• Created by Unknown User (daynae@mit.edu), last modified by Unknown User (adamsa@mit.edu) on May 17, 2019 16:00

Description

Two very similar carbon-fiber fin cans were made for Hermes 2, differentiated by changes in manufacturing accuracy and number of layers of carbon fiber. In order to determine whether the second flight candidate fin can is suitable for launch, we devised a static load test involving a rig constructed out of 80/20, and an Instron applying a load to the outside edge of one fin. As the second fin can is a candidate for flight, we used the first carbon fiber fin can for the static load test (because once testing is complete, one should not use the hardware that was tested because of the deformation that has been induced by loading). The differences between the first and second iteration of the carbon fiber fin can are briefly summarized below:

Carbon Fiber Fin Can #1

  • Plain phenolic tube 
  • Tube overwrapped with 3 layers carbon fiber
  • 6 additional tip-to-tip layers on each side, tapered on all edges

Carbon Fiber Fin Can #2

  • Fiberglass-overwrapped tube
  • Tube not laid up before tip-to-tip layup
  • 6 tip-to-tip layers on each side, tapered only on trailing edge

Testing Procedure

  1. Design a test rig
  2. Calculate expected flight loads
    1. A preliminary estimate of the flight loads was 40Nm --> 100Nm with a safety factor of 2.5 (100/40 = 2.5)
    2. Based on where the load is applied, assumed the moment arm (length of the fin perpendicular to the direction of flight) to be 6 inches = 0.1524 m
    3. Using T = rF, where T = 100Nm, calculated necessary force to apply as F = 100Nm/0.1524m = 657.89N. Rounded up to get F = 660N, which is the force we tested up to.
  3. Construct jig and secure fin can in jig
  4. Fit check jig with Instron --> had to make some adjustments that took longer than expected
  5. Set up proper attachment on Instron (thin steel bar placed vertically so that a linear load could be applied to one fin)
  6. Set up computer
  7. Calculated actual moment arm (once Instron attachment was secured) to be r = 114.32mm
  8. Put on PPE (safety goggles)
  9. Set up cameras in front of and behind fin can
  10. Started recording video
  11. Began the test

Test Results

Data File: m--19_04_01_19_20.raw


 

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