HPR Design

Design tips for High Power Rocketry

Articles to Read:

Search [topic] + "apogee newsletter" and you can often find great results

• Specific articles coming soon

Design Check:

• Make sure you allocated enough space for your parachutes. Too much space is better than not enough space!

  • TODO: how to determine/estimate packing size

• Do you have rail buttons? (Most likely you should have 1010 rail buttons)

• Does your motor mount fit the motors you plan on using?

  • The motor can be longer than the motor mount, but then the motor may take up parachute space!

  • A lot of H motors are 38mm.

  • A lot of J motors are 54mm (but the BAR L2 special [the J350W] is 38mm).

• Ground hit speed should be <20ft/s. Is your main parachute big enough?

• (For dual deployment) Speed at main deployment should be <70-80ft/s. Is your drogue big enough? (TODO: should I say <50 ft/s instead?)

• Velocity off the rail (our rails are at least 6 ft) should be >50 ft/s.

Design

• Stability = (CG - CP) / rocket diameter, with CG and CP measured from the bottom of the rocket. It is unitless, but usually written as a number of “cal”s.

  • Stability should be between 1.5 cal to 2.0 cal. Stability of 1.8 cal is good.

  • Consider adding a mass to the nosecone-payload tube region if the rocket is under-stable for a large motor

• Tubing:

  • Fiberglass is expensive (?).

  • Carbon fiber is more expensive (?).

  • Blue tube is strong and relatively cheap.

  • Don’t use cardboard for HPR.

• Shoulders:

  • Recommended shoulder length (i.e. extent of coupler tube) is about tube diameter (i.e. 1 cal).

• Nose cones:

  • 4:1 tangent ogive is nearly optimal. (?)

• Fins:

  • Plywood is good up to around 330 ft/s. Above this, there is significant risk of fin flutter, which can break your fins right off the rocket.

  • G-10 fiberglass has flutter speeds of over 1 Km/s (~3330 ft/s), so for L1/L2 it should be fine.

• Tube size:

  • Hands tend to be less than 4” across -- so if you want to be able to reach all the way inside your rocket, 4” should be big enough.

• Fin mounting:

  • Sandwich between bulkheads.

  • Epoxy the shit out of the fins.

• Bulkheads:

  • 0.25” plywood is a good choice.

• Motor mount:

  • Usually a phenolic tube; may be fiberglass.

  • Design around the length of the motor(s) you plan on using.

  • If using a threaded motor retainer, allocate enough room for this by having enough of the motor mount tube extended beyond the aft centering ring