![Model B747-400 - SINGAPORE AIRLINES](https://upload.wikimedia.org/wikipedia/commons/a/a9/Model_B747-400_-_SINGAPORE_AIRLINES.jpg)
A model aircraft is a small unmanned
aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air. It 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 engine ...
. Many are replicas of real aircraft. Model aircraft are divided into two basic groups: flying and non-flying. Non-flying models are also termed static, display, or shelf models.
Aircraft manufacturers and researchers make
wind tunnel
Wind tunnels are large tubes with air blowing through them which are used to replicate the interaction between air and an object flying through the air or moving along the ground. Researchers use wind tunnels to learn more about how an aircraft ...
models for testing aerodynamic properties, for basic research, or for the development of new designs. Sometimes only part of the aircraft is modelled.
Static models range from mass-produced toys in
white metal
The white metals are a series of often decorative bright metal alloys used as a base for plated silverware, ornaments or novelties, as well as any of several lead-based or tin-based alloys used for things like bearings, jewellery, miniature f ...
or
plastic
Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...
to highly accurate and detailed models produced for museum display and requiring thousands of hours of work. Many are available in kits, typically made of
injection-moulded polystyrene or resin.
Flying models range from simple toy
glider
Glider may refer to:
Aircraft and transport Aircraft
* Glider (aircraft), heavier-than-air aircraft primarily intended for unpowered flight
** Glider (sailplane), a rigid-winged glider aircraft with an undercarriage, used in the sport of glidin ...
s made of sheets of paper,
balsa
''Ochroma pyramidale'', commonly known as the balsa tree, is a large, fast-growing tree native to the Americas. It is the sole member of the genus ''Ochroma''. The tree is famous for its wide usage in woodworking, with the name ''balsa'' being ...
,
card stock
Card stock, also called cover stock and pasteboard, is paper that is thicker and more durable than normal writing and printing paper, but thinner and more flexible than other forms of paperboard.
Card stock is often used for business cards, ...
or foam
polystyrene to powered
scale models built up from balsa,
bamboo
Bamboos are a diverse group of evergreen perennial flowering plants making up the subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family. The origin of the word "bamboo" is uncertain, ...
sticks, plastic, (including both moulded or sheet polystyrene, and
styrofoam
Styrofoam is a trademarked brand of closed-cell extruded polystyrene foam (XPS), commonly called "Blue Board", manufactured as foam continuous building insulation board used in walls, roofs, and foundations as thermal insulation and water barrie ...
), metal, synthetic
resin
In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on n ...
, either alone or with
carbon fibre
Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...
or
fibreglass
Fiberglass (American English) or fibreglass (Commonwealth English) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass clo ...
, and skinned with either
tissue paper
Tissue paper or simply tissue is a lightweight paper or, light crêpe paper. Tissue can be made from recycled paper pulp on a paper machine.
Tissue paper is very versatile, and different kinds of tissue are made to best serve these purposes, w ...
,
mylar
BoPET (biaxially-oriented polyethylene terephthalate) is a polyester film made from stretched polyethylene terephthalate (PET) and is used for its high tensile strength, chemical and dimensional stability, transparency, reflectivity, gas and a ...
and other materials. Some can be very large, especially when used to research the flight properties of a proposed full scale aircraft.
Aerodynamic research and mock-ups
![LN-10 mg 7893](https://upload.wikimedia.org/wikipedia/commons/0/07/LN-10_mg_7893.jpg)
Models are made for
wind tunnel
Wind tunnels are large tubes with air blowing through them which are used to replicate the interaction between air and an object flying through the air or moving along the ground. Researchers use wind tunnels to learn more about how an aircraft ...
and free-flight research tests and may have components that can be swapped to compare various fittings and configurations, or have features such as controls that can be repositioned to reflect various in flight configurations. They are also often fitted with sensors for spot measurements and are usually mounted on a structure that ensures the correct alignment with the airflow, and which provides additional measurements. For wind tunnel research, it is sometimes only necessary to make part of the proposed aircraft.
Full-scale static engineering models are also constructed for production development, often made of different materials from the proposed design. Again, often only part of the aircraft is modelled.
Static display models
![Focke-Wulf FW B 200 Condor](https://upload.wikimedia.org/wikipedia/commons/9/91/Focke-Wulf_FW_B_200_Condor.jpg)
Static model aircraft cannot fly, and are used for display, education and are used in
wind tunnel
Wind tunnels are large tubes with air blowing through them which are used to replicate the interaction between air and an object flying through the air or moving along the ground. Researchers use wind tunnels to learn more about how an aircraft ...
s to collect data for the design of full scale aircraft. They may be built using any suitable material, which often includes plastic, wood, metal, paper and fiberglass and may be built to a specific scale, so that the size of the original may be compared to that of other aircraft. Models may come finished, or may require painting or assembly, with glue, screws, or by clipping together, or both.
Many of the world's airlines allow their aircraft to be modelled for publicity. Airlines used to order large scale models of their aircraft to supply them to travel agencies as a promotional item. Desktop model airplanes may be given to airport, airline and government officials to promote an airline or celebrate a new route or an achievement.
