Radio-controlled helicopter
A radio-controlled helicopter is model aircraft which is distinct from an RC airplane because of the differences in construction, aerodynamics, and flight training. Several basic designs of RC helicopters exist, of which some are more maneuverable than others. The more maneuverable designs are often harder to fly, but benefit from greater aerobatic capabilities.
Flight controls allow pilots to control the collective, the cyclic controls, and the tail rotor. Controlling these in unison enables the helicopter to perform the same maneuvers as full-sized helicopters, such as hovering and backwards flight, and many other maneuvers that full-sized helicopters cannot, such as inverted flight.
The various helicopter controls are affected by means of small servo motors, commonly known as servos. A solid-state gyroscope sensor is typically used on the tail rotor control to counter wind- and torque-reaction-induced tail movement. Most newer helicopters have gyro-stabilization on the other 2 axis of rotation as well. Such 3-axis gyro is typically called a flybarless controller, so-called because it eliminates the need for a mechanical flybar.
The engines typically used to be methanol-powered two-stroke motors, but electric brushless motors combined with a high-performance lithium polymer battery are now more common and provide improved efficiency, performance, and lifespan compared to brushed motors, while decreasing prices bring them within reach of hobbyists. Gasoline and jet turbine engines are also used.
Just like full sized helicopters, model helicopter rotors turn at high speeds and can cause severe injuries. Several deaths have occurred, some as recently as 2013.
Types of R/C helicopters
Common power sources of remote control helicopters are glow fuel, electric batteries, gasoline and turbine engines. For the first 40 years, glow fuel helicopters were the most common type produced. However, in the last 10 years, electric powered helicopters have matured to a point where power and flight times are better, but typically not as long as glow fuel helicopters.There have been two main types of systems to control the main rotors, mechanical mixing and electronic cyclic/collective pitch mixing. Most earlier helicopters used mechanical mixing. Today, nearly all R/C helicopter use eCCPM.
Practical electric helicopters are a recent development but have rapidly developed and become more common, overtaking glow fuel helicopters in common use. Turbine helicopters are also increasing in popularity, although the high cost puts them out of reach of most people.
Internal Combustion (Nitro, Gas)
The first RC helicopters have been powered by combustion engines. Original helicopter "classes" were based on the engine size. For example, a helicopter with a engine was a 30 class and a helicopter with a engine was referred to as a 90 class helicopter. The bigger and more powerful the engine, the larger the main rotor blade that it can turn and hence the bigger the aircraft overall. Typical flight time for nitro helicopters is 7–15 minutes depending on the engine size and tuning.Electric
Two small electric helicopters emerged in the mid-1990s. These were the Kalt Whisper and the Kyosho EP Concept, flying on 7–8 × 1.2 Ah NiCad batteries with brushed motors. However, the 540-sized brushed-motors were on the limit of current draw, often 20–25 amps on the more powerful motors, hence brush and commutator problems were common.Recent advancements in battery technology are making electric flying more feasible in terms of flying time. Lithium polymer batteries are able to provide the high current required for high performance aerobatics while still remaining very light. Typical flight times are 4–12 minutes depending on the flying style and battery capacity.
In the past electric helicopters were used mainly indoors due to the small size and lack of fumes. Larger electric helicopters suitable for outdoor flight and advanced aerobatics have become a reality over the last few years and have become very popular. Their quietness has made them very popular for flying sites close to residential areas and in places such as Germany where there are strict noise restrictions. Nitro helicopters have also been converted to electric power by commercial and homemade kits.
The smallest remote-controlled production model helicopter made is the Silverlit Nano Falcon XS sold at many toy stores, electronics stores and internet stores, costing about $30. The next smallest is the Nano Falcon, which previously held the record for the smallest rc helicopter.
Several models are in contention for the title of the smallest non-production remote-controlled helicopter, including the Pixelito family of micro helicopters, the Proxflyer family, and the Micro flying robot.
Coaxial
A recent innovation is that of coaxial electric helicopters. The system's simple direction control and freedom from torque induced yaw have, in recent years, made it a good candidate on small models for beginner and/or indoor use. Models of this type, as in the case of a full-scale helicopter, eliminate rotational torque and can have extremely quick control response, both of which are very pronounced in a CCPM model. Most cheaper models do not have a swashplate, but instead use a third rotor on the tail to provide pitch control. These helicopters have no roll control and have limited mobility.While a coaxial model is very stable and can be flown indoors even in tight quarters, such a helicopter has limited forward speed, especially outdoors. Most models are fixed-pitch, i.e. the collective pitch of the blades cannot be controlled, plus the cyclic control is only applied to the lower rotor. Compensating for even the slightest breeze causes the model to climb rather than to fly forward even with full application of cyclic. More advanced coaxial constructions with two swash plates and/or pitch control have been realized as models in individual projects but have not seen the mass market as of 2014.
