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How To: Build Scale Models Using Foam

Before I start any scratch build model, I usually draw up a rough plan in CAD or computer-aided design as it helps with making the build a little bit easier. Although, at times I do love just winging it with some builds and just making things up as I go along. However, if I am going to be building scale ( stand-off scale anyway) models, they need to be reasonably accurate and well designed.

The CAD program I have been using to draw up my plans is a nice, simple and inexpensive version called ‘Total Cad 2D/3D’. This can be bought from Maplins or Amazon for the princely sum of £8.00 to £10.00. Total Cad does seem to work OK for simple plans and drawings and so far I have managed to design and build six or seven models using it without any major issues.

Below is the start of my plan for the Vickers Varsity that I have been working during the evenings.

The way I design my models might not be the correct way, but it has worked quite well for me this far. What I do first is to search the internet for a good three view of my chosen subject and then I import the picture into the CAD program.

After this, using red to enable me to see the lines I trace round the drawing, trying to be as accurate as possible. By using the layer set up you can then delete or hide the three view to leave the red outline behind. You can always bring the hidden layer back up if you have missed a line or to check that you have got the outline right.

Now, this is where it starts to get fun, you can now tidy up the outline and redo all the red lines in black. From this, we can move onto filling in the construction details in each section. If you do each section in a new layer, it makes it easier to separate the parts for printing. I tend to do the fuselage as one layer, the wings as another and the nacelles as a third.
I also use a fourth layer for all the odds and ends.

hobbyking scale models The image to the left is a basic wing design drawn out. Yes, I know that at this point I still need to draw up all the wing ribs and spars, but this gives you the basic idea of how to build the wing. Having some good pictures of the full-size aircraft helps at this stage, as you can use them to work out some of the shapes needed for the aircraft. After many hours of work and lots of coffee and head scratching, you should end up with a finished or nearly finished plan to build from.

The beauty with CAD is that if anything does not look right you can change it easily before committing knife to foam. Yes sometimes the parts you draw just do not look right when constructed, so the drawing will have to be altered to reflect this. But again I find this easier to do on the pc than with pencil and paper (well I think so anyway).

Once fully happy with the design I split the plan up into separate sections, ie:- wings, tail, fuselage ready for printing out. As I do not have an A0 printer I have to print my plans out on A3 paper using the tile print facility on my printer.

To do this I go into the print set up box and choose custom print, then I set the scale to 1:1 and can then print out the dozen or so pages needed for each section of the model.
The separate pages are then cut and glued together to make up the full-size plans and templates needed to enable me to start building.

To use the templates, I first cut round the part I need to cut out and then I glue the template to the Foam using a Prit Stic. You can then cut around the outline of the paper template to get the required part. If I need more than one of each part I will use the one I have just cut out as another template to cut round to make as many of the parts I need.


As you can see in the picture above when I build a scale/semi-scale model I cut two cores from 3 mm foam and then cut all the half formers from 6mm foam. These are then glued onto each separate core while it is held down flat to the building table, making sure that you build a left and a right-hand side (don’t worry I have built many wrong sides in my time).

Once all the formers are glued to the core, I then run a 6mm foam stringer down the side to hold it all together and keep the formers vertical. This also acts as a glueing surface for when we sheet the fuselage with 3mm foam later.

On the Varsity I sheeted part of the top of the fuselage straight away in order to give each halve enough strength to enable me to handle it without bending it. The main wing sits underneath the fuselage stringer so I have left the bottom open to enable me to fit the wing later.

On the Armstrong whitworth Ensign the wings sit on top of the fuselage, so I was able to sheet nearly all of the fuselage apart from where I have to make the removable sections needed to fit the wings and the flight battery. I have done this one in white 3mm foam as it will have to have a silver paint finish and white will cover better than the grey.

The next job is to join the two halves together and then set it aside while I construct the wings. To do this I use most of the wife’s clothes pegs and lashings of Uhu Por glue. The best way I have found to do this is to just simply smear Uhu Por over both joining surfaces and then just press them together. The pegs are there to hold it all square as the glue dries, do not use the glue as a contact adhesive when doing this job as it will grip before you have a chance to line the two halves up properly. Don’t ask me how I know this. (He he he)

On the big models, I use a different method as you need a bit more strength than this method gives you. Well on the smaller models most of the strength actually comes from the outer skin of the model and the internals are just there to give shape to the fuselage, but the large models need some extra strength as the foam skin is not quite man enough on its own. So on the larger models, I tend to use a 6mm foam cruciform construction for the central core.

You can see the 6mm foam cruciform core, the formers are all cut from 6mm as well. The stringers are all 6x6mm Balsa as this monster needs all the extra strength it can get. I cut oodles of holes in the internals to try and reduce the weight as much as possible while still keeping the maximum strength. I am aiming for a ¼ scale model that weighs under 25lbs when fully finished (fingers crossed).

To help keep the weight down I have been cutting lots of holes in the formers and cores. To do this I use a sharpened aluminium tube, I just place the tube against the foam and gently twist while applying some pressure. If you cut some small notches in the tube they will act as a saw blade and will help you to cut neater holes. I know that by cutting holes it makes the structure look weak, but in truth as long as the outer edges are intact the formers will retain their strength enough for general use.

Next time I will explore how to build and join the wings to the fuselage. In the meantime, below is a slideshow of every stage of the process.










Written by Tony Bennett


 

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