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05/08 - Ground Reference Maneuvers, Part 2

S-Turns & Turns Around a Point
By Steve Krog
Steve Krog is a flight instructor and EAA member

S-turns and turns around a point are basic ground reference maneuvers designed to teach you subconscious control coordination, how to fly a balanced pattern over a given terrain, and how to recognize and overcome the effects of wind drift while flying a pattern. They also help you divide your attention inside and outside of the plane while mastering the art of flying.

All of the flight maneuvers you are taught prior to the ground reference training phase focused on understanding and applying control inputs in a coordinated manner. You were learning to comfortably and confidently fly the airplane with little concern for the effects of the wind.

In the last newsletter we began flying the airplane more closely to the ground and adjusting our flight path so that we could fly a straight-line track over the ground. We flew a rectangular course adjusting for the effects of the wind by establishing a “crab angle” or “wind correction angle.” In so doing, we flew a straight track over the ground parallel to the roads that formed a rectangular course.

This month we will focus on the two additional ground reference maneuvers required for both the sport and private pilot certificates.

S-turns

The S-turn is a series of 180-degree turns made across some straight line on the ground, such as a road, fence line, or railroad, which lies at approximately 90 degrees to the direction of the wind. For example, if the wind is blowing from the north, we’ll select a road that runs east and west. Each arc or half of the turn should have an approximate half-mile diameter and a quarter-mile radius. The illustration below shows what our ground track should look like.

Just as we did for the rectangular course, we’ll first descend to a level flight attitude at approximately 600’ above the ground (AGL). Then we will enter the maneuver flying directly into the wind (north).

Remember: When flying into the wind our ground speed will be slower, and when flying with the wind our ground speed will be faster. This is important because it will affect our constant changing angle of bank throughout the maneuver.

When first introducing the S-turn, I like to have the student enter the maneuver using a constant medium or 30-degree bank angle. As we cross the road, begin the medium bank turn to the right. Hold the angle of bank constant until completing a 180-degree turn, and then cross the road bringing the airplane to a wings-level attitude. Continue the maneuver now using a medium bank turn to the left. Complete the 180-degree turn again crossing the road. Your track over the ground will look like the dotted line track shown in the illustration below.

By not compensating for the effects of the wind in the first half of the S-turn, we’ve not been able to fly a symmetrical arc of a half-mile diameter nor a quarter-mile radius. During the second half of the S-turn the wind will have drifted or pushed us well beyond the quarter-mile radius, and if we continued, the turn the diameter would also be well beyond the desired half-mile diameter.

By noting the change in the radius of curve of the dotted line, you’ll soon realize that the bank must be changing constantly from shallow to steep when making the turn on the up-wind side of the road; and from steep to shallow in making the turn on the down wind side of the road.

Now that we know the wind’s effect on our ground track when not compensating for it, let’s begin again.

Enter the maneuver by flying perpendicular to the road on a north heading into the wind. As soon as we cross the road begin a shallow bank to the right. Remember, this is where we have a head wind - or slowest ground speed - so we will need a shallow bank to achieve the desired quarter-mile radius. As the turn progresses, we transition from a head wind to cross wind and finally to a down wind, increasing our ground speed. With ground speed increasing, we increase the angle of bank to accomplish the turn in a symmetrical arc of a half-mile diameter. The turn should be completed and our wings level just as we cross the road on a south heading.

Immediately after crossing the road, begin turning to the left, employing a steep angle of bank equal to the steepest angle used before crossing the road. We have a tail wind, or fast ground speed, at this point. As the turn progresses we transition from tail wind to cross wind to head wind, slowing our ground speed. The slowing ground speed necessitates bank angle changes from steep to shallow to maintain the half-mile diameter and quarter-mile radius of the symmetrical arc. If we judged the wind correctly we’ll complete the arc and cross the road perpendicular to the road and with our wings level.

