Trimming for aerobatics is different from just using trimmer. It involves a series of setups designed to correct your plane’s bad tendencies and to lay the foundation necessary for all aerobatics. Eliminating cross coupling is the key. By "Eliminating cross coupling'' i mean that when you add rudder, the plane yaws without showing a tendency to pitch or roll. Likewise, when you apply aileron, your plane must roll on an imaginary line without making a heading change. Before you can ever hope to do precision aerobatics, your plane must be able to follow pure inputs without any cross coupling. This concept may be new to you. If you follow the setup procedures and practice the flight maneuvers described, you’ll be able to successfully set the aeroplane Competition Aerobatics

GROUND CHECK

Before putting your plane through any set of aerobatics, make sure its static setup is perfect. Eliminating setup flaws now will ensure that your aeroplane in the air will be predictable. this step will allow your plane perform consistently enough for you to make sense out of the flight-trimming procedure.

To prevent pressure equalisation (which is bad, causes loss of Lift & Increase in Drag) Top and Bottom portion of wing, make sure all the hinge gaps are sealed with covering. More important, the air transfer will vary with speed and attitude, making it trimming of the plane erroneous.

To avoid this problem, disconnect the ailerons from the linkage; extend the ailerons to the maximum upward position and cover the V-shaped crevice. Do the same for the elevators, and seal your rudder gap as well.


Now buy a good-quality deflection meter and measure the throw of each control surface.



Each elevator half must travel the same distance up and down. The same goes for the ailerons; if one aileron has greater travel than the other, you will not achieve a perfect roll.  Check all of the incidences. Be sure they match those called for on the plans. Check and double-check to make sure that your stab and wing are perfectly aligned.

Eliminate control-linkage slop by using superior hardware. If you have any slop in your system, your surfaces will not center properly, and will not respond precisely to control inputs.

Set your control throws to the minimum settings given in the plan. Contrary to popular belief, most precision aerobatics are done using very little control throw. If your setup allows too much travel, it will be difficult to make minor flight-heading adjustments, and this will make maneuvers look jumpy and erratic. Typically on a  30 % Extra 300S, 8 degrees up- elevator and 10 degrees down. Ailerons at 11 degrees up and 9 down (for differential, which we will discuss later). The rudder at about 20 degrees is good enough (Except for Low Speed Hard 3D)

BASIC FLIGHT TRIMMING

Aerobatics flight trimming is highly dependent on the airplane’s thrust line and CG. Before beginning, make sure that the CG and engine thrust are perfectly set. Changing them after you’ve started trimming for aerobatics will change the airplane’s characteristics and flight trim. CG and engine thrust as your foundation; if you change them, you change everything. Start with the CG. To test for proper CG, roll the plane inverted and gauge how much down-elevator is required for level flight. You should be able to fly inverted while adding only a little down-elevator. Another test is to roll to knife-edge from straight flight and observe how your plane falls. If the nose falls first, the plane is probably nose-heavy; if the tail falls first, it is tail-heavy. Change the CG by moving the battery pack. Resist the temptation to add weight; after all, lighter is better. Now that the CG is set, you need to work on the thrust line. Fly your plane through a set sequence of vertical uplines to quickly see exactly what is needed. (See Image), and make the appropriate changes before proceeding. If your plane won’t track vertically on its own, you will have to wrestle with it constantly. the goal is to have your plane fly as true as possible at any attitude without your having to make constant inputs.

FLIGHT TRIMMING FOR AEROS

The secret is rudder! In aerobatics, the rudder is the most important control surface. Without it, competitive aerobatics pilots would have a very difficult time flying. In a a ral aeroplane, rudder would be required in only a few maneuvers, such as hammer stall, snaps, spins and knife-edge. In RC flying without using rudder to correct a bad entry or exit is difficult. Crosswinds and gusts can also necessitate the extensive use of rudder. 

Eliminating cross coupling

First, set up your computer radio with two mixes. Make rudder the master and ailerons the slaves. On the second mix, make rudder the master and elevator the slave. Be sure to turn off every other mix that may have come with your radio—especially the aileron-to-rudder mix, which plays no part in aerobatics. Now you’ll fly the plane in knife-edge and program out the bad tendencies or coupling using these two mixes. (Coupling is the airplane’s tendency to roll or pitch with the application of rudder.) Fly your plane from left to right, roll right 90 degrees, and apply just enough left rudder to sustain knife-edge flight. Do not apply full rudder. Observe what your plane tends to do. A scale aerobatics design will usually pitch downward (toward the wheels) and roll left. Do this a few times to be sure. Now, land the plane, turn off your engine and begin to program out the coupling. If your plane pitched down during knife-edge, program a few percent up-elevator with the application of left rudder. If your plane also rolled left, program a few percent right aileron with the application of left rudder.  Continue until you can achieve knife-edge flight by using only rudder. Now fly the plane from right to left, and make the same observations and adjustments until the plane will fly knife-edge in either direction using only rudder. You are very close to having pure inputs, but you need to check a few more things. Fly the plane straight and level at 1⁄2 to 3⁄4 throttle, and apply a little rudder to get the plane to slide. Does the plane begin to slide nicely into a beautiful, large, flat turn? If it doesn’t, observe what it tends to do (note that a little pitch-down is normal owing to the extensive drag you introduced by turning the fuselage). Now fly the plane from any direction, and pull it straight up in front of you so you see only its side. Apply a little rudder as it flies straight up, and observe it. Finally, fly the plane inverted in the same direction as before and apply the same amount of rudder. If the plane pitched or rolled in the same direction during the flat, vertical and inverted tests, go back into the mix and correct it. If the plane pitched or rolled in a different direction in each test, you  may have a misaligned tail group. Keep in mind that few aerobatics designs will ace all of these tests. Sometimes, the best you can achieve is an acceptable average. Your plane now has pure inputs. Go through some simple maneuvers, maintaining a constant heading by using rudder. You should easily be able to make deliberate heading corrections with rudder without having to add coupling.  To further enhance your flying abilities and your plane’s flight characteristics, you may need to check a few more things. Fly the plane straight and level at  1⁄2 to 3⁄4 throttle, and apply a little rudder to get the plane to slide. Does the plane begin to slide nicely into a beautiful, large, flat turn? If it doesn’t, observe what it tends to do (note that a little pitch-down is normal owing to the extensive drag you introduced by turning the fuselage). Now fly the plane from either direction, and pull it straight up in front of you so you see only its side. Apply a little rudder as it flies straight up, and observe it. Finally, fly the plane inverted in the same direction as before and apply the same amount of rudder. If the plane pitched or rolled in the same direction during the flat, vertical and inverted tests, go back into the mix and correct it with mix

Shoot your questions, take 10-12 flights to setup your aeroplane properly, fly smoothly, be observant, do these tests in nil wind conditions