Radio-controlled aircraft

A radio-controlled (model) 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 communicates with a receiver within the craft that sends signals to servomechanisms (servos) which move the control surfaces based on the position of joysticks on the transmitter. The control surfaces, in turn, affect the orientation of the plane.

Flying RC aircraft as a hobby has been growing worldwide with the advent of more efficient motors (both electric and miniature internal combustion or jet engines), lighter and more powerful batteries and less expensive radio systems. A wide variety of models and styles is available.

Scientific, government and military organizations are also utilizing RC aircraft for experiments, gathering weather readings, aerodynamic modeling and testing, and even using them as drones or spy planes.

History

RAE Larynx on cordite fired catapult of destroyer HMS Stronghold, July 1927. The man on the box is Dr George Gardner, later Director of the RAE^[1]

The earliest examples of electronically guided model aircraft were hydrogen-filled model airships of the late 19th century. They were flown as a music hall act around theater auditoriums using a basic form of spark-emitted radio signal.^[1] In the 1920s, the Royal Aircraft Establishment of Britain built and tested the pilotless Larynx, a monoplane with a 100-mile (160 km) range. It was not until the 1930s that the British came up with the Queen Bee, a gunnery target version of the de Havilland Tiger Moth, and similar target aircraft. Radio control systems for model aircraft were developed in the late 1940s and early 1950s by English enthusiasts such as Howard Boys, who patented his 'Galloping Ghost' system of proportional control and became a regular contributor to Aeromodeller on the topic.^[2]

In the United States, two pioneers in the field of controlling model planes by radio were Ross Hull and Clinton DeSoto, officers of the American Radio Relay League. During 1937, these two men successfully built and flew several large R/C gliders in the first public demonstration of controlled flights, in the course of which their sailplanes made more than 100 flights. A scheduled R/C event at the 1937 National Aeromodeling Championships attracted six entrants: Patrick Sweeney, Walter Good, Elmer Wasman, Chester Lanzo, Leo Weiss and B. Shiffman, Lanzo winning with the lightest (6 pounds) and simplest model plane, although his flight was rather erratic and lasted only several minutes. Sweeney and Wasman both had extremely short (5-second) flights when their aircraft took off, climbed steeply, stalled and crashed. Sweeney, however, had the distinction of being the first person to attempt a R/C flight in a national contest. The other three entrants were not even able to take off, although Good, with his twin brother William, persisted with developing R/C systems, culminating in first placings in the 1940 US Nationals and again after the end of World War II, in 1947. Their historic R/C model airplane, which they named the “Guff,” was presented to the National Air and Space Museum in Washington, D.C., in May, 1960, where it can be seen today.^[3]

Types

There are many types of radio-controlled aircraft. For beginning hobbyists, there are park flyers and trainers. For more advanced pilots there are glow plug engine, electric powered and sailplane aircraft. For expert flyers, jets, pylon racers, helicopters, autogyros, 3D aircraft, and other high-end competition aircraft provide adequate challenge. Some models are made to look and operate like a bird instead. Replicating historic and little known types and makes of full-size aircraft as "flying scale" models, which are also possible with control line and free flight types of model aircraft, actually reach their maximum realism and behavior when built for radio control flying.

Radio control scale aircraft modeling

This Kyosho "Phantom 70" biplane is a semi-scale replica of a class winner and record holder from the 2007 Reno Air Races. In this example, the fuselage with its complex curves as well as the engine cowl, wheel pants and wing struts are rendered in fiberglass. The wings and horizontal stabilizer are traditional balsa/plywood construction

Perhaps the most realistic form of aeromodeling, in its main purpose to replicate full-scale aircraft designs from aviation history, for testing of future aviation designs, or even to realize never-built "proposed" aircraft, is that of radio control scale aeromodeling, as the most practical way to re-create "vintage" full-scale aircraft designs for flight once more, from long ago. RC Scale model aircraft can be of any type of steerable airship lighter-than-air (LTA) aviation craft, or more normally, of the heavier-than-air fixed wing glider/sailplane, fixed-wing single or multi-engine aircraft, or rotary-wing aircraft such as autogyros or helicopters.

Full-scale aircraft designs from every era of aviation, from the "Pioneer Era" and World War I's start, through to the 21st century, have been modeled as radio control scale model aircraft. Builders of RC Scale aircraft can enjoy the challenge of creating a controllable, miniature aircraft that merely "looks" like the full scale original in the air with no "fine details", such as a detailed cockpit, or seriously replicate many operable features of a selected full scale aircraft design, even down to having operable cable-connected flight control surfaces, illuminated navigation lighting on the aircraft's exterior, realistically retracting landing gear, etc. if the full-sized aircraft possessed such features as part of its design.

Various scale sizes of RC scale aircraft have been built in the decades since modern digital-proportional, miniaturized RC gear came on the market in the 1960s, and everything from indoor-flyable electric powered RC Scale models, to "giant scale" RC Scale models, in scale size ranges that usually run from 20% to 25%, and upwards to 30 to 50% size of some smaller full scale aircraft designs, that can replicate some of the actual flight characteristics of the full scale aircraft they are based on, have been enjoyed, and continue to be built and flown, in sanctioned competition and for personal pleasure, as part of the RC scale aeromodeling hobby.

