“A good F3F competition plane deserves a good CG setting, which requires the appropriate tool.” While not absolutely required to determine your aircraft’s centre of gravity, anything which makes it easier and more accurate is an asset. See Resources, below for a link to Pierre Rondel’s Digital CG Balancer article. (image/quote: Pierre Rondel)

Trimming Model Aircraft

A short primer for beginners.

For the Newcomer

What does trimming mean? It means adjusting various settings on a model until it flies straight-and-level (SL) under cruise throttle or level gliding flight. For some, but not all, models it means you can take your fingers off the sticks and the model will fly SL.

  • The neutral positions of the control surfaces
  • The throws on the control surfaces
  • How much small stick movements move the control surfaces (sensitivity)
  • Lateral balance
  • The thrust line of the motor or engine
  • The angle of attack of the wings and tailplane (incidence)
  • The dihedral
  • The control surfaces to make sure they are solidly and freely hinged

Basic Trimming

Centre of Gravity (CG)

The Maiden Flight

We all feel a bit nervous at this point, but it’s only money (and pride). You could of course ask someone else to do the maiden flight but really it is best to do it yourself unless you are very nervous or the model is a big step up. Get the model into the air and find the throttle setting that gives level flight. Ideally have someone standing with you to observe and to move the trim buttons if you feel you can’t. Here’s what to look for:

  • The model banks — adjust with aileron trim.

And Now the Advanced Stuff — Aerobatic Aircraft

If you do all of the above you should now have a stable model that responds well to your control. If you are moving to a truly aerobatic model there are further things to think about. The model needs to be more neutral than for sport flying to reduce the corrections you need to make. The higher speeds make the control surfaces bite better too.

  • Model dives — reduce down thrust
  • Model turns left — increase right thrust
  • Model turns right — decrease right thrust
  • Model climbs — move CG forward
  • Model’s nose goes down — increase wing incidence or reduce tailplane incidence
  • Model turns in opposite direction as roll — decrease differential
  • Model rolls to upright — decrease dihedral


These are different in two main ways:




RC Soaring Digest (RCSD) is a reader-written monthly publication for the RC sailplane enthusiast and has been published since 1984.

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