Prusa Mk 4

And now for a continuation of how I got FreeCAD to create ribs to match a complex airfoil...

With the extruded rectangles 'un-hid' the STL mesh to check that the extent of the STL is fully covered by the extrudes.

 

Now the 'glad someone else figured this out' begins.  The idea is to use the STL mesh to slice apart that set of extrusions. Each extrusion will have an inner part which will become the rib and an outer part that gets tossed. In the image below I have started the tossing process....

 

The composition of each slice is made up of one of the extrusions and the solid created from the STL mesh.

 

The inner 'slice' objects can now be extruded to what ever thickness is appropriate. A dialog box allows you to edit the thickness and to make it symmetric or not. Say you wanted to print LW-PLA ribs from this you probably want 3-4mm and then print it with only bottom and sides or otherwise punch holes or ovals (there were posts about that ages ago).

 

After applying the extrude you have a collection of separate extruded bodies.  Here is a side view and a view along the length of the wing.  

I think this a rather useful option for aero folk.  One might print out such ribs or convert into CNC instructions for laser cutting etc.  Or the start of custom bulkheads in a fuselage. A nominally printed plane form could be re-imagined with traditional materials and coverings. Or a hybrid of print and foam coverings....

   
 

Here is a single rib - this one was cut where two of the tabs for joining happen to be. Sorting that without the 'slice-apart' would be tedious beyond belief and also not so accurate.

 

WHAT ELSE MIGHT ONE DO?

As earlier wings I have created used multiple printed spars I attempted to create thin blocks to slice away sections of the ribs to form spars. As each rib was different this was
a) tedious
b) it did't loft correctly because of the randomly dense set of edge points would not resolve.

 

I tried to trace around these ribs to create the kind of 'sketches' that had a uniform density of points. This was even more tedious. 

There must be another way.  That uses the CAD to do the heavy lifting.  A teaser...  it results in a end section wing that is 2g less than the Gyroid normal print, takes 15 minutes less time to print and feels as stiff as the 'official' approach.  

Super chuffed.  Gathering photos and weights to present that in my next post....

 



 

A sort of printed version of my all foam multi shear web wing.
 
Note it is both tapered and swept.
Nothing clever just some fag packet sketches and make sure everything is cut in exact pairs so at least both wings are the same....
 

I captured the bulk of the text and images for using FreeCAD to create a set of ribs that match a complex wing form and turned it into a YouTube video.  I know some of you don't like videos as a medium and for those that don't mind, here is a summary and a link.  

  Summary:
Creating CAD designed ribs for simple wing forms is much less a challenge than for complex wing shape with multiple airfoils. Say you had an STL file describing a wing you wanted to study (the video uses a wingtip STL file from a PlanePrint model as an example).  Capturing multiple sections along the wing would be a great way to understand the wing.In this video the slice-apart function and curves workbench of FreeCAD V1 are used with a STL wing file and a set of user defined slicing bodies. The general workflow is based on a YouTube video from MangoJelly (). The workflow is not intuitive so watching the referenced might help. The result of the work flow are a set of rib bodies which exactly fit the complexity of the wing form. Each can be further edited for CF spars and wiring in case you want to use a tradition spar-rib-covering approach.



Perhaps there are others you know who might like to derived useful stuff from STL files.....Ah - and how many times have you imported a STL file into CAD and it was way off from the origin.  Worked out a way to shift it!  That will be in an upcoming post....

Not a seagull....  It is the end of a PlanePrint Rise Nano which is way more complex and transitioning than my usual Clarke-Y.

In the end what I wanted to try out was to substitute multiple spars vase printed rather than the 6% gyroid infil. Below are the test prints. On left is the gyroid and right is vase print.

 

The other side - left is the vase print at a bit over 7g.  On the right is the official gyroid infil at a bit over 9g.  Both seem the same stiffness.The gyroid infil has easily sanded off hints of the infil. The vase print expresses the spars on one side.  If one was clever the design could ensure that the smooth side was the upper face.  The gyroid infil is, of course also stuffed with stringing.

 

Note - I setup the slicing initially for vase print and then switch to 1 perimeter so that the internal tabs would print properly. Because of the minimal clutter inside it printed almost as fast as a pure-vase print (with the advantage that the tip of the wing is better filled in).