Safety
Control-line flying is generally quite safe when all prescribed safety measures are followed. The airplane is constrained to fly in a circle, which is generally marked. A pilots' circle is also provided, so as long as the pilot stays in the pilot's circle and everyone else is outside the outer circle, it can hit no one. In most competition categories, a "safety thong" connecting the control handle to the pilot's wrist is also required, so if the pilot inadvertently releases the handle, the airplane cannot fly outside the circle (and, frequently crashes, safely for others if not the airplane, when control is lost). 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. For example, the pull test is around 40 lb (18 kg) for a 4 lb (1.8 kg) Stunt model (a 10G load), and the in-flight pull is around 10 lb (4.5 kg). This provides a 2x margin of safety even if one line should fail. One failed line immediately moves the elevator to the extreme of its movement, which almost always results in a crash but safely in the circle. Other categories of model are tested in a similar way, with the loads set to correspond to the expected speeds with around a factor of 4 margin.
Combat models, albeit very rarely have their lines cut or otherwise broken by the other airplane, and can fly outside the circle. 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. This can work by either using the centrifugal force to keep the shutoff from pinching the line, or by using the line tension to hold the pinch-off device open. This way, the engine is not running and tends to decelerate very quickly instead of accelerating quickly (since the drag of the lines is removed) as it would otherwise. This technique has proved to be very effective in practice. Many combat events also require the engine to be attached to the bellcrank with a cable, so that a mid-air collision will not result in the engine flying off and into the spectators. Competitors in some forms of combat competition are also required to wear helmets.
Another potential safety issue is overhead power lines. Contact with power lines, or approaching high-tension power lines, is potentially fatal and has caused several deaths.
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. This allows a pilot to practice with no helper, and is common with stunt fliers trying to practice extensively. This has the potential to be dangerous if the pilot fails to properly reset the stooge, the wire connecting the stooge to the airplane (usually attached to the tail wheel) breaks, the stooge moves under the thrust/vibration of the engines, or the pilot's feet get tangled in the stooge release line. If anything does go wrong, and the pilot is injured, there is no assistance.
The other safety issues are common with other powered model categories. Hand-starting very powerful engines as used in stunt, with very sharp propellers, can be quite hazardous if proper precautions are not followed. The use of an electric starter can help in some cases, but other hand-starting methods are reasonably safe. One such method is the "back-bump" method, where the engine is choked and flipped through with no battery attached to create favorable starting conditions. Once prepared, all that is necessary is to rock the engine backwards so that it coasts up to compression, and if done correctly, starts forwards. This provides time to move the hand out of the way and the fingers are not in contact with the propeller or spinner when the engine starts. Care must be taken even choking the engine as modern engines with their excellent piston/cylinder fit can "bump" or even start without the battery attached. Once the engine is running, extreme care must be taken when preparing for flight and adjusting the engine to not allow any body part to get into the prop disc. 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.
Pulse jet engines get extremely hot once started, and use very volatile fuels like gasoline or methyl-ethyl-ketone (as contrasted to relatively benign, although flammable, glow engine fuel). Contact of any type with the tailpipe of the engine is certain to result in severe burns, as the engine reaches red-hot temperatures in seconds. The airplane itself needs some sort of insulation to prevent catching fire on the ground before forward motion provides cooling air, and fully enclosed engines can set the airplane on fire after landing. The airplane should be launched as soon as possible after the engine starts to prevent heat-buildup. The spark unit used for starting can also deliver a substantial electrical shock. Extreme care should be taken and a fire extinguisher should be at hand at all times when operating the engine. The engine is exceptionally loud when operating and should be operated with hearing protection to prevent damage.
Read more about this topic: Control Line
Famous quotes containing the word safety:
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—Lewis P. Lipsitt (20th century)
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—Gerald R. Ford (b. 1913)
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—Roger Gould (20th century)