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Trimming Your Bird!

A good guide for setting your aircraft's trim adjustments...

[bullet] Theres a lot more to getting your airplane trimmed, than just sliding the tabs on your transmitter. A correctly trimmed airplane is much more stable and fun to fly! When building a model airplane, it is important that the plane be balanced and wing incidences be set correctly. Take your time with these procedures! If you don't have an incidence meter, borrow or buy one.  This is the only correct way to check and set your incidence. Check the balance on the CG front to rear, and from left to right.   One of the easiest ways to do this is by finding the CG on the fuselage, then finding the center, (left to right) of the plane. Screw in a  small eye hook, and hang your plane. It should balance front to rear, and side to side. The engine thrust angle and the CG interact with each other. Double check both to make sure that they are set according to plans. Yaw and lateral balance create similar symptoms. If you are having problems in this area, check to see if the fin is straight.  It's far easier to make changes in the building stage than after the model is covered. If you follow the trim adjustment below, and still have problems, check for non centering servos, play in control linkages, and aileron and elevator gap.

Control Centering Fly general circles and random  
Try for hands off, straight  
and level flight.
Readjust linkages so Tx  
trims are centered.
Control Throws Random maneuvers. A. Too sensitive.  
B. Insufficient control.
A. Change linkage to  
reduce throws.  
B. Change linkage to  
increase throws.
Engine Thrust Angle 1. From fast straight flight, cut throttle.
2. With throttle on, pull to vertical flight.
1A. Aircraft continues straight flight for a short distance.  
1B. Plane pitches nose up.  
1C. Plane pitches nose down.
2A. Plane tends to yaw right
2B. Plane tends to yaw left
1A. Thrust angle is OK.  
1B. Decrease downthrust.  
1C. Increase downthrust.
2A. Add leftthrust.
2B. Add rightthrust.
Center of Gravity  
Longitudinal Balance
From level flight at low throttle and in trim, push the nose to 45 dive and neutralize controls. A. Plane continues in dive for  a short distance, and gradually pulls out.  
B. Nose pitches up abruptly.  
C. Nose pitches down more (tucks under). 
A. CG is good.  
B. Add nose weight. 
C. Remove nose weight.
Split Elevators  
Yaw and CG
Into wind, Pull open loops using only elevator. Repeat test with outside loops to inverted entry. A. Wings are level throughout.  
B. Plane tends to left when right side up, and to right when inverted.  
C. Planes tends toward right when right side up and left when inverted.  
D. Plane goes left, right side up and inverted.  
E. Plane goes right, right side up and inverted. 
A. Trim is fine.  
B. Add right rudder, or weight to right wing.  
C. Add left rudder, or weight to left wing.  
D. Raise right half of elevator, or lower left half of elevator.  
E. Raise left half of elevator, or lower right half of elevator.
Yaw2 Into wind, do open loops, using only elevator. Repeat tests using outside loops from inverted entry. A. Wings are level throughout.  
B. Yaws to right in both inside and outside loops.  
C. Yaws to left in both inside and outside loops.  
D. Yaws to  right on inside loops, and left on outside loops.  
E. Yaws to left on inside loops, and right on outside loops.
A. Trim is correct.  
B. Add left rudder trim.  
C. Add right rudder trim.  
D. Add left aileron trim.  
E. Add right aileron trim.
Lateral Balance Into wind, do tight inside loops, or pull to straight up flight into hammerheads. Repeat test from inverted entry. A. Wings stay level and plane falls randomly in each direction from hammerheads.  
B. Falls off to left from both inside and outside loops.  
C. Falls off to right in both inside and outside loops.  
D. Falls off in opposite directions on inside and outside loops.
A. Trim is correct.  
B. Add weight to right wing.  
C. Add weight to left wing.  
D. Change Aileron trim.
Aileron Rigging. With wings level, pull to vertical  climb , and neutralize controls. A. Climb continues same path. 
B. Nose tends to go to inside loop. 
C. Nose tends to go to outside loop.
A. Trim is correct. 
B. Raise both ailerons slightly. 
C. Lower both ailerons slightly.
Wing Incidence Knife edge flight. A. Plane tends to nose up position (as if up elevator is applied). 
B. Plane tends to nose down position (as if down elevator is applied). 
A. Reduce wing incidence. 
B. Increase wing incidence.
Aileron Differential. With wings level, roll repeatedly left or right. A. Model stays on heading. 
B. Model yaws in direction of roll (barrel roll). 
C. Model yaws opposite the direction of roll.
A. Aileron Differential is correct. 
B. Too little differential (reduce down throw). 
C. Too much differential (increase down throw).

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