A well-trimmed RC airplane flies predictably with the sticks near center. Good trimming begins with mechanical setup on the bench—not with a screen full of transmitter adjustments.
Start mechanically neutral
- Center trims and subtrims in the transmitter.
- Power the receiver so every servo moves to center.
- Install servo arms as close to 90 degrees as practical.
- Adjust pushrods or clevises until the control surfaces match the plans or manual.
- Verify hinges move freely and linkages have little slop.
Control direction
Stand behind the airplane. Right aileron input should raise the right aileron and lower the left. Up elevator input should raise the elevator. Right rudder input should move the rudder right. Check every model before every flight.
Set control throws
Measure throws where the manufacturer specifies. Change linkage geometry first when practical: moving the pushrod inward on the servo arm reduces movement and increases mechanical advantage; moving it outward on the control horn also reduces movement.
Dual rates and expo
Dual rates provide selectable control travel. Exponential softens stick response around center while retaining full travel at the extremes. Expo direction varies by radio brand, so verify the result in the servo monitor and by feel. Start with the manufacturer’s recommendations.
End points and binding
Adjust travel so servos do not buzz, stall, or force a surface against a mechanical stop. Check the full range of every mix, rate, and flight mode. Binding wastes current and can damage a servo or linkage.
Trim in flight
Use calm weather and a safe altitude. Establish a moderate cruise speed and make small trim corrections. Land before making major changes. After the flight, adjust the mechanical linkage to preserve transmitter trim range, then recenter the electronic trim when appropriate.
Diagnose instead of hiding problems
Large trim requirements may indicate an incorrect CG, warped surface, misaligned wing or tail, thrust-angle problem, unequal control geometry, or structural damage. Fix the cause before adding mixes.
Final checklist
- Correct model memory
- Servo arms and linkages secure
- Controls centered and moving correctly
- Throws measured
- No binding at full travel
- Rates, expo, mixes, and throttle cut verified
Related reading: servos, pre-flight checks, and servo buzzing at an endpoint.