1. This Tutorial is the first of a series on the subject of paper/card model design, using various 3D modelling and graphic software. I will try to keep the operations as generic as possible so you can use other similar programs. I will be using Rhino version 3 ( www.rhino3d.com ), CorelDraw version 9 ( www.corel.com ), Wings3D ( www.wings3d.com ) and Pepakura ( http://www.e-cardmodel.com/pepakura-en/ ). Oh, and Paint Shop Pro. ( www.jasc.com ) You can get demo versions of most of these programs from their respective websites, although CorelDraw is now up to version 12. I am using version 9 because it has all the tools I need as well as being able to read and write pdf files. I have seen version 9 on eBay for silly money.
In addition to these tutorials, there is a seperate thread at http://www.cardmodels.net/phpbb2/viewtopic.php?p=4224&sid=1545ac12e870af4a02e1d12e1b750902#4224 to raise points, make suggestions, ask questions for any matters arrising from this series. I will have to assume readers are reasonably familiar with the software being used, these will not be key by key, mouse-click by mouse-click instructions! But if you need particular help don't hesitate to ask, either in the discussion thread, or send me a private message, and I will do what I can.
For subject matter, I went to Sky Corner ( http://www.airwar.ru/indexe.html ) and downloaded some drawings of the Sukhoi Su-7. subject matter for the tutorial will be a Su-7BKL. There are some useful articles and pics of this aircraft on the net, see what you can find. There are also a number of useful books and magazine articles which I will mention along the way. I have picked this aircraft because it has a relatively simple airframe, it makes into a big and impressive model, there are some very attractive colour schemes applicable. I don't think anyone has done a commercial kit of it, and finally, I like it. After all, the prototype took flight for the first time on my birthday! OK, 3 years before I was born, but my birthday nonetheless!
Rhinoceros is a 3D modelling package which uses NURBS (Non-Uniform Rational B-Splines) to describe curves and surfaces. While the mathematics under the hood are mind-bendingly complicated, the software itself has been very carefully designed so it is intuitive, most users being able to pick things up very quickly. The interface is fully customisable, and there are several plug-ins to do photo and non-photo rendering, animation and lots more. One of the most important commands for our purposes is the 'UnRollSrf' command, which does just that; it takes a curved surface and flattens it out.
While Rhino will help us calculate all the shapes of the parts needed for this model, I will use CorelDraw to lay the parts out on the paper and card pages, to colour them, and apply labels, cutting and folding indicators and so on. I will also use these two programs to create any illustrations needed for the assembly instructions.
Rhino can generate mesh models from its original surfaces. Mesh models are quite different to NURBS models, and uses points in 3D space to form lots of triangles, which approximate to the surface being modelled. There are many software packages that can create and manipulate meshes. However, to make such meshes useable as paper model designs they must also be 'flattened', and to do this work I will be using a Japanese program called Pepakura which has been designed especially for the paper model designer. Not only can it unfold a mesh, it can add tabs, numbers, layout parts on a page and lots besides.
I will have a look at using a mesh modeller called Wings3D during the project. This will illustrate some of the differences between surface and mesh modelling techniques. There is nothing to stop you using Wings3D to design your model in its entirety, if you prefer. And being a free program, it is fantastic value!
Paint Shop Pro will be used to handle any bitmap images required. The first work done on the project will be to arrange some scanned images for use as backgrounds within Rhino, and I will do this work in Paint Shop Pro. Again there are plenty of bitmap editors available, so if you have a prefered bitmap program, use that!
I appreciate that Rhino is not a cheap program to buy, especially when compared with the other programs mentioned here which range from $100 or so down to free, but I hope the following tutorials will show something of its power and usefulness. But more importantly, I hope that the 'work-flow' of the project will be useful for designing using any modelling software package.
OK, I know, paper and card..... One of the reasons I wanted to make a model with a bare metallic finish was to try out some of the metal paper and card that is now available. These materials will be used for the surface skins. The main structure will be of 1 mm card, as this will go through my Epson printer without too many nasty noises. If your printer will not take heavy card, no problem, I will look at the considerations needed if you are to laminate thinner stock. I am not a 'Paper Fundamentalist', so other materials will also be considered if appropriate. I am thinking 'vacformed canopy' here...
The standard scale for paper model aircrcaft is 1:33. I personally find 1:33 a bit 'weedy' having grown up with 1:32 from the plastic kit world. Also, as most of my paper model aircraft are 1:32 Digital Navy and ModelArt items, I will stick with the scale I know and love, but it will be straightforward to print out the parts to the slightly smaller 1:33 size if required.
With a full-size length of just over 18.5m, including the air sensor boom, and a span of 9.32m, in 1:32 scale this gives a model approximately 580mm long and 290mm in span. Fuselage is about 50mm in diameter, so quite a reasonable size for a model.
To be continued....
Rhino can work in a variety of different units. I prefer using millimeters, but you can set whatever suits you. The model will be designed 'full-size' for the model, not the real aircraft, so that any allowances for materials can be measured directly. Also any exported data will (usually!) keep these units, so will appear in other software at the correct size. The mesh and grid settings can also be adjusted to suit, I have set my grid snap spacing to 0.5 mm, and the visual grid extends 600 mm along each axis, with minor grid lines marked every 20 mm, major lines every 100 mm. Notice the grid will extend 600 mm positive x,y and z, AND 600 mm negative x,y and z, so in ach view the grid will appear as a 1200mm square centred on the origin. All these settings are controlled with the Rhino Options dialogue box, and will be saved as part of the current document. You won't need to reset then next time you open it. There are lots of other settings for different tools which you can tweak at any time.
As with many 3D modelling programs, Rhino can display a bitmap image within each view of you model build space. This could be a photo or a scan of a drawing, and you can use this image as a guide while making your model around it. Usually the desk top is arranged with several views, a side, front and plan view, with a perspective view to watch how the model is developing. Rhino allows a different background image in each window (except the 3D view) so three views, a side, rear and plan view are required. Have a look at the gif downloaded called Su7c2-b.gif, it has plenty of appropriate images, and some very handy dimensions. Using Paint Shop Pro, select an area covering each of the views we want and save these selections as seperate files. Make sure the views you pick are of the same version of the aircraft. These copies can then be opened seperately and cleaned up, making sure no details are lost.
These images will be black lines on a white background, which is fine if you want to print them out, but not so appropriate for tracing over. I have my Rhino workspace set up with a neutral grey background; easy on the eyes and most colours show up well against it. Opening the background bitmaps again, add a mid grey to their colour palette.Then using the colour replacing tool, firstly chance the white background to the mid grey, then change the black lines of the image to white.White lines are easy to trace over, and when you zoom in you can adjust the curve position relative to the scanned image very easily. Then save the files. For some reason, Rhino is not set up to see .gif files, so save your images as .tiff or .png images.
Bringing the images into Rhino is very simple. The Background Bitmap toolbox is under the Views button, or alternatively in the Views menu. Click in the view window where the image is to be placed, select the Place Background Bitmap tool and pick the image file required. The cursor changes to a 'top-left corner' , click and drag to locate the bottom right corner and the image will appear in the view. Using the other tools in the Background Bitmap toolbox allow you to shift the location of the image, and then scale it to match the model size required. Make sure the aircraft datum line (a long dash-dot-long dash line along the centre of the fuselage) is centred on the axis in each view, and that it follows the axis along its length. If it doesn't it means the scan of the original plan was not parallel with the scan head, and you really need to re-scan the image. You will distort the image if you try any of the Paint Shop Pro 'skew' commands on a bitmap. Repeat this for the other two views ( not the perspective one) so you have a side view in the Right window, a Rear view in the window labeled Front, and a plan view in the Top window. (Edit-add) The names of the various views relates to the standard 'First Angle Projection' convention, and might not neccessarily corespond with the top, front and sides of the item you are modelling. If you want to change the wording used to label each window, go to the 'Viewport Properties...' item on the 'Views' menu. Here you can rename ithe title to something more useful, as well as adjust anumber of other features and settings for that particular window. (Edit-add)
There are several conventions regarding which direction is x, which y and z, but in this model the y axis goes along the fuselage from tail to nose with y = 0 at the aft tip of the pod on the tip of the fin, above the rudder. The model is therefore 581 mm long in the y axis, to the tip of the air sensor probe. The x axis runs from the centre datum line to the wing tips, with positive x going right, negative x going left. The z axis runs vertically upwards, with z = 0 also on the centre datum line. A look at the screen views will show this. Notice all the windows have a little axis indicator in the bottom left corner, and a green and red indicator in the mesh, so you can alays work out which way your axes run. Also in the tool bar at the bottom of the screen is a read-out showing the location of the cursor in x,y,z coordinates.[b](Edit)[/b]These co-ordinates are a little confusing as they refer to the active view on screen, and not the world co-ordinates. Had me fooled for a minute or two.... So, if you are in the Top view, x is across, spanwise, y is up the screen, towards the nose, and z is out of the screen, towards you. However, in the Right view, the x co-ordinate increases as you move right on th screen, but that is now the y co-ordinate in the model, and so on. Easy way to remember, those three co-ordinates on the bottom of the workspace are SCREEN related, not WORLD related. I can go into this apect in more detail if anyone needs further examples to make this clear. [b](Edit)[/b]
OK, bitmaps all loaded and scaled, your desktop looking at the Right view should look something like this:
A start on the basic structure has also been added in this view, but more on that next time.
