Editing Control line (section)

==Competitions==
Competitions for control line aircraft are held in various classes. These include speed, precision [[aerobatics]] (AKA stunt), team racing, combat, naval carrier, and scale.

For competition the lines are tested before flight with a "pull test" that varies with the model weight and category to verify that the lines and control system (primarily the bellcrank and its attachment to the rest of the model) will withstand the line tension during flight.

===Speed (F2A)===
[[Image:faispeed 2004wc.jpg|thumb|320px|A typical FAI {{convert|0.15|cuin}} speed model - with control lines stored on reel between flights. The very long inboard wing acts as a fairing for the control lines, greatly reducing aerodynamic drag]]
Speed is divided up into different [[engine]] capacity classes and a Jet class (using pulse jet engines). As the name suggests, the idea is to have the model go as fast as possible. The model is timed over a number of laps, and the pilot must hold the handle controlling his model in a yoke on top of a pole in the center of the circle. This is in order to stop the pilot from assisting the model to go faster by increasing the line [[tension (physics)|tension]] and leading the model (known as whipping). Monoline control systems are common in the US, but international classes require the use of two-line control. Speeds of the fastest models - Class D {{convert|0.60|cuin}} and Jet - have in the past exceeded {{convert|220|mi/h|km/h|abbr=on}}. Current US rules limit the speeds to <{{convert|200|mi/h|km/h|abbr=on}} by requiring the use of larger lines if {{convert|200|mi/h|km/h|abbr=on}} is exceeded. Speed models are usually launched from a "dolly" - a cart that permits a lengthy ground roll for takeoff, but drops away in the air to reduce drag. The airplane lands on a skid or belly pan.

===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.

==="Old time" stunt===

<!-- Deleted image removed: [[Image:ringmaster goldenstate.jpg|thumb|320px|'Ringmaster" Old-Time Stunt model]] -->Much like the "old timer" vintage design movement in [[free flight (model aircraft)#Old Timers|free flight]] aeromodeling, several specialized classes of Stunt include  "Old Time Stunt" where simpler maneuvers are performed with a model that was designed before a specific date (Pre 1953 per US rules) and "Classic" stunt which uses the current stunt "pattern" of maneuvers and airplanes designed prior to 1970.

===Racing (F2C)===
[[Image:tr pitstop muncie.jpg|thumb|300px|FAI Team Race model about to be caught by pit man during pit stop practice at the 2004 World Championships in Muncie, IN. Pressurized fueling tank with pressure gauge can be seen on the pitman's left arm.]]
Racing is an event for two-person teams—the pilot and the pit crew.  There are various racing classes of various levels of difficulty: F2C (the class flown internationally and at World Championships), Goodyear (semi-scale models of 'Goodyear era' full-size racers), Vintage classes and so on.

The basic idea of all the events is that a number of models (up to three) fly together, aiming to complete a given number of laps before any of the others. The model is also required to make multiple [[pit stops]] during the race, where it is refueled, the engine restarted, and the model re-launched.  This is the job of the pit crew.  There are rules describing how the pilots must walk around each other, and how to pass (harder than one might think, as each model is on the end of a pair of control lines and travelling as fast as 140&nbsp;mph). Pit stops require that the model be refueled and restarted - which can be a problem with a very hot racing engines. The best FAI Team Race pit stops take around 2–3 seconds for the pilot to cut the motor and land, allowing the pit-man to catch the model which only moments ago was flying at {{convert|140|mi/h|km/h|abbr=on}}, fill the tank with 7cc of model fuel from a pressurized tank, adjust the engine mixture and compression if needed, restart, and relaunch the model.

===Combat (F2D)===
[[File:CL Combat.jpg|thumb|Denmark versus Australia at the Danish Combat World Cup 2008]]
[[File:CL Combat Launch.jpg|thumb|Mechanics launch an F2D combat model]]
Combat is an event where two pilots "dogfight" for cuts on their opponent's streamer, for a perscribed amount of time called the "Match". Models are fast and highly maneuverable typically of flying-wing types, which chase each other around the sky at speeds in excess of {{convert|100|mi/h|km/h|abbr=on}}. Despite deliberate mid-airs being banned, the carnage rate is high, and pilots commonly bring 10 or more models to a competition.

