Do you use pins/tape only on larger rockets or on all dual deploy rockets? Someone said only necessary at near mach speeds.
Obviously "someone" doesn't quite understand how things work.
Think of traveling in your car, going up & down in high hills or mountains. Your ears "pop" trying to equalize the pressure trapped inside, with changing pressure outside. Same goes with your rocket.
You need pressure relief vent in each section...fincan & payload ...to bleed of the differential as rocket goes higher.[not same as altimeter vents]
Faster it travels up...the faster you need to equalize internal pressure with exterior.[larger vent for extreme speeds]
If you don't, pressure inside, will cause premature separation of fincan/payload or payload/nosecone. This usually happens at Max-Q [ motor burn out]. No longer is there a force acting on front of rocket pushing parts together. Things pop apart...chute comes out, while moving at high speed and wham-o ....shred or zipper.
Also using to short of an apogee shock cord will snap hard/stop abrupt and forces will continue on parts, causing NC to come off, opening main at apogee.
Some cases the drag on lower section can be higher than upper, once again you get parts separating when they are not supposed to.
SO.....it just happens faster when using hard hitting motors or ones that get you to mach quicker.
Shear pins/tape, alleviate all this.
So...I use them on all flight where DD is used. I only do main pins, some folks use them for apogee,to hold fincan to payload . My recovery designs never need them. It's a delicate dance between ejection charge sizes, length of shock cord, number of pins.
Now you're going to hear some folks telling you "always use 2-3 pins" or risk the parts cocking/wedging from off center thrust of charge.....pure BS...urban legend passed from one to another reading something and repeating it.
May have had some validity years ago when part tolerances were nothing like today's or with very loose fitting plastic NC's having "ribs" on them used with sloppy tolerance cardboard tubes. I'm talking fiberglass here.
So...I [and many, many of my experienced friends]use just 1 pin on 38mm airframe
2 pins on 54 & 3in. airframes
3 pins on 4 & 5in. airframe
6& 7.5 & 8 in. use 4-40 pins [4 of them] due to how much more those NC's weigh.
12 in. airframe 6 pins 6-60.
I have used shear tape on 54mm to 4in airframes. Same amount of BP used for both pins/tape. Experience has shown...for me..it works, same.
How you build/fit parts...tight or loose determines how you use them.:wink: