I thought I would start a new thread about this.

What I want to do is accurately model an aircraft. When I say accurately, I don't mean millimetre perfect but it should when finished look like the real aircraft and not vaguely resemble it.

I chose the F9F Panther as it is a relatively simple design and should be a perfect candidate for nurbs.

The purpose of this thread is to try to find solutions to problems that I encounter when trying to model this aircraft and export a good clean mesh of it to my polymodelling software for uvmapping and rendering. That software will be 3DS Max 9.

This thread should also help Michael understand the problems users face when trying to model real world objects with nurbs and MoI which might assist him in further development of MoI.

All suggestions or help is welcomed and appreciated and I have included 3DM files and the blueprints to make it easy for people to help if they wish.

Here is walkaround reference photos of the aircraft in question http://www.cybermodeler.com/aircraft/f9f/f9f4.shtml

Attached are the blueprints and 3DM file.

First problem. When I switch from the top view to the bottom view I have to hide my top view image and unhide my bottom image. Is there way to switch views without having to unhide and hide my reference images ?

Here are the first problems encountered.

Problem 1. Pinching of the surface behind the cockpit.

Problem 2. Cant join the surfaces created together which I need to do to create a good mesh when exporting out to my polymodelling software.

My strategy when modelling this aircraft is to only model half of the fuselage and then export that half out as a mesh and mirror the mesh in polymodelling software.

Is that the right way to go about it with nurbs or is it better to model the fuselage as one ?

Next problem.

I've drawn a circle and then attached another curve to the circle with the trim and join commands.
This unfortunately results in a kink in my curve which will do doubt cause surfacing problems later on.

Is there a way to fix this point so it becomes a smooth curve ?
I don't want to redraw the curve as one piece as it would be difficult to draw a circle freehand using the freeform curve tool.

< Is there a way to fix this point so it becomes a smooth curve ?
Select curve
then Fillet!
Select your point as "corners Point"!
Select an Radius Fillet with any regulates you want
Enter :)

Ok

Here is the next problem I face. Lets assume I want to model the fuselage as one piece sweep or network and then boolean out the cockpit opening.

Michael suggested to me this is the best way to work with nurbs rather than the approach in my first post.

Lets assume I decide to create a boolean from the side view to cut out the cockpit opening. How do I know or how can I work out what shape my cross section curves need to be in the cockpit area (yellow curve) so that when the boolean is done the cockpit shape matches the plan view ?

Thanks Frenchy but I can't get that to work. I entered a fillet of 3.

If you have time can you please try on the attached 3dm file.

Let skip the cockpit for the moment as that problem is beyond me.

I've created the surface from the curves and as expected it has warped, buckled and twisted into all sort of unsual shapes.
However the nose part of the aircraft is looking pretty good so far.

I'll try and add more cross section curves to contain it in my next post.

I don't take your curve but that will be the same :)
Function fillet add 2 points to the existant

It doesn't work on my curve or I can't get it to work anyway. I tried 1 this time and still got nothing. Maybe it is a bug in latest beta ?

? I have made my example with the last beta!
Can you isolate your curve because I don't see it on your file!
And post it :)

It that case it must be something about my curve that is different than yours.

I created a 2 new curves in a new file, joined them and filleted them ok. The problem is now that both points on the end of the fillet have the kink when dragged around. So you now have two problem points in your curve instead of one, so fillet is not the answer in the case.

I do appreciate you taking the time to help though.

So Use Function Blend for the extremities and the other curves and you will choice The angle G1 G2 G3 of Tangency
And even play with the Bulge cursor!

Blend works good but still has the same problem as fillet. As soon as you move the points at each end of the blend, you get a kink in your curves.

As your curve will not be alone with an extremity, as soon as it will be blend to something, this kink will be disapear ;)

you can also use "add point" on either side of the corner point, then delete the corner point in the middle.

When you add point, it can be added "ON the curve" or "ON the Weight line". You want to add it to the weight line.

Also, you're getting deeper into your model before you solve your begining surface creation. If you start to jump around to fast and to much, it will get out of hand. Just a thought.

Hi Kevin,

> First problem. When I switch from the top view to the bottom
> view I have to hide my top view image and unhide my bottom
> image. Is there way to switch views without having to unhide
> and hide my reference images ?

If you don't have transparency you can do that by separating them slightly in depth so that they are not stacked right on top of one another, some details here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=1710.3

If they are transparent then there currently isn't any way to have them turn off automatically, but it should be possible to set up a keyboard shortcut that would toggle a particular image on or off with a single keystroke, let me know if that would be helpful.

It is on my todo list to handle reversed view images work more easily, I think that probably the best way would be to remember if an image was placed in a reversed view or not, and if there is an image placed in both the regular view and the reversed view I will skip drawing the one that is opposite from your current view. That should make it work with transparency as well.

- Michael

Hi Kevin,

> Problem 1. Pinching of the surface behind the cockpit.

It looks like you've built the center piece trying to make single surface match a somewhat irregular outline with a sudden change in shape near the top where it flares out.

I would recommend building a more simple tubular shape and building the flare-out part as another surface with a separate construction.

It tends to get hard to control single surface constructions if you try to build them to irregular outlines and incorporate sudden shifts directly within a single surface - try to break things like this up into more component pieces rather than doing them all at once.

It's also not unusual for pieces that are built as "separate patches" to have pinching or creases where they meet up with one another. There is some previous discussion and illustration of why that happens here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=1398.18
http://moi3d.com/forum/index.php?webtag=MOI&msg=1398.19


Usually the easiest way to avoid that problem is to build things as larger pieces.

Again, the main idea is to build single large sheets that are as simple as possible and then trim them to make more complex outlines.

So for your case here, I would probably try to make one longer streamlined tube initially and then cut a piece out for the canopy, rather than trying to incorporate the opening for the canopy directly into your initial surfaces.



> Problem 2. Cant join the surfaces created together which I need
> to do to create a good mesh when exporting out to my
> polymodelling software.

Typically that means that they do not have edges that are close enough.

You can see this in this case if you zoom in:





Again probably the easiest way to solve this is to have a larger single simple tube as a starting piece rather than a separated patchwork.

- Michael

Hi Kevin,

> I've created the surface from the curves and as expected
> it has warped, buckled and twisted into all sort of unsual
> shapes.
> However the nose part of the aircraft is looking pretty good so far.

Yup, as we previously discussed if you try to make cross sections go through big changes, like pull an elongated piece out from a single surface construction, it will tend to be much harder to control and generate things like that.

So I would recommend not doing that since it causes problems.

Notice how the front part is formed nicely where the cross-sections are not going through any major changes in shape? Keep that system going towards the back, focusing just on making a smooth tube shape and do not attempt to build the protruding tail fin out as part of the same single surface construction.

Instead, get a smooth body piece built first, then build that tail fin as a totally separate construction, then they can be blended or filleted together.

- Michael