topic Re: Workflow question with Shell command & Airfoils in Fusion Design, Validate & Document Forum

Workflow question with Shell command & Airfoils

ReeceEngineering — Sat, 21 Jan 2023 02:24:40 GMT

I tested my desired workflow in the attached "workflow test 2 v3" and achieved the result I wanted; the ability to freely vary the wall thickness using the final shell command. The wings were splines that connected fully.

However when I try this workflow using the correct dimensions & import airfoils Fusion360 is no longer able to shell the part at 3mm; seen in the attached "Point Loft v3". The airfoils import with trailing edges that are not closed, so I clicked and dragged the top/bottom end points to a center between them.

Is this the correct assessment that the issue is in how the wing's splines are closed at the trailing edge? Is there a better way to close off the trailing edge of an imported airfoil?

Re: Workflow question with Shell command & Airfoils

davebYYPCU — Sat, 21 Jan 2023 02:35:16 GMT

Probably.

Better to extend the Spline with Tangent connection, then trim the extensions.

3mm thickness, what is the chord size?

Might help......

Re: Workflow question with Shell command & Airfoils

ReeceEngineering — Sat, 21 Jan 2023 02:47:40 GMT

I tried making a 3 point arc and using the tangent constraint, however it didnt work. Is there a better way?

The 3mm shell is because my test prints have shown this to be a good strength to weight ratio for flight, given my slicer settings.

I think the cord is 200mm. Its shown in the "Point Loft" part file. The plan is to run a carbon tube between the wingtips and have 4 contact locations inside the fueslage. The outer segments of the wings will be modeled solid with a sweep cut for servo wires.

Re: Workflow question with Shell command & Airfoils

davebYYPCU — Sat, 21 Jan 2023 04:02:29 GMT

I don’t have access to the files, (till mid Feb).

If both extensions are tangent connected, should work,

However, I get best results with a top and bottom spline with four point Splines.

Might help......

Re: Workflow question with Shell command & Airfoils

jeff_strater — Sat, 21 Jan 2023 17:12:48 GMT

"Is this the correct assessment that the issue is in how the wing's splines are closed at the trailing edge? Is there a better way to close off the trailing edge of an imported airfoil?"

Surprisingly, no. A good technique to use with Shell is "divide and conquer". Try splitting the body at different places to isolate where the problem is. The trailing edge seems to be OK - I can shell the back half, including that part of the wing OK at 3 mm:

It's the front part of this model that seems to be the problem. Not sure if it is the leading edge of the wing (I doubt it), or possibly the nose that is the problem:

Re: Workflow question with Shell command & Airfoils

jeff_strater — Sat, 21 Jan 2023 17:21:25 GMT

well, so much for my geometric intuition... The nose is fine:

further splits isolate the problem to the wing leading edge:

I'm surprised by this, as the curvature here does not seem extreme. I will have to send this by the geometry team to see if they have any clues...

Betreff: Workflow question with Shell command & Airfoils

wersy — Sat, 21 Jan 2023 18:22:37 GMT

Hi @ReeceEngineering

3mm wall thickness is way too thick, it will be a brickett 😉
For wings I use 0.5 mm with internal structure.
For fuselages 1.0 mm, in this case you need no or only little inner structure.

Trailing edges should always be as sharp as possible. For printing, 0.4 mm is OK.

By the way, since two years I print planes only with LW-PLA (light weight).

Re: Workflow question with Shell command & Airfoils

TrippyLighting — Sat, 21 Jan 2023 22:28:28 GMT

That shoddy fillet would keep me up at night!

Re: Workflow question with Shell command & Airfoils

ReeceEngineering — Sun, 22 Jan 2023 05:13:52 GMT

I managed to get it a bit better

Re: Workflow question with Shell command & Airfoils

ReeceEngineering — Sun, 22 Jan 2023 05:15:20 GMT

Thank you for your help! I hope the geometry team will have a solution.

Thats a great idea to cut it into sections to identify the area with the error.

Re: Workflow question with Shell command & Airfoils

wersy — Sun, 22 Jan 2023 12:21:35 GMT

Quite apart from the flyability and printability, developing a plane is not exactly a beginner's project.
Here, requirements are added that can only be reasonably solved with surface modelling. So the sooner you get to learn about surface modelling, the better.
Whenever I could, I always avoided surface modelling, but now I am very happy, because many things can only be done with it.
So far, I have been able to solve even the most difficult problem - especially thanks to @TrippyLighting infinite patience... 🙂

Just like in your case, when it was a matter of blending a wing to a fuselage.

Unfortunately, I can't find the video that shows this in a more simple way.
In principle, it is done in the same way as in this video with Solidworks. The video is particularly good because everything is explained in detail.

https://www.youtube.com/watch?v=Nc-5qKbAdCk

This video is interesting because the loft is made across the wing.

https://www.youtube.com/watch?v=-1EEXCGC2UA

Re: Workflow question with Shell command & Airfoils

TrippyLighting — Sun, 22 Jan 2023 12:52:28 GMT

Achieving smooth transition s between an Airfoil and Fuselage of an airplane can be very trickly business!

That is the case even when the curvature of the surfaces involved is spiffy clean!

When troubles arise it is often because the curvature of the surfaces has problems.

Particularly with airfoils, people resort to publicly available Airfoil generators which create a series of points. Then in Fusion 360 those points are connected using a fit point spline. However, the math and algorithms behind fit point splines and the algorithm which created these airfoil points are different.
That mismatch then leads to curves in Fusion 360 which are not smooth.

The curves in this case are actually better than others I've seen in the past, but still, there are problematic areas at the wing tip and at the trailing edge :

Betreff: Workflow question with Shell command & Airfoils

wersy — Mon, 23 Jan 2023 15:00:32 GMT

For practice, I once again made a transition from surfaces.
However, the result only allows a shell of 2.5 mm.

With an exported stp file, more is usually possible. With this I can reach 4 mm.

Anyway, I would print the fuselage in 1 mm wall thickness and the wings in thin wall with inner structure.
With such a small plane the wing loading should not be much more than 43 g/dm². In this case it corresponds to a total weight of 900 grams.