Unable to Keep Spline Curve Straight Between Sletches

[MaxHugen]

Apologies for being long-winded, struggled to explain this in simpler terms.

Designing a wingsail for an F50 catamaran in the SailGP. It consists of a wing and a flap, each in 4 segments. Created the wing and flap profiles in the initial XY plane, then created 4 construction planes with new sketches, and copied the objects to each sketch. These were appropriately resized, positioned, and angled at 4°.

Each individual flap segment can be "twisted".  That is, the flap profile in one sketch is at a different angle to the one above/below it.  Aerodynamically, this allows the complete wingsail to have a different Camber and Angle of Attack, from bottom to top.

The following image shows how one of the sketches is "tilted", and how the flap alone is rotated around an axis. I've also added a Screencast below, on how I'm doing this.

The Lofting for the lower 2 flap segments is simple, as the Trailing Edges on these are straight. However the top 2 segments have curved Trailing Edges, so spline curves were used to join the top and bottom profiles, and used as a Rail during Lofting.

The issue I'm faced with is that this spline curve should appear curved in the Front view which it correctly does, but straight in the Top view - which it doesn't:

What's more, it appears as though the the profile on sketch "Profile Plane2" has somehow been "split" by the Lofting:

And I got Loft warnings:

As a novice I've already learned quite a lot, but I'm getting out of my depth here, and can't find anything on the Internet/YouTube to help me resolve this.

Any advice would be really welcome!

[MaxHugen]

Screencast seemed to cause problems, wouldn't load with initial post:

<iframe width="640" height="650" src="https://screencast.autodesk.com/Embed/Timeline/e06d22f4-a3a8-477b-bd2c-7cbeb867e8f7" frameborder="0" allowfullscreen webkitallowfullscreen></iframe>

[davebYYPCU]

I am a few days away from a Desktop, so can’t see / Edit your file.

Seems like you want sails that are planar (flat plate sail - unusual)

if so make a sketch plane, 3 points, both trailing edge points, and a leading edge point.  Project > Project the TE points, and draw the curve.  

Rail not tangent means a separate loft for this panel with that curve as one of the rails.

Home Tuesday to assist further.

Might help....

[MaxHugen]

Thanks Dave

Had multiple problems with my previous iterations, every time I deleted one of the vertical "rail" lines, the points of the flap were moved, ruining the profile. These have all been removed. Also, I had all the profile sketches "pitched" at 4° but got rid of this as I think it was causing additional problems, by raking the entire wing instead. This is how the wingsail would be positioned in reality anyway.

The latest version (attached) has been cleaned up and simplified as much as possible.  I have set the flap angles as they could be in strong wind.  They start at the bottom at 30°, then 25°, 15°, 0°, and at the top the flap is set at negative angle of -10°.  This is done on the catamarans to reduce the heeling forces, by adding righting moment.  From the screencast in previous post you can see how I use a rotation axis.

I did create a sketch "Flap Curve" in the XZ plane for the curve of the top 2 flap segments, but was unable to use this as Rails - F360 reported errors.

Cheers, Max

[davebYYPCU]

I think you are over thinking, or not sure of the Loft Tool.

One Loft with 5 profiles, and Fusion will give best fit "Rails", without drawing them.

So I would be happy with this Flap but if not, let me know, and the trailing edge and leading edge curves would be required.

Might help....

[MaxHugen]

Hi Dave, thanks for having a look at it.

Due to the way the 4 Wing sections and 4 Flap sections are built, from the Front view every line is straight except for the Trailing Edge of the top 2 Flap sections.  This is reasonably accurately shown in the sketch "Elevation", best viewed in Edit mode.

The curved section of the trailing edges of the top 2 flap sections was drawn by a 3 point spline in the sketch "Flap Curve". I tried to use this as a rail but had problems.

When viewing from the Right (ie aft), only straight lines should be seen between each profile, to match the construction methods.

[davebYYPCU]

I have added a new Flap, (same file name!)

If you have to have flat panels, then you need a 3d sketch, and 2 more 2d sketches, creating panel Loft rails.

Create 3d sketch and Project > Include 3d Geometry, select the five LE points, and the lower 2 TE points.  Create the six (black) straight lines, snapping to those points.  Finish sketch.

Using Plane on 3 points, select the 2 TE points and one LE point for the plane of the respective panel and create a sketch on that plane. 

Project > Project the 2 TE points into the sketch. 

Create a 3 point arc - snap to the 2 TE points, unhide the elevation sketch and approximate the 3rd arc point.  You may know its radius dimension.

Repeat for the last panel.

Edit your Flap Lofts, and select the panel rails.  You need the front and back rails, because just the back rails on their own will distort the LE.

Might help.... 

[MaxHugen]

Thanks Dave, but the leach (Trailing Edge) still shows a curved edge from top to bottom.

I've had another idea, which I'll try - for each of the top two segments of the wing, I'll add another plane and sketch at the approximate point of widest curvature (from a straight line), and then loft these segments using 3 profiles in each.

