ABCS OF THE ROLLING CIRCLE

Model Airplane News, Jun 2005 by Patrick, Dave

TAKING IT ONE STEP AT A TIME

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THE ROLLING CIRCLE IS ONE OF THE most crowd-pleasing maneuvers. Properly performed, it's quite a sight. To most of us, mastering this impressive maneuver just doesn't seem possible! It is, of course, extremely difficult to do successfully, but if you take it one step at a time, you'll be able to master it. For those who aspire to add the maneuver to their flight routine, I'll go through the basics and offer a few pointers.

THE BASIC MANEUVER

A rolling circle isn't a big, 360-degree horizontal turn with a lot of rolls thrown in; nor is it a continuous roll in which the pilot uses elevator to constantly change the heading. A true rolling circle is a continuous 360-degree turn with a specific number of rolls (usually one, two, three, or four). Because there are so few rolls, they are, in fact, slow rolls, and that's where the difficulty comes in. To perform a four-turn rolling circle, you must execute four rolls while maintaining a constant heading change, and every roll must be completed at every 90-degree quadrant of the circle.

THE PLANE

You'll need a highly acrobatic aircraft with a particularly effective rudder. Certain pattern ships will do, but many aren't designed to perform this kind of maneuver. The Conquest series, for example, would have a tough time, but the Finesse 1.20 would do the maneuver acceptably well. Scale acrobatic aircraft such as the Ultimate bipe, the Extra 300 and the Sukhoi fly the rolling circle really well. Many other good designs can do it as well, but I'm most familiar with these airplanes and am in a better position to comment on their flight characteristics.

How your plane responds to rudder input will determine whether it's a good candidate for a rolling circle. It should be able to sustain knife-edge, but being able to climb in knife-edge would be even better. There shouldn't be any pitch or roll coupling when the rudder is used in knife-edge; pitch and roll coupling make it much more difficult to fly the maneuver properly. Before attempting it, use your radio's mixing features to adjust your model's flight responses until there isn't any pitch or roll coupling.

BIT BY BIT

I'll assume that you're already pretty good at straight slow rolls. If you aren't, practice until you are. Because the rolling circle is so complex, don't try to do it all at once. As an example, let's fly the four-turn (rolling to the outside) from an upright entry, starting from the left and flying to the right in a counterclockwise rolling circle (whew!). Got it?

Starting from your left, do four continuous slow rolls, using right aileron. There will be a 90-degree heading change for each completed slow roll. Focus on getting through the first slow roll while making a 90-degree heading change.

As you roll slowly to the right, apply left top rudder earlier than you would for a typical slow roll. Before the plane arrives at a knife-edge attitude, this top rudder will start the heading change and will help your plane to maintain altitude. Also, as you approach the knife-edge position, apply a little down-elevator to continue the heading change. Simultaneously, as your plane passes the knife-edge position, slowly remove the top rudder so that when the plane is inverted, all left rudder has gone; then apply right rudder. As you rotate past knife-edge, reduce down-elevator so that by the time the plane is inverted, you have only enough down-elevator to sustain inverted flight. Don't stop that down-elevator input too fast because it will also provide your plane's continued heading change.

Now, as you pass inverted, you must apply right rudder; this will continue the heading and maintain altitude. At the same time, start to apply up-elevator to provide a heading change again and to maintain altitude as you pass through the next knife-edge position. When the plane is upright again, you have completed the first slow roll and the first 90-degree heading change. This is easier said than roll and the first 90-degree heading change. This is easier said than done, especially when you're constantly mixing the control input proportions as you roll and change heading.

Now practice this first part of the circle until you feel comfortable and can execute the moves consistently well.

After you've mastered the first roll (this may take quite a few flights), do two rolls, and so on. You'll quickly find that the most difficult part is the last roll. That last quadrant (see Figure 1) presents you with a very unusual situation: you're trying to do a slow roll with your plane coming towards you. I can offer you no help here other than to tell you to practice at a comfortable altitude. If you build your rolling-circle skills bit by bit, you'll become proficient enough to work out the last roll.

I've focused on a particular version of the rolling circle; here are a couple of variations: how about a four-turn roll, but alternate the direction of rotation and start from inverted? Or try a two-roll rolling circle or a single roll (see Figure 2).