To Be Continued...
Once an understanding is gained of the way the views of the Rhino workspace relate to each other, it is very easy to start adding boxes, spheres, curves, surfaces and then using the Boolean operations to stick bits together, take bites out of other pieces and so on. The 'grammar' of the commands is very consistant, so once one command is understood, the logic of the way it works will apply to the other commands. Time spent just fiddling around with the workspace, and then going through the tutorials that ship with the software, will be time very well spent. However, to model accurately, the various Snap and Constraint controls must be understood and mastered.
Working on a 3D subject with a 2D screen takes a bit of getting used to, but having the perspective view which can be rolled about to see all around your creation is very handy, and you will soon be relating what is drawn in the other views to how the model changes in 3D space. There are lots of ways to indicate where in space are the points required, but just relying on the absolute cursor position is not going to be accurate enough for our purposes. Wiggle the cursor in the workspace and see how the xyz read-out on the bottom of the workspace reflects the movement. Even if it is to 3 decimal places, there is no way you can keep the cursor at exactly the right location; especially when Rhino is actually working to many more decimal places! Accuracy is not just in the numbers, but in the CONTROL of the numbers...
You could just type in the x,y,z co-ordinates of every point you need. That could to be a bit tedious, but is still very handy to do sometimes, so make sure you understand how to do this. Watch the command line as you work through an operation, you can type in numbers instead of clicking, and each point or dimension can be added by any method at any time in each operation.
Mostly though, the mouse will be the main tool for directing Rhino. The grid settings, available under the Tools/Options... menu, look like this.
The settings here were discussed above, but the most important one for modelling work is the last one, Grid Snap Spacing; here I have set it to 0.5 mm. Once set, and then activated by clicking the Snap button bottom right of the workspace,
the cursor will now move in steps of 0.5 mm, rather than smoothly. Imagine the whole workspace filled with a wire mesh box, and the cursor can only 'stick' to where the wires cross. Try and put it anywhere else and it will jump to the nearest grid intersection. Zoom in on a small area and you can see this happening as you move the cursor. Turn 'Snap' off, and the cursor will move smoothly again.This works in all 3 dimensions; practise! Remember that the visual grid might be at a different pitch, as I have here, so the snap locations might be different to the visual ones. Remember it is the grid snap settings that determines where the cursor ends up, NOT the visual grid; that is just a guide!
With the snap set on, you can now draw boxes, cylinders, lines, whatever, but all the construction lines and points will be on that grid, adjacent parts will line up exactly provided you pick the same grid locations, and any dimensions along the grid will be exactly in 0.5 mm steps. Accuracy, with control...
Ortho and PlanarWhile looking at those 4 buttons, bottom right of the Rhino workspace, the next two need a brief explanation. Selecting 'Ortho' limits the angle between two sequencial lines or surfaces. Default setting is 90 degrees, but you can change that to whatever angle you need, under the Tools/Options.../Modelling Aids menu. 'Planar' makes sure that if you select a point in space in one view, then switch to another view to continue drawing, the additional points will keep the same 'height' as the original one, and the drawing will be 'up in the air'. If this switch is off, then points added in a different view will 'drop down' onto the construction plane (where the visual grid is, in other words) and will not be on the same plane as the starting point. Again, try these out until you understand what is going on.
Clicking on the Osnap button activates a whole new set of snap options. The default workspace layout has a toolbar along the bottom of the window, like this
but I prefer to have these options on a seperate box. You can 'rip off' any of the tool bars so they float seperately. Just by click-dragging the little bar at the left or top end of each line of buttons, indicated by the red arrow, you end up with a layout like this
You can move the Osnap box wherever it is convenient, and gain some valuable elbow-room in the workspace.
