Pattern rules require staying within 2 meters span and length, 11 lbs in weight. The only place they typically measure and weigh is at the Nats though. The airplane should be reasonably quiet too: 96 db at 3 meters. Again, I've only seen it measured at the Nats, but if you are blatantly loud, you will no doubt raise some eyebrows. Pattern airplanes are notoriously quiet and if you're obviously too loud, someone could easily challenge your entry.

Actually, there are several key differences between Precision Aerobatics (AKA Pattern) and Scale Aerobatics (AKA IMAC). In IMAC, although there is some description of a box of a certain depth, height and width, it does not exist for all practical purposes. That is because IMAC eliminated the 75 degree boundaries on each side and also dispensed with the concept of zones. Formerly, you could be penalized for box violations with anything ranging from a loss of points if the offending figure was partially outside, to a zero if it were entirely outside of the box. Zones were used as a way of framing the sequence, in particular for center zone figures. IMAC also dispensed with center zone centering points deductions. It used to be that your center zone figure had to be, well, centered in order to earn all the points possible. That is no longer the case. One last thing, IMAC also added something called a Presentation Score, which effectively is another 'figure' from a scoring standpoint. The judges will arbitrarily assign a presentation score after the sequences is complete. No one has ever been able to define how to objectively arrive at a score, so it's not something you can really practice for or predict. You get what you get based on each judges personal notion of what a presentation score should be. I'm not sure of the current status of the presentation score. It's been on again, off again. In 2003, IMAC was trying to force its use before it officially became a rule in 2004, then advised not to use it after it was official. Very confusing. It's still on the books, so I don't know what you can expect to run into for 2006.

Anyway, in Pattern, there is a box, 60 degrees each side. You get downgrades based on the percentage of the figure that is outside of the box, plus other normal downgrades. There are three zones and in the true spirit of flying precision aerobatics, you get downgraded if center zone figures are not centered. In other words, you are expected to exhibit control of where the model is when you perform the sequence and you get objectively downgraded if you dont do it as wel as the other guy.

There are other key differences, such as the use of 1 point per 15 degrees of error in Pattern vs. 1 point per 10 degrees of error in IMAC. No unknowns in Pattern, except in certain circumstances in FAI Pattern, such as the Precision Aerobatics World Championships. Another key difference can be noted in sequence design and in how often sequences change. IMAC changes sequences every year, Pattern changes every two years. IMAC sequences are very short these days, typically only 10 figures, whereas Pattern sequences are around 20 or more, depending on class. IMAC sequences place alot of emphasis on high K factors for each figure, especially in the upper classes and do it mostly by sprinkling snap rolls liberally into the figures. In pattern, the sequence design emphasis is much more oriented towards geometric design and flow. It is often said that Pattern sequences are easy to fly, but hard to fly well and it is true. IMAC sequences are generally harder to fly and are even harder to fly well. They are also much harder to judge objectively and in my opinion anyway, harder to objectively arrive at who the best pilot was.

Last thing, though it's not in the rules, you typically wind up in an equipment "arms race" from the very beginning in IMAC. It is very common to be competing against 35% to 40% models in Basic. In Pattern, though you can also spend a boatload of money on equipment, you don't need to overspend to get a size advantage. 2 meters is the limit in every class and even a good .90 size model is very viable in Sportsman. In 2004, our D1 Sportsman champion flew a .60 Kaos. That kind of equpment won't cut it beyond Sportsman, but you can be extremely competitive all the way through Masters with a $450 ARF and a $250 engine with a $60 pipe and a $40 header.