Tips on finding materials to build Level 1 / 2 cert rocket.

Discussion in 'High Power Rocketry (HPR)' started by Ben Schultz, Jan 19, 2020.

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  1. Jan 20, 2020 #31

    Nytrunner

    Nytrunner

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    I don't recall any prohibition against it
     
  2. Jan 20, 2020 #32

    boatgeek

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    I think you can do sparkies for a cert but definitely not if you're under 18.
     
  3. Jan 21, 2020 #33

    blackjack2564

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    Sparks ARE allowed for cert flight BUT some clubs do NOT allow flying them on their fields, usually do to fire concerns.
     
    samb likes this.
  4. Jan 22, 2020 #34

    David Schwantz

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    I know I read sparkys were not allowed for something, thought it was cert flights, but cannot find what I read again. My mistake.
     
  5. Jan 22, 2020 #35

    Flyfalcons

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    To be fair, I built an L2-capable Big Daddy for probably less than 80 dollars. But I wouldn't recommend that to a high power aspirant.
     
  6. Jan 22, 2020 #36

    blackjack2564

    blackjack2564

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    Possibly this;
    you should be L-1 to buy G sparks, this is also to prevent fires being started by low/mid power fliers that don't belong to clubs, NAR or Tripoli.
    As walk into Hobby Lobby, and buy a sparky with G-64 etc. Go fly in school football field, or local park and set the dry grass on fire.

    Also CTI sparks are shipped pre-assembled,[just push into case] so they also are considered high power for that reason and you must be certified to buy G's or shipped hazmat. [more than 30 [?] grams per grain]
     
  7. Jan 22, 2020 #37

    David Schwantz

    David Schwantz

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    Maybe, guess I am just getting old!
     
  8. Jan 22, 2020 #38

    jlabrasca

    jlabrasca

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    I just looked at American Science and surplus -- they are out of stock for the $7.50 pop chutes.

    At a big public launch two years ago we had a mess of students from a university aerospace club show up to (attempt to) certify L1 with with BMS 3 inch School rockets (the same kit as the Mercury Engineering School Rocket mentioned by @dhbarr in #10). They were not well prepared (the rockets all had to be modified in the field to be stable on the DMS H motors the students were loading) and the results of the attempts were varied. Most students either certified, or lost the rockets when they came apart at deployment. I saw one blow-through (which was pretty alarming), and saw another rocket leave its fins at the pad and squirrel around before doing a power dive into the sod (which was terrifying). I was thinking about that adventure when I posted here.

    If the OP would consider building separate L1 and L2 rockets, the School Rocket would be a good kit for L1 -- modified with a more robust fin can and some nose weight. Making the modifications for a safe L1 attempt would be more of a kit-bash than a scratch-build, but maybe that counts? The kit, a piece of 29mm motor tube, and a sheet of 3mm plywood comes to about $35 (before shipping) from BMS. That'll leave the OP about $115 for the L2 rocket. Easily in reach if he res-uses the the nose-cone from the School Rocket,
     
  9. Jan 22, 2020 #39

    KilroySmith

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    Some great responses above. I'll give you my $0.02 worth...

    I'd suggest planning a simple three-fin-and-a-nosecone rocket. Complexity and unique design aren't incompatible with reliability and a low budget, but they certainly don't get along well. I'd also recommend planning on using an Aerotech DMS (single-use) motor rather than a reloadable motor system, unless you can hook up with someone who already has cases, and knows how to use them. Some believe that motor building skill is a prerequisite for high-power rocketeers; I applaud their skills, but don't happen to agree with them. You'll pay about $10 more for the DMS than an equivalent reload - but you don't have to buy the cases and go through the learning curve of building them.

    Your first choice should be motor size. Level 1 rockets will generally be 29mm and 38mm motors, Level 2 will generally be 38 and 54mm motors. You can buy/make adapters that would let you put a 38mm motor into a rocket built for a 54mm motor, or a 29mm in a 38mm rocket, if you wish, but that's a bit of complication. Choose 38mm and be happy. In general, level 1 motors will generally cost from $25 to $50 apiece, and level 2 anywhere from $65 to $90 (http://www.buyrocketmotors.com/38-mm/). You really don't want to know how much the N and O and bigger motors that you read about cost.

    The materials you've gonna need for a 3FNC:
    1 - Nosecone
    2 - Body Tube
    3 - Motor Centering Rings
    4 - Motor Tube (not strictly necessary)
    5 - Motor retention
    6. Fins
    7 - Parachute
    8 - Dual-deploy altimeter, Electronics bay, and second parachute (really not necessary, but if I were mentoring you I'd strongly suggest it for any L2 attempt just from an experience POV).

