Second Flight: Catastrophe
This really sucks! I took the Argent out for its second flight. Spent the whole day preparing the rocket. It was fairly cold and it took a lot longer than it should have. After a successful ground test of the main chute I was ready to prep for flight--needed a new chute, since it had been scorched during the ground test.
Ground test results
Just enough charge to fully extend the shock cord. The shock cord is ~10' of 900 lb test Kevlar, shorted in the center with 6' of elastic. This is not the usual arrangement where the two are coupled directly. If the elastic breaks, there is still a solid section of kevlar (See below).
The elastic caused the recoil on the nose. So what you see above from left to right is parachute, Nose, Nomex, rocket.
Shock Cord
Flight
Flight Data
Notice, no change in slope after Main chute charge well fires. I also visually confirmed the well fired in the post mortem.
Aftermath
Both charge wells and ematches fired, but the main chute (upper section) did not deploy. I can only guess that the nomex parachute protector, in which the chute and elastic portion of the shock cord were attached, was too tight in the tube despite that it deployed fine during the ground test.
The fin was dangling so I finished the job and pulled it the rest of the way off. Clearly the fin itself was the weak point.
The upper body tube buckled along the tube spiral in the center. The nose, to which this tube was still attached, took a two inch core sample. The nose was fine after wiping away the dirt. The component that impacted was nose-upper BT-AV bay and the AV bay ways almost 500 grams, so I think it was just the weight of the AV bay upon impact that buckled the tube.
Unfortunately my video tracking was off and the rocket is out of frame during the important parts of the flight, also I was distracted anticipating the main chute deployment that never occurred. The video does contain a segment on the trip to Berwick as well as the launch finale, which is the launch of a 16 pound pumpkin on a J motor.
[video=vimeo;79014565]https://vimeo.com/79014565[/video]
Where to go from here
Upper body tube
I have a few extra 2" body tubes, so replacement would be easy. Also, I think I will make the upper section at least 6 inches longer so that the laundry (24" chute, shock cord, 9" nomex cloth) is not so tight in there. As it is now, there is no free space at all. The nose has to be forced on (compressing the laundry). I think this is the culprit. I will reuse the lower portion of this tube and combine with another new section via a tube coupler, which I already have on hand.
Fin Can Replace Option
On this one I am divided. I have an extra 2.5" body tube and tube couplers but would have to buy a new motor tube, fins, and centering rings. Or I could make the latter two. I have plenty of 1/4" birch plywood. If I did rebuild it, I might want to put fiberglass in the fillets or maybe even do a tip-to-tip glassing on the fins since they are obviously the weak link. Just not sure. Input here is appreciated! According to the flight data, the rocket was coming in at 30 mph and when it hit the ground, the acceleration was somewhere between 3/4 g and 2.2 g's. Is it reasonable to expect the fins to snap in this case?
Fin Can Repair Option
I am not sure how I would proceed with a straight repair. I guess I could cut out the fin inside the body tube with a dremel and buy a new set of fins and use just one. I could also try and reattach the damaged fin with epoxy. Maybe implant some metal rods (clothes hangers) for rigidity?
At this point, I would appreciate any advice you may have. I understand that some of you may advocate a complete rebuild, but I'd like to try and salvage what I have here. I have little experience in major rocket repair, so I look at this as a learning opportunity (or teaching moment in the present vernacular).