A large (~40 inch wingspan) scale remote control P-51 Mustang.

Sailplanes and gliders

F3A Pattern Ship – ZNline Alliance by CPLR

Shinden by Bryan Hebert

Gliders are planes that do not typically have any type of propulsion. Unpowered glider flight must be sustained through exploitation of the natural lift produced from thermals or wind hitting a slope. Dynamic soaring is another popular way of providing energy to gliders that is becoming more and more common. However, even conventional slope soaring gliders are capable of achieving speeds comparable with similar sized powered craft. Gliders are typically partial to slow flying and have high aspect ratio, as well as very low wing loading (weight to wing area ratio). 3-channel gliders which use only rudder control for steering and dihedral or polyhedral wing shape to automatically counteract rolling are popular as training craft, due to their ability to fly very slowly and high tolerance to error.

Powered gliders have recently seen an increase in popularity. By combining the efficient wing size and wide speed envelope of a glider airframe with an electric motor, it is possible to achieve long flight times and high carrying capacity, as well as glide in any suitable location regardless of thermals or lift. A common method of maximising flight duration is to quickly fly a powered glider upwards to a chosen altitude and descending in an unpowered glide. Folding propellers which reduce drag (as well as the risk of breaking the propellor) are standard. Powered gliders built with stability in mind and capable of aerobatics, high speed flight and sustained vertical flight are classified as 'Hot-liners'. 'Warm-liners' are powered craft with similar abilities but less extreme thrust capability. Many powered beginner craft are based upon or considered borderline gliders.

To avoid ambiguity, unpowered gliders are typically referred to as 'slope soarers' or 'thermal soarers' respectively.

Jets

Jets tend to be very expensive and commonly use a micro turbine or ducted fan to power them. Most airframes are constructed from fiber glass and carbon fiber. For electric powered flight which are usually powered by electric ducted fans, may be made of styrofoam. Inside the aircraft, wooden spars reinforce the body to make a rigid airframe . They also have kevlar fuel tanks for the Jet A fuel that they run on. Most micro turbines start with propane, burn for a few seconds before introducing the jet fuel by solenoid. These aircraft can often reach speeds in excess of 320 km/h (200 mph). They require incredibly quick reflexes and very expensive equipment, so are usually reserved for the expert.

In the U.S.A the FAA heavily regulates flying of such aircraft to only approved AMA Academy of Model Aeronautics sites, in where certified turbine pilots may fly. Also, the AMA requires model aviation enthusiasts who wish to operate miniature gas turbine powered RC model aircraft, to be certified in the operation of the type of gas turbine engine, and all aspects of safety in operating such a turbine-powered model aircraft, that they need to know in flying their model.. Some military bases allow such high tech aircraft to fly within limited airspace such as Kaneohe Marine base in Hawaii, and Whidbey Island NAS in Washington State.

An average turbine aircraft will cost between $150–$10,000 with more than $20,000 all-up becoming more common. Many manufactures sell airframes such as Yellow Aircraft and Skymaster. Turbines are produced from The Netherlands (AMT)to Mexico (Artes Jets). The average microturbine will cost between $2500 and $5000 depending on engine output. Smaller turbines put out about 12 lbf (53 N) of thrust, while larger microturbines can put out as much as 45 lbf (200 N) of thrust. Radio control jets require an on board FADEC (Full Authority Digital Engine Control) controller, this controls the turbine, just like a larger turbine. RC Jets also require electrical power. Most have a lithium polymer (LiPo) battery pack at 8-12 volts that control the FADEC. There is also a LiPo for the onboard servos that control ailerons, elevator, rudder, flaps and landing gear.

Of much less complexity are the types of RC jet aircraft that actually use an electric motor-driven ducted fan instead to power the aircraft. So called "EDF" models can be of much smaller size, and only need the same electronic speed contoller and rechargeable battery technology as propeller-driven RC electric powered aircraft use.

Pylon racers

Racers are small propeller-driven aircraft that race around a 2, 3, or 4 pylon track. They tend to be hard to see and can often go over 240 km/h (150 mph), though some people do pylon races with much slower aircraft. Although several different types of aircraft are raced across the world, those flown primarily in the US are; Q500 (424 or ARPRA, and 428), and Q40. 424 is designed as a starting point into the world of pylon racing. Inexpensive (under $200 for the airframe) kits with wing areas of 3,200 square centimetres (500 sq in) are flown with .40 size engines that can be purchased for less than $100. The goal is for the planes to be not only inexpensive, but closely matched in performance. This places the emphasis on good piloting. APRA is a version of 424 with specific rules designed for consistency. 428 aircraft are similar to 424 in appearance. The difference is in engine performance and construction. The planes are primarily made of fiberglass with composites used at high load points. Wings are often hollow to save weight. (All aircraft must meet a minimum weight. A lighter wing moves more of the weight closer to the center of gravity. This requires less control deflection and its resulting drag to change the planes attitude.) They also use .40 cu in size engines but unlike 424 they are much more expensive. They have been designed to put out the maximum amount of power at a specific RPM using a specific fuel. Nelson manufactures the most predominantly used engine. Speeds are very fast in this class with planes capable of reaching 290 km/h (180 mph). Q40 is the highpoint of pylon racing, as their aircraft resemble full-size race planes. They are not limited to the simple shapes that Q500 planes are, which have much cleaner aerodynamics and less wing area. They use the same basic Nelson engine used in 428, but the engine is tuned to turn a much smaller prop at a much higher rpm. The planes accelerate much more slowly than 428, but their clean airframes allow them to reach higher speeds, and maintain them around the turns. These planes can fly in excess of 320 km/h (200 mph) on the course. Because of their limited wing area however, Q40 planes must fly a larger arc around the pylons to conserve energy. Although faster, they ultimately fly a larger course. Ironically the best times for a 10 lap 3 pylon Q40 race are very close to the same in 428.

