Every RC helicopter needs to control their direction and altitude. Most often, this is accomplished by changing the pitch of the rotor blades. This results in a change in airflow from the blades and causes the RC heli to move in the desired direction. By changing the pitch of the rotor blades, fine control can be achieved. RC helicopters can be built that eliminate the need for pitch control. Fixed pitch RC helicopters are a great way to start flying rc helicopters, because of their simple controls. In this article, how they work will be explained.

In order to understand how fixed pitch RC helicopters work, we will consider a fixed wing aircraft. Airplanes fly because as air moves over the wings, a difference in air pressure between the top and bottom is created, causing lift. Increasing the lift we can be done in two ways. The velocity of the air moving over the wings can be increased, or the curve of the wing can be steepened. The rotors on an RC helicopter are like like the wings on a plane, so the simplest way to increase lift is to make them spin faster. This will make the helicopter travel upwards. Likewise, when we want the helicopter to descend, the speed of the rotors is decreased.

RC Heli Design - Quad Rotor

Several RC helicopters are built with four main rotors, mounted at a right angle to the aircraft. The quad rotor 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, so that the direction of the helicopter changes. This also allows automatic stabilization of the helicopter.

RC Heli Design - Conventional

A fixed pitch RC helicopters direction of travel can be changed in two ways. If a rear rotor is included, which is mounted at a right angle to the fuselage (body of the helicopter), it can be used to push the helicopters nose in a certain direction.

RC Heli Design - Coaxial

Two main rotors can be linked to separate motors. By spinning each rotor at a different rate, the yaw (direction) of the helicopter can be controlled. Each rotor can be placed on the same axial. The coaxial design reduces the size of the helicopter, so that it can fly indoors. More about coaxial helicopters. The fixed pitch coaxial design also frees an extra channel of control. If we don’t need the tail rotor to control the direction (yaw or pitch, depending on the application) of the RC helicopter, we can instead mount it in the same direction as the main rotor blades, allowing pitch control of the helicopter.

Cyclic collective pitch is used by RC helicopters to control flight. In a previous article, fixed pitch helicopters were explained. Fixed pitch helicopters change their direction and altitude by changing the rate at which their rotors spin, and sometimes by using a tail rotor. Finer control can be achieved by changing the pitch of the rotor blades. By changing the pitch of the blades, the airflow from them can be changed, moving the helicopter in different directions. Changing the pitch of the blades is more efficient than just increasing the speed of the blades. In this article, the mechanics of variable pitch helicopters will be explained.

How The Swashplate Works on RC Helicopters

In order for the rotor blades of an RC helicopter to change pitch, there must be a way to transform the linear motion of a servo arm into the rotating motion required by the rotor blades; this is accomplished by using a swashplate. The swashplate is a mechanical device, consisting of two plates mounted to the main rotor shaft. One of these plates is attached to the servo controls and the helicopter body, and the other rotates with the helicopter rotors. As can be seen in the picture, the swashplate transforms the motion of the servo arms into motion of the upper plate. Each rotor is connected to the upper disk of the swashplate, and so they will move as the bottom disk moves. The horizontal rods visible in the picture represent where the servo arms would connect, the number of rods included depends upon the individual helicopter. Every RC helicopter that can change the pitch of its rotor blades will have a swashplate attached to its main axial. There are many different implementations of swashplates, but each follows the same basic design shown in the image. In a conventional RC helicopter, two servos are used to control the swashplate. One servo is used to control the horizontal motion (bank) and the other is used to control the forward and aft motion (pitch).

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.

In Summary

• Every RC Helicopter that can change the pitch of its blades has a swashplate.
• The swashplate consists of two disks, one which spins and one that does not.
• The bottom swashplate does not spin, and is connected to the servo control rods.
• The swashplate consists of two disks, one which moves and one that does not.
• To rise or descend, the rotor blades move collectively
• Pitch and bank require the swashplate to move cyclically.
• Pitch links control the position of each blade.

