of looking like piloted aircraft. There are also models of birds and flying dinosaurs. The reduced size affects the model's Reynolds number which determines how the air reacts when flowing past the model, and compared to a full sized aircraft the size of control surfaces needed, the stability and the effectiveness of specific airfoil sections may differ considerably requiring subtle changes to the design.Flying model aircraft used in the range of different aeromdeling activities can be placed in one of three groups:Free flight (F/F) model aircraft fly without external control from the ground. This type of model pre-dates manned flight.[8]Control line (C/L) model aircraft use cables (usually two) leading from one wing to the controller. A variation of this system is theRound-the-pole flying (RTP) model.Radio-controlled aircraft have a transmitter operated by the controller, sending radio signals to a receiver in the model which in turn actuates servos which manipulate the model's flight controls in a similar manner to a full sized aircraft.[edit]Construction(...)Jet and rocketMiniature jet turbineDucted Fans Early "jet" style model aircraft utilized a multi-blade and high pitched propeller (fan) inside ductwork, usually in the fuselage of the aeroplane. The fans were generally powered by 2 stroke piston engines that were designed to operate at high RPM. Early brands of these units were the Kress, Scozzi, and Turbax, among others. They generally used 0.40 to 0.90 cubic inch displacement engines, but Kress made a model for engines as small as 0.049 (1/2cc). This basic fan-in-tube design has been adopted very successfully for modern electric powered "jet" aircraft and are now quite popular. Glow engine powered ducted-fan aircraft are now relatively uncommon.Turbine engines A major development is the use of small jet turbine engines in hobbyist models, both surface and air. Model-scale turbines resemble simplified versions of turbojet engines found on commercial aircraft, but are in fact new designs (not based upon scaled-down commercial jet engines.) The first hobbyist-developed turbine was developed and flown in the 1980s by Gerald Jackman in England, but only recently has commercial production (from companies such as Evojet in Germany) made turbines readily available for purchase. Turbines require specialized design and precision-manufacturing techniques (some designs for model aircraft have been built from recycled turbocharger units from car engines), and consume a mixture of A1 jet fuel and synthetic turbine engine or motorcycle-engine oil. These qualities, and the turbine's high-thrust output, makes owning and operating a turbine-powered aircraft prohibitively expensive for most hobbyists. Jet-powered models attract large crowds at organized events; their authentic sound and high speed make for excellent crowd pleasers.Pulse jet engines, operating on the same principle as World War II V-1 flying bomb have also been used. The extremely noisy pulsejet offers more thrust in a smaller package than a traditional glow-engine, but is not widely used. A popular model was the "Dynajet". Due to the noise, the use of these is illegal in some countries.Rocket engines are sometimes used to boost gliders and sailplanes, such as the 1950s model rocket motor called the Jetex engine. Solid fuel pellets were used, ignited by a wick fuse.