A few HPR questions...

Discussion in 'High Power Rocketry (HPR)' started by K'Tesh, Nov 19, 2019.

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  1. Dec 13, 2019 #31

    emckee

    emckee

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    I had always presumed the advice about use of metals in rockets was more about limiting shrapnel in case of a severe motor cato. As such, Aluminum and other ductile metals may be OK, as they will deform rather than break apart, but something harder and more brittle (like high carbon steel) would tend to break into pieces (like a grenade) which would pose a higher risk of injury (they fly farther and faster than a big chunk of deformed aluminum).
     
  2. Dec 14, 2019 #32

    Andrew_ASC

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    Well I’ve put about ten flights on it. Was my first HPR rocket but you do bring up valid points. Epoxy used was rockeypoxy. Haven’t had that bond fail. I have had too short of a shock cord snap and that was how I found out how much the nose actually penetrates the ground. And to be honest if I had to do it again I would use a tungsten based putty for pinewood cars to eliminate the shot pellet hazard.
     
  3. Dec 14, 2019 #33

    Andrew_ASC

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    Oof. Scary story but thanks for the sharing of it.
     
  4. Dec 14, 2019 #34

    Ez2cDave

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    Terry,

    Was the rocket called "Shotgun Wedding" ?

    LOL !

    Dave F.
     
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  5. Dec 14, 2019 #35

    Zman1961

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    I also use 3 brass rod pieces (not the two suggested) perpendicularly placed through the nose cone which mechanically holds the mass of BBs and epoxy once it all hardens. John Coker has a great video on this, and many others, here is the link - http://jcrocket.com/plastic-nose-mods.shtml. I have never had any failures of this system.
     
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  6. Dec 15, 2019 #36

    Richard Dierking

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    Using something like sand is best for nose weight if you can't adjust the CG with some other means to keep the rocket stable. You shouldn't use something that is commonly used by people (the bad kind) that is intended to do the most harm when a device comes apart, like bolts or shot. If a rocket hits the ground with considerable velocity and comes apart, you want some thing like sand or even water to be ejected, not pieces of metal. Nose weight is non-structural and doesn't need to be metal.
    Also, by providing a fitting on a bulkhead to the volume for the nose weight, you can remove the sand and use the nose for another rocket. I used sand for one rocket and then replaced the sand with kitty litter for another rocket that required less mass.
    Btw, when I flew my Delta II, I used several pounds of M and M's for the nose weight. Great to share after the flight.
     
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  7. Dec 15, 2019 #37

    Andrew_ASC

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    Ummm I chose lead for its density. There wasn’t much room in that particular rocket design for say sand. You would’ve filled up the entire cone, it still wouldn’t be stable, and also the shock cord and chute take up all the rest of the nosecone not filled with lead. Maybe I shoulda used a washers or casted a solid lead slug lol. Hell I had some RSO dare say I needed to lengthen the rocket and Crazy Jim called them choice words then showed me how to pack everything into stumpy rockets. I was struggling to put 15 ft of cord and chute into nose. Jim got 25 ft into it barely. No room for JLCR or tracker. Plus on another bigger L2/3 Saab Rb05a build the guy used lead shot. And lots of it. Whatever. I think epoxied shot works as long as it’s not lose.
     
  8. Dec 15, 2019 #38

    Steve Shannon

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    This!
     
  9. Dec 15, 2019 #39

    K'Tesh

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    My L1 rocket used a can of Diet Coke as a nose weight. It was the source of my first attempt failing (it came loose upon landing (hard) and busted the nosecone). Some duct tape was used to repair the nosecone, a better restraint for the can was fashioned, and the next attempt was successful. I must say that it was fortunate that I used a drink as the launch had a vendor on site with food, but the vendor for some reason didn't bring drinks (water, or soda). At the end of the day, I had a nasty headache from dehydration (I also had a rather nasty sunburn). After the headache had already started, someone was kind enough to share a few bottles of water that they had, but it was too little, too late. A can of water would have been a much better payload for the dehydration, but it was what it was.
     
    Last edited: Dec 15, 2019
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  10. Dec 15, 2019 #40

    mikec

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    If you have the available volume, sure. Sand is roughly 8 times less dense than lead, though, and for some applications (e.g., small MD rockets with big motors) it just won't work.
     
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  11. Dec 15, 2019 #41

    jlabrasca

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    Somewhere I have a pair of lazy dog bombs purchased mail order from Jerryco (before they became American Science and Surplus -- I am old). As an aside, I distinctly remember the copy in the catalog NOT describing them as antipersonnel weapons. I think there was something about "damaging factory machinery" in the description. I was only recently corrected on that.

    I think about those bombs every time I put something hard and dense into the nosecone of rocket.

    I've used tungsten Pinewood Derby weights in more than one rocket. Also tungsten fishing weights. The thinking has been that tungsten is denser and less of an environmental hazard than lead. But it worries me.

    I got some of the tungsten putty Andrew mentions, and used it in one rocket. It didn't want to stick to the inside of a Big Daddy nosecone, and I ended up making a cardboard bulk-head -- secured with epoxy. Which pretty much defeated any safety benefits from using the sort-of-malleable putty in place of a rigid piece of tungsten.

    I found this stuff in the golf department at a sporting goods store.

    20191216-untitled-shoot-00232.jpg
    20191216-untitled-shoot-00262.jpg

    It is a very fine powder. I am trying to figure out a way to incorporate it into an energy dissipating design -- something that would still pack small but that wouldn't necessarily turn a lawn-dart into a flechette bomb.
     
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  12. Dec 15, 2019 #42

    numbo

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    A nose cone with a plug at the tip would be great. Fill it with water for the trip up and let it drain away on decent for an easier landing.
     
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