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Thread: Bigger Daddy CG

  1. #1
    Join Date
    30th June 2010
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    UK
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    Bigger Daddy CG

    I've just loaded up my Bigger Daddy with 4 x D12-7's and found the CG. It is 13.5cm from the base of the bodytube , is this stable ?

    [/newbie mode on] Could someone explain please , where the CG should be for a rocket to be stable [\newbie mode off]

    Karl


  2. #2
    Join Date
    2nd May 2002
    Posts
    1,217
    The general rule of thumb requires the knowledge of the CP (center of pressure) of the rocket.

    At least one caliber of stability is what's wanted, a caliber being the same length as the diameter of the rocket...

    So to put this all together, you want the CG one caliber above or toward the nose, of the CP.

    In a 3" rocket that has the CP 20" from the nosecone, if the CG was 17" from the nosecone it would then have one caliber of stability.. CG 14" from the nosecone and you have two calibers of stability...

    EMRR has several listings in the CP library for the big daddy, they all put the CP between 14 and 15" from the nosecone.. You want your CG to be about 11 or 12" from the tip of the nosecone..for one caliber of stability....

    Jason V.
    TRA 9672 L3
    www.firemanrocketry.com

  3. #3
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    Well I've just the digital callipers and found out that my CG is 19.152" from the tip of the nosecone . So this mean I need more noseweight?
    Karl

  4. #4
    Join Date
    21st January 2004
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    45

    Nose Weight

    Yes. I just finished my 4x24mm big daddy and I had to add 4 oz to the nose to get the CG right. Depending on how you've built yours, you may need to add a little more or a little less.

    Zonker

  5. #5
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    Hmmm! This thing weigh's so much allready Im not sure it's even gonna be worth modding it for 4 x 24mm's

  6. #6
    Join Date
    21st January 2004
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    45

    Heavy

    I ran into the same problem. The most powerful motors I can get in my area are Ds, so the only way to get more power was to cluster. As you mentioned, the downside is the weight....my big daddy is a pig. I have yet to launch mine, but I'm not expecting a lot of altitude (it simmed to 900ft, but I think that's being optimistic). Once I find a place to launch, I'll give it a shot and let you know what happens.

    Zonker

  7. #7
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    Maybe Ill have to come up with a Big Daddy 2 Stage design with some spare 3" tubing.....

  8. #8
    Join Date
    2nd May 2009
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    Talking it's kinda funny

    the Big Daddy is the only rocket i've built basically stock!
    hehehhe!

  9. #9
    Join Date
    18th January 2009
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    North of Detroit
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    Totally Tubular now has the 3" tube for the Big Daddy.

    He mistakenly marked it a BT-100 IT IS NOT A BT-100!

    It is an old NCR size tube and the same size as the Pro Series 4 engine cluster Patriot Missle.

    http://www.dars.org/jimz/est2066.htm

    THAT would be a neat clone to do since it uses the Big Daddy nose cone too!

    sandman
    "I'm a sandman. I've never killed anyone. I terminate runners when their time is up." Logan from "Logan's Run".

    www.sandmandecals.com

  10. #10
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    Sweet Sandman! Im sure my mate has that rocket , he does have a Estes 4 24mm Patriot......!
    Yep the tube im getting is gonna be a TT 3" tube that is listed on the Apo11o website here.
    It is actually called the Big Daddy tube , and the specs are :

    ID
    2.217

    OD
    2.175

    Wall
    0.021

    Legnth
    34.00

    Weight
    75.330

    EDIT:

    The Big Daddy is not the same as BT-80 , and if i where to make a 2stage BB , the biggest coupler I can get is to couple BT-80 :-/

  11. #11
    Join Date
    6th May 2004
    Posts
    107
    Originally posted by Karl
    Sweet Sandman! Im sure my mate has that rocket , he does have a Estes 4 24mm Patriot......!
    Yep the tube im getting is gonna be a TT 3" tube that is listed on the Apo11o website here.
    It is actually called the Big Daddy tube , and the specs are :

    ID
    2.217

    OD
    2.175

    Wall
    0.021

    Legnth
    34.00

    Weight
    75.330

    EDIT:

    The Big Daddy is not the same as BT-80 , and if i where to make a 2stage BB , the biggest coupler I can get is to couple BT-80 :-/
    You might want to check those dimensions you listed again...those are the specs for BT-70 tubing...not to mention you mixed up the ID with the OD

    As for a coupler, just cut off a couple inches of the tube you're using, slice it lengthwise, overlap it inside the tube you want it to fit inside of, mark the overlap, cut off the excess, then glue it in place as a coupler.
    Scorching blast of golden fire, as it slowly leaves the ground
    Tears away with a mighty force, the air is shattered by the awesome sound - Countdown, Rush

  12. #12
    Join Date
    18th January 2009
    Location
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    Totally Tubular has the tube as a T-100 tube and it's exactly the same as the Big Daddy tube...I have one here in my hands.

    I just think the specs. on the Apo11o web site are a misprint. It is 3.00" O.D.

    It's thicker too to match the Big Daddy nose cone.
    "I'm a sandman. I've never killed anyone. I terminate runners when their time is up." Logan from "Logan's Run".

    www.sandmandecals.com

  13. #13
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    Hmmm Im not sure that there is any way to add a booster to the Big Daddy , at the aft centering ring , theres no space to fit a coupler.Unless you cut the booster BT up , so the fins can sit in them?

  14. #14
    Join Date
    6th May 2004
    Posts
    107
    Originally posted by Karl
    Hmmm Im not sure that there is any way to add a booster to the Big Daddy , at the aft centering ring , theres no space to fit a coupler.Unless you cut the booster BT up , so the fins can sit in them?
    Try putting 3/16" launch lugs in the centering rings, then gluing 3/16" dowels in the booster to line up with and slip into the lugs. You could even use a small coupler section that would just stick out of the booster 1/4" or so, just to maintain alignment of the stages.

    Scorching blast of golden fire, as it slowly leaves the ground
    Tears away with a mighty force, the air is shattered by the awesome sound - Countdown, Rush

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