All RC helicopters need a way to control their altitude and direction. In most cases, this is accomplished by altering the angle (pitch) of each rotor blade. The resulting change in airflow from the blades causes the RC helicopter to move in the desired direction. Changing the pitch of the rotors provides very fine control. There are ways that an RC helicopter can be built that eliminate the need for pitch control. These fixed pitch RC helicopters are a great way to start flying rc helicopters, because of their simplified controls and low cost. In this article we will look at how they work, and see some good examples of this design in actual RC helis.
In order to understand how fixed pitch RC helicopters work, it is useful to consider a fixed wing aircraft. Airplanes can fly because air moves over the wings, resulting in a difference in air pressure between the top and bottom, which causes lift. To increase the lift we can do one of two things. The speed of the air moving over the wings can be increased, or the curve of the wing can be made steeper. If we think of the rotors on a RC helicopter like the wings on a plane, the easiest way to increase lift is to cause them to spin faster. This will send the helicopter upwards. When the helicopter needs to descend the rotor speed is decreased.
Some RC helicopters are built using four main rotors, each mounted at a right angle to the aircraft. This design allows four channel control, without the complexity of variable pitch. A flight computer can read the input from a radio receiver and then change the speed of each motor accordingly. Using a flight computer also allows automatic stabilization of the helicopter. The flight computer is a sophisticatedcircuit board, which is capable of changing the motion of the helicopter under different conditions. This makes quad rotor helicopters perfect for aerial video and surveillance. The Draganflyer helicopters use this design, and are available in several different models.
There are two ways in which a fixed pitch RC helicopters direction of travel can be changed . If we include a rear rotor, which is mounted at a right angle to the fuselage (body of the helicopter), we can use it to push the helicopters nose in the desired direction. Our Mini Bell Helicopters are a good example of this design, and are able to be built to very small dimensions because of the reduced complexity.
We can also use two main rotors, each linked to a separate motor to turn the helicopter. By spinning each rotor at a different rate, the yaw (direction) of the helicopter can be controlled. Our Bladerunner Series and Lama V4 R/C helicopters use this fixed pitch coaxial design. Each rotor can be placed on the same axial. This reduces the size of the helicopter, so that they can be flown indoors. Learn more about coaxial helicopters.
Another benefit of the fixed pitch coaxial design is that it frees an extra channel of control. If we don’t need to control the direction (pitch or yaw, depending on application) of the RC helicopter with the tail rotor, we can mount it in the same direction as the main rotor blades, allowing pitch control. This design is found in our Micro Mosquito RC helicopter, where two main rotors are complemented by a tail rotor.
