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Fin Design Overview

The shape of the fins for Hermes 2 was almost identical to Hermes 1, except for the addition of a phenolic leading edge with a taper of 15 degrees. The fin core was made out of 1/8" G10 (garolite sheet), and the phenolic leading edge was cut from a sheet of 1/4" phenolic which was later tapered and milled down 0.020" on each side. “Fins Design Process”

Description of the Part

  • Function of the part:

    • Provide stability for the rocket as it flies

    • They will be attached to the fin can and flown on the rocket

  • Requirements:

    • Needs to be able to withstand heat from flying up to mach 3.5 (for stage 1)

    • Cannot break or flutter too much as the rocket flies

    • Need to attach to the body tube of the rocket

Pictures/Equations

  • Any CAD you made or old CAD that you are using as a starting point

Image Removed

Test Fin Can Fins

Below is a picture of the fins used for the test fin can layup. These dimensions were obtained from our OpenRocket sim, but were not the updated shape of the fins. This was acceptable for the test fin can layup, but for the flight candidate layup the shape was different.

Image Added


Flight Candidate Fin Manufacturing Process

The fins for the flight fin can were made out of a 1/8" sheet of G10, with a phenolic leading edge made from 1/4" phenolic sheet. Below were the steps used to manufacture them. All of the machining was done in Gelb (Todd's shop in the basement of the Unified Lounge). 

Materials Required:

Part One: Waterjet G10 Fin Core

Part Two: Waterjet Phenolic

Part Three: Cut G10 Tab

Part Four: Cut Phenolic Slot

Part Five: Cut Phenolic Taper

Part Six: Mill Down Phenolic

Part Seven: Assemble Fins


Lessons Learned:

  • When waterjetting 1/8" G10, delamination is a concern because G10 is a composite (made of several layers of fiberglass) and 1/8" is pretty thin. Make sure to use the "Low Pressure" and "Brittle Material" settings on the OMAX waterjet. 
  • Make extra fins and phenolic leading edges. That way, if anything goes wrong, you won't have to go back and make them all over again. 
  • When making the tab on the G10, don't mill everything in one go- use several passes on the mill so that you take off a little bit of material each time. This way, the tab will be more uniform/even. 

  • Any drawings you made (even hand-drawn)- sketches of ideas, even if they won’t be used later

  • Equations you used in the design process

Software

  • I used Solidworks to model the fins that were used on Hermes. Solidworks will also be used to design the phenolic - G10 interface and assemblies.

  • Are there any limitations of this software? Make suggestions for how you could design the part better if we had a different program/more time

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