Scale model
A scale model is a physical model that is geometrically similar to an object. Scale models are generally smaller than large prototypes such as vehicles, buildings, or people; but may be larger than small prototypes such as anatomical structures or subatomic particles. Models built to the same scale as the prototype are called mockups.
Scale models are used as tools in engineering design and testing, promotion and sales, filmmaking special effects, military strategy, and hobbies such as rail transport modeling, wargaming and racing; and as toys. Model building is also pursued as a hobby for the sake of artisanship.
Scale models are constructed of plastic, wood, or metal. They are usually painted with enamel, lacquer, or acrylics.
Model prototypes include all types of vehicles, buildings, people, and science fiction themes.
Methods
The models are built to scale, defined as the ratio of any linear dimension of the model to the equivalent dimension on the full-size subject, expressed either as a ratio with a colon, or as a fraction with a slash. This designates that 1 length unit on the model represents 8 such units on the prototype. In English-speaking countries, the scale is sometimes expressed as the number of feet on the prototype corresponding to one inch on the model, e.g. 1:48 scale = "1 inch to 4 feet", 1:96 = "1 inch to 8 feet", etc.Models are obtained by three different means: kit assembly, scratch building, and collecting pre-assembled models. Scratch building is the only option available to structural engineers, and among hobbyists requires the highest level of skill, craftsmanship, and time; scratch builders tend to be the most concerned with accuracy and detail. Kit assembly is done either "out of the box", or with modifications. Many kit manufacturers, for various reasons leave something to be desired in terms of accuracy, but using the kit parts as a baseline and adding after-market conversion kits, alternative decal sets, and some scratch building can correct this without the master craftsmanship or time expenditure required by scratch building.
Purposes
Scale models are generally of two types: static and animated. They are used for several purposes in many fields, including:Hobby
Most hobbyist models are built for static display, but some have operational features, such as railroad trains that roll, and airplanes and rockets that fly. Flying airplane models may be simple unpowered gliders, or have sophisticated features such as radio control powered by miniature methanol/nitromethane engines.Slot car racing
Cars in 1:24, 1:32, or HO scale are fitted with externally powered electric motors which run on plastic road track fitted with metal rails on slots. The track may or may not be augmented with miniature buildings, trees, and people.Wood car racing
Children can build and race their own gravity-powered, uncontrolled cars carved out of a wood such as pine, with plastic wheels on metal axles, which run on inclined tracks.The most famous wood racing event is the Boy Scouts of America's annual Pinewood Derby which debuted in 1953. Entry is open to Cub Scouts. Entrants are supplied with a kit containing a wooden block out of which to carve the body, four plastic wheels, and four axle nails; or they may purchase their own commercially available kit. Regulations generally limit the car's weight to, width to, and length to. The rules permit the cars to be augmented with tungsten carbide weights up to the limit, and graphite axle lubricant.
Wargaming
Miniature wargames are played using miniature soldiers, artillery, vehicles, and scenery built by the players.Television and film production
Before the advent of computer-generated imagery, visual effects of vehicles such as marine ships and cyber vehicles were created by filming "miniature" models. These were considerably larger scale than hobby versions to allow inclusion of a high degree of surface detail, and electrical features such as interior lighting and animation. For Star Trek: The Original Series, a pre-production model of the Starship Enterprise was created in December 1964, mostly of pine, with Plexiglass and brass details, at a cost of $600. This was followed by a production model constructed from plaster, sheet metal, and wood, at ten times the cost of the first. As the Enterprise was originally reckoned to be long, this put the models at 1:344 and 1:83.9 scale respectively. The Polar Lights company sells a large plastic Enterprise model kit essentially the same size as the first TV model, in 1:350 scale. It can be purchased with an optional electronic lighting and animation kit.Engineering
Structural
Although structural engineering has been a field of study for thousands of years and many of the great problems have been solved using analytical and numerical techniques, many problems are still too complicated to understand in an analytical manner or the current numerical techniques lack real world confirmation. When this is the case, for example a complicated reinforced concrete beam-column-slab interaction problem, scale models can be constructed observing the requirements of similitude to study the problem. Many structural labs exist to test these structural scale models such as the Newmark Civil Engineering Laboratory at the University of Illinois, UC.For structural engineering scale models, it is important for several specific quantities to be scaled according to the theory of similitude. These quantities can be broadly grouped into three categories: loading, geometry, and material properties. A good reference for considering scales for a structural scale model under static loading conditions in the elastic regime is presented in Table 2.2 of the book Structural Modeling and Experimental Techniques.
