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Any full scale pilot will tell you that the secret to smooth precisionflying is to have the plane trimmed up, always. This is especially importantto formation work, instrument flying, bombing runs, and so on.
Keeping our RC aircraft in trim is also important to our flying, althoughthere are some important differences.
But, first, what do we mean by "trimmed up"? We generally trim for straightand level flight conditions -- such that if we take our thumbs off thesticks, the plane will continue flying straight and level, within the scopeof the stability of the plane. A couple of facts to ponder: 1) A planecan only be trimmed for ONE flying speed; 2) The more stable the plane,the more trim change occurs when the speed is altered. Note that we'respeaking of mostly PITCH (elevator) trim here -- lateral and directional(aileron and rudder) trim will generally not change as speed increases-- if they do, you've got other problems, such as warped wings, crookedtailfin, or thrust line problems.
In a full size airplane, the trims are located where it's easy to dothe trimming, without having to go "hands off" the stick or wheel. Unfortunately,the RC transmitter is not so convenient, and it's just not very easy toconstantly be messing with the trim. So most pilots trim for the fastestcondition they normally fly, usually full throttle, and full speed. Thatmeans that in any slower condition, some back stick is required for levelflight. For most of us, this is best -- because pushing on the stick seemsto give less precise control than pulling on it. And if your normal flightinvolves flying around at 1/2 throttle, then by all means trim for thatcondition, keeping in mind that the addition of more throttle (and speed)will result in a nose up climb.
Now, a bit about rudder and aileron trim. Assuming that you don't havewarped wings, a crooked tailfin, or bad thrust alignment problems, theaileron trim should, once you get it set, remain set. That's because thelinkage is short, and even if the links shrink or expand, they will bothraise or lower the ailerons the same amount. But the rudder link, unlessyou have a pull-pull system, will deflect the rudder with shrinkage orexpansion of the pushrod. And that pushrod is usually pretty long, meaningsignificant expansion in the heat of the day. If your rudder is offsetto one side, your plane will fly oddly, because it will be in a continuousslip, or skid, and may also want to roll to one side.
The point here is that you are wise to check the rudder trim (by lookingat the rudder) frequently, if not every flight. And if you get airborneand the plane flies weird and wants to roll, it's more likely to be ruddertrim than aileron trim that is at fault. This is especially true of trainertype planes because of the high wing dihedral, and is most true of planesusing "nyrod" type pushrods -- because the nyrods have a rather large expansionrate compared to other type pushrods.
Those of us who have flight instructed in full size planes can quicklyrecognize the symptoms of out of trim flying -- the plane constantly veeringoff course in the same fashion (left, right, up, or down) then being abruptlycorrected, then veering off again -- the cycle being constantly repeated.In such a situation, the pilot is more fighting the plane than just flyingit! And flying an out of trim plane is not an enjoyable experience!
If you relate to all this, seek out a more experienced flyer to helpyou get the beast in trim, and to show you ways to check it for yourself.You might be amazed at how much easier flying your plane can be! ... Clay
