EAA No Longer Has Free SolidWorks

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bhooper360

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Regardless of the word choice,[ the part you posted would not be economical].
(...)3D printing [is] not there yet.

The way you use the optimization software is by first defining a volume, next defining the loads. Finally, the software provides an optimized surface.

Notice that "New bellcrank" photo on the right looks a bit like a spaceframe chassis:

csm_image1_03_bfc2801398.jpg


usually you have things like fuel tanks or humans, and you would prefer not to put steel tubes going through them, so you remove that area from the volume. The picture on the left "Original bellcrank" represents this volume.

Looking at the output "New bellcrank," you try to mimic this structure using chromoly tubes. You can vary the thickness or placement of the tubes depending on the thickness or color of the structure in "New bellcrank." That's how you get your spaceframe layout that I showed above. Then you still have to do the hand calculations. But the intent is that you should end up with an optimized truss, which means that you end up either using less tubing, thinner walls, or your structure deflects less under load, or some combination of these advantages.

In the EAA homebuilder's week welding seminar, the presenter included pictures of race car space frames (like the one in this post), paramotor cages, and airplane fuselages, and he said that the key advantage of 4130 is strength to weight ratio, which applies to all those situations. So, I'm not convinced by what you wrote in your first paragraph.

Once again, a summary of the process:

Code:
define a volume
input forces
use software to generate an optimized structure
place your structural members based on the optimized structure
analyze your truss as usual
 

stanislavz

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Some small improvements. Easier to draw, only one element have to be copied for each second join connection (166.137 and 101.22), all others are "grown from same one. Tried to understood Maxwell diagram principle And draw all members in one place - i was not able to do this. In original aprroach - we are calculating reactions from known loads and leverage, and only them we draw that diagram. So that article from sport aviation have something different ?

1653164144543.png
 

stanislavz

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And one more, this one is 16x1 longerons + 12x1 vertical members. optimized to hold even more load. But with one mistake :) Due to messy units - fuselage frame is 1 to 10 scale, load of 250 (mm) is equal to 500 kg of tail downforce, divided by two for each side. Red numbers are constraints, blue one are derived. :

1653167051604.png
 

Vigilant1

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Stanislav, the truss analysis looks cool (and useful). I do have problems understanding your examples.
There seems to be a large number of FreeCAD online tutorials. Have you seen one that explains how FreeCAD can be used to do this graphical truss analysis?
 

stanislavz

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Vigilant1

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Hello. All theory about graphic truss analysis is here in pdf. EAA No Longer Has Free SolidWorks

But as i can see it not this one Cremona diagram - Wikipedia
You've done a nice bit of work here, using FreeCAD to do these force diagrams. I'll bet a lot of folks in the FreeCAD community would be interested in learning about it. If you didn't want to do a video, one of the folks making FreeCAD tutorials would probably like to publicize it. Just a thought.

Mark
 
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stanislavz

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You've done a nice bit of work here, using FreeCAD to do these force diagrams. I'll bet a lot of folks in the FreeCAD community would be interested in learning about it. If you didn't want to do a video, one of the folks making FreeCAD tutorials would probably like to publicize it. Just a thought.
I will do it. Just need to make Bilski button in Python for automatic calculation of lenght for equal load for each tube.
It is similar to Chuck Norris button
 

stanislavz

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Ok.. not where yet, digged out some old french book. It looks like mine variand did have some mistake, redo all :

1653778502203.png

Even easier to draw :

1653778524306.png
 

bhooper360

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Bilski button for automatic calculation of lenght for equal load for each tube.

If the critical failure mode is buckling, then the susceptibility varies with the length of the tube, and not just the compression force, right?
 

pfarber

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stanislavz

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Notice how the 1980s edition os Sport Aviation has freaking stress analysis while the 2020s issues have crap about rich people restoring barn finds that you will never, ever own.
It is called progress on this side of the pond.
 

pfarber

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Have you looked at the July, 2022, Sport Aviation?


BJC
Yes, and other than mostly certificated AC, the building portion was so light it almost floated away. The only thing that stopped it was that complete garbage comic insert which is laughably bad.

I don't think you ever read the 80s versions of Kitplanes or SA as they have decayed from valuable learning tools to 'look what some rich white guy did!'

The 80s Kitpanes issues were goldmines. The current Kitplanes is used to line a canaries cage.
 

cblink.007

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I am still learning workflow on FreeCAD (version 0.20 was just released), but using these two tutorial books I have and the videos out there, I am becoming more and more of a fan of it by the day.

One of our fatigue/fracture guys uses it to do quick analyses in lieu of having a reliable CATIA connection...and the results are on par!
 
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