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- The triangle control frame (TCF), similar to the A-frame, is widely used in hang gliders, powered hang gliders, and ultralight aircraft. TCF is just one of many sorts of control solutions. TCF resolves a means of using weight-shifting attitude control in parasol aircraft. Also, a large use of the TCF in aircraft has been the holding of landing wheels and bracings for the wings. Flying like a bird has become possible and practical partly because of the isosceles triangle. Beginning with Abbas Ibn Firnas and Leonardo da Vinci, the triangle played a role in the control of flying machine experiments. The vast majority of modern hang gliders, and foot-launch powered hang gliders (FLPHG) use a triangle control frame (TCF) to help control the flight experience during gliding and soaring. Aircraft that are towed, onboard powered, or used in gliding-or-soaring-unpowered mode have structures and airframes that allow successful flight, controlled flying, and takeoff and landing mechanisms. A nearly ubiquitous elementary truss or triangle has found its way into airframes in a very strong way, when it comes to control, safety, flight performance, economical construction, handiness, and even aerobatic flying. TCF disadvantages and advantages both lead to a culture of TCF improvement. Beginning as the most simple truss, the TCF evolved its place in aviation through experiments, use, and commercial competition. The design and use of particular TCF affects points won in sport competitions. Pricing varies from pennies for three bamboo sticks to several hundred dollars for yacht-level design and quality. The most elementary simple truss - the single triangle - stayed in aircraft airframes by cables or rigid struts has shown itself over at least three centuries in aircraft. When the triangle is collapsed to a single post (two down tubes joined as one), then a head-butting control part occurs. When the triangle loses the lower tube, then control is achieved only by using the two downtubes. When the triangle is stayed by struts, some advantages occur for some aircraft. When the triangle is cable stayed, then some benefits and disadvantages occur. The A-frame control sub-assembly has a colorful history spanning over at least three centuries; crafts from the following aircraft makers are included: Abbas Ibn Firnas, Leonardo da Vinci, Percy Pilcher, Augustus Herring, John J. Montgomery, Gottlob Espenlaub, George A. Spratt, Charles Richards, Barry Hill Palmer, Mike Burns of Aerostructures, and others in the manned ski-kite sport, and then many in the modern hang glider, trike, and ultralight world. Variously, the A-frame allowed both rigid and non-rigid pilot holds while the A-frame permitted various ways of controlling the aircraft from foot-rest all the way to the simple single-point pendulum swing-seat hold of the pilot exhibited by George A. Spratt in 1929 for hang gliders—after which any designer was free to use the same efficient arrangement. This article will study the history, physics, specifications, modifications, advantages, disadvantages, safety interfaces, and other aspects of the triangle control airframe part that is nearly ubiquitous in modern manned towed ski kites, hang gliders, trikes, and ultralights.
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