Scale
Static model aircraft are primarily available commercially in a variety of
scales
Scale or scales may refer to:
Mathematics
* Scale (descriptive set theory), an object defined on a set of points
* Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original
* Scale factor, a number w ...
from as large as
1:18 scale to as small as
1:1250 scale. Plastic model kits requiring assembly and painting are primarily available in
1:144,
1:72,
1:48,
1:32, and
1:24 scale. Die-cast metal models (pre-assembled and factory painted) are available in scales ranging from
1:48 to
1:600.
Scales are not random, but are generally based on divisions of either the
Imperial system
The imperial system of units, imperial system or imperial units (also known as British Imperial or Exchequer Standards of 1826) is the system of units first defined in the British Weights and Measures Act 1824 and continued to be developed th ...
, or the
Metric system
The metric system is a system of measurement that succeeded the decimalised system based on the metre that had been introduced in France in the 1790s. The historical development of these systems culminated in the definition of the Interna ...
.
For example, 1:48 scale is 1/4" to 1-foot (or 1" to 4 feet) and 1:72 is 1" to 6 feet, while in metric scales such as 1:100th, 1 centimetre equals 1 metre.
1:72 scale was introduced with
Skybirds
Skybirds was a brand name for a series of 1:72 scale wood and metal aircraft model kits produced during the 1930s and 1940s, manufactured by the A. J. Holladay & Co.
Some of the Skybird-branded products were die-cast scale model cars, aircraft ...
wood and metal model aircraft kits in 1932 and were followed closely by
Frog
A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-frog" ''Triadobatrachus'' is ...
which used the same scale from 1936 with their "
Frog Penguin" brand. 1:72 was popularized in the US during the Second World War by the US War Department after it requested models of commonly encountered single engine aircraft at that scale, and multi-engine aircraft in 1:144th scale. They hoped to improve aircraft
recognition
Recognition may refer to:
*Award, something given in recognition of an achievement
Machine learning
*Pattern recognition, a branch of machine learning which encompasses the meanings below
Biometric
* Recognition of human individuals, or biomet ...
skills and these scales compromised between size and detail. After WWII, manufacturers continued with these scales, however kits are also added in other divisions of the imperial system. 1:50th and 1:100th are common in Japan and France which both use Metric. Promotional models for airlines are produced in scales ranging from 1:200 to 1:1200.
Some manufacturers made 1:18th scale aircraft to go with cars of the same scale. Aircraft models,
military vehicles
A military vehicle is any vehicle for land-based military transport and activity, including combat vehicles; both specifically designed for, or significantly used by military and armed forces. Most military vehicles require off-road capabilit ...
,
figures
Figure may refer to:
General
*A shape, drawing, depiction, or geometric configuration
* Figure (wood), wood appearance
*Figure (music), distinguished from musical motif
* Noise figure, in telecommunication
* Dance figure, an elementary dance patt ...
,
cars
A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, Car seat, seat one to eight people, have four wheels, and mainly transport private transport#Personal transport, people in ...
, and
trains
In rail transport, a train (from Old French , from Latin , "to pull, to draw") is a series of connected vehicles that run along a railway track and transport people or freight. Trains are typically pulled or pushed by locomotives (often know ...
all have different common scales but there is some crossover. There is a substantial amount of duplication of more famous subjects in different scales, which can be useful for
forced perspective
Forced perspective is a technique that employs optical illusion to make an object appear farther away, closer, larger or smaller than it actually is. It manipulates human visual perception through the use of scaled objects and the correlation ...
box
dioramas.
Older models often did not conform to an established scale as they were sized to fit the box, and are referred to as being to "Box Scale".
Materials
![Dornier Do](https://upload.wikimedia.org/wikipedia/commons/4/48/Dornier_Do.X_papiermodell_Schnoor_Juli_2009_005.jpg)
The most common form of manufacture for kits is
injection moulded polystyrene plastic, formed in steel forms. Plastic pellets are heated into a liquid and forced into the mould under high pressure through trees which will hold all the parts, and ensure plastic flows to every part of the mould. This allows a greater degree of automation than other manufacturing processes but moulds require large production runs to cover the cost of making them. Today, this takes place mostly in Asia and Eastern Europe. Smaller runs are possible with copper moulds, and some companies use resin or rubber moulds, but while the cost is lower for the mould, the durability is also lower and labour costs can be much higher.
Resin kits are made in forms similar to those used for limited run plastic kits, but these moulds are usually not as durable, which limits them to smaller production runs, and prices for the finished product are higher.
Vacuum forming
Vacuum forming is a simplified version of thermoforming, where a sheet of plastic (in various forms HIPS (High impact polystyrene) for low impact products, or for Bathroom shower trays ABS, and exterior vehicle parts HDPE, plus various other ty ...
is another common alternative but requires more skill, and details must be supplied by the modeller. There is a handful of
photo etched metal kits which allow a high level of detail and they are unable to replicate compound curves.
Scale models can also be made from
paper
Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, rags, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre evenly distrib ...
or card stock. Commercial models are mainly printed by publishers in Germany or Eastern Europe but can be distributed through the internet, some of which are offered this way for free.
