DRAFT
A bulkhead is a hard point within the rocket body. They are typically used for attachment points for recovery hardware, ballast, and/or electronics. They are also used to seal different sections from pressurization from a separation event.
Porous bulkheads, or baffles, are sometimes used for a rocket for motor ejection. This provides an attachment point for recovery hardware while allowing ejection gases from the motor ejection charge to pass through to pressurize the recovery section.
Below is a table of materials, their densities, and some notes. Note that the plywood + composite bulkheads and full composite bulkheads are usually used for high-stress flights (Mach 0.85+, 15+ G's, etc.), and/or larger rockets (>4" ID). Their typical thicknesses reflect that they are typically used for those types of flights. It is certainly possible to go thinner than the below recommendations to save mass, but these are tried-and-true from team experience.
| Material | Cardboard | MDF | Plywood | Plywood + Fiberglass | Plywood + Carbon Fiber | Full-composite |
|---|---|---|---|---|---|---|
| Typical Use | Estes rockets | Small bulkheads, sealing, fast machining | General-purpose | High-strength, general purpose | High-strength, general purpose | High-strength, low weight |
| Density /[kg/m^3/] | 70 | 710 | 451 | (Assuming 1/2 in bulkhead) 500 | (Assuming 1/2 in bulkhead) 520 | 1850 |
| Typical Thickness (Inner diameter : thickness ratio) | Use what comes in the kit | For sealing: 20:1 For structure: ~8:1 (e.g. 1/2" bulkhead for 4" rocket) | For sealing: 24:1 For structure: 12-16:1 | For sealing: 30:1 For structure: 12-16:1 | For sealing: 30:1 For structure: 12-16:1 | Not typically used for sealing For structure: 16:1 |
| Notes | Only for estes rockets. | Weak. Good for sealing off areas, but avoid attaching recovery hardware to MDF if you can. Easy to laser-cut. Definitely reinforce attachment points. | Most common bulkhead material. Cheap, easy to use. Slightly more difficult to laser cut, but worth the extra strength. Standard for HPR. Typically needs reinforcement near attachment points. | Excellent compromise between strength and cost. Not necessary for most HPR flights, good for 4"+ diameter rockets and high-stress flights. If lay-up occurs before machining, be careful when using the waterjet to cut to avoid delamination. | Not RF-transparent. See notes for fiberglass. | Strongest and most expensive. More difficult to machine. Use in dire weight situations. |