Osnap works by relating the position of the cursor to elements of your model, rather than an external grid or geometry. To activate any, or several, of the options, just click to put a check mark in the appropriate box. You can disable ALL of the Osnap functions be clicking the Disable button. Most of these snaps are self-explanatory, and you should try them out on some boxes and spheres to see just how they work. Some require a little knowledge of how Rhino builds objects. Quad points are found on circles and elipses and can be thought of as the North, South, East and West points. An elipse is constructed from a major and minor axis, and the Quad points are the ends of these axes. Knots are points used in the construction of surfaces, Int is short for Intersection, and so the cursor will snap to where two lines, or a line and a surface, cross. One warning with this last one, Rhino has a setting for Apparent Intersections, which I find is best switched OFF. This is done on the Tool/Options...Modeling Aids window. Apparent Intersections are those where two lines appear to cross because of the viewing angle, even though they don't actually cross in 3D space.The reason for switching it off is that if you are working in the perspective view the cursor can snap to an apparent intersection that is off the construction plane instead of a true intersection, which is on the construction plane. When using Osnaps a little label appears beside the cursor to let you know which one is being used, but there is no distinction between apparent or true intersections; it just says 'Int' . Be warned, a slightly off-plane point will put a kink in a surface, and if you don't spot it (it might be tiny) it will seriously foul up any unrolling!
Generally, only switch on the Osnaps you are actively using. Turning them all on will have Rhino fighting over where exactly to place a point and if you are not zoomed in close enough, it is easy to snap to the wrong element without realising it, with similar results to the apparent intersection problem. You can turn Osnaps on and off in mid-command, as you can with all the other snap and constrain commands, so if you have a tricky sequence of points to pick, you can change the snap to suit for each point.
So, snaps and constraints help you greatly to work accurately. Watch the cursor, it jumps to a snap location and the little label highlights the function used. Have a practise with them all, and remember any questions or comments, check out the discussion thread.
To be continued...
Well, almost. A quick look at the Layers controls will be useful at this point. The word Layers is more appropriate to 2D programs where you can easily imagine elements of your drawing being on seperate layers of (ultra-transparent!) tracing paper, all lined up; a bit like the cells of a drawn film animation. In the 3D world, they are really bits of models that occupy the same space, but the way you use them is the same. When you make a new Rhino file, the default settings already provide you with 6 layers, and you can control them by clicking on the Layers button; looks like a red, white and blue piece of cake. Yummy.
The first layer is called Default, the rest Layer 01 to Layer 05, but you can, and should, change these to something more meaningful. Just double-click on the name and type in what you want. The tick (check mark) indicates which layer is active. This means anything created will be drawn on this layer. As a check while you are working, there is a little repeater on the bottom line of the workspace, to the left of the snap buttons. You can click on this to bring up an abreviated layer list where you can change the active layer, without bringing up the main layer box. This is a handy short-cut while working.
Back to the main layers box, the little padlocks click on and off, and lock their layer so you cannot select, create or delete anything on that layer. The Light bulb switches the layer from visible to invisible, and the colour block indicates what colour will be used to draw anything on that layer. Double clicking on the colour block will bring up a colour picking tool, so you can have as many colours as you want. The white circle after the colour indicates any materials assigned to that layer, but that is more to do with rendering, which is beyond this tutorial. Don't let that stop you trying it out though!
As you can see, I have started changing the names to something useful. You can add as many layers as you want, and you can resort the layer listing by clicking the grey bar above each column. This means you can quickly bring all the locked layers together, or alphabetise your name list, and so on. It even works with the colours! This is especially useful if you are careful with your layer names, naming them so they sort meaningfully. Use the buttons along the top of the layers box to add, delete and sort them, and remember if you don't know what a button does hold the cursor over it for a second or two, and a tool tip will appear. This is common to all buttons in Rhino, and will include left and right mouse button tips if these are different.
