I am going to be starting some ground tests in the next couple of weeks and wanted to get a better idea on where to start. Shear pins are new to me, and up until this rocket I have successfully used static ports to vent any differences in pressure, but now that the rockets are getting bigger and faster I need to take the next step into the shear pin realm.
Initially I thought of 4-40 nylon shear pins, not sure why, but then I was told by another flier to go with 2-56...below is the setup
I m not sure if velocity plays a factor in the decision but for what it is work RockSim has it at a max velocity of 1300MP or 1.7Mach
Body Tube:
ID = 2.165"
OD = 2.295"
Filament wound carbon fiber centerless ground / smooth (I believe it is ProLine 54mm tubing)
Drogue section:
6" long, contains a 15" drogue/w 3" nomex, and a 20' Kevlar 11/32 harness. It is tight and when I say tight I mean when it is packed it tries to force the sections apart by about .25". I can easily push it down and screw 4-40 shear pins in. Packing volume of the drogue is 4.3"^3, not sure about the shock cord and the 3" Nomex.
Main section:
12" long, contains a 48" main/w 4" nomex, and a 20' Kevlar 11/32 harness. It is also tight, same as above, and again I can easily push it down and screw 4-40 shear pins in. Packing volume of the main is 26"^3, and again I am not sure about the shock cord and the 3" Nomex, but it would be very similar to above.
So the two questions are do I stick with 4-40 or skip to 2-56, obviously the answer will effect the BP requirements. I did some quick calculations and based on the rough number of requiring about 40lbs of force for a 4-40 shear pin for a 20in^3 volume the BP charge should be about .25 grams.
Okay now throw it at me :bangpan:
Initially I thought of 4-40 nylon shear pins, not sure why, but then I was told by another flier to go with 2-56...below is the setup
I m not sure if velocity plays a factor in the decision but for what it is work RockSim has it at a max velocity of 1300MP or 1.7Mach
Body Tube:
ID = 2.165"
OD = 2.295"
Filament wound carbon fiber centerless ground / smooth (I believe it is ProLine 54mm tubing)
Drogue section:
6" long, contains a 15" drogue/w 3" nomex, and a 20' Kevlar 11/32 harness. It is tight and when I say tight I mean when it is packed it tries to force the sections apart by about .25". I can easily push it down and screw 4-40 shear pins in. Packing volume of the drogue is 4.3"^3, not sure about the shock cord and the 3" Nomex.
Main section:
12" long, contains a 48" main/w 4" nomex, and a 20' Kevlar 11/32 harness. It is also tight, same as above, and again I can easily push it down and screw 4-40 shear pins in. Packing volume of the main is 26"^3, and again I am not sure about the shock cord and the 3" Nomex, but it would be very similar to above.
So the two questions are do I stick with 4-40 or skip to 2-56, obviously the answer will effect the BP requirements. I did some quick calculations and based on the rough number of requiring about 40lbs of force for a 4-40 shear pin for a 20in^3 volume the BP charge should be about .25 grams.
Okay now throw it at me :bangpan:
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