    So let's take these one at a time.
    1 Nosecone - Build one. The current rocket I'm building has a bright-orange 3D printed nosecone, and after four iterations (to get the fit into the body tube perfect, etc), total cost has been about $2 worth of filament. Find a friend with a 3d Printer (or go to your public library; many have one), download a nosecone generator for one of the free 3D design packages (I like SCad, but then I'm a programmer so it's pretty natural), and print your own. I wouldn't suggest doing so for a minimum-diameter Mach-3 rocket, because aerodynamic heating will likely cause failure and a spectacular RUD at altitude, but I wouldn't recommend doing such a rocket for your cert flights anyway.
    2. Body tube - lot of good suggestions upthread. I happen to have a used 6'x4" shipping tube out in the garage that will someday become a rocket named "Postage Due". However, buying one isn't unthinkable - Apogee Rockets has a nice 4" tube set for $15 (https://www.apogeerockets.com/Build...n-Tubes/4in-Airframe-Tube-Set?cPath=42_43_55&) that enables a break-in-the-middle rocket, which would be easy to upgrade with an EBay and dual deploy later. The 0.05" thick tubing should also stand up to L1 and smaller L2 motors.
    3. Motor Centering Rings - These will be difficult to "find", and moderately difficult to fabricate. The cheapest approach is to buy some 1/4" hardwood plywood, print templates from OpenRocket, glue the templates to the plywood, and cut out the centering rings. But cutting circles reasonably precisely requires a certain amount of equipment, skill and time - I don't have the time, but you might. Otherwise, Apogee Rockets will sell you a pair for $9 (https://www.apogeerockets.com/Build...h_Power_Centering_Rings/Centering_Rings_38-98)
    4. Motor Tube - once again, difficult to "find" unless you have a friend into rocketry. Difficult to build. Once again, Apogee will sell them to you, $6 for a pair: https://www.apogeerockets.com/Building-Supplies/Body-Tubes/29mm-to-54mm-Tubes/38mm-Engine-Mount-Tube.
    5. Motor retention - as suggested above, a screw into the rear centering ring with either a washer or a bent metal clip (https://www.amazon.com/Hillman-Group-121155-Mirror-Holder/dp/B0050GGPIU/) (don't buy this for $6, that's outrageous) will do fine to hold the motor in place. I do recommend going to a launch to see how HPR motors are held in by a band at the rear of the motor, rather than a stop inside the motor tube, to understand how this would work.
    6. Fins - Difficult to find. Can be purchased (for example, http://www.balsamachining.com/tarc_parts.pdf), or can be fairly easily fabricated by printing templates from OpenRocket, gluing them onto a piece of 1/4" hardwood plywood (you could use 1/8" if you used 5-ply), and cutting them out as long as you use a simple design. Let's be generous, and suggest the piece of plywood might cost you $10 at the local hobby store (https://www.amazon.com/Midwest-Products-Plywood-Sheet-Beige/dp/B004BPO538/).
    7. Parachute - You can build one of these yourself if you have access to a sewing machine (there are threads here about using a canopy from an old umbrella, also). These can get expensive; OpenRocket will be your friend in choosing the right size, but expect to spend anywhere from $30 to $100 for one (e.g. https://www.apogeerockets.com/Build...48in-Printed-Nylon-Parachute?cPath=42_309_79&).

    So, if you built your own nose cone and parachute, you could buy the body tube, centering rings, and motor tube for roughly $30. Add plywood for the fins, and you're up to $40. Add $10 for a couple cheap cans of spray paint and you're up to $50, That gives you a 3 foot tall, 4" diameter rocket and $100 to spend on motors.

    If you wanted to pursue this project, I'd suggest getting an idea of what you want to build (look at threads here; lots of people asking "what should I build for my Level 1 Certification"), then install OpenRocket on a PC somewhere (preferably somewhere you have permission to do so) and whip up a design - many of the commercial rockets that you'll find in the "level 1 build" threads have OpenRocket files already available that you could start from. Look through a bunch of vendors - Apogee isn't the cheapest, but they're the most professional and comprehensive that I've found - to find prices on various sizes of components (3" body tube is cheaper than 4", for example). Post your progress here along with any questions or problems you have, and you'll get plenty of help (just make sure that everyone recognizes your cost targets). In a week or so, you could probably have a completed design and a full list of parts that either need to get built or bought.

    And that's my opinion. Take it for what it's worth, and what you paid for it.
     
  10. Jan 22, 2020 #40

    KilroySmith

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    jlabrasca -
    I bought several of those a couple years ago. Take out the spring, and they're a great, strongly constructed (but heavy due to the skirting) chute that are just about perfect for drogue chutes on bigger rockets. Blowing one out would take a concerted effort.
     
  11. Jan 22, 2020 #41

    jlabrasca

    jlabrasca

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    me too >smile<


    [​IMG]

    they are nice. no strings to tangle and (once you cut away the canvas bits) the springless model isn't really any harder to pack than the nylachutes from modelrocketparachutes.com (they take dye pretty well too)

    With thru-wall fins, in a design where the fin tabs contact the aft center ring and transfer the thrust to the airframe, you really don't need plywood centering rings. Heavy chipboard (14-ply illustration board for those of us who draw on the stuff) will do. Cut's easily with an Olfa circle cutter or an Xacto compass cutter. Two rings laminated together will be more than equal to the stresses of a high power launch. And thats just for the aft ring. The forward rings could be foam-core or shirt cardboard.
     
    Last edited: Jan 22, 2020

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