From World War I through the 1950s, static model airplanes were also built from light weight bamboo or balsa wood and covered with tissue paper in the same manner as with flying models. This was a time-consuming process that mirrored the actual construction of airplanes through the beginning of
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...
. Many model makers would create models from drawings of the actual aircraft.
Ready-made desk-top models include those produced in fiberglass for travel agents and aircraft manufacturers, as well as collectors models made from die-cast metal, mahogany, resin and plastic.
Carbon fibre
Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...
and
fibre glass have become increasingly common in model aircraft kits. In model helicopters, main frames and rotor blades are often made from carbon fibre, along with ribs and spars in fixed-wing aircraft wings.
Flying models
![Airplane](https://upload.wikimedia.org/wikipedia/commons/2/2f/Airplane.JPG)
Generally known collectively as aeromodelling, 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
Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 ...
s (usually
ornithopter
An ornithopter (from Greek ''ornis, ornith-'' "bird" and ''pteron'' "wing") is an aircraft that flies by flapping its wings. Designers sought to imitate the flapping-wing flight of birds, bats, and insects. Though machines may differ in form, ...
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 (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.
*
Control line
Control line (also called U-Control) 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 ...
(C/L) model aircraft use strings or wires to tether the model to a central pivot, either held by hand or to a
pole
Pole may refer to:
Astronomy
*Celestial pole, the projection of the planet Earth's axis of rotation onto the celestial sphere; also applies to the axis of rotation of other planets
*Pole star, a visible star that is approximately aligned with the ...
. The aircraft then flies in circles around that point, secured by one cable, while a second provides
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 .
*
Radio-controlled aircraft
A radio-controlled aircraft (often called RC aircraft or RC plane) is a small flying machine that is controlled remotely by an operator on the ground using a hand-held radio transmitter. The transmitter continuously communicates with a receiver ...
have a controller who operates a
transmitter
In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the ...
which sends signals to a
receiver in the model to actuate servos which adjust the model's flight controls similarly to a full sized aircraft. Traditionally, the radio signal directly controlled
servos
In control engineering a servomechanism, usually shortened to servo, is an automatic device that uses error-sensing negative feedback to correct the action of a mechanism. On displacement-controlled applications, it usually includes a built-in ...
, 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
A quadcopter or quadrotor is a type of helicopter with four rotors.
Although quadrotor helicopters and convertiplanes have long been flown experimentally, the configuration remained a curiosity until the arrival of the modern UAV or drone. T ...
s. Rudimentary flight controllers were first introduced in model helicopters, with standalone electronic gyroscopes used stabilise the tail rotor control. Much like quadcopters, this has now extended to all flight controls.
Construction
![S](https://upload.wikimedia.org/wikipedia/commons/f/f2/S.E.5a_model_aircraft_from_E-flite_ARF_kit.JPG)
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
balsa
''Ochroma pyramidale'', commonly known as the balsa tree, is a large, fast-growing tree native to the Americas. It is the sole member of the genus ''Ochroma''. The tree is famous for its wide usage in woodworking, with the name ''balsa'' being ...
to duplicate the
formers,
longerons,
spar
SPAR, originally DESPAR, styled as DE SPAR, is a Dutch multinational that provides branding, supplies and support services for independently owned and operated food retail stores. It was founded in the Netherlands in 1932, by Adriaan van Well, ...
s, and
ribs
The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels.
The sternum, together known as the thoracic cage, is a semi- ...
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
In woodworking, veneer refers to thin slices of wood and sometimes bark, usually thinner than 3 mm (1/8 inch), that typically are glued onto core panels (typically, wood, particle board or medium-density fiberboard) to produce flat panels s ...
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 very 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 moulded 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 labour-intensive, depending on the model in question.
To increase the hobby's accessibility, some vendors offer
Almost Ready to Fly (ARF) models which minimize the skills required, and reduce build time to under 4 hours, versus 10–40 or more for a traditional kit.
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
Gliders do not have an attached
powerplant
Propulsion is the generation of force by any combination of pushing or pulling to modify the translational motion of an object, which is typically a rigid body (or an articulated rigid body) but may also concern a fluid. The term is derived from ...
. Larger outdoor model gliders are usually
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 gr ...
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 cords equipped with metal hooks
A bungee cord (sometimes spelled bungle; 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 ...
. The newer
"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
Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ho ...
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 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
A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...
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
Lift or LIFT may refer to:
Physical devices
* Elevator, or lift, a device used for raising and lowering people or goods
** Paternoster lift, a type of lift using a continuous chain of cars which do not stop
** Patient lift, or Hoyer lift, mobil ...
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
A walkalong glider is a lightweight, slow-flying model aircraft designed to be kept aloft by controllable slope soaring in the rising air generated by the pilot who walks along with the glider as it flies, usually holding a paddle. Hands or eve ...
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
Controllable-slope soaring (also known as Walkalong gliding) is a type of slope soaring where a slope is made to follow a walkalong glider (a lightweight toy aircraft), both sustaining and controlling the glider's trajectory by modifying the wi ...
).
Power sources
![James Pelly-Fry flying models](https://upload.wikimedia.org/wikipedia/commons/f/fd/James_Pelly-Fry_flying_models.jpg)
Powered models contain an onboard ''powerplant'', a mechanism powering propulsion of the aircraft through the air.
