solid motors, with a watermarked PDF report. Saving projects, DXF export, the port flow, and burn videos need a license. Personal ($10/month or $99/year, noncommercial work) and Business ($29/month or $290/year, commercial work) both include the whole application: liquid engines, solid and hybrid motors, vehicle and flight, and all of the CFD, with no plan-tier mesh cap. See pricing.