I'm not sure of the correct terms.

for example:
If I want the control surface to go up 3/8" and down 1/4" where to I make this adjustment?
Is this called differential? Do you have to do it with the TX or can it be done with control linkages?

Am I correct that the control horn should always be mounted with the holes lined up exactly above the hinge point?

Connecting to the control arm on the servo, the farther away from the servo gives me more movement.
When I attach the control arm to the servo, I just want to make sure the linkage does not bind when maxed out.


I'm using a spectum DX6i TX

TIA

Pops

Yes. You want the dual rates/differentials (D/R&EXPO) set to control the throws. For dual rates, I usually have the switches down for low rates and up for high rates. Just my preference. This is done from the DX6i TX. It's the 2nd or 3rd option. I forgot which one.

Each control surface has a switch assigned to it (and they are labeled on the dx6i). Default is 100%, say you want to control the throws on the rudder. Scroll down to rudder and then move the rudder dual rate switch to your desired position (up or down) and adjust the throw from 100% to whatever you want. Now when you flip the swith the other way, you'll have 100% throw, when you flip it back, you'll have dual rates.

This applies to bothways (up and down, left and right). Sometimes you will throw more one way than the other. You can adjust this by going to travel adjustment.

Manual has a lot of this info in detail

so far you are dead on. The amount of movement can be adjusted at the transmitter if you have a computer radio or it can be adjusted by linkage if you have a more conventional transmitter. The secret to mechanical adjustment is that you don't want the arm to start perpendicular to the control surface. the further along in the arc the servo horn is the less movement it will have available. in the arc of movement the maximum verticle displacement is when the servo arm is perpendicular to the control surface. As you complete more of the circle arc you get a greater percentage of lateral translation instead of the verticle translation, so less control throw hence forth the diferential.

Try to get it as close as you can through mechanical means before you start with the radio programming.

Yes


Also correct - and the opposite is true for the control horn on the elevator (Rudder, Aileron, etc) The further OUT you go, the LESS control surface movement you'll get.


Yes, it is called differential and it can be done with either the Tx (providing you have a computer radio) or with the linkages.

To do it with the Tx, check your manual because they are all different and I'm not familiar with the DX6i

To do it mechanically, Refer to the images below

Elaborating on rlipsett's comment...

If you are really attempting to set up a differential situation, it is better to do this with the TX.

"Differential" is used to compensate for yaw introduced by the applicaiton of aileron.

The surface that moves DOWN produces far more drag than the surface which moves up, so the plane tends to yaw into the direction of the side that is down.

You can compensate for this by causing the downward moving surface to move less than the upward moving one.

Usually this can be done quite easily with any good computer controlled transmitter.

It CAN also be done by carefully placing your control horns, linkages and/or servo horns. However doing it mechanically may result in a permanent configuration that cannot be undone, while with a computer controlled TX, you can adjust things at will.

Differential is not the same as Expo and throw amounts. Your radio may have a seperate "page" where differential adjustments may be made.

Everyone is assuming you want differental in the ailerons. There is also the assumption that you are using dual aileron servos. If not, then you are limited to mechanical differental from either the servo arms/wheel, or location of the horns. Aileron horns do no necessarily line up with the hinge line to achieve differental. It also maters if the wing is on top or bottom of the fuselage when done mechanically.

You may find that most airplanes needs a slight amount of differental in the elevator travel as well to achieve equal sized loops with equal stick movement.

Wouldn't the plane act strange if this was done to the ailerons? With one side lifting or lowering more rapidly than the other wouldn't this cause a problem? I was assuming that he was referring to the elevator.

From Opjose's post:
Most airplanes are adjusted to minimize the adverse yaw with aileron differental. But rudder is usually necessary too for fine tuning. Keep the ball centered as the full size do it.

Rudder is not so applicable to high speed rolls though, etc. where-in having the differential is important for axial rolls.

Brett65:

One side does not "lift" or "lower" more rapidly. Lift is developed by the wing and since the wings are interconnected there is no independant movement.

Roll induced yaw is corrected by the use of differential. It permits a plane ( particularly pattern type midwingers ) to roll axially.

Highplane's reference to elevator differential is even more "advanced" a bit beyond a beginner's forum... and gets into very fine tuning of a performance plane.

I have a flat bottom, high wing trainer I'm putting the finishing touches on.
I made a guage with a scale on it that mounts on the plane and I can measure the movement of the control surfaces.
I am getting just over 3/8" up and just under 3/8" down on the elevator and was trying to figure out why.

MinnFlyer, youre diagram is interesting. that was not obvious to me. I'll check the position of my servo horns tonight.

I havent started with the ailerons yet!

I would like to set up mechanicaly as close as I can before resorting to the radio for adjustments...



thanks

Pop

This isn't quite correct. First you get everything (throws) as close as you can mechanically. Then (on high rate if used at 100%) set the end points with the EPA function. Following that you can set low rate and expo values if desired. Mechanical first and THEN tweak the TX for fine tuning.

You should consider trimming it out first, then reset your surfaces with zero trim and start adjusting the way you want it.

It is differential. You can get it with the TX in some cases. It can always be done with the control linkages.

No you are not. A line drawn along the pushrod should turn at the connecting point and make a 90degree angle when drawn to the hinge line.

yes yes
And you want a line drawn along the pushrod to make a 90degree angle when drawn to the center of the servo's output gear.

The 90 degree deal at the servo arm connect point and at the horn connect point gives you equal control surface movement. No differential.

If you want differential from your rigging, THEN the line will NOT have the 90 degree angle. You can either do it at the servo or at the horn. Most people do it at the servo. It's really easy to change it for more differential or less there. The output shaft has teeth. You can simply move the arm one tooth more or one tooth less to adjust the differential. For ailerons, you often start out with that line at the servo making a 45degree angle.

Not strange, just "differently". The ailerons would work just fine if you only lowered the aileron opposite the direction you want to bank and didn't move the opposite side up at all. Depending on the model you might get something of a "barrel-roll" going on for a complete roll but it would bank just fine.

Lowering an aileron gives that wing some added drag and lots more lift. Raising an aileron causes the wing to have a lot of drag (remember, the air travels faster on the upper surface - hence the ability of a model (or any aircraft) to fly - and acts as a spoiler that "kills" lift and lowers the net angle-of-attack. That drag tends to pull the wing behind the opposite one which is lifting, giving yaw. A model can be balanced by altering the up vs. down throws so it rolls axially along it's central axis (pattern fliers especially want this).

No, this is not correct. The aileron going down has a higher drag than one rising the same amount. So for differental, the ailerons move up more than go down to balance drag between the wing panels thus preventing yaw.

Secondly, if the model is going faster than landing speeds, raising both ailerons will cause the airplane to climb, so they do not alway act as spoilers, they can act as elevons as in a flying wing. Raising both or lowering both have some interesting trimming effects.

The plane already acts strange or we wouldn't be trying to fix it's behavior with differential.

When an aileron goes down, the wing on that side creates more lift. Creating lift creates drag. Creating more lift creates more drag. So the wing on that side creates more lift and more drag. And slows down.

When the aileron on the other side goes up, the wing on that side creates less lift. Creating less lift creates less drag. That wing speeds up.

You wanted to turn left. The left wing goes down because it's producing less lift and forward because it's producing less drag. The right wing goes up and back. The airplane yaws to the right.

Differential aileron isn't really sound byte simple.

Symmetrical wings don't respond the way cambered wings react. Different airfoils react differently from each other.

The aileron moving up reduces lift almost always. And that reduces drag. But then it often starts to produce lift in the other direction. And that starts to create drag. So the wing on that side has lost drag and then starts to gain drag.

Aerodynamics is seldom sound byte simple.

So we rig the ailerons to move with differential.

And we have two ways that differential can help that airplane. We can stop the downgoing aileron from creating more drag so fast and so much.

The other side isn't so simple. We need to get that aileron producing drag, and to do it quickly. With most airfoils that wind up needing differential ailerons on them, move the aileron up just a little and you won't get much differential effect. And the other wing/aileron has had it's throw reduced, so you've got an airplane that has less effective ailerons right around zero deflection.

So you want differential that move the up aileron up faster and considerably more than before. Well, depending on the wing's airfoil.

Nope, aerodynamics ain't sound byte simple.