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simple loft the wing profiles
fractal_paradigm
Member Posts: 2 ✭
Hi,
learning Onshape for a month or so, Im trying to loft between two identical wing shapes, spline with over 100 points. I did split to upper and lower part as suggested. Those wing profiles are identical and on the same axis, only offseted on X.
The loft is rough and doesnt match the spline. I started to make offset front planes with guiding lines, but after 20 of them I just gave up.
Isnt there some better, simple approach to match the loft with spline profile?
Thanks in advice.
Gabriel
PS: The wing is not NACA certified and my spline is already a slight derivation of the 700 points the original contain. And the "original" is likely not 100% original… I dont want more derivation on that design.
Answers
Are you lofting the airfoil as a 1 piece solid? Try doing the top and bottom as separate surfaces. Then fill the ends and Enclose to create a solid if needed.
Or maybe Sweep instead of loft?
I'm still pretty new to this (~3 months, on and off), and I still often struggle with lofts.
100 points in a spline is a recipe for disaster. More points is not better. Even if those points came from a perfectly smooth degree 3 Bézier, if they have the least bit of rounding error (which they will due to the way floating point numbers work), when you create a curve through those points you will get something lumpy. When you try to loft between two such curves, you’ll get a ridiculously complex surface with small perturbations in curvature.
If you can share a public document, we can help more.
Simon Gatrall | Product Development, Engineering, Design, Onshape | Ex- IDEO, PCH, Unagi, Carbon | LinkedIn
This Custom feature is purpose-built for such use cases.
https://cad.onshape.com/documents/33795c7f9b39612da14ee99a/w/18b7ca07fb26d7eb2815ea1d/e/7d0549e4402995ffee27b9c5
Heh, I used that FeatureScript on my current project and already forgot about it. In my defense, it has been nearly 2 weeks! :-)
@GregBrown is there a way to enter coordinates for an airfoil that isn't in the library? I couldn't figure that out. I ended up using the AG04 which is very close to the Zone V2 I'm using on the glider.
Yes in fact there is! Have a look in the UI, there is a pull down option for the
Profile source, namelyCustomvsLibrary:If you choose Custom then you can provide your own set of data points, as specified here:
https://holbrookaerospace.com/sample-havf-airfoil-arrays/
TLDR: the numbers are space separated and represent the x and y locations for the locations around the profile starting at the trailing edge and working their way anti-clockwise around. The profile consists of two degree-6 Bezier curves (one for upper, one for lower). The 0.000 0.000 point at the leading edge is not repeated in the list. The data (in meters) are all normalized for a chord length of 1.000 meters and the scaling will be taken care of in the feature.
Footnote:
Here is a quick example using HAVF profiles and a couple of boundary surfaces (with and without V-direction guides) for very smooth initial wing skins. Boundary surfaces are superior for this since they maintain the high order (degree-6 in this case) of the curves. The example link has washout and dihedral for demo purposes… not saying this will fly, it was just a quick thing to get you going.
Thank you Greg! I'll give it a try in my next project.