Troy,
Greetings and welcome to RC Universe and RC as well.

IMAA is an organization that promotes fun flying of giant scale model aircraft. The minimum size for a monoplane is 80" wingspan and 60" for a biplane. True 1/4 (quarter scale) is also allowed by the rules so an Extra will make it in at about 73" or so. Most flying is done with much larger aircraft however. See the website http://www.fly-imaa.org/index.html

You wrote 12A size in your question.
Do you mean 1/2A (normally referred to as "half A")? If so this means planes that are of a small size and use engines in the 0.049 ci range of engine displacement. In the airplanes discussion form see the following: http://www.rcuniverse.com/forumdispl...s=&forumid=161