Vent Hole Calculations¶
Purpose¶
Vent holes (static ports) allow the altimeter to sense ambient air pressure during flight. Without proper venting, pressure differentials can cause:
- Inaccurate altitude readings
- Premature or delayed deployment
- Structural stress on airframe
Vent Hole Formula¶
Minimum vent hole area:
\[A_{vent} = \frac{A_{tube} \cdot V_{descent}}{V_{sound}} \cdot N\]
Simplified rule of thumb:
\[A_{vent} \geq \frac{V_{bay}}{100}\]
Where:
- \(A_{vent}\) = Total vent area (in²)
- \(V_{bay}\) = Bay internal volume (in³)
Practical Guidelines¶
Number of Holes¶
- Minimum: 2 holes (180° apart)
- Recommended: 3-4 holes (evenly spaced)
- Prevents asymmetric pressure effects
Hole Size¶
Common sizes for 4" diameter rockets:
| Hole Diameter | Area per Hole | 4 Holes Total |
|---|---|---|
| 1/8" (3mm) | 0.012 in² | 0.049 in² |
| 3/16" (5mm) | 0.028 in² | 0.110 in² |
| 1/4" (6mm) | 0.049 in² | 0.196 in² |
Placement¶
Hole Location
- Place in e-bay coupler section
- Position near altimeter sensor
- Avoid direct line to ejection charge
- Not too close to tube joints
Peregrine Vent Holes¶
To be determined during build
| Parameter | Value |
|---|---|
| E-bay length | TBD inches |
| Number of holes | TBD |
| Hole diameter | TBD |
| Total vent area | TBD in² |
Additional Considerations¶
Breather Holes vs Static Ports¶
- Static Ports: For altimeter pressure sensing
- Breather Holes: For recovery bay equalization
Both may be needed in different locations.
Switch Hole¶
If using external arming switch:
- Switch mounting hole also provides venting
- Account for this area in calculations
- Use switch band for clean installation
Testing¶
Verify altimeter function after drilling:
- Power on altimeter
- Seal one end of e-bay
- Gently blow into/suck on other end
- Altimeter should show altitude change
- Altitude should return to zero when released