Helicopters

Radio-controlled helicopters, although often grouped with RC aircraft, are in a class of their own because of the vast differences in construction, aerodynamics and flight training. Hobbyists will often venture from planes, to jets and to helicopters as they enjoy the challenges, excitement and satisfaction of flying. Some radio-controlled helicopters have photo or video cameras installed and are used for aerial imaging or surveillance. Newer "3d" radio control helicopters can fly inverted with the advent of advanced swash heads, and servo linkage that enables the pilot to immediately reverse the pitch of the blades, creating a reverse in thrust.

Flying bird models, or ornithopters

Some RC models take their inspiration from nature. These may be gliders made to look like a real bird, but more often they actually fly by flapping wings. Spectators are often surprised to see that such a model can really fly. These factors as well as the added building challenge add to the enjoyment of flying bird models, though some ARF (almost-ready-to-fly) models are available. Flapping-wing models are also known as ornithopters, the technical name for an aircraft whose driving airfoils oscillate instead of rotate.

Toy-class RC

Since about 2004, new, more sophisticated toy RC airplanes, helicopters, and ornithopters have been appearing on toy store shelves. This new category of toy RC distinguishes itself by:

• Proportional (vs. "on-off") throttle control which is critical for preventing the excitation of phugoid oscillation ("porpoising") whenever a throttle change is made. It also allows for manageable and steady altitude control and reduction of altitude loss in turns.
• LiPo batteries for light weight and long flight time.
• EPP (Expanded Polypropylene) foam construction making them virtually indestructible in normal use.
• Low flying speed and typically rear-mounted propeller(s) make them harmless when crashing into people and property.
• Stable spiral mode resulting in simple turning control where "rudder" input results in a steady bank angle rather than a steady roll rate.

As of 2013, the toy class RC airplane typically has no elevator control. This is to manage costs, but it also allows for simplicity of control by unsophisticated users of all ages. The downside of lack of elevator control is a tendency for the airplane to phugoid. To damp the phugoid oscillation naturally, the planes are designed with high drag which reduces flight performance and flying time. The lack of elevator control also prevents the ability to "pull back" during turns to prevent altitude loss and speed increase.

Costs range from 20 to 40 USD. Crashes are common and inconsequential. Throttle control and turning reversal (when flying toward the pilot) rapidly become second-nature, giving a significant advantage when learning to fly a more costly hobby class RC aircraft.

3D flight

Model of an mx2, a 3D aerobatic aircraft with a wingspan of 121 cm.

3D flight is a type of flying in which model aircraft have a thrust-to-weight ratio of more than 1:1 (typically 1.5:1 or more), large control surfaces with extreme throws, low weight compared to other models of same size and relatively low wing loadings. Simply put, 3D flight is the art of flying a plane below its stall speed (the speed at which the wings of the plane can no longer generate enough lift to keep the plane in the air).

These elements allow for spectacular aerobatics such as hovering, 'harriers', torque rolling, blenders, rolling circles, and more; maneuvers that are performed below the stall speed of the model. The type of flying could be referred to as 'on the prop' as opposed to 'on the wing', which would describe more conventional flight patterns that make more use of the lifting surfaces of the plane.

3D has created a huge market for electric indoor 'profile' types similar to the Ikarus 'Shockflyers' designed to be able to fly inside a gym or outside in little wind. These generally make use of small brushless motors (often outrunners, but also geared inrunners) and lithium polymer batteries. There are also many larger 3D designs designed for two and four stroke glow engines, two stroke gas engines and large electric power systems. The most common and which most pilots describe as the best size of a 3D plane is a 40%/150cc class.

Video piloting (first-person view)

A typical FPV video feed with an on-screen display showing navigational data

First-person view (FPV) flight is a type of remote-control flying that has grown in popularity in recent years. It involves mounting a small video camera and television transmitter on an RC aircraft and flying by means of a live video down-link, commonly displayed on video goggles or a portable LCD screen. When flying FPV, the pilot sees from the aircraft's perspective, and does not even have to look at the model. As a result, FPV aircraft can be flown well beyond visual range, limited only by the range of the remote control and video transmitter. Video transmitters typically operate at a power level between 200 mW and 1500 mW. The most common frequencies used for video transmission are 900 MHz, 1.2 GHz, 2.4 GHz, and 5.8 GHz.^[4] Specialized long-range UHF control systems operating at 433 MHz (for amateur radio licensees only) or 869 MHz^[4] are commonly used to achieve greater control range, while the use of directional, high-gain antennas increases video range. Sophisticated setups are capable of achieving a range of 20–30 miles or more.^[5] FPV aircraft are frequently used for aerial photography and videography, and many videos of FPV flights can be found on popular video sites such as YouTube and Vimeo.

