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| Issue 38 (August 2009) |
Words: Jim Innes |
The flybar is one of the staples of the model-helicopter industry. Even with the use of flybarless systems on the rise, the vast majority of helicopters in the hobby still use flybars. You can find a flybar on any type of model from a beginning RTF toy heli on up to the latest competition-level machine. One of the great things about a flybar system is that a quick and simple change or adjustment can drastically alter how the helicopter flies. Let's discuss some of those adjustments and what to expect from them.
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Flybar basics
Without going into too much detail, the flybar on a modern RC helicopter performs two important tasks:
1. The flybar acts as a mechanical gyro for the rotor system. Much like a spinning top, the flybar tries to keep the helicopter in a stable plane. It stabilizes the rotor head and counteracts external forces such as the wind. Stabilization is the reason flybars were invented, and they do it amazingly well. 
2. The flybar keeps the overall cyclic rate of a model helicopter at a rate that a pilot can handle. On most modern helicopters, a Bell-Hiller mix is used to control the cyclic pitch on the rotor head. This mixing combines the direct cyclic commands from the servos with the tilting of the flybar to control how much the main blades deflect for a given command. If you were to take a standard 3D model, remove the flybar, and link the blade grips directly to the swashplate, you would find the heli very unstable and twitchy to fly. (This is, of course, assuming that no electronic stabilization systems or special blades are being used.)
The reverse is true, as well. If you were to take a model and give the flybar 100 percent of the authority over moving the blade grips (removing the Bell part of the mix), you would end up with a very stable but very sluggish helicopter that would be slow to respond to cyclic commands.
The job of heli designers and pilots is to find a balance between response and stability by adjusting the various components of the flybar system to suit their needs.
Power steering?
One unintentional byproduct of mixing the flybar with the direct cyclic commands is that a little power-steering effect gets added at the blade grips. This is because the servos are putting some of their force on the smaller and easier-to-move flybar disc instead of the larger main disc. As the flybar disc moves to its new plane, a mechanical force is placed on the blade grips through the Bell-Hiller mixer to change their pitch and tilt the model to follow along.
This process, in theory, takes a small amount of load off the cyclic servos. Please note, though, that the energy saved from the power-steering effect is minimal, and I doubt there is any real-world benefit from the assist, especially considering the more-than-adequate high-quality servos used nowadays. The bottom line is that while there definitely is a small power-steering component to a flybar, it isn't one of the intended purposes of the system. As the flybarless guys have proven, modern servos are more than up to the task with or without the flybar's help.
Adjusting a flybar to fit your needs
So now that you know some of why the flybar is there, what can you do with it? There are four basic areas of the flybar system that pilots can quickly modify or adjust to change how their models fly. These areas are: paddle size, flybar weights, flybar length, and flybar ratio.
Adjustment area one: Paddles
Perhaps the fastest and easiest way to change the speed of the cyclic on your model is by swapping out the paddles. Flybar paddles play significant roles in the performance of your model. If you are looking for stability, put on a set of heavy paddles that have a thick airfoil. The extra weight of heavy paddles adds to the gyro affect that the flybar plays. If speed is your thing, go with lighter paddles that have a large surface area. A set of really light paddles really livens up the cyclic on a helicopter.
There is always a trade-off between stability and response. In general, as you go lighter on the paddles, you trade some stability for speed. The best thing you can do is experiment with different paddle shapes and weights to find what suits your style and flying level. This is really easy to do, especially if your model has removable weights in the paddles. 
Adjustment area two: Flybar weights
Flybar weights are exactly what the name implies. They are simply small, weighted collars that are put on a flybar and held in place with a setscrew. The cool thing about flybar weights is that they are extremely easy to adjust once they are installed. The rule with these weights is the farther out on the flybar (away from the head block) you place them, the more stable the heli will be. Make sure that the weights are set the same distance on both sides of the flybar.
I know some people who use a set of flybar weights to modify their heli from flight to flight. They will move the weights all the way in against the seesaw if they are doing an aerobatic flight composed of maneuvers they know well. Then they will occasionally move the weights out for the next flight to slow things down a bit and practice some inverted flight or another maneuver that they are working on.
Just as with changing the paddles, there is that trade between stability and response depending on how far out the weights are placed. 
Adjustment area three: Flybar length
The length of the flybar plays a large role in its influence on the helicopter. A longer flybar, within reason of course, will generally result in a more responsive and a more stable helicopter, all other things being equal. The added length gives the flybar more authority over the blade pitch than a shorter unit and results in faster response. At the same time, the size of the stabilizing disc is increased, strengthening the gyro effect of the flybar.
A number of manufacturers offer longer flybars as an option for their models. These are usually right around 10 percent longer than stock. There is usually no need to go much longer than that. Going too long can have a negative effect on the model or even have the flybar hitting the frame or canopy at full deflection. 
Adjustment area four: Flybar ratio
Lastly, if the helicopter has provisions to do so, you can change the cyclic speed of your model through changes to the Bell-Hiller ratio. You may have noticed that your heli has other location holes to install the control balls on the seesaw, mixing arm, blade grips, or even the washout arms. Changing the location of the links at these points will change how much influence the flybar is allowed to have over the blade grips.
In cases where the mixing arm is mounted to the blade grip, such as on the Vibe 50, the closer you put the flybar side control to the blade grip the more stable the heli will be. If the seesaw has different mounting options, the further out from the head block the link is placed the more the flybar will be able to control the blades.
On some helis there are literally dozens of different mounting combinations for these links that allow the pilot complete control over how the heli reacts. Most heli manuals have these different location options labeled with which ones will result in more stability versus quicker responses. Experiment with the different mixing options to find what suits your style.
Flybar setup pointers
Before you begin making adjustments to the flybar system, make sure it is set up properly from the beginning.
• Your flybar should be exactly centered at the rotor head. Use a ruler or calipers to verify - don't just guess that it's in the middle.
• When you install the paddles, make sure they are installed the right away around (with the leading edge in front) and that they are both installed the same distance onto the flybar. Again - verify with a ruler.
• Lastly, the paddles need to be lined up with each other, as well as with the seesaw cage or rotor head of the heli. A set of paddle gauges can help you get them exactly straight. 
Conclusion
Flybars are amazing little things. They efficiently fulfill their primary role of bringing the response rate of our models down to a level that is manageable while still offering near-infinite adjustability. Making those adjustments is an easy and inexpensive process that allows pilots the ability to make their helicopters fly as they would like. Though we are just arriving at a crossroads as flybarless systems come of age, I believe that the tried-and-true flybar will still be aiding pilots for years to come. See you at the field - and keep those flybars out of the dirt!
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