I just started reading a book called Radio Control Model Helicopter Handbook. Its a bit old, but the physics of how a rc helicopter flies doesn't change too much over the years. Anyway there are 2 words/terms, so far, that I don't understand.
1. Chord
ex in book: There are very sofisticated mathimatical equationswhich would show that the spanwise distrobution of lift for our untwisted constant chord rotor blade would look something like fig ....

2. NACA
ex in book:So what kind of airfoil do we look for? In general the classes of airfoils that meet the above requirements are (1) the semetrical sections including the NACA (00) series (0012 or 0015) or the NACA (230) series (23012 or 23015)......... and what do those numbers signify?
Also if you know of a website with these & other helicopter terms let me know, so I don't have to keep bothering you guys when reading this, technical, but very interesting book.
Thanks!
Joe

http://www.net-express.com/nexus/glossary.html
All the terms you need

That's Great! Thanks very much! Bookmarked

First, the chord of an airfoil is simply the straight line distance from the most forward point of an airfoil (leading edge) to the most rearward point (trailing edge).

Now on to the NACA airfoil numbering scheme... The numbering scheme specifies an airfoils key characteristics.

For example, the 1 series NACA airfoils are designated with 5 digit numbers. The first number is the series number (1 obviously). The second number indicates the distance (in tenths of chord) from the leading edge to the point of minimum pressure (with the section at the zero lift angle of attack). The next number (usually following a dash) indicates the design lift coefficient in tenths and the last two number together indicate the total thickness of the section (again as a percentage of the chord).

So, if you had a NACA 16-212 wing section, and the section chord was 1 meter, the point of minimum pressure would be 0.6 chord lengths behind the leading edge (60 cm), the design lift coefficient would be 0.2 and the maximum thickness of the section is 0.12 chord lengths (12 cm).

The other airfoil series' numbering conventions follow some of the above with some variations (gets more complicated).

Thanks! That's what I thought, but wasn't sure. In the book they show a straight line through the rotor blade

U R DA MAN! Thanks very much for the explanation!

Joe