A basic FPV system consists of a camera, video transmitter, video receiver, and a display. More advanced setups commonly add in specialized hardware, including on-screen displays with GPS navigation and flight data, stabilization systems, and autopilot devices with "return to home" capability—allowing the aircraft to fly back to its starting point on its own in the event of signal loss. On-board cameras can be equipped with a pan and tilt mount, which when coupled with video goggles and "head tracking" devices creates a truly immersive, first-person experience, as if the pilot was actually sitting in the cockpit of the RC aircraft.^[4]

Both helicopters and fixed-wing RC aircraft are used for FPV flight. The most commonly chosen airframes for FPV planes are larger models with sufficient payload space for the video equipment and large wings capable of supporting the extra weight. Pusher-propeller planes are preferred so that the propeller is not in view of the camera. Flying wing designs are also popular for FPV, as they provide a good combination of large wing surface area, speed, maneuverability, and gliding ability.

In the United States, the Academy of Model Aeronautics' (AMA) Safety Code (which governs flying at AMA affiliated fields) allows FPV flight under the parameters of AMA Document #550, which requires that FPV aircraft be kept within visual line of sight with a spotter maintaining unaided visual contact with the model at all times.^[6] Because these restrictions prohibit flying beyond the visual range of the pilot (an ability which many view as the most attractive aspect of FPV), most hobbyists that fly FPV do so outside of regular RC clubs and flying fields.

Types of kits and construction

There are various ways to construct and assemble an RC aeroplane. Various kits are available, requiring different amounts of assembly, different costs and varying levels of skill and experience.

Some kits can be mostly foam or plastic, or may be all balsa wood. Construction consists of using formers and longerons for the fuselage, and spars and ribs for the wings and tail surfaces. More robust designs often use solid sheets of wood to form these structures instead, or might employ a composite wing consisting of an expanded polystyrene core covered in a protective veneer of wood, often obechi. 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. Some of these are made by bringing frames of balsa wood and carbon fiber up through water to pick up thin plastic films, similar to rainbow colored oil films. The advent of "foamies," or craft injection-molded from lightweight foam and sometimes reinforced with carbon fiber, have made indoor flight more readily accessible to hobbyists. "Crash proof" EPP (Expanded Polypropylene) foam planes are actually even bendable and usually sustain very little or no damage in the event of an accident, even after a nose dive. Some companies have developed similar material with different names, such as AeroCell or Elapor.

The late 1980s saw a range of models from the United States company US AirCore cleverly using twinwall polypropylene material. This double skinned 'Correx' or 'Coroplast' was commonly used in advertising and industry, being readily available in flat sheet form, easily printed and die cut. Models were pre-decorated and available in ARTF form requiring relatively straightforward, interlocking assembly secured with contact adhesive. The material thickness (usually 3~6mm) and corresponding density meant that models were quite weighty (upwards of 5 lb or 2 kg) and consequently had above average flying speeds. The range were powered using a clever (interchangeable) cartridge motor mount designed for the better, more powerful 0.40 cu in (6.6 cm³) glow engines. Aircore faded from the scene around the Millennium.

Coincidently this is when the material was used experimentally by Mugi – the small tough delta glider was invented. This rapidly developed into a high performance design – the Mugi Evo. Popular worldwide as the plans were immediately launched freely on the internet. Any grade or thickness of the material can be used by appropriate scaling. However the optimum material is twinwalled polypropylene sheet in 2mm thickness and at 350gsm (density)

Amateur hobbyists have more recently developed a range of new model designs utilizing the corrugated plastic or "Coroplast" material. These models are collectively called "SPADs" which stands for Simple Plastic Airplane Design. Fans of the SPAD concept tout increased durability, ease of building, and lower priced materials as opposed to balsa models, sometimes (though not always) at the expense of greater weight and crude appearance.

Flying models have to be designed according to the same principles as full-sized aircraft, and therefore their construction can be very different from most static models. RC planes often borrow construction techniques from vintage full-sized aircraft (although they rarely use metal structures).

Ready to fly

ParkZone P-51D Mustang

Ready to fly (or RTF) planes come as pre-assembled kits that usually only require wing attachment or other basic assembly. Typically, everything that is needed is already in the kit, including the transmitter, receiver and battery. RTF planes can be up in the air in just a few minutes and 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, fabrication and even design as integral to the hobby.

Almost ready to fly

This Great Planes Supermarine Spitfire LF Mk XII wears the markings of the 222 Squadron and is an example of an almost ready to fly model

Almost ready to fly (or ARF or ARTF) kits are similar to RTF kits; however usually require more assembly and sometimes basic construction. The average ARF aircraft can be built with less than four hours of labor, versus 20–50+ hours (depending on detail and desired results) for a traditional kit aircraft. The fuselage and appendages are normally already constructed. The kit will usually require separate purchase and installation of servos, choice of motor (petrol (gasoline), glow fuel, or electric), speed controller (electric) and occasionally control rods. This is an advantage over RTF kits, as most model aircraft enthusiasts already own their equipment of choice, and only desire an airframe.

