Saint_Tiki
Well-Known Member
Hi everyone. Here is my attempt at a build log!
I’m going to do a scratch build as my first high power rocket. Constructive feedback and advice are very welcome.
The Plan
3” diameter, split fin, configurable booster-only/dual-deploy for future tinkering
MAC canvas phenolic custom kit, tubes, e-bay, fins, etc
38mm motor mount
I’m designing a rocket that I can launch on G motors here at “home” in a single deploy configuration that I can use for my level 1 certification. It will be designed such that I can add dual-deploy down the road.
I’ll launch it a few times at my local launch site on G motors to make sure it holds up, practice my checklist discipline, parachute packing technique with the JLCR, etc. Then I’ll do a level 1 cert in the single-deploy config. After I get some experience like this, I’ll start tinkering with adding electronics for a dual-deploy.
It’s quite the engineering challenge to make a rocket that is stable in both configurations and with various sized motors, but I love a good challenge.
The Design
I love the look of split fin so I’m starting with that. I’m going with 3” diameter to keep the altitude down a touch and give me room to work with inside the rocket. I want a waterproof rocket since my home field (about 2,500’ square) has a pond as the bullseye and I also have no desire to fill spirals. That left me with Quantum Tube, Canvas, or Fiberglass. I chose canvas as a good balance of weight, strength, altitude, etc. and I’ve heard nothing but great things about the fit and finish of MAC kits. Mike makes it easy by essentially building out a full custom kit for my design. Awesome.
Decision point: Head-end-dual-deploy (HEDD) or traditional DD?
In the traditional dual-deploy design, my primary concern is “over stability.” I’m not sure how much is too much. In the booster only config, the rocket is stable at about 1.3-1.8 cal with all intended launch motors G-H. After I add the payload section for the dual-deploy configuration, the rocket gets a lot longer and the stability number goes up quite a bit and I’m not sure how bad it is to be in the 3+ cal range, besides the obvious exaggerated weather-cocking effect. There’s not a good way around this as the added length and weight of the payload section just naturally moves the CG forward and the fin size/shape is bound by the stability in the stubby config.
Alternatively, I’m highly considering a HEDD design. I’m already planning to use a Wildman FWFG nose-cone (need the extra weight up there for either design) that’s about 17 inches long and I think is used in the Punisher 3 kit as a HEDD, so a chute should fit in there no problem. If I went this route, I’d avoid most of the problems with trying to make a short rocket stable but then having a long rocket that is over-stable since with HEDD, the rocket dimensions would be virtually the same whether I use dual or single deploy. However, this means there will be less of a weight different between my two configurations so less motor flexibility. It would end up a bit heavier even in the lightest configuration and therefore a little harder to pull off a G motor at home. I think I can do it by removing the e-bay entirely and just using the nose-cone in the traditional manner with a piece of coupler as the shoulder. I’d pin the coupler/shoulder in through the same holes that I would use for shear-pins in the HEDD mode.
Attached are some screengrabs and files of OpenRocket for both designs. Let me know what you think. I’m partial to the HEDD design currently.
Motors
Surprisingly, I haven’t seen that much about CTI vs ATI reloads. From what I can gather, CTI reloads look simpler and that appeals to me, but all of them require haz shipping fee. Some ATI G and even H reloads can be shipped without haz, which is a big plus, but they look more complicated to assemble. Right now, I’m leaning towards a CTI 38mm 3-grain case with 2 spacers. I could always buy single-use or DMS/loadable Aerotech G or H motors if I wanted. I’ll also probably pick up a 38 to 29mm adapter to fly some single-use 29mm motors.
More to come!
I’m going to do a scratch build as my first high power rocket. Constructive feedback and advice are very welcome.
The Plan
3” diameter, split fin, configurable booster-only/dual-deploy for future tinkering
MAC canvas phenolic custom kit, tubes, e-bay, fins, etc
38mm motor mount
I’m designing a rocket that I can launch on G motors here at “home” in a single deploy configuration that I can use for my level 1 certification. It will be designed such that I can add dual-deploy down the road.