Electric motor
An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate for ...
s and
internal combustion engine
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal c ...
s are the most common propulsion systems, but other types include
rocket
A rocket (from it, rocchetto, , bobbin/spool) is a vehicle that uses jet propulsion to accelerate without using the surrounding air. A rocket engine produces thrust by reaction to exhaust expelled at high speed. Rocket engines work entirely fr ...
, small
turbine
A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating ...
,
pulsejet
300px, Diagram of a pulsejet
A pulsejet engine (or pulse jet) is a type of jet engine in which combustion occurs in pulses. A pulsejet engine can be made with few or no moving parts, and is capable of running statically (i.e. it does not need t ...
, compressed gas, and tension-loaded (twisted) rubber band devices.
Rubber
The oldest method of powering free flight models is
Alphonse Pénaud
Alphonse Pénaud (31 May 1850 – 22 October 1880), was a 19th-century French pioneer of aviation design and engineering. He was the originator of the use of twisted rubber to power model aircraft, and his 1871 model airplane, which he called ...
's elastic motor (or extensible motor) of 1871, essentially a long
rubber band
A rubber band (also known as an elastic band, gum band or lacky band) is a loop of rubber, usually ring or oval shaped, and commonly used to hold multiple objects together. The rubber band was patented in England on March 17, 1845 by Stephen P ...
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.
Compressed Gases
Stored compressed gas, typically
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
(CO
2), can power simple models in a manner similar to filling a balloon and then releasing it. Compressed CO
2 may also be used to power an expansion engine to turn a
propeller. These engines can incorporate speed controls and multiple cylinders, and are capable of powering lightweight scale
radio-controlled aircraft
A radio-controlled aircraft (often called RC aircraft or RC plane) is a small flying machine that is controlled remotely by an operator on the ground using a hand-held radio transmitter. The transmitter continuously communicates with a receiver ...
. Gasparin and Modela are two recent makers of CO
2 engines. CO
2, 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
aviation history
The history of aviation extends for more than two thousand years, from the earliest forms of aviation such as kites and attempts at tower jumping to super sonic flight, supersonic and hypersonic flight by powered, heavier-than-air flight, h ...
, but is now rarely used. In 1848,
John Stringfellow flew a steam-powered model, in
Chard, Somerset,
England
England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...
.
Samuel Pierpont Langley
Samuel Pierpont Langley (August 22, 1834 – February 27, 1906) was an American aviation pioneer, astronomer and physicist who invented the bolometer. He was the third secretary of the Smithsonian Institution and a professor of astronomy a ...
built both steam- and internal-combustion-powered models that made long flights.
Baronet Sir
George Cayley built, and flew, internal and external combustion
gunpowder
Gunpowder, also commonly known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, carbon (in the form of charcoal) and potassium nitrate (saltpeter). Th ...
-fueled model aircraft engines in 1807, 1819, and 1850. These had no crank, working
ornithopter
An ornithopter (from Greek ''ornis, ornith-'' "bird" and ''pteron'' "wing") is an aircraft that flies by flapping its wings. Designers sought to imitate the flapping-wing flight of birds, bats, and insects. Though machines may differ in form, ...
-like flappers instead of a propeller. He speculated that the fuel might be too dangerous for manned aircraft.
Internal combustion
![c-130j](https://upload.wikimedia.org/wikipedia/commons/3/34/C-130j.hercules.model.arp.jpg)
For larger and heavier models, the most popular powerplant is the
glow plug engine. Glow engines are fueled by a mixture of slow burning
methanol,
nitromethane
Nitromethane, sometimes shortened to simply "nitro", is an organic compound with the chemical formula . It is the simplest organic nitro compound. It is a polar liquid commonly used as a solvent in a variety of industrial applications such as in ...
, and lubricant (
castor oil
Castor oil is a vegetable oil pressed from castor beans.
It is a colourless or pale yellow liquid with a distinct taste and odor. Its boiling point is and its density is 0.961 g/cm3. It includes a mixture of triglycerides in which about ...
or
synthetic oil), which is sold pre-mixed as glow-fuel. Glow-engines require an external starting mechanism; the
glow plug
A glowplug (alternatively spelled as glow plug or glow-plug) is a heating device used to aid in starting diesel engines. In cold weather, high-speed diesel engines can be difficult to start because the mass of the cylinder block and cylinder he ...
must be heated until it is hot enough to ignite fuel to start.
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.
![Model Aircraft Engines](https://upload.wikimedia.org/wikipedia/commons/d/db/Model_Aircraft_Engines.JPG)
These are rated by
engine displacement
Engine displacement is the measure of the cylinder volume swept by all of the pistons of a piston engine, excluding the combustion chambers. It is commonly used as an expression of an engine's size, and by extension as a loose indicator of the ...
and range from to over . The smallest engines can spin a 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
A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a power cycle with two strokes (up and down movements) of the piston during one power cycle, this power cycle being completed in one revolution of t ...
