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The LW-2 motor is my second aluminum casing rocket motor. It, or they, are being built to be used as twin outboards for a new rocket. The LW-2 motor will closely mirror the reliable steel "T" series of motors, of which I have grown rather fond of. Both are of similar dimensions, and hold just over one pound of propellant. There the similarities end. The LW-2, out of necessity, will be of ultra light weight design. Utilizing 6061 T-6 aluminum casing material .065" thick, a graphite nozzle, and a cast and machined 360 aluminum upper bulkhead.
The cast 360 aluminum bulkhead is a new endeavor for me. A home foundry page has been started detailing my attempt at home casting of aluminum. I did some research on the 360 aluminum alloy. When sand cast, it has an ultimate tensile strength of 33,000 psi. After calculating the minimum bulkhead thickness, I came up with a .1498" thick bulkhead at 900 psi chamber pressure. Now we need a little margin of safety, so doubling it up to .3" would be sufficient. That should result in a bulkhead of about 27 grams. Assuming I had very poor quality aluminum with a tensile strength of only 12,000 psi. a bulkhead with a safety margin of 1.6x would yield a bulkhead thickness of .3976", with a weight of 35.76 grams. I can live with the extra 10 grams, so I'll make the bulkhead .4" thick to be on the safe side.
The 6061 T-6 casing is a no brainer, but I'll do the math to prove it.
Min Wall Thickness=(Max Expected Chamber Pressure x Chamber Diameter) / (2 x Ultimate Tensile Strength)
(900 x 1.75) / (2 x 45,000)
1,575 / 90,000=.0175"
.065" / .0175"= 3.714x safety margin
Like I said, a no brainer. The 6061 T-6 could handle 1,700 psi and still have a 2x safety factor.