Let’s Talk Giant Scale

Understanding flaps and their setup

Watching a giant-scale pilot properly use flaps throughout a flight is a sight to behold. Seeing the flaps deflect at a scale speed during a touch-and-go or an overshoot, or as an airplane is turning onto final is not only enjoyable for the spectators but also a fun and gratifying experience for the pilot. Not all models, however, behave the same with flaps. A heavy giant-scale warbird with flaps deployed, for example, can transform how it behaves at slower speeds and will allow the pilot to decrease airspeed while flying a steeper approach angle. On the other hand, for a sport model like the Hangar 9 Ultra Stick 30cc, flaps can be used in a traditional sense or with various mixes to transform the aircraft and add stability, or act as airbrakes to decelerate quickly. Let’s take a closer look.

THE FOUNDATION

While building your model, you need to think, right from the start, about what functions you’ll want and how they will accomplish each task using your computer radio. With my Ultra Stick, there are eight servos, and each one is plugged into a separate receiver port on my 9-channel receiver. I use a single battery to power the receiver and all the servos; the setup is as follows:

Port 1: Throttle

Port 2: RAL (right aileron)

Port 3: REL (right elevator)

Port 4: RUD (rudder)

Port 5: LFL (left flap)

Port 6: LAL (left aileron)

Port 7: RFL (right flap)

Port 9: LEL (left elevator)

Some builders may want to use a simple Y-harness for the ailerons and another Y-harness for the flaps, mechanically reversing the second flap servo, or using a servo reverser for proper operation. While this approach will work to allow basic control of the aircraft, it will not allow you to fully utilize certain mixing abilities common with computer radio systems today. Examples include aileron differential to counteract any adverse yaw shown in a turn or, in the case of the Ultra Stick, having a mode that will allow the flaps to move with the ailerons to increase the roll rate.

I prefer to disconnect all servo arms before the model is initially powered on and only connect

the servo arms after the initial programming is completed. This prevents any unwanted binding that can lead to a possible servo failure. Throughout the initial process, I perform many mixes by simply using the servo monitor screen and the aircraft’s receiver switched off. This feature is helpful because you can see which servos are being commanded at which times. You also must think about switch assignments and which switches on the radio system will control specific functions.

MIX FUNCTIONS

Let’s explore a few different mixes and examine their specific benefits. On my Spektrum iX12, Switch D is the three-position switch, where position 0 activates the crow mix, position 1 activates a mode where the flaps move the same amount and in the same direction as the ailerons, and position 2 activates normal flap deflection. All the functionality is verified using the monitor screen. Had this been a scale bird, switch D would be used to control three different normal flap positions, which include no flaps, half-flap, and full-flap deflections. I prefer to keep switch assignments consistent from one model to the next to avoid confusion. Also, with a radio system like the iX12, you can add audio alerts to specific switch positions using the Switch Change Report Details feature. Until I had a variety of different models in my fleet, I never appreciated the advantages of voice alerts. They add simplicity while at the airfield when changing from one airplane to the next.

FLAP SYSTEM BASICS

If your programmable radio system features a flap system, choose an aircraft type that uses flaps to enable this feature. For the Ultra Stick, I chose the Two Ailerons Two Flaps wing type and the Dual Elevator One Rudder tail type. Settings found within this menu include Switch Input, Flap Position, Elevator Mix Value, and Speed of Movement.

While setting up the flap system, I performed the following:

1. Assigned switch D to control all flap commands

2. Assigned 100% flap deflection in position 0

3. Assigned 0% flap deflection in position 1

4. Assigned 100% flap movement in position 2

For traditional flap use, position 2 is used. You’ll note that 100% flap deflection is also used in position 0 and coupled with another mix to activate what is called a “crow mix.” For a scale project, however, I prefer to dedicate a threeposition to flap usage, where one position contains no flap deflection, the second position contains roughly half-flap use, and the third position will allow full-flap deflection for landings. Generally, a safe starting point for half-flap deflection is about 20 degrees. Flap deflection setup, however, is dependent on the full-scale

A variety of different flap-mix possibilities exist to change the flight characteristics of an aircraft, depending on the needs of the pilot.

subject. For the Supermarine Spitfire, for instance, only one flap setting is used, and this should be replicated on the model using a two-position switch. While some pilots prefer to use a slider switch for flap control, this method is not accurate because it can be difficult to know exactly how much deflection is being used.

