A lot depends on how you plan to set-up the motor.
Glider pilots use the left stick for flaps and camber control and put the motor on a switch or a slider. What will you do?
This was written for a pure glider. Ignore any reference to spoilers.
Minimum Recommended Surface Mixes
After model memories, surface mixes are one of the great features that computer radios bring to the game. Input to one control can move 2 or more servos in a coordinated fashion to create the kind of surface control you are looking for. This can reduce the pilot's workload while providing very consistent behavior. In most cases, when it makes sense, these mixes can be overridden during the flight or can be turned on and off.
Where two surfaces are listed, the first is the master and the second follows, sometimes called the slave channel. I will discuss these in more detail later, but wanted to get the list part stated up front as people are usually looking for these lists. Most are focused on planes with ailerons or full house planes, but I note where even simpler planes can benefit.
The following list is what I would consider the minimum set I would want in a radio that would be used for flying sailplanes, be it thermal or slope. These minimum mixes may be available under the â€śairplaneâ€ť menu and may not be called out specifically for sailplanes. Even entry level computer radios are likely to have these.
* Exponential on aileron and elevator. Rudder would be a plus. (all gliders)
* Flapperon/Spoileron - requires two aileron servos on separate channels
* Aileron differential - requires two aileron servos on separate channels
* Aileron-rudder mix (coordinated turns)
* Flap or spoiler to elevator mixing for landing and glide path control. This can be very useful on RES, REF or full house planes and aileron only planes that are set-up for flapperons.
The goal of these mixes is to make the glider easier to fly more smoothly or more efficiently with less drag and more controllability. In addition we gain some level of glide path control to assist with landing accuracy or to help us get out of booming thermals. The landing mixes can also be helpful to slope pilots to land their glides in tight slope sites. With these tools you can have a more enjoyable sport flying experience or be more competitive than would be easily achievable with a standard radio.
Glider Mixes and Flight Modes
Now we are getting to mixes that would normally be implemented with specific glider/sailplane programming. These are usually used on gliders that have ailerons or ailerons and flaps (full house) rather than R/E or RES gliders. Some of these may be able to be implemented by using your user mixes on a radio that does not have glider programming, but it can get complicated. I don't consider those glider/sailplane radios, but you can make them work to some degree.
Flight modes can be thought of as changing your radio set-up to meet the needs of a specific situation. They often involve a change to the shape of the wing to better meet a special situation. You can think of your normal flying set-up as your cruise mode. All of your settings are based on your basic flying needs while you cruise around the sky looking for lift.
Flight modes might include launch, thermal, reflex, landing and perhaps others. As you can see by the names, these are modes of flying that occur under special situations other than when you are cruising. These modes would typically be controlled by a switch which may move surfaces to presets, change expo or surface rates and might even modify other settings from your normal cruise mode.
An example of a launch mode mix would depend on what kind of a glider you are flying. If this is a winch or hi-start launched glider you might drop the flaps 20 degrees and the ailerons 20 degrees giving your wing a more under cambered shape. This might also include some up or down elevator, depending on your glider. This generates tons of lift but also creates more drag. While this might be detrimental during normal fight, when you have the force of the hi-start or the winch pulling your plane up, you can afford this extra drag to gain higher launches. Once you are off the line you turn off launch mode which puts you back in cruise mode.
If this is a discus launched glider, DLG, you might have a launch setting that includes a slight bit of up elevator and maybe a tiny bit of rudder mixed in to help get the launch straight. This would be controlled on a switch that is convenient to your non throwing hand so you can flip the launch mix off just after release of the DLG. Some people like this to be a spring loaded switch that can just be released upon launch. What mix and what switch you use is going to be specific to you and your glider but if you throw with your right hand you would typically want this switch by your left index finger.
Flight modes could change how you use one of your control sticks. For example you might have your left stick controlling the throttle of an e-glider during your launch mode then flip a switch to cruise and the throttle would no longer respond to the left stick. That left stick might now be responsible for your landing mix. The motor would no longer respond to the left stick.
You could go through the entire flight and not use all of these modes but they give you that extra measure of control or convenience when you want it.
How sophisticated and complex these modes will be depends on the software in your radio. The degree of control you have could be thought of as the difference between a basic sailplane radio and an advanced sailplane radio.
The Four Servo Wing
Clearly a four servo wing is of little importance on a 2 servo wing such as the typical DLG or many aileron only slope gliders. But if you plan to fly full house (R/E/A/F) gliders in the future you may want this ability.
One of the features that I feel sets apart the "sport radios" from the "advanced" radios is the ability to directly address all four or more wing servos, each on its own channel. The sport radios can fly a plane with 4 servos in the wing, but they require that the flaps be on one channel through the use of a Y cable. This means that you have 4 servos but you are controlling them on three channels. You don't have individual control of each flap servo.
Where the 4 servo wing support comes in handy is in trimming and in aileron-flap mixing. There may be others, but these are where I have used this capability. Typically you don't find this on a radio with less than seven channels, and most have eight or more channels. Read the manual or the specs and look for this feature. If you don't see it mentioned, look for how flaps are set-up. If both flap servos are assigned to the same channel, you don't have 4 wing servo control.
When you have both flaps on a Y cable you must trim them mechanically to get them synchronized. This is not hard but it is time consuming. It is very important that the flaps move together. Flap trimming can be done using servo arm/control horn arm placement. Then you can trim the flaps together using the radio to get that final zero point and the end point for down flaps.
However if you can address each flap individually from the radio you can do final trimming from the radio, which is a great convenience. You can also use an aileron/flap mix to have the flaps follow the ailerons for more, or smoother roll authority. I use this on my full house gliders when I am flying in windy or gusty conditions. This would be useful on the slope for aerobatics. This is not a necessary feature but if you are going to invest in a "serious" sailplane radio, you will want to be able to address the four wing servos individually.