Structural engineering scale models can use different approaches to satisfy the similitude requirements of scale model fabrication and testing. A practical introduction to scale model design and testing is discussed in the paper "Pseudodynamic Testing of Scaled Models".
Aerodynamic
Aerodynamic models may be used for testing new aircraft designs in a wind tunnel or in free flight. Models of scale large enough to permit piloting may be used for testing of a proposed design.Architectural
Architecture firms usually employ model makers or contract model making firms to make models of projects to sell their designs to builders and investors. These models are traditionally hand-made, but advances in technology have turned the industry into a very high tech process than can involve Class IV laser cutters, five-axis CNC machines as well as rapid prototyping or 3D printing. Typical scales are 1:12, 1:24, 1:48, 1:50, 1:100, 1:200, 1:500, etc.Advertising and sales
Military
With elements similar to miniature wargaming, building models and architectural models, a plan-relief is a means of geographical representation in relief as a scale model for military use, to visualize building projects on fortifications or campaigns involving fortifications.In the first half of the 20th century, navies used hand-made models of warships for identification and instruction in a variety of scales. That of 1:500 was called "teacher scale." Besides models made in 1:1200 and 1:2400 scales, there were also ones made to 1:2000 and 1:5000. Some, made in Britain, were labelled "1 inch to 110 feet", which would be 1:1320 scale, but are not necessarily accurate.
Manned ships
Many research workers, hydraulics specialists and engineers have used scale models for over a century, in particular in towing tanks. Manned models are small scale models that can carry and be handled by at least one person on an open expanse of water. They must behave just like real ships, giving the shiphandler the same sensations. Physical conditions such as wind, currents, waves, water depths, channels, and berths must be reproduced realistically.Manned models are used for research, engineering and for training in shiphandling. They are usually at 1:25 scale.
Materials
Models, and their constituent parts, can be built out of a variety of materials, such as:Plastic
This includes injection molded or extruded plastics such as polystyrene, acrylonitrile butadiene styrene, butyrate, and clear acrylic and copolyester. Parts can also be cast from synthetic resins.Wood
wood is sometimes used; balsa wood, a light wood, is good for flying airplane models.Metal
Aluminum or brass can be used in tubing form, or can be used in flat sheets with photo-etched surface detail. Model figures used in wargaming can be made of white metal.Glue
Styrene parts are welded together using plastic cement, which comes both in a thick form to be carefully applied to a bonding surface, or in a thin liquid which is applied into a joint by capillary action using a brush or syringe needle. Ethyl cyanoacrylate aka "super-glue", or fast-setting epoxy, must be used to bond styrene to other materials.Paint
Glossy colors are generally used for car and commercial truck exteriors. Flat colors are generally desirable for military vehicles, aircraft, and spacecraft. Metallic colors simulate the various metalsEnamel paint has classically been used for model making and is generally considered the most durable paint for plastics. It is available in small bottles for brushing and airbrushing, and aerosol spray cans. Disadvantages include toxicity and a strong chemical smell of the paint and its mineral spirit thinner/brush cleaner. Modern enamels are made of alkyd resin to limit toxicity. Popular brands include Testor's in the US and Humbrol in the UK.
Lacquer paint produces a hard, durable finish, and requires its own lacquer thinner.
Enamels have been generally replaced in popularity by acrylic paint, which is water-based. Advantages include decreased toxicity and chemical smell, and brushes clean with soap and water. Disadvantages include possibly limited durability on plastic, requiring priming coats, at least two color coats, and allowing adequate cure time. Popular brands include the Japanese import Tamiya.
Some beginner's level kits avoid the necessity to paint the model by adding pigments and chrome plating to the plastic.