On a scale project, you can also adjust the flap speed to slow the surfaces’ movements for more realistic operation and to help prevent sudden changes in aircraft behavior as flaps are being deployed. While I decrease flap speed for scale projects, I generally leave flap speed at the default setting for giant-scale sport aircraft, especially with crow mixing, as I prefer all commands to be executed quickly.

AILERON-TO-FLAP MIXING

In this instance, once aileron input is commanded, the flaps are activated as well. To accomplish this mix, the aileron channel is used as the master channel and the flap channel is the slave. Assign this mix to your switch of choice, and if the flap servos each connect to a separate receiver port, independently adjust the left and right flap movements. For giant-scale sport models, like the Ultra Stick, this type of mix is great as it allows the flaps and ailerons to move in unison to increase overall roll rate.

CROW MIXING

Borrowed from the glider guys, crow mixing is a function where, once activated, the ailerons will both deflect upward and the flaps will deflect downward. This function creates large amounts of drag to control spot landings, enhancing the aircraft’s overall maneuverability, and has become quite popular within the RC aerobatic community. Again, using the three-position switch D, I activated the crow mix, using P-Mix 1, and assigned the

FLP channel as the master channel and LAL as the slave channel. I then entered the appropriate deflection percentage and direction for the ailerons to move once flaps are activated with position

0. For all other switch positions, this mix was deactivated. When using this particular mix, the roll rate of the aircraft will be reduced but will be controllable. Once you get comfortable with the crow mix activated, you’ll not only use this mix to perform vertical descents to a landing but also use the throttle to fly at high angles of attack.

Some pilots prefer to link the crow function to the throttle so that, once the throttle stick is near idle, the mix activates in a linear fashion until maximum flap and aileron deflection are reached once the throttle is at idle. I prefer to activate the mix with a switch because I enjoy flying at high angles of attack, with the mix being used at higher throttle settings. Like all things, personal preferences differ.

FLAP-TO-ELEVATOR MIXING

In this example, flap is the master channel that, when activated, commands a small amount of elevator to be applied to correct for any changes in trim. This also decreases the pilot’s workload. With certain models like the Ultra Stick, application of large amounts of flap deflection will pitch the model’s nose upward. Using the flap-system function, an additional programmable mix is not required for the elevator-trim correction, and you can enter the elevator-deflection percentage for a given switch position. The elevator-compensation amount should be adjusted so that the model maintains level flight at each flap position. Examine your radio system’s features to eliminate any duplicate programmable mix efforts.

BOTTOM LINE

A variety of different flap-mix possibilities exist to change the flight characteristics of an aircraft, depending on the needs of the pilot. This column only serves as a foundation, and it is recommended that you seek the advice of experienced giantscale enthusiasts to assist in your model’s setup. And remember, enjoy the hobby and seek out every learning experience possible.

There is a lot one can learn by looking at the wing configurations and various programmable mixes that large-scale gliders regularly use.

Since the Ultra Stick features flaps that move both up and down, the servo arm is to be parallel to the aileronservo arm. Aircraft that feature traditional flaps will have an offset where the servo arms face rearward when the flaps are fully retracted.

For crow mixing, the inboard flaps deflect downward and the ailerons go up to increase drag and reduce lift—a nice feature on an aircraft like the Ultra Stick.

I prefer to center all servos before they are installed in the aircraft. Shown here, all servos have been connected and initial programming on the iX12 has been completed.

On this particular aircraft, corrective elevator input is required when flaps are fully extended. On the iX12, this input is achieved through the flap-system function.

If a given receiver does not have enough ports for all servos, one can use a servo synchronizer or channel expander, as needed, for proper component functionality.

Left: If your radio system does not feature a flapsystem function, remember that various programmable mixes can be applied to achieve the same result.

Right: To accomplish the crow mixing that was mentioned in this column, programmable mixing is a must.

Always deflect full flaps at slower speeds and incorporate corrective elevator commands through a mix to decrease your workload.