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  1. #1
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    Up Scale BT / Rocket Chart

    I'm not sure what many of you use to figure out your up scaling on rockets, but I've been doing mine in Auto-cad based on tube size. Say, if I want to turn a Baby Bertha into a BT 80 size model, I'd have to go through the whole trial and error CAD scaling process because I don't know the formula for skewing things to scale. There is a way and I'll figure that out some day. But tonight I sat here and meticulously scaled every standard low powered tube from BT 20 to BT 80. I did this because I often have to scale for myself and LW, and now and again some random request from someone on the forum.

    SO...for anyone that uses Auto-cad to draw their rockets, and want to know the formulas for upsizing your favert kit, see the attached PDF file. This is going to make up scaling a breeze from now on.

    Attached Files Attached Files
    Thinking outside the box is normal for me. Went inside the box once and got claustrophobic.
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  2. #2
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    Here's another tool for up and down scaling rockets...John Coker's Upscale Calculator.

    It's based on a suggestion that I made in my scale "slider" thread. Which in turn was inspired from my upscale/downscale chart:


    Last edited by K'Tesh; 21st November 2013 at 06:13 AM.
    Making the rockets I dreamed of as a kid (and then some).

    "The Guide says there is an art to flying", said Ford, "or rather a knack."
    "The knack lies in learning how to throw yourself at the ground and miss."


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    I survived the Heyford bone. USAF RAF UH 77th AMU 1988-90 46250

  3. #3
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    Excuse me if I'm incorrect here, but isn't this chart just for tubes? And what software are we using these numbers on? None of them match the numbers I posted. My numbers are for Auto-cad, (and I'm prolly very alone with that kind of design tool). As I mentioned in another thread, I usually scale the entire rocket based on tube size. This takes care of the nose cone, tube and fins all at once. Hence, I usually discover that if I want an exact replica of the same nose cone, it winds up on the lathe for turning. My Constellation was no exception. Along with a great many of my up scaled rockets.
    Thinking outside the box is normal for me. Went inside the box once and got claustrophobic.
    Can't never did!
    Inventions weren't created by skeptics.
    There's a bright side to every screwed up week.


  4. #4
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    OK Jim, This morning I realized why your chart wasn't working for me. I have to place the % decimal 2 digits to the left and punch that number in. The only one that didn't work was the BT 20 to BT 60. Where your chart reads 216.67% ( or in my case, 2.1667 ) comes up 3/64" shy. The numbers I found that seem to nail it are, 2.224, ( or in your chart would read, 222.4% ) 3/64" isn't a huge deal in the big picture of it all but none the less,it's a noticeable difference. I am curious why you omitted the BT 70. And would someone please tell me what the significance of the BT 56 is?
    Thinking outside the box is normal for me. Went inside the box once and got claustrophobic.
    Can't never did!
    Inventions weren't created by skeptics.
    There's a bright side to every screwed up week.


  5. #5
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    Quote Originally Posted by Gary Byrum View Post
    OK Jim, This morning I realized why your chart wasn't working for me. I have to place the % decimal 2 digits to the left and punch that number in. The only one that didn't work was the BT 20 to BT 60. Where your chart reads 216.67% ( or in my case, 2.1667 ) comes up 3/64" shy. The numbers I found that seem to nail it are, 2.224, ( or in your chart would read, 222.4% ) 3/64" isn't a huge deal in the big picture of it all but none the less,it's a noticeable difference. I am curious why you omitted the BT 70. And would someone please tell me what the significance of the BT 56 is?
    Honestly, up until a few weeks ago, I didn't know about the BT-70, that's why it was omitted. My LHS stocks the BT-80, which I have one tube, but unfortunately seems to have never bothered to buy Sunward's 29mm to BT-80 MM. They have a lot of 29mm to BT-70 mounts though.

    I think I read that the BT-56 was something that Estes got when they acquired Centuri, and it was originally used for scale models, but I'm not 100% certain of that.
    Last edited by K'Tesh; 21st November 2013 at 04:22 PM.
    Making the rockets I dreamed of as a kid (and then some).

