Model aircraft
A model aircraft is a physical model of an existing or imagined aircraft, and is built typically for display, research, or amusement. 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 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 or plastic 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-molded polystyrene or resin.
Flying models range from simple toy gliders made of sheets of paper, balsa, card stock or foam polystyrene to powered scale models built up from balsa, bamboo sticks, plastic,, metal, synthetic resin, either alone or with carbon fiber or fiberglass, and skinned with either tissue paper, mylar and other materials. Some can be large, especially when used to research the flight properties of a proposed full scale aircraft.
Aerodynamic research and mock-ups
Model aircraft are made for wind tunnel and free-flight research tests and often contain 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 necessary only 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 modeled.
Static display models
Static model aircraft cannot fly, and are used for display, education and are used in wind tunnels 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 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 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, or the Metric system.
For example, 1:48 scale is 1/4" to 1-foot and 1:72 is 1" to 6 feet, while in metric scales such as 1:100th, 1 centimeter equals 1 meter.
1:72 scale was introduced with Skybirds wood and metal model aircraft kits in 1932 and were followed closely by Frog, 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 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, figures, cars, and trains 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 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
The most common form of manufacture for kits is injection molded polystyrene plastic, formed in steel forms. Plastic pellets are heated into a liquid and forced into the mold under high pressure through trees that hold all the parts, and ensure plastic flows to every part of the mold. This allows a greater degree of automation than other manufacturing processes but molds 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 molds, and some companies use resin or rubber molds, but while the cost is lower for the mold, the durability is also lower and labor costs can be much higher.Resin kits are made in forms similar to those used for limited run plastic kits, but these molds are usually not as durable, which limits them to smaller production runs, and prices for the finished product are higher.
Vacuum forming 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 that allow a high level of detail and they are unable to replicate compound curves.
Scale models can also be made from paper 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. 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 fibers and fiberglass have become increasingly common in model aircraft kits. In model helicopters, main frames and rotor blades are often made from carbon fiber, along with ribs and spars in fixed-wing aircraft wings.
Flying models
Aeromodelling is the building and operation of flying model aircraft. Some flying models resemble scaled down versions of full scale aircraft, while others are built with no intention of looking like real aircraft. There are also models of birds, bats and pterosaurs. The reduced size affects the model's Reynolds number, which determines how the air reacts when flowing past the model, and compared to a full sized aircraft the size of control surfaces needed, the stability and the effectiveness of specific airfoil sections may differ considerably requiring changes to the design.Control
Flying model aircraft are generally controlled through one of three methods- Free flight model aircraft 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 model aircraft use strings or wires to tether the model to a central pivot, either held by hand or to a pole. 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 have a controller who operates a transmitter that sends signals to a receiver in the model to actuate servos that adjust the model's flight controls similarly to a full sized aircraft. Traditionally, the radio signal directly controlled servos, however, modern examples often use flight control computers to stabilize the model or even to fly it autonomously. This is particularly the case with quadcopters. Rudimentary flight controllers were first introduced in model helicopters, with standalone electronic gyroscopes used stabilize the tail rotor control. Much like quadcopters, this has now extended to all flight controls.
Construction
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 to duplicate the formers, longerons, spars, and ribs of a vintage full-size aircraft, or, on larger models where weight is less of a factor, sheets of wood, expanded polystyrene, and wood veneers 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 heat-curing or heat shrink covering plastic films or heat-shrinkable synthetic fabrics are applied to the model. Microfilm covering is used for the lightest models and is made by spreading few drops of lacquer out over several square feet of water, and lifting a wire loop through it, which creates a thin plastic film.
Flying models can be assembled from kits, built from plans, or made completely from scratch. A kit contains the necessary raw material, typically die- or laser-cut wood parts, some molded parts, plans, assembly instructions and may have been flight tested. Plans are intended for the more experienced modeller, since the builder must make or find the materials themselves. Scratch builders may draw their own plans, and source all the materials themselves. Any method may be labor-intensive, depending on the model in question.
To increase the hobby's accessibility, some vendors offer Almost Ready to Fly models that minimize the skills required, and reduce build time to under 4 hours, versus 10–40 or more for a traditional kit. Ready To Fly radio control 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 have made indoor flight more accessible and many require little more than attaching the wing and landing gear.