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

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