Model aircraft
Encyclopedia
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
using a variety of materials including plastic, diecast metal, polystyrene
Polystyrene
Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...
, balsa wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
, foam
Foam
-Definition:A foam is a substance that is formed by trapping gas in a liquid or solid in a divided form, i.e. by forming gas regions inside liquid regions, leading to different kinds of dispersed media...
and fibreglass. Flying designs range from simple glider aircraft
Glider aircraft
Glider aircraft are heavier-than-air craft that are supported in flight by the dynamic reaction of the air against their lifting surfaces, and whose free flight does not depend on an engine. Mostly these types of aircraft are intended for routine operation without engines, though engine failure can...
, to accurate scale model
Scale model
A scale model is a physical model, a representation or copy of an object that is larger or smaller than the actual size of the object, which seeks to maintain the relative proportions of the physical size of the original object. Very often the scale model is used as a guide to making the object in...
s, some of which can be very large; static display models range from tiny metal toys to large, accurate models for display by aircraft manufacturers and travel agencies.
Static model aircraft
Scale model
A scale model is a physical model, a representation or copy of an object that is larger or smaller than the actual size of the object, which seeks to maintain the relative proportions of the physical size of the original object. Very often the scale model is used as a guide to making the object in...
s built using plastic, wood, metal, or paper. Some static models are scaled for use in wind tunnel
Wind tunnel
A wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...
s, where the data acquired is used to aid the design of full scale aircraft.
Models are available that have already been built and painted; models that require construction, painting and gluing; or models that have been painted but need to be snapped together.
Promotional use
Most of the world's airlines allow their fleet aircraft to be modeled as a form of publicity. In the early days, airlines would order large models of their aircraft and supply them to travel agencies as a promotional item.Scale
Static models are primarily available in a variety of scales from as large as 1:321:32 scale
1:32 scale is a traditional scale for models and miniatures, in which one unit on the model represents 32 units on the actual object. It is also known as "three-eighths scale", since 3/8-inch represents a foot...
to as small as 1:600. Plastic model kits requiring assembly and painting are primarily available in 1:72
1:72 scale
1:72 scale is a scale used for scale models, most commonly model aircraft, corresponding to one sixth of an inch representing one foot . In other words, 72 of a given model placed end to end would represent the length of the real thing. In this scale, a man who is six feet tall would be exactly...
and 1:48
1:48 scale
1:48 scale is popular among modelers both as diecast models, plastic models made from kits, and construction toys. It is especially popular with manufacturers of model airplanes and model trains...
, followed closely by 1:32. Diecast metal models (pre-assembled and factory painted) are primarily available in 1:72
1:72 scale
1:72 scale is a scale used for scale models, most commonly model aircraft, corresponding to one sixth of an inch representing one foot . In other words, 72 of a given model placed end to end would represent the length of the real thing. In this scale, a man who is six feet tall would be exactly...
, 1:400, 1:200, and 1:500
1:500 scale
1:500 scale is a scale mainly used by Europeans for pre-finished die-cast airliner models, such as German manufacturer Herpa. This scale is also used by Japanese model kit manufacturer Bandai, Nichimo Co Ltd. and Fujimi Model for ship and Sci-Fiction model kits.-Ship models for the military:During...
. 1:48
1:48 scale
1:48 scale is popular among modelers both as diecast models, plastic models made from kits, and construction toys. It is especially popular with manufacturers of model airplanes and model trains...
, 1:250, 1:300, 1:600, and a variety of odd scales (e.g. 1:239) are also available but less common.
1:72 scale was first introduced in the Skybirds
Skybirds
Skybirds was the brand name of a series of 1:72 scale wood and metal aircraft model kits produced by A. J. Holladay & Co. in the United Kingdom during the 1930s and 40s....
wood and metal model aircraft kits in 1932. According to "Fine Scale Modeler" magazine, 1:72 was also popularized by the US War Department (renamed the Department of Defense) when it requested models of single seat aircraft at that scale. The War Department also requested models of multi-engine aircraft at a scale of 1:144. The War Department was hoping to educate Americans in the proper identification
Aircraft spotting
Aircraft spotting or plane spotting is the observation and logging of the registration numbers of aircraft: gliders, powered aircraft, balloons, airships, helicopters, and microlights....
of aircraft. These scales provided the best compromise between size and detail. After WWII, the toy manufactures continued to favor these scales. More detailed models are available at 1:32
1:32 scale
1:32 scale is a traditional scale for models and miniatures, in which one unit on the model represents 32 units on the actual object. It is also known as "three-eighths scale", since 3/8-inch represents a foot...
and 1:24
1:24 scale
1:24 is a very popular size for Die-cast toy vehicles, which are collected by children and adults. Primarily automobiles are made in this scale, with a few examples of tractor trailers and other larger equipment. Plastic automobile kits are frequently made in this scale.1:24 is the largest of the...
. Some manufacturers introduced 1:50 scale
1:50 scale
1:50 scale is a popular size for diecast models from European manufacturers such as Conrad, Tekno, NZG, WSI and LionToys. Typically they produce scale models of construction vehicles, tower cranes, trucks and buses. These are often the official models distributed by the manufacturers of the real...
and 1:30 scale. Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
offers 1:100. The French
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
firm Heller SA
Heller SA
Heller SA is a French company that produces plastic scale model kits of aircraft, cars, and ships. As of July 21, 2006 the company is in the French equivalent of administration .- History :...
is the only manufacturer to offer models in the scale of 1:125. Herpa
Herpa
Herpa, or Herpa Miniaturmodelle GmbH, is a German manufacturer of die-cast model aircraft under the Herpa Wings trademark and plastic car models under the Herpa Cars & Trucks trademark. The mainstay of Herpa Wings is in the 1/500 scale, although models are also produced in the 1/400, 1/200, and...
and others produce promotional models for airlines in scales including 1:200, 1:400, 1:500, 1:600, 1:1000 and more. A few First World War
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
aircraft were offered at 1:28 by Revell
Revell
Revell is the brand name today of two manufacturers of scale plastic models. The original US company merged with another, Monogram, but now trades only under the Revell name. European Revell Germany separated from the US company in 2006.-Early history:...
.
Other less popular scales are 1:50, 1:64, 1:96, and 1:128; however, old models
are often revived in these scales. Many older plastic models, such as those built by Revell
Revell
Revell is the brand name today of two manufacturers of scale plastic models. The original US company merged with another, Monogram, but now trades only under the Revell name. European Revell Germany separated from the US company in 2006.-Early history:...
do not conform to any established scale. They are sized to fit inside standard sized boxes. These kits are often called "box-scale" and are often reissued in their original, unusual scales. Some helicopters used to be offered in 1:32 scale
1:32 scale
1:32 scale is a traditional scale for models and miniatures, in which one unit on the model represents 32 units on the actual object. It is also known as "three-eighths scale", since 3/8-inch represents a foot...
, similar to some fixed-wing aircraft models. The trend is to issue helicopters in 1:35 scale, similar to most land vehicle models.
Media
The most common form of manufacture for kits is injection molded polystyrenePolystyrene
Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...
plastic, using carbon steel molds. Today, this takes place mostly in China, Taiwan, the Philippines, South Korea, and Eastern Europe. Injection molding allows a high degree of precision and automation not found in other manufacturing processes. Smaller and cheaper runs can be done with cast copper molds, and some companies do even smaller runs using cast resin molds, but the quality and precision is of a lower standard than carbon steel.
There is a handful of photo etched
Photolithography
Photolithography is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate...
metal kits which allow a high level of detail but can be laborious to assemble. Specialized kits cast in resin are available from companies such as Anigrand, Collect Aire, CMK, and Unicraft.
Scale models can be made from paper
Paper model
Paper models, also called card models or papercraft, are models constructed mainly from sheets of heavy paper, paperboard, or card stock.- Details :...
(normal or heavy) or card stock. Commercial models are printed by publishers mainly based in Eastern Europe. Card models are also distributed through the internet, and several are offered this way for free. Card model kits are not limited to just aircraft, with kits being available for all types of vehicles, buildings, computers, firearms and animals.
From World War I through the 1950s, model airplanes were built from light weight balsa wood and often covered with tissue paper. This was a difficult, time consuming procedure that mirrored the actual construction of airplanes through the end of World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. The Cleveland Model and Supply Corporation made the most challenging kits, while Guillow's made relatively easy kits. Many model makers soon became adept at creating models from actual aircraft drawings.
Ready-made models (desk-top models) include those produced in fibreglass for travel agents and aircraft manufacturers, as well as collectors models made from die-cast metal, mahogany and plastic. Snap Fit plastic plane models are manufactured by Wooster
Wooster
- People :* David Wooster , brigadier-general in the Continental Army during the American Revolution* Fred Wooster , cofounder of the Saanich Lacrosse Association, Canadian Lacrosse Hall of Fame...
, Long Prosper, and Flight Miniatures
Flight Miniatures
Flight Miniatures is a brand of plastic snap-fit style desktop display model aircraft. The majority of models they produce are of commercial airliners in 1:200 scale. Other scales and a limited range of military aircraft models are also available....
.
Flying model aircraft
- Free flightFree flight (model aircraft)The segment of model aviation known as free flight is the original form of the aeromodeling hobby, extending back centuries.- Description :...
(F/F) model aircraft fly without any method of external control from the ground.
This type of model pre-dates the efforts of the Wright BrothersWright brothersThe Wright brothers, Orville and Wilbur , were two Americans credited with inventing and building the world's first successful airplane and making the first controlled, powered and sustained heavier-than-air human flight, on December 17, 1903...
and other pioneers. - Control lineControl lineControl line is a simple and light way of controlling a flying model aircraft. The aircraft is connected to the operator by a pair of lines, attached to a handle, that work the elevator of the model. This allows the model to be controlled in the pitch axis...
(C/L) model aircraft use cables (usually two) leading from the wing to the pilot. A variation of this system is the Round-the-pole flyingRound-the-pole flyingRound-the-pole flying is a form of flying model aircraft, in which the model is attached via a line from its wingtip or fuselage to a central support structure. Control signals can be passed to the model via wires alongside or integral with the attachment line. The operator can control the...
(RTP) model. - Radio-controlled aircraftRadio-controlled aircraftA radio-controlled aircraft is controlled remotely by a hand-held transmitter and a receiver within the craft...
have a transmitterTransmitterIn electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
operated by the pilot on the ground, sending signals to a receiverReceiver (radio)A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
in the craft.
Some flying models resemble scaled down versions of piloted
Aviator
An aviator is a person who flies an aircraft. The first recorded use of the term was in 1887, as a variation of 'aviation', from the Latin avis , coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne...
aircraft, while others are built with no intention of looking like piloted aircraft. There are also models of birds and flying dinosaurs.
Construction
The construction of flying models is very different from most static models. Flying models borrow construction techniques from (usually vintage) full-sized aircraft (although models rarely use metal structures.) These might consist of forming the frame of the model using thin strips of light wood such as balsa, then covering it with fabric and subsequently dopingAircraft dope
thumb|right|[[United Kingdom military aircraft serials|2699]] a [[World War I]] [[Royal Aircraft Factory B.E.2]] finished in a clear dopeAircraft dope is a plasticised lacquer that is applied to fabric-covered aircraft...
the fabric to form a light and sturdy frame which is also airtight. For very light models, thin tissue paper can be substituted for fabric. First it is shrunk by water spraying, allowed to dry, then coated with dope. Heat-curing plastic films ("heat shrink covering", "Solarfilm") or heat-shrinkable synthetic fabrics ("Solartex" or "Coverite") can be ironed on — a hand-held iron causes the film or fabric to shrink and adhere to the frame. A heat gun can also be used.
Other model construction techniques consist of using former
Former
thumb|right|150px|Interior of an F-16B with the engine removed showing frames or formers.A former is a structural member of an aircraft fuselage, of which a typical fuselage has a series from the nose to the empennage, typically perpendicular to the longitudinal axis of the aircraft...
s and longeron
Longeron
In aircraft construction, a longeron or stringer or stiffener is a thin strip of wood, metal or carbon fiber, to which the skin of the aircraft is fastened. In the fuselage, longerons are attached to formers and run the longitudinal direction of the aircraft...
s for the fuselage
Fuselage
The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...
, and spar
Spar
In sailing, a spar is a pole of wood, metal or lightweight materials such as carbon fiber used on a sailing vessel. Spars of all types In sailing, a spar is a pole of wood, metal or lightweight materials such as carbon fiber used on a sailing vessel. Spars of all types In sailing, a spar is a...
s and rib
Rib
In vertebrate anatomy, ribs are the long curved bones which form the rib cage. In most vertebrates, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity. They serve to protect the lungs, heart, and other internal organs of the thorax...
s for the wings and tail surfaces. More robust designs may use solid sheets of wood to form these instead, or might employ a composite wing consisting of an expanded polystyrene core laminated with a surface veneer
Wood veneer
In woodworking, veneer refers to thin slices of wood, usually thinner than 3 mm , that are typically glued onto core panels to produce flat panels such as doors, tops and panels for cabinets, parquet floors and parts of furniture. They are also used in marquetry...
of wood, often obechi, which protects the core and provides strength. Such designs tend to be heavier than an equivalent sized model built using the traditional method, and would be much more likely to be found in a power model than a glider.
The lightest models are suitable for indoor flight, in a windless environment. The covering for the very lightest of these aircraft can be made by bringing an open framework up through water to pick up thin plastic films, perhaps just a few drops of lacquer spread out over several square feet (known as microfilm). The advent of "foamies," or aircraft injection-molded from lightweight foam and sometimes reinforced with carbon fiber rods and strips, have made indoor flight more accessible to hobbyists. Many come ready-to-fly, requiring little more than attachment of the wing and landing gear. See ParkZone Slo-V
ParkZone Slo-V
The Slo-V is an electric powered, radio controlled aircraft designed and distributed by ParkZone, a division of Horizon Hobby of Champaign, Illinois....
;Slow Stick.
Flying models can be built from scratch using published plans, or assembled from kits. Plans are intended for the more experienced modeller, since all parts must be sourced separately. The kit contains most of the raw material for an unassembled plane, a set of assembly instructions, and a few spare parts to allow for builder error. Assembling a model from plans or a kit can be very labour-intensive. In order to complete the construction of a model, the builder assembles the frame, covers it, and aligns the control surfaces.
Almost Ready to Fly
Almost Ready to Fly is a term used for radio-controlled airplane kits that come partially built, usually just requiring final assembly to complete them. They normally include partially assembled wings, along with a fuselage and stabilizers already pre-covered in plastic film sheeting material such...
(ARF) designs. Compared to a traditional kit design, an ARF design reduces the amount of time, skill, and tooling required for assembly. The average ARF aircraft can be built with less than 4 hours of labor, versus 10-20+ for a traditional kit 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.) Among traditional hobbyist builders, RTF models are a point of controversy, as many consider model assembly as integral to the hobby.
Entry Level
A popular entry level flying model aircraft for beginners is the AMA Cub designed by Frank Ehling around 1967 (AKA MAAC Cub and Delta Dart). It can be purchased at most hobby stores and is available through mail order.http://www.sigmfg.com/IndexText/SIGFF5.html
Other notable designs are the Squirrel (Darcy Whyte), Denny Dart (Neil Dennis), Canarsie Canarie (Don Ross) and Canarsie Courier (Don Ross).
Gliders
Glider aircraftGlider aircraft
Glider aircraft are heavier-than-air craft that are supported in flight by the dynamic reaction of the air against their lifting surfaces, and whose free flight does not depend on an engine. Mostly these types of aircraft are intended for routine operation without engines, though engine failure can...
do not have an attached powerplant. Larger outdoor model gliders are usually radio-controlled glider
Radio-controlled glider
A radio-controlled glider is a type of radio-controlled aircraft that normally does not have any form of propulsion. They are able to sustain continuous flight by exploiting the lift produced by slopes and thermals, controlled remotely from the ground with a transmitter...
s and hand-winched against the wind by a line attached to a hook under the fuselage with a ring, so that the line will drop when the model is overhead. Other methods include catapult-launching, using an elastic bungee cord
Bungee cord
A bungee cord , also known as a shock cord, is an elastic cord composed of one or more elastic strands forming a core, usually covered in a woven cotton or polypropylene sheath...
. The newer "discus" style of wingtip handlaunching 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.
As gliders are unpowered, flight must be sustained through exploitation of the natural wind
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
in the environment. A hill or slope will often produce updrafts of air which will sustain the flight of a glider. This is called slope soaring, and when piloted skilfully, 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
Thermal
A thermal column is a column of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation, and are an example of convection. The sun warms the ground, which in turn warms the air directly above it...
s, which are bubbles or columns of warm rising air created by hot spots on the ground. As with a powered aircraft, lift
Lift (force)
A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...
is obtained by the action of the wings as the aircraft moves through the air, but in a glider, height can only be gained by flying through air that is rising faster than the aircraft is sinking relative to the airflow.
Sailplanes are flown using thermal lift. As thermal
Thermal
A thermal column is a column of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation, and are an example of convection. The sun warms the ground, which in turn warms the air directly above it...
s can only be indirectly observed through the reaction of the aircraft to the invisible rising air currents, pilots find sailplane flying challenging.
Hang gliders are composed of rigid & material delta wings with a harness (payload) suspended from the airframe. Control is exercised through the movement of the harness in opposition to a control frame,
Paragliders are aircraft consisting of its parts: wing, strings, and mass that falls. Usually the wing part of a paraglider is flexible, fabric wings, whose shape is formed by its suspension lines made taut by the paragliders falling payload and the pressure of air inflating either a single-skin or double-layered wing. Some wings are ram-air where air enters vents in the front of the wing. Control is exercised through lines that deform the trailing edge of the airfoil or the wing's end regions.
Walkalong glider
Walkalong glider
A walkalong glider is a lightweight, slow flying model aircraft designed to be kept aloft by slope soaring in the lift generated by a paddle held by the pilot who walks along with the glider as it flies. Hands or even the forehead can also be used to do this...
s are lightweight model airplanes flown in the ridge lift
Ridge lift
Ridge lift is created when a wind strikes an obstacle, usually a mountain ridge or cliff, that is large and steep enough to deflect the wind upward....
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
Controllable slope soaring
Controllable-slope soaring is a type of slope soaring where a slope is made to follow the airplane in gliding flight, both sustaining and controlling the airplane's trajectory by modifying the wind in the vicinity of the airplane. A controllable slope is any object which can be used to affect the...
).
Power sources
Powered models contain an onboard powerplant to propel the aircraft through the air. Electric motor and internal combustion are the most common propulsion systems, but other types include rocket, small turbine, pulsejet, compressed gas and tension-loaded (twisted) rubber band.Rubber and gas propulsion
An old method of powering free flight models is Alphonse PénaudAlphonse Pénaud
Alphonse Pénaud , was a 19th-century French pioneer of aviation, inventor of the rubber powered model airplane Planophore and founder of the aviation industry.-Biography:...
's elastic motor, essentially a long rubber band
Rubber band
A rubber band is a short length of rubber and latex formed in the shape of a loop and is commonly used to hold multiple objects together...
that is wound up prior to flight. It is the most widely used powerplant for model aircraft, found on everything from children's toys to serious competition models. The elastic motor offers extreme simplicity and survivability, but suffers from limited running time, an exponential reduction of thrust over the motor's operational cycle, and it places substantial stress on the fuselage. Even so, a competitive model can achieve flights of nearly 1 hour.
Stored compressed gas (CO2), similar to filling a balloon and then releasing it, also powers simple models.
A more sophisticated use of compressed CO2 is to power a piston expansion engine, which can turn a large, high pitch prop. These engines can incorporate speed controls and multiple cylinders, and are capable of powering lightweight scale radio-controlled aircraft
Radio-controlled aircraft
A radio-controlled aircraft is controlled remotely by a hand-held transmitter and a receiver within the craft...
. Gasparin and Modella are two recent makers of CO2 engines. CO2, like rubber, is known as "cold" power because it becomes cooler when running, rather than hotter as combustion engines and batteries do.
Steam, which is even older than rubber power, and like rubber, contributed much to aviation history
Aviation history
The history of aviation has extended over more than two thousand years from the earliest attempts in kites and gliders to powered heavier-than-air, supersonic and hypersonic flight.The first form of man-made flying objects were kites...
, is now rarely used. In 1848, John Stringfellow
John Stringfellow
John Stringfellow was born in Sheffield, England and is known for his work on the Aerial Steam Carriage with William Samuel Henson....
flew a steam-powered model, in Chard, Somerset
Chard, Somerset
Chard is a town and civil parish in the Somerset county of England. It lies on the A30 road near the Devon border, south west of Yeovil. The parish has a population of approximately 12,000 and, at an elevation of , it is the southernmost and highest town in Somerset...
, England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
. Hiram Stevens Maxim
Hiram Stevens Maxim
Sir Hiram Stevens Maxim was an American-born inventor who emigrated to England at the age of forty-one, although he remained an American citizen until he became a naturalized British subject in 1900. He was the inventor of the Maxim Gun – the first portable, fully automatic machine gun – and the...
later showed that steam can even lift a man into the air. Samuel Pierpont Langley
Samuel Pierpont Langley
Samuel Pierpont Langley was an American astronomer, physicist, inventor of the bolometer and pioneer of aviation...
built steam as well as internal combustion models that made long flights.)
Baronet Sir George Cayley
George Cayley
Sir George Cayley, 6th Baronet was a prolific English engineer and one of the most important people in the history of aeronautics. Many consider him the first true scientific aerial investigator and the first person to understand the underlying principles and forces of flight...
built, and perhaps flew, internal and external combustion gunpowder
Gunpowder
Gunpowder, also known since in the late 19th century as black powder, was the first chemical explosive and the only one known until the mid 1800s. It is a mixture of sulfur, charcoal, and potassium nitrate - with the sulfur and charcoal acting as fuels, while the saltpeter works as an oxidizer...
-fueled model aircraft engines in 1807, 1819 and 1850. These had no crank, working ornithopter
Ornithopter
An ornithopter is an aircraft that flies by flapping its wings. Designers seek to imitate the flapping-wing flight of birds, bats, and insects. Though machines may differ in form, they are usually built on the same scale as these flying creatures. Manned ornithopters have also been built, and some...
-like flappers instead of a propeller. He speculated that the fuel might be too dangerous for manned aircraft.
Internal combustion
All internal combustion engine
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
s generate substantial noise (and engine exhaust) and require routine maintenance. In the 'scale-R/C' community, glow-engines have long been the mainstay until recently.
For larger and heavier models, the most popular powerplant is the glow engine. Glow engines are fueled by a mixture of slow burning methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
, nitromethane
Nitromethane
Nitromethane is an organic compound with the chemical formula . It is the simplest organic nitro compound. It is a slightly viscous, highly polar liquid commonly used as a solvent in a variety of industrial applications such as in extractions, as a reaction medium, and as a cleaning solvent...
, and lubricant (castor oil
Castor oil
Castor oil is a vegetable oil obtained from the castor bean . Castor oil is a colorless to very pale yellow liquid with mild or no odor or taste. Its boiling point is and its density is 961 kg/m3...
or synthetic oil
Synthetic oil
Synthetic oil is a lubricant consisting of chemical compounds that are artificially made . Synthetic lubricants can be manufactured using chemically modified petroleum components rather than whole crude oil, but can also be synthesized from other raw materials...
, 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
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...
, which is the engine's primary power-output. (Some power is lost in the form of waste-heat.)
Engine displacement
Engine displacement is the volume swept by all the pistons inside the cylinders of an internal combustion engine in a single movement from top dead centre to bottom dead centre . It is commonly specified in cubic centimeters , litres , or cubic inches...
. Common sizes range from as small as 0.01 cubic inch (in3) to over 1.0 in3 (0.16 cc–16 cc). Under ideal conditions, the smallest .01 engines can turn a 3.5" (9 cm) propeller at speeds over 30,000 rpm, while the typical larger (.40-.60 cubic inch) engine will turn at 10-14,000 rpm.
The simplest glow-engines operate on the two-stroke cycle
Two-stroke cycle
A two-stroke engine is an internal combustion engine that completes the process cycle in one revolution of the crankshaft...
. These engines are inexpensive, yet offer the highest power-to-weight ratio
Power-to-weight ratio
Power-to-weight ratio is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement of actual performance of any engine or power sources...
of all glow-engines. Glow engines which operate on the four-stroke cycle
Four-stroke cycle
A four-stroke engine, also known as four-cycle, is an internal combustion engine in which the piston completes four separate strokes—intake, compression, power, and exhaust—during two separate revolutions of the engine's crankshaft, and one single thermodynamic cycle.There are two...
(or six-stroke cycle) offer superior fuel-efficiency (power-output per fuel-consumption), but deliver less power than two-stroke engines of the same displacement.
Diethyl ether
Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula . It is a colorless, highly volatile flammable liquid with a characteristic odor...
and kerosene
Kerosene
Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin or paraffin oil in the United Kingdom, Hong Kong, Ireland and South Africa, is a combustible hydrocarbon liquid. The name is derived from Greek keros...
(with lubricating oil).
Jet and rocket
Ducted fan
A ducted fan is a propulsion arrangement whereby a fan, which is a type of propeller, is mounted within a cylindrical shroud or duct. The duct reduces losses in thrust from the tip vortices of the fan, and varying the cross-section of the duct allows the designer to advantageously affect the...
s
Early "jet" style model aircraft utilized a multi-blade and high pitched propeller (fan) inside of ductwork, usually in the fuselage of the airplane. 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 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 engine
Jet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...
s.) The first hobbyist-developed turbine was developed and flown in the 1980s by Gerald Jackman in England, but only recently has commercial production 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
Turbocharger
A turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...
units from car engines), and consume a mixture of A1 jet fuel and synthetic 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 engine
Pulse jet engine
A pulse jet engine is a type of jet engine in which combustion occurs in pulses. Pulsejet engines can be made with few or no moving parts, and are capable of running statically....
s, operating on the same principle as World War II V-1 flying bomb
V-1 flying bomb
The V-1 flying bomb, also known as the Buzz Bomb or Doodlebug, was an early pulse-jet-powered predecessor of the cruise missile....
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".
Rocket engine
Rocket engine
A rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...
s are sometimes used to boost gliders and sailplanes, such as the 1950s model rocket motor called the Jetex engine
Jetex engine
The Jetex engine was a type of solid-fuel rocket engine produced for use as a powerplant for model aircraft. Originally developed in 1947, by Wilmot, Mansour & Company Ltd of Southampton, it was first demonstrated to the modelling press in early 1948, and was available to the public in June 1948,...
. Solid fuel pellets were used, ignited by a wick fuse. Flyers mount readily available model rocket
Model rocket
A model rocket is a small rocket that is commonly advertised as being able to be launched by anybody, to, in general, low altitudes and recovered by a variety of means....
engines to provide a single, short (less than 10 second) burst of power. (US?)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 availability of the 'cartridge' motors ensures a future.
Electric power
In electric-powered models, the powerplant is a batteryBattery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
-powered electric motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
. Throttle control is achieved through an electronic speed control
Electronic speed control
An electronic speed control or ESC is an electronic circuit with the purpose to vary an electric motor's speed, its direction and possibly also to act as a dynamic brake...
(ESC
ESC
-As an abbreviation:* Ecole Supérieure de Commerce, a business school in the French system of "Grandes Ecoles"* Edison State College* Edmonton Ski Club* Electronic stability control* Electronic Systems Center* Electronic speed control...
), which regulates the motor's output. The first electric models were equipped with DC
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
-brushed motors and rechargeable packs of nickel cadmium (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 motor
Brushless DC electric motor
Brushless DC motors also known as electronically commutated motors are electric motors powered by direct-current electricity and having electronic commutation systems, rather than mechanical commutators and brushes...
s and higher-capacity nickel metal hydride (NiMh) batteries, yielding considerably improved flight times. The recent development of lithium polymer batteries (LiPoly or LiPo) now permits electric flight-times to approach, and in many cases surpass that of glow-engines. There is also solar power
Solar power
Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available...
ed flight, which is becoming practical for R/C hobbyists. In June 2005 a record of 48 hours and 16 minutes was established in California for this class.
Electric-flight was tested on model aircraft in the 1970s, but its high cost prevented widespread adoption until the early 1990s, when falling costs of motors, control systems and, crucially, more practical battery technologies came on the market. Electric-power has made substantial inroads into the park-flyer and 3D-flyer markets. 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 2008 the entry of Chinese direct-to-consumer suppliers into the hobby market has dramatically decreased the cost of electric flight. It is now possible to power most models weighing less than 20 lb with electric power for a cost equivalent to or lower than traditional power sources. This is the most rapidly developing segment of the hobby as of end of year 2010.
Control Line
Also referred to as U-Control in the USA, it was pioneered by the late Jim Walker who often, for show, flew three models at a time. Normally the model is flown in a circle and controlled by a pilot in the center holding a handle connected to two thin steel wires. The wires connect through the inboard wing tip of the plane to a mechanism that translates the handle movement to the aircraft elevator, allowing maneuvers to be performed along the aircraft pitch axis. The pilot will turn to follow the model going round, the convention being anti-clockwise for upright level flightFor the conventional control-line system, tension in the lines is required to provide control. Line tension is maintained largely by centrifugal force
Centrifugal force
Centrifugal force can generally be any force directed outward relative to some origin. More particularly, in classical mechanics, the centrifugal force is an outward force which arises when describing the motion of objects in a rotating reference frame...
. To increase line tension, models may be built or adjusted in various ways. Rudder offset and thrust vectoring
Thrust vectoring
Thrust vectoring, also thrust vector control or TVC, is the ability of an aircraft, rocket or other vehicle to manipulate the direction of the thrust from its engine or motor in order to control the attitude or angular velocity of the vehicle....
(tilting the engine toward the outside) yaw the model outward. The position where the lines exit the wing can compensate for the tendency of the aerodynamic drag of the lines to yaw the model inboard. Weight on the outside wing, an inside wing that is longer or has more lift than the outside wing (or even no outside wing at all) and the torque of a left rotating propeller (or flying clockwise) tend to roll the model toward the outside. Wing tip weights, propeller torque, and thrust vectoring are more effective when the model is going slowly, while rudder offset and other aerodynamic effects have more influence on a fast moving model.
Since its introduction, control line flying has developed into a competition sport. There are contest categories for control line models, including Speed, Aerobatics (AKA Stunt), Racing, Navy Carrier, Balloon Bust, Scale, and Combat. There are variations on the basic events, including divisions by engine size and type, skill categories, and age of model design.
The events originated largely in the United States, and were later adapted for use internationally. The rules for US Competition are available from the Academy of Model Aeronautics. The international rules are defined by the Fédération Aéronautique Internationale (FAI). World Championships are held semiannually throughout the world, most recently in 2008 in France, with a limited slate of events - special varieties of Racing (F2C or "Team Race"), combat (F2D), and speed (F2A), all limited to engines displacing 0.15 cu. in (2.5cc), and Stunt (F2b) which is essentially unlimited with regard to design and size.
Team Race
The international class of racing is referred to as F2C (F2 = Control-line, C=racing) or Team Race. A pilot and a mechanic compete as a team to fly small (370 grams)(13 oz.) 65 cm (25 in.) wingspan semi-scale racing models over a tarmac or concrete surface. Lines are 15.92 meters long (52.231 ft).
Three pilots, plus mechanic teams, compete simultaneously in the same circle, and the object is to finish the determined course as fast as possible. Tank size is limited to 7 cc, thus 2-3 pitstops for refueling are needed during the race.
The mechanic stands at a pit area outside the marked flight circle. The engine will be started and the model released at the start signal. For refuelling, the pilot will operate a fuel shutoff by a quick down elevator movement after the planned number of laps so that the model can approach the mechanic at optimum speed, around 50 km/h (30 mph). The mechanic will catch the model by the wing, fill the tank from a pressurized can by a hose and finger valve, then restart the engine by hitting the carbon fiber/epoxy resin propeller with his finger. Ground time of a good pitstop is less than three seconds.
The race course is 10 km, corresponding to 100 laps. Flying speeds are around 200 km/h (125 mph), which means that the pilots have to turn one lap in 1.8 seconds. Line pull due to centrifugal force is 85 N (17 lb). A faster model will overtake by the pilot steering it above the slower one while he moves his handle with lines over the opponent pilot's head.
After two rounds of elimination heats, the 6, 9 or 12 fastest teams enter two semifinal rounds, and the three fastest teams in the semifinals go to the final, which is run over the double course.
Maximum engine size is 2.5 cc (.15 cu.in.). Diesel, i.e. compression ignition engines are used. They are single cylinder two-stroke, designed for this purpose. At the world championship level it is not uncommon that the competitors design and build their own engines. Their output power is approaching .8 horsepower at 25,000 rpm.
Airscrew types
Most powered model-aircraft, including electric, internal-combustion, and rubber-band powered models, generate thrust by spinning an airscrew. The propellerPropeller (aircraft)
Aircraft propellers or airscrews convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal...
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.
Propellers
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-pitchBlade pitch
Blade pitch or simply pitch refers to turning the angle of attack of the blades of a propeller or helicopter rotor into or out of the wind to control the production or absorption of power. Wind turbines use this to adjust the rotation speed and the generated power...
offers greater thrust 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. Model aircraft propellers are usually specified as diameter × pitch, given in inches. For example, a 5x3 propeller has a diameter of 5 inches (127 mm), and a pitch of 3 inches (76.2 mm). 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).
There are two methods to transfer rotational-energy from the powerplant to the propellor:
- With the direct-drive method, the propeller is attached directly on the engine's spinning crankshaft (or motor-rotor.) This arrangement is optimum when the propellor and powerplant share overlapping regions of best efficiency (measured in RPMRevolutions per minuteRevolutions per minute is a measure of the frequency of a rotation. It annotates the number of full rotations completed in one minute around a fixed axis...
.) Direct-drive is by far the most common when using a fuel-powered engine (gas or glow). Some electric motors with high torque and (comparatively) low RPM's can utilize direct-drive as well. These motors are typically outrunners.
- With the reduction method, the crankshaft drives a simple transmissionTransmission (mechanics)A machine consists of a power source and a power transmission system, which provides controlled application of the power. Merriam-Webster defines transmission as: an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a...
, which is usually a simple gearbox containing a pinionPinionA pinion is a round gear used in several applications:*usually the smallest gear in a gear drive train, although in the case of John Blenkinsop's Salamanca, the pinion was rather large...
and spur gear. The transmission decreases the output RPM by the gear ratioGear ratioThe gear ratio of a gear train is the ratio of the angular velocity of the input gear to the angular velocity of the output gear, also known as the speed ratio of the gear train. The gear ratio can be computed directly from the numbers of teeth of the various gears that engage to form the gear...
