Editing Model aircraft (section)

==Flying models==
[[File:Airplane.JPG|thumb|A free-flight hand-launched glider]]
'''Aeromodelling''' is the building and operation of flying model aircraft. Some flying models resemble scaled down versions of full scale aircraft, while others are built with no intention of looking like real aircraft. There are also models of birds, bats and [[pterosaur]]s (usually [[ornithopter]]s). 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 changes to the design.

===Control===
Flying model aircraft are generally controlled through one of three methods
*[[Free flight (model aircraft)|Free flight]] (F/F) model aircraft are uncontrolled other than by control surfaces that must be preset before flight, and must have a high degree of natural stability. Most free flying models are either unpowered gliders or rubber powered. These pre-date manned flight.<ref>{{cite web |url=http://www.geocities.com/aerohydro/mfm/model.htm|archive-url=https://web.archive.org/web/20091028062404/http://www.geocities.com/aerohydro/mfm/model.htm|title=Model Flying Machines|archive-date=28 October 2009|work=geocities.com}}</ref>
*[[Control line]] (C/L) model aircraft use strings or wires to tether the model to a central pivot, either held by hand or to a [[round-the-pole flying|pole]]. The aircraft then flies in circles around that point, secured by one cable, while a second provides [[Aircraft principal axes|pitch]] control through a connection to the elevator. Some use a third cable to control a throttle. There are many competition categories. Speed flying is divided into classes based on engine displacement. Class 'D' 60 size speed planes can easily reach speeds well in excess of {{cvt|150|mph}}.
*[[Radio-controlled aircraft]] have a controller who operates a [[transmitter]] that sends signals to a [[receiver (radio)|receiver]] in the model to actuate servos that adjust the model's flight controls similarly to a full sized aircraft. Traditionally, the radio signal directly controlled [[Servo (radio control)|servos]], however, modern examples often use flight control computers to stabilize the model or even to fly it autonomously. This is particularly the case with [[quadcopter]]s. Rudimentary flight controllers were first introduced in model helicopters, with standalone electronic gyroscopes used stabilize the tail rotor control. Much like quadcopters, this has now extended to all flight controls.

===Construction===
[[File:Saalflugf1d.jpg|thumb|Extremely light F1D-class indoor-flight model with microfilm covering]]
[[File:S.E.5a model aircraft from E-flite ARF kit.JPG|thumb|Flying model of a WW1 [[Royal Aircraft Factory S.E.5]]a with foam flying surfaces, from a kit.]]
Flying models construction may differ from that of static models as both weight and strength are major considerations.

Flying models borrow construction techniques from full-sized aircraft although the use of metal is limited. These might consist of forming a frame using thin planks of a light wood such as [[Ochroma pyramidale|balsa]] to duplicate the [[former]]s, [[longeron]]s, [[spar (aviation)|spar]]s, and [[rib (aeronautics)|ribs]] of a vintage full-size aircraft, or, on larger (usually powered) models where weight is less of a factor, sheets of wood, [[expanded polystyrene]], and [[wood veneer]]s may be employed. It is then given a smooth sealed surface, usually with [[aircraft dope]]. For light models, tissue paper is used. For larger models (usually powered and radio controlled) heat-curing or heat shrink covering plastic films or heat-shrinkable synthetic fabrics are applied to the model. Microfilm covering is used for the lightest models and is made by spreading few drops of lacquer out over several square feet of water, and lifting a wire loop through it, which creates a thin plastic film.
Flying models can be assembled from kits, built from plans, or made completely from scratch. A kit contains the necessary raw material, typically die- or laser-cut wood parts, some molded parts, plans, assembly instructions and may have been flight tested. Plans are intended for the more experienced modeller, since the builder must make or find the materials themselves. Scratch builders may draw their own plans, and source all the materials themselves. Any method may be labor-intensive, depending on the model in question.

To increase the hobby's accessibility, some vendors offer [[Almost ready to fly|Almost Ready to Fly]] (ARF) models that minimize the skills required, and reduce build time to under 4 hours, versus 10–40 or more for a traditional kit. [[Ready to Fly (radio control)|Ready To Fly]] (RTF) radio control aircraft are also available, however model building remains integral to the hobby for many. For a more mass market approach, foamies, injection-molded from lightweight foam (sometimes reinforced) have made indoor flight more accessible and many require little more than attaching the wing and landing gear.

===Gliders===
[[File:KN Modelloldtimer Sindbad.JPG|thumb|model glider showing typical internal structure]]
[[Glider (aircraft)|Gliders]] do not have an attached [[aircraft engine|powerplant]]. Larger outdoor model gliders are usually [[radio-controlled glider]]s and hand-winched against the wind by a line attached to a hook under the fuselage with a ring, so that the line drops when the model is overhead. Other methods include catapult-launching, using an elastic [[bungee cord]]. The newer [[Discus Launch Glider|"discus" style]] of wingtip hand-launching has largely supplanted the earlier "javelin" type of launch. Also using ground-based power winches, hand-towing, and towing aloft using a second powered aircraft.

Gliders sustain flight through exploitation of the [[wind]] in the environment. A hill or slope often produces updrafts of air that sustain the flight of a glider. This is called [[slope soaring]], and  radio controlled gliders can remain airborne for as long as the updraft remains. Another means of attaining height in a glider is exploitation of [[thermal]]s, which are columns of warm rising air created by differences of temperature on the ground such as between an asphalt parking lot and a lake. Heated air rises, carrying the glider with it. As with a powered aircraft, [[lift (force)|lift]] is obtained by the action of the wings as the aircraft moves through the air, but in a glider, height is gained by flying through air that is rising faster than the aircraft is sinking.

[[Walkalong glider]]s are lightweight model airplanes flown in the [[ridge lift]] produced by the pilot following in close proximity. In other words, the glider is [[slope soaring]] in the updraft of the moving pilot (see also [[Controllable slope soaring]]).

===Power sources===
[[File:James Pelly-Fry flying models.jpg|thumb|Typical rubber powered model having the rubber band (hidden in the fuselage) tightened by turning the propeller backward, here being done with a handcrank]]
Powered models contain an onboard ''powerplant'', a mechanism powering propulsion of the aircraft through the air. [[Electric motor]]s and [[internal combustion engine]]s are the most common propulsion systems, but other types include [[rocket engine|rocket]], small [[Gas turbine|turbine]], [[pulsejet]], compressed gas, and tension-loaded (twisted) rubber band devices.

====Rubber====
The oldest method of powering free flight models is [[Alphonse Pénaud]]'s elastic motor (or extensible motor) of 1871, essentially a long [[rubber band]] that is twisted to add tension, prior to flight. It is the most widely used powerplant, found on everything from children's toys to competition models. The elastic offers simplicity and durability, but has a short running time, and the initial high torque of a fully wound motor drops sharply before plateauing to a steady output, until the final turns unwind and power drops off completely. Using it efficiently is one of the challenges of competitive free-flight rubber flying, and variable-pitch propellers, differential wing and tailplane incidence and rudder settings, controlled by timers, can help to manage the torque. There are also usually motor weight restrictions in contest classes. Even so, models have achieved flights of nearly 1 hour.<ref>Testing Commercial Rubber – R.J. North, Model Aircraft magazine, Feb 1961</ref><ref>{{cite web |url=http://www.indoornews.com/indoorrecords/record_list.php |title=Archived copy |access-date=2007-10-23 |url-status=dead |archive-url=https://web.archive.org/web/20080629140125/http://www.indoornews.com/indoorrecords/record_list.php |archive-date=29 June 2008  }}</ref>

====Compressed gases====
Stored compressed gas, typically [[carbon dioxide]] (CO<sub>2</sub>), can power simple models in a manner similar to filling a balloon and then releasing it. Compressed CO<sub>2</sub> may also be used to power an expansion engine to turn a [[propeller (aircraft)|propeller]]. These engines can incorporate speed controls and multiple cylinders, and are capable of powering lightweight scale [[radio-controlled aircraft]]. Gasparin and Modela are two recent makers of CO<sub>2</sub> engines. CO<sub>2</sub>, like rubber, is known as "cold" power because it generates no heat.

Steam is even older than rubber power, and like rubber, contributed much to [[history of aviation|aviation history]], but is now rarely used. In 1848, [[John Stringfellow]] flew a steam-powered model, in [[Chard, Somerset]], [[England]]. [[Samuel Pierpont Langley]] built both steam- and internal-combustion-powered models that made long{{quantify|date=December 2022}} flights.

Baronet Sir [[George Cayley]] built, and flew, internal and external combustion [[gunpowder]]-fueled model aircraft engines in 1807, 1819, and 1850. These had no crank, working [[ornithopter]]-like flappers instead of a propeller. He speculated that the fuel might be too dangerous for manned aircraft.

====Internal combustion====
[[File:c-130j.hercules.model.arp.jpg|thumb|"Giant scale" {{convert|18|ft|6|in|m}} wingspan [[Lockheed C-130 Hercules]] radio control flying model powered with four internal combustion engines. A crew of five fly and maintain it.]]
{{Main|Model engine}}
For larger and heavier models, the most popular powerplant is the [[Glow plug (model engine)|glow plug 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 heated until it is hot enough to ignite fuel to start. [[Reciprocating engine|Reciprocating]] cylinders apply torque to a rotating [[crankshaft]], which is the engine's primary power-output. Some power is lost from converting linear motion to rotary and in lost heat and unburned fuel, so efficiency is low.
[[File:Model Aircraft Engines.JPG|thumb|Model Aircraft Engines]]
These are rated by [[engine displacement]] and range from {{cvt|0.01|cuin|cc}} to over {{cvt|1.0|cuin|cc}}. The smallest engines can spin a {{convert|3.5|in|cm}} propeller to over 30,000 rpm, while the larger engines turn at 10–14,000 rpm.

The simplest glow-engines use the [[two-stroke cycle]]. These engines are inexpensive, and offer the highest [[power-to-weight ratio]] of all glow-engines, but are noisy and require substantial [[expansion chamber]] mufflers, which may be [[tuned exhaust|tuned]]. [[four-stroke cycle]] glow engines, whether using [[poppet valve]]s or more rarely [[rotary valve#Use in engine design|rotary valves]] are more fuel-efficient, but deliver less power than similar two-stroke engines. The power they deliver is more suited to turning larger diameter propellers for lighter weight, higher drag airframes such as with in [[biplane]]s. Four-stroke engines are now popular as they are quieter than two-stroke engines, and are available in [[flat-twin engine|horizontally opposed twins]] and [[radial engine]] configurations. Variations include engines with multiple-cylinders, spark-ignition gasoline operation, carbureted diesel operation and variable compression-ratio engines. Diesels are preferred for endurance and have higher torque, and for a given capacity, can "swing" a larger propeller than a glow engine. Home manufacture of model aircraft engines is a hobby in its own right.

====Jets and rockets====
[[File:PST Model Airplane Jet Trainer.png|thumb|Miniature jet turbine]]
Early "jet" style model aircraft used a multi-blade propeller [[ducted fan]], inside ductwork, usually in the fuselage. The fans were generally powered by 2 stroke engines at high RPM. They generally had {{cvt|0.40|to|0.90|cuin|cc}} displacements, but some were as small as {{cvt|0.049|cuin|cc}}. This fan-in-tube design has been adopted successfully for electric-powered jets while glow engine powered ducted-fan aircraft are now rare. Small [[jet turbine]] engines are now used in hobbyist models that resemble simplified versions of the turbojet engines found on commercial aircraft, but are not scaled-down as Reynolds numbers come into play. The first hobbyist-developed turbine was developed and flown in the 1980s but recently have commercial examples become readily available. Turbines require specialized design and precision-manufacturing, and some have been built from car engine [[turbocharger]] units. Owning or operating a turbine-powered aircraft is prohibitively expensive and many national clubs (as with the USA's [[Academy of Model Aeronautics]]) require members to be certified to safely use them.<ref>{{cite web |url=http://www.modelaircraft.org/documents.aspx#Turbines |title=AMA Documents – Turbines |author=AMA |publisher=AMA |access-date=5 October 2012}}</ref> 
[[V-1 flying bomb]] type [[Pulsejet]] engines have also been used as they offer more thrust in a smaller package than a traditional glow-engine, but are not widely used due to the extremely high noise levels they produce, and are illegal in some countries.
[[File:Mohinhmaybayphanluc.jpg|thumb|A Vietnamese pilot prepares his model jet (Bien Hoa Air Base, Vietnam)]]
[[Rocket engine]]s are sometimes used to boost gliders and sailplanes. The earliest purpose-built rocket motor dates back to the 1950s, with the introduction of the [[Jetex]] motor, which used solid fuel pellets, ignited by a wick fuse, in a reusable casing. Flyers can now also use single-use [[model rocket]] engines to provide a short, under 10 second burst of power. Government restrictions in some countries made rocket-propulsion rare but these were being eased in many places and their use was expanding, however a reclassification from "smoke producing devices" to "fireworks" has made them difficult to obtain again.

====Electric power====
[[File:Bleriot type traversée de la Manche.jpg|thumb|Small electric powered model of a pre-WW1 era [[Bleriot XI]]]]
Electric-powered models use an [[electric motor]] powered by a source of electricity - usually a [[battery (electricity)|battery]]. Electrical power began being used on models in the 1970s, but the cost delayed widespread use until the early 1990s, when more efficient battery technologies, and [[brushless DC electric motor|brushless motors]] became available, while the costs of motors, batteries and control systems dropped dramatically. Electric power now predominated with ''park-flyer'' and ''[[3D-flyer]]'' models, both of which are small and light, where electric-power offers greater efficiency and reliability, less maintenance and mess, quieter flight and near-instantaneous throttle response compared to internal combustion engines.

