Drawing Nose Cones

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tHoagland

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Since I'm laid up recovering from foot surgery, I'm using the time to start on my L3 documentation and planning. As part of my planning, I wanted to draw the rocket in CAD, particularly, in Rhino 5. Since I was looking for a fair level of accuracy in the drawing, I spent some time looking for tools to create an "exact" nose cone curve. I was surprised to find it wasn't straight forward. So I wrote a small python script to produce a list of of points that define a Haack series nose cone profile. This list of points can be copied into a rhino iron python script to create the curve. If anyone is interested in the script, it is copied below.

How have you accomplished this? Did I miss a simpler solution?


This was written under the influence of heavy pain meds, so use with caution....


Code:
#########################################################
#  Haack Series Nose Cone Designer
#########################################################
# This simple script will design and plot the a Haack
# series nose cone based on the Equations found at
#   https://en.wikipedia.org/wiki/Nose_cone_design
#
# The author was only interested in a Von Karman nose
# cone with C=0, and therefore it is the only value tested.
# 
# This code uses numpy for calculation and matplotlib for
# display.  If you set plot to False, matplotlib is
# ignored
#


import numpy


plot =True          # Set to False if you don't want to display the result
createTuples=True   # If true will create point tuples for import into Rhino


noseLength  = 33    # Total nosecone length in the units of your choosing
baseDia     = 6.25  # Diameter at the base of the nose cone in the same units as noseLength
xResolution = .1    # Determines how often the equation is evaluated 
c           = 0     # C=0 for LD-Haack (Von Kaarman)


x = numpy.arange(0, noseLength+xResolution, xResolution)  # X values evaluated
th = numpy.arccos(1-(2*x/noseLength))                     
sc = 0.5*baseDia/numpy.sqrt(numpy.pi)                     # sclaing coefficent 
y = sc *numpy.sqrt(th-(numpy.sin(2*th)/2)+(c*numpy.sin(th)**3))  # Half nose cone profile


if createTuples:
    z=numpy.zeros_like(x)
    tList = (numpy.array([numpy.flipud(y),z, x]).T).tolist()    #y,z,x will transpose y/X so that the nosecone points up
    


if plot:
    from matplotlib import pyplot as plt
    plt.plot(x,y, color='b')
    plt.plot(x,-1*y, color='b')
    plt.axes().set_aspect('equal', 'datalim')
    plt.show()

*********************************************************************************************************************
Rhino Script:

Code:
import rhinoscriptsyntax as rs
tList = [[3.125, 0.0, 0.0]... [3.1245578867946904, 0.0, 0.1]]      # Copy from resulting tList from top script here
rs.AddInterpCurve(tList)
 
I cheat and use SolidWorks.
Fortunately for me, it has an Equation-Driven line tool where I can input the function for Haak, parabolic, etc.... nosecones.
Check if Rhino has such a feature that could save you time.

BlackBrandt, if you still.have access to SldWrks, you should play around with it. Good for creating complex curved-fin routing profiles too.
 
I'd hoped that Rhino had an equation-line tool, and it might, but I couldn't find any documentation for it. Solidworks is great but at ~$4k, it wasn't in the budget. On the plus side, this forced me to start exploring the Rhino Python interface which may open up a lot of other projects.
 
Go to Dan at Python Rocketry and let him do the math and build for you... He does great work for a reasonable price. Otherwise you are wasting your time and $'s doing it yourself...
 
I already have the nose cone. I'm playing with designing a nosecone AV bay and want to make sure it fits. Also, there is some level of satisfaction from doing it yourself. Its a hobby, by definition a waste of time and money.
 

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