RC helicopter radio controls have in recent years become somewhat demystified through the advent of the new toy grade 3-channel radio controlled model helicopters of the coaxial kind (the ones with two main rotors rotating in opposite directions), which are often impressively demonstrated in toy shops.
3-Channel Radio Controlled Model Helicopters
RC helicopter controls of this type are simple: left stick is for up and down (power or speed of rotors); right stick is for turning the nose left or right (turning is controlled by changing the relative speed of the two main rotors on coaxials) as well as for forwards and backwards (lifting or lowering the tail with its horizontal rotor). Each of these types of control corresponds to a channel on the 3-channel transmitter.
Radio controlled model helicopters of the 3-channel toy grade kind have fairly limited control, as a number of "real" helicopter controls are missing, and this brings us to RC helicopter radio controls of the 4-channel variety.
Above: Coaxial RC helicopter Swordfish in flight picture.
4-Channel RC Helicopter Radio Controls
With 4-channel RC helicopters the picture is somewhat different, and it starts with the hobby grade coaxial RC helicopters. Take for example the Nine Eagles Swordfish coaxial machine. Although this heli has no functioning tail rotor, it is much more advanced and much more maneuverable than any of the toy grade helicopters with horizontal tail rotors.
So ho does it work, and where does the fourth channel come into the picture?
The RC helicopter controls in this bird start with the left stick which controls the speed of the twin rotors, in other words the power to go up or down (forwards and backwards on the stick; this represents the 1st channel); the left stick also controls the direction the nose is pointing (left or right on the stick; this is the 2nd channel) by varying the relative speeds of the two rotors (this is why it doesn't "need" a functioning tail rotor!).
The right stick represents the cyclic controls, firstly moving the heli forwards or backwards by tilting the whole rotor in the appropriate direction (channel 3); and lastly controlling sideways banking movements by tilting the lower rotor left or right (channel 4).
6-Channel RC Helicopter Controls
The Belt CP2 (Belt CP Version 2) is a popular entry-level 6-Channel RC helicopter. This helicopter has the same cyclic controls on the right stick as those in the Swordfish example above, representing two of its 6 channels: forwards, backwards and sideways banking.
The difference with 4-channel helis lies in the capabilities of the left stick. As any Belt CP V2 review will probably explain, engine power (main rotor speed) is similarly controlled by the up and down range of the stick movement (3rd channel), but the same stick movement also controls variations in the pich angle of the rotor blades (collective pitch or CP): moving the stick up (power up) also results in an increase in positive angle of attack, and a lower stick position gives a lower or negative pitch; CP control takes up another channel.
The 5th channel is used by the tail rotor control, which is the left-right movement on the left stick. This controls the direction your heli's nose points.
And the 6th channel? This channel is reserved for the gyro. An RC helicopter such as the Belt CP2 has an advanced heading lock gyro which assists in keeping the nose pointing where you command, regardless of other forces like wind on the aircraft. The gyro can be remotely engaged with a switch on top of the transmitter unit.