Even if you take all the care in the world building your plane right and level and "perfectly", is it true that you may still have to trim off during flight constantly?(even if only a little bit)?

Green Flier,

You shouldn't have to trim constantly. Depending on the type plane and airfoil, you will probably have to make slight trim adjustments when you change power settings if you want to stay at that power setting for some time. For example, a plane with a flat bottom airfoil is very sensitive in pitch with power changes. This is especially true if the airfoil also has a few degrees of positive incidence. You add power and the speed increases causing the airfoil to make more lift and the plane climbs. If you trim for high speed, when you throttle back, the plane tends to descend more than normal.

This is one reason that when you get out of the trainer phase, most people go to a plane with a symmetrical airfoil. It doesn't change pitch with speed changes, or changes very little.

While you are learning, you should set the plane for a mid range power and trim for this. Leave the power at this setting while you are practicing turns and lining up with the runway.

Roll trim is another thing. If you have minor differences in leading edge curvature or slight warps in the wing or ailerons, your roll can change with speed changes. In addition, a servo that doesn't center very well can make you think the plane isn't trimming properly. Always put your best servo on ailerons. A third thing that can afect aileron trim is not having the trailing edge-aileron gap sealed. No matter how tight you think the ailerons are hinged, at flight speed, some air will bleed through from the underside of the wing. As you change flight attitude, this "bleed through" can change, affecting roll trim. It is always a good thing to seal your ailerons.

While everything Ed said is true, I generally do it this way; when I first fly the plane I get it to a safe altitude and in a straight and level flight path (preferably on a day with little or no wind), then release the controls. If the plane tries to roll slightly to one side, I'll adjust the aileron trim a bit to compensate. Same for any of the surfaces.

Unless you're flying IMAC, 3D, or Patern, chances are once set, you won't need to adjust trim again.

However, if you had to add more than a click or two of anything, you should mechanically adjust the clevises so that the transmitter trims can be reset to neutral. A computer radio can "remember" the trim settings for a number of planes, but the servos will be slightly off their neutral setting, and have a bit less throw in one direction than the other.

Once you've flown for awhile, you tend to compensate for slight trim changes during flight automatically. ie. your finger compensate without you realizing it. (Or mine do.)

Simplified version, bit hope it helps.
Dennis-

One of the things you can use to your advantage while flying a flat bottomed airfiol, like the ones on most trainers, is that you can then set the trim for crusing speed, which typically is about 1/2 to 3/4 throttle. Set the plane to fly level at this power setting, and then to descend, as in when making your landing approach, all you have to do is back down the throttle a little. to climb, use full throttle. Doing this will teach you throttle management, make it easier to take off and land, and will make you a better pilot.

On my 3D planes that start out tail heavy I generally have to give a click or 2 of elevator when landing bc when the tank is empty it is even more tail heavy.

Also, on the first flight of the day I always check the trim right of the bat, but I its very rare that I have to change something.

In general a well trimmed out aircraft stays trimmed out.