Made with Xara Web Designer How To: TRIM AND MIX FOR AEROBATICS Your plane can fly straight in any attitude. Thanks to Peter Goldsmith. compiled by Jim Brink 1. Insure that controls are centered, surfaces are straight, and that throws are appropriate. Select the prop you will use. If you must change props, start over. 2. Trim for straight and level flight at mid to 2/3 throttle. 3. Check for proper CG by pulling to a 45 degree upline at full throttle. Roll the plane over on its back and release the sticks. It should make a slow arc toward the ground. If it arcs too fast, it is nose heavy, and if it goes straight or climbs, it is tail heavy. Adjust the CG, re-trim (#2) and repeat #3 until it is correct. A second way to test for CG is to fly inverted and see how much push it takes to maintain level flight. Too much push can be corrected by moving the CG aft, and too little requires moving the CG foreword. Most pilots prefer 1/8 to 1/4 inch of stick push inverted, but that is a matter of feel. 4. Check for a heavy wing by flying high and pushing to a vertical downline at low throttle. When the speed is high pull sharply to horizontal. (Pull high enough to recover if it snaps.) If one wing is heavy, it will drop. Land and add weight to the other wing until even a sharp corner does not cause a wing to drop. Coins and tape work well for temporary weight. This test is surprisingly sensitive. 5. In level flight, advance the throttle to full. If the plane climbs, add down thrust. If it dives, add up thrust. 6. Check for corkscrew in both outside and inside loops by flying directly away and pull or push multiple loops. Be sure that the wings are level. If the plane corkscrews one way or the other, correct with an opposite elevator/rudder mix. 7. Most aerobatic planes yaw left on vertical uplines due to the effect of the prop tornado on the rudder. This can be corrected with right thrust of the engine or high throttle to right rudder mix in the transmitter. Fly the plane straight up at full throttle and watch to see if it yaws. Adjust the right thrust and/or throttle/rudder mix until the plane climbs straight. A combination of these two adjustments works, too. 8. A plane that rolls in knife-edge will roll right and left at different rates. Also, point rolls will not hesitate cleanly. Put the plane in knife-edge and observe if it tends to roll to canopy or wheels. Correct this tendency with a rudder/aileron mix. Do one side at a time. 9. If the plane pitches in knife-edge, rolls and point rolls will corkscrew. Put the plane in knife-edge and observe if it pitches to canopy or wheels. Correct this tendency with a rudder/elevator mix. Do one side at a time. HINTS: These tuning steps must be done in this order. A change in any step setting, will change all following steps. This process can be greatly accelerated if your transmitter can be programmed in flight. An assistant will be necessary. Not all planes will need all these trims and mixes, but most will. A 7CAP transmitter or equivalent can do all these mixes. Use the 3 available mixes on steps 6, 8 and 9. Calm conditions are necessary for these tests. Take your time on steps 2, 3 and 4. 15 flights at least. Think of this process as part of the building cycle. I find it the most fun part because I can see my planes improve daily and my maneuvers improve. Any size aerobat from electric flat wing foamys to 40% IMAC planes will benefit from this process. You will get faster with each plane you trim and your understanding of aerodynamics will take off. (Pun intended) It will surprise you how much a properly tuned plane makes all aerobatics easier and you will hate to fly planes that don’t fly straight. If you run into trouble, call Jim Brink or Jerry Craig. Good luck and have fun. 1954- Rocky Mountain Modeleers