Quick diagnosis: Small elevator inputs produce abrupt climbs, dives, or stalls, and the airplane feels difficult to hold at a steady attitude.
What This Symptom Usually Means
Start with the simplest observable cause and work toward radio programming and component replacement. Before touching the propeller, motor, engine, or linkage, make the model safe. Use the correct model memory and inspect the airplane in its normal flight-ready configuration.
Symptom, Cause, and Corrective Action
| Possible cause | What to look for | What to do |
|---|---|---|
| CG too far aft | The model is unstable and may tuck or stall abruptly | Move the battery or ballast forward within the approved range |
| Too much elevator travel | Tiny stick movement creates a large surface movement | Set measured low-rate travel to the manual |
| Too little expo | The center of the stick feels nervous | Add moderate expo in the correct direction for the radio |
| Poor linkage resolution | Servo uses very little rotation for full surface travel | Move inward at the servo or outward at the horn |
| Pitch gain too high | The nose bobs or hunts as speed increases | Reduce pitch-axis stabilization gain |
Step-by-Step Diagnostic Procedure
- Verify the model is assembled exactly as it will fly, including battery, spinner, canopy, and accessories.
- Measure the center of gravity using the manual’s recommended starting location. Do not rely on appearance or a previous model.
- Check elevator neutral, stabilizer incidence, hinge security, and whether both elevator halves move together.
- Measure elevator travel at the trailing edge and set low and high rates from the manufacturer’s values.
- Improve mechanical resolution if a small servo rotation creates excessive elevator movement.
- Set exponential in the correct direction for your transmitter and confirm the result on the channel monitor.
- Disable unexpected flap-to-elevator, throttle-to-elevator, or flight-mode mixes.
- If stabilization is installed, verify correction direction and reduce only the pitch gain if the airplane bobs without pilot input.
Common Mistakes
- Moving the CG aft to make a trainer feel more aerobatic.
- Using expo to hide dangerously excessive mechanical travel.
- Copying expo signs from another radio brand without verifying the channel monitor.
- Testing high rates immediately after a major CG or linkage change.
Controlled Test Procedure
Begin with the CG at the conservative published location and use low rates. Have an experienced pilot climb to a safe altitude, make gentle elevator inputs, and check stall behavior with adequate recovery height. Change CG, travel, or expo one variable at a time.
If the Problem Continues
Stop making unrelated changes. Photograph the installation, write down the current CG, rates, expo, gain, propeller, battery, and relevant telemetry, and ask an experienced pilot or builder to inspect the model. Change one item at a time and record the result.
Frequently Asked Questions
How much expo should I use?
Use the manual as a starting point. Moderate expo can soften the center, but the correct value depends on the airplane, mechanical travel, and transmitter convention.
Will moving the CG forward fix everything?
It can improve stability, but it will not correct excessive elevator throw, linkage slop, a bad mix, or excessive gyro gain.
Why is it worse at high speed?
Control surfaces become more powerful as airspeed increases. Excess travel, airframe flex, and excessive stabilization gain therefore become more obvious.
Related RC Plane Lab Guides
Return to the RC Airplane Troubleshooting Center. Use the hub to compare related flight-control, radio, stabilization, and electric-power symptoms.
RC Plane Lab provides general educational information. Follow the instructions for your specific airplane, radio, receiver, motor, ESC, battery, engine, and stabilization system.