Both IMAC & NSRCA fly precision aerobatics competitions. The big difference is in the planes they fly. IMAC planes are scale (more or less) models of full-scale aerobatic planes--Extras, Sukhois, CAP's, Staudachers, etc.--"real" airplanes that have a human pilot sitting in the cockpit. Go to an IMAC meet and you will typically see gas powered 1/3 scale models weighing from the 'teens on up to 30 pounds and more.

Pattern (NSRCA) planes are not scale models of anything, but a design class unique to pattern, aimed at neutral trim and coupling to make them well-behaved in maneuvers. The model is limited by FAI rules to a two-meter span and two-meter length maximum, with a five kilogram weight limit. Most planes you'll see at a meet are close to these limits, although state-of-the-art composite materials can sometimes get the weight close to 10 pounds (5 kg = 11 pounds). They're powered typically with YS 4 stroke 1.40 engines, or with piped two-strokes in the 1.40 to 1.70 range.

Most of the maneuvers are the same between IMAC & NSRCA, although they may go by a diffferent name. There are fine points of difference in judging criteria, but on the whole both groups stress perfect geometry in maneuvers, smooth transitions from one maneuver to the next. Their schedules--the string of maneuvers to be performed in each class of competition--are similar but different, mostly made up of the same individual maneuvers, strung together in unique sequences.

Back in the days when the Bridi Chaos was the hot plane, pattern was popular and flown 'everywhere'; but pattern has shrunk over the years as the planes have become more expensive. I believe I saw a figure recently to the effect that there are maybe 400 active competitors flying pattern these days in the U.S.

IMAC on the other hand seems to be booming. The ongoing improvement in light & powerful gas engines and the wider availability of well-designed and constructed 1/3 scale ARFs has made it easier to break into formerly more exclusive IMAC competition (although these planes can be even more expensive than pattern models, especially as the size goes up).

Which is "better" is pretty much a matter of personal preference. Some fly both, but if you're driven to win your class, the level of practice and dedication required will typically drive you to one or the other. Personally, I have total respect for a good flyer in either category, especially for those who build what they fly. If I had to decide which way to go, I'd lean in favor of where I could get a good coach, accessiblity of practice fields, calendar of competitive events within easy travel distance, community of other flyers on whom I could depend for assistance and sharing knowledge.

You don't have to spend big bucks to sample the thrills of either style. You can compete in the entry-level class in either group with a .40-.60 sized ARF or kit-built, and fly a season or two with almost any model that can do loops and rolls. You'll find both groups welcome new members, happy to give advice on equipment & set-up. Finding a coach/instructor/mentor is to me the key to success, just as it was in breaking into radio control at the basic trainer level. Go to meets. Talk to people. Ask for help.