Bind-N-Fly

Bind-N-Fly (BNF) aircraft are similar to Ready to fly aircraft, except they do not come with a transmitter (some have a receiver included, and some do not). Because they do not come with a transmitter, they can be bound to one instead. This means that a pilot can have hundreds of planes all bound to one transmitter, meaning that he does not have to switch radios when he switches planes. This also means that it is cheaper to buy the planes, as they do not have a transmitter included, saving money in the long run. Like Ready to fly aircraft, they generally come with a minimum amount of assembly required.

Balsa kit

A large model J-3 Cub, scale RC models are often made of balsa and covered with lightweight plastic covering for a more realistic appearance.

Balsa kits come in many sizes and skill levels. The balsa wood may either be cut with a die-cut or laser. Laser cut kits have a much more precise construction and much tighter tolerances, but tend to cost more than die-cut kits.

The kit usually contains most of the raw material needed for an unassembled plane, a set of (sometimes elaborate) assembly instructions, and a few spare parts to allow for builder error. Assembling a model from plans or a kit can be very labor-intensive. In order to complete the construction of a model, the builder typically spends many hours assembling the frame, covering it, and polishing/refining the control surfaces for correct alignment. The kit does not include necessary tools, and these have to be purchased separately. A single overlooked error during assembly could compromise the model's airworthiness, leading to a crash that destroys the model.

Smaller balsa kits will often come complete with the necessary parts for the primary purpose of non-flying modeling or rubber band flight. These kits will usually also come with conversion instructions to fly as glow (gas powered) or electric and can be flown free-flight or radio-controlled. Converting a kit requires additional and substitution parts to get it to fly properly such as the addition of servos, hinges, speed controls, control rods and better landing gear mechanisms and wheels.

Many kits will come with a tissue paper covering that then gets covered with multiple layers of plane dope which coats and strengthens the fuselage and wings in a plastic-like covering. It has become more common to cover planes with heat-shrinking plastic films backed with heat-sensitive adhesive. These films are generally known as 'iron-on covering' since a hand-held iron allows the film to be attached to the frame; a higher temperature then causes the film to tighten. This plastic covering is more durable and makes for a quick repair. Other varieties of heat shrinkable coverings are also available, that have fibrous reinforcements within the plastic film, or are actual woven heat shrinkable fabrics.

It is common to leave landing gear off smaller planes (roughly 36" or smaller) in order to save on weight, drag and construction costs. The planes can then be launched by hand-launching, as with smaller free-flight models, and can then land in soft grass. Flute board or Coroplast can be used in place of Balsa Wood.

From plans or scratch

Planes can be built from published plans, often supplied as full-sized drawings with included instructions. Parts normally need to be cut out from sheet wood using supplied templates. Once all of the parts have been made, the project builds up just like another kit. A model plane built from scratch ends up with more value because you created the project from the plans. There is more choice of plans and materials than with kits, and the latest and more specialized designs are usually not available in kit form. The plans can be scaled to any desired size with a computer or copy machine, usually with little or no loss in aerodynamic efficiency.

Hobbyists that have gained some experience in constructing and flying from kits and plans will often venture into building custom planes from scratch. This involves finding drawings of full-sized aircraft and scaling these down, or even designing the entire airframe from scratch. It requires a solid knowledge of aerodynamics and a plane's control surfaces. Plans can be drawn up on paper or done with CAD software. Many CAD packages exist for the specific purpose of designing planes and perfecting airfoils.

Airframe materials

Several materials are commonly used for construction of the airframe of model radio controlled aircraft.

The earliest model radio controlled aircraft were constructed of wood covered with paper. Later, plastic film such as Monokote came to be widely used as a covering material. Wood has relatively low cost, high specific Young's modulus (stiffness per unit weight), good workability and strength, and can be assembled with adhesives of various types. Light-weight strong varieties such as balsa wood are preferred; basswood, pine and spruce are also used.^[7]

Carbon fiber, in rod or strip form, supplements wood in more recent models to reinforce the structure, and replaces it entirely in some cases (such as high performance turbine engine powered models and helicopters). The disadvantage of using carbon fiber is its high cost.

Expanded polystyrene and extruded polystyrene foam (Styrofoam) came to be used more recently for the construction of the entire airframe. Depron (the type of foam used for meat trays) blends rigidity with flexibility, allowing aircraft to absorb the stress of flying. Expanded polypropylene (EPP) is an extremely resilient variety of foam, often used in basic trainers, which take considerable abuse from beginners.

