Radio-controlled helicopter
From Wikipedia, the free encyclopedia
Radio controlled (RC) helicopters are model aircraft which are distinct from RC airplanes because of the differences in construction, aerodynamics, and flight training. Several basic designs of RC helicopters exist, some more maneuverable than others (such as helicopters with collective pitch). The more maneuverable designs are often harder to fly, but benefit from greater aerobatic capabilities.
Flight controls allow pilots to control the collective and throttle (usually linked together), the cyclic controls (pitch and roll), and the tail rotor (yaw). Controlling these in unison enables the helicopter to perform most of the maneuvers an aeroplane can do, and many that aeroplanes cannot, such as hovering and backwards flight; in this manner, they are quite similar in operation to full-sized helicopters.
The various helicopter controls are effected by means of small servo motors. A piezoelectric gyroscope is typically used on the tail rotor (yaw) control to counter wind- and torque-reaction-induced tail movement. This "gyro" does not apply a mechanical force, but rather, electronically adjusts the control signal to the tail rotor servo.
The engines used are typically methanol-powered two-stroke motors, but gasoline, jet turbine and increasingly electric brushless motors combined with a high-performance lithium ion polymer battery are also used.
RC helicopters can range in price from as little as $30/£20 to several thousands of dollars or more.
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[edit] Types of R/C Helicopter
- Nitro (internal combustion)
- Electric
- Gas turbine
- Petrol / gasoline
Nitro helicopters are currently more common than electric helicopters. Practical electric helicopters are a relatively recent development and are rapidly developing and becoming more common. Gas-turbine helicopters are also increasing in popularity, although the large cost puts them out of reach of most people.
[edit] Nitro
Nitro helicopters come in different sizes: 15, 30, 50, 60 and 90 size. These numbers originated from the size of nitro engine used in the different models (0.30 cu in, 0.50 cu in and so on). The bigger and more powerful the engine, the larger the main rotor blade that it can turn and hence the bigger the aircraft overall.
[edit] Electric
The smallest radio-controlled helicopter made (Guinness World Records 2006) is the Picoo Z sold at many toy stores, electronics stores and internet stores, costing about $40/£30. The next smallest is the Micron FP helicopter, which is also a battery-operated R/C helicopter. but the picoo z is different to most helicopters as it is not steered using the main rotor blade but by using the rudder.
Recent advancements in battery technology make electric flying more feasible in terms of flying time. However, these lithium polymer batteries can explode upon overheating. U.S. Consumer Product Safety Commission Recall Alert.
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 home made kits.
[edit] Radio gear
[edit] Radio
Brands: Spektrum, Futaba, JR, Hitec, Airtronics, Sanwa, Multiplex
Small fixed-pitch helicopters need a 4-channel radio (throttle, elevator, aileron, rudder) while collective-pitch models need a minimum of 5 channels with 6 being most common (throttle, collective pitch, elevator, aileron, rudder and gyro gain).
Radio prices vary from $199-$3,000 USD.
[edit] Modulation
Radios emit the FM signal in two types of modulation.
PPM is cheaper than PCM and is generally used in low-end helicopters. The lack of a failsafe in PPM makes it more suited to small, less dangerous models. Higher-end radios offer PCM and PPM modulation for better compatibility with all radio receivers.
[edit] PCM
Pulse Code Modulation. A scheme in which the commanded position for each servo is transmitted as an encoded number. Manufacturers use their own proprietary system to encode this number with various bits of precision. JR use Z-PCM (10 bits, 512 values) then S-PCM (11 bits, 1024 values). Futaba use PCM-1024 and G3 PCM (12 bits, 2048 values). PCM also includes a feature called Fail Safe to set servo positions to a predefined position, or to hold them at the last valid position, should a valid radio signal be lost.
[edit] PPM
Pulse Proportion Modulation. A scheme in which the commanded position for each servo is transmitted as the duty-cycle of the transmitted pulses 1 per servo position.
[edit] Construction
Construction is typically of plastic, glass-reinforced plastic, aluminium or carbon fibre. Rotor blades are typically made of wood, fibreglass or carbon fibre. Models are typically purchased in kit form from one of about a dozen popular manufacturers and take 5 to 20 hours to completely assemble.
These model helicopters contain many moving parts, from the swashplate to the mechanical linkages that allow the rotor to be tilted thus controlling direction.
The construction of helicopters has to be more precise than for fixed-wing model aircraft, because helicopters are susceptible to even the smallest of vibrations, which can cause problems when the helicopter is in flight.
[edit] Competition
Aerobatic helicopter flying has historically followed the Fédération Aéronautique Internationale rules, which for helicopters are labelled F3C. These include a predetermined routine of hovering and aerobatics.
An advanced form of RC helicopter flying is called 3D. During 3D flying, helicopters perform advanced aerobatics, sometimes in a freestyle form, or in a predetermined set of moves drawn up by the organisers of the competition. There are a number of 3D competitions around the world, two of the best known being the 3D Masters in the UK and the eXtreme Flight Championship (XFC) in the USA.
[edit] Commercial applications
Although RC helicopters are generally used by hobbyists for recreational purposes, they are sometimes used in applications such as aerial photography, filming, and remote observation or inspection. Some companies make RC helicopters specifically for these uses.
