Setting up your radio for fun-fly models

Model Airplane News, Oct 2001 by Edberg, Don

You can greatly increase your fun-fly model's control responses if you use a computer radio. These models are very aerobatic, and when they fly, they can tie knots in the sky!

Usually, fun-fly models have at least five servos: two for ailerons and one each for elevator, rudder and throttle (Figure 1). The two huge ailerons are there to ensure good roll authority. With a computer radio, you can couple the two aileron surfaces to the elevator to make very tight loops and sharp corners. Also, you can make both ailerons go up at the same time for very steep but controlled landing approaches.

It's pretty easy to set up the model for all these functions. Most computer radios have built-- in mixing functions for flaperons, airbrakes and elevator/flap coupling. Use these functions to get the best flying characteristics possible for these fun models. Of course, you may also want to use standard aerobatics functions, such as snap roll switches.

FLAPERONS

"Flaperons" is the name coined for the combined function of ailerons and flaps. The aileron surfaces move opposite each other for roll control (like normal ailerons), and they also move up and down in unison for flap action whenever the flap control (usually a knob) is moved (Figure 2).

Occasionally, a model's instructions will specify more up-aileron travel than down-- aileron travel. This is called "differential." Some radios will not allow you to have both flaperon and differential functions operating at the same time. Though at first this might seem troublesome, it isn't a big deal. Within its menu, the flaperon function allows you to separately specify the up and down motions of each aileron, so you can create differential within the flaperon menu.

ELEVATOR-TO-FLAP MIXING

The use of mechanically coupled flaps and elevators began in the 1950s with control-line models such as the Nobler. Someone discovered that if you made the flaps drop with up-elevator, you would be able to do square loops much more effectively. These days, it works equally well when used with RC fun-fly models. Elevator-to-flap mixing applies channel mixing from elevator to flap, as shown in Figure 3. When you turn on this mix function, your aircraft will make very crisp corners in maneuvers, and loops will become very tight. The rate of mixing may usually be set differently for up- and down-elevator commands (outside and inside loops).

If flaperons and elevator-to-flap mixing are activated, both ailerons will droop when you pull up-elevator.

AIRBRAKES AND LANDING MODE

In some brands of radio, the airbrake mixing function is called "landing mode." This mixing function is useful for increasing the model's drag so you can increase the approach angle, making landings shorter, easier and more precise.

When activated, the airbrake function offsets the neutral positions of dual aileron servos and elevator to new positions. The idea is to raise both ailerons simultaneously and trim the elevators to regain the lift lost by the up-aileron movement (Figure 4). This arrangement adds much drag to steepen the approach.

The airbrake function may be activated in several ways, depending on your make and model of radio. The first, and most commonly used, is in proportion to the throttle-stick position. If the airbrake function is turned on, once the throttle stick moves below a defined set point, the airbrake motion is controlled proportionally by the throttle stick, and maximum offsets occur at the low-throttle stick position. This is sometimes called the "linear" airbrake mode. Another way to set up the function is to set the airbrake function to deploy to its new position as soon as the throttle stick passes below the defined set point.

A third way you may choose to activate airbrakes is by flipping a switch. When you do this, it all happens at once: all the controls snap to their offset positions, regardless of the throttle-stick position. No matter which type of airbrake setup you use, the aileron and elevator controls allow you to make normal flying commands as your model descends steeply.

Some systems, such as Futaba's Super 8, provide a delayed-elevator-motion setting in the airbrake function. This delay slows the movement of the elevator servo so that it reaches its offset airbrake value at the same time as the aileron and flap servos do, even though they have to travel much farther than the elevator servo. This helps to prevent sudden trim changes when you activate the airbrake function. Note that the delayed-elevator function still allows the elevator to respond normally to the elevator stick as it slowly progresses to its offset position. Along with this feature, the Super 8 will emit a loud beep if it's powered up with its airbrake mixing switch turned on; this is to prevent you from taking off with the airbrake function turned on.

SETUP INSTRUCTIONS FOR A DUAL-- AILERON-SERVO FUN-FLY MODEL

1. First, select your radio's aerobatic-- model-type menus. These are often labeled "ACRO." This set of menus usually has the best functions preprogrammed for a fun-fly model. Select the desired model memory to work within, and if your system allows you to specify an alphabetic name, name the model now. Otherwise, make a note of the memory number so you won't forget which memory it's in.