Steam, which is even older than rubber power, and like rubber, contributed much to aviation history , is now rarely used. Hiram Stevens Maxim later showed that steam can even lift a man into the air. Samuel Pierpont Langley built steam as well as internal combustion models that made long flights.
Baronet Sir George Cayley built, and perhaps flew, internal and external combustion gunpowder -fueled model aircraft engines in , , and These had no crank, working ornithopter -like flappers instead of a propeller. He speculated that the fuel might be too dangerous for manned aircraft. All internal combustion engines generate substantial noise and engine exhaust and require routine maintenance. For larger and heavier models, the most popular powerplant is the glow engine.
Glow engines are fueled by a mixture of slow burning methanol , nitromethane , and lubricant castor oil or synthetic oil , which is sold pre-mixed as glow-fuel. Glow-engines require an external starting mechanism; the glow plug must be electrically heated until its temperature can trigger fuel-ignition, upon which the engine's combustion-cycle becomes self-sustaining. The reciprocating action of the cylinders applies torque to a rotating crankshaft , which is the engine's primary power-output. Some power is lost in the form of waste-heat.
Vendors of model engines rate size in terms of engine displacement. Common sizes range from as small as 0. Under ideal conditions, the smallest. The simplest glow-engines operate on the two-stroke cycle. These engines are inexpensive, yet offer the highest power-to-weight ratio of all glow-engines, but can often generate a great deal of noise, requiring substantially-sized expansion chamber mufflers to reduce their noise output, of both tuned exhaust and non-tuned varieties.
Glow engines which operate on the four-stroke cycle , whether using ordinary poppet valves or occasionally rotary valves offer superior fuel-efficiency power-output per fuel-consumption , but deliver less power than two-stroke engines of the same displacement — yet, often because the power they deliver is more suited to turning somewhat larger diameter propellers for lighter weight, more drag-producing airframe designs such as biplanes and scale aircraft models of pre-World War II full-scale subjects, four-stroke model engines, fueled either with methanol or gasoline fuels are slowly increasing in popularity from their generally lower noise output when compared to similar displacement two-stroke engines, and are available for larger displacement, multi-cylinder four-stroke engines in opposed twin and radial engine layouts.
Internal combustion IC engines are also available in upscale and up-price configurations.
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Variations include engines with multiple-cylinders, spark-ignited gasoline operation, and carbureted diesel operation. The term "diesel" is in fact a misnomer, as such engines actually operate by compression-ignition. The compression-ratio is controlled by an adjustable threaded T screw on the cylinder head, bearing onto a contra piston within the cylinder bore. Diesels are preferred for endurance competition, because of their fuel's higher energy content, a mixture of ether and kerosene with lubricating oil. They have higher torque, and for a given capacity, they can usually "swing" a larger propeller than a glow engine.
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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. 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. 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 s 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, as well as many nations' national aeromodeling clubs as with the USA's AMA requiring their users to be certified to know how to safely and properly operate the engines they intend to use for such a model.
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, the earliest being the s model rocket motor called the Jetex engine.
This uses solid fuel pellets, ignited by a wick fuse; the casing is reuseable. These days, flyers can also mount single-use model rocket engines to provide a short less than 10 second burst of power.
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In some countries, government regulations and restrictions initially rendered rocket-propulsion unpopular, even for gliders; now, though, their use is expanding, particularly in scale model rocketry. Self-regulation of the sport and widespread European availability of single use 'cartridge' motors seemed to ensure a future, but in recent years the cartridges known as "Rapier" units have become difficult to obtain, due to a reclassification from "smoke producing devices" to "fireworks". In electric-powered models, the powerplant is a battery -powered electric motor.
Throttle control is achieved through an electronic speed control ESC , which regulates the motor's output. The first electric models were equipped with brushed DC motors and rechargeable packs of nickel cadmium cells NiCad , giving modest flight times of 5—10 minutes. A fully fueled glow-engine system of similar weight and power would likely provide double the flight-time.
Later electric systems used more-efficient brushless DC motors and higher-capacity nickel metal hydride NiMh batteries, yielding considerably improved flight times. The recent development of cobalt -content lithium polymer batteries LiPoly or LiPo now permits electric flight-times to approach, and in many cases [ example needed ] surpass that of glow-engines — however, the increasing popularity of the much more rugged and durable, cobalt-free lithium iron phosphate -celled batteries is increasingly attracting attention away from LiPo packs.
In June a record of 48 hours and 16 minutes was established in California for this class. Electric-flight was tested on model aircraft in the s, but its high cost prevented widespread adoption until the early s, when falling costs of motors, control systems and, crucially, more practical battery and electric power technologies, with the increasing adoption of brushless motors powered with better battery chemistries and controlled with an electronic speed control in place of a throttle servo came on the market.
Electric-power has made substantial inroads into the park-flyer and 3D-flyer markets.
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Both markets are characterized by small and lightweight models, where electric-power offers several key advantages over IC: greater efficiency, higher reliability, less maintenance, much less messy and quieter flight. The 3D-flyer especially benefits from the near-instantaneous response of an electric-motor. Starting around the year the entry of Chinese direct-to-consumer suppliers into the hobby market has dramatically decreased the cost of electric flight.
This is the most rapidly developing segment of the hobby as of end of year , along with the increasing popularity of FPV radio control aeromodeling , most often with electric-powered model aircraft, especially multirotor designs.
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Most powered model-aircraft, including electric, internal-combustion, and rubber-band powered models, generate thrust by spinning an airscrew. The propeller is the most commonly used device. Propellers generate thrust due to the angle of attack of the blades, which forces air backwards. For every action there is an equal and opposite reaction, thus the plane moves forwards. As in full-size planes, the propeller's dimensions and placement along the fuselage or wings are factored into the design.
In general, a large diameter and low- pitch offers greater thrust and acceleration at low airspeed, while a small diameter and higher-pitch sacrifices thrust for a higher maximum-airspeed. In model aircraft, the builder can choose from a wide selection of propellers, to tailor the model's airborne characteristics.
A mismatched propeller will compromise the aircraft's airworthiness, and if too heavy, inflict undue mechanical wear on the powerplant.
The pitch is the distance that the propeller would advance if turned through one revolution in a solid medium. Additional parameters are the number of blades 2 and 3 are the most common. Ducted fans are propellors encased in a cylindrical housing or duct, designed to look like and fit in the same sort of space as a model jet engine but at a much lower cost.
They are available for both electric and liquid-fuelled engines, although they have only become widely used with the recent improvements in electric-flight technology for model aircraft. It is possible to equip a model jet aircraft with two or four electric ducted fans for much less than the cost of a single jet turbine or large petrol or methanol engine, enabling affordable modeling of multi-engine planes, including military bombers and civilian airliners.
The fan-unit is an assembly of the spinning fan a propellor with more blades , enclosed inside a shaped-duct. Compared to an open-air propellor, a ducted-fan generates more thrust per crossectional-area. The shaped-duct often limits installation to recessed areas of the fuselage or wings.