OK, onwards. On the Construction |Lines layer ( the Default layer, renamed), in the Right view, with Snap and Ortho buttons selected, draw a vertical line with the single line tool, passing through the lip of the intake. You can zoom in to make sure it is close to the background image. With the grid snap on, it will be within 0.25 mm of the right place. The line will be yellow when selected, black when not; either way it is easy to see it over the white line and grey background of the bitmap image. Select it and copy it (button with one white square and three blue ones) along the length of the fuselage, lining up each copy with the major vertical panel lines. These lines will mark where each of our model fuselage frames will be located. They are all being drawn on the plane of the visual grid, where the bitmap is located, like a line of posts running down the centre of our model. Then, using the Inertolated Curve tool, switch the snap and ortho functions off, and the Osnap function 'Near' on, draw 2 lines along the top and bottom of the fuselage, clicking where the bitmap image is, and snapping to the vertical 'posts' drawn previously.
You should end up with the fuselage shape marked out like this.
Roll this perspective image, looking along the fuselage lines. Any kinks or unsmooth areas should stick out like sore thumbs, and you can then make any tiny adjustments by turning the points markers on, (curve with two white dots) selecting the out-of place points and miving them up or down to suit. Do this from the Right view, with Ortho and Planar switched on, so there is no risk of moving the points out of the vertical plane.
Note, these two lines are NOT going to be used to form the skins of the model, but they are just to ensure the straight-sided cones we must use on a paper model, transition from one to another in a smooth, visually pleasing manner. Remember the limitiations of modelling in paper; we cannot use compound curved surfaces, unless we mesh them, and that would not be appropriate for this structure.
Now, to put some frames in. This aircraft is circular in cross section, so this is just a matter of creating a series of circles from the upper to the lower intersections between our 'posts' and the fuselage lines. Selecting the Circle, Vertical, Diameter tool, setting the Osnap tool to Int only, and looking at the Right view, click on the intersections between the top fuselage line and the first nose 'post', then the bottom fuselage line and the 'post'.
Nothing will appear to have happened, but that is because the circle has been drawn between the two points, but edge-on to your view. If you switch to the perspective view, there is the lip of the air intake! Repeat this along the fuselage, making sure you start each circle on the top line, finish on the bottom. You should end up with something like this
Starting to look like a fuselage now....
Next time, we will look at the various options for creating the skins between our frames.
Don't forget the discussion thread at http://www.cardmodels.net/phpbb2/viewtopic.php?p=4224&sid=1545ac12e870af4a02e1d12e1b750902#4224
To Be Continued...
This is the Rhino command that must have been developed with paper modellers in mind! However, as with most things Rhino, there are a few things to consider before this command will work well. Firstly the surface to be unrolled, must be unrollable; obvious I know, but it is so easy to model flowing organic shapes with this software it is easy to forget this limitation. Until Rhino has a 'Do your best and I'll beat it out flat with a hammer later on...' command, this is just a design constraint we have to work with. Most of the surfaces to be unrolled are going to be tubes, or sections of tubes, so provided they are made using straight lines between the cross-sections, things should work out. There is one glitch, but we will come to that shortly.
First off, we need something to unroll. Here are two circles of different diameters, and a few units apart. They are on the same axis, so a surface generated by a straight line between them will be the side of a truncated cone.
Selecting the Loft command from the Surface menu, and selecting the two circles, a line with two marker arrows appears, indication where the loft will start, and as it is a circular form, where it will finish.
Accept these, and a dialogue box appears. From the drop-down styles list select 'Staright Sections. and apply, and we have our surface.
If we had selected 'Developable Surfaces', a selection that might be the obvious one, the surface would have been mangled; I am still trying to work out what is happening here! For the moment, avoid this setting! It looks like this...
Changing the Cross-section curve options from 'Do Not Simplify' to Rebuild, and typing in another number, increases the number of points used to create the geometry, and this adds to the number of isolines drawn on the surface. If you need to locate things on the unrolled surface this is a good way of doing it. The isolines will unroll with the rest of the surface, and be exported to your drawing software.
I used a value of 16 here, then created the conic surface. Going to the Surface menu again, this time selecting Unroll Developable Srf and then clicking on the surface,
you get this. Bingo! Well, nearly....
We can work out that the small diameter edge is the inside of the unrolled surface, but is it the inside surface facing up, or down, and which end is which? Switching on the rendered modelling view option ( grey ball on a grid) The surfaces are rendered so they are easier to see. I have cut a small notch in one part of the narrow end, so we can locate just where it ends up on the unrolled surface. Now we can see that the surface was split where the two white arrow markers located themselves when we created the loft. The notch shows us that it is the inside surface of the cone that is facing upwards, and since this will be the orientation we use to export the flattened surface to our drawing software, the image is up-side-down. We want the outer surfaces facing upwards.
