Ejection Charge Calculations¶
Black Powder Charge Formula¶
The standard formula for calculating black powder ejection charge:
\[m_{BP} = \frac{\Delta P \cdot V \cdot C}{R \cdot T}\]
Simplified practical formula:
\[m_{BP} (grams) = \frac{D^2 \cdot L}{2270}\]
Where:
- \(D\) = Tube inside diameter (inches)
- \(L\) = Bay length (inches)
Safety Factor
Add 10-20% to calculated charge for reliable deployment.
Peregrine Bay Calculations¶
Known Values¶
| Parameter | Value |
|---|---|
| Body Tube ID | ~3.9" (actual ID of 98mm tube) |
| Pressure | 15 psi (typical) |
Drogue Bay (Forward)¶
To be measured during build
| Parameter | Value |
|---|---|
| Length | TBD inches |
| Volume | TBD in³ |
| BP Charge | TBD grams |
Main Bay (Aft)¶
To be measured during build
| Parameter | Value |
|---|---|
| Length | TBD inches |
| Volume | TBD in³ |
| BP Charge | TBD grams |
RockSim Calculation¶
RockSim includes a built-in ejection charge calculator:
- Open Peregrine design file
- Go to Simulation menu
- Select "Ejection Charge Calculator"
- Enter bay dimensions
- Get recommended charge size
Ground Test Procedure¶
Always Ground Test
Never fly without ground testing ejection charges!
Test Procedure¶
- Assemble rocket without motor
- Load recovery gear as for flight
- Install e-match with calculated charge
- Secure rocket horizontally
- Clear area and fire charge
- Verify clean separation and chute deployment
Test Criteria¶
- [ ] Clean separation
- [ ] All sections stay connected via shock cord
- [ ] Parachute(s) fully deploy
- [ ] No damage to components
- [ ] Adequate force (increase charge if weak)
Alternative: CO2 Ejection¶
Apogee offers a CO2 ejection system:
- No black powder required
- Peregrine Starter Kit includes:
- 4x 8-gram cartridges
- 4x 12-gram cartridges
- Hardware for 2 systems
Charge Quantities Summary¶
To be filled after bay measurements
| Bay | Primary | Backup (+15%) |
|---|---|---|
| Drogue | TBD g | TBD g |
| Main | TBD g | TBD g |