May 18, 2011 6 Comments by

Making the most of your computer radio’s features can improve your flying. Setting up a plane with the right radio programming will make performing all kinds of maneuvers much easier. Let’s see which programs will help improve our 3D flying.


ABOVE LEFT: dual rates allow you to switch from one control deflection to another. On the Airtronics RD8000, the screen shown is where you program that in. When the dual-rate screen is in position 2, the aileron servo has 125-percent throw.

ABOVE RIGHT: exponential programming is used mainly to soften or decrease the stick sensitivity of the control around center stick. Expo helps pilots by allowing them to fly more smoothly and with larger control throws. On this screen, when the dual rates switch is in position 2 (high), the ailerons have 70-percent exponential.

On this screen, when the throttle stick is moved, it also affects the elevator’s movement. This helps the plane to maintain a straight downline.

Before we address programming, let’s talk about using dual servos for the ailerons. Although most planes over .25 already use one servo in each wing, we just want to plug each servo into its own channel on the receiver. By not using a “Y” harness on the aileron servos, we can independently set each one to react differently to stick input, and that allows the plane to respond to inputs more precisely.

The advantages of having two separate aileron servos more than compensate for the weight added by the extra servo. By having a servo for each aileron plugged into its own channel, you can now use the spoileron and flaperon programs; these mixes will allow both servos to work in conjunction with the aileron stick. Both of these programs allow the ailerons to have dual functions. By setting them up on a 3-way switch, you can flip the switch in one direction and have both ailerons drop down and function as flaps while still working as ailerons. If you flip the switch the other way, the ailerons will move up and act as spoilerons while still functioning as ailerons. Flaperon and spoileron can both be used during high-alpha maneuvers to help stabilize the plane.

Both of these mixes also allow aileron differential programming. This refers to the ratio of up to down movement of each aileron. Many planes need more movement from the upward-deflection aileron than from the downward deflection aileron. This allows the plane to roll true and eliminates unwanted yaw when the ailerons are applied. This is important because it will keep the plane flying true through all aerobatic maneuvers.

Dual rates allow you to reduce or increase control deflections by simply flipping a switch. This feature comes in handy when your plane is used for normal flying and hard 3D flipping around. You use standard or low rates (small deflections) to fly the plane smoothly, but right before it enters a big 3D maneuver, flip a switch, and now you have, movements of 45 degrees and larger on the control surfaces. Although you may need that much deflection for the maneuver, it would be difficult to fly the plane smoothly and with precision at normal speeds with those deflections. That’s where dual rates come in: after the maneuver is over, dual rates allow you to flip the rate switch back to standard rates and continue flying with lower deflections.


Radio mixing allows one transmitter control input to affect two or more flight functions. On this screen, when the rudder stick is moved, it also affects the elevator’s movement. This mix is used for knife-edge flight.

The spoileron or flaperon program allows you to have a servo for each aileron yet still allows them to function as one. The advantage is that you have control of the rates, endpoint adjustment, centering and the amount of differential for each servo; this lets you refine your plane’s flying characteristics. The Stylus’s Spoiron screen is shown.

Aileron-to-rudder mixing is useful if your model has a problem with adverse yaw when ailerons are deflected. You can adjust the percentage of mix to fine-tune the control response.

Mixing throttle to rudder also is useful when flying an upline at full throttle. Using a little rudder helps keep the model on track. The mix can be used to fine-tune the amount of right and engine downthrust you have to eliminate any veering offline that occurs at full power.

Another program that works hand in hand with dual rates is exponential. Exponential (expo) programming is used mainly to soften or decrease the control-stick sensitivity around center stick. Without exponential, a control-surface servo will move in an amount proportional to the amount of stick movement. For example, if you move the stick 50 percent of its available movement, the servo will also move 50 percent of its available travel. This is called “linear throw” or “linear movement.”

Using exponential changes the relationship between stick deflection and servo travel. With expo, you could move the stick 50 percent of its available movement and have the servo move only 20 percent of its available travel. The amount of servo travel depends on the amount of exponential programmed in. Keep in mind that exponential settings do not change the amount of servo travel available at 100 percent of control-stick deflection. If the stick is at the end of its deflection, the servo will be at the end of its available travel. Exponential changes the amount of servo travel that will occur with stick deflections of less than 100 percent. Servo travel is small at center stick, but as the stick moves closer to the end of its travel, servo travel speeds up to reach the end of its travel at the same time.

Expo reduces stick sensitivity at center stick and allows pilots to fly more smoothly with larger control throws. Imagine having large 45 percent throws on a control surface with a plane that you are flying straight and level. You move the stick 1/4 inch, and the control surface moves 1/4 inch; that causes the plane to veer off course quite a bit and makes your flight look jerky and erratic. With expo programmed in, that slight stick movement wouldn’t cause any surface deflection, and your flight would look smooth and controlled. Exponential is great when you have first flight jitters because if your hands shake expo prevents that anxiety from being transferred to the control surfaces.

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About the author

West Coast senior editor About me: I’ve been involved with RC aircraft since high school and have flown just about everything. I started my RC career with scratch-building, but now like many pilots I rely on ARFs to get me in the air. My main focus is on pylon racing, aerobats, combat and scale warbirds.


  1. Randy says:

    Thanks for explaining ‘Expo’. I have been wondering about it as I’m new to R.C. but learning. Gained a lot of info from your article..
    Randy……..Dallas, Oregon

  2. Scott Orten says:

    I could use a book to help me do the programing

  3. Wayne....Exeter,CA says:

    Thank you for a great explanation. No wonder my friend’s sport plane was so smooth when he let me try it! Of course he was an old pattern flyer so duh…

  4. canewalker says:

    Thanks for the explanations. You gave me more info on DR and EXPO than the whole booklet ($35.00 for the print version I might add) that came with the Spektrum DX6i that I traded a guy for. I’m still not sure if the (-) or (+) value slows the expo down at center point. The booklet wasn’t real clear about that either so I’m going back to reread it right now.

    Good Gawd I hate getting old!!! My mind wanders worse than an airplane with an uncentered rudder.

    Also, glad to hear I’m not the only one out there whose hands shake on first flights!

  5. TheDocSA1 says:

    I am very satisfied with my Airtronics RDS 8000 radio and have implemented these tips to improve my flying. Thanks for sharing!

  6. c.s.ang says:

    I m wondering about Dual rate, I & 0 which is for high rate & which for low rate?

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