Collective Pitch Works on RC Helicopters

RC Helicopter Collective Pitch - Climbing and Descending


When a RC helicopter needs to climb or descend, it uses collective pitch. When the command is given for the helicopter to climb, the servos push the entire swashplate upwards. This has the effect of simultaneously increasing the pitch of all the rotor blades. When the pitch is increased, the rotors grab more air as they move, and so lift produced is increased. This increase in lift occurs evenly, so the helicopter does not turn. When the helicopter needs to descend, the swashplate is lowered in the same way. This will decrease the amount of lift produced from the rotor blades.


RC Helicopter Cyclic Pitch - Attitude Control


Changing the bank and pitch of the helicopter requires the swashplate to tilt. This is accomplished by tilting the lower disk of the swashplate. When the lower disk is tilted, the upper disk will also tilt, while it is spinning. The main rotors, which are attached to the upper swashplate will also tilt. In order for this to happen however, each rotor must be given time to "fly up", or "fly down" to the location where it needs to be. This is accomplished by using pitch links, which provide each rotor with the information of where it needs to go, before it has to be there. The net effect is that the blades move cyclically, and tilt the motion of each rotor in one direction. The swashplate can be tilted in any direction, so the helicopter can change its pitch and bank in proportion to the commands given by the transmitter.


RC Helicopter Cyclic Collective Pitch Mixing (CCPM)


Model RC helicopters can use more than two servos in combination to control the motion of the swashplate. Software running on the rc transmitter (radio) tells each servo how much to move to achieve the desired motion of the RC helicopter. Each linkage to a servo is represented by a silver rod in the above picture. All of these rods are placed equidistant from each other. A swashplate mix refers to the number of linkages attached. For example: a two linkage swashplate would be controlled by two servo rods, placed 180 degrees apart from each other. A three linkage swashplate would use a 120 degree swash plate mix. The swash plate in the picture above has 6 control rods, and so it would use a 60 degree swash plate mix. Most RC helicopters will use a swashplate with between two or four control rods. The largest RC Helicopters use 4 control rods, because of the extra strength they give the swashplate mechanism.