Charge
Size black-powder ejection charges — then validate them against your own ground tests.
Charge sizes the black-powder ejection charge for your airframe. Give it the tube inner diameter, the length of the pressurized section, and how hard the airframe is to separate — a target pressure, or shear pins plus friction — and it returns a starting charge in grams, showing the full formula and every constant so the number is never a black box.
It's built around the loop every flyer runs: size, ground-test, validate, fly. A browser-local ground-test log surfaces the charge you actually proved on the bench above the estimate, warns when your setup has drifted from what you tested, and exports a build/ground-test card and recovery report for a cert package. Always ground-test a charge before you fly it.
What it does
Pressure or force sizing
Size by target chamber pressure, or by separation force — shear pins (with presets) plus friction.
Built-in safety margin
Size above the bare separation force or your target pressure, so a leaky real airframe still separates.
Single & dual-deploy
Separate drogue and main wells, with redundant backup charges for a second altimeter.
Vent-hole sizing
Size the static sampling ports for your altimeter bay by the standard one-port-per-100-in³ rule.
Shows all the math
The full formula, every constant, and a worked example from your own inputs — with references.
Ground-test log
Keep a browser-local log of bench tests — the charge that actually separated the airframe is the one to fly.
Closes the loop
Surfaces your validated charge above the estimate and warns if the setup has drifted from what you tested.
Cards & reports
Export a build/ground-test card and a recovery report as HTML or PDF — self-contained and offline.
Try it out
Free to use, no account required.