3D Printing Big Bertha Nosecone is NOT an Ellipsoid (not a default one anyway)

[BigMacDaddy]

Does anyone have more precise equations/ellipsoid settings to define the Bertha nose cone?

I am 3D printing some Super Bertha sized nose cones for the Breast Cancer Awareness rocket. I went to some of the ellipsoid nosecones I have made in the past (for example, for the Neptune) and it was more pointy than the Bertha cone. I also looked at a bunch of the Bertha nosecone designs online and all of them are too pointy.

Basically it looks like the Bertha nosecone is not a default ellipsoid. I was able to adjust the base portion of the cone to better match the cones I have here by setting a negative tangent slope (basically it gets a little wider before it gets more narrow). However, the tip is still a bit too narrow.

Anyone have any insights?

 

[RCBrust]

I've been modeling the Fatboy nosecone so that I can 3D print different size versions of it. I believe that the FB nosecone is similar to the Bertha.

I photographed an original Fatboy nosecone in profile using a long lens to minimize perspective effects. I tried to match up various mathematical shapes to it and the best thing that I found was a classic french curve. It is definitely not elliptical.



In CAD, a spline curve also matches up very nicely.



Hope this helps.

Randy

 

[jmasterj]

Isn't the Fat Boy nose cone the same one as the SBB? The plastic one that's also available separately and fits BT-80.

 

[BEC]

The Fat Boy nose cone is the same one used for Super Big Bertha (and Mega Mosquito) and perhaps others I don't recall, yes.

 

[BigMacDaddy]

I've been modeling the Fatboy nosecone so that I can 3D print different size versions of it. I believe that the FB nosecone is similar to the Bertha.

I photographed an original Fatboy nosecone in profile using a long lens to minimize perspective effects. I tried to match up various mathematical shapes to it and the best thing that I found was a classic french curve. It is definitely not elliptical.

View attachment 531823

In CAD, a spline curve also matches up very nicely.

View attachment 531822

Hope this helps.

Randy

Thank you for this -- I followed your lead: took a flat picture, converted to an SVG, imported into Fusion360, and traced a spline curve along the edge of it, and finally revolved into a 3D object. Definitely can see the difference and has a Big Bertha look to it now!

Thanks again!

 

[RCBrust]

You're welcome!

For others playing around with this, a little more info on my approach. As you can see in the pics, the top of the nosecone is circular. The spline curve only has two vertices, one at each end. At the bottom, the curve is constrained to be vertical (perpendicular to the base) and at the top, it's constrained to be tangential to the circle. Then the "pull" of each vertex is adjusted until the curve lines up with the underlying picture.

Also, for those wondering what the purple stripe is on the nosecone in the picture, I had trouble getting the camera focused so I added a piece of tape to give some contrast.

Randy