Trimming a model
This article by Eric Brownbill, gives advice on basic model trimming and recommends that you make better use of your model's natural stability.
Some of model flying’s best kept secrets :
Sometimes, the words we use to talk about things can mislead. A good example in aeromodelling is when we talk about ‘flying a model’, it can give the impression that we have to do something in order for the model to fly, or even that the model will stop flying at all unless we are doing something. Some years ago we had a young gentlemen at Aston Down who really did seem to believe that a constant twitching of the sticks was essential to keep the model aloft. Nothing would persuade him otherwise and as a result his model had a flight path similar to that of a demented moth!
If you’re of my vintage, you probably remember free flight models, and you may have started your aeromodelling career by building some. They were simply launched into the air and left to get on with it all by themselves. The reason they managed it was that they had a degree of positive stability designed in; this meant that if they were displaced from their flight path, say by a gust of wind, the forces acting on them tended to return them to a stable, predetermined flight path. The flight path they returned to was determined by the trim of the model, the alignment of the wings, tailplane and fin etc. Adjustment was a matter of repeated trial and error, and very thin (e.g. Bits of card or 1/32nd balsa etc.) were used as packing under the trailing edge of the tailplane to make the necessary adjustment.
Now to our radio control efforts. They too have built in positive stability, indeed some models, such as those kitted by Colin Buckle, actually started life as free flight designs. This means that they can fly very well all by themselves provided you trim them, and trimming them is very easy. You don’t have to wait until the model lands and then insert some packing and then try again, you can do it in the air. Those little levers (the ones you never use) beside the transmitter sticks enable you to adjust the trim while flying, (one click equals a sliver of balsa) and you can instantly see the results and try again. The only problem is that you have to let go of the sticks for a second or two so you can see what the model is actually trying to do before you make the adjustments, and if you’ve never tried it before that can be a bit scarey. A little hint - try and sense where you are holding the sticks for most of the time, if you are having to hold them off centre to fly straight and level, you’re almost certainly out of trim.
What you’re aiming for is a model which flies straight and level all by itself. If the model wants to dive you feed in up elevator trim until it will hold it’s height without you having to hang onto the elevator. If it’s veering left or right you feed in aileron trim until it flies straight. If you’ve got it right you should be able to take the model to a safe height, point it in the right direction, put the transmitter on the ground and watch while the model fly itself across the airfield.
Why bother with all this trimming? The reason is that your flying improves and the stress level decreases. The model does the straight and level bit, and better than you ever could, and you don’t have to worry all the time about the model doing something nasty like stalling, veering off course or diving into the ground. You can then concentrate on the bits where you’re going against the models inbuilt stability such as turning corners.
So here are some of aeromodellings best kept secrets :
1. The model knows more about flying than you ever will.
2. The more you interfere with the model’s flying, the worse it will get.
3. Most of us are flying glorified free flight models anyway.
4. Trimming your model is one of the most important thing you can do to improve your model’s flying and your own flying.
5. Basic trimming is easy to do and easy to learn.
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