This maneuver is very close to the S-turn across a road because you’re correcting for wind while in a turn. It is suggested that the steepest bank should be approxi- mately 45° and the altitude should not be lower than 500 feet above the highest obstruction in the maneuver pattern. The idea of the turns about a point is to show the check pilot how well you can fly the plane when your attention is directed outside. Your check pilot will also want to find out if you understand wind drift cor- rection principles (Figure 16-1).
Procedure
1. Pick a tree or some other small but easily seen object and set up the radius small enough so that the steepest bank is approximately 45°.
2. Enter the pattern downwind. Practice both left and right turns around the point. Many students only practice left turns and get a rude awakening when they are asked to make a turn around a point to the right on the check flight. The best altitude for keep- ing the point in sight is about 700 feet above the surface.
3. Vary the turn as needed to maintain a constant dis- tance from the point — the greater the ground speed, the steeper the bank.
4. Maintain a constant altitude.
5. Keep your eyes open. This is a perfect place to have a low-altitude emergency thrown at you.
6. The check pilot may give you a free turn to get set up, but will keep up with the number of turns after the maneuver is started.
Figure 16-1. Turns around a point. The steepest bank is required when the plane is flying directly downwind.
Postsolo Precision Maneuvers 16
16-2 Part Three / Postsolo Maneuvers Common Errors
1. Starting the maneuver with the plane too far from the point so that the steepest bank does not reach 2. Poor altitude control.45°.
3. Pointing the wing at the tree — trying to keep the plane’s attitude the same in relation to the point rather than having the plane’s path constