ORIGINAL: rhall999
I don't really disagree with any of your argument, but you're leaving things out. When you increase the angle of attack of a plane that's banked, some of the increase keeps you from dropping and some of it makes you turn tighter because, as you say, the lift vector is not vertical. If you are banked 45 degrees, which isn't unusual for a model, about half the angle of attack increase contributes to the the turn. If you're banked 85 degrees, most of it does.
Hi Top, well, I did mention it in there actually:
This increases the total lift vector, which allows the vertical component to again equal the weight. Now, looking at that diagram again, you can see how in a set angle of bank, simply applying up elevator will cause the airplane to climb. There will be a small increase in the horizontal component too, but in a ''normal'' turn, not enough to even notice the increase in turn radius.
BUT, look what happens if we steepen the bank further. Now, the total lift vector is still being split, but the steeper the bank, the more of the lift is given to the horizontal vector. This will cause a tighter turn. (Remember, the tail area will cause the airplane to ''yaw'' when that horizontal lift ''pushes'' us sideway, thus turning the airplane.) So, now we have a large portion of our lift going to the horizontal vector and less to the vertical vector, now the airplane really wants to drop, so we need to increase the total lift a lot more. So, to do this we need to pull back some more to increase the angle of attack enough to increase the total lift to increase the vertical component to keep us up in the sky. Whew, lots going on here isn't there.
I fly full scale as well as models, and the result of using elevator in a turn is VERY easy to see in a full size when you can physically feel and see out the windscreen what is happening. Less visible when you are standing on the ground.
Anyhow, I totally aggree with what you are saying in regards to beginners, especially the bit about not such steep banks!! Personally, I don't teach to pull up to turn tighter, simply because at the early stage when this is even a problem, most students can not run the throttle and turn and everything at the same time, so the risk of stalling if they pull to hard is greater. For the same reasons they turn too steep, they also pull too hard. I gotta admit, I have never had the ''split S'' problem happen to me with a beginner though, but I can see it happening.