Nose Weights & Building In CG Flexibility

Discussion in 'Techniques' started by Curtis Enlow, Apr 20, 2019.

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  1. Apr 20, 2019 #1

    Curtis Enlow

    Curtis Enlow

    Curtis Enlow

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    Hey all,

    I am wondering how you approach building in the option to add/remove nose weight for rockets where your CG may vary due to using a wide variety of motors and/or motor tube adapters or standard vs. dual deployment/e-bay recovery modes?

    I have done the ubiquitous nosecone mod but have not epoxied it into place yet. I have not finished the rocket, so I do not have a final weight to start plugging in numbers. An additional complicating factor is that - providing the weight works out to 1500g. or under - I would like to be able to fly it at the local field on smaller 29mm reloads, but would like to build an HP option with an electronics bay coupler and extended BT to obtain my L1 and use HP 38mm loads.

    It may well be that with the coupler and larger motors I might not even need the option for nose weight adjustment, but I would like to have the option if needed.

    Might it be good to install a small stud, or two, in the nosecone bulkhead in anticipation of as a method of installing pre-drilled, measured lead weights to accomplish the optimum CG depending on the configuration? Or could that additional weight at such a relatively long arm/moment bite me on smaller, 29mm 'small field' motors?

    How do you deal with the need for CG adjustment flexibility?

    [​IMG]
     
  2. Apr 20, 2019 #2

    boatgeek

    boatgeek

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    I only have a couple of rockets that want some ballast on some flights. On those, I add 3-4 large quick links (5/16" or 3/8") to the U-bolt on the nose. They are easy to remove later and won't fall down into the body tube. If I need a little more weight, some heavy washers on the quick links do the trick. There are probably more elegant solutions, but this worked really well.

    In your spot, I might put some large-ish (#12 or 1/4") T-nuts in the bulkhead to the right and left of the U-bolt. You can then thread a bolt or machine screw into the T nut to hold a stack of washers in place. How much weight do you think you'll need to add?
     
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  3. Apr 20, 2019 #3

    cavecentral

    cavecentral

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    I don't adjust weight in my rockets, but a length of all thread or a long bolt in the nose tip or between 2 bulk plates is what I would do. Stack fender washers on the all thread as needed. some people cast lead weights for a similar purpose.

    Most I just add shot and epoxy to the tip - be careful with plastic nose cones because it will not bond well to the plastic / mold release.
     
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  4. Apr 20, 2019 #4

    Curtis Enlow

    Curtis Enlow

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    Thanks, guys.

    That's a great idea.

    In a couple weeks I should have the answer of how much (if any) I will need. I was just looking at the nose cone assembly and wondering if i should just go ahead and epoxy it in, and that got me to thinking about the mistake of putting my aft bulkhead in without installing the aft rail button (ooops, luckily I caught it in time) and nose weight mods I have seen, and thought I might put it off for a while. Of course, I hope I won't need any weight at all; I am going to do everything I can to keep electronics bay weight to a minimum, but nutplates are a light option.

    Thanks for the idea!

    Kevin, I don't think I will need that much, at least not in a permanent installation, but you might check out John Coker's video on installing cross-rods in a nosecone to hold epoxy embedded shot in place - it's brilliant!
     
  5. Apr 20, 2019 #5

    cavecentral

    cavecentral

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    I've done the cross rods, used screws, and also filled the remainder with 2 part expanding foam. All are options depending on the scenario.

    Lots of good ideas out there.
     
  6. May 12, 2019 #6

    David Schwantz

    David Schwantz

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    This is a LOC 5" V-2. It is their RNWS, removable nose weight system. It works great. It is 2 bulkheads that overlap, the one that gets glued into the NC, lower in pic, has a tube that goes to the tip. In this tube there is another set of tubes that telescope down into the first one, they hold your different weights. These tubes have a bulkhead glued in place that has your eyebolt mounted to it. Then the upper bulkhead is screwed down over this assembly. Attach shock cord to eyebolt. Makes it very easy to change weights for different motors. Make a different weight tube for each motor that you are going to fly with, and in about 5 minutes it is ready to go.
     

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  7. May 12, 2019 #7

    Bill Hanson

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    Depending on how much weight you need, you can just attach a quick-link to your u-bolt with some 1/2" ID flat washers. Turns out that 2 of them = 25 grams (Everbuilt zinc-plated from Home Depot), so it's easy to get the weight you want. It works up to 150-200 grams, and you don't have to make any further mods.

    That's what I did for my L1. Just wrapped some duct tape around the link+washers to keep everything steady.
     
  8. Jul 28, 2019 #8

    gary7

    gary7

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    David, what adhesive did you use to secure your bulkhead to that Loc nosecone?
     
  9. Jul 28, 2019 #9

    David Schwantz

    David Schwantz

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    I like to use Hysol 9462. Comes in tube, need gun to use it. But is very good, will not drip or run, I think they used it to repair the shuttle in orbit :)
     
  10. Jul 28, 2019 #10

    David Schwantz

    David Schwantz

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    Hi Bill, that sounds like a great idea, but that would be a lot of washer to make 4 lbs :)
     
  11. Jul 28, 2019 #11

    mpitfield

    mpitfield

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    I prefer to get the weight as far forward as possible, so I create lead plugs that hang from threaded rod that holds the tip on.

    To create the plugs I mix up more lead shot and epoxy than I need, and pour it into double seran wrap. Then while keeping the washer that holds the nosecone tip on, I drop it in, let it settle and cure. 24 hours later I knock it out, drill a hole down the center and grind the faces flat, to the desired weight. Then I use an oversized washer on the back face and secure it with the appropriate sized threaded rod or eye bolt.
     
  12. Jul 29, 2019 #12

    Mike Haberer

    Mike Haberer

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    I do a nose cone mod with two bulkheads, the inner is epoxied to the inner shoulder of the nose cone, the outer that fits into a hole in the inner, holds a forged eye bolt in the center for recovery connection and is screwed into the inner bulkhead into epoxied weld nuts. Washers can be added to the eyebolt to adjust weight as needed. I also can put an eggfinder in the nose cone on the eyebolt if needed, so the configuration is quite flexible...
     

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