; There will be 3 sets of bolts connecting the bulkhead to the nose cone and/or the AV bay.
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Next, the force due to acceleration. According to recent sims, the greatest acceleration will be when the entire rocket goes from 0 to Mach 4.09 in about 8 secs. Assuming a temperature of 30°C (86ºF),
Mach 4.09 = (349.02 m/s)*(4.09) = (1427.49 m/s).
That's an acceleration of
(1427.49 m/s)/(8 s) = 178.44 mRecent sims (Simulations log) predict a maximum acceleration of about 800 ft/(s^2), which is approximately 18.21G.Rounding up and 25G. After applying the safety factor of two, we can expect an acceleration of 50G. The bolts on the bulkhead have to be able to withstand the force of everything attached to the bulkhead (AV tower, piston, recovery, NC assembly) accelerating with the rocket. Assuming they weigh about 50lbs and accelerate at 50G, then the
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To calculate the arrangement, number, and size of bolts, we'll analyze the shear strength of the bolts.
Stress = Force/Area
Shear Area = (Number_bolts)*(Diameter_bolt)*(Thickness)
The thickness depends on the bulkhead design, but if we assume the NC is thinner, then thickness = 0.9 in. If we look at the shear strength of steel bolts to determine the amount of force they can withstand, we find a maximum allowable stress of 15 ksi (http://www.ssina.com/download_a_file/fasteners.pdf; table at the bottom of page 9). We can plug these in along with the maximum force to find
(Number_bolts)*(Diameter_bolt) = (2498.35lbf)/(15000 lbf/(in^2) * .9 in) = .1851 in
Ideally, we want the Number_bolts to be 6 so that even if half of them were loaded at any time (and there have to be at least 3 bolts fully loaded at any time because 3 points define a plane), they would be able to withstand the force since the safety factor was 2. Therefore, we have
Diameter_bolt = .1851/6 = .031 in
However, we also need to analyze the shear strength of the G12 fiberglass so that we know it won't deform under the force.