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Control
Horns & Mechanical Advantage
I also
notice that some guys tend to make the control horns on the
rudder as short as possible. This gives up mechanical
advantage. As I mentioned last month, long control horns
on the surface give us mechanical advantage over the
surface. Then we can size the servo arms or wheels to get
the required throw. I use rudder horns that measure from
1.5 to 1.75 inch from the center of the rudder's hinge line.
I don’t
like the pulley type wheels. They are only good if you have
a pulley on the rudder side too. I've only seen this done a
couple times. It's more of a pain than it's worth. Check
Figures #1 and #2 above for proper geometry configurations.
With the long control horns on the rudder it means you need
to put a bigger servo wheel on to handle the deflection
needed, but the mechanical advantage is given back to the
servo.
Rules Are Made to be Broken?
Again, only
use dual rates down in the 80% range of what you're flying
on. There may be an exception on the rudder though.
Sometimes models with highly effective rudders are tough to
fly on this high rudder travel. If you're flying such a
plane, I'd say you won’t need this much throw—not even for
stall turns—and you can decrease your travel mechanically.
Another solution is to dial the rudder expo up. It's not
uncommon for me to run rudder expo up around 60, 70, or 80%
on a rudder. You want to avoid the "knee" in the expo
curve, but this amount of expo won't hurt anything.
You'll see
a better performance from your rudder, and have less of a
"spongy" feel, if you give the linkage some attention. Only
FAI in the F-03 sequence had a ½ knife-edge loop. So if your
model can do knife edge loops with your current rudder
setup, I'd bet you can help your rudder response by
improving the linkage.
In FAI
finals schedules, we do rolling loops and circles that can
require high rudder rates. But most guys at the FAI finals
level are not still trying to optimize their rudder
linkages. These guys already have that figured out. If you
get a better linkage then it’s easier to "hide" rudder
corrections and make them smoother. |
