Saturday, August 2, 2014

HPR L1 - part three - (Successful!) Certification

The start date for NARAM 56 finally arrived (I plan to write another post with my impressions) and we made our way down to Pueblo. On the advice of one of the NAR board members I met at check-in, we spent Saturday just watching the ULA launches and "enjoying the festivities", and had a relaxing day Sunday doing a bit of low power sport launching of our own. I planned to try for certification on Monday, when the sport range would be much more low-key.

The only drawback to this was that over the course of the weekend, I witnessed about a dozen other certification attempts, three or four of which were unsuccessful (including an L2 attempt that blew to pieces a few hundred feet up). That didn't exactly bolster my confidence, but on the other hand, I'd done my homework and was confident in my build and planning.

The weather on Monday was slightly windy, but otherwise good. As soon as we got to the field, I began my prep, loading up a 38mm Cesaroni H120 Red Lightning motor and preparing my payload. In addition to my own data logger, I also included my Jolly Logic 2 altimeter. (Actually my new Jolly Logic. I'd lost my old one the previous day when it came detached from my Mozzie, presumably at ejection. Two zip ties to attach it, from now on.)

The certification process was exactly as I think it should be. Steve Lubliner of SARA (Tuscon) did my cert. He was friendly, and - more importantly - thorough. He checked out the rocket, asked me several questions about the build, and sent me out to the pad. One small comment - "Nice build" - boosted my confidence immensely.

My kids were out there with me to help as I loaded the rocket onto the pad, and my wife took photos. Then there were many agonizing minutes spent waiting for my turn for launch. I was fortunate to have the moral support of family and new friends as I paced about.

Finally - countdown and liftoff! I honestly couldn't have asked for a better flight. Straight up, flawless recovery system deployment (I used motor ejection - no need to complicate things on a cert attempt - plenty of opportunity to get fancy later), and soft touchdown in the field about 100 meters away from the pad.

Loading it onto the rail.

This photo is actually from the second flight (on Tuesday) using a CTI H123 Skidmark motor. Less total impulse, but it makes for a better photo :)

Launch video - also on the Skidmark motor. The camera got bumped and we missed video of the cert flight.

One other change I made to the standard kit: I swapped the 36" flat chute for a 36" elliptical Fruity Chute. Expensive, but I think it lowered the descent rate to a much more acceptable 19 fps (compared to an estimated 28 fps with the stock chute).

Recovery team.

Final inspection and "welcome to high power."

A plot from the data off of my data logger. Two interesting things: First, the GPS seems like it wasn't able to keep up during the quick boost phase, which didn't surprise me. Second, the barometric pressure sensor reported a height about 16% hight than either the GPS or the Jolly Logic altimeter. The accelerometer also reported a peak acceleration slightly higher than the Jolly Logic. But otherwise the data looks as I expect it would. It will take more analysis and testing before I can decide what to trust.

Flight Stats (from the Jolly Logic)
  • Height (AGL): 1449 ft
  • Top Speed: 223 mph
  • Peak/Average Acceleration: 6.6/5.5 G
  • Thrust duration: 1.85 s (seems low compared to the motor thrust curve)
  • Coast to Apogee: 8.3 s
  • Apogee to Ejection: 1.0 s
  • Descent Rate: 13mph
  • Total Duration: 82.5 s

Final Thoughts

I'd like to say that I learned something from the certification process, but that's really not the case. The cert was almost a formality. The learning was all in the advance prep and research. Here would be my advice to anyone else pursuing L1:
  1. Don't get ahead of yourself. Learn the hobby and don't skip steps. Become proficient with low power and mid power first. There is a lot to learn along the way.
  2. Keep it simple. Go with a solid, basic kit and motor ejection. I also chose Cesaroni reloads since they are so much simpler to use than Aerotech.
  3. An absolute must: use simulation software - OpenRocket (my choice) or RockSim. I used this to determine CP/stability, descent rate (and proper parachute choice), and ejection delay.

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