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Old 10-09-2019, 03:35 AM
Diderick A. den Bakker's Avatar
Diderick A. den Bakker Diderick A. den Bakker is offline
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Join Date: Jul 2009
Location: Zeist (near Utrecht), Holland
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scon10: not really, but we are making progress!
We have now reached the most difficult stage of the design:translating the curved surfaces of the 3D drawing back to 2D, flat parts.
If you have lost touch, go back to the explanation about single curved parts and double curved parts.
For single curved, just imagine the simple parts of the fuselage - all are just elements of a simple tube or cone. It is the parts where the designer has to suggest a double curve by adding cuts (or 'darts') that are most difficult for the designer: the darts will allow the builder to approach the correct shape.

Study the first picture. The meshes come straight from the 3D picture; the more lines, the sharper the curve.
Concentrate on the cockpit roof. It has been cut in two - the finished part will later simply be mirrored.The second picture shows how the mesh works. Picture 1 is just the 3D shape, broken up (or down?) into flat rectangles, which when folded along all the lines will give a fair impression of a double curve. The narrower each rectangle, the stronger the curve.

Now imagine flattening (unfolding) that shape by just pushing it down on a flat surface - you will realise this will result in at least a few tears in the paper. It will be strong enough to survive very slight curves (in other words, you will manage to mage a light double curve by making use of the elasticity of the material - experienced builders will use a teaspoon for this).
This is what the computer does in the second mesh. It marks the areas which will need shaping with a diagonsal line; the smaller these areas, the stroger the curves - and the need for cuts becomes visible.
Enlarging this ad lib will show how wide even the small tears will have to be. The last picture shows where the designer has to make a cut (appropriately called a dart in dressmaking - ask you wife).
So as I explained before, the more lovely aerodynamic curves a plane has, the more work for a designer. I expect that explains why our Skymaster is not yet appoaching Schiphol...
Attached Thumbnails
Douglas DC-4 / C-54 for Paper Trade: Berlin Airlift.-21-elementgroepen_cockpit.jpg   Douglas DC-4 / C-54 for Paper Trade: Berlin Airlift.-22-unfolding_practice_1.jpg  
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