In the US there are three A.M.A. Events, which are Fast Combat (up to a .36 c.i.d. engine is allowed), Speed Limit Combat and 1/2A (up to a .051 c.i.d. engine is allowed) Combat which can be flown high or low performance.  In any event where the model exceeds 75&nbsp;mph, the model must be equipped with a fuel shut-off, which shuts the engine off, when the control lines are cut. Combat may be held as a kill event, or a no-kill event.  A kill is scored when one competitor cuts the string that holds the streamer (of his opponent), to the plane, and is an instant win of the match. Cutting the streamer however results in an award of points.  In No-Kill combat cutting the string is the same as cutting the streamer and only points are awarded. There are a lot of unofficial events held throughout the US, such as Northwest 80&nbsp;mph Combat, WWII combat, Formula GX Combat, 15 Fast and the like.  Combat requires perhaps the fastest reflexes of any CL event, and pilots skilled at combat typically compete well in other events like Stunt or Racing.  Combat has been described as a team sport, with the pilot relying on up to a two-person pit crew. As may be imagined, with two pilots not cooperating with each other, line tangles can happen suddenly, and crash landings are common. Despite the high speed of the models, most combat models are made to be quite robust, and when time allows may hit the ground and suffer little damage and be relaunched.  Although for the Speed limit events up to a .40 c.i.d. engine may be used, for the AMA fast event, there is only one manufacture of a high performance .36, that being Henry Nelson.  A well-tuned and fueled Nelson 36 may achieve 25,000 r.p.m. while statically running on the ground and gain significant r.p.m. in the air.  Current 1/2A engines in use are all from former soviet republics and include the Fora and Cyclon, both of which will run well above 33,000 r.p.m.  In all the AMA events pressure fed fuel systems are allowed and virtually every combat plane is equipped with a fuel "Bladder".  The Fuel Bladder gives the most consistent fuel feed while the aircraft is undergoing sudden and violent maneuvers, typical of flying in a match.

'''F2D combat''' - the international class for combat - is most popular in Russia and Europe, where some countries have professional or semi-professional teams. Russia and the former Soviet countries are currently the main producers of world-class equipment for this sport, including engines. Their combination of the latest engineering and design, with exotic metallurgy and experience, results in combat engines which reliably turn 32,000 rpm, and can be restarted easily in the event of a crash. Requiring lightning-fast reflexes, combat has frequently been used as a training-ground and/or hobby for many commercial and military pilots {{citation needed|date=September 2020}}.

=== Diesel (F2E/F2F) ===
'''F2E diesel combat''' -

'''F2F diesel team''' -

=== Electric (F2G) ===

===Navy carrier===
<!-- Deleted image removed: [[Image:trostle bearcat lowspeed.jpg|thumb|320px|A "Bearcat" Navy Carrier model built/flown by Keith Trostle, with [[Flap (aircraft)|flap]]s deployed and [[tailhook]] extended in low-speed flight]] -->
Navy carrier is an event where semi-scale models of real [[Naval aviation|naval aircraft]] are flown. The event replicates the requirements of full-scale [[Carrier-based aircraft|carrier aircraft]], which need high speed for combat performance, and low speeds and toughness for safe carrier landings. Takeoff and landing are from a simulated [[aircraft carrier]] deck, with [[Arresting gear|arrestor wire]]s.

The aim of the flight is to complete a number of fast laps, flown as quickly as possible, followed by a number of slow laps, flown as slowly as possible. This is followed by the carrier deck landing, attempting to snag the arrestor wire. The score depends on the difference of the high and low speed, and the arrested landing. Carrier models usually have a third control line, worked by a finger trigger in the handle. This line allows the throttle setting of the engine to be controlled and the arrestor hook to be dropped. Often, a carrier model will have flaps. Unlike a stunt model, however these flaps are worked separately from the elevator. A large amount of flap is usually applied during the slow laps, and a large amount of line sweep is added to yaw the model out of the circle to maintain line tension at the very low ground speeds. Low speeds are frequently no faster than a fast walk, and when aimed into a light breeze forward motion may stop completely with the model hanging at a very high angle of attack from the propeller.

===Scale===
Scale is an event where an accurate scale model of a real aircraft is flown. Scoring is based on static judging of how closely the aircraft resembles the full-size prototype and on the flight performance. Extra points are often awarded for "working" features of the model, such as a retractable landing gear, droppable bombs, and other functions or operations. The number of features used to be limited by the number of lines that could be practically used to mechanically control them.

Some complex scale models use a fly-by-wire approach to allow a multitude of extra working features. A radio-control transmitter's encoder unit can be adapted, with no RF signal board present, to send its control signals along insulated control lines, instead of broadcasting them using radio frequencies. If signals are sent down the lines, the normal serial multiplexing of the control signals by such an adapted RC transmitter's encoder unit, solely sending those signals along the usual duo or trio of control lines, gets picked up by decoding gear in the model - usually adapted from an RC receiver, without an RF "front end" section - and permits many functions to be controlled without the use of additional lines. Standard [[Servomechanism|servo]]s can then be used in the model. From 2013, in the USA, the radio control "over the airwaves" of any moveable feature of control-line Scale or Carrier models (except the elevator) is permitted - this may spread to Europe and beyond in time.