From the Air Age Archives—World Aerobatic Champion and the “Father of 3D Aerobatics” Quique Somenzini, offers his advice for you to get the most from your aerobatic machine.
Although specific flying techniques are important in 3D aerobatics, setting up your airplane correctly will greatly help you to perform maneuvers better and more easily. Let’s take a closer look at the airplane and radio setup.
CONTROL SURFACE AREA
To perform most 3D aerobatic maneuvers, your plane must have large control surface areas. In fact, the rudder, elevator and aileron surfaces are the heart of 3D aerobatics. How large should they be? Well, as a percentage, the elevator should be at least 40 percent of the total horizontal stabilizer area, the rudder at least 50 percent of the fin area and the ailerons at least 20 percent of the total wing area.
The deflection is as important as the area. The elevator should deflect at least 45 degrees each way, the rudder at least 45 degrees and the ailerons at least 35 degrees. The combination of these large surface areas and deflections allows you to control the airplane even when less air flows over the control surfaces. During the Roller Coaster, for instance, the airplane is flying at such a low airspeed that the airflow generated by the propeller (the prop wash) is the only thing that allows the plane to continue to perform such a large change in attitude. At the top of the Roller Coaster, when the airplane is at zero airspeed, the prop wash blows over the tail surface and the inside area of the ailerons. To maneuver in this situation, your plane must have large control surfaces that will be able to use this very small airflow. Extra long and wide ailerons help considerably to better maneuver the airplane at zero airspeed.
Even with extra-large control surfaces that have enough deflection, you must be able to move those surfaces safely and with authority. That’s why a good linkage system and powerful digital servos are important. Digital servos have a greater holding power than standard servos do; it is so important to avoid any chance of flutter, which is significantly increased when you enlarge the control surface and its deflection!
CENTER OF GRAVITY
Your plane’s center of gravity (CG) is also a key factor in performing wild 3D aerobatics. As you move the CG rearward, the plane becomes less stable but the pitch and yaw control becomes more responsive and more sensitive. Most aerobatic airplanes have CGs around 32 to 33 percent of the wing’s mean aerodynamic chord (MAC). If you move the CG farther back, you will gain even more pitch and yaw authority, but the airplane will simply be too unstable. It depends on the airplane, but the best balance between aerobatic and unstable is usually achieved when the CG is about 37 to 40 percent of the MAC.
When you fly maneuvers such as the Roller Coaster, flat spin, Cobra (Harrier), waterfall, Pendulum, etc., your plane’s CG is very important; simply having large control surfaces isn’t enough to allow the plane to pitch properly. Note: when you do a maneuver that’s like a torque roll, the CG is not a key element. For this a plane with a standard, aerobatic CG of about 32 percent “MAC” will be fine, and you won’t gain any more maneuverability by moving the CG rearward.
As you know, the best CG position for 3D aerobatics is a compromise; the real challenge is to find the CG that will give the airplane the best overall balance for most maneuvers. A freestyle program should be balanced with a good mixture of 3D and precision aerobatic maneuvers, and your performance should be smooth and show control at all times. If you move the CG rearward, your plane will more easily perform wild 3D maneuvers, but it won’t fly as precisely or solidly. On the other hand, if the airplane is nose heavy, you’ll have a solid airplane with show precision, but you won’t be able to execute wild 3D aerobatics! You need to end up with a CG that’s between these extremes. For their freestyle routines at TOC, most pilots move the CG rearward by adding weight at the tail.
This point may differ for various planes and pilots. I like to fly a plane that has a CG that’s at 35 percent of the MAC for precision maneuvers and then move it back to about 38 percent for the freestyle portion of the competition. The illustration shows how to find the MAC and then the CG. I like to use these numbers as a reference, but I adjust the final CG by flying the airplane. I’ve found this is the best way to correctly set my airplanes, so they all “feel” the same and have the same trim characteristics.
FLIGHT-TESTING THE CG
It’s easy to fine-tune the CG for precision maneuvers: fly the airplane upright and level, pull to 45 degrees (at full throttle), and do a 1/2 roll to inverted. The airplane should fly inverted by itself in a straight, 45-degree line for 2 to 3 seconds and then start to fall toward the canopy (you should barely have to push the elevator stick forward to keep the airplane flying in a straight line).
To perform 3D maneuvers, fly your plane upright and level at about 1/2 throttle. Roll the plane to inverted; it should fly by itself in a straight, level line for 3 to 3 1/2 seconds and then start to fall down toward the canopy, (you should barely have to push the elevator stick forward to maintain level inverted flight). If your airplane climbs when it is inverted, it is too tail-heavy; in my opinion, you crossed the line between precision and instability.
If you were to watch my CG flight tests with the model flying inverted, you would notice that for precision flying, I try to fly the plane at a 45-degree angle; for freestyle, I fly it level. The difference of 2 to 3 percent in the CG locations is the real difference between precision and freestyle airplane setups.
When you know the CG that is best for various aerobatic maneuvers, you can prepare the airplane for optimum performance. For example, when you use torque rolls, snap rolls and other precision maneuvers in your freestyle routine, it’s time to fly your plane with the same CG as you use for precision aerobatics. This is not the case if your freestyle program has more 3D maneuvers involved.
To perform 3D aerobatics, you must have a good radio setup. Your radio is a key element to perform a freestyle mixture of 3D and precision aerobatics. This doesn’t mean that you must have top-of-the-line radio equipment to do freestyle aerobatics, but there are two radio features that will make your flying a lot easier: dual rates and exponential.
With its large control surfaces, high deflection and rear CG, your airplane will be very sensitive and responsive, so you’ll need to make good use of your radio programming. Flying smooth, precise and graceful aerobatics while maintaining a good “geometry” at high airspeed is completely different from flying at low speeds and making big pitch, yaw and rotation changes, such as those demanded by 3D aerobatics. This is where using exponential and dual rates comes in.
There are probably as many ways to program a radio as there are pilots because most pilots fly by “feel.” With this in mind, I will explain how I adjust my radio for freestyle. I hope this will help you with your setup.
Many 3D aerobatics need maximum deflection on all three control surfaces, so I set the high rates on elevator, rudder and ailerons to 140 percent. Always check the linkages, arms and control horns and make sure that the servos move freely at this deflection. Make sure that each elevator travels the same distance up as it does down, and do the same for the ailerons. After you’ve checked everything, adjust the low rates. But first consider, “When will I use the low rates?” I use low rates for “normal” flight and use high rates for flying snap rolls, spins and, of course, 3D aerobatics.
Adjustment of the low rates is more complicated because each includes the rate and the exponential, while the high rate just involves the exponential. Low rates can also vary a lot between pilots. For my low rates, I use 25 to 30 percent for the elevator, 80 to 90 percent for rudder and 60 to 70 percent for ailerons. I’m sure that these numbers will be a good place for you to start, too; these are what I use with a new airplane before I give it a last fine-tuning at the field.