I'm trying to get a handle on the proper approach to take when blending a wing to a fuselage. Using V3 beta, I thought a simple blend would do the trick ... and it nearly does. The only problem is that I'm left with a nasty pinch and overlapping geometry at the front and back of the wing. I've tried both G1 and G2. If I drop the Bulge down to .4 I can eliminate the pinch, but then I'm left with a hard line at the edges of the blend. Any idea how I can solve this?

I think Michael is planning to work on some additional options for Blend that would allow you to add definition shapes along the blend result and a method that tries to match the isocurves on a more parallel/perpendicular basis.

For now, try using Trim to cut the edge curves at points offset from the end, so that the Blend does not go all the way to the end. Then try fulling the gap with an N-sided patch.

Thanks Mike. That got me a little closer, but the n-sided patch isn't a great solution. I'm still seeing some pinching on the edge of the resulting shape. Also, the patch doesn't blend perfectly with the rest of the surface.

Your kindof forcing the blend to match/meet at an unnatural location which yeilds the "gotta twist up to do that" result.

If you change your method slightly, you can get a good blend.

So the hole you cut in the fuselage could be more of a natural result edge. I untrimmed the hole (old red) to recover the surface, then I extracted the lower edge of the wing (red) and ran offset on it to meet the old holes edge (blue). I used the new shape to trim the fuselage and then could get a good blend with the wing.

Hi Brandroid, currently the way Blend works is that it makes the cross-section shapes of the blend to be coming off perpendicular to the edges. In areas that are more tightly curved that can lead to this kind of bunching, basically the sections are running into each other like this:




Notice in Burr's example above that he's made a cut shape that does not have quite as tight of a bend in it, that then helps to avoid this kind of bunching.

In the future I also want to add in a different mode for blending that will make more of a straight-line connection between the edges rather than having things be perpendicular to the edges, that should also help for these kinds of things.

- Michael

BurrMan, just tried your approach and it worked perfectly! Thanks for the tip.

Michael, thanks for the explanation. I assumed this was down to just know what the software was expecting of me. Now that I know more about how it works, I'll be able to better avoid this in the future.

Curious!
I apply the Burr method with it file and obtain that!
Closure is on the oposite side!
What is this prodigy ?

Hi Pilou, which particular side happens to get picked as the seam location might be different depending on the pick order. I had previously wrote on another thread that there wasn't any difference depending on pick order, but I guess this can be an exception to that for some cases at least (probably for when the first curve's natural seam also coincides with the "twist minimized" seam location as well).

But why are you concerned about it? It doesn't really make any difference where the surface closure seam is at.

If you like you can move it by dragging the points that you see inside the viewport, but there isn't really any reason to do that.

If it helps to clarify what you are seeing, you can use the "MarkCurveStart" plugin (http://moi3d.com/forum/index.php?webtag=MOI&msg=5288.21) to place a point at the closure point for the edges you are blending between. You will likely see that one of them has its natural start position at that location where you get the blend surface closing seam.

- Michael

Sure no difference just surprising! :)
(and the funny i believe that i have tryed all orders and positions of clicks and never with the multiple blend i obtain the same than Burr! )

I remember at the beginning of Moi! You will have made this tricky thing! ;)
Position of the click makes different results!
"Oops, your graphic there is not quite right - you don't want to click near the middles, you want to click closer to one end than in the middle, but it needs to be on the same ends that you want to have matching.

Hi Pilou,

> "Oops, your graphic there is not quite right - you don't want to click near the middles,
> you want to click closer to one end than in the middle, but it needs to be on the same
> ends that you want to have matching.

Yup, but that was only for much earlier versions of MoI, I think before v1 was even released...

Since the problem of misaligned things like you show there was happening pretty frequently I switched the behavior later on so that the location of your pick spot did not make any difference for determining the matching direction.


> Position of the click makes different results!

Only in that old version though, not anymore! If you repeat the same thing you show there in the current version you'll see it does not make any difference where you pick anymore.

If the automatic direction finder gets things wrong, you can still flip the direction of the blend edges by clicking on one of the blend edges while you are in the final "Adjusting parameters" stage of the command.

- Michael

This is a great thread. I have gotten a lot of good information from everyone, thanks for posting it Brandroid. I'm also having difficulties in this area. I was trying to blend a fuselage and it won't connect right to the wing using a G2 blend @ 1.0. I have the same amount of trim points on the edges for both body and wing, however, when I use the blend it wants to place the created edges off the points of the original edge. The original points lined up on the horizontal plane. I can move the start point of the curve to link up, but only for the back side of the wing., so front side is still twisted up. Is there any way to remedy this?

Hi samuraijkm, can you please post the 3DM model file with the surfaces in it that you're trying to blend? Preferably with just those surfaces pertinent to your particular problem with other stuff removed.

That would make it a lot easier to examine your particular geometry and try to give some tips. It's difficult in general to give good information just looking at a screenshot alone.


> I have the same amount of trim points on the edges for both body and wing,

The specific number of control points in the curves used to trim things doesn't really have any specific effect on Blend - Blend is based on following the geometric shape of the edges, it adds in more sections to make the blend follow that geometric shape, it doesn't really follow anything about control point counts directly...

- Michael

Thanks for taking a look Michael... I uploaded a cropped version of the fuselage and the wing. I projected the curve that I was using to trim the shape onto the fuselage and marked it in Red. I left it untrimmed in case the curve needs modification before trimming. Let me know your thoughts...

Hi samuraijkm, the sharp crease in your fuselage body will prevent things from getting a good blend in there - usually to get a nice blend surface the things you're blending between should be smooth. In your case there is a sharp corner in part of the blend area here:




I'd recommend getting that fuselage smooth first - with it sharply creased like that basically the blend will be trying to adapt to 2 totally different surface normals at the crease spot, that means that the blend will be separated into 2 different blends that have different shapes in that spot rather than being able to be just one single smooth blend surface.

One quick way you can try to smooth out your fuselage is to select the crease edge and put a Fillet on it.


If you want to keep the fuselage with a sharp crease on it, then instead of using Blend you'd probably want to run the wing directly through the fuselage and then boolean them together and try to use a Fillet to round out the juncture rather than doing Blend. Blend only tries to build one single big smooth juncture piece, while edge filleting can do things with sharp juncture areas by putting in smaller corner patches in between different fillet segments. So usually for things with sharpness to them it would be filleting that you'd use and not Blend.

- Michael

Trim this way and you will solve all your problems..



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