Stability Calculations¶
Stability Criteria¶
For a stable rocket flight:
\[\text{Stability Margin} = \frac{X_{CP} - X_{CG}}{d} \geq 1.0\]
Where:
- \(X_{CP}\) = Center of Pressure location (from nose tip)
- \(X_{CG}\) = Center of Gravity location (from nose tip)
- \(d\) = Body tube diameter (caliber)
Target
CG should be 1 to 2 calibers ahead of CP
- Less than 1 caliber: marginally stable
- More than 2 calibers: will weathercock
Peregrine Stability¶
With 4" diameter body:
- 1 caliber = 4 inches
- Target: CG 4-8" ahead of CP
| Configuration | CG | CP | Margin | Status |
|---|---|---|---|---|
| To be filled from OpenRocket |
Measuring CG¶
Method: Balance Point¶
- Fully load rocket (motor, recovery, electronics)
- Balance on finger or rod
- Mark balance point
- Measure from nose tip
Weight Considerations¶
| Item | Approx Weight | Notes |
|---|---|---|
| Airframe (empty) | ~5 lbs | As built |
| Altimeter | 0.5-2 oz | Varies by model |
| Motor (H180) | ~8 oz | Loaded |
| Recovery gear | ~4 oz | Packed |
CP Calculation Methods¶
Barrowman Equations¶
Classic analytical method for CP location. Implemented in:
- RockSim
- OpenRocket
Cardboard Cutout Method¶
Simple physical approximation:
- Draw rocket profile on cardboard
- Cut out profile
- Balance cutout
- Balance point ≈ CP
Conservative Method
Cardboard cutout gives a conservative estimate. Actual CP is usually further aft.
Dynamic Stability¶
Beyond static stability, dynamic factors include:
- Launch velocity (affects weathercocking)
- Wind conditions
- Fin size and shape
- Mass distribution
RockSim/OpenRocket simulate these factors.
Simulation Results¶
Insert OpenRocket stability analysis here
See OpenRocket Results for full simulation data.