A model plane built from scratch ends up with more value because you created the project from the plans. Some model planes are designed this way because it's often cheaper and lighter to control the speed of a motor than it is to actually provide a moving control surface. Model aircraft are flying or non-flying models of existing or imaginary aircraft, often scaled down versions of full size planes, using materials such as balsa wood, foam and fiberglass. Models may be built either as static non-flying models, or as flying models (also known as aeromodelling). Some static models are scaled for use in wind tunnels, where the data acquired is used to aid the design of full scale aircraft. Control line (C/L) model aircraft use cables (usually two) leading from the wing to the pilot. Some flying models resemble scaled down versions of piloted aircraft, while others are built with no intention of looking like piloted aircraft. More recently, Ready To Fly (RTF) radio control aircraft have all but eliminated assembly time (at the expense of the model's configuration options. Powered models contain an onboard power plant to propel the aircraft through the air. Jet-powered models attract large crowds at organized events; their authentic sound and high speed make for excellent crowd pleasers. The first electric models were equipped with DC-brushed motors and rechargeable packs of nickel cadmium (NiCad), giving modest flight times of 5-10 minutes. Ducted fans are popular with scale-models of jet-aircraft, where they mimic the appearance and feel of jet engines, as well as increasing the model's maximum airspeed. A radio-controlled aircraft (often called RC aircraft or RC plane) is a model aircraft that is controlled remotely, typically with a hand-held transmitter and a receiver within the craft. Spectators are often surprised to see that such a model can really fly, and real birds are often surprised by these unexpected visitors in their aerial domain. Many radio controlled aircraft, especially the low end `toy' models, are designed to be flown with no movable control surfaces at all. RC planes often borrow construction techniques from vintage full-sized aircraft (although they rarely use metal structures). Hobbyists will often venture from planes, to jets and to helicopters as they enjoy the challenges, excitement and satisfaction of flying.