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.

There are many different accessories that an rc helicopter pilot will use. Certain accessories will be necessary wherever you fly your model. We will look at a sample of the different items that are good to keep on hand, and what they are used for.

Spare Batteries and Charger:
A good battery is an essential part of your rc helicopter system. Your battery must be able to supply enough power to operate your electronics for at least one entire flight plus a safety reserve. You will need a charger to top up the battery between uses, or have a spare battery to use while the depleted one charges.

Hex and Nut Drivers:
These are essential for maintaining (and also building) your rc helicopter. A good set will last a long time, and make adjusting hard to reach bolts at the flying field easier.

Ball Link Pliers:
Ball link pliers are specially designed to disconnect the ball links on your model. These pliers make disconnecting ball links easier, but the same task can be performed with a pair of needle nose pliers.

Pitch Gauge:
To adjust the pitch of the rc helicopter’s rotor blades, you will need a pitch gauge. Make sure to get one with a large, easy to read scale.

Fuel and Fuel Accessories:
In addition to adequate fuel, a mechanical or electrical fuel pump with a few feet of fuel tubing makes filling easier. Spare silicone fuel tube to replace worn lines, a spare fuel filter, and a spare air filter are good to keep on hand.

Glue/Filler:
When you are flying your model, it is always useful to have some glue to do repairs with. With both CA glue and epoxy you will be prepared for most minor mishaps.

Spare Fasteners and Rotor Blades:
Spare nuts and bolts are needed in case one on your rc helicopter breaks. Keep a small case of these in your field box. Spare rotor blades are very important, because a broken rotor blade can put an end to a practice session.

Field Box:
A field box is ideal to carry all of your tools, fuel, and other accessories in when you fly your rc helicopter.

Having these parts along with you when you go out to fly your rc helicopter can be a great time saver.

The single most important thing you can do when assembling your rc helicopter is to follow the instructions. This may seem obvious at first, but it is the single biggest factor in determining whether the construction of your model is successful. I can speak from experience on this. When I was building my first model I rushed through the construction, taking many shortcuts. This lead to me spending the entire flying season undoing the damage I did to get it to fly. The moral: do not let this happen to you. Take your time, read the instructions before starting, and if something doesn’t make sense, ask before going any further.

Now that we have clarified that, I will show you the general guidelines for building your first rc helicopter model.

The first thing to do when your rc helicopter kit arrives is to not open the box. Do no open the box until you are completely ready to start construction. All of the parts will be packed neatly and efficiently, so if you take them out, you are likely to lose them. Find a place to work on your rc model where it will not be disturbed by dogs, cats, or small children. The work surface should be flat, and large enough to set out all of the rc helicopter components neatly. Refer to the article titled “Basic Tools for RC Helicopter Repair & Maintenance” for a list of the tools you will likely need. Once you have the place, time, and tools to work on your model, you can begin construction.

As you proceed through the instructions, check off each step after you complete it. This way you will not lose your place when you come back. Nuts used in the rc helicopter sometimes have an insert in them that prevents them from vibrating loose while the model is in flight. If they don’t, use blue locktite to secure them. Be sure not to confuse this with red locktite, which is permanent. It is very easy to strip the heads and threads of the different screws that you will be using during assembly. Getting a stripped screw out of its hole is not an easy task, and it is better to simply not over tighten them in the first place.

Ensure that the engine cooling fan is balanced, because if its not, the resulting vibration will affect the entire rc helicopter. If it isn’t perfectly balanced when you get it from the manufacturer, you can correct it with a small amount of sanding. Once installed, make sure that this fan runs true.

It is critical that the mesh between the main gear and the pinion gear is correct. If it is too tight, friction will waste power and wear out both gears. If the mesh is too loose, then the gears will rattle back and forth, causing vibrations and wear in the system. Some rc helicopters are made to such a low tolerance that there is no way to adjust the mesh of the gears. If the rc helicopter allows it, move them in or out until they turn freely, without either friction or excessive play.

When assembling the smaller components of the head, swashplate, and washout unit, be careful to do it accurately. Use locktite to secure all of the bolts, and do not overtighten. Make sure that the resulting parts have freedom of movement and that the control is not sloppy.

Constructing the tail rotor gearbox requires special care. The gears must mesh properly, for the same reasons mentioned above. Align the position of the setscrews so they tighten against the flat spots on the shafts. Some gearboxes provide a way to lubricate the gears after construction. If yours does not, then you will have to lubricate it well before it is sealed. The gears will wear out quickly if you do not apply enough lubricant.

Balancing the tail rotor blades is also important. To do this, mount the blades on the center hub and place the system on a high point balancer. Adjust the balance by sanding, or adding blade covering material. When installing the tail rotor blades, make sure that they are not too loose or too tight. This is essential for smooth operation. They should be tight enough to not fall under their own weight, and loose enough to move freely.

