I first came up with this maneuver for my aerobatics routine back in the 2002 Tournament of Champions in Las Vegas. The maneuver is so named because during the descent, the airplane's nose swings back and forth like a pendulum as the model pivots at a point very near the tail. The CG location plays a big role in performing this maneuver properly; it should be at its aft-most position. The combination of aft CG placement, generous elevator-surface areas and a high elevator rate makes it possible to perform this very-large-pitch-change maneuver. These settings also affect the speed at which the model can change from the full-up to the full-down pitch position. Let's take a closer look.
Bring your model up to a high altitude as if you were going to do a spin. Fly the maneuver into the wind; this will help stabilize the wings and make the airplane easier to control. Reduce power and airspeed while maintaining full up-elevator to stall the airplane. Remember to set all the dual rates high so you have maximum control travel. After the stall, push full down-elevator and keep the engine at idle. Your model will do a very tight outside loop while almost pivoting on the CG. When the airplane is almost in an inverted position, quickly add some power and pull full up-elevator. As the airplane gets close to a vertical down line, cut power back to idle, but keep holding full up-elevator until the airplane's nose pivots back up. Keep pulling elevator until the nose stops rotating. The airplane will have a tighter rotation when you change from negative to positive pitch.
Your airplane will be at a lower altitude but roughly in the same attitude as it was for the entry: upright and in a stalled condition. Now simply repeat the control-input sequence as many times as you want. Your airplane will lose a lot of altitude, so keep an eye on the ground and estimate a safe recovery altitude.
To make the maneuver look very smooth, keep the roll and yaw movements to a minimum. While applying up- and down-elevator, keep your wings level with ailerons and correct for the engine torque with rudder. Since the airplane's wing stalls several times during this maneuver, it is helpful to have an airplane that remains stable in a stall.
A good way to exit this maneuver is to bring the nose up and then go to a torque roll. Add full power and pull up-elevator until the airplane is in a vertical up line. Reduce the power to enter a hover, then do the torque roll.
The pendulum is a fun maneuver that's relatively easy to do. Set up your airplane correctly, and practice at high altitude until you perfect the control inputs; you'll know when it feels right.
MORE FLIGHT MODES
In the February 2004 issue, I explained how convenient it is to use your computer radio's "Flight Mode" switch to manage the five flight groups and get the most out of your 3D aircraft. I already discussed general flight, so this time, let's look at the snap roll.
A big consideration for how you set up your model is how you manage your servoto-receiver connections and whether or not you use special mixing. Since some competition rules allow mixing and others do not, I keep it simple and use only a standard setup. I don't use mixing to improve my aerobatics! If you do use mixing (elevator to flap, flaperons, aileron to elevator, etc.), turn the mixing off for snap rolls.
SNAP-ROLL FLIGHT MODE
When done properly, the snap roll is a beautiful maneuver. It is also quick-probably the quickest to execute in the Aresti catalog. Basically, it is a high-speed stall while the model rotates around its main centerline. The airplane rolls, pitches and yaws all at the same time. Snap rolls can be either positive or negative, depending on whether you pull (up) or push (down) the elevator stick. Competition rules do not allow the use of a snap-roll switch, so you need to learn how to set up your model to snap roll it consistently. The control inputs are:
* Positive left snap roll (left aileron, up-elevator, left rudder)
* Positive right snap roll (right aileron, up-elevator, right rudder)
* Negative left snap roll (left aileron, down-elevator, right rudder)
* Negative right snap roll (right aileron, down-elevator, left rudder)
Note that with negative snap rolls, rudder input is opposite to the direction of the ailerons. Aileron always controls the rotation direction.
To do all four types of snap rolls with precision, you must adjust the rates for aileron, rudder and elevator, so you can perform them consistently. Starting from the general flight-mode settings, most airplanes will require increased aileron, reduced rudder and slightly increased elevator rates. Once you assign the flight mode to your favorite switch, start with the general flight group settings and adjust them to the following settings:
* Aileron 100%
* Rudder 50%
* Elevator 30%
These are good starting points and, of course, will need to be fine-tuned for various airplanes.
Without flight-mode settings, it is possible to set up your model by adjusting its high and low rates. Use low rate for the general flight settings and high rate for the snap-roll settings. If you have only dual-rate adjustment for elevator and aileron, adjust your rudder throw to a rate that will work best for all your maneuvers. As I've said before, it is possible to do nice snap rolls without dual rates and at the same time do all the Aresti and 3D maneuvers, but it will be very hard to fly in a consistent manner.
That's it for now! Go out, practice your 3D maneuvers, and have fun!
Copyright Air Age Publishing Apr 2004
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