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  1. #1
    Join Date
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    Newbie question - rocket casings

    Hello,

    We are slowly working on "DIY" rocket motors. Yes, we've read many pages of safety advice, and are taking a number or safety precautions. At this point, the build is roughly as follows:
    3/4" tube, packed with
    3/4" clay plugs at each end
    3" sugar fuel (white mix)
    7/32" nozzle punched through one of the clay plugs.

    There is no recovery charge yet, and nothing else fancy. We're just trying for a build that works.

    For the casing, we have been following some popular advice of schedule 40 PCV pipe. However, as a part of that safety research, I have learned that although it is popularity recommended, PVC has the tendency to shatter if it fails. Schedule 40 PVC has a 480 PSI capacity rating. For better or worse, we have used this PVC pipe in successful tests, and the PVC has not failed so far. We haven't dared to reuse the PVC, but if that is the only disadvantage, that's fine with us.

    Our fuel is the basic [ed. - formula removed by mods] blend, used in powder form (and packed firmly)

    My questions are:
    1. Does anyone have some idea what kind of PSI this build contains, or suggestions on how to measure it?
    2. What kind of casings are viable and fairly safe? Suggestions?
    3. Any other thoughts, suggestions, or dire warnings of catastrophic explosions?


    We have made a build using layered paperboard for a casing, but we have not been able to set up a safe launch environment to test it yet. My concerns with that are that
    1. The casing might burn out too quickly, and fail catastrophically in flight (we considered treating the casing with baking soda, be decided to try it plain)
    2. The casing might stretch enough to eject the clay plugs (including the nozzle)

    Any thoughts on this are also welcomed.

    Thank you!


  2. #2
    Join Date
    14th March 2009
    Location
    Ohio
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    3,359
    We don't talk about homemade motors here as it is against forum rules. Expect to see this thread locked or deleted very soon.

    Zeus-cat
    NAR# 92125 L1
    Total Impulse for 2018: 491.6 N/s Flights: 10
    2017: 1/2A:0, A:2, B:1, C:2, D:2, E:1, F:1, G: I have NEVER launched a G motor, H:0, I:1

  3. #3
    Join Date
    4th April 2018
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    Ah, ok. I thought I had reviewed the rules suitably. Very good, thanks for letting me know.

  4. #4
    Join Date
    22nd January 2009
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    Plano, TX
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    Full disclosure... I've never built a rocket motor. This forum may not be that best place to get your questions answered. Have you found Richard Nakka's site yet ? http://www.nakka-rocketry.net/

  5. #5
    Join Date
    22nd August 2015
    Location
    Rhode Island
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    Even though you aren't discussing formulas, this thread may get locked. But before it does, I want to discourage you from using PVC. I have built similar kinds of motors, but I have stayed away from PVC. I use 3/4" polyethlene tubing. You can buy it at Home Depot in the irrigation section. It is lighter than PVC, and it doesn't shatter. Going forward, I'd like to try cardboard tubing, like Estes BP motors. You can buy stuff like that at fireworks supply websites.
    Last edited by BDB; 10th April 2018 at 03:54 PM.
    NAR #100940, RIMRA & CMASS
    L1 - 4/17/16, Tyrannosaur (by Binder Design), Loki H144
    L2 - 8/19/17, Terrordactyl (by Binder Design), CTI J250

  6. #6
    Join Date
    18th January 2009
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    2,122
    http://www.skylighter.com/fireworks/...er-rockets.asp

    Use parallel wound paper tubing as the case, bentonite clay for the nozzle and your propellant mixture.

    Paper tubes are *much* safer than PVC.

    http://www.skylighter.com/mall/produ...ils.asp?id=203

    With a little bit of sanding, these will fit into a standard 29mm motor mount.
    Aaron Head
    NAR 83209 L2

  7. #7
    Join Date
    18th January 2009
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    Virginia - Central
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    4,104
    Quote Originally Posted by Zeus-cat View Post
    We don't talk about homemade motors here as it is against forum rules. Expect to see this thread locked or deleted very soon.
    ...unless it is in the restricted access "research" section?
    We got two categories of pilots around here. We got your prime pilots that get all the hot planes, and we got your pud-knockers who DREAM about getting the hot planes.
    Now what are you two pud-knockers gonna have?... Huh?
    Pancho Barnes-
    The Right Stuff
    http://www.mwavs.com/0053148414/M4RS...udknockers.m4r

    Tripoli #2747

  8. #8
    Join Date
    7th May 2017
    Posts
    118
    Took just one eye-opening incident to convince me that PVC is not, and never will be, suited for rocket casings.

