RE: Difference between IMAC and Pattern
I'll take a quick stab at it...
The main difference is in the upper classes.
In Basic (IMAC) or Sportsman (NSRCA or Pattern) you can fly any plane that is AMA legal. So the difference for the newbies is very minor and is seen in the sequences and the box (Manuevering area). Now this is a very minor difference as the same maneuvers are flown in both IMAC and Pattern.
At the second level Sportsman (IMAC) and Intermediate (NSRCA-Pattern) it starts to become different. The game is still similar in that you fly the plane through a series of sequences and you are judged on how well you perform them. Here are some of the differences. The higher you go in each class the more challenging the sequences. The basic set of rules apply to all classes.
Here are the main difference:
Planes...
IMAC - Any plane that represent a competition full scale aerobatic plane within 10% scale. Weight must be within AMA rules. IMAC planes normally have some level of coupling in control surfaces because of the design requirements. I believe some designs are getting close to purpose built Pattern planes.
Pattern - Any plane that is 11 pounds or under, and the wing span and length is not more than 2 meters. In the lower classes the pilot skills will have more bearing on the scoring than the plane itself. In the upper classes (Advanced and higher) the pilots skills are closer from pilot to pilot and the purpose built 2M Pattern plane will start to serve it's purpose. The purpose built Pattern plane is designed to fly very nuetral (little to no coupling). A good plane in bad hands still flies poorly...Don't ask me how I know...
Cost...
Very close at each level. you can spend a little or go full blown with similar cost in both.
Plane Set up...
It is the same for both, use the same trim methods for both. If not trimmed well, both types of planes will not fly well. If trimmed properly, the difference in feel will be minimal between the two.
Contests...
Both are very similar but each have there own rules with regard to the sequences and manuevering area or Box. Having competed in both at the lower level, I got the same feeling and were ran very similar. Some pilots fly both.
In summary, both are very rewarding and it becomes a personal preference. Both styles of planes will draw attention at the flying field when you enter contest and watch your skills improve.
My recommendation is take your favorite aerobatic plane and attend both types of contest. You will have someone there willing to help you. Then decide which way to go.
Conclusion...If anyone tells you one is better than the other, and eventually someone will, they have probably not flown the other type. It is really what you prefer....For me, I enjoy both...Basic in IMAC and Intermediate in Parttern.
Don't know if this helps you, but good luck and go find a contest...It's shouldn't be legal to have that much fun...
Larry Diamond
AMA 5024