New 102mm project - Chimichunga-I

Discussion in 'High Power Rocketry (HPR)' started by snrkl, Mar 20, 2018.

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  1. Mar 27, 2018 #31

    Steve Shannon

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    That’s correct. Don’t put the drogue right in the middle; you don’t want the parts smacking together.
    Long shock cords are used so the parts slow down slightly from drag rather than bouncing back towards each other.
    Having the drogue in the bottom makes it more likely the rocket will be unstable during descent and reduces the chance of shearing shear pins that prevent the main from deploying at apogee.
     
  2. Apr 9, 2018 #32

    snrkl

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    Design updated to using quantum tube airframe and phenolic coupler per the advice from my Local Rocketry Vendor (LRV)...

    He’s working up the price on parts and slotted airframes.

    I’ve also adjusted the design to use a 48” PML durachute. I’m wondering how to sim spill holes in OpenRocket.


    Sent from my iPhone using Rocketry Forum
     
  3. Apr 9, 2018 #33

    Nytrunner

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    I've looked up spill holes and calculation, but haven't found a satisfactory conversion for OR. You may want to reach out to the chute provider and inquire.

    Also mind the Quantum tube lol, it has a speed limit.
     
  4. Apr 9, 2018 #34

    LithosphereRocketry

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    Why? I personally would just stick with LOC tube. Then again, I live in a climate where it snows half the year, and plastic doesn't tend to like that too much...

    It should be plenty strong, and you can slot & cut it with a hobby knife. It's lighter, too, so you can use smaller motors and a smaller parachute.

    I don't know what the best way to sim spill holes is- I don't think they change descent rates that much, so I just don't bother.
     
  5. Apr 9, 2018 #35

    snrkl

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    The quantum and phenolic combo was based on recommendations from my LRV taking our rather humid climate into account and the longevity they’ve seen with this combo (if you aren’t using FG that is..)

    Not worried about speed limits - the goal with this one is for an ascent and two stage descent that I can watch with the naked eye, so no airspeed records sought with this build.

    Also, LRV is laser cutting fin slots for me, so nothing to worry about there.


    Sent from my iPhone using Rocketry Forum
     
  6. Apr 10, 2018 #36

    Handeman

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    If you stay under 0.8 mach and just want to see everything, Quantum tubing will work great.

    I've got a rocket that's 15 years old built from Quantum tubing and the only issue I ever had was the tube broke in half in 26 deg F weather. Avoid below freezing launches and it should last a long, long time.

    Sounds like your LRV is giving you some good advice.
     
  7. Apr 10, 2018 #37

    snrkl

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    LOL - I’ll heed the advice if we enter another ice age... I live in the tropics... [emoji12]
     
  8. Apr 10, 2018 #38

    grouch

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    If you are using wood for the fins, don't go nuts with the fillets. If the fin breaks, it will break past the fillet making repair a nightmare. A 4" body with I power won't be scooting along all that fast to be concern with huge fillets. Keep it simple and light.

    BTW, kudos on the 38mm mount. Even though I love me some 29mm, 38mm is way more appropriate for the rocket you are planning. 4" and dual deploy will get piggy quick.
     
  9. Apr 11, 2018 #39

    Andrew_ASC

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    The chute manufacturer should have a drag coefficient if it's worth it's silk. Call up tech support for the chute manufacturer and ask for it. They'll find you an engineer and tell you directly or they'll say proprietary.
     
  10. Apr 19, 2018 #40

    snrkl

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    Still waiting for my LRV to get back to me on pricing and parts availability.

    They have a big launch at our VERY HIGH launch site this weekend, so I assume he’s flat out with that.

    Hopefully I get pricing and lead times soon, and I can start ordering bits to build...
     
  11. May 16, 2018 #41

    snrkl

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    Design update: the LRV can't laser slot tubes longer than 600mm, so the fin can is now in two parts with an extra coupler...

    OpenRocket068.jpg

    parts are ordered.. If I am REALLY lucky, there might be bits for me to collect from the launch on Sunday, which means I can finally start building this sucker...
     
  12. May 21, 2018 #42

    snrkl

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    Partial delivery of parts - I got the electronics, tailcone, nosecone and recovery elements.

    No tubes, CRs or Fins yet...
     
  13. Jun 30, 2018 #43

    snrkl

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    So I picked up the rest of the parts late last week.