(thereby also increasing output torqueTorqueTorque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
by approximately the same ratio). Reduction-drive is common on larger aircraft and aircraft with disproportionately large propellers. On such powerplant arrangements, the transmission serves to match the powerplant's and propeller's optimum operating RPM. Geared propellers are rarely used on internal combustion engines, but very commonly on electric motors. This is because most inrunner electric motors spin extremely fast, but have very little torque.
Ducted fans
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 engineJet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...
but at a much lower cost. They are available for both electric and gas 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 gas 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. 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. Speeds of up to 200 mph have been recorded on electric-powered ducted fan airplanes, largely due to the high amount of RPMs produced by ducted fan propellors. But they are also found on non-scale and sport models, and even lightweight 3D-flyers. Like propellors, fan-units are modular components, and most fan-powered aircraft can accommodate a limited selection of different fan-units.
Other
With OrnithopterOrnithopter
An ornithopter is an aircraft that flies by flapping its wings. Designers seek to imitate the flapping-wing flight of birds, bats, and insects. Though machines may differ in form, they are usually built on the same scale as these flying creatures. Manned ornithopters have also been built, and some...
s the reciprocating-motion of the wing structure imitates the flapping-wings of living birds, producing both thrust
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
and lift
Lift (force)
A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...
.
Model aerodynamics
The flight behavior of an aircraft depends on the scale to which it is built. The Reynolds number depends on scale and speed. Drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
is generally greater in proportion at low Reynolds number so flying scale models usually require larger than scale propellers.
Mach number
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...
depends on speed. Compressibility of the air is important only at speeds close to or over the speed of sound
Speed of sound
The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at , the speed of sound is . This is , or about one kilometer in three seconds or approximately one mile in five seconds....
, so the effect of the difference in Mach number between a slow piloted aircraft and a small model is negligible, but models of jets are generally not efficient flyers. In particular, swept wing
Swept wing
A swept wing is a wing planform favored for high subsonic jet speeds first investigated by Germany during the Second World War. Since the introduction of the MiG-15 and North American F-86 which demonstrated a decisive superiority over the slower first generation of straight-wing jet fighters...
s and pointed noses are used at high Mach number to reduce compressibility drag and tend to increase drag at small Mach number.
Angular momentum
Angular momentum
In physics, angular momentum, moment of momentum, or rotational momentum is a conserved vector quantity that can be used to describe the overall state of a physical system...
also depends on scale. Since torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
is proportional to lever arm length while angular inertia is proportional to the square of the lever arm, the smaller the scale the more quickly an aircraft or other vehicle will turn in response to control or other forces. While it may be possible for a pilot to fly an unstable aircraft (such as a Wright Flyer
Wright Flyer
The Wright Flyer was the first powered aircraft, designed and built by the Wright brothers. They flew it four times on December 17, 1903 near the Kill Devil Hills, about four miles south of Kitty Hawk, North Carolina, U.S.The U.S...
), a radio control scale model of the same aircraft would only be flyable with the center of gravity
Center of gravity
In physics, a center of gravity of a material body is a point that may be used for a summary description of gravitational interactions. In a uniform gravitational field, the center of mass serves as the center of gravity...
moved forward, or with avionics. On the other hand, angular inertia, and therefore large scale, generally degrades stability, because it introduces a delay. Static stability
Static stability
Static stability is the ability of a robot to remain upright when at rest, or under acceleration and deceleration.Static stability may also refer to:In aircraft or missiles:...
, resisting sudden changes in pitch and yaw, is generally required for all models and is usually considered a requirement for piloted aircraft. Dynamic stability is required of all but tactical piloted aircraft.
Free flight models and flight trainers need to have both static and dynamic stability. Static stability is the resistance to sudden changes in pitch and yaw and is typically provided by the horizontal and vertical tail surfaces, respectively, and by a forward center of gravity. The three dynamic stability modes are phugoid
Phugoid
A phugoid or fugoid is an aircraft motion where the vehicle pitches up and climbs, and then pitches down and descends, accompanied by speeding up and slowing down as it goes "uphill" and "downhill." This is one of the basic flight dynamics modes of an aircraft , and a classic example of a positive...
, spiral and Dutch roll
Dutch roll
Dutch roll is a type of aircraft motion, consisting of an out-of-phase combination of "tail-wagging" and rocking from side to side. This yaw-roll coupling is one of the basic flight dynamic modes...
. An aircraft with too large horizontal tail on a fuselage that is too short may have a phugoid with increasing climbs and dives. With free flight models, this usually results in a stall or loop at the end of the initial climb. Insufficient dihedral and sweep back will generally lead to increasing spiral turn. Too much dihedral generally causes Dutch roll. However, these all depend on the scale, as well as details of the shape and weight distribution. For example the paper glider shown here is a contest winner when made of a small sheet of paper but will go from side to side in Dutch roll when scaled up even slightly.