There is a quick visual check for this, if you notice the inside and outside surfaces of the cone are slightly different colours, and these colours are matched by the unrolled surface. However, to actually change this, we need to use the Analyse Direction Display tool button and select the surface. A little forest of white arrows will appear on our cone, in this case all on the inside surface, pointing inwards. Sorry, they are a little difficult to see in this pic!
Hitting the F key will 'flip' the direction of the arrows, and the facing of the surface, which is what we are altering here. The arrow display will look like this
Press the Enter key to accept the new direction, and notice the colours have changed over as well. Repeating the unroll command now brings the outer surface uppermost. Much better!
However, imagining this part as a section of a model, the joint will be on the top of the fuselage, and it might be better to have it on the underside. We could go back to the original lofted surface and move the two arrowed start points, you can drag them anywhere along each circle. Alternatively, we can cut the cone in half, unroll the surface
and then mirror/copy this surface.
This has the advantage that all parts treated this way will be aligned along the centre of the fuselage, a much neater way of presenting the parts on the final artwork. You can of course move these parts where-ever you want, but sometimes it pays to think ahead a little!
Phew! A busy weekend.... Hope this all makes some sense, comment if you will on the discussion thread.
To Be Continued...
The rest of the fuselage sections can be created now, using whichever tools are appropriate; usually lofts with straight sections will give the best results. If you have any parts that appear in a different colour, check their facing with the analyse tool and flip the directions so that they match the rest of the fuselage.
Using the various rendering options the overall 'look' of the structure can be checked. Provided the original fuselage outlines were carefully drawn, the skins will flow smoothly from one to another, without any obvious changes of direction; unless the kinks are intentional, of course! At this stage, make sure you have saved your work. Rhino can be set up to make auto back-up copies, but as it does not have a 'tree' structure to its model files ( not one that you can access, anyway) it is wise to save regularly, and save sequentially. Then if disaster strikes you can go back to the previous file and carry on. I usually call my first file 'project_name_001.3dm', then I just 'Save As...', and advance the number in the file name by one. Rhino will load the new file and let the work continue. As with all Windows programs, hitting the 'Ctrl' and 'S' keys together will save the file immediately; much quicker than pulling down menus!
The master fuselage skins should now be moved to a seperate layer. To move any item to a different layer, select it, then access the 'Properties' box (Rainbow ring...) Just select a different layer from the drop down list. Usually the part will then display in the layer colour, but you can select a different colour if you prefer. There are other part properties that can be accessed and edited from this box, but we will look at those some other time.
I prefer to keep such master parts seperate from the actual working elements of my model, using copies of the masters rather than the masters themselves. This is another defence against something going wrong! Layers containing such original parts can be named so they group together alphabetically, and they can be locked so the parts are protected. To transfer a copy to a working layer, unlock the master layer, copy and past the required part; it will appear in exactly the same place as the original, so you will not see an obvious visual change. Unselect everything, then select the copy; if Rhino cannot determine which particular part you require, it pops up a list of possible items, from which you can select the item you want. Rolling your mouse wheel, clicking on the list or using the 'up and 'down' arrow keys will change the current selection, 'enter' will make the selection. Edit the properties of you copy to change its layer from the Master layer, to your working layer. Finally lock, or hide, the master layer, and the copy will now be ready to edit further, while your original will be untouched and safe. Ctrl + S....
A start can now be made on trimming the fuselage surfaces. As we found above, the skins are a little easier to handle if they are half sections, so first of all split all of the working copies and discard all half sections on one side. Easiest way to do this is draw a rectangular surface on the construction plane as seen in the 'Right' view, and use this plane to split the fuselage rings. Depending on just how you constructed the original fuselage sections, the remaining skin sections might actually be two pieces split along the horizontal axis, but they can be joined together. They will still unroll as if they were one piece.
It should be clear at this stage, it would be perfectly possible, indeed sensible, to have just modelled one side of the model right from the beginning! However, I thought this sequence would introduce a number of important concepts and techniques which will be very useful to understand. And as with most things there is no 'correct' way to work with this software, just lots of alternate routes. Generally you should use whatever is comfortable and appropriate for your own project.