Twinwall extruded polypropylene sheet has been used from the mid nineties. Commonly known as Correx in the United KIngdom, it is mentioned in the sections above. Currently the Mugi group based in West Yorkshire still promote and use this material in 2mm thickness sheet form. Very tough and lightweight it has only two disadvantages. Firstly it needs particular two-part contact glues. Secondly the material is difficult to paint due to low surface adhesion. Self-adhesive coloured tapes were the answer. Components are often laminated, taking advantage of differing flute directions for strength and forming. Models tend to exceed 900mm wingspan with carbon fibre tubing used for local reinforcement. The thickness used among modellers is from 2mm to 4 mm thickness. Models made out of this material are commonly known among modellers as "Spad" types (simple plastic aeroplane design).

Plane characteristics

Wing location

High-wing planes

The easiest planes to fly are typically ones that have a high wing, or a wing that is on top or above the plane's fuselage. Wing dihedrals (bend or change of angle in wing relative to fuselage) or polyhedrals are also common. Most trainers and park flyers have this configuration.

These planes hold most of their weight under the canopy of the wing structure and tend to react more like a glider. For this reason, they are very stable and easy to fly. If a high-wing plane is out of control, stability can often be regained by returning the controls to a neutral position, allowing the plane to naturally fall back into a gliding position.

High wings are typical of many vintage private planes, such as the Piper Cub and the Cessna 170.

Low-wing planes

This .60 cubic inch/10cc glow-powered Vinh Quang Model Mudry CAP 10 is a fully aerobatic, low-wing, "sport scale" model plane with slight dihedral

Low-wing planes offer a higher level of flying difficulty because the weight of the plane sits on top of the wing structure, making the balance a bit top heavy. Most wing configurations provide a slight dihedral to provide a bit more balance during flight.

The weight distribution and wing position of a low-wing plane provides a good balance of stability and maneuverability. The plane's moment of inertia about the rotation axis is lower because it is closer to the wing, therefore rolls require much less torque and are more rapid than with a high-wing plane.

Low wings are typical of World War II war planes and many newer passenger planes and commercial jets.

Mid-wing planes

This Electrify/Great Planes model of a Yakovlev Yak-54 is an example of a high-performance, fully aerobatic mid-wing plane with no dihedral

Mid-wing planes are usually considered the most difficult to fly. The wings are usually located right in the vertical middle of the fuselage, near the bulk mass of the aircraft. Very little leverage is needed to turn and rotate the plane's weight.

Mid-wings are often straight without any dihedral providing an almost symmetrical aerodynamic structure. This allows the plane to be relatively balanced whether right-side-up, upside-down, or any other position. This is great for military jets, sport planes and aerobatic planes, but less advantageous for the learning pilot. Because of this symmetry, the plane does not really have any natural or stable flying position, like the high-wing planes, and will not automatically return to a stable gliding position.

Number of channels

The number of channels a plane requires is normally determined by the number of mechanical servos that have been installed (with a few exceptions such as the aileron servos, where two servos can operate via a single Y harness (with one of the two servos rotating in the opposite direction). On smaller models, usually one servo per control surface (or set of surfaces in the case of ailerons or a split elevator surface) is sufficient. Generally, for a plane to be considered fully functional, it must have four channels (throttle, elevator, rudder and aileron).

• Ailerons – controls roll.
• Elevator – controls pitch (up and down).
• Throttle or, if electric, motor speed.
• Rudder (or vertical stabilizer)- controls yaw (left and right).
• Gear/retracts – controls retractable landing gear (usually in conjunction with gear doors).
• Flaps – Increase lift, but also increase drag. Using flaps, an aircraft can fly slower before stalling. Flaps are often used to steepen the landing approach angle and let the plane land at a slower touchdown speed (as well as letting the aircraft lift off at a slower takeoff speed). In both cases, flaps enable using a shorter runway than would otherwise be required.
• Auxiliary control – Additional channels can control additional servos for propeller pitch (such as on 3D planes), or control surfaces such as spoilerons, flaperons, or elevons.
• Misc – bomb bay doors, lights, remote camera shutter can be assigned to extra channels. Additionally, if there is a flight assist or autopilot module on the craft (more common on the multi-rotor copters), features such as gyro-based stabilization, GPS location hold, height hold, return home, etc., can be controlled.

Three channels (controlling rudder, elevator and throttle) are common on trainer aircraft. Four channel aircraft add aileron control.

For complex models and larger scale planes, multiple servos may be used on control surfaces. In such cases, more channels may be required to perform various functions such as deploying retractable landing gear, opening cargo doors, dropping bombs, operating remote cameras, lights, etc.Transmitters are available with as few as 2 channels to as many as 18 channels.

The right and left ailerons move in opposite directions. However, aileron control will often use two channels to enable mixing of other functions on the transmitter. For example, when they both move downward they can be used as flaps (flaperons), or when they both move upward, as spoilers (spoilerons). Delta winged aircraft designs commonly lack a separate elevator, its function being mixed with the ailerons and the combined control surfaces being known as elevons. V-tail mixing, needed for such full-scale aircraft designs as the Beechcraft Bonanza, when modeled as RC scale miniatures, is also done in a similar manner as elevons and flaperons.

Tiny ready to fly RC indoor or indoor/outdoor toy aircraft often have two speed controllers and no servos, as very small and inexpensive servos are not yet available. There can be one motor for propulsion and one for steering or twin motors with the sum controlling the speed and the difference controlling the turn (yaw).