    "Oh, I've never had one blow up" isn't far from "Hold my beer and watch this!" Ya really need to remember: it only takes one. Please. People learn from experiences; wise people learn from others' experiences. Had mine. Don't want nummore. Learn.

    Best --Terry
    The difference between science and the fuzzy subjects is that science requires reasoning, while those other subjects merely require scholarship.
    It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so.
    Be wary of strong drink. It can make you shoot at tax collectors---and miss.
    ----R. Heinlein

  9. #9
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    Quote Originally Posted by prfesser View Post
    Took just one eye-opening incident to convince me that PVC is not, and never will be, suited for rocket casings.

    "Oh, I've never had one blow up" isn't far from "Hold my beer and watch this!" Ya really need to remember: it only takes one. Please. People learn from experiences; wise people learn from others' experiences. Had mine. Don't want nummore. Learn.

    Best --Terry
    BTW, prfesser is the guy who's book is/almost is required reading for entry level composite motor fuel making...
    Rich

    NAR# 99154

    L3-4x upscale Estes Cherokee-D- AT M1297W 5/28/2016 http://www.rocketryforum.com/showthr...r-rharshberger

    TriCities Rocketeers NAR section# 736 http://www.tricitiesrocketeers.org/

  10. #10
    Join Date
    14th March 2009
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    Ohio
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    Quote Originally Posted by MaxQ View Post
    ...unless it is in the restricted access "research" section?
    That is correct, but these guys don't qualify for access so I saw no sense in mentioning it.
    Zeus-cat
    NAR# 92125 L1
    Total Impulse for 2018: 491.6 N/s Flights: 10
    2017: 1/2A:0, A:2, B:1, C:2, D:2, E:1, F:1, G: I have NEVER launched a G motor, H:0, I:1

  11. #11
    Join Date
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    Since the OP has no real chance of following a discussion if I moved the thread to the Research forum, I just removed the formula in his post. The rest of his questions are valid and you are giving him good answers and directions. For sugar rockets I have often heard that Richard Nakka's website is the "go to" standard. I also want to discourage the use of PVC and the best reason, besides being prone to shattering, is that PVC is transparent (or nearly so) on x-rays so when it lodges inside of you, the ER docs are going to have a really hard time finding it. That's not a good thing.
    Blessings,

    John
    NAR#87984
    L1 - Airfest - September 6, 2015

    It can't be my second childhood, I haven't finished my first one yet.

    "If I were giving a young man advice as to how he might succeed in life, I would say to him, Pick out a good father and mother, and begin life in Ohio." - Wilbur Wright, January 10, 1910

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  12. #12
    Join Date
    10th January 2017
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    Arcadia, Florida
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    Curious Amateur
    Get your level 2 cert and join the Research area, that is what we have done. There is many formulas for igniters, fuel. Discussion on about anything.
    Get Prof. Terry McCreary's and John H Wickman's books. They are my go to reference
    Bill

  13. #13
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    samb: I have been there a few times, thanks! In many cases it is a bit advanced for us at this point, but it definitely looks like a great resource! We've already learned a few techniques from him.

    BDB: Thanks for the specific suggestion! We will look for that tubing. Cardboard does seem to be the material of choice, and from a safety standpoint, I can see why. I wish we could get it any way other than mail order.

    prfesser: That's what we've been hearing--thanks for the confirmation.

    rharshberger: We haven't tied composite fuels yet, just the previously mentioned (apparently secret) sugar formula. Still, I've made note of this. Thanks!

    Peartree: Thanks for keeping this accessible to me! I haven't heard the x-ray visibility aspect of PVC, but it is a good insight. Unfortunately, unless we use metal, this will be true with most casings. That brings us back to the shattering issue, I suppose.

    r66astro: It seems I need to do more research on this forum, to learn what this level 2 certification is. I may do this, thanks! We do have a number of fuel formulas, but we're staying with the simple sugar composition for now, since it was our assumption that less energetic materials are safer when doing experiments.

  14. #14
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    heada: it seems I missed you post initially. Thanks for the suggestion--this is pretty much what we did with paperboard, and have not yet tried. We will try paper too. It doesn't burn through too quickly to work? No fire retardants required?

