Thanks for posting this. It gave me just enough information to start looking up what I needed to learn and run with. Should give me what I’m looking for.
FWIW: Not saying it's the case here, but in my experience drag separation is frequently blamed for problems just after burnout but not always the real cause. It's harder than one might expect to get drag separation unless the forward section is heavy and the aft section draggy, as John's equations will tell you. I've never managed to get it to happen when I wanted it to (staging.)
This was a single stage drag separation not a two stage. But I should still be able to duplicate the method for the forward section and the fincan if I can make it stable.
OR under component analysis gives you the CD of each component on you rocket. Use this information and the masses and plug into the drag sep equation mentioned earlier.
Are you saying that you had shear pins and it still separated? Something doesn't sound right... either your nose was very heavy and the momentum broke the shear pins, or your shear pins were very loose and ineffective. What was the deceleration at burnout? If you multiply that by the mass of the NC/AV bay assembly, you'll get the force that the shear pins "saw", then you can use a shear pin force calculator ( https://www.rimworld.com/nassarocketry/tools/chargecalc/index.html , it's for BP charge sizing but you can use it to back into the force) to determine if the separation was indeed due to the mass of the nose assembly.
^ This and what Mikec posted. It would be unusual to drag separate shear pins. Are absolutely positively sure you didn't get a premature apogee charge? Did you see it? Was the separate AT motor burnout or a little after?
Weight of rocket after burnout is 12lb weight of nosecone is not exactly known but I'd guess 2-3lb. The nosecone and Ebay assembly however is close to 5lbs total. This was Head end deployment arrangement. I believe based on the destruction of the drogue assembly that the nosecone detached as the main survived and the electronics were safely recovered thanks to this. Drogue was in the nosecone. Other things of note that I believe contributed to this is an excessively hot day on the salt. My kydex knife sheath deformed sitting in the sun so it was definitely hot enough to weaken the two shear pins. Another things of note that I've kicked myself for is that the dog barf was packed just tight enough to create some resistance during closing. Normally there's no resistance. The arrangement was flown immediately before this (3 hours earlier) to verify the drogue arrangement on a less aggressive K motor. In addition to the other mentioned contributors My ventilation was awkward as I had it vented from the nosecone into the Ebay and from there to atmosphere. If I had packed the dog barf tightly enough to cause resistance it could have easily blocked the passages to the Ebay enough to restrict the flow combined with a much more aggressive flight profile and the weakened shear pins has lead me to believe the drag separation occurred. In the future for 4" the plan right now is to replicate the same flight using larger shear pins and new deployment testing and change nothing else. I have a good video of the flight I can show but I have to figure out how to upload to Youtube as I haven't done that in a while.
Here's the rocket so you get an idea of the profile. Not an ideal fincan for supersonic but it worked until after motor burn out. All fins where attached after the impact and bounce so I don't suspect the fins. And I imagine fin damage would occur during the most intense portion of the flight under acceleration not during a lesser moment after burnout. The comments in the video are from another member who was there when talking about suspected areas of failure before the flight.
It may be correct. Perhaps I incorrectly over generalized. I was speaking in the context of a staged flight and the deceleration at stage separation. Usually you are not that fast when the booster burns out on a heavy stack.
