I am having a mental block about a balloon I am trying to model. It is one of these barrage balloons used during WW2, mostly in the UK. At least this is the British standard model.

The body is fairly easy, but I cannot find a way to model the fins properly, with their three overlapping sections and soft lines. loft, sweep etc create kinks in the sharp turn near the tip. I tried to do a boolean union of three shapes, but the base (where it meets the body of the balloon) should be one single smooth area.

Any suggestions ? Thank sin advance.

Jean-Paul

Hi Jean-Paul, maybe something along these lines - starting with some curves arranged liek this:



The outside ring gets extruded to make a solid, then use Boolean difference to cut that solid by the other 2 inner pieces, so you've got 3 solids like so:



Put a big fillet on the outside edge:



A little bit less fillet radius on the inside parts:



Maybe use the G2 Blend fillet shape rather than a circular fillet cross-section, and another possibility might be to slice off the front face with a slightly rounded surface to make it look less totally flat in front, see for example this previous post for an example of that kind of thing:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4296.5

It's also possible that you may want to make some kind of tubular sweep for the outermost one instead of a filleted block but maybe the inside pieces would be good to do with fillets on extruded pieces.

- Michael

JPBWEB,

You could also try making the profile of the fin contours and guiding that along a rounded triangular rail using Revolve by Rail.

It will allow you to tweak the proportions and placement via it's built in history, and the overlapping in the middle that would occur with a regular sweep is taken care of by the Revolve command.




The smooth transition between the fin and the body could be performed by a series of blends, so that the parts maintain a good tangentcy.

Nice revolve!!!