Editing Control line (section)

===Precision aerobatics (F2B)===
Precision aerobatics consists of flying a fixed sequence of [[Aerobatic maneuver|maneuver]]s which are judged by a panel of judges for accuracy and precision. The event was originally dubbed "stunt" and current participants refer to it that way informally. Factors such as height of the maneuver bottoms, shapes, corner radius, and other factors are considered.<ref name="modelaircraft.org">{{Cite web |url=http://www.modelaircraft.org/files/events/CLAero.pdf |title=Archived copy |access-date=2009-04-24 |archive-date=2010-11-26 |archive-url=https://web.archive.org/web/20101126235403/http://modelaircraft.org/files/events/CLAero.pdf |url-status=dead }}</ref> The judges at large competitions are typically trained for several days on how to assess the maneuvers and apply a score. Judging well is generally considered at least as difficult as flying in competition.

Stunt models tend to be among the larger control line models, wings usually spanning from around {{convert|45|-|60|in|m}}. Top competition models have been traditionally powered by a two-stroke engine in the {{convert|0.35|cuin}} to {{convert|0.60|cuin}} range, with [[Four-stroke engine|four-stroke]] model engines and electric power also becoming popular as power sources. The airplanes, while possessing high thrust-to-weight ratios by full-scale standards (usually at least 1:1), are intended to fly quite slowly to enhance pilot control, typically around {{convert|55|-|60|mph|km/h|abbr=on}}, with a single lap of the circle taking around 5.5 seconds.

Engines are commonly set to increase their power output when under load. This permits low speeds but very good speed stability, so the climb performance is excellent. The original scheme used was to take advantage of the tendency of a nominally two-stroke glow engine to change from running in a four-stroke when set with extremely rich mixtures, to running in a two-stroke when the load increases.<ref>Bair, Scott: "The Two-Cycle Stunt Engine" monograph circa 1984, published in "Stunt News" circa 2000</ref> This is called a "4-2 break". More recently, tuned exhausts have been used to provide regulation of the speed in flight. Combined with propellers of relatively low pitch, this has permitted much more control over the engine's speed and power response to maneuvering. Electric system contain feedback control system that govern the RPM of the motor to a constant value regardless of load.

Most competitive aircraft are fitted with flaps on the wings, which work in conjunction with the elevator to increase the pitch maneuverability. When up-elevator is applied, the flaps on the wings go down, and vice versa. This results in the wing, which is otherwise of a symmetrical section, to be cambered in the direction needed to enhance maneuvering. Aircraft without flaps can be flown successfully and are typically simpler, but flapped models typically fly more smoothly and can be heavier. Some of the simpler stunt models make excellent control-line trainers, as the predictable control response, low speed, and strong line tension make them easy to fly successfully.

[[Image:zealot inflight big.jpg|thumb|320px|2008 Concours d'Elegance winner - Phil Granderson's "Zealot". The model received a perfect score in appearance judging.]]
Stunt models are often beautifully painted. Stunt rules include the appearance of the model in the score, and creating the most perfectly finished and attractive models is a competition in and of itself. A "Concours d'Elegance" award is voted on by the pilots at the [[Academy of Model Aeronautics]]' US Nationals in [[Muncie, Indiana]] for the prettiest airplane, and is very highly prized.

Stunt is flown in many countries, with World Championships being held on alternate years. These are open for any flier who makes his or her respective national team. Competition at the highest levels (National or World Championships) can take many years or decades of practice to master the intricacies of designing, building, finishing, adjusting, and controlling the power of the airplanes, in addition to the high piloting skills. Many top competitive pilots have coaches.

Many competitions separate pilots into 4 different skill levels (beginner, intermediate, advanced and expert) allowing pilots to compete against other pilots of similar skill levels.