L2 Cert – Plan B

Forums Knowledge Base L2 Cert – Plan B

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    Jack Matthews

    Plan A – Ambitious plan to build a dual-deploy bird specifically for certifying L2 (kit build, PML Eclipse). Gathered all the parts and pieces,, started asking questions, reading, scanning the forums, putting together a construction plan — Holy Crapoli — I’ll be climbing 17 learning curves at the same time – programming electronics, pre-mature ejections, Faraday cages, calculating black powder charges, sheer pins, ground testing,… (… gasp…. 😯 )

    Plan B – decouple the L2 cert from the complicated build. Got a PML Miranda (I call her ‘Ugly’) that I’ve flown 4 times on 3 different I-impulse motors – nary a scratch,,, and I’ve used a dog collar tracker in her with unqualified success (not that I needed it, but just to see if it worked).

    Thought I might try to L2 cert with a baby-J in that bird and then do the complicated dual-deploy without the added pressure of the cert. Looking at the Cesaroni 54 mm/2g J210. Comparing the RockSim results,,, the maximum acceleration for the I236 I flew last Saturday is more than the J210. The max velocity puts the J210 at Mach 0.75,,, less than the Mach 0.85 maximum recommended by PML for the Quantum Tubing airframe, but higher than what she’s seen so far (Mach 0.55). The fins are G10, through the wall, and encapsulated with epoxy foam in the annular space between airframe and motor mount. Seems like Ugly Miranda should be able to handle the J210. Agree or disagree??

    Any advice and/or admonitions? Have I missed something I should be worried about?


    Either sounds like a good plan.

    I like plan B for a cert. I get very nervous about a cert. And
    like simple.

    When doing My level 1 cert, I tried a duel deploy that did
    not work as planned. An hour later I put a motor in My EZI 65
    and flew with no hitch. The pressure was off.

    have a great flight


    I like what Mike said, so I go for plan B. When I did my L2, I used my Intimidator 3, on a small “I”. It stayed in sight, no too high, so I did not have to walk too far on motor deployment. Worked great. Now the pressure is off. Now pretend that your L2 flights, after the cert flight are preparations for an eventual L3. So you build yourself a check list, and start working on the different areas at your own pace and comfort level.

    If you are going a mile or more in altitude, (maybe as low as 3,000 ft.) then you need to have sheer pins.

    So for me, in prep for my L3 cert, I design the whole thing in RockSim. Then I build lists of everything I need to do and build a launch checklist. I will then have everything I need to duplicate for my L3. Then I start breaking the whole thing into smaller bites. (The easiest way to eat an elephant is in small bites, one bite at a time; you are building an elephant of a project) So where is my electronics bay, and how much room do I have on each side? John Wilke told me that in his DD flights, he never uses a drogue chute, he just has aerodynamic braking by breaking the rocket apart at the fin can below the upper portion. Gives you more room above.

    You design the electronics bay, design it for redundant altimeters (like on an L3 cert flight) build it, and then install ejection charges, add shear pins, and ground test on the upper part. Then you can do the lower part, and test. Put it all together, and test. There are forums (especially http://www.rocketforum.com) that have discussions on sizes of ejection charges and show you how they developed their calculations, or you can just test. On my 4″ Intimidator 4, I am following what Steve Jensen told me that he uses on his. 2.3 grams of BP on the fin can section for the primary charge and 3.5 grams for the back-up charge. For the upper portion for main chute deploy, he uses 2.0 grams and 3.0 grams. Those are working for me. If you do it this way, you will have the practice in prep for your future L3, and will have a comfort level with the whole thing. This takes a lot of stress out. Then you are not rushed and you can take your time.

    I am doing it this way in prep for my L3 flight when we get back to the north site. I will be using a Tele-Metrum and a Missile Works altimeters. I also have an Adept short wave transmitter in the nose. I have at least 5 times my overall rocket length in Kevlar shock cord. I have modified it further and I am planning on flying the bird on a hybrid M motor, so I have gotten even more complicated. Ground test, ground test, ground test. Practice tracking. Make as much as possible second nature, and, although your success will not be completely insured, because Murphy can still be lurking in the background, you will have a much better chance. I apologize for being so long winded with my opinion. I hope it helps though.


    No need to stress out about the cert, or rush it. You can do plenty of playing around with dual-deploy at L1 power levels. I did motor eject for my L1 and the next 2 flights, then electronics ever since. No L2 plans yet, and my L1 has since expired (no time to build or fly lately). By messing around with it at the low power levels, I’m now comfortable with electronics, ground testing, charges, etc. especially when I can see all the events unfold within visible altitude.

    Jeffrey Joe Hinton

    Tie your hands and feet together behind your back, adjust blindfold and dive in head first – what could possibly go wrong? KISS has always been a mantra – lots of opportunity to screw things up after you’ve earned the priviledge of playing with higher thurst motors. Climb every mountain one step at a time. Just don’t over study for the written exam.

    Jack Matthews

    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.

    Bret Packard

    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.

    Jack Matthews

    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.


    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.


    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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