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FSXA Gmax cross sections

orb505

orb505

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unitedkingdom
Hi all,

I kicked FSDS to the curb and decided that if most people are using GMax then there must be something in it!

Anyway, I've read Milton's excellent tutorial on building a Cessna, he makes it look so easy (False sense of security I think on my part).

I have my 3D view of a Cessna 177, complete with cross sections. Unfortunately in Milton's tutorial he skips the part of actually creating the cross section and in true Blue Peter style 'here's one I made earlier'. I could follow from the tutorial from the 'old way' of modelling from a cylinder but I'd like to have a bash at the cross section method, especially since I have the info and understand it's make for a more accurate model.

Does anyone know of a tutorial for creating the cross sections? I've searched Google and 'cross section' brings up some weird and wonderful results :confused: I found the Cross section tutorial on FreeFlight design (making wings) but from the screen shots it looks like a different method then Milton is using.

Cheers chaps!

Mark
 
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Ahhh one more that strays from the Path of the True Luddites!!


You will find that the "Cross section" as known in FSDS does not exist in gmax/max.

That is, you cannot create a cylinder and go into cross section mode, etc.

The closest you can come to it is spline modelling.


for your first cross section, create a spline "ngon" of however many points per section you want. convert to editable spline and adjust to the shape desired.

Personal Preference Hint: *I* like to convert the vertices to "corners".

For your second cross section, either create a new ngon, and reshape, or if the changes from one to the other aren't much, shift-drag the first one to the desired location (this clones the section) and reshape.

Suggestion: Start from FRONT of the model to the back

Once you've completed the sections, select the FIRST section created, and ATTACH each successive section created.

With all attached as one object, add a "cross section" modifier, then a "surface" modifier. Play around with the interpolation settings, and you may have to "flip surfaces", but you get the basic shape... usually.

If the basic shape is as you want it, now you can either add an edit mesh modifier and be on your happy (modelling) way, or convert to editable poly/mesh and be off.

-----------------------------------------------------------------

If you need to ADD a cross section, don't do it at this point, you really can't (in FSDSspeak). That's what "slice plane" in ePoly/ eMesh is for.


(Yes, I still do most of my modelling in FSDS, but one does need to "know thine enemy" .. :) )
 
Thanks Felix,

I think what you are explaining is the method in the other tutorial I've seen on FreeFlight Design, although I'm no gmax guru Milton seems to be using a different method.

http://www.flightsimonline.com/C162/fusex/

I'm sure you have all seen this (above). Milton seems to be using a plane shaped to cross-section shape, deleting the poly to leave only the vertices and then making new poly's between the vertices on two of the cross section shapes (easier to see than explain).

Although I can see pertectly in Miltons tutorial how is is doing this he doesn't explain how to create this initial cross section shapes. I've got the cross section shaps on the 3V drawing but getting them into gmax with the correct scaling is a little mystry. I mean, I can bring side/top views in to the correct scale as I know the nose to tail length of the aircraft. But I don't know the size of each of the cross section shapes...especially as they are only half the shape of the fuselage as well! Then if and when I do get them in gmax, how is he creating them?
 
It appears to me as though Milton simply used the Line tool to trace out a spline shape for one-half of the fuselage shape, then performed a Convert to E-Poly on the result.

Having gone to the trouble of creating the Spline objects though, I should think that using the Attach tool to join them into a single Spline object might have been faster...

The following four screenshots illustrate the basic sequence of tasks to perform. The major advantage of this method is that -until the stack is collapsed- you can easily select the Spline Object level and edit the vertices as required to "fine-tune" your shape to perfection.

Disclaimer: there is no attempt at being "accurate or realistic" in the following. The end result looks like a beer bottle rather than a fuselage... :)

splinemodeling01.jpg

Shot at 2009-12-06

splinemodeling02.jpg

Shot at 2009-12-06

splinemodeling03.jpg

Shot at 2009-12-06

splinemodeling04.jpg

Shot at 2009-12-06
 
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Cheers Bill,

If the result is basically the same but quicker then I'll follow your steps.

Next is to actually get the cross section bmp's into gmax at the correct scale. I'm not entirely sure but I've got an idea that might work, if I can run it by you then perhaps someone can tell me if I'm wrong.

I import my top, side, front views as normal (that is to scale on the sides of a box). If I then put all the cross section bmp's onto a single plane (not to scale) and then draw around them using the line tool. I then take them to their correct position on the side view and then uniformly scale them down to the correct height according to the side view (and thus correctly scaled).

Hope that makes sense! :confused:

Mark
 
That sounds like a good plan.

I will point out that perhaps the single most important part of doing a 1/2 Spline Cross Section is using the exact same number of vertices for each Spline object.

One way to achieve that is to create a single Spline with the number of vertex points desired, for example 18 if you wish to capture a complex curve, in a vertical row...

...spacing each vertex precisely the same distance vertically.

Clone the "vertically spaced Spline object" as you go, then adjust the vertices of the cloned "vertically spaced Spline object" by dragging them to the right to align with your cross-section backdrop.

This will ensure that all vertex points are evenly spaced vertically and horizontally in relationship to one another before you apply any Uniform Scaling.
 
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