Trim Question--Long

[Troy Newman]

Dan,
 since the plane has a counter balance.......I would say I have seen some
funny things happen with the counter balanced rudders that so many planes
have today.

Not totally sure why its happening but probably do in some part to control
Snatch. This happens when the control surface tab grabs the air and reaches
a point where it overrides the flight forces normal on the surface. What
happens is when you reach a certain point in rudder deflection the tab gabs
and all of a sudden the load on the servo reverses from pulling the left
cable to hold left rudder...to the result of the tab...trying to get more
left rudder than commanded. The servo is then driving right to hold the
commanded position left rudder. Not sure if I'm explaining it correctly or
not....

Where I have seen this happen most is rolling from inverted to a knife or an
8th point position.  The coupling in the model is mixed perfectly for knife
edge flight even to the point of extreme rudder throws and knife edge
loops....but when the model is rolling in certain orientations the coupling
changes. I have seen this tendency with almost all counter balanced rudder
models I have flown. The counter balance works very well at making the
rudder servo work less....However in these certain conditions its putting
bigger loads on the servo in the snatch condition...


My theory on this as rolling from inverted the rudder and specifically the
tab is in clean air below the model....it digs in and has some more
effective responses than we are used to. Since you are flying in a normal
almost no rudder or no rudder situation perhaps the tab is catching in the
clean air....How is your rudder trim? Is the rudder straight to the
fuse....not the tab but the rudder...Look from the belly of the model while
inverted back at the rudder and see if its tracking straight...If it is here
How is the tab centered on the fin....Basically is the rudder straight, and
tab sanded correctly to track straight... Next rudder cable tension? Tighter
cables may help.....Next geometry on your pull pull system? Can you get more
leverage for the servo.....Sometimes crossing the cables can do this.
Sometimes not.

Solutions I have found work.....Better rudder servo. If you are not using an
8411SA this is what you need...I even know of some very loyal Futaba flyers
that found the 8411SA to be a solution to their rudder problems. Not bashing
any servos here just stating the facts I have experienced. I minimized this
on my Smaragd with a rudder tab using the 8411SA....then I tested an 8611 on
the rudder and the issue went away...This proved to me it was servo power
and precision related.

Better geometry on the linkage. Final thing is the knife and put the rudder
tab on top of the fin with some clear tape and see if it solves it. We have
found that it can be minimized using better servo setups...and eliminated
with the removal of the tab. This is one really good reason to have a
removable rudder...You can just take the rudder off...remove the tab and
then attach it temp style with tape to the fin and fly it....

Another solution to minimize the problem is CG....Change the way the model
is flying....Maybe add some nose weight and see if the problem minimizes And
I don't mean a 1/2 oz....Like 4-6-8ozs and see what happens. As the guys on
this list gasp for air....I'll say that big CG changes can tell you a  ton
about the way the model is flying. If you make a huge shift forward like
4ozs on the nose. Most models will tend to chage the little settle down
things like you are dealing with. If the 4ozs helps a littl...then go
another 4ozs. I hate to say move the CG back as I feel many pilots fly their
CG too far aft as it is......
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