drone aircraft

Radio-controlled aircraft

A radio-controlled aircraft (often called RC aircraft or RC plane) is a model aircraft that is controlled remotely, typically with a hand-held transmitter and a receiver within the craft. The receiver controls the corresponding servos that move the control surfaces based on the position of joysticks on the transmitter, which in turn move 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

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. In 1920s, the Royal Aircraft Establishment of Britain built and tested the Larynx, a monoplane with a range powered by a Lynx engine. It was not until the 1930s that the British came up with the Queen Bee, a modified de Havilland Tiger Moth, and similar target aircraft.

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. You can also build scale models of manned aircraft. Some models are made to look and operate like a bird instead. Other sport aircraft are designated for scale-like flying referred to as "scale". Scale is a very demanding but rewarding aspect of the hobby.

Sailplanes and gliders

Gliders are planes that do not typically have any type of propulsion, as a general rule. Because most gliders are unpowered, 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 propulsion to gliders and is commonly employed today.

Jets

Jets tend to be very expensive and commonly use a micro turbine or ducted fan to power them. Airframes are constructed from fiber glass and carbon fiber. 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. The micro turbines start with kerosene, then burn for a few seconds before introducing the jet fuel by solenoid. These aircraft can often reach speeds in excess of 200 mph. They require incredibly quick reflexes and very expensive equipment, so are usually reserved for the expert. The FAA heavily regulates flying of such aircraft to only approved AMA (Aeronautical Modelers Association) sites, in where certified turbine pilots may fly. 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 $5000-$20,000. 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 LIPO (Lithium Ion Polymer pack) at 8-12 volts that control the FADEC. There is also a LIPO for the onboard servos that control ailerons, rudder, flaps and landing gear. The Federal Government has recently prohibited such use of RC Jets in urban areas (2006).

Pylon racers

Racers are small propeller aircraft that race around a 2, 3, or 4 pylon track. They tend to be hard to see and can often go over , 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 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 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 . 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, with 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 on the course. Because of their limited wing area however, Q50 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, and real birds are often surprised by these unexpected visitors in their aerial domain. 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.

3D flight

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, and relatively low wing loadings.

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.

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

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. 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

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 4 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 (gas, 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.

Balsa kit

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. Die-cut kits can work and look just as good with a little sanding, cutting and use of basic woodworking principles.

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 throwing and can then land in soft grass.

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 you have finished making all the parts, 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.

Plane characteristics

Wing location

High wing

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. Because of the wing shape, wing position, and drag under the wing due to the fuselage, these planes fly slower than their mid and low wing counterparts, but can usually do some aerobatic maneuvers.

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

Low wing

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 a high wing plane.

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

Mid-wing

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 doesn't 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 determined by the number of mechanical servos that have been installed. 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.

  • Ailerons - controls roll.
  • Elevator - controls pitch (up and down).
  • Throttle or, if electric, motor speed.
  • Rudder - controls yaw (left and right).
  • Retracts - controls retractable landing gear.
  • Flaps - used to steepen the landing approach angle, let the plane land at a slower touchdown speed, and get the plane off the ground slightly faster during takeoff.
  • Auxiliary 2 - controls lights, cameras or other device.

If you are a complete beginner there are planes with three channels which operate on only Throttle, Elevator and Rudder. It is suggested to practice simulation before operating a RC aircraft as it will reduce any damage or disappointment on your very first flight. People who have mastered their simulation flights should move on to 4 channel aircraft for their first flight experience. Four channel aircraft are controlled by throttle, elevator, rudder, and ailerons.

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.

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). Some delta winged aircraft designs, such as the Concorde do not have an elevator. When that function is mixed with ailerons the surfaces are known as elevons. Each of these mixes is common on radio control planes and is increasingly performed electronically within the RC transmitter. 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).

Turning

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, turning is accomplished by rolling the plane left or right and applying the correct amount of up-elevator. If the plane has a rudder instead, the wing needs to have a significant amount of dihedral (V-bend in the wing). The rudder will turn the plane so that one wing will turn into the wind, causing it to lift and roll the aircraft. Many trainers and electric park fliers use this technique.

A more complex four channel model is usually turned like a full size aircraft; it is rolled into a turn with ailerons and then 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.

For the perfectionist, a small amount of rudder can be applied when rolling into or out of a turn, in the direction of the rolling motion to correct adverse yaw.

Many radio controlled aircraft, especially the low end `toy' models, are designed to be flown with no movable control surfaces at all. Instead, the planes typically have two propellers or ducted fans, one on each wing and the plane is controlled only by this. Usually the planes only have two control channels -- throttle and yaw. In general this results in a plane that flies poorly and is very difficult to fly, though some fly better than others.

Some model planes are designed this way because it's often cheaper and lighter to control the speed of a motor than it is to actually provide a moving control surface. Full-scale planes are generally not designed without control surfaces like this because 1) it rarely produces good control even under ideal conditions and 2) a loss of engine power would lead to a total loss of flight control and an almost certain crash.

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 you will have incorrect ratios of elevator and rudder.

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 stoke engines. Glowplug engines which use nitro-methanol as fuel, compressive ignition ('diesel') burn parafffin with ether as an ignition agent. Larger engines can be glowplug but increasingly common gasoline is the fuel of choice.

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.
  • 50/53 MHz: for all vehicles, with the operator holding a valid amateur radio (FCC in the USA) license.
  • 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)

US frequency chart available at , Canadian frequency chart available at

European reserved frequency bands

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

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)
  • 2.4 GHz is permitted under NZMAA and MED/RSM regulations, provided equipment bears a C-Tick compliance label

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)

Remarkably, there are specific bands in 35 MHz called A and B bands. Some European countries allows only use in A band, whereas others allow use in A and B band.

Channels

Most RC aircraft in the USA utilize 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, 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.

Some new controllers use spread spectrum technology. Spread spectrum allows multiple applications (pilots) to transmit in the same band (2.4 GHz) 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.

Monitoring of RC Aircraft Performance

The increased complexity of aircraft power systems has created the need for tools to measure model performance, both during ground testing and in-flight.

As of 2008, the popularity of lithium-polymer (LiPo) based electric power systems increased the need for in-flight monitoring, due to the fragility of LiPo batteries. Several light weight and low cost in-flight monitors and meters designed specifically for RC are available in 2008, such as the one pictured at right.

Military usage

Radio-controlled aircraft are also used for military purposes, with their primary task being intelligence-gathering reconnaissance. These are usually vehicles not designed to contain a human pilot (see Unmanned aerial vehicle. Remotely controlled drone aircraft were used to train gun crews.

See also

References

External links

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