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How to make wing with curved bottom? - airfoil tool and/or loft

lucas_vargas968lucas_vargas968 Member Posts: 4 EDU
Hi, 

I'm working on a project and I'm trying to make a wing that has a curved bottom that progressively gets thinner as it goes along. I've tried using the onshape airfoil script but I can't get the same effect when I loft - instead I get straight lines. I've tried using guides when lofting but that is difficult because (from what I know) you can't really constrain the airfoils to a specific size - I've just been using guess and check (not very accurate, I know). Any ideas? Maybe i just need to make more airfoils or give up on the script and make manual splines? 

Here is a copy of the doc: https://cad.onshape.com/documents/43ce99ee73d24c27261fa73f/w/297506089651cec539fc672b/e/48ab397a2f6d7b8c6aa9f924?renderMode=0&uiState=663fa9bdf08a9a25bbfc02c5

Photos: you can see the problem area in the first photo. I essentially want the wing shape to meet the grey-outlined area.

Answers

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    GregBrownGregBrown Member, Onshape Employees Posts: 111
    edited May 11
    You can certainly control a loft in the way you'd like, though the curvature of the path near the centerline seems pretty extreme?
    One thing before you get too far into this, the profiles you are generating are going to need significant work if you look at the curvature you'll see why:

    You'll likely have issues thickening, offsetting, splitting etc with these. The Profile generator custom feature (3rd party generated, not sure if the author is still active on it) is quite old and needs a bit of TLC. At the very least it could benefit from a rewrite with approximate spline (https://cad.onshape.com/FsDoc/library.html#approximateSpline-Context-map) instead of the approach used that just puts an interpolated spline through a whole bunch of data which is potentially noisy. I've looked at the source dat files in the past... This in fact exactly what I did for my own forked copy of this custom feature. In addition you'll probably want to use two splines (upper and lower) for the profile, there's an option for that. This will help get a clean leading edge. 

    Another resource worth checking out is https://holbrookaerospace.com/?post_type=product

    I'll have another look later on - please update the thread if you make progress!
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    lucas_vargas968lucas_vargas968 Member Posts: 4 EDU
    Thanks so much, I really appreciate it. 
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