I am currently designing an aircraft to compete in a competition with
a specific goal and the way I'm proceding is as follows:

1) Select a published airfoil with characteristics that meet the
design goal/s. Use a free program like xfoil to help in the analysis.

2) Create a spreadsheet to compute the mass of the various components
based on material densities which is then tied to the airfoil lift
coefficient and vehicle speed to size the wing. It will calculate the
required moment arms to keep the MAC, aerodynamic center and CG where
they should be in relation to each other and size the wing and tail.
The wieght can also tie to the aircraft performance issues important
to you to size the power requirement which determines engine weight to
loop back through the previous calculations with the weight
correction. You could carry it further to cover strength analysis.

3) Create a model in the 3d modelling software you have access to (I
used Solidworks) and import it into a 3d CFD program to verify the
validity of your design (I used Ansys). You could probaly get a local
university student to take care of this step for you for next to
nothing.

4) Build and fly the prototype.

5) Repair the prototype and make adjustments.

I saw no need to create an executable. The spreadsheet was fast and
easy to adjust as required along the way.
There are quite a few programs available to do this that are not very
expensive but I personally didn't care for any of the ones I saw.



On Tue, 25 Sep 2007 21:17:19 -0700, Le Chaud Lapin
wrote:

Hi All,

I have never really used a CAD program to design anything. I toyed
with AutoCAD back in 1987 but nothing more.

I'd like to design a small model aircraft, about one meter in length.
Even though it's small, it's still complex. There are many mechanical
pieces.

The most important feature I need, by far, is interdependencies of
paramters. [There is probably a fancy name for this]. In other words,
if I change an artifact of the aircraft from one material to the
other, I would like the change to manifest in every aspect of the
aircraft that depends on the material. I guess this is standard
feature. I would like to be able to program interelationships also,
preferrably in C++, but a scripting language will do.

The other important feature is that I need the tool to be "3D-aware"
from the outset. I'm hearing others in rec.aviation.piloting that
AutoCAD is not entirely 3D-aware. I don't know what that means, and I
am definitely not interested in finding out by trial and error.

I post to CCS because the presentation of SolidWorks on its website
gives me the feeling that they understand these issues and attacked
them head on, but any CAD package would do.

Finally, I prefer cheap over expensive.

-Le Chaud Lapin-