This is a new sticky FAQ thread to post up links to various online calculators, simulators and other online software tools that can be used to explain principles or calculate aerodynamic design factors. I'll edit this post to include all links as they come up to save users from wading through all the posts. Headings for some but not all categories are shown below and the links along with a short description are posted under the headings. If you have suggestions for other heading topics please post.

Bring 'em on folks!
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Airfoil analysis and airflow simulation:
http://www.grc.nasa.gov/WWW/K-12/airplane/foil2.html - Foilsim, a simple airflow simulator. Let's you play with camber, AoA and determine the Cl of your basic design size and speed. Very educational - BMatthews

CG calculators:

MAC (Mean Aerodynamic Chord) calculators:
http://perso.wanadoo.fr/scherrer/mat...glish/mce.html - multi panel entry allows more complex shapes -Tall Paul

Tail Volume Coefficients- Horizontal and Vertical: