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Plugging in numbers, we find the minimum radius of the piston bore:
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rbore, min = 0.092 in
Now, we seek to find an upper bound on the possible piston radius. Another At this stage of the analysis, radius can be constrained further: another requirement of the piston is that it cannot break the shear pins prematurely due to an internal build-up of pressure caused by the altitude difference. Between 4,245 ft (the altitude of Truth or Consequences, NM) and 152,945 ft ASL (a simulated upper bound on performance as of January 4, 2018), the pressure difference is approximately (given by the 1976 Standard Atmospheric Calculator using no temperature offset) -86600 Pa ≈ 12.56 psi.
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rbore, max = 1.51 in
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Of course, an additional constraint on piston radius is the allowable space inside the Avionics Bay Coupler. The Team previously found that 6491K254, which had a 1in radius, was large and provided little room for Avionics to house its hardware, especially the batteries. Thus, a logical conclusion is to restrict the new piston geometry to radii below 1in, which will provide an even larger safety factor on premature drag separation.
Resources:
The following resources are useful materials for learning about pressure vessel and piston theory:
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