There are different ways that coaxial RC helicopters can be designed. The main rotors of a RC helicopter can be mounted in two ways. In conventional helicopters, a main rotor is mounted on the top of the fuselage, and a smaller tail rotor is added to the end of the fuselage. The tail rotor is used to control the yaw, and every other aspect of flight is controlled by changing the pitch of the main rotor blades. It’s also necessary to have a tail rotor so that the torque from the main rotors can be canceled out. Torque is created when the main rotor spins. For every action, there is an equal and opposite reaction, so the nose turns in the opposite direction.

Coaxial Helicopters - How Do They Work

Besides using the tail rotor to control the yaw, two main rotors can be mounted on the helicopter, and spun at different rates. The difference in thrust causes the helicopters nose to turn. This duel rotor design is used in several full scale helicopters. The CH-47 Chinook is a good example of this duel rotor design, and is frequently used as a military transport helicopter because of its large lifting capacity. RC Helis use the same principle, but most of the time each rotor is mounted on the same axial, hence the term “coaxial”.

Twin rotors that spin in opposite directions

The rotors of a coaxial helicopter need to spin in opposite directions to cancel out the gyroscopic force. On some helicopters, both rotors are mounted on top of each other The main axial of a coaxial helicopter is actually two separate axils. One axial is mounted inside the other. Each sub axial is connected to a gear at the base of the main shaft, and each gear is connected to an electric motor. These two motors operate independently of each other, so the speed of each rotor can be changed.

Since the rotors need to spin in different directions, the top and bottom rotor blades are curved in different directions. This is because each rotor needs to be traveling into the air flow in order to work. The bottom rotor spins in a clockwise direction, and the top rotor spins in a counterclockwise direction.

Two Channel Coaxial RC Helis

It is possible to build a coaxial helicopter so that it only needs two main rotors, and eliminate the tail rotor entirely. Tilting the main rotors forward slightly, results in a constant forward movement. These helicopters are great for beginners due to their simple controls.

Three Channel Coaxial RC Helis

In some coaxial helicopters, a tail rotor is still added. The tail rotor is oriented in the same direction as the main rotors. The forward and reverse rate of the helicopter can be changed, because this system allows pitch control. You can fly forwards, backwards and also hover with this kind of helicopter.

Four Channel Coaxial RC Helis

Even though the coaxial design is most frequently used in small, fixed pitch RC helicopters, it can also be used for models with cyclic collective pitch. The only difference between these models and the conventional designs is their lack of a tail rotor. As with the models above, yaw is controlled by changing the rate at which each rotor spins, but the rotors can change their pitch. This allows the helicopter all four degrees of freedom: pitch, bank, throttle, and yaw. The Esky Lama V4 is good example of the four channel coaxial design.

How The Coaxial Design Benefits RC Helicopters

• Yaw can be controlled by changing the speed of the main rotors, so the pitch can be controlled with the tail rotor.
• The main rotors spin in opposite directions, which gives the helicopter stability.
• Coaxial RC helicopters are a good way to learn how to fly, because they are very stable.

MiniCopter: Adventure Flight for the Nintendo Wii is a new video game where you control various RC Helicopters. The game is controlled by the Wii remote or a classic controller - your choice. MiniCopter: Adventure Flight has 42 different missions and 7 landscapes making this game a blast for any RC helicopter fan. Your RC helicopters can be modified with various body kits and performance parts to improve performance. A two player mode lets you and a friend race your rc helis in an effort to collect the most rings.

Here are some screen shots from the MiniCopter: Adventure Flight for the Nintendo Wii.

See 117 more screen shots

Read more about MiniCopter: Adventure Flight, an RC helicopter video game, at the IGN Web site.

Officer.com recently published an article about police department creativity. “When the right tool for the job isn’t available, law enforcement can get remarkably creative.”

One department even outfitted a hobbyist’s remote-control mini-helicopter with a wireless camera to create an inexpensive yet functional piece of aerial surveillance equipment.

They don’t say what brand of RC helicopter they used or even what kind of wireless video camera system they retrofitted it with. One popular wireless video platform used by some police departments, videographers, and hobbyists is the Draganflyer SAVS from Draganfly Innovations Inc.

A remote controlled (RC)mini-helicopter may appear to be a neighborhood child’s toy but could be outfitted with a wireless camera to provide surveillance without moving officers too close to the situation.

Read the entire Officer.com article, The Products of Ingenuity.