Allowable Aircraft Designs

[Tom Speer]

I'm new to RC flying and want to get into aerobatics. My club is pretty much all sport pilots, but I want to have more purpose to my flying than just randomly flying in circles. Although I'm unlikely to ever enter a contest, I want to learn aerobatics correctly from the start and to have a plane that could potentially participate in a contest. At the same time, I'd like to fly something that is not just another Extra or Yak. To me modern IAC planes have converged to the point that they all look much the same, so I want to consider a wider range of designs.

Section 3.1 of the rules says the planes must be, "replicas of types known to have competed in International Aerobatic Club (IAC) competition, or replicas of types known to be capable of aerobatic competition within the airspace known as the “Box.”" Just as an example, say I wanted to fly a fighter replica instead of a plane designed for aerobatics. Something like a P-51 would not fit the rule because while it is fully aerobatic, it is too fast to be able to stay in the Box. But a fighter from the Golden Age, with its slower speeds, could have been capable of both the maneuvers and staying in the box even though it was never used in IAC competition.

Would such a plane be legal to enter the Sportsman class?

[Dave Dupre]

Very interesting question. The usual rule I hear is that the design actually flew in an IAC competition. You can fly anything you want in Basic, including a P-51. However, for any class from Sportsman on up, it has to be a design that is legal for full-scale IAC competition (within 10%). Usually, if you can produce evidence that it flew in an IAC competition, then you're good. Now, if you showed up with a scale Sopwith Camel, I'm not sure what a CD would do. Obviously, it is a scale aircraft capable of IAC competition, but I don't think it was ever flown in IAC.

If you want to get away from the usual Extras, there are many options:

Pitts Special
Pitts Model 12
Christen Eagle
Decathalon
Many variants of Cap monoplanes
RV-8
Piper Cub
Stearman
Bücker Bü 133 Jungmeister
Yak-52

As long as it has 1 single propellor motor and no retracts, you should be good. Does need to be within 10% of scale, but that does give some wide latitude. The 10% rule is tough. It we got really picky about it, I venture to guess that many ARFs would not qualify.

[Wayne Matthews]

Just two corrections to the above post that will throw some light on the original question.

1) Here is the actual rule from the rulebook: 3.1: The events accommodate aerobatic monoplanes and biplanes which are replicas of types known to have competed in International Aerobatic Club (IAC) competition, or replicas of types known to be capable of aerobatic competition within the airspace known as the “Box.”
3.2: All classes except Basic require that the pilot must meet the requirements defined in Rule 3.1. The Basic Class is open to all competitors with a monoplane or biplane aircraft. There is no minimum size requirement for any class. Contest Directors may make an exception for a model of a full scale aircraft that was built for IAC competition, but has not yet competed. Proof of the latter is the responsibility of the contestant.

2) There was actually an aerobatic aircraft that was built for IAC competition that had retracts....Hence, it is a model that can be flown in IMAC legally, with retracts. It was a Staudacher S300 registration N126RG. A photo of it is shown below.
Wayne

[David Pierce]

I wrote IAC a couple years ago for a record of planes that had competed. Their records aren’t complete as they will tell you. But the list above covers the ones they have records for.

[Dave Dupre]

I need to look in the rules again, but I thought I saw "no retracts" in there somewhere.

[Dave Dupre]

Read the rules again. Nothing in there against retracts. I must have confused our rules with those from pattern.I

I guess that means you could add a Dalotel and a Super Chipmunk to the list of allowed designs.

I’m still a little confused by the rules since they sort of contradict themselves.

3.1: The events accommodate aerobatic monoplanes and biplanes which are replicas of types known to have competed in International Aerobatic Club (IAC) competition, or replicas of types known to be capable of aerobatic competition within the airspace known as the “Box.”
3.2: All classes except Basic require that the pilot must meet the requirements defined in Rule 3.1. The Basic Class is open to all competitors with a monoplane or biplane aircraft. There is no minimum size requirement for any class. Contest Directors may make an exception for a model of a full scale aircraft that was built for IAC competition, but has not yet competed. Proof of the latter is the responsibility of the contestant.

Rule 3.1 suggests that the plan is “capable” of aerobatic competition within the airspace. Rule 3.2 suggests that the design must have flown in or expected to the flown in IAC. Which is it? A scale aircraft capable, or a scale aircraft that has competed in IAC?

[Tom Speer]

Yes, that's my question. The intent is for models of airplanes that have flown in IAC competition. But that's not what the rules say.

So what does it take to be capable of competition within the Box? The full-sized plane needs to be stressed for substantial positive and negative g's, control power adequate for abrupt maneuvers, and a wing loading low enough that it can do the maneuvers within 1,000 m horizontal and under 3,500 ft vertical. Wikipedia has a list of aerobatic aircraft. Many would fit the definition of the rule, although some would not. The Super Tucano is a good example - it's fully aerobatic, but I doubt it could stay within the IAC Box. And I suspect the majority of planes on the list were never used in competition.

I don't see any restrictions on the aircraft in the IAC contest rules. Since the IAC is a division of the EAA, it would make sense that they'd allow just about anything a competitor can dream up or modify from a production aircraft.

I think the second phrase of 3.1 is the primary criterion - a known type, capable of competing in the Box. The first phrase, concerning types known to have flown in competition, seems to be aimed at the "known to be capable" part of the second phrase. If a plane has competed, then it has satisfied the known to be capable requirement. If it's never competed, then it could be debatable as to whether or not it was capable.

I don't see any reason why Dave's Sopwith Camel example wouldn't be perfectly acceptable.