Cheers, Max

[davebYYPCU]

Check again from the rear those flap trailing edges are 4 straight lines, curved in side view. Latest version I sent, making sure it overwrites the previous version.

[barry9UDQ6]

As Fusion is a predominantly a solid modeller and has limited surfacing abilities, I fear that you will never achieve a single cohesive surface without the breaks you can see in the zebra analysis above.

You are putting a huge amount of effort into this, and maybe you should consider using a surface modeller instead, which would allow you to manipulate the surface as a single entity directly, without trying to shoehorn it to your sketches. Which will always give you inconsistencies in the surface each time it passes through one of your sketches?

[MaxHugen]

Hi Barry, I'm really just an enthusiastic "hobbyist". Just started with F360 a couple of weeks ago, after becoming reasonably OK with 2D Inkscape.

So getting this right would be cool, but not critical if I can't get it exactly right. Might have to live with the straight lines where I want those curves.

I had planned to move on to the F50 catamaran hulls next. I think I can do it using sketches for each hull "frame", and then using rails to generate a Loft.

Just not sure if F360 is the right tool though. At least the "Personal" version is the right price for a retiree. I don't know what a surface modeller is, or how it works.

Cheers, Max

[davebYYPCU]

So did you find my straight TE file version?

If so, you do not need to scale any other intermediates.  Too much work, and Fusion does not like scaling splines as you see.

Hull - your intent is typical of new guys, so much work making (too many) bulkheads when you get a better job from the chines, gunnels and keel.  Make the outline panels then slice for the bulkheads, much easier.

When you get the layout sketches done, share the file....

@barry9UDQ6  Sorry, I didn’t understand your post.

[barry9UDQ6]

Chines, gunwales and keel lines work fine for developable surfaces, but not for compound curvature. Then you need some transverse information.

This is a good example:

https://www.youtube.com/watch?v=SbkEGe-AdqM 

And being used on a hull:

https://www.youtube.com/watch?v=FDdwXXSKQ9g 

PolyCad is free (as in no cost) free surfacing software that could really give you the type of geometry that you are looking for here. After modelling up the hull, export it as an iges and carry on in Fusion with the rest of your design.

https://www.polycad.co.uk/index.html 

[MaxHugen]

Hi Barry, PolyCad reminds me a bit of FREEship which I used decades ago, although I found it quite difficult. It looks pretty good from the videos, especially the fairing tools etc.

There are no hull coordinates available for the SailGP F50 catamaran I'm trying to model, so I'm using a lot of images from videos to create sections myself using Inkscape - still in progress. The hulls do have some rather complex curves which I think would be quite difficult to model in Fusion 360, so PolyCad seems a much better option.  Just hope the learning curve isn't too steep though?

This is what I have in Inkscape so far, with many layers hidden:

Can an image or svg from Inkscape be initially used in PolyCad to help derive the required curves?

Cheers, Max

[barry9UDQ6]

I guess we're going off topic in terms of Fusion, but let me answer your question.

You can export from Inkscape to DXF, and import that, I'm not sure if you can import from svg's, though.

And you can also import jpegs, and then scale them.

[MaxHugen]

Thanks, going to give it a go, and then import to Fusion... will post the file here when I get there, will take me some time though I'm sure. 🙂

[davebYYPCU]

Have you researched all the posts here about the SVG / DXF comparability with Fusion?

You will be better off, draughting in Fusion, that same data.  

Might help.....

[MaxHugen]

No I haven't, did find some apparent limitations with curves when I imported an SVG from Inkscape to Fusion. Unless it's just me.

I'm still at the "what-questions-should-I-be-asking" stage, as a greenhorn.  🙂

[davebYYPCU]

Maybe I am the wrong one to ask, but I see 100s of short lines imported to Fusions sketches from Inkscape, that bogs down the Fusion sketch engine, in fact the sketch engine import algorithm, strips all dimensions and constraints, creates gaps, locks them as green lines, and we get asked why does this not work.

Where as Fusion would have one spline curve, or arc do the job.

Simplistic, but I haven't seen / use Inskscape.

When in Rome, speak Italian.

[MaxHugen]

Said I'd post the file if/when I managed to get a hull done - did one after a lot of trial and error that I'm reasonably happy with.

I tried PolyCAD, but although it seems to have heaps of lofting options (in my limited opinion), I didn't like the fact that I couldn't import a fully editable version into F360 from PolyCAD.  Anyway, managed to loft it in F360 despite some challenges, such as some sections that F360 was initially unable to loft.  Worked out a way to make it happy eventually.

The only thing I couldn't achieve was the sharp bow line, ended up using a really thin section to loft to instead. It will do.

My next challenge is to turn this into a solid object - but as a "shell", so I think I have to check out thickness?  This is so that I can cut holes in the hull, where the crew reside.

Does anyone know of a video example etc, on how to do this?