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Liebeck and Benzing profiles
eric_segalerba
Member Posts: 1 EDU
Hi everybody,
I'm an engineering student and I'm working on my thesis using OnShape. I found a problem and I was wondering if someone could help me to sort it out.. I need to design a sport car wing and to do it I need high-lift airfoils (used upside down to generate downforce).. The profiles I was searching for are the Liebeck's and Benzing's profiles that I could find (at least the first ones) in the UIUC database but not in the list of the profile generator.. Does anybody knows if and how it's possible to add those profiles?
Thank you in advance for any answer!
0
Answers
1. Get profile from http://airfoiltools.com/airfoil/details?airfoil=l1003-il
2. Clean up the data with this Processing script:
a. Delete row 26 - it's not a correct data point. Use best judgement for other airfoil shapes.
b. In column D, set rows 1-25 to be "one"
c. In column D, set rows 26-50 to be "two" (these names separate out the two splines for the airfoil)
final file:
4. Upload the CSV file to an Onshape document
5. Use the "3D CSV" custom feature from:
https://cad.onshape.com/documents/a5566bc4a7c123d4958fd925/v/74ef42fd67330626670210c7/e/97994fc552ad661c4611715d
With the following setup:
6. Create a new sketch and use the edges:
7. Offset the sketch a distance of 0 to create a surface:
8. Transform the surface as needed and create a path curve:
9. Sweep!
Link to final document:
https://cad.onshape.com/documents/b30404da8802dd459d5a092f/w/106d68cf7993b88980d841cd/e/a21eaf992bdbb12e0ccf54e9
I'm no aerodynamics expert, so I may have made some sort of grave mistake. This work is presented with no warranty or liability whatsoever ! I attached the csv output file I used in the document. Also, there is almost certainly a much easier and simpler way to do this with a custom feature, but I don't know enough FeatureScript yet to do it.
If you're going to simulate this, check out SimScale. They're pretty well integrated with Onshape and I've done some CFD studies for a lightweight hand-thrown glider I'm designing (though that's on the back burner for now):
https://youtu.be/NzYPIAJ3qtQ
I hope this helped!
@alnis is my personal account. @alnis_ptc is my official PTC account.
There is almost certainly a better way to do this, but I'm having trouble figuring out what it might be.
@alnis is my personal account. @alnis_ptc is my official PTC account.
That script is very powerful, but it seems to suffer from similar issues. If you look at the curvature of many of the examples, there are all kinds of lumpy things going on in the airfoils. The density of points in the source data is very high, and that's fine if it's being used to turn into a paper template and then someone will bandsaw and hand sand the ribs. However, if this data is being used for very fine CNC work, the surfaces are not going to be as smooth as they should.
Here's an example where someone has analyzed this sort of problem and come up with a better parametric solution in Rhino/Grasshopper: https://blog.naver.com/plusplastic/221848442739
www.virtualmold.com
Here's a paper which shows that for certain types of NACA profiles, Beziers can perfectly reproduce the NACA math:
https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=3150&context=facpub
When you have a zillion tightly spaced points and try to run a spline through them, you're likely to get bad curves. It's a basic issue of trying to fit a spline to points. Here's a good summary of that kind of problem:
https://tamino.wordpress.com/2014/01/01/smooth-1/
In the case of airfoils, you generally want the top or bottom curve to be convex, or maybe smoothly change between convex and concave very gently, with a single inflection point. You don't expect it to turn into a high frequency sine wave.
www.virtualmold.com