How i trim an airplane

[Frank v B]

On my last visit to Rogo I was asked to trim out two planes.  Always happy to do it.  Here is an outline of the steps I use.

This assumes the basic stuff works correctly (AER&T servo direction, motor direction, balance per plan, etc).  This also assumes a plane has flown before but just needs to be trimmed for hand-off flight. See my post on "How I maiden airplanes" https://temac.ca/smf/index.php?topic=3826.0

1) Before take-off Center all controls, especially rudder.
2) Take off, fly circuits two mistakes high and do all tests and corrections on the upwind leg of the circuit. Speed should be about 3/4 throttle when the adjustments are made.
3) Handle the most out-of-trim axis first.  I usually handle pitch first (up and down).
If the plane keeps diving, adjust the trim lever a few clicks of "up" elevator*.  Click the trim in the same direction of the correction on your stick.  As it gets closer to stopping the diving let the stick go to see how close it is to neutral flight.  Keep clicking trim until it gets close to neutral flight when you let the elevator stick go.  I usually trim an airplane so it has a little bit of downward flight.  This way there is always back (up) pressure on the elevator stick.
4) If you are out of trim adjustments (no clicks left on the trim lever), bring the plane down to make a mechanical adjustment at the elevator horn or the servo horn.  Center the elevator trim on the transmitter so the elevator is in the same position as it was when you landed. Get back in the air and continue trimming to neutral level flight.
5) Then focus on the roll axis (aileron).  Do the adjustments the same way until the plane is neutral in roll. If you are out of trim before you find neutral flight, land, do a mechanical adjustment and take off again.  Find neutral flight.
6) Rudder- Trim the rudder by going to level flight, go to full throttle, a shallow dive and give full "up" elevator until you achieve vertical flight.  See which way the plane falls (left or right).  Adjust the rudder until it goes up straight.
7) Adjust aileron again if needed.  Go back to level flight and adjust aileron again to counter the newly trimmed rudder.  The re-trim should be minor.

If the trim changes when the plane flies at full throttle then it is a thrust line issue. I only adjust this if it is really bad.  It is usually a problem on really small planes, not 20 size or larger.  If the plane goes "up" at full throttle, add "down thrust" to the motor.
If it pulls the plane left or right, use side thrust to find neutral flight.

Hope this helps.

Frank

* "up" elevator means the way the elevator moves, not the transmitter stick.  The trim lever should be adjusted the same direction as the stick correction on the transmitter.