    "The Guide says there is an art to flying", said Ford, "or rather a knack."
    "The knack lies in learning how to throw yourself at the ground and miss."


    http://www.rocketryforum.com/image.php?type=sigpic&userid=12734&dateline=136453  7186
    I survived the Heyford bone. USAF RAF UH 77th AMU 1988-90 46250

  6. #6
    Here's a spreadsheet that works for me:

    https://docs.google.com/spreadsheet/...xTWQwYXc#gid=0

    For reference it includes some common tube sizes (in metric and imperial units) on the first page, and a whole buttload of tube sizes on the second page taken from a file posted by Luke Strawwalker.

  7. #7
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    Quote Originally Posted by K'Tesh View Post
    Honestly, up until a few weeks ago, I didn't know about the BT-70, that's why it was omitted. My LHS stocks the BT-80, which I have one tube, but unfortunately seems to have never bothered to buy Sunward's 29mm to BT-80 MM. They have a lot of 29mm to BT-70 mounts though.

    I think I read that the BT-56 was something that Estes got when they acquired Centuri, and it was originally used for scale models, but I'm not 100% certain of that.
    Thank you for shedding some light there. I never knew why there was a 56. The 70 on the other hand has to be one of my favorite tubes along with the 55. BRShobbies.com carries all the standard sizes including the 56 as well as a great many cluster mounts for 13mm, 18mm & 24mm motors. Unfortunately I can't get 29mm stuff from there.
    Thinking outside the box is normal for me. Went inside the box once and got claustrophobic.
    Can't never did!
    Inventions weren't created by skeptics.
    There's a bright side to every screwed up week.


  8. #8
    Join Date
    18th January 2009
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    Here's a chart that gives the ratios (upscale or downscale percentage) when upscaling or downscaling a rocket from one body tube size to another... Print them out, line them up, and look across the line of whatever tube size you have to whatever column of tube size you want to go to, and read the ratio... then multiply all the dimensions of the rocket, nosecone, etc. by that ratio to get the upscaled or downscaled proportional dimension.

    BodyTubeRatios.pdf

    Works the same whether you're upscaling a BT-20 rocket to a BT-50 or BT-80, or downscaling a real Saturn V rocket to BT-50... the principles are exactly the same... divide the diameter of one by the diameter of the other to get a ratio, then multiply every other dimension by that ratio to make it proportional.

    Not exactly rocket science...

    Later! OL JR
    The X-87B Cruise Basselope- THE ultimate weapon in the arsenal of homeland defense and only $52 million per round!

  9. #9
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    I guess I'm old fashioned and just like to do the math for my upscales.
    http://www.rocketreviews.com/widgets/flights-1369-6522.gif

  10. #10
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    Quote Originally Posted by paul.nortness View Post
    I guess I'm old fashioned and just like to do the math for my upscales.
    yeah, me too... I don't usually bother with the chart, but hey, if it helps someone out, good...

    Later! OL JR
    The X-87B Cruise Basselope- THE ultimate weapon in the arsenal of homeland defense and only $52 million per round!

  11. #11
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    As much as I like doing the math, sometimes it's nice not to have to reinvent the wheel.
    Making the rockets I dreamed of as a kid (and then some).

    "The Guide says there is an art to flying", said Ford, "or rather a knack."
    "The knack lies in learning how to throw yourself at the ground and miss."


    http://www.rocketryforum.com/image.php?type=sigpic&userid=12734&dateline=136453  7186
    I survived the Heyford bone. USAF RAF UH 77th AMU 1988-90 46250

  12. #12

    Thumbs up up or down scaling easy with Open Rocket

    When I want to scale a rocket, I try to get an original kit first, then using Open Rocket, start measuring and entering in the various parts. Then when I get an original rocket size, I use the scale option in the edit drop down menu to scale to whatever body tube size I want.

    No math needed. Open Rocket nails the upscale pretty close and a little adjusting is usually needed but not much. And I will often make adjustments to the design anyway to help with survivability. Long skinny fins are fine in a light rocket flying on a small A, but upscaling to say a 38mm motor mount will add challenges to keep rocket construction sound through launch and recovery.

    Working through this very issue now with a scaled up 220 Swift. Long skinny fins on a 1/2 A are one thing, but those long fins on a 4 inch body tube with a 38mm motor mount version adds new issues. Fin flutter, landing damage, finding the right nose cone.

    Getting fins and rings cut soon and I will be getting LOC body tube and other bits later. Already have a cone.

    Built a BT-60 with an 18mm motor mount version also. Also adjusted the fin dimensions a bit keep with the look but survive launch and recovery. Still looks like a Swift but with much sturdier fins.

    See ya,
    Rod


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