The first electric models used [[brushed DC electric motor|brushed DC motors]] and [[nickel cadmium]] (NiCad) rechargeable cells that gave flight times of 5 to 10 minutes, while a comparable glow-engine provided double the flight-time. Later electric systems used more-efficient [[brushless DC electric motor|brushless DC motor]]s and higher-capacity [[nickel metal hydride]] (NiMh) batteries, yielding considerably improved flight times. [[Cobalt]] and [[lithium polymer batteries]] (LiPoly or LiPo) permit electric flight-times to surpass those of glow-engines, while the more rugged and durable, cobalt-free [[lithium iron phosphate]] batteries are also becoming popular. [[Solar power]] has also become practical for R/C hobbyists, and in June 2005 a record flight of 48 hours and 16 minutes was set in California. It is now possible to power most models under {{cvt|20|lb}} with electric power for a cost equivalent to or lower than traditional power sources.

Recent developments have resulted in the use of brushless three-phase motors in model aviation. Brushless motors are more powerful and offer greater torque and efficiency. The design of brushless motors also means less internal friction, as there is no requirement for brushes to be in contact with any rotating parts. This increase in efficiency results in longer flight times.<ref>{{Cite web|title=MAS.865 2018 How to Make Something that Makes (almost) Anything|url=https://fab.cba.mit.edu/classes/865.18/motion/brushless/index.html|access-date=2022-01-21|website=fab.cba.mit.edu}}</ref>

===Propulsion types===
Most powered model-aircraft, including electric, internal-combustion, and rubber-band powered models, generate thrust by spinning an airscrew. The ''[[propeller (aircraft)|propeller]]'' is the most commonly used device. Propellers generate thrust due to lift generated by the wing-like sections of the blades, which forces air backward.

====Propellers====
A large diameter and low-[[blade pitch|pitch]] propeller offers greater thrust and acceleration at low airspeed, while a small diameter and higher-pitch propeller sacrifices acceleration for higher maximum speeds. The builder can choose from a selection of propellers to match the model but a mismatched propeller can compromise performance, and if too heavy, cause undue wear on the powerplant. Model aircraft propellers are usually specified as diameter × pitch, in inches. For example, a 5 x 3 propeller has a diameter of {{convert|5|in}}, and a pitch of {{convert|3|in}}. The pitch is the distance that the propeller would advance if turned through one revolution in a solid medium. Two and three bladed propellers are the most common.

Three methods are used to transfer energy to the propeller:
*''Direct-drive'' systems have the propeller attached directly to the engine's [[crankshaft]] or driveshaft. This arrangement is preferred when the propeller and powerplant both operate near peak efficiency at similar [[revolutions per minute|rpms]]. Direct-drive is most common with fuel-powered engines. Rarely, some electric motors are designed with a sufficiently high ''torque'' and low enough speed and can utilize direct-drive as well. These motors are typically called ''outrunners''.
*''Reduction drive'' uses gears to reduce shaft rpm, so the motor can spin much faster. The higher the gear ratio, the slower the prop rotates, which also increases torque by roughly the same ratio. This is common on larger models and on those with unusually large propellers. The reduction drive matches the powerplant and propeller to their respective optimum operating speeds. Geared propellers are rare on internal combustion engines, but are common on electric motors because most electric motors spin extremely fast, but  lack torque.
*A built-in 2:1 gear reduction ratio can be obtained by attaching the propeller to the [[camshaft]] rather than the crankshaft of a four stroke engine, which runs at half the speed of the crankshaft.<ref>{{cite web|url=http://www.rcvengines.com/pdf_files/saepaper.pdf |title=The Rotating Cylinder Valve 4-stroke Engine (SAE Paper 2002-32-1828) |author=Keith Lawes |access-date=2012-01-03 |url-status=dead |archive-url=https://web.archive.org/web/20111112180807/http://www.rcvengines.com/pdf_files/saepaper.pdf |archive-date=12 November 2011 }}</ref>

====Ducted fans====
[[Ducted fans]] are multi-blade propellers encased in a cylindrical duct or tube that may look like and fit in the same space as [[jet engine]]. They are available for both electric and liquid-fuelled engines, although they have become common with recent improvements in electric-flight technology. A model aircraft can now be fitted with four electric ducted fans for less than the cost of a single jet turbine, enabling affordable modelling of multi-engine airplanes. Compared to an unducted propeller, a ducted fan generates more thrust for the same area and speeds of up to {{cvt|200|mph}} have been recorded with electric-powered ducted fan airplanes, largely due to the higher RPMs possible with ducted fan propellers. Ducted fans are popular with scale models of jet aircraft, where they mimic the appearance of jet engines but they are also found on non-scale and sport models, and even lightweight 3D-flyers.
[[File:Nano Hummingbird.jpg|thumb|Small ornithopter, made to resemble a hummingbird]]

====Other====
With [[ornithopter]]s the motion of the wing structure imitates the flapping-wings of living [[birds]], producing both [[thrust]] and [[lift (force)|lift]].