Meet Enlil
During the Fall Semester of 2021, I decided to attempt my level 2 high powered rocketry certification. Enlil was the rocket I built for this challenge.
Enlil is a fiberglass Wildman Darkstar 3 kit. The rocket was 83” tall with a 3” diameter. Its final weight was approximately 11 lb and it had a 54 mm motor mount.
Structure and Recovery
One of the biggest challenges in this rocket was handling the fiberglass. I can’t even say how many shards of fiberglass I had to dig out of my hands after spending a day working on the construction of this rocket. Additionally, working with just 3 inches of space was a nightmare. I couldn’t fit my hand down to tighten my rail buttons and needed to rely on a friend with better agility to help me fasten them in. In the end though, the process was similar to my experience with DUMBO I as far as fins and motor mount. This was my first time using shear pins however, and I learned to use weld nuts with thick bolts to secure the non-separating parts of the rocket together. All in all, the structure came together quite nicely and I’m proud of how well it turned out.
My recovery scheme was another source of headache for me. I wanted to deploy both the main and drogue out of one airframe section instead of using up both sections to leave room for a potential payload (as seen in the recovery diagram below). To do this, I used a tender descender setup. The parachutes I sized using an online calculator as well as by keeping in mind the diameter (3”) I had to work with. In the end, I used a Rocketman 5’ diameter main with a 2’ diameter drogue. This ended up being quite a tight fit and that caused tangling issues during my flight. In the future, I don’t think I would fly with this recovery scheme as it’s just too risky (tangling). For future flights I will deploy using both airframe sections.
Avionics
For Avionics, I intended to use a RRC2+ as the primary altimeter with an Eggtimer Quantum as a backup. Additionally, I would use a Big Red Bee 70cm RF Transmitter Beacon for tracking the rocket should it land a far distance away. While the RRC2+ and 70cm Transmitter worked flawlessly, I had quite a few issues assembling the Quantum. Unfortunately, the problem ended up being that the 2s Lipo Battery I had was wired incorrectly and that issue destroyed the Quantum. My second attempt at a backup flight computer was the Eggtimer Quark. I chose this computer as it was the cheapest and I wanted to try my hand at assembly again. Unfortunately, it appeared that the barometer on the Quark was damaged as it continued to give me incorrect pressure readings. After this issue, I determined to take a risk and fly with only the one functional flight computer, the RRC2+, due to time constraints. To fix avionics into the rocket, I designed and printed an avionics bay and soldered a physical switched that could be flipped on the launch pad to activate the electronics.
Reflection
For the flight, I loaded up a J355-CTI Red into Enlil and launched it. The rocket flew beautifully and reached an apogee of 5484ft according to the RRC2+. The rocket deployed its drogue at apogee, however the parachute got tangles in the shock cord. Luckily, the main deployed perfectly and Enlil had a (relatively) soft landing. Post flight, I noted that one of the fillets had a crack running up the side, but the fin was not at risk of coming off. Thankfully, this did not disqualify my certification attempt and I received my L2 cert!
After repairing the previously damaged fillet to ensure it would not cause any further issues, I flew the rocket again. For Enlil’s second flight, the same setup was used and once again it flew beautifully reaching an altitude of approximately 5000ft. No issues with the fillets this time!
After dealing with the recovery setup twice now, I can certainly see some areas for improvement. For one, the dual deployment with a tender descender is prone to tangling and getting jammed in the small 3” diameter airframe of Enlil. Future work should be done to improve some of these issues.