ORIGINAL: Shogun
Something that nobody has mentioned yet, at least I don't recall reading it in the htread so excuse me if it has already been mentioned....
Seal the gaps on the control surfaces. I have found that for small models, by that I mean ANYTHING under 35%, this really can help a grat immensely. I don't care how tight your gaps are the airflow through the ailerons will differ on either side and hence they are not operating in a balanced state. This same rule applies the elevator halves as well, just do it if you haven't already, you might be surprised at the results.
The lateral balance is crucial and if you have a heavy wing it will start the rocking process every time you pull the nose up and slow down.
As NEAR to perfect symetrical elevator throws as can be acheived on dual elevator servo equipped planes is a must. Make 2 pointers from a pair of clothespins and carbon rods that are about 12 inches long and clip them on the elevators. Next cycle the elevators up and down and observe the pointers, do they track each other to within an 1/8th of an inch of each other throughout the arc from full up to full down throw? If they don't fix it so they do.
Is the model touchy in a hover in calm air? If so you probably have too much throw or too little expo. If your chasing the plane to keep the nose up and in one place you need to work on getting it stable in a hover where small, quick corrections are all that is needed to hold a steady position. My rule is if you are fighting the plane in a hover you will fight it in other maneuvers as well, like harriers, especially harriers.
Too much expo, this will get you every time. I have found that the less the better, but you still will NEED some to be able to smoothly control and correct small errors. The problem is, if you use too much you will always be behind the plane every time you attempt a correction. If you use to little your corrections will have to be almost perfectly timed and executed. So how much is too much expo? I've found that most planes are happy with between -20 and -30(Futaba or Hitec) on the rudder and about the same on the elevator, sometimes a bit more but never more than -35. It seems that once you start cranking in more than -35 the controls it's extremely difficult to maintain any feel for the plane as the controls become far too soft. Sure I know some guys that can fly this way and I know just as many that use no expo at all....most of us are not goine to be successful if we try flying in either of these categories IMO.
Servo blow back can also be an issue that many might neglect to check for. Make sure your controls are maximizing servo power and resolution. I can't recall the number of times that I helped a guy out at the field or on-line by telling them to move their clevises all the way out on their horns and in some on their servo arms and then fly the plane. Without fail they noticed a big improvement in control response immediately even though their control throws were sometimes cut nearly in half. It's my humble opinion that more guys get into trouble by worrying about having big throws than any other single issue, all of my planes use about 30 degrees on the rudder and elevators and will do whatever I want, ailerons are a matter of personal preference so set them up for a roll rate that doesn't give you a headache and fly it.
He speaks.....[X(]
Excellent post Scott. Every bit of that is excellent information IMO. I had not thought about the gaps but you are right on.
On the expo and how it effects response, for me, it depends on the amount of throw you have. For me, the less throw I have the less expo I need. I judge this by getting my low rate expo exactly where I want it first. Once I have the low rate expo and throw setup just right I go into the high rates and look at the curves on the transmitter screen. My 9C and 9Z both have a chart display that let you see the curves and you can actually see the curve move as you manipulate the expo on the transmitter. What I try to do I set the expo on high rate so that at the bottom of the curve (around the neutral point) on low rate and high rate match. Basically that means that while looking at this screen you flip the rate switch back on forth and the high/low rate curves are exactly the same within say 25% of center. Beyond 25% the low rate curve will actually not curve all that much (less expo = more linear) and the high rate will sharply curve upward and the expo loses effect as you increase throw and the control moves rapidly towards full deflection (more expo= less linear/bigger curve.)
However,
on the rudder I do not use dual rates on a 3D plane. I am always setup for max throw which may be as much as 50 degrees or basically all I can get. Then I dial in about -60 expo, what that does is makes the rudder "feel" like it is on low rates whn I am trying to make feathering rudder corrections, but when I am hovering or doing a rolling harrier where I am using a lot of deflection anyway, at the point out on the curve where I am operating the expo has become uneffective and I have that linear feel. This only really works for me on the rudder though. I cannot make it feel right on the elevator or ailerons, ESPECIALLY the elevator. There I use dual rates.
I am not disagreeing with you in any way, I think your comments are right on. Just interjecting a little detail on how I have found to make good use of expo.[8D]