So, having read bunches of threads around here on staging, there were several things I figured I'd "play it safe" on for my first attempt. I'd heard that CTI motors are easier to light (and had proven during ground testing that my RRC3 with a new 9V battery could NOT light an AeroTech FirstFire ignitor, I know that I'll have to do more to stage to an AT motor), and that certain propellants like Smoky Sam were even easier(/faster). I also knew that I wanted to keep things pretty low the first flight, both so that I could see everything and because it was fairly windy so I didn't want things blowing too far. Fortunately, Bay Area Rocketry had just gotten their first post-fire shipment from CTI a month ago, and was at least somewhat re-stocked on 38mm motors (not all of the propellants, but Whites and Smoky Sams at least seemed to have one or two in each size). When I saw that I could pick up the J400SS (Pro38-6G) and the I212SS (Pro38-3G) and the OR sim suggested ~1200' for the booster and ~3800' for the sustainer I figured I had a good set of motors. Of course there was no need for the booster to also be a SS since it was being lit by the pad electronics, but I figured I'd use the same look for both stages.
The rocket worked out to 14 lbs, 15 oz fully-loaded. Cg was 49.75" compared to an OR-calculated Cp of 53.395" (1.17 cal). Would have preferred a bit higher margin on the Cg/Cp, as it was I used a short A3854 adapter in the booster and my older, larger A3854 in the sustainer since that was more weight (barely) ahead of the Cp. I opted for a single #2-56 shear pin on the nose and a single pin on the ISC-booster coupling, no pins (or even holes for pins) on the ISC-sustainer coupling or the av-bay drogue separation point (I do have vent holes in each airframe section). The ISC-booster coupling also needed shored-up with a bit of blue tape to make for a tighter fit, to reduce the wobble of the sustainer as I held the rocket by the booster. Here's the OR model with the weight/Cg dialed-in to actual measurements, and the pre-flight sim plot based on that model.
Going by the nice write-up on staging Cris has in his Eggtimer Quantum Airstart Manual, I used the expected burn time of the J400SS (1.8s) to pick a separation time on the Eggtimer Quantum of 2.2s. I added 0.6s to set the RRC3 AUX channel firing delay (2.8s). The RRC3 was also configured with the altitude lockout, set to 500' since the simulation showed the rocket would be at ~557' at 2.8s (the sims actually said more like 600' when I programmed the RRC3, once I had the final weights it went down a bit, so I was realizing that I was pushing it when I went out to the pad, though I figured I'd rather fail-safe and not light the sustainer than lower the limit since it can only be programmed in units of 100').
Out at the pad things turned into a bit of a disaster. Fortunately I was put on the away pad (even though it was only a complex J, I didn't mind as I wanted it called as a heads-up flight anyway) and wasn't in competition with anyone else, as I tied up one of the two pads for a good hour or so. When I connected the battery to my Eggtimer Quantum at camp it didn't emit its usual beeping, which on my Quantum's speaker is more of a gurgle, and I've noticed times where I didn't hear it beep before but things seemed to work fine, so I didn't give it a second thought. Well, when I got out to the pad my phone wasn't even seeing the Quantum's WiFi network. So I realized that I needed to open-up the ISC and power-cycle the Quantum, but I didn't bring out the hex wrench I needed to undo the lower bulkplate screws, the screwdriver to remove the ISC shear pin, or the stick that I generally need to push the rather tight lid out of the coupler. So there was the first trip back to my camp to grab tools that I'll need to bring with me on future 2-stage launches just in case, but had never needed before. After opening the bay and power-cycling the Quantum it came up normally and I was able to connect. But for reasons I still don't quite understand it failed to arm, reporting lack of continuity on one of the channels (I forget which). Of course I'd already re-assembled the bay at this point, so here I was taking it apart again. The Quantum had gone unresponsive, I couldn't re-load the main page after the continuity failure.
