Kittiwake 23 JR Conversion

  • 08 Aug 2019 17:12
    Reply # 7818499 on 7817591
    Deleted user
    Anonymous wrote:

    Arne, miraculously I am actually beginning to find my way through some of the calculations. Two questions have come up:

    For anyone wishing to go beyond rules-of-thumb for unstayed mast design Sponberg's publication on the subject is pretty complete.

    The mast specifyed here is carbon fiber but the process and equations are the same for any free standing mast...just need to substitue the strengths of aluminum for the strengths of CF laminate.

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  • 08 Aug 2019 16:52
    Reply # 7818467 on 7816901
    Deleted user
    Anonymous wrote:

    The weights in Reply # 7816554 on 7815815 are shipping weights. These poles are cone-tapered such that the bottom half or so are straight wall (see ECXA25 pdf attached). So using the you can estimate the weight of the pole alone . I got an estimate of 70 lbs weight for the ECXA25 which is 5" x 5/32" x 33 ft, 6063-T6.

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    Last modified: 08 Aug 2019 23:44 | Deleted user
  • 08 Aug 2019 12:49
    Reply # 7818139 on 7804871

    Thanks, Arne – the online converter seemed to say that, about those units, but I wasn't sure if I was understanding it correctly. Too easy!

    David W, would you mind showing the formula for your calculation? As in, just what one does to use it? That would be great.

    Shemaya

  • 08 Aug 2019 10:18
    Reply # 7818029 on 7817733
    Anonymous member (Administrator)
    David Webb:


    I did a quick calculation on Arne's mast for Ingeborg and came up with comparative figures at 0.8 of 18,140 Nm and at 0.88, 19,954 Nm. The latter figure is very close to his calculated strength for his mast and is a much simpler calculation.

    I hope this is of some interest/use.

    All the best with the project, David


    David, where do the factors 0.8 and 0.88 come from?

    Arne

  • 08 Aug 2019 10:07
    Reply # 7818012 on 7817591
    Anonymous member (Administrator)
    Anonymous wrote:

    Thanks for all of that, David and Scott. So interesting, about the tapering process.

    Arne, miraculously I am actually beginning to find my way through some of the calculations. Two questions have come up:

    Is it correct that for all practical purposes, 1 MPa is equal to 1 N/mm^2 ?

    And then, in the calculation for max bending moment of a round tube, do D^4 and d^4 mean the value of D or d to the fourth power? Am I understanding that right? This is from the attached screenshot from your chapter on hybrid masts…

    Thanks so much!


    Shemaya, a 'yes' to both questions.

    1 MPa (megaPascal) = 1N/square millimeter since ..

    1 Pascal = 1 Newton/sqm  -  by definition.

    (.. and there is a million square-millimeters in one square meter...)

    When playing around with these formulas, it pays to have a decent scientific calculator. Mine is a Casio fx-82ES. This lets me go back and edit my algorithms, which saves a lot of time.

    Last modified: 08 Aug 2019 10:22 | Anonymous member (Administrator)
  • 08 Aug 2019 03:20
    Reply # 7817733 on 7804871

    When in College I had a lecturer in Structural Engineering who told us Architects "you don't need to know how to design something to a "gnats ass", all you need is a rule of thumb that will get you approximately the same result and is quick and easy to calculate as well as easy to remember". I have always remembered that advice and it has saved me from mistakes on a number of occasions.

    So when calculating the strength of tubes in bending I imagine the tube as an I beam with a top and bottom flange, each equal to a quarter of the circumference of the tube multiplied by the wall thickness. The flanges of the tube are separated from each other by the diameter of the tube, but because of the curve of the tube not all is at this distance. I use a correction factor of 0.8 which is a little more conservative than the actual .88 or thereabout. The simple bending moment formula is then used to calculate the strength.

    I did a quick calculation on Arne's mast for Ingeborg and came up with comparative figures at 0.8 of 18,140 Nm and at 0.88, 19,954 Nm. The latter figure is very close to his calculated strength for his mast and is a much simpler calculation.

    I hope this is of some interest/use.

    All the best with the project, David

  • 08 Aug 2019 01:10
    Reply # 7817591 on 7804871

    Thanks for all of that, David and Scott. So interesting, about the tapering process.

    Arne, miraculously I am actually beginning to find my way through some of the calculations. Two questions have come up:

    Is it correct that for all practical purposes, 1 MPa is equal to 1 N/mm^2 ?

    And then, in the calculation for max bending moment of a round tube, do D^4 and d^4 mean the value of D or d to the fourth power? Am I understanding that right? This is from the attached screenshot from your chapter on hybrid masts…

    Thanks so much!

    1 file
  • 07 Aug 2019 20:40
    Reply # 7817221 on 7817145
    Scott wrote:
    Shemaya wrote:

     But also, my flagpole mast on AUKLET was a lot thicker at the top, where it had been tapered. About 1/4 inch, when the butt was 1/8. So maybe in the interest of being lighter weight, the straight tube and wood topmast might be an advantage. 


    The tapering technique usually takes a uniform tube and squeezes it down by rolling it.  You don't save weight with a tapered aluminum pole, but do save windage.

    Not so, Scott. Some of the material moves inwards, thickening the wall, and some is extruded lengthways*. For example, a parallel tube 9.2m long, 17.7cm dia x 3.2mm wall: 43.4kg. My actual mast tube, after tapering: 36kg.

    * exact proportions dependant on the machinery used, I suppose.

    Last modified: 07 Aug 2019 20:42 | Anonymous member
  • 07 Aug 2019 20:10
    Reply # 7817145 on 7816624
    Deleted user
    Shemaya wrote:

     But also, my flagpole mast on AUKLET was a lot thicker at the top, where it had been tapered. About 1/4 inch, when the butt was 1/8. So maybe in the interest of being lighter weight, the straight tube and wood topmast might be an advantage. 


    The tapering technique usually takes a uniform tube and squeezes it down by rolling it.  You don't save weight with a tapered aluminum pole, but do save windage.
  • 07 Aug 2019 19:41
    Reply # 7816989 on 7804871

    Oh my goodness! I go off to the country for a few days without phone service or internet and return to all this wonderful discussion and input. It’s going to take me a sec to digest it all!

    Thank you all yet again! Huge amounts of gratitude to Shemaya for acting as proxy. I have no doubt that without her I’d be totally lost with all this

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