The tail boom can be secured to the fuselage with a small bolt, inserted into a hole drilled into the boom and the main frame. This can prevent the boom coming loose if its attachment to the main frame fails. The horizontal fin does not affect the flight characteristics of the helicopter in any significant way, but the vertical fin does. The vertical fin contributes to the helicopters yaw stability, and it is important to have a large one while learning to fly your model. You can make one with light plywood, but be sure to fuel-proof it. If the fin extends below the tail rotor, and can help protect it.

Fuel tanks are mounted differently between models, but here are some points to consider when mounting your tank:

• Protect the tank from vibration with foam rubber, to prevent the fuel from foaming with small vibrations
• The clunk in the fuel tank should be able to move freely, and should also reach the bottom of the tank
• Fuel filters are good, they can be either attached to the fuel system, or the fuel can filtered before use
• Pressurize the fuel tank by attaching one line to the muffler, this will increase fuel flow
• Adding an extra, or header tank is also fine, but it does not affect the fuel flow to the engine

The blades for your rc helicopter will need to be balanced. This is one of the cheapest and easiest ways to do it:

1. Find the spanwise center of gravity by balancing the leading edge of each blade on a pencil, and then mark the center of gravity.
2. Determine if the balance points on each blade are the same by lining them up. If the balance points match, then no further adjustments are necessary.
3. If the balance points do not match up, then add electrical tape to the tip or root of the blade as required.
4. Mount the blades on a blade balancer to determine their relative weights. These need to be equal, so if they are not, add electrical tape to the centre of gravity of the light blade, until balance is achieved.

The blades of the rc helicopter will have to be made visible, while in flight. You will need to tell between the two different blades, and see the rotor disk. The former can be accomplished by placing different colors of tape on the ends of each blade. The former can require strips of blade covering material, in a color that contrasts the rotor blade, to be applied to both rotor blades.

After the assembly process is complete, you should have a finished model that you can be proud of. Make sure that everything looks right, and enjoy flying your new rc helicopter.

There are several basic tools that you will need to get the most out of your RC helicopter.

Basic tools that you will need are as follows:

• Standard pair of needle nose pliers
• Screwdrivers, both standard and Phillips
• Hex drivers of various sizes
• Hobby knife with assorted blades
• Rulers - both metric and imperial scale
• Drill - cordless is best
• Sandpaper - several grades
• Glue - thin and thick CA, slow and long cure epoxy
• Soldering iron and solder
• Scissors
• Wire cutters
• Rubber bands
• Grease and light oil
• Loctite to prevent parts from vibrating loose

There are several other, more specialized tools that you may need as well. They are:

• Rotary tool - Extremely useful for grinding, polishing, and sometimes drilling
• Servo tape - Comes in several different thicknesses, double sided and good for securing radio and other components
• Ball link pliers - These make it easy to remove ball links from your servos
• Ball link driver - like hex nut driver, but holds a ball link
• Small screwdrivers - Sometimes really small screws are used in model construction
• Metric tap and die set
• Open end wrenches - you only need the smallest ones
• Toolbox - to carry your tools with you and store them in an organized way

If you have all of the basic tools, and even some of the more specialized ones, you will have a complete toolbox that will help you in both building and repairing your rc heli.

Using the Draganflyer electric remote control helicopter (manufactured by Draganfly Innovations Inc) Vanderbilt University has developed the Vanderbilt Embedded Computing Platform for Autonomous Vehicles (VECPAV). This system is able to control an aerial or ground vehicle autonomously (without a pilot).

Saskatoon, Saskatchewan (PRWEB) November 20, 2007 — Vanderbilt University in Nashville, TN has successfully used the Draganflyer electric rc helicopter for autonomous vehicle research, involving flight by computer control without human input. The project is called VECPAV (Vanderbilt Embedded Computing Platform for Autonomous Vehicles). VECPAV is intended to create and develop autonomous control systems for unmanned aerial and ground vehicles. These control systems eliminate the need for an operator by substituting intelligent control software and electronics. This research is part of a larger project aimed at improving the design of hybrid systems which use embedded electronics and software to control mechanical devices used in performance-critical and safety-critical applications.

Vanderbilt University in Nashville, TN has successfully used the Draganflyer electric rc helicopter for autonomous vehicle research, involving flight by computer control without human input. The project is called VECPAV (Vanderbilt Embedded Computing Platform for Autonomous Vehicles). VECPAV is intended to create and develop autonomous control systems for unmanned aerial and ground vehicles. These control systems eliminate the need for an operator by substituting intelligent control software and electronics. This research is part of a larger project aimed at improving the design of hybrid systems which use embedded electronics and software to control mechanical devices used in performance-critical and safety-critical applications.