I’ll launch it a few times at my local launch site on G motors to make sure it holds up, practice my checklist discipline, parachute packing technique with the JLCR, etc. Then I’ll do a level 1 cert in the single-deploy config. After I get some experience like this, I’ll start tinkering with adding electronics for a dual-deploy.
It’s quite the engineering challenge to make a rocket that is stable in both configurations and with various sized motors, but I love a good challenge.
The Design
I love the look of split fin so I’m starting with that. I’m going with 3” diameter to keep the altitude down a touch and give me room to work with inside the rocket. I want a waterproof rocket since my home field (about 2,500’ square) has a pond as the bullseye and I also have no desire to fill spirals. That left me with Quantum Tube, Canvas, or Fiberglass. I chose canvas as a good balance of weight, strength, altitude, etc. and I’ve heard nothing but great things about the fit and finish of MAC kits. Mike makes it easy by essentially building out a full custom kit for my design. Awesome.
Decision point: Head-end-dual-deploy (HEDD) or traditional DD?
In the traditional dual-deploy design, my primary concern is “over stability.” I’m not sure how much is too much. In the booster only config, the rocket is stable at about 1.3-1.8 cal with all intended launch motors G-H. After I add the payload section for the dual-deploy configuration, the rocket gets a lot longer and the stability number goes up quite a bit and I’m not sure how bad it is to be in the 3+ cal range, besides the obvious exaggerated weather-cocking effect. There’s not a good way around this as the added length and weight of the payload section just naturally moves the CG forward and the fin size/shape is bound by the stability in the stubby config.
Alternatively, I’m highly considering a HEDD design. I’m already planning to use a Wildman FWFG nose-cone (need the extra weight up there for either design) that’s about 17 inches long and I think is used in the Punisher 3 kit as a HEDD, so a chute should fit in there no problem. If I went this route, I’d avoid most of the problems with trying to make a short rocket stable but then having a long rocket that is over-stable since with HEDD, the rocket dimensions would be virtually the same whether I use dual or single deploy. However, this means there will be less of a weight different between my two configurations so less motor flexibility. It would end up a bit heavier even in the lightest configuration and therefore a little harder to pull off a G motor at home. I think I can do it by removing the e-bay entirely and just using the nose-cone in the traditional manner with a piece of coupler as the shoulder. I’d pin the coupler/shoulder in through the same holes that I would use for shear-pins in the HEDD mode.
Attached are some screengrabs and files of OpenRocket for both designs. Let me know what you think. I’m partial to the HEDD design currently.
Motors
Surprisingly, I haven’t seen that much about CTI vs ATI reloads. From what I can gather, CTI reloads look simpler and that appeals to me, but all of them require haz shipping fee. Some ATI G and even H reloads can be shipped without haz, which is a big plus, but they look more complicated to assemble. Right now, I’m leaning towards a CTI 38mm 3-grain case with 2 spacers. I could always buy single-use or DMS/loadable Aerotech G or H motors if I wanted. I’ll also probably pick up a 38 to 29mm adapter to fly some single-use 29mm motors.
More to come!
Attachments
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HEDD in dual mode.PNG297.9 KB · Views: 36
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HEDD in single mode.PNG324.2 KB · Views: 31
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DD in dual mode.PNG353.7 KB · Views: 29
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DD in single mode.PNG354.3 KB · Views: 25
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3 inch canvas HEDD Single.ork3.5 KB · Views: 3
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3 inch canvas HEDD.ork3.6 KB · Views: 2
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Scratch Built 3 inch_v3_LONGConfig CTI Motors.ork4.6 KB · Views: 1
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Scratch Built 3 inch_v3_ShortConfig CTI Motors.ork771.3 KB · Views: 2