    Now that the house move is finished, I have a double garage of stuff that needs to be sorted and unpacked and a space cleared out so I can get to the rocket lab nook for building....

    I intentionally buried the rocket lab so I’m forced to clean and unpack if I want to build...
     
  14. Jun 30, 2018 #44

    snrkl

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    I’ll be laying out the parts and checking off the list tomorrow hopefully... I’ll take some pics when I do...
     
    Last edited: Jul 3, 2018
  15. Jul 3, 2018 #45

    snrkl

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    So this is going to be a little bigger than anything else I’ve built yet...

    IMG_9242.jpg
     
  16. Jul 3, 2018 #46

    Nytrunner

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    Coming along well. What's the weight of the dry fit?

    That looks like.....~74"/185cm?
     
  17. Jul 3, 2018 #47

    snrkl

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    You’d be just about right on the money height wise.

    Haven’t weighed anything yet, rocket scales are:
    1) yet to be unpacked, and
    2) probably too small as they max out at 500g...

    Also, this dry fit totally omitted MMT as the tailcone CR is about 2.5mm too small (web specs were loose) and the ebay internals are still in a bag...
     
  18. Aug 6, 2018 #48

    snrkl

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    Last parts arrived from AusRocketry today.

    9” drogue, replacement tailcone CR and replacement NC CRs.

    Turns out the replacement NC CRs are 3ply not 6ply, so I’ll likely shuffle them to where the layers aren’t needed as much as the load bearing ones in the NC.

    I’ve taken the end cap off the nosecone to prep it for the internal Tracker bay.

    I’ve also done first pass CWF on the 3mm 7ply fins. More to come yet...

    Tomorrow is parts washing and weighing day, followed by light sanding.

    I’m thinking about MMT / Shock cord adhesion:

    I have 1” Kevlar strap that I’m pondering epoxying on the side of the MMT tube and passing under the CR...

    I also have welded eye bolts that I can use...

    I haven’t decided yet. Any advice from someone wiser than me?
     
  19. Aug 8, 2018 #49

    OverTheTop

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    As many have said, go bigger or go home :).

    I have always regretted putting too small motor mounts in rockets.

    You could always put a 54mm mount in and adapt down (38/29) and remember you don't have to use the 6GXL casing ;).
     
  20. Aug 8, 2018 #50

    snrkl

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    It’s 38mm..

    Bigger motors will be a new build in a new bird.


    I am interested it people’s thoughts on shock cord attachment however... [emoji12]
     
  21. Aug 10, 2018 #51

    snrkl

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    After reading about glued Kevlar being a rocketry mortal sin, I’ve opted for the welded eye bolt.

    Eyebolt wasn’t long enough any more as I decided to double the front CR for strength.

    IMG_9577.jpg

    This meant a trip to find forged or welded eye bolts in m6 that were longer than 12mm

    Got the last three at the local hardware store.

    Problem fixed. Dremel cutoff wheel to trim the bolt down from 80mm to the 40ish I wanted:

    IMG_9583.jpg

    Figure I can always trim back if it’s in the way.

    Shaped and installed the internal CR in the nose ring:
    IMG_9591.jpg

    And the tail cone:
    IMG_9589.jpg

    Knocked the gloss of the QT, and roughed up the fin fillet areas.
    IMG_9588.jpg
    IMG_9586.jpg
     
    Last edited: Aug 10, 2018
  22. Aug 10, 2018 #52

    jqavins

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    I see I'm too late to answer your months old call for thoughts on the tail cone. But I can't resist anyway.

    I've got a 3/4 build 4" 54 mm build* that I'll finish when I've got a house and a better place to work. It'll be my L2 rocket, eventually. Anyway, I added an Aeropack retainer to the kit design, and also a PML 4"-to-75mm tailcone. The 54 mm retainer just fits up inside the cone with enough space to reach in and screw/unscrew it. A 38 mm retainer would fit generously. With the retainer up inside the tailcone it looks great, if I do say so myself.

    * No, I'm not saying you should've gone with 54, that's just what my kit came with, and I'm adapting down to 38 anyway. But you were definitely right to go with the 38 instead of 29.
     
  23. Aug 10, 2018 #53

    snrkl

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    Tailcone is a 54 and the retainer would fit inside it, I would just NEVER be able to thread the retainer ring on or off (I considered it...)

    Plus, this way the HAMR retainer also has the small CR to jbweld to and not just the cardboard MMT tube.
     