The illustration above shows in detail where our bank is steep and shallow. Throughout the maneuver we will constantly be adjusting our bank angle to fly the symmetrical “S” pattern back and forth across the road.

In addition to the bank angle continually changing we must also remember to fly the airplane at a constant altitude of 600 feet above the ground. To accomplish this our field of vision will continually be changing. As you cross the road look over the nose of the airplane to assure that you are in a level flight attitude, then enter the bank and look down your wing to confirm your desired bank angle.

Flying this maneuver may be a bit frustrating at first. Trying to compensate for wind by constantly changing the bank angle, then keeping the airplane at 600’ and still flying a symmetrical arc will keep you very busy! However, with a little coaching from your instructor, you’ll soon be thinking ahead of the airplane and able to fly the S-turn.

There are several tips that I share with my students when first flying the S-turn. I point out reference points along the road that are about half-mile apart. This will help greatly in knowing where we should be crossing the road each time. Driveways, fence lines, farmhouses, tree lines and intersections are easy to spot and greatly help in maintaining the desired half-mile diameter. I also point out reference points on the up wind and down wind side of the road that are about quarter-mile beyond the road. Field lines, fence lines, or tree lines are most often used. This helps to establish the desired symmetrical arc on either side of the road.

One final tip: Remember when we were practicing medium and steep turns? As our angle of bank increases we experience a slight loss of lift requiring an increase of backpressure on the yoke or control stick to increase lift for maintaining a constant altitude. As we practice the S-turns we will need to increase and decrease back pressure slightly to compensate and assure that we maintain a constant altitude.

Don’t get discouraged when first practicing S-turns. There is a lot going on requiring your attention both in and out of the cockpit. But with more practice you’ll soon master the S-turn.

Turns around a point

The final ground reference maneuver we need to learn and perform is the turn around a point. You’ll find this maneuver to be quite easy to accomplish after practicing S-turns as it is nothing more than bringing the two symmetrical half-circles together as one full circle.

First, we’ll pick a good ground reference point like a road intersection. Our desire is to fly a complete symmetrical circle around that point while maintaining a constant radius and altitude of 600 feet. Select reference points on all four sides of the intersection that are approximately quarter-mile away from the intersection.

It doesn’t matter where you enter the turn, but I like to do it flying into the wind just as we did in the S-turn. We’ll begin by doing a left turn around the point. Immediately after crossing the road begin applying a shallow bank angle. Remember, we’re flying into the wind so we have a slow ground speed. Through the first eighth of the turn we’ll maintain the shallow bank so that our distance away from the intersection remains at a constant quarter-mile. As we near completion of the first quarter of the turn we transition from a head wind and slow ground speed to a cross wind and an increasing ground speed, necessitating a slight increase in the bank angle. As our turn progresses we transition from a cross wind to a down wind (tail wind) increasing our ground speed. The increased ground speed requires additional bank angle to maintain a constant radius. We’ve completed the first half of the maneuver as we cross the road. Continue maintaining the steep bank angle until we again transition to a cross wind slowing our ground speed. Decrease the bank angle while maintaining a constant distance from the intersection. While the turn progresses we’re again approaching the head wind requiring us to lessen the angle of bank even more. As we cross the road we’ll maintain the shallow bank. There, you’ve just completed a turn around a point!

The steepest bank is required when the plane is flying directly down wind.

After you have made 3-4 turns around a point to the left, try it using right turns.

It is best to practice both the S-turn and the turn around a point on a day with a moderate wind of approximately 10-15 mph. In so doing you will find that the airplane is always in a bank varying from 4-5 degrees to as much as 45 degrees in order to maintain a constant radius.

Ground reference maneuvers are practiced for several reasons:

1. To recognize the effect of the wind and how to correct for it.
2. To fly the airplane safely and at a constant altitude while dividing pilot attention.
3. To prepare for flight in the airport traffic pattern in preparation for practicing takeoffs and landings.

In the next newsletter we’ll begin flying the traffic pattern and working on take offs and landings.

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