    BDB/others: I thought poly tubing sounded familiar, but I couldn't remember why. I looked back in my notes and found out. We did consider it a while back, but here's the thing: Sched. 40 PVC is rated to 480 PSI, and should not be used due to risk of failure. The only poly we could find was rated to 100 PSI, which is much weaker than the PVC. Is 100 PSI rated poly really good enough, or do we need higher quality stuff from somewhere other than Home Depot? The 100 PSI stuff is also quite thin, and often comes on a roll. My concerns there are that it might explode (I still have no idea how much PSI is in there), or it might melt through. Are these fears unfounded? Sure, it's safer if it fails, but it sounds much more likely to fail. Just holding the stuff, I really don't feel safe packing pyrotechnics into it. If you've had this type work then we'll test it, but I just wanted to make sure that this was the stuff you are talking about first.

  15. #15
    Join Date
    18th January 2009
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    2,122
    Since you're using a sugar based propellant, read and understand Richard Nakka's site and data. He covers most of what you're doing. I would highly recommend using the parallel wound paper casings for a few reasons. 1) as paper, if for some reason you do have a case rupture, there will be no shrapnel of any kind. 2) since the nozzle is compressed clay, if there is an over-pressure, the nozzle should blow out before the casing ruptures. 3) paper is a very good insulator and could be re-used if you wanted but I wouldn't recommend it for anything important, mostly just testing modifications to propellant/process/etc. 4) they're really cheap compared to aluminum cases 5) fireworks industry (and Estes!) have been using paper cases for many decades and they have a very long safety record

    The second link I included was a direct link to a vendor that sells the paper casings in 30inch lengths. From the 10 tubes, you cut them down and can get 40 cases for the 1 purchase of $37, so less than $1 each casing

    http://www.skylighter.com/mall/produ...ils.asp?id=203

    That company is also a good place to get other things needed like your oxidizer of choice.

    The recommendation to join one of the national organizations and get your level 2 certification is that it will make many more resources available to you including peers and mentors so that you don't have to invent the wheel and you skip the dangerous steps that have been done hundreds of times before you.

    Good luck and be safe
    Last edited by heada; 12th April 2018 at 05:05 PM. Reason: poor grammar
    Aaron Head
    NAR 83209 L2

  16. #16
    Join Date
    23rd March 2011
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    Germantown, Ohio
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    Also find a mentor. There is a lot to learn from "hands on" and you get your questions answered in real time. Of course, unless you are TRA L2, this may be a mute point.....
    Last edited by pondman; 12th April 2018 at 04:30 PM. Reason: spelling
    Gary Dickinson - Prefect
    Tripoli Mid Ohio #31
    TRA #5520 - L3 - TAP

  17. #17
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    I agree that paper would be better, though I don't know it’s pressure rating, so I can't compare it to PVC on that basis. As for the pressure rating for the polyethylene tubing, it is considerably less than PVC, but it’s not brittle like PVC, so explosive ruptures are not as much of a threat. As others have pointed out, any failures I have seen resulted in the nozzle being ejected.
    Last edited by BDB; 12th April 2018 at 06:18 PM.
    NAR #100940, RIMRA & CMASS
    L1 - 4/17/16, Tyrannosaur (by Binder Design), Loki H144
    L2 - 8/19/17, Terrordactyl (by Binder Design), CTI J250

  18. #18
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    heada: I'll do more reading on his site, then. Thanks for the suggestion of that and this store! I thought at first when you mentioned the cert, you meant something on this site only, but I found the page discussing what it actually means. I do not have this certification yet, but I will consider it.
    pondman: I would love to find one, but I'm not sure how/where. Without the cert, and hundreds of miles from the nearest rocketry club, our options are limited.
    BDB: We are using clay plugs in our current builds for this purpose. It was our understanding that 3/4" of clay would fail before the 480 PSI PVC. However, general consensus seems to be that PVC is just a bad idea anyway. I just don't see how the Poly will have a chance in, well, this pyrotechnics simulated hell, of surviving the heat and pressure if PVC with much higher ratings tends to fail. Still, we'll give it a try, since you say it will. Perhaps we will need a poly/paper hybrid casing....

  19. #19
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    I’ve proabably built and fired 100 of these motors with no failures of the polyethylene tubing, so I can attest that it works. That said, I want to move to cardboard for safety and environmental reasons. I don’t really want to intentionally litter our launch site (public property) with plastic casings.

    NAR #100940, RIMRA & CMASS
    L1 - 4/17/16, Tyrannosaur (by Binder Design), Loki H144
    L2 - 8/19/17, Terrordactyl (by Binder Design), CTI J250

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