Some .049 glow models use two controls: elevator and rudder with no throttle control. The plane is flown until it runs out of fuel then landed like a glider.

Turning

Turning is generally accomplished by rolling the plane left or right and applying the correct amount of up-elevator ("back pressure").

A three channel RC plane will typically have an elevator and a throttle control, and either an aileron or rudder control but not both. If the plane has ailerons, rolling the wings left or right is accomplished directly by them. If the plane has a rudder instead, it will be designed with a greater amount of Dihedral Effect, which is the tendency for the airplane to roll in response to sideslip angle created by the rudder deflection. Dihedral Effect in model airplane design is usually increased by increasing the Dihedral Angle of the wing (V-bend in the wing). The rudder will yaw the plane so that it has a left or right sideslip, dihedral effect will then cause the plane to roll in the same direction. Many trainers, electric park fliers, and gliders use this technique.

A more complex four channel model can have both rudder and ailerons and is usually turned like a full-sized aircraft. That is, the ailerons are used primarily to directly roll the wings, and the rudder is used to "coordinate" (to keep the sideslip angle near-zero during the rolling motion). Sideslip otherwise builds up during an aileron-driven roll because of adverse yaw. Often, the transmitter is programmed to automatically apply rudder in proportion to aileron deflection to coordinate the roll.

When an airplane is in a small to moderate bank (roll angle) a small amount of 'back pressure' is required to maintain height. This is required because the lift vector, which would be pointing vertically upwards in level flight, is now angled inwards so some of the lift is turning the aircraft. A higher overall amount of lift is required so that the vertical component remains sufficient for a level turn.

Many radio controlled aircraft, especially the toy class models, are designed to be flown with no movable control surfaces at all. Some model planes are designed this way because it is often cheaper and lighter to control the speed of a motor than it is to provide a moving control surface. Instead, "rudder" control (control over sideslip angle) is provided by differing thrust on two motors, one on each wing. Total power is controlled by increasing or decreasing the power on each motor equally. Usually, the planes only have only these two control channels (total throttle and differential throttle) with no elevator control. Turning a model with differential thrust is equivalent to and just as effective as turning a model with rudder. Lack of elevator control is sometimes problematic if the phugoid oscillation isn't well-damped leading to unmanageable "porpoising". See "Toy class RC" section.

V-tail systems

A V-Tail is a way of combining the control surfaces of the standard "+" configuration of rudder and elevator into a V shape. These ruddervators are controlled with two channels and mechanical or electronic mixing. An important part of the V-Tail configuration is the exact angle of the two surfaces relative to each other and the wing, otherwise the ratio of elevator and rudder outputs will be incorrect.

The mixing works as follows: When receiving rudder input, the two servos work together, moving both control surfaces to the left or right, inducing yaw. On elevator input, the servos work opposite, one surface moves to the "left" and the other to the "right" which gives the effect of both moving up and down, causing pitch changes in the aircraft.

V-Tails are very popular in Europe, especially for gliders. In the US, the T-Tail is more common. V-Tails have the advantage of being lighter and creating less drag. They also are less likely to break at landing or take-off due to the tail striking something on the ground like an ant mound or a rock.

Powerplants

Most planes need a powerplant to drive them, the exception being gliders. The most popular types for radio-controlled aircraft are internal combustion engines, electric motors, jet, and rocket engines. Three types of internal combustion engines are available being small 2 and 4 stroke engines. Glowplug engines use nitro-methanol as fuel, compressive ignition ('diesel') burn paraffin with ether as an ignition agent. Larger engines can be glowplug but increasingly common gasoline is the fuel of choice.

In recent years electric powered models have increased in popularity due to the reducing cost and weight of components and improvements in technology, especially Lithium Polymer (LiPo) batteries and the choice of brushed motors and brushless motors. Electric systems are quieter and as they do not require fuel/exhaust, are cleaner. The advantage of electric power is the ease of starting the motor as compared to the starting of engines; electric motors that are comparable to engines are cheaper. Any form of lithium-chemistry battery cell technology packs have to be charged with "smart" chargers that have connections to every electrical connection in the pack to "balance-charge" the cells in the pack, and even with proper use of such chargers lithium-polymer battery packs can have the serious risk of fire or explosion, which has led to the increasing acceptance of lithium iron phosphate battery technology in their place as a much more rugged and durable lithium-chemistry power source.

Frequencies and sub-channels

Frequency

Frequency determines the line of communication between a receiver and transmitter. The transmitter and receiver must both be on the same frequency so the plane can be controlled.

Reserved frequencies

Many countries reserve specific frequency bands (ranges) for radio control use. Due to the longer range and potentially worse consequences of radio interference, model aircraft have exclusive use of their own frequency allocation in some countries.