  24. Aug 11, 2018 #54

    snrkl

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    Ok - a little progress last night and today:


    Tee nuts on the NC shoulder CR fitted and tested with the gnurled captive nuts I found on eBay (makes field access much easier - no tools needed and the washers won’t fall off!

    IMG_9596.jpg
    IMG_9597.jpg
    IMG_9598.jpg

    Shock cord for NC attachment is done. I figured out a good trick with my L1 NC ebay that I’ve made a standard in my HPR NC ebays now: heat shrink tube to prevent a) epoxy getting into the shock cord and b) to prevent running on the things it passes though from severing it.
    IMG_9600.jpg

    And with the bulkhead fitted:

    IMG_9601.jpg

    Shoulder NC all epoxied with a good internal fillet and curing now, face down.

    IMG_9602.jpg
     
  25. Aug 11, 2018 #55

    snrkl

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    Forward CRs now epoxied and filleted.

    The CRs were a little loose on the MMT tube, so I had to build up a tape ring to hold them straight while they glued on top, then removed the tape to fillet the underside.

    IMG_9606.jpg

    I’ve also done the measuring twice and double checking thrice (before the second CR that buts against the front of the fins was glued) to make sure the MMT tube fits perfectly into the tail cone and HAMR retainer...

    I will have to remember to round the front of the root edge of each of the fins, to leave room to fit around the fillet on the fin front CR when I glue the fins - I forgot with my L1 and it made for a mad dash to clean, quickly file and re-insert the first fin before the epoxy set up...
     
  26. Aug 11, 2018 #56

    snrkl

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    I’ve been thinking about rail button attachment.

    FWD button, my plan is to drill and tap into the (now) 8mm fwd CR using the tap, CA, then tap again process someone suggested on my “how much thread is enough” thread.

    The aft button, I’m thinking of drill/tapping into the 8mm where the tail cone shoulder and Quantum tube overlap right at the base of the rocket.

    Buttons will be 10/10...

    I got a “Workzone” brand metric drill/tap/die set at Aldi a while back, but haven’t had a need to use it yet.
     
  27. Aug 11, 2018 #57

    jqavins

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    Putting on a lovely little round to closely fit the fillet sounds to me like more trouble than it's worth. I'd just clip the corners at 45° or so and call it good.
     
  28. Aug 11, 2018 #58

    Steve Shannon

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    I round mine. I tape them together and do them all at once on a sander or with a file, whichever is closest. Not much needs to come off and they don’t have to fit perfectly.
     
  29. Aug 11, 2018 #59

    snrkl

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    This is what I meant... not a lot of effort (unless you’re doing it while racing 5min epoxy...)
     
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  30. Aug 14, 2018 #60

    snrkl

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    Further progress today. But first, a learning point:

    The design has three sets of CRs on the MMT (four if you include the one that centres the tailcone).

    The forward CR is doubled to increase strength for the eye bolt for shock cord attachment.

    There’s a CR that sandwiches the TTW fins fwd, and one aft.

    As you saw from earlier pictures, the fwd and fin fwd CRs were glued to the MMT tube.

    Plan is for the one aft of fins to be put in after internal fillets are done, then the tailcone can be glued last.

    Tailcone is being used to keep the MMT level while gluing into the airframe fin can.

    So the plan was to do as I’ve done many times before: glue ring above fin slots for the fin fwd CR, half insert the MMT from the front, tip the MMT, apply the glue in a ring for the fwd CR, straighten, insert all the way, then fillet where I can from the outside and clean up any drips or over runs.

    Well, it turns out that I’ve managed to PERFECTLY align the two sets of fwd CR’s such that I can’t get to the spot for the fwd CR glue, without dragging the fwd fin CR through it.

    So a learning lesson there...

    Solution? Best I could come up with was to push it in 8mm too far (so the fin CR is inside the fin slot area) ring the fwd CR glue with a stick, then inject some 15min epoxy onto the front of the fin fwd CR, and then push the MMT forward and then roll the can to try to dribble as much of the injected epoxy into some kind of fillet.

    IMG_9641.jpg IMG_9642.jpg

    So there’s the fin can upright now and curing...

    IMG_9645.jpg


    Incidentally, I did remember to loctite and tighten the fin can shock cord before I glued it all in.
    IMG_9639.jpg
    IMG_9640.jpg
     
    Last edited: Aug 14, 2018

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