Control line
The origins of control-line flight are obscure, but the first person to use a recognizable system that manipulated the control surfaces on the model is generally considered to be Oba St. Clair, in June 1936, near Gresham, Oregon.
[3] One of the most coveted prizes in control-line aerobatics competition sanctioned by the AMA, awarded to the winner of a flyoff between the US Junior, Senior, and Open age class Champions, was originally provided by and is named for Walker.
They are typically built with traditional materials like balsa wood, plywood, paper, plastic, spruce, and polystyrene foam, but modern composite and graphite/epoxy are occasionally used in high-load applications.
Racing models need to be both relatively light for good acceleration from the start, or after a pit stop, and to reduce the pitch of the airfoil required to maintain lift.
By convention, tilting the hand so the top is closer to the pilot than the bottom results in "up" elevator, much like pulling back on a full-scale airplane control stick.
Flying clockwise has a slight advantage in some situations because most engines run so that the torque will roll the airplane away from the pilot, increasing line tension in upright level flight.
Other control methods were devised early on to avoid having to pay royalties on the "U-Control" patent, including systems with the lines connected directly to the elevator with pulleys to change the pitch, methods that connected the lines directly to the pushrod through screw eyes, but most worked very poorly compared to conventional 2-line control.
Control line models tend to run a varying mix of fuel however 10% nitromethane, 20% castor oil and 70% methanol is common.
Some older-technology engines commonly used for control line can be very quickly damaged with typical R/C fuels because of low oil content.
The spark box and air source are disconnected and then model launched as quickly as possible to prevent the heat generated by the engine from causing the airplane to catch fire.
The propellers used for control-line models are commonly made of wood (usually maple), fiberglass-reinforced plastic (GRP), or graphite/kevlar/fiberglass and epoxy.
The high pressure of fuel delivery permits the use of a larger intake on the engine, allowing more air flow than would otherwise be possible, and thus more power.
Most speed and combat models omit the landing gear in the interest of drag and weight reduction, and are launched from hand or a "dolly".
These include speed, precision aerobatics (AKA stunt), team racing, combat, naval carrier, and scale.
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 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 55–60 mph (89–97 km/h), with a single lap of the circle taking around 5.5 seconds.
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.
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.
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 mph).
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 100 mph (160 km/h).
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.
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.
Extra points are often awarded for "working" features of the model, such as a retractable landing gear, droppable bombs, and other functions or operations.
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.
The lines, handle, and control system are subjected to a "pull test" before flight to ensure that they are in good shape with some significant margin.
Other categories of model are tested in a similar way, with the loads set to correspond to the expected speeds with a safety margin around a factor of 4.
Most combat competition today requires that the airplane be equipped with a device that shuts off fuel to the engine if the lines are cut.
Sometimes models with landing gear are flown by using a "stooge" that holds the airplane until released by the pilot from the center, usually with a spring-loaded pin pulled with a string.
A starting accident frequently results in a small cut to the finger, but once the engine is at full speed any injury that is encountered is likely to be quite severe.
