3D flight is one of the fastest growing areas of our hobby. As these
3D airplanes like the Seagull Harrier and Hangar 9 Funtana become more
and more popular, the ideas and concepts of a good mechanical setup become
ever increasingly important. A good mechanical setup not only makes the
3D flight easier, but also decreases the chances of flutter.
A good setup starts when we're building the airplane. The following things
apply to the new breed of ARFs as well so don't overlook them.
Hinges: Hinge lines should be straight and centered on the surface.
Pivot Point of Control Horns: Control horns should be installed
such that the pivot point of the horn is exactly on the hinge line to
avoid building in a differential.
Servo Arms: The arm on the servo should be exactly parallel to
the hinge line. Servo arms should be switched around until you get the
spline alignment correct. Always try to avoid using the radio to center
the servos whenever possible.
Seal Hinge Lines: Hinge lines should be sealed so no air can pass
It doesn't matter how tight you think it is, seal it on the bottom with
Last but certainly not least is mechanical advantage. You might have
heard this term before, but what does it mean? Put simply, mechanical
advantage means giving your servos the leverage necessary to move these
huge control surfaces in flight. Even the strongest servos can be rendered
useless by a poor mechanical setup.
Let's start with the radio. Select the ATV feature and set all used channels
up to 140% in both directions. Don't forget the flap and aux channels
if your using multiple aileron or elevator servo setups.
This step allows for the maximum travel out of your servos and therefore
maximum servo resolution. Most modern computer radios are 1024 radios,
meaning there are 1024 steps of servo resolution for it's full range of
travel. By running your ATV up to maximum, you utilize all 1024 steps
to command the servos.
Now that we have the radio set up, we need to connect the pushrods. At
neutral stick, you should always have your pushrod 90 degrees to the servo
arm. Ideally, your pushrod geometry should look like the diagram below:
But what if you need more throw than your current setup is giving you?
The best solution here is to use a longer servo arm. Use only the length
necessary to give you the throw you need. Try to avoid moving the pushrod
closer to the surface on the control horn if you can as this reduces the
leverage applied by the servo.
If after changing the servo arms you find you need less throw, move the
pushrod in closer to the center on your servo arm. Try to avoid using
dual rates or ATV's to reduce throw whenever possible. You should always
make large adjustments mechanically, and then use the radio to make fine