Help me understand Pro75 weights.

Discussion in 'Propulsion' started by Bat-mite, Feb 17, 2016.

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  1. Feb 17, 2016 #1

    Bat-mite

    Bat-mite

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    Using this spec sheet: http://pro38.com/products/pro75/motor/MotorData.php?prodid=5198M1101-P

    Loaded weight - propellant weight = hardware weight.

    No?

    Burnout weight = hardware weight + burnt propellant weight.

    No?

    So, 4938 - 2993 = 1945. 1945 should be my hardware weight. But that is higher than the burnout weight, which should also include the burnt propellant.

    Help!
     
  2. Feb 17, 2016 #2

    mikec

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    Don't forget the mass of the part of the reload that's not hardware and not propellant, like the nozzle, liner, etc.

    Loaded weight should be the burnout weight plus the propellant weight. I'm not sure why it's off by a few oz in this case.
     
  3. Feb 17, 2016 #3

    COrocket

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    The specific motor you linked to must have an error of some kind, because burnout shouldn't be lower than loaded minus propellant.

    Edit: I looked at a few other motors and all of them seem to have burnouts that are lower than loaded minus propellant. I must be missing something about what's included in those weights
     
    Last edited: Feb 17, 2016
  4. Feb 17, 2016 #4

    bobkrech

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    The loaded motor weight = the case weight + the propellant weight + the casting tube weight + the liner weight + the smoke column + casting tube + insulator + O-rings + nozzle weight.

    The propellant weight is not the reload weight as it does not include the casting tubes, liners, smoke column, o-rings and nozzle. The propellant and some of the casting tubes, liners, O-rings and nozzle + the entire smoke column are consumed. The difference is 103 grams.

    Bob
     
  5. Feb 17, 2016 #5

    Bat-mite

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    Thanks.
     
  6. Feb 17, 2016 #6

    webtech

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    I am going to do some work with the scale here soon.
    open rocket has a launch mass and a empty mass.

    so i am assuming openrocket will factor after burn it has the case weight there.

    my problem is I am going to be using a CTI 6G case with two spacers and not a 4G case, so there is some extra wight that I need to factor in.
     
  7. Feb 17, 2016 #7

    Titan II

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    You may want to look on the CTI website.
     
  8. Feb 17, 2016 #8

    webtech

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    Yeah I have been there.. the weights check out from what I can tell for my motor.. but open rocket has it in a 4G case.. and I am adding a 6G case plus two spacers.. more weight.. so I need to add the difference between the two cases..

    I am guessing it's not much, but it's something.
     
  9. Feb 17, 2016 #9

    Titan II

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    The weight difference of the case plus spacer(s) is on the website using either a single, or two spacers. At least for 29-54mm. I did not check larger sizes.
     
    Last edited: Feb 17, 2016
  10. Feb 17, 2016 #10

    Bat-mite

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    Where? I'm right there with Webtech. I have a Pro75 4G motor, but a 5G casing with a spacer. I can weigh my own HW, but I need a weight for the 4G HW to subtract from it to get the difference. Then I can add a mass object to the front of the motor in OR to see the effect on the CG and stability thru Mach.
     
  11. Feb 17, 2016 #11

    Titan II

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    As I mentioned, I did not check above 54mm. If this helps, a 75mm CTI 4G case (old style with thrust ring) weighs 38.30 oz.
     
  12. Feb 17, 2016 #12

    Bat-mite

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    Thanks. That's helpful. But where are you finding the weights for smaller motors? I looked all over CTI's site. I know I'll feel dumb when you point it out to me. :facepalm:
     
  13. Feb 17, 2016 #13

    webtech

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    in op -> go to motors and configuration .. -> double click on your motor in the "motor tube side" or the same way you select the motor, or select motor button..

    tab on the top right, click ' show details ' .. it has the weights right there.
    m1830 op.PNG

    So CTI site says for the propellant wight of a M1830 it's 2542g ~ 5.6lb ...
    Op says launch weight is 9.97lb - empty mass 4.1lb = 5.87 lb two numbers are very very close.. which extra empty mass could be burn liner and what nots.

    so i have to add a weight object to the front of the case in open rocket.
     
  14. Feb 17, 2016 #14

    Titan II

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    I was only referring to the weight difference with spacers. Look under spacer instructions, under hardware. Here is the one for 54:

    http://www.pro38.com/pdfs/Pro54_Case_Spacer.pdf
     
  15. Feb 17, 2016 #15

    Bat-mite

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    Bummer. One, I would not have thought to look in an "instructions" document to get product dimensions. I don't know why it isn't on their "dimensions" sheets. Two, the spacer instructions for Pro75 do not include mass. :(
     
  16. Feb 17, 2016 #16

    Jeroen_at_CTI

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    410 grams for the spacer + 1G length of motor case tubing.

    Jeroen
     
  17. Feb 18, 2016 #17

    webtech

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    Thank you :)

    Jeroen is there much weight different between gen 1 and gen 2 hardware ?
     

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