Having autonomous control over a vehicle creates many benefits and removes the need for continuous human input. This could be applied to full size vehicles, allowing cars to drive themselves, or allowing automated vehicles to perform tasks in hazardous conditions. This would eliminate the risks normally faced by an on-board operator. By removing the operator and related systems from the vehicle, it also allows for increased payloads, smaller sizes, and increased mobility.

The VECPAV system uses a sensor tracker to monitor the motion and position of a Draganflyer rc helicopter by using identifier points on the helicopter. The system then analyzes this data and sends commands back to the Draganflyer rc helicopter through a radio control transmitter, telling the Draganflyer rc helicopter to maintain position or move through its flight plan. Videos of Draganflyer helicopters flying autonomously can be found on the VECPAV homepage, and This YouTube Video. In addition to being successfully used to control Draganflyer electric rc helicopters, the VECPAV system has also been implemented on ground based scale model vehicles.

As a result of his efforts on the VECPAV project, team leader Prof. T. John Koo has been recognized with an NSF (National Science Foundation) CAREER Award: Computation Platform for the Design of Hybrid Systems. This award is considered a highly prestigious honor. Prof. T. John Koo is now at Shantou University, China, where he plans to build on and extend what he has achieved at Vanderbilt.

The Draganflyer radio control rc helicopter has also been used in similar projects such as the MIT Aerospace Controls Laboratory’s UAV SWARM Health Management Project and the Stanford Testbed of Autonomous Rotorcraft for Multi-Agent Control. The Draganflyer rc helicopter is well suited for these applications because it is a stable aerial platform with fewer moving parts than a standard rc helicopter. The Quad-Rotor Draganflyer rc helicopter manoeuvres by varying the thrust generated from each of its four rotors. With one rotor at each corner, differential thrust causes the airframe to rotate and change direction. This eliminates the need for the linkages and components used on conventional rc helicopters that vary the pitch of the main rotor blades in order to manoeuvre. With fewer moving parts, there are fewer things to wear out, and less maintenance required. Because it is an electric rc helicopter, the Draganflyer is safe to use indoors. Its small size allows it to be used in smaller areas than conventional rc helicopters. The Draganflyer rc helicopter is manufactured and sold by Draganfly Innovations.

It is possible for an RC helicopter to use more that two main rotor blades. With four evenly spaced rotors (quad-rotor) the thrust from all the RC helicopter’s rotors is combined to generate lift, and the thrust produced by each individual rotor can be varied to allow the RC heli to maneuver.

Decreasing thrust on rotors at or near the front will cause the RC helicopter’s nose to drop. This results in a forward tilt and forward motion. The same method can be applied to the rotors on the back or side, allowing the RC helicopter to move backward and side to side. Draganflyer RC Helicopters use quad-rotor design.

More information can be found in Wikipedia’s quad-rotor helicopter article.

Most radio control helicopters use a common layout, with one large main rotor on top generating lift, and a small tail rotor. This is called the Sikorsky layout.

When the rc heli’s horizontal main rotor turns generating upward thrust, it also generates torque which causes the helicopter to rotate in the direction opposite to the rotation of the main rotor. This is countered by sideways thrust generated by a vertically mounted tail rotor. An explanation about the way this works can be found in the Antitorque section of the helicopter article on Wikipedia.

Also, by varying the thrust produced by the tail rotor the RC heli can remain in one position, or intentionally rotate clockwise or counter-clockwise.

An example of a conventional RC helicopter is the eXtreme 450 Brushless 3D electric helicopter made by Thunder Power RC. Smaller examples include indoor mini helis and mini bell IR helicopters.

An RC helicopter using a contra-rotating propulsion system will have two rotors spinning in opposite directions. This allows the torque generated by the rotor blades to be canceled out, and removes the need for a tail rotor to keep the RC helicopter from spinning. Without a tail rotor, the rc helicopter’s tail boom can be eliminated, saving weight.

One possible contra-rotating layout has one rotor blade mounted at each end of a long fuselage, as it is for the full scale Boeing CH-47 Chinook, and is known as a tandem rotor. This concept is explained well by the Tandem Rotor article on Wikipedia. Alternatively, both contra-rotating rotors can be placed on the same shaft, resulting in a coaxial design (sharing the same axis). Another good Wikipedia article on Coaxial Rotors explains the theory behind this.

Coaxial rc helicopters are very stable and easy to fly. The Bladerunner series of indoor rc helicopters made by Interactive Toy Concepts, and the ESky Lama V3 and Lama II V4 electric RC helicopters are examples of designs using co-axial rotor blades.