martinjaymckee
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So, this past Saturday I made my L2 attempt with a scratch-built, 4" blue tube airframe. The rocket, the "Fish out of Water" has a 38mm motor-mount and was designed around a a fiberglass nose-cone I've had for several years ( I found it cheap ). Here's the required pre-flight shot.
What was supposed to be a fish, ended up as something of a whale -- at liftoff, it was over a pound above the weight I had intended ~8lbs. Still, well within the safety range of the selected engine -- a CTI J357. Results? A beautiful flight up to 2807' with a perfect recovery... 60' from the pad! Cool, a successful L2 certification flight.
Since I missed doing a build-log, I thought I'd do a bit of a post-mortem of the whole design/build/fly process. So, I'll begin with the end. As I said, the flight ended around 60' from where it started. No one in their right mind would expect such a short walk to recover an almost 3000' flight -- dual-deploy or not. When I started planning for an L2, I was working on a completely different design ( to be launched on a CTI J530 ) that would have gone to 7500'. As such, I wanted a tracker just to make sure I recovered the rocket. For controlling the dual deployment and doing the tracking, I chose an Eggtimer TRS. The construction was fun and testing went well. I designed and built a magnetic switch to go with it. I also built a tracking box that combined the Eggtimer LCD with a GPS module and a microcontroller -- it was programmed to direct me right to the landing location. What I learned though, on this flight, was that the week-and-a-half that I spent on building the tracking box was wasted if it's going to be used on flights that are are never going to go out of sight. Of course, now I have a nifty tracking box.
The Eggtimer TRS has proven to be quite nice to work with. Having downloaded the data from the flight, I've lashed up some initial graphs of the flight.
The graph shows a vertical line at some particular events: apogee, drogue and main. It shows exactly what I wanted to see. Smooth altitude data, drogue event right at apogee and main event around 600' ( which is where it was configured to be ). While the flight used dual-deployment, it was not a standard two-compartment arrangement. I used a Tender Descender to release the main chute. So, this was my first DD bird. Moreover, I designed the drogue/pilot chute, main chute and deployment bag. I was lucky enough to have my mother ( much better at sewing than I ) help me with constructing the whole recovery system. Neither of us had done much with rip-stop nylon ( just a couple of kites we built when I was a kid ). We also made a Nomex protector and a d-bag casing out of Nomex. In two flights ( I did a recovery system test last month ), the recovery system has worked flawlessly. What I do find interesting, however, is that during one of the tests I did ( towing the parachutes behind the truck ), the main chute was able to deploy just fine but would not inflate. So, have I just been lucky? I don't know. It always works fine opening in just a small wind, so I felt comfortable flying it.
What else needs a postmortem? Quite a bit, probably. At some point I need to analyze the paint job. Another thing I learned on this one is -- I need to plan at least twice as long to paint as I think it's going to take.
Martin Jay McKee
What was supposed to be a fish, ended up as something of a whale -- at liftoff, it was over a pound above the weight I had intended ~8lbs. Still, well within the safety range of the selected engine -- a CTI J357. Results? A beautiful flight up to 2807' with a perfect recovery... 60' from the pad! Cool, a successful L2 certification flight.
Since I missed doing a build-log, I thought I'd do a bit of a post-mortem of the whole design/build/fly process. So, I'll begin with the end. As I said, the flight ended around 60' from where it started. No one in their right mind would expect such a short walk to recover an almost 3000' flight -- dual-deploy or not. When I started planning for an L2, I was working on a completely different design ( to be launched on a CTI J530 ) that would have gone to 7500'. As such, I wanted a tracker just to make sure I recovered the rocket. For controlling the dual deployment and doing the tracking, I chose an Eggtimer TRS. The construction was fun and testing went well. I designed and built a magnetic switch to go with it. I also built a tracking box that combined the Eggtimer LCD with a GPS module and a microcontroller -- it was programmed to direct me right to the landing location. What I learned though, on this flight, was that the week-and-a-half that I spent on building the tracking box was wasted if it's going to be used on flights that are are never going to go out of sight. Of course, now I have a nifty tracking box.
The Eggtimer TRS has proven to be quite nice to work with. Having downloaded the data from the flight, I've lashed up some initial graphs of the flight.
The graph shows a vertical line at some particular events: apogee, drogue and main. It shows exactly what I wanted to see. Smooth altitude data, drogue event right at apogee and main event around 600' ( which is where it was configured to be ). While the flight used dual-deployment, it was not a standard two-compartment arrangement. I used a Tender Descender to release the main chute. So, this was my first DD bird. Moreover, I designed the drogue/pilot chute, main chute and deployment bag. I was lucky enough to have my mother ( much better at sewing than I ) help me with constructing the whole recovery system. Neither of us had done much with rip-stop nylon ( just a couple of kites we built when I was a kid ). We also made a Nomex protector and a d-bag casing out of Nomex. In two flights ( I did a recovery system test last month ), the recovery system has worked flawlessly. What I do find interesting, however, is that during one of the tests I did ( towing the parachutes behind the truck ), the main chute was able to deploy just fine but would not inflate. So, have I just been lucky? I don't know. It always works fine opening in just a small wind, so I felt comfortable flying it.
What else needs a postmortem? Quite a bit, probably. At some point I need to analyze the paint job. Another thing I learned on this one is -- I need to plan at least twice as long to paint as I think it's going to take.
Martin Jay McKee