Several sections of the fuselage are a little more complex than simple conic tubes. As a general rule, the best way of making a complex surface is to make an over-size, but simple surface, then trim away the surplus material. Rhino remembers this sequence of events when it stores the item data and it is easy to edit or remove 'trim' operations, restoring the original surface. More importantly though for us, a simple surface is much more likely to unroll successfully, and the trim operations will follow on the unrolled surface in the same way they worked on the curved one. Trying to construct a complex shape by adding different surfaces together is much more likely to result in problems, even though Rhino will enable you to make surfaces that way.
As an example, the very last section of the fuselage, around the nozzle of the engine, has two little extensions inboard of the tailplane trailing edges; these offer some protection to the tailplanes from accoustic, heat and shock damage from the engine. The last fuselage cone was made 'full length', including these extensions. Looking from the 'Right' view, the true outline is drawn using the Polyline tool, so that the line is on the construction plane.
This line is then extruded so that it passes through the last fuselage skin,
and then it is used to split the fuselage skin into three pieces.
The surplus pieces, and the extrusion, can then be discarded.
This process can be repeated for all the other apertures we need, the cockpit, wheel well, air brake panels and so on. The locations of these holes will help us locate and construct the internal frames for our model. Modelling only half the aircraft will reduce the number, and complexity of our work, as well as giving a clear view of the internal AND external structures. It will also cut our file size considerably too. Just remember to note any features that are not symmetrical, and model these accordingly.
Next time, Starting the Internal Structure.
So far, the model consists solely of some skins. As far as Rhino is concerned they have zero thickness, and without any internal structure our model would not support itself. There are many different approaches to building paper models, each with their advantages and disadvantages. Some designers prefer a very light-weight approach, with sections of the model being simple tubes rolled to the correct shape. Others prefer a more 'engineered' solution with a substantial internal structure. Yet another method treats each section as a little model on it's own, with a bulkhead at either end. Several such sections can then be glued together to form the complete fuselage. If you have some experience of building paper kits you may well have your own preferences. If there is a lot of internal detail, cockpits, undercarriage bays, engine intakes and nozzles and so on, the internal structure approach might be more appropriate, whereas the simple rolled tube method would be better for a small, less detailed design. Another consideration is the amount of handling the model might require, especially during construction.
This model jet is quite a large construction and as a fair bit of detail will be incorporated the 'substantial structure' method will be used. A circular frame will be placed at every joint between fuselage sections, with internal strips to reinforce and align the joints. The cockpit and nose undercarriage bays will need 'boxing in', while the air intake and afterburner nozzle will be open tubes built through the frames in those areas. Some structure will be needed to carry through the wing, and the frames will also have to be strong enough to support the fin and tailplanes. There are numerous intakes, exhausts, air brake panels, and the intake centre body (radar nose) to include as well. It will be very useful to carefully study the drawings and other reference photos of the real aircraft. This will show how the original was designed and built, and this knowledge will be very useful in the preparation of our design.
The fuselage can be divided into three main sections. The area forward of the wing contains the intake, cockpit and nose undercarriage bay. The centre section has the wing spar box and part of the main undercarriage bays, while the tail section has the fin, tailplanes and afterburner nozzle. To simplify the work, it will be sensible to create new layers for these areas so they can be modelled seperately. Remember, Rhino will work more quickly the fewer parts it has to redraw and render, and having an uncluttered work space is always a good thing! In this picture I have added some more layers, labeled them appropriately, and then will copy the skins to their own layers. The original skins will be locked and hidden, in case I need to refer to them later.
You can set Rhino to use the layer colour to paint the parts, as well as the outlines. This is very useful to make sure things stay on the correct layer, and it is a useful reminder as to which layer is the current one.
Before we can move ahead with the structure, some decisions regarding material choices have to be made. I am going to use some Letraset Inkjet Metal finish card for the main skins. This has a nice flat aluminium finish rather than the bright chrome effect seen on other metallised inkjet papers.
There are several smaller items where the bright finish will be appropriate, as well as smaller items where a thinner paper will be easier to work, but we will look at those at a later time. Measuring the Letraset material with a dial guage gives a thickness of 0.2mm. If joining strips are used, the glue and paper will add about another 0.2mm, so the frames will need to be smaller by about 0.4mm on all skins. This will be a starting point, no doubt some tweaks will be needed after the first test build. The frames need to be fairly substantial, so I have chosen to use some heavier white board which is about 0.6mm to 0.7mm thick. It does vary a bit, but so do most papers and cards!
