Aerodynamic fillet?

[Anonymous]

Hi all,

I'm completely new to Fusion (and CAD tools) and am trying to model a power pod for (scale) powered glider.  The pod itself will have a teardrop nacelle shape, circular in cross section, and will be mounted in top of an airfoil-shaped post.

I'm attaching a very simple design I put together using a cylinder (approximating the pod) and a sketched airfoil pod, with the standard fillet command.  It's a good concept but nowhere near what I really want!

I need some basic, basic pointers to get me going, but think I can get most of the way there except for an aerodynamic non-constant radius fillet I'd like to make where the post meets the pod.  This will look somewhat like the fillet on many aircraft where the wing meets the fuselage (see a picture of a P-51, attached, for what I'm talking about).

I'd like to do everything with splines, at least if that's the best way to go.

Here are some basic questions:

- I assume I should model the pod and the airfoil post seperately, then join them -- correct?  How do I join them (if I'm using splines) in such a way as to make a continuous spline surface?  (I may also want to join at slightly less than a 90 degree angle, and ideally it would be nice if I can play with that angle even after doing the join without doing a lot of redesign).

- I'm thinking about modeling the pod as a series of circles in their own planes, then doing a loft.  There is a whiskey bottle video on youtube that I'd use as an example.  Alternately, I could sketch a nice arc and rotate it 360.  What's best?

- Finally, how do I make a nice aerodynamic fillet that has a very small radius toward the leading edge, gets larger towards the trailing edge, and has a kind of parabolic outline in profile aft of the trailing edge?

Thank you for any pointers!

Rick

[michallach81]

Usually you don't have to adjust profiles, rather give more information for loft to succeed. I will make another screencast to show what I do mean by that. In my first vid I've showed basic example. We don't need to loft from one loop to another loop. Just wait for screencast.

[michallach81]

Ok, here it is, my screencast. Just note that I'm showing only strategy, how you should try to provide more data for loft to complete. As you will see surface is far from perfect, but except tools limitations main issue is that this object is abstract for me, and I don't know how is should look at the end. If you know what you're looking for, you will be also able to master your model.

[donsmac]

Really a wonderful solution, breaking it down like that. Much Thanks! 

[TrippyLighting]

Very educational and useful thread!

[Anonymous]

Yes, this thread is a great resource, thanks everybody for the great discussion!

As for me, I'm going to continue riding the horse I started, though if I had to do it again I'd start with those screencast techniques first as it looks much simpler than what I've tried to do with tsplines and I think would give great results for my particular project.

As an update, I found that by placing an enclosing box around my finished tspline object (this is in Rhino), then doing a "booleandiff" between the box and the tspline object, and finally cutting everything down the middle and extruding a couple of holes for placement/guidance pins, I think I'm just about in business with a mold.  The guidance pins are used once both halves of the object are molded, cured and trimmed, then they are kept in the molds, the molds are placed together, and the two halves joined.

Next step -- look into cost-effective printing, or machining, the molds.

[donsmac]

You can do the same thing inside of Fusion. I've never used Rhino but in Fusion you would use the 'Combine' tool to do the 'cut' operation. 

First convert the T-spline body to a 'Solid' body before the 'cut' operation.

I'd like to ask anyone, how would the solid box, with the cavity in it, be split if the parting line is not planar. 

I had never used the 'silhouette split' tool but thought that might work for this, but I have no idea really what it does or how to use it. All I can get it to do is cut flat through an objects midplane.

I thought the tool might determine the outer edge of the cavity or the object that was cut from the cavity and use that line to create the split through the "mold" in this case.

Is that possible.

So how is the silhouette split command supposed to work? What is it for?  

[Oceanconcepts]

The silhouette split tool is designed to find the parting line perpendicular to a plane or axis direction. If you are designing molded parts this is critical.  It has no trouble creating parting lines on complex surfaces, but in my experience if you are not dealing with a shelled body the “split face” option is much more likely to be successful. I then go to the patch environment and create a patch around the parting line where the faces are split, expand it slightly, and use that surface in the Model environment to split the body. I use silhouette split like the “find parting line” tool I have seen in other CAD programs. 

The “split solid body” rarely seems to be successful, it says it only can create coplanar parting lines. 

I’m often wanting to create a parting line that allows me to split just a portion of a body, this method allows for flexibility.