| The Great Circle is the most commonly seen RC landing approach. Visit any RC flying field and note the landing approaches each pilot makes. Probably somewhere near 75% of them will be the Great Circle in one form or another. As you watch these approaches, also note how many aircraft land on, or at least near, the runway’s centerline; with the touchdown point somewhere near the pilot’s latitude. You will find that most of these landings are either “long”, well past the pilot’s position, or close to the opposite runway boundary, or maybe both.
Why? Because, although the most common RC landing style, the Great Circle approach is the most difficult RC landing approach to master. During this style approach, the pilot must simultaneously adjust the aircraft’s descent rate, airspeed, runway centerline position and touchdown point while the airplane is in a spiraling descending turn. These are too many tasks to manage while the airplane is in an unfavorable position.
Most RC pilots don’t realize they are trying to accomplish so many tasks at once because the Great Circle has one major advantage that seems to make it the easiest approach to use. During this approach, the aircraft is usually closest to the pilot of any approach and easy to see. The Great Circle affords excellent visual references because it is flown close in to the field. This makes the approach appear easy to accomplish when it is not in reality. But a few approach modifications do help to simplify this approach without losing it good visual references advantage.
While as old as powered flight itself, the Great Circle was perfected in the 1920’s by pilots trying to land on a moving aircraft carrier. Biplanes do not afford the pilot good visibility, as the wings and struts always seem to be in the way. Things didn’t improve much when carrier pilots switched to low wing WW II fighters with cockpits located right over that broad wing. These wide wings were also always blocking just where the pilot wanted to look.
Landing while in a constant turn kept the moving carrier always in sight. Since there was only one turn, the downwind could be flown close to the carrier affording a good situational view. The Landing Signals Officer (LSO), the man with the flags you see on deck in the old movies, kept track of the airplane’s speed and descent rate allowing the pilot to concentrate on aligning the aircraft with the centerline of that tiny deck. The pilot was sitting in the airplane, where he could both feel and see the approach unfold, and had the LSO to help manage the simultaneous tasks. In this situation, the Great Circle approach worked well.
But the RC pilot has none of these advantages. He is alone and in the position of the LSO with no “feel” for the aircraft through the control system. The perfect Great Circle is shown in Fig. 1.
The RC pilot flies the Downwind Leg about 100 ft. high and 100 ft. out from the runway centerline. At about the end of the runway, the aircraft begins a descending, 180 deg. turn to align with the centerline about 20 ft. high over the end of the runway. From there, the airplane lands in front of the pilot. Sounds easy, doesn’t it. Let’s see just what is happening in this approach.
First the airplane must start to turn and begin to descend at the same time. There is little time to establish the descending glide before making the turn. Therefore the pilot must establish to proper descent rate that will leave to airplane with 20 ft. of altitude just over the runway’s edge. At The same time, the pilot must also establish the correct turn diameter to be sure the aircraft is aligned with the centerline when the turn is completed. Again at the same time, the pilot must control the airspeed so that the airplane is not traveling too fast, or too slowly, to land in the middle of the runway. This is a lot or work.g
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