What Is Trim And How Do You Trim An RC Airplane?

Question: What Is Trim And How Do You Trim An RC Airplane?

Moveable control surfaces such as rudder, elevators, and ailerons are what allow your RC airplane to do more than just fly in a straight line in whatever direction you launch it. Trimming or making trim adjustments means tweaking those control surfaces so the airplane flies correctly -- maintaining altitude and making turns -- when you send commands to those control surfaces through your transmitter.

Answer: Most RC airplane transmitters have some type of trim adjustment features. There is usually a little trim lever, one for each control surface that you can adjust.

With the control stick in its neutral position, adjustments to the trim lever help to fine-tune the corresponding control surface on the plane (or fine-tune the movement of the servos that control that surface). For example, if your plane tends to turn to the left even though you haven't touched the rudder control, you can use the trim lever for the rudder to tweak it just enough that when the rudder control stick is in the neutral position, the plane flies straight like it should.

Ways to Make Trim Adjustments

In order of preference:

1. Before Flight. Do a complete inspection of the airplane.
   • Balance. R/C Airplane World explains this method of checking balance:

     To test your airplane's balance, place the tips of each index finger under each wing, 1/3rd of the way back and a couple of inches off the fuselage. Gently lift the model up so it balances on your fingertips. If the balance is correct, the model should be either level or with its nose pointing slightly downwards. -- Pete Carpenter, R/C Airplane World

     Some pilots suggest adding strategically placed small weights to wing tips, nose, or tail as needed to get the plane balanced.

   • Control Surfaces. Check all the moveable control surfaces, looking for parts that don't move adequately, are stuck, or are too loose. Make repairs as needed.

   • Assembly. Be sure the aircraft is put together properly. Look for missing pieces, parts hanging loose. Make sure the wings and horizontal stabilizer (tail) are level. Make sure the vertical stabilizer (fin) is centered on the horizontal stabilizer. Over time or after rough landings or after maintenance parts can become misaligned, throwing off the trim so you'll need to do this periodically over the life of the aircraft as well as anytime you notice it out-of-whack while flying.

2. After-Flight Trim. While flying take note of what controls seem off-kilter or which direction the plane wants to go when you aren't touching the stick. After landing change the trim settings. Fly the plane again and see if those adjustments correct the problem sufficiently. If not, land, readjust, fly again. Repeat as necessary until the plane is balanced and flying straight.

3. In-Flight Trim. While flying the RC airplane make trim adjustments using the trim levers or tabs on the transmitter, as needed to keep the plane on course. This should not be your main method of trimming the plane but it as an emergency measure.

There are some inexpensive, basic RC airplane toys that have no trim controls. If these planes don't fly straight you can sometimes make physical adjustments to the wings or tail to compensate. This could include bending the edges slightly or adding a touch of weight to bring the plane in better balance. Check the manufacturer's instructions first for recommendations. But with some cheap models you're on your own.