USA and Canada reserved frequency bands

• 72 MHz: aircraft only (France also uses US/Canada channels 21 through 35).
• 75 MHz: surface vehicles.
• 53 MHz: all vehicles, only for older equipment on 100 kHz spacing, with the operator holding a valid amateur radio (FCC in the USA) license. The 53 MHz band began to become vulnerable to amateur radio repeater stations operating on the 53 MHz area of the 6-meter band during the early 1980s. The 53 MHz bands can still be used with relative safety for ground-based (cars, boats/ships) powered modeling activities.
• 50.8 to 51 MHz: on the 6-meter band for all vehicles at 20 kHz spacing, with the operator holding a valid amateur radio (FCC in the USA) license. Added in the 1980s as the amateur radio repeater interference problem on the earlier 53 MHz bands in the United States began to manifest itself.
• 27 MHz: general use, toys.
• 2.400-2.485 GHz: Spread Spectrum band for general use (amateur radio license holders have 2.39-2.45 GHz licensed for their general use in the USA) and using both frequency-hopping spread spectrum and direct-sequence spread spectrum RF technology to maximize the number of available frequencies on this band, especially at organized events in North America.

US frequency chart available at , Canadian frequency chart available at

European reserved frequency bands

• 35 MHz: aircraft only.
• 40 MHz: surface vehicles or aircraft.
• 27 MHz: general use, toys, citizens band radio.
• 2.4 GHz spread spectrum: surface vehicles, boats and aircraft.

Within the 35 MHz range, there are designated A and B bands. Some European countries allow use only in the A band, whereas others allow use in both bands.

Singapore reserved frequency bands

• 29 MHz: aircraft only

Australian reserved frequency bands

• 36 MHz: aircraft and water-craft (odd channels for aircraft only)
• 29 MHz: general use
• 27 MHz: light electric aircraft, general use
• 2.400-2.485 GHz: Spread Spectrum band for general use (ACMA references available at )

New Zealand reserved frequency bands

• 35 MHz: aircraft only
• 40 MHz: aircraft only
• 27 MHz: general use
• 29 MHz: general use
• 36 MHz: general use
• 72 MHz: general use (US 72 MHz "even-numbered" channels 12 through 56, at 40 kHz spacing)
• 2.400-2.4835 GHz: general use

The frequencies are permitted under legislation, provided equipment meets the appropriate standards, bears the New Zealand supplier's Supplier Code Number and has the correct compliance documentation (Radio Spectrum Management information available on the RSM website)

Detailed information, including cautions for transmitting on some of the 'general use' frequencies, can be found on the NZMAA website.

Amateur radio license reserved frequency bands

• 50 and 53 MHz in the USA and Canada
• 433–434 MHz in Germany (some of these German "ham RC" UHF band channels are also usable by "hams" in Switzerland)

Channels

Traditionally most RC aircraft in the USA utilized a 72 MHz frequency band for communication. The transmitter radio broadcasts using AM or FM using PPM or PCM. Each aircraft needs a way to determine which transmitter to receive communications from, so a specific channel within the frequency band is used for each aircraft (except for 2.4 GHz systems which use spread spectrum modulation, described below).

Most systems use crystals to set the operating channel in the receiver and transmitter. It is important that each aircraft uses a different channel, otherwise interference could result. For example, if a person is flying an aircraft on channel 35, and someone else turns their radio on the same channel, the aircraft's control will be compromised and the result is almost always a crash. For this reason, when flying at RC airfields, there is normally a board where hobbyists can post their channel flag (or "frequency pin", based on a spring-loaded clothespin with the channel marked upon it) so everyone knows what channel they are using, avoiding such incidents.

A modern computer radio transmitter and receiver can be equipped with synthesizer technology, using a phase-locked loop (PLL), with the advantage of giving the pilot the opportunity to select any of the available channels with no need of changing a crystal. This is very popular in flying clubs where a lot of pilots have to share a limited number of channels. Latest receivers now available use synthesiser technology and are 'locked' to the transmitter being used. Double conversion radio reception is normal and can offer the advantage of a built-in 'failsafe' mode too. Using synthesised receivers saves on crystal costs and enables full use of the bandwidth available, for example the 35 MHz band.

Newer Transmitters use spread spectrum technology in the 2.4 GHz frequency for communication. Spread spectrum technology allows many pilots to transmit in the same band (2.4 GHz) in proximity to each other with little fear of conflicts. Receivers in this band are virtually immune to most sources of electrical interference. Amateur radio licensees in the United States also have general use of an overlapping band in this same area, which exists from 2.39 to 2.45 GHz.

Military usage

Radio-controlled aircraft are also used for military purposes, with their primary task being intelligence-gathering reconnaissance. An Unmanned Aerial Vehicle (UAV), also known as a drone, is usually not designed to contain a human pilot. Remotely controlled target drone aircraft were used to train gun crews.

See also

• 3D Aerobatics
• British Model Flying Association
• Bruce Simpson who used RC flight control systems in the construction of a homemade cruise missile
• Discus Launch Glider
• Hotliner
• International Miniature Aerobatic Club
• Model Aeronautics Association of Canada
• Radio-controlled model
• RC Aircraft Kit Manufacturers
• RC flight simulator

References

External links

Wikimedia Commons has media related to Radio-controlled aircraft.

Wikibooks has a book on the topic of: RC Aircraft

• RC Discussion Forums
• Dedicated Wiki For Electric RC Flight
• Hooked on RC Airplanes
• Northern Ireland Association of Aeromodellers
• spadtothebone.net