Flybar balance & paddle pitch
The flybar is the short bar perpendicular to the main rotors. It has an airfoil paddle at each end and controls the cyclic movement of the helicopter, as well as acting to stabilize the spinning main rotors.
While the main rotors will be the biggest culprit when it comes to vibration, the flybar is not completely innocent.
Outlined below are a couple of ways to balance the flybar if you don't have access to an accurate balancing tool. I'm not saying that these methods are correct, but they have worked fine for my Dragonfly 4.
A flybar balance weight is located immediately inside each paddle, secured by a small grub nut. Flybar weights give stability to the helicopter, by creating a greater gyroscopic effect. Personally I have to say that the DF4 weights are so light that I didn't notice any difference with or without them! (but maybe that's just my flying...)
Moving one of these weights fractionally inwards along the flybar should naturally alter the flybar balance, but again, I found the weights alone to be too light to have any real effect.
Because of this, I have tried both of the methods outlined below - whichever one you use, it's really a case of trial-and-error.
Moving the paddles
First you need to check whether or not the flybar actually is causing any vibration.
With the main blades removed from the holder, hold the heli securely and fire it up. At the same time, move the yaw tx stick fully to the left to stop the tail motor operating, so that only the flybar is rotating. Feel for any vibration coming through the airframe. If there is noticeable vibration, it's likely that the flybar does need balancing.
Shut down the motor and mark one paddle so that you know which one you're working with. Loosen both the paddle retaining screw and the balance weight, and slide them both outwards very slightly - even just 1mm can make a big difference!
Tighten up both screws and fire up the heli again - check for vibration. If the vibration is less, shut down and move the paddle and weight a bit more. If the vibration is worse, move the paddle and weight back to their original positions (put tape around the flybar at the rotor head side of the weight before moving anything) and move the other paddle and weight.
Keep moving and testing until no vibration is felt through the airframe.
By the way, moving the paddles will more than likely result in an unintentional change of paddle pitch. Keep both paddles at the same pitch (0 degrees) for optimum results.
Moving the flybar
The second method is to move the whole flybar on the rotor head. This is actually more effective because you are dealing with both sides of the flybar at the same time.
The disadvantage to this method, I found, is that repeated tightening of the flybar securing grub nuts eats into the flybar, causing a potential weak spot. But if you do want to try it this way, here's what you do...
Accurately measure the distance A-B in the photo below:
Loosen the two grub nuts (on each side of the rotor head assembly) that secure the flybar and carefully push the flybar to one side or the other, after marking a reference point of its original position. Don't go mad, half a millimeter or so is enough to start with. You may need to twist the flybar slightly to get it moving.
As for marking its original position, I found that lightly scoring the flybar at point 'A' in the photo was easiest. Use a knife blade, but mark the flybar very gently.
Don't forget to tighten the grub nuts afterwards, but don't over tighten - the casing thread is only plastic and it's easily stripped, as well as the point mentioned above about eating into the flybar.
Now, fire up the heli and feel for vibration. If there isn't any, then the flybar is balanced. If there is, shut everything down and move the flybar some more, or back the other way.
Keep playing with it until you can run the motor and not feel any vibration coming through the airframe. And don't forget to tighten the grub nuts every time you move the flybar!
It's important to note that you should set the paddles to have equal pitch (as outlined in the following section) each time you move a paddle or the flybar. Uneven pitch angles between the two paddles can give the illusion of the flybar being out of balance, because each paddle is generating a different amount of lift to the other one if the pitch angles are different.
Flybar paddle pitch
The flybar paddles directly influence the cyclic movement of the rotor disc, and both paddles must have identical pitch angle - which should be zero degrees. If they differ they will be generating different amounts of lift, causing all kinds of stability problems and making your life a lot harder.
Now, factory set the paddles on the DF4 have a few degrees positive pitch (well, mine did!) in relation to the angle of the main blade holder. I'm not sure if this is intentional - flybar paddles should run parallel to the holder, in terms of the horizontal.
However, I have played around with changing the pitch angle of the paddles (very slightly, and all the time keeping both the same) and the helicopter is noticeably more stable with a few degrees of pitch in the paddles, than it is with the paddles level.
But, this is only true for hovering practice - the adverse effects of having any pitch in the paddles appear in forward flight, where the paddles really should be level with the main blade holder for absolute stability.
(My own conclusion about the paddles being factory set with a slight pitch angle is that Walkera assume that 99% of Dragonfly 4 usage is going to be hovering in the living room, with no forward flight. If you're going to progress to flying it properly, then the paddles do need to be level).
If you don't have access to a proper pitch gauge (shown right) then a sliding bevel (the carpenter's tool) is ideal for matching the flybar paddle pitch.
Rotate the flybar so that it is at right angles to the tail boom. Stand the bevel on its end and hold it firm, and adjust the bevel blade to match the angle of the paddle as viewed from the end - you need to be looking at it at eye level to do this accurately.
Turn the flybar through 180 degrees and line the other paddle up with the bevel blade, again at eye level. Make any adjustments to the paddle so that it exactly matches the angle of the bevel, and hence the other paddle.
Start by setting the paddles to match the line of the blade holder, as they should be, but you might want to play around with changing the pitch of the flybar paddles yourself to see what effect it has on the helicopter. Just remember that putting a bit of pitch into them is only beneficial for hovering practice, not forward flight.
If you do change the angle, always match both paddles every time!
Related pages
Rotor blade balancing - a crude but effective way if you don't have a balancing tool.
Rotor blade tracking - how to get the blades tracking correctly.
Training tips - get used to your DF4 at floor level.
Getting airborne - for when you've done the floor bit.
Main frame replacement - guidelines for the worst job of them all!
Battery upgrade - time to go Li-Po.
Motor upgrade - fit a better quality brushed motor.
Landing gear & skids upgrade - add a touch of class to your helicopter.
Index - to all Walkera Dragonfly 4 related pages.
