December 6, 2012 at 2:54 am #56355
Thanks to all for taking the time to respond — think I will try Plan B,,, although there is a lot of wisdom in what Ken says,, but that “within visible altitude” line keeps getting lower as I get older, so it doesn’t matter much – 1,000 feet might as well be 10,000 at my age.December 6, 2012 at 9:58 pm #56356
You can do an awful lot of great DD practice with I motors, that way it isn’t new when you do your L2. OR, what I did was build a 4″ rocket that can fly either way. I certed on a J350 with motor ejection and now I fly the same booster DD with an ebay and longer payload bay for a bigger chute.December 7, 2012 at 2:59 am #56357
You can do an awful lot of great DD practice with I motors, that way it isn’t new when you do your L2. OR, what I did was build a 4″ rocket that can fly either way. I certed on a J350 with motor ejection and now I fly the same booster DD with an ebay and longer payload bay for a bigger chute.
…so it occurs to me,, how low can you go? I’ve seen a lot of crazy good craftsmanship out on the range. Might be an interesting challenge to see how small a rocket you could build to successfully execute a DD. What would be the limiting factor? Electronics? Power for the electric matches? Resolution on the altimeter (assuming the main chute deployment is altimeter based)? Could you count on an altimeter to see and deploy at ground level + 100 feet? Rookie questions, I’m sure.December 7, 2012 at 3:44 am #56358
I certainly wouldn’t count on an altimeter to deploy at 100′, even a Raven altimeter. Most of us have seen deployments that took longer than they should. It isn’t unusual for it to take 5 seconds for a chute to unfurl and open, and I’ve seen a few that take 10 seconds. Plus there has to be some precision error in the altimeter and I can’t imagine the airflow over a falling rocket is such that a good reading through a small vent port is 100% reliable.
I’ll throw out a rule of thumb here. If you are descending drogue less (about 100′ per second) you want to deploy your chute at a minimum of 1000′. If you are descending with a drogue (about 50′ per second) you want to deploy your main chute at a minimum of 500′. Also keep in mind that some altimeters must sense a definitive boost in order to activate the deployment sequence. This filter is designed to avoid a wind gust on the pad causing a premature deployment.December 14, 2012 at 11:46 pm #56359
Whether simple or complicated, the main thing for a certification is that you should use materials, building techniques, and recovery systems that you are FAMILIAR with. IMO, certification flights are not the place to reinvent the wheel. There is no shame in using motor ejection for an L2 flight, but if you want to use DD, then build a rocket or two using DD on I motors, get familiar with how it works, then go for the cert.
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