Multirotor model helicopters
More recently, multirotor designs have become popular in both the RC hobby and unmanned aerial vehicle research. These vehicles use an electronic control system and electronic sensors to stabilize the aircraft. Multirotors are generally more affordable, easier to construct, and simpler to operate than RC helicopters. This made multirotor aircraft an appealing platform for amateur model aircraft projects and aerial photography.Size classes
Nitro RC helicopters are categorised under the following classes:- 30 size : Engine 0.3 cubic inch, Main Blades 550-600mm
- 50 size : Engine 0.5 cubic inch, Main Blades 600-620mm
- 60 size : Engine 0.6 cubic inch
- 90 size : Engine 0.9 cubic inch, Main Blades 690-710mm
- Micro
- Mini - classically called 300–450.
- 500
- 600
- 700
- 800
Radio gear
Transmitter
RC helicopters generally require between 3 and 7 channels for control. Small fixed-pitch helicopters use a 4-channel radio ; while collective-pitch models need a minimum of 5 channels. 6th channel is often used for gyro gain. 7th channel commonly used for engine governor control for fuel powered models. Because of the normal interaction of the various control mechanisms, advanced radios include adjustable mixing functions, such as throttle/collective and throttle/rudder. Radio prices vary from $50–$3,000 USD.Early radio controls systems used amplitude modulation to transmit their signals. In the late '70s, frequency modulation became more commonplace.
Spread spectrum
Starting with the Spektrum DX6 park flyer transmitter system in 2006, RC flying began the departure from various lower frequencies which were subject to interference and were less reliable than the new spread spectrum protocols. Systems such as Spektrum and JR use the DSM2 and later, DSMX direct-sequence spread spectrum method, where they transmit on a pair of fixed channels chosen when the radio and receiver are turned on. Any subsequent systems would avoid using these channels and continue searching for another unused pair of channels.Systems such as frequency-hopping spread spectrum used by Futaba employ frequency hopping on the 2.4 GHz band instead of the various frequencies in the lower MHz ranges. The advantage is that radios are no longer using a fixed frequency during flight, mitigating the risk of interference on that fixed frequency.
With either method many radios can be transmitting at once without interfering with each other. The Futaba systems change frequency approximately every two milliseconds, so even if two transmitters are using the same channel they are not doing so for long. The pilot will not notice any abnormal behavior of the model in the 1/500th of a second that they are interfering. This gives one the advantage of turning on a transmitter without regard to channels currently in use by other pilots' radios.
One downside to 2.4 GHz is that precautions must be taken during installation since certain materials such as carbon fiber can mask the signal. In some cases, satellite receivers with secondary antennas need to be used to maintain better line-of-sight with the transmitter radio. Another drawback is that a 2.4 GHz standard has yet to evolve so that receivers and transmitters can be mixed regardless of their respective manufacturer.
Controls
Learning to fly a collective pitch RC helicopter takes time and practice. Many modelers join a club so they can be instructed by experienced RC pilots, or follow on-line guides.RC Helicopters usually have at least four controls: roll - cyclic pitch, elevator, rudder and pitch/throttle. For simple flight, the radio is usually configured such that pitch is around −1 degree at 0% throttle stick, and somewhere around 10 degrees at 100% throttle stick. It is also necessary to modulate the throttle in conjunction with the pitch so that the model maintains a constant rotor speed. This is beneficial for consistent and smooth flight performance.
If aerobatic '3D' performance is desired, then automatic throttle, or idle up, mode of flight is used. In this mode, the collective pitch ranges from its negative limit at 0% throttle stick input, up to its positive limit at 100% throttle stick. The throttle, on the other hand, is modulated automatically to maintain a constant rotor speed and is usually at its lowest value when the throttle stick is centered and the pitch is 0. This mode allows the rotor to produce a thrust upwards which, when the model is inverted, allows sustained inverted flight. Usually a more advanced computer radio is used for this kind of flying, which allows customization of the throttle-collective mix.
The cyclic and yaw controls are not by definition different in these two modes, though 3D pilots may configure their models to be much more responsive.