My MCRN torpedo scratchbuild

Discussion in 'Scratch Built' started by Bill S, Dec 6, 2019.

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  1. Dec 6, 2019 #1

    Bill S

    Bill S

    Bill S

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    I built a model rocket of the Martian Congressional Republic Navy's light torpedo from the Sci-Fi show "The Expanse".

    It is 24.5" long, and has a 24mm engine mount, and weighs 5.15oz empty (6.78oz with a D12-5). Estimated launch height is about 640 feet on a D12-5 engine, and I plan to try out some Aerotech D10/D21 engines in it.

    If the rocket flies well, my son has convinced me to build a second one for display purposes only.

    I also have a United Nations heavy torpedo on the drawing board (Rocksim) and hope to do a Belter torpedo also.

    I altered the original design and added 65lb cardstock exterior raised "panels" to the design to add more detail.

    One potential glitch is that due to the limited clearance between rear body tube (BT-80) and inner main body tube (BT-70), there was only room for a internal 1/8" launch lug. Redesigning the rear to allow a 3/16" lug would have required using a larger and much heavier-walled piece of body tube. I won't know how it works until spring, when I can fly the rocket.

    The hardest part of the build was the decals. I had planned to print them out on white backed decal paper, and then use some of the spraypaint from the can (decanted and applied with a brush), but it was pretty difficult to blend the metallic paint, and I am not at all happy with the results.

    Another problem was that even while using white backed decal paper, the metallic basecoat showed through the white portion of the decals, requiring me to handpaint white on the white areas of the "Navy" and "CR" decals.

    I will be building a UN torpedo, and plan to have vinyl stickers made for it and a second MCRN torpedo (if it flies well enough).

    [​IMG]

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    Internal 1/8" launch lug in the rear of the body tube:
    [​IMG]


    Rear view of the rocket, showing the internal launch lug. There is a standard launch lug on the front of the rocket as well. I also used a removeable Kevlar shock-cord and a 24" parachute.

    [​IMG]

    Original images (screenshots) from the show:
    [​IMG]

    [​IMG]
     
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  2. Dec 6, 2019 #2

    mbeels

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    Very nice, I like your added detail. Looking forward to launch reports!
     
  3. Dec 6, 2019 #3

    kuririn

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    Nice work!
    I received an email a few days ago from Fantastic Plastic. They have a resin kit of the Rocinante, if you're a fan of "The Expanse". A little too heavy for my wallet, though.
     
  4. Dec 6, 2019 #4

    DAllen

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    That is hands down the best sci-fi series since Firefly and possibly the best ever. Very nice build. Can't wait to see it fly!
     
  5. Dec 6, 2019 #5

    neil_w

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    Did you sim that? Those fins look pretty small to me. Just wondering.
     
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  6. Dec 6, 2019 #6

    SecondRow

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    One of our club members built the Razorback. I’ve only seen it fly once - I think it’s on 13mm motors. It looks very cool. I’ll see if can dig up a picture.

    The Expanse is the best sci-fi show ever made.
     
  7. Dec 6, 2019 #7

    Daddyisabar

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  8. Dec 6, 2019 #8

    Bruiser

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    Very cool!

    Hey Neil, did ya see those fins :)

    -Bob
     
  9. Dec 6, 2019 #9

    BABAR

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    First,
    really cool looking rocket!

    I love internal launch lugs, especially with scale or fantasy rockets where a standard launch lug just "don't look right." As long as there is a continuous tube that runs from the front to the back (I use paper soda straws) to make sure the rod goes from hither to yon through the rocket without catching on anything (like a chute or shroud line or shock cord) they are the bees knees.

    I'm with @neil_w on this one, the fin size fails my "MindSim", FWIW. Especially with the multiple transitions up front, which are cool but draggy. To use my favorite SciFi Quote: "I've got a bad feeling about this."

    This might be a good rocket to swing test fully loaded with planned launch engines, wadding, and chute.

    Any chance you can load it up like you're gonna launch it, balance it on your finger, and take a pic and show us where the CG is?

    If it wasn't such a neat looking bird, I'd probably use the @Daddyisabar approach, call a heads up launch, put on your construction helmet and push the button, but if it skywrites and lands badly, you may have an irreparable "formerly" cool rocket. A shame when you've put so much creativity and work into it.

    If it fails the swing test, any chance you could somehow add extensions to the clear fins to make them bigger, wider, longer, more Steve Austin-ish?
     
  10. Dec 6, 2019 #10

    Bill S

    Bill S

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    I used Rocksim to sim it... file enclosed
    I tried to swing test it earlier in the construction phase (with smaller clear fins), but wasn't able to get it to work. After doing a fair bit of research, I came to the realization that swing-testing wouldn't be all that useful due to the difficulty in a) getting it up to a semi-accurate speed, and b) getting an appropriate angle of attack while doing said swing testing. After the discussion in a thread here, I decided to trust the sim software and not worry about my inability to get the swing testing to work right.

    https://www.rocketryforum.com/threads/actual-weight-cg-vs-rocksim-cg-please-help.155421/

    I am probably going to build a second one for display purposes or to use as a backup in case the first one ever goes splat.
     

    Attached Files:

  11. Dec 6, 2019 #11

    Bill S

    Bill S

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  12. Dec 6, 2019 #12

    neil_w

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    Those numbers look OK. I'm guessing you must have significant weight up front (nose?) to get the CG there. Definitely check the CG in ready-to-fly configuration to make sure it matches.

    Will be interested to see how it flies.

    My biggest takeaway from this thread is that I should probably be watching the Expanse. :)
     
  13. Dec 6, 2019 #13

    Bill S

    Bill S

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    Neil, no, no noseweight. I just checked the CG with an D12-5 engine in it, and the sim says 15.4" from the nose, and I got about 15.6 or so. Close enough, given the 1.7 safety margin, I would think. Yes, no?

    Heck yes, you should watch the show. Bear in mind the first 3 episodes start off a little slowly to immerse you in the background, but episode 4 is where the real action starts... I have the first 3 seasons on disk, but Amazon picked up the series and season 4 is due in the next couple weeks (or less), though it may not be on disk - streaming only.
     
  14. Dec 6, 2019 #14

    SecondRow

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    DD2C0BEA-AA70-4FDB-8DB1-A8F5D09D86B6.jpeg Season 4 premieres on amazon streaming next Friday.

    I found the Razorback. I snapped a pic at a club meeting. It was still a work in progress at this point. He printed up some decals afterward.
     
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  15. Dec 6, 2019 #15

    Bill S

    Bill S

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    Not bad at all. :)
     
  16. Dec 7, 2019 #16

    kuririn

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    Please be sure to remove any bio-weapons from the payload area before launch.
    Failure to do so could be...…...
    Disastrous!:D
     
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  17. Dec 7, 2019 #17

    Bill S

    Bill S

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    Someone on the a Facebook group suggested a clear container with blue simulated protomolecule that ejects and comes down on a separate parachute. Great idea, not sure if I can pull it off or not. :)
     
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