Responsible: Jack Ansley

Facilitated by Timothy Stubbs

Conducted in the Aerospace Materials and Structures Laboratory

Goal:

Determine which method of turning the tecnora lines into loops will be strong enough to withstand the opening shock force, and secondarily determine if easier methods of looping the lines will be sufficiently strong and can be used instead of insertion joints.

Context:

The standard method for making lines on the Phoenix rocket was insertion joints, which are known to be very strong but are somewhat more complex than a knot because (a) they require special equipment like a sewing machine and a fid, (b) there's a small learning curve to teach a team member how to make them properly, and (c) are somewhat difficult to undo and change if necessary. 

These challenges were simply dealt with for Phoenix, but if the team could use a standard knot to make lines it would simplify the process, since we would not need to use any special equipment and most knots are fairly easy to learn, with plenty of online resources as well.

Checklist:

Test Specimens:

• Specimen 1 - Bowline knot
• Specimen 2 - Bowline knot
• Specimen 3 - Insertion knot
• Specimen 4 - Insertion knot
• Specimen 5 - Figure-8 knot
• Specimen 6 - Figure-8 knot

Equipment:

• 3/4 x 10 eye bolt for lifting
• M10 x 1.5 eye bolt for lifting
• Instron
• USB flash drive (for data)
• Camera (phone)

Procedure:

• For each specimen:
  • Use a lark's head knot to secure each end to one eye bolt
  • Jog the instron head until the specimen is almost taut
  • Set the movement rate to 15 mm/min
  • Use the computer to begin a test
  • Allow the test to run until the rope breaks or the gauge reads 4.5 kN of load
• Save data to the flash drive

Data:

Specimen_RawData_6_cord1_bowline.csv

Specimen_RawData_5_cord2_bowline.csv

Specimen_RawData_2_cord3_insertion.csv

Specimen_RawData_1_cord4_insertion.csv

Specimen_RawData_3_cord5_figure8.csv

Specimen_RawData_4_cord6_figure8.csv

Plotted with:

importtensiledata.m

Tensile_Data_Analysis.m

Media:

Google Drive Folder with videos of each test 

Analysis:

• Insertion joints maxed out the instron (5 kN), which was to be expected
• Figure 8 did second best, broke near knot around 4.3 kN and 3.3 kN
• Bowline was the worst, broke around 3 kN (and broke inside the knot, not on the rest of the cord)
• Expected slippage of the figure 8 knot but did not observe any, which is interesting (indicates stopper knots would not be required)

Conclusions:

• Figure-8 knots can be used on the Medusa lines
• Parachute gore lines should be switched from bowline knots to figure-8 knots