After looking at several possibilities for CAD software, it appears to me that the main criteria are:

• Online connection required or not
• 2D or 3D

2D or 3D

2D software is sufficient for existing (paper) plans, or simple designs. The main problem is that parts cannot be interpolated. Take a wing for example. If the wing is rectangular, we only need to draw/create a single rib and can then manufacture as many as we need. However if the wing is tapered in any way, it becomes necessary to create each rib separately which is a lot of work.

The same applies to the fuselage. If it has a lot of curves, things get messy in 2-d very quickly.

Hence my preference is for 3-D CAD software that is capable of interpolating complex shapes to arrive at rib, stringer and other complex shapes.

Online or stand-alone

It is a lot of work to create a 3D CAD software. And software companies face a problem: in order to exist, they have to keep selling software. But once a customer buys an application, how do you get the customer to spend money on an upgrade? While this may work the first few times, soon the application will reach a level that is sufficient for most users, any they will start to delay upgrading or foregoing them entirely. For this reason, software companies have switched en-masse to subscription services.

And since 3D CAD is complex, and rather a speciality, these returning fees tend to be rather high. Wel, high for incidental private use. For a company that uses CAD software a lot, it is still rather cheap. Sure, one can download a trial version, a ‘student’ version etc. But as long as we depend on an internet connection to have a working software, we are also at risk of suddenly being cut off. That is especially annoying if -after a couple of years- we suddenly need to access our old design again.

For this reason I have chosen for an offline, stand-alone 3D CAD application. In addition costs is an issue, I strongly prefer a freeware application. I am quite willing to pay something once I find the software really useful, but I first want to see how things work as I cannot see from the descriptions if the software will fullfil my needs.

I don’t know if there are many 3D CAD programs that are freeware, but the one that pops up almost immediately is FreeCAD. It is available for Windows, Linux and Mac (I use a Mac, but can also run Linux).

I have had a first go at it. And it is not easy ;-), i.e. one does need to read and follow instructions. I have now worked through two examples, but am not yet at a point where I feel capable of creating a design from scratch. At least the terminology is starting to become familiar.