. 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.
four-stroke cycle
A four-stroke (also four-cycle) engine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either directi ...
glow engines, whether using
poppet valve
A poppet valve (also called mushroom valve) is a valve typically used to control the timing and quantity of gas or vapor flow into an engine.
It consists of a hole or open-ended chamber, usually round or oval in cross-section, and a plug, usua ...
s or more rarely
rotary valves
A rotary valve (also called rotary-motion valve) is a type of valve in which the rotation of a passage or passages in a transverse plug regulates the flow of liquid or gas through the attached pipes. The common stopcock is the simplest form of rot ...
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
biplanes. Four-stroke engines are now popular as they are quieter than two-stroke engines, and are available in
horizontally opposed twins and
radial engine
The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, and is ...
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
![PST Model Airplane Jet Trainer](https://upload.wikimedia.org/wikipedia/commons/6/6c/PST_Model_Airplane_Jet_Trainer.png)
Early "jet" style model aircraft used a multi-blade propeller
ducted fan
In aeronautics, a ducted fan is a thrust-generating mechanical fan or propeller mounted within a cylindrical duct or shroud. Other terms include ducted propeller or shrouded propeller. When used in vertical takeoff and landing
(VTOL) applicati ...
, inside ductwork, usually in the fuselage. The fans were generally powered by 2 stroke engines at high RPM. They generally had displacements, but some were as small as . 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 Renold's numbers come into play. The first hobbyist-developed turbine was developed and flown in the 1980s but only recently have commercial examples become readily available. Turbines require specialized design and precision-manufacturing, and some have been built from car engine
turbocharger
In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pro ...
units. Owning or operating a turbine-powered aircraft is prohibitively expensive and many national aeromodelling clubs (as with the USA's
Academy of Model Aeronautics
The Academy of Model Aeronautics (AMA), based in Muncie, Indiana, United States at , is a non-profit organization dedicated to the promotion of model aviation as a recognized sport as well as a recreational activity. It is the largest organizati ...
) require members to be certified to safely use them.
V-1 flying bomb
The V-1 flying bomb (german: Vergeltungswaffe 1 "Vengeance Weapon 1") was an early cruise missile. Its official Ministry of Aviation (Nazi Germany), Reich Aviation Ministry () designation was Fi 103. It was also known to the Allies as the buz ...
type
Pulsejet
300px, Diagram of a pulsejet
A pulsejet engine (or pulse jet) is a type of jet engine in which combustion occurs in pulses. A pulsejet engine can be made with few or no moving parts, and is capable of running statically (i.e. it does not need t ...
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.
Rocket engine
A rocket engine uses stored rocket propellants as the reaction mass for forming a high-speed propulsive jet of fluid, usually high-temperature gas. Rocket engines are reaction engines, producing thrust by ejecting mass rearward, in accorda ...
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
A model rocket are small rockets designed to reach low altitudes (e.g., for model) and be recovered by a variety of means.
According to the United States National Association of Rocketry (NAR) Safety Code, model rockets are constructed of ...
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
![Bleriot type traversée de la Manche](https://upload.wikimedia.org/wikipedia/commons/d/d9/Bleriot_type_travers%C3%A9e_de_la_Manche.jpg)
Electric-powered models use an
electric motor
An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate for ...
powered by a source of electricity - usually a
battery
Battery most often refers to:
* Electric battery, a device that provides electrical power
* Battery (crime), a crime involving unlawful physical contact
Battery may also refer to:
Energy source
*Automotive battery, a device to provide power t ...
. 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 motors became available, while the costs of motors, batteries and control systems dropped dramatically. Electric power now predominated with ''park-flyer'' and ''
3D-flyer
A radio-controlled aircraft (often called RC aircraft or RC plane) is a small flying machine that is controlled remotely by an operator on the ground using a hand-held radio transmitter. The transmitter continuously communicates with a receiver ...
'' 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 gas engines.
The first electric models used
brushed DC motors and
nickel cadmium
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...
(NiCad) rechargeable cells which 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 motors and higher-capacity
nickel metal hydride
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to r ...
(NiMh) batteries, yielding considerably improved flight times.
Cobalt
Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...
and
lithium polymer batteries
A lithium polymer battery, or more correctly lithium-ion polymer battery (abbreviated as LiPo, LIP, Li-poly, lithium-poly and others), is a rechargeable battery of lithium-ion technology using a polymer electrolyte instead of a liquid electro ...
(LiPoly or LiPo) permit electric flight-times to surpass those of glow-engines, while the more rugged and durable, cobalt-free
lithium iron phosphate
Lithium iron phosphate or lithium ferro-phosphate (LFP) is an inorganic compound with the formula . It is a gray, red-grey, brown or black solid that is insoluble in water. The material has attracted attention as a component of lithium iron phosp ...
batteries are also becoming popular.
Solar power
Solar power is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Photovoltaic cells convert light into an electric current using the photovolta ...
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 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.
Propulsion types
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 lift generated by the wing-like sections of the blades, which forces air backwards.
Propellers
A large diameter and low-
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 , and a pitch of . 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
rpms. Direct-drive is most common with fuel-powered engines. Very 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 will rotate, 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.
Ducted fans
Ducted fans
In aeronautics, a ducted fan is a thrust-generating mechanical fan or propeller mounted within a cylindrical duct or shroud. Other terms include ducted propeller or shrouded propeller. When used in vertical takeoff and landing
(VTOL) applicatio ...
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 only 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 aeroplanes. Compared to an unducted propeller, a ducted fan generates more thrust for the same area and speeds of up to 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.
Other
With
ornithopter
An ornithopter (from Greek ''ornis, ornith-'' "bird" and ''pteron'' "wing") is an aircraft that flies by flapping its wings. Designers sought to imitate the flapping-wing flight of birds, bats, and insects. Though machines may differ in form, ...
s the motion of the wing structure imitates the flapping-wings of living
birds, producing both
thrust
Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that sys ...
and
lift
Lift or LIFT may refer to:
Physical devices
* Elevator, or lift, a device used for raising and lowering people or goods
** Paternoster lift, a type of lift using a continuous chain of cars which do not stop
** Patient lift, or Hoyer lift, mobil ...
.
Competitions
World competitions are organised by the
FAI in the following classes:
*Class F – model aircraft
**F1(x) – Free Flight (A,B,C,D,E,G,H,P,Q)
**F2(x) – Control Line (A,B,C,D,E)
**F3A – Radio Control Aerobatics
**F3B – Radio Control Soaring (Multi-task)
**F3C – Radio Control Helicopters
**F3D – Pylon Racing
**F3F – Radio Control Soaring (Slope)
**F3J – Radio Control Soaring (Duration)
**F3K – Hand Launch Gliders
**F3M – Large Radio Control Aerobatics
**F3P – Radio Control Indoor Aerobatics
**F5B – Electric Motor Glider – Multi Task (held in alternate years only)
**F5D – Electric Pylon Racing
**F5J – Electric Motor Glider – Thermal Duration
**FAI – Drone Racing (F3U)
*Class S – space model
*Class U – unmanned aerial vehicle
Free flight (F1)
The Wakefield Gold Challenge Cup is an international modelling competition named for the donor,
Lord Wakefield which was first held on 5 July 1911 at
The Crystal Palace
The Crystal Palace was a cast iron and plate glass structure, originally built in Hyde Park, London, to house the Great Exhibition of 1851. The exhibition took place from 1 May to 15 October 1851, and more than 14,000 exhibitors from around th ...
in England. There were contests in 1912, 1913 and 1914. No contests were held again until 1927, when the
Society of Model Aeronautical Engineers (SMAE) approached Lord Wakefield for a new larger silver trophy for international competition. This trophy is the present Wakefield International Cup and was first awarded in 1928. The SMAE organized the international competitions until 1951 when the
FAI took over, and has since been made the award for the rubber-power category at the FAI World Free Flight Championships.
The FAI free flight (F1) classes include:
*F1A – Gliders
*F1B – Model Aircraft with extensible (rubber band) motors – Wakefield Trophy
*F1C – Power model aircraft (combustion powered )
*F1D – Indoor model aircraft
*F1E – Gliders with automatic steering
*F1N – Indoor hand-launch gliders
*F1P – Power model aircraft (combustion powered 1.0cc)
*F1Q – Electric power model aircraft
*F1G – Model aircraft with extensible (rubber band) motors « Coupe d’hiver » (provisional)
*F1H – Gliders (provisional)
*F1J – Power model aircraft (provisional) (combustion powered )
*F1K – Model aircraft with motors (provisional)
*F1L – Indoor zone EZB model aircraft (provisional)
*F1M – Indoor model aircraft (provisional)
*F1R – Indoor model aircraft “Micro 35” (provisional)
*F1S – Small electric power model aircraft “E36”
Control Line (F2)
![F2C flying models](https://upload.wikimedia.org/wikipedia/commons/9/92/F2C_flying_models.jpg)
Also referred to as U-Control in the US, 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 flight.
For the conventional control-line system, tension in the lines is required to provide control. Line tension is maintained largely by
centrifugal force
In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It is directed away from an axis which is parall ...
. To increase line tension, models may be built or adjusted in various ways. Rudder offset and
thrust vectoring
Thrust vectoring, also known as thrust vector control (TVC), is the ability of an aircraft, rocket, or other vehicle to manipulate the direction of the thrust from its engine(s) or motor(s) to control the attitude or angular velocity of the ve ...
(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.
CIAM (FAI Aeromodelling Commission) designed this classes for F2 Control Line category:
;F2A : CL Speed
;F2B : CL Aerobatics
;F2C : CL Team racing
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
wingspan
The wingspan (or just span) of a bird or an airplane is the distance from one wingtip to the other wingtip. For example, the Boeing 777–200 has a wingspan of , and a wandering albatross (''Diomedea exulans'') caught in 1965 had a wingspan o ...
semi-scale racing models over a tarmac or concrete surface. Lines are long.
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 , requiring 2 or 3 refueling pitstops during the race.
The mechanic stands at a pit area outside the marked flight circle. The engine is started and the model released on 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, of around . 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 flicking the propeller with his finger. A pitstop generally takes less than three seconds.
The course is , with 100 laps. Flying speeds are around , which means that the pilots will turn one lap in roughly 1.8 seconds. Line pull due to centrifugal force is . An overtaking model will be steered over the heads of the competing pilots of slower models.
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. Single cylinder two-stroke
Diesel compression ignition engines designed for this purpose of up to are used. At the world championship level it is common for competitors design and build their own engines. Output power approaches at 25,000 rpm.
F2D – CL Combat
CLASS F2D - Control Line Combat Model Aircraft - Two pilots compete, with four mechanics in the pit. The aircraft are light and very stubby so as to manoeuvre quickly in the air. Each has a crepe paper streamer attached to the rear of the aircraft by a string. Each pilot only attacks the other aircraft's streamer, to attempt to cut it with their propeller or wing. Each cut scores 100 points. Each second the model is in the air scores a point and the match runs for 4 minutes from the starter's signal. At the almost speeds of the aircraft, mistakes often lead to crash damage so two aircraft are permitted for each match. The mechanics are prepared for crashes and will quickly start the second aircraft and transfer the streamer to the reserve model before launching. The action is so fast that an observer may miss the cuts of the streamers. A second loss eliminates a competitor, and the last pilot still flying wins
FAI AEROMODELLING COMMISSION (CIAM)
Radio Controlled Flight (F3)
;F3A : RC Aerobatic Aircraft
;F3B : RC Multi-Task Gliders
;F3C : RC Aerobatic Helicopters
;F3D : RC Pylon Racing Aeroplanes
Pylon racing refers to a class of air racing for radio controlled model aircraft that fly through a course of pylons.
The sport is similar to the full-scale Red Bull Air Race World Series.
;F3F : RC Slope Soaring Gliders
;F3J : RC Thermal Duration Gliders
;F3K : RC Hand Launch Gliders
;F3M : RC Large Aerobatic Aircraft
;F3N : RC Freestyle Aerobatic Helicopters
;F3P : RC Indoor Aerobatic Aircraft
;F3H : RC Soaring Cross Country Gliders
;F3Q : RC Aero-Tow Gliders
;F3R : RC Pylon Racing Limited Technology Aeroplanes
;F3S : RC Jet Aerobatic Aircraft
;F3T : RC Semi-Scale Pylon Racing with Controlled Technology Aeroplanes
;F3U : RC Multi-rotor FPV Racing
The FAI Drone Racing World Cup is in the F3U class (Radio Control Multi-rotor FPV Racing). This is a highly competitive activity, involving mental exertion and big cash prizes.
Model aerodynamics
![International contest paper glider](https://upload.wikimedia.org/wikipedia/commons/d/d2/International_contest_paper_glider.svg)
The flight behaviour of an aircraft depends on the scale to which it is built, the density of the air and the speed of flight.
At subsonic speeds the relationship between these is expressed by the
Reynolds number. Where two models at different scales are flown with the same Reynolds number, the airflow will be similar. Where the Reynolds numbers differ, as for example a small-scale model flying at lower speed than the full-size craft, the airflow characteristics can differ significantly. This can make an exact scale model unflyable, and the model has to be modified in some way. For example, at low Reynolds numbers, a flying scale model usually requires a larger-than-scale propeller.
Maneuverability depends on scale, with stability also becoming more important. Control
torque
In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...
is proportional to lever arm length while angular inertia is proportional to the square of the lever arm, so the smaller the scale the more quickly an aircraft or other vehicle will turn in response to control inputs or outside forces.
One consequence of this is that models in general require additional
longitudinal
Longitudinal is a geometric term of location which may refer to:
* Longitude
** Line of longitude, also called a meridian
* Longitudinal engine, an internal combustion engine in which the crankshaft is oriented along the long axis of the vehicl ...
and
directional stability
Directional stability is stability of a moving body or vehicle about an axis which is perpendicular to its direction of motion. Stability of a vehicle concerns itself with the tendency of a vehicle to return to its original direction in relation ...
, resisting sudden changes in pitch and yaw. While it may be possible for a pilot to respond quickly enough to control an unstable aircraft, a radio control scale model of the same aircraft would only be flyable with design adjustments such as increased tail surfaces and wing dihedral for stability, or with
avionics
Avionics (a blend of ''aviation'' and ''electronics'') are the electronic systems used on aircraft. Avionic systems include communications, navigation, the display and management of multiple systems, and the hundreds of systems that are fit ...
providing artificial stability. Free flight models need to have both static and dynamic stability. Static stability is the resistance to sudden changes in pitch and yaw already described, and is typically provided by the horizontal and vertical tail surfaces respectively, and by a forward center of gravity. Dynamic stability is the ability to return to straight and level flight without any control input. The three dynamic instability modes are pitch (
phugoid
In aviation, a phugoid or fugoid is an aircraft motion in which the vehicle pitches up and climbs, and then pitches down and descends, accompanied by speeding up and slowing down as it goes "downhill" and "uphill". This is one of the basic flig ...
) oscillation, spiral and
Dutch roll. An aircraft with too large a horizontal tail on a fuselage that is too short may have a phugoid instability 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 or sweep back will generally lead to increasing spiral turn. Too much dihedral or sweepback generally causes Dutch roll. 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.
See also
*
Control line
Control line (also called U-Control) 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 ...
also called U-Control
**
Round-the-pole flying Round-the-pole flying (RTP) 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 th ...
*
Model engine
A model engine is a small internal combustion engine typically used to power a radio-controlled aircraft, radio-controlled car, radio-controlled boat, free flight, control line aircraft, or ground-running tether car model.
Because of the s ...
**
Cox model engine
Cox model engines are used to power small Model aircraft, model airplanes, model cars and model boats. They were in production for more than 60 years between 1945 and 2006. The business is named for founder Leroy M. Cox. He started L.M. Cox Manufa ...
**
Thunder Tiger
Thunder Tiger Corporation () is a Taiwan manufacturer of radio controlled models including airplanes, helicopters, cars, boats, accessories and engines. Thunder Tiger is the maker of MT4-G3, Raptor e720, Ghost+ drone, award-winning R/C submar ...
**
O.S. Engines
O.S. Engines is a Japanese model engine manufacturer.
The company was founded in 1936 by machinist Shigeo Ogawa ("Ogawa Shigeo" in the Japanese surname-first tradition) for the production of model steam engines. The name of the firm could have eit ...
*
Die-cast toy
A die-cast toy is a toy or a collectible model produced by using the die casting, die-casting method of putting molten lead, zinc alloy or plastic in a mold to produce a particular shape. Such toys are made of metal, with plastic, rubber, glass ...
*
Free flight (model aircraft)
Free flight is the segment of model aviation involving aircraft with no active external control after launch. Free Flight is the original form of hobby aeromodeling, with the competitive objective being to build and launch a self controlling airc ...
*
History of aviation
The history of aviation extends for more than two thousand years, from the earliest forms of aviation such as kites and attempts at tower jumping to supersonic and hypersonic flight by powered, heavier-than-air jets.
Kite flying in Chi ...
*
International Miniature Aerobatic Club
*
International Plastic Modellers' Society
The International Plastic Modellers' Society (often shortened to IPMS) is an international organisation of hobbyists interested in building plastic model kits. The Society is made up of national branches, and within these, local clubs who usually r ...
(IPMS)
*
List of model aircraft manufacturers
The following companies manufacture, or have manufactured, model aircraft.
Flying Ready-to-fly
A ready-to-fly model has the airframe assembled but may or may not have an engine or other equipment fitted.
Almost Ready-to-fly
* Guillow
Kits
A ...
*
List of model airplane fields in the USA
*
List of scale model kit manufacturers
*
Micro air vehicle
A micro air vehicle (MAV), or micro aerial vehicle, is a class of miniature UAVs that has a size restriction and may be autonomous. Modern craft can be as small as 5 centimeters. Development is driven by commercial, research, government, and mil ...
*''
Model Airplane News''
*
Model airport
*
Model ship
Ship models or model ships are scale models of ships. They can range in size from 1/6000 scale wargaming miniatures to large vessels capable of holding people.
Ship modeling is a craft as old as shipbuilding itself, stretching back to ancient t ...
*
Paper plane
A paper plane (also known as a paper airplane in American English or paper aeroplane in British English) is a toy aircraft, usually a glider made out of single folded sheet of paper or paperboard. A simple nose-heavy paper plane, thrown like ...
*
Radio-controlled aircraft
A radio-controlled aircraft (often called RC aircraft or RC plane) is a small flying machine that is controlled remotely by an operator on the ground using a hand-held radio transmitter. The transmitter continuously communicates with a receiver ...
*
Radio-controlled model
A radio-controlled model (or RC model) is a model that is steerable with the use of radio control. All types of model vehicles have had RC systems installed in them, including ground vehicles, boats, planes, helicopters and even submarines and ...
*
Simple Plastic Airplane Design
Simple Plastic Airplane Design (SPAD) is a type of radio controlled model airplane.
The R.C. aircraft is usually, though not always, built with the body consisting of a lightweight plastic material such as PVC gutter downspout or an aluminium r ...
*
Walkalong glider
A walkalong glider is a lightweight, slow-flying model aircraft designed to be kept aloft by controllable slope soaring in the rising air generated by the pilot who walks along with the glider as it flies, usually holding a paddle. Hands or eve ...
Footnotes
References
*''RCadvisor′s Model Airplane Design Made Easy'', by Carlos Reyes, RCadvisor.com, Albuquerque, New Mexico, 2009.
*''The Great International Paper Airplane Book'', by Jerry Mander, George Dippel and Howard Gossage, Simon and Schuster, New York, 1967.
*''Model Aircraft Aerodynamics'', by Martin Simons, Swanley: Nexus Special Interests, 1999. 4th ed.
*''How to Design and Build Flying Model Airplanes'', by Keith Laumer, Harper, New York, 1960. 2nd ed., 1970.
*''The Middle Ages of the Internal-Combustion Engine'', by Horst O. Hardenberg, SAE, 1999.
*''Model Airplane Design and Theory of Flight'', by Charles Hampson Grant, Jay Publishing Corporation, New York, 1941.
*''Pulling Back the Clouds'', by Mike Kelly, Limerick Writers' Centre Publishing, Ireland, 2020.
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