So once again I opened up the ISC, and power-cycled the Quantum again. I had also re-checked the connections, but this time connected from my phone with the bay open. I figured I'd test continuity one charge at a time, so I had the lower bulkhead connector unplugged the first time I checked (only the separation charge, on the main channel, connected). I was incredibly lucky that things had gone so sideways that I wound up here, because something I had totally not noticed up to this point was that I had paired a 4-wire Doghouse header built by Bill (previous owner) with a 4-wire Doghouse header built by Binder (new owner), and the orange/brown wires were swapped between the two headers! So while I expected the main to show continuity and the drogue to show open, I saw the opposite on the Quantum's screen. It was immediately obvious what was wrong looking at the mated connector, and I had actually run into the same issue the day before while ground testing a different av-bay I'd built for a rocket that didn't make its first flight at October Skies due to my work on this 2-stager. I had ground tested the ISC as well, but I guess wasn't thinking about which match should have fired when as I did the testing, it didn't seem wrong at the time but it must have been backwards then as well.
At first I figured I could just re-configure the Quantum to make the 'main' channel handle the apogee charge and the 'drogue' channel handle the separation, but while the drogue channel could be programmed to the 2.2s delay, the main channel didn't offer nose-over as one of its options. So I needed to swizzle the pins on the 4-pin header before I could fly. Needless to say I didn't have the tool for that at the pad, so now I was carrying the ISC assembly back to my camp to do a quick pin-swap. That took all of a few seconds after the long walks back to camp (fortunately I was about as close to the LCO/RSO tent as one could park, but the ground was like walking on sand so it was slow going), and had verified continuity on both channels (with the right assignments) before leaving camp.
So after re-assembling everything it was all finally working as expected. The Quantum definitely got funny after arming it for flight, the load of the status page seemed to hang for a minute or two, and I thought I'd be tearing things apart yet again, but suddenly it started refreshing and seemed happy. I had left the sustainer's RTX/RRC3 (and the A3) running during all of this, since I wasn't concerned about battery life and didn't want to disturb things, though I hadn't considered that the RTx only records the GPS track for so long on a given flight (thankfully I hadn't used up all of the time yet). So I was listening to the seemingly-random squawks coming from the RTx base unit this entire time. Bruce, the club's Prefect, had come out to offer any help a bit earlier, of course it was mostly me bumbling around and 2 trips back to camp so there wasn't much for him to do, he did take a picture with me rather than the one I took of the rocket alone earlier.
I guess I should have been more shaken after getting so far before realizing that the ISC connector pinout was wrong, but it was the only thing that hadn't been flight-tested up to this point, so I was glad that I caught that before the flight (even if it was by complete accident) and was ready to fly.
Honestly, having seen so many 2-stage flight attempts where the sustainer failed to light, I was already assuming that's what was going to happen to me, either due to pushing it on the lock-out altitude or just because there's a lot of things that can go wrong in an airstart. I've always enjoyed the excitement of that moment where you're waiting to see if the second stage lights, such that I knew I'd want to build 2-stage rockets myself. I didn't realize how much more exciting it is when its your own rocket, after the sustainer lit I was euphoric the rest of the day.
Anyway, here's the actual flight plot, combining the Eggtimer Quantum and RRC3 data. To get the separation events aligned I had to add 0.55s to all of the RRC3 times. And, going by the Quantum's clock, separation occurred as intended at 2.2 seconds, sustainer ignition occurred at 4.85s instead of the intended 2.8s. So I updated the simulation for ignition at 4.85s instead of 2.8. Things match pretty well, though there are a few things I still need to correct. The apogee for both flights wasn't as high as expected, they're (barely) within the 20% motor tolerances and probably more due to some extra angling into the wind, I've never really played with the wind values in my sims but might give it a shot here to see how much it affects things. I also never loaded a second chute into the booster in the sim, though the descent rates between my 18" drogue and 36" main aren't all that different, I clearly could use to reduce the size of my drogues in this rocket for future flights.