Hi OSTexo, I think that weird shape is a bug that I can do something about, it seems to be triggered when the "chord line" connecting the two sides is fairly slanted compared to the edge tangent at that point. It tries to use the chord line as an indicator direction for which side to orient towards but it looks like that's not so good to use when it gets slanted basically.

I think I can do something about that part, but there is a larger problem remaining for this type of sharp trailing edge thing which is that the blend is trying to do 2 different things at the sharp discontinuity area, and it doesn't really help that the shapes are on the same plane there, they're trying to be smooth to 2 different shapes right there. I think that the blend mechanism would need a pretty substantially different strategy in order to handle those sharp areas.

So I'm going to see what I can do about the sudden internal shift thing, that's probably fixable. But it will probably work better for a planar sections blend to avoid the sharp discontinuity on the trailing end and instead have a small tightly bent corner (which in other kinds of cases tends to be bad, but in this situation it's probably needed though, since "Planar sections" behaves quite differently than things that come away perpendicular).

Some kind of corner patch construction like you have on the other side may be a better strategy for a sharp trailing edge... Maybe if the blend would sort of have an "extended rail" type of shape more like how filleting happens that might work for that kind of thing.

- Michael

The "extended rail" type thing would be something like this - the blend would be synchronized to each side like you've got here:



But instead of it actually stopping there, the blend would continue on with the shorter surface being implicitly extended so it would form an extended blend piece like this:



Then the extended pieces are intersected and the blend would be trimmed to form the trailing edge of the blend, like this:



I guess that seems more likely to work than trying to directly make a single surface cross section in the sharp corner...

That seems pretty tricky to attempt in an automated way, and I'll need to look at various other discontinuity cases to see how generally feasible it is... Could be something to try in v4. Probably until then a tight bend in the wing surface trailing edge rather than an actual discontinuity would probably work with Planar sections.

- Michael

Hello Michael,

I can see that extended rail Blend being very useful for a few different surfacing problems, especially if you're able to keep G1/G2 continuity between the surface and the blend itself. I'm really enjoying being able to stay in MoI more and more even for some of these surfacing operations, great job.

Here I've attached a test run of the extension technique, this one was done by actually making the wing out of an extended self-intersecting curve to start with in order to do the blends. The blend here was done in 2 separate pieces, with just regular blend not planar sections. Then it was a bit tricky to trim them, they did not intersect cleanly because of their shallow overlapping area so I had to generate an intersection curve, tweak a couple of points on it and then trim both surfaces to that common curve. Then I deleted the self-intersecting extended wing, trimmed the extensions off the self intersecting curves and then lofted those to get the final wing.

Final result is on the left, extended pieces working pieces on the right.

Seems to be a really good result, what do you think?



During some of the recent Blend overhauls I did experiment some with other ways to deal with discontinuities, without success... One attempt was to make an average of the 2 different cross section shapes at the corner and then gradually morph that back to the regular blend shapes as it travels some distance away from the corner. The problem with that is the loss of continuity in those areas.

- Michael

Hello,

The result does look very good, it looks like you've kept G2 on the wing/fuselage connection. I think I tried something similar before and trimming that trailing edge junction but I either got that weird surface flipping or problems with the trimming because the two surfaces were skimming each other. The blend issues were part of the reason I asked the question about continuity options in other tools. Having that capability puts MoI into an entirely different area of solution. I'm not complaining, but I think it would be great to have such tools within MoI, if nothing more than for MoIs legendary implementation of the features.