To create a frame, use the Offset Curve command to create a curve inside the skin by 0.4mm. Join the ends with a straight line, then make a solid by extruding the frame outline. If you want the frame to have one of its surfaces level with the original curve, extrude the whole thickness required in one direction. If the frame is centred on the original line, you can extrude half the required thickness, in both directions; the extrusion will grow forwards AND backwards from the original curves. Remember now we are dealing with objects with 3-dimensional thickness, rather than infinitely thin skins! If we don't include the thickness of the material in our design, the model parts will not fit together properly.
In this picture, two nose frame outlines have been created, one shown green, the other yellow (because it is selected) The Extrude tool is being used on the selected frame outline, with the Both Sides option, so half the thickness required is typed into the command line; 0.35mm (abreviated to .35 here) Before the enter key is hit to complete the command, a preview extrusion follows the movement of the cursor, and a read-out of the distance extruded is shown next to the xyz world co-ordinates on the bottom of the screen. The movement of the cursor will be constrained by whatever snap, grid etc functions are operating at that moment,
but pressing the enter key will finish the command using the typed in figure.
Notice the part is created on the selected active layer, and will be coloured to match the layer colour. All the other frames can now be added, with holes appropriately sized and located for the intake ducting and the afterburner. Remember to offset the curves to allow for the material which will form these internal skins as well as the external ones!
To make the cut out sections to accept the afterburner and intake ducting, make solid cylinders, cones etc and use them to cut away the surplus material using the Boolean Subtract command. The boolean operations work by adding, subtracting or intersecting objects in 3D, and they are a very powerful tool set. Careful study of the boolean Help files, and some practise, will be time very well spent! This image shows the frames and ducts in place, although the workspace is starting to get a bit crowded.
Remember you can always render a view using lights and surfaces to get a better idea of what the model will look like. If you want to do more detailed rendering, two specialised plug-ins called Flamingo and Penguin are available from www.rhino3d.com. Flamingo is photo-realistic, Penguin produces sketch illustrations, and two very simple examples are shown here.
Having designed the basic fuselage skins and the major frames, some work can continue on the internal details needed for this model. Keep in mind how the model will be built, physically, however. While this particular design is being done 'outside-in', the card and paper parts will probably be assembled 'insides first, skins later'. It is easy to end up with a structure that either cannot be assembled, or will be too weak to hold itself together while additional parts are being added. Looking at the Sukhoi fuselage I wanted the centre section to be very robust. The wing spars will pass through this area, and apart from the small cut-outs where the main undercarriage bays break through the skin under the wing roots, it is essentially a simple, solid tube. The aft end of the fuselage is also tubular, but will have to be open at the rear end, and contain a smaller tube structure for the engine afterburner. Still, fairly simple to build. The cockpit area however is much more involved!
Using the bitmap background as a guide, a couple of lines are drawn onto the construction plane in the side view, to make cutting planes.
Extruding these and using the extrusions to trim the fuselage skin gives a neat cockpit opening.
Remember to keep these cutting parts on a seperate layer, so you can make them invisible to check the parts that have been trimmed. If a correction is made, just 'undo' a few times and make whatever adjustments are needed and repeat the cut. Also, once you hit the 'Save' button, (or Ctrl + S, remember!) you loose the 'undo' stages since the last 'save', so don't save until you are happy with the parts prepared.
A quick look at the outside view,
The nose undercarriage bay on this aircraft is directly under the cockpit and the intake trunking is divided around the cockpit. This means the structure around this area is a little bit 'busy'! However, with Rhino you can just add the parts in much the same way you will do so with the final model, and so it will not take long to position and trim the shapes needed for the rest of the cockpit area. I generally work on a half model so I can quickly see inside and outside areas of the model just by swinging the view around. This is done in the perspective view by clicking somewhere in the view but NOT on anything selectable, and just dragging the view around. This quickly becomes second nature, so much so you will probably find yourself trying the same trick in other programs! Just let go the mouse button when you have the view you want.
In this view, the nose u/c bay is sketched in...
..and then the nose frames and intake ducting built up. Finally the slanted cockpit side walls, which are formed by the inside of the intake trunking, are drawn in and extruded, then trimmed with the fuselage skins and frames.
Another change of view, and switching a few layers on and off, we can start to see how the final structure might build up.
Next time, the wing spar and main undercarriage bays.
And a little taster of another project using a box structure rather than tubes.
Notes