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 From:  kevjon
2292.1 
Hi Michael

I'm just wondering if there is a way to create a surface that when trimmed would match a curve exactly or very closely.

I suspect there is not a way of doing it but thought I would ask the question. If there is a way or technique for achieving it then it would make my nurbs modelling so much easier when trying to model to blueprints without attempting a panel by panel approach.

I'm trying to create a wing fillet for an aircraft.

The question I have is there a way to include the red curves in my model so that I can model the wing fillet in one smooth continuous surface and when it is trimmed it would match the profile of the yellow curve ?

If I could solve this problem, would be fantastic as I find myself coming across this problem all the time when modelling with nurbs.
~Kevin~
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 From:  Michael Gibson
2292.2 In reply to 2292.1 
Hi Kevin,

> I'm just wondering if there is a way to create a surface
> that when trimmed would match a curve exactly or very
> closely.

If you do something like a Loft, then the lofted surface will pass through all the cross-sections that you picked, so if you then trim with one of those it would make for an "exact match".

But you seem to be asking about making the resulting surface match a curve which is totally separate from the cross-sections given to the surfacing command? With the curve running in a different direction than the cross-sections? No, there isn't anything to produce that.

You generally just kind of have to attempt to "reverse engineer" how the original larger uncut stock material was formed as best you can...

If you could find more original design documents that included more details for each individual part, that could possibly help, rather than trying to work on only a "finished model" blueprint that has many of the construction steps omitted from it...

- Michael
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 From:  kevjon
2292.3 In reply to 2292.2 
Ok, thanks Michael

>But you seem to be asking about making the resulting surface match a curve which is
>totally separate from the cross-sections given to the surfacing command?

Kind of, the yellow curve is my guide line so that when I trim the surface it matches the profile of the yellow curve in plan and side view.

The problem I have is figuring out what shape the red curves need to be so that when the surface is trimmed it will be close match to the profile of the yellow curve.


I never considered loft to create the fillet as both network and 2 rail sweep work for the fillet.
~Kevin~
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 From:  Michael Gibson
2292.4 In reply to 2292.3 
Hi Kevin,

> I never considered loft to create the fillet as both network
> and 2 rail sweep work for the fillet.

I wasn't really thinking of Loft for that particular case, just that when you Loft through some curves the surface that is created will pass through those curves... That's the kind of "make the surface go through here" control that you would need for that kind of exact trim to work, if I understand what you are talking about.

But you probably can't use Loft for the situation that you show there because you'll get weird wiggles if you try to incorporate a loft cross section that is so differently aligned than the others...

- Michael
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 From:  kevjon
2292.5 In reply to 2292.4 
Ok thanks Michael for the clarification.

I just tried loft and surprisingly it does work for this shape but doesn't quite hold its edge along the existing wing.

I found that if I extrude the yellow curve in the Z direction the resultant surface gives a better guide when adjusting the red curves as I can see how the two surfaces intersect before trimming. That solution will have to do for now.
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 From:  DannyT (DANTAS)
2292.6 In reply to 2292.5 
Hi Kevin, I had a quick look at this if you didn't mind, and as Michael says that yellow curve can't be included in the building of that surface or else it won't be smooth, it hasn't got the same curvature as the other cross strings, unless you intend to project that curve onto the surface or extrude it in the x minus direction to trim with.

Anyhow, for what it's worth I've attached your wing tip showing a plane that I used to extend the curves, then swept the last cross string and used the resultant edge at the end for the last cross string for a network, as you can see the surface is quite smooth but the yellow curve you mentioned is nowhere near that surface.
Another thing I noticed is that the main curves you have there have a lot of control points, was this a result of it being a projected curve ?


---------
~Danny~
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 From:  kevjon
2292.7 In reply to 2292.6 
Thanks Danny

I appreciate you taking the time to look into this.

>Another thing I noticed is that the main curves you have there have a lot of control points,
>was this a result of it being a projected curve ?
Yep, those curves have been projected onto the fuselage of the aircaft and the one on the wing has been generated from wing surfaces edge.

The yellow curve represents the trailing edge of the wing fillet (according to the blueprint reference I am using) but I am beginning to doubt that it is accurate or else you can't get a smooth flowing wing fillet as you have generated. I'll do some more checking of photos of the real aircaft to see if it differs from the blueprints.

Thanks for the tip about extending curves to a surface, I didn't know you could do that, so that is a really good thing to know. I think I would use it a lot.

You've certainly helped me solve this problem on all aircraft that I do which contain wing fillets !

EDITED: 5 Jan 2009 by KEVJON

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 From:  Michael Gibson
2292.8 In reply to 2292.7 
Hi Kevin - one other thing that may possibly be useful to you is to use the Construct / Curve / Isect command, which will generate the intersection beween 2 surfaces as a curve object, that may help with visualization.

It is also possible to enable history updating on the intersection curve - to do that select it and run Edit/History and click "Enable update". Then if you adjust one of the surfaces that intersection curve will update. If you mouse over the intersection curve you will get that selection halo around it, it may help you to more easily see what is going on there.

- Michael
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 From:  kevjon
2292.9 In reply to 2292.8 
Thanks Michael. Thats a very handy tip which I didn't know. I can see myself using that a lot to get my surfaces to conform to the approx shape I require.

It seems to be the best way to create larger surfaces that are later trimmed (to avoid the panel by panel approach) and yet still model reasonably close the profiles I require.
~Kevin~
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