; There will be 3 sets of bolts connecting the bulkhead to the nose cone and/or the AV bay.
The first are radial bolts along the base of the nose cone that connect to the bulkhead. These will have to withstand forces from two sources: the piston and the acceleration of the rocket. So, we need to find the approximate maximum forces due to both (with a safety factor of 2), and use the greater force to determine which arrangement and size of bolts we'll need.
First, the maximum force from the piston. According to recent sims, the maximum force it'll exert on the whole system will be 2250lbs during main deployment. However, the nose cone only feels its inertia, so
F_nc_section = F * M_nc_section/M_whole_rocket.
Currently, the mass budget of the rocket has a dry mass of 79 lbs. Assuming that the
M_nc_section = M_nc + M_nc_tip + M_nc_extension = 5.6 lbs,
then
F_nc_section = (2250lbs)*(5.6lbs)/(79lbs) =160 lbs.
Applying the safety factor of two and adding a couple pounds to the nose cone in case it goes over its mass budget,
F_nc_section = (2250lbs)*(10lbs)/(79lbs)*2 = 570lbs.
Next, the force due to acceleration. Recent sims (Simulations log) predict a maximum acceleration of about 800 ft/(s^2), which is approximately 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
F = (50lbs)(50G) = (22.68kg)*(490 m/(s^2)) = 11113.2 N = 2498.35 lbs.
So it's clear that this will be the maximum amount of force that the bolts will have to withstand.
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
All this means is that the bolt will be able to withstand the shear stresses on it, and it won't snap under those forces. Now, we need to calculate the yield strength of the bolts given that they're loaded in tension.
However, we also need to analyze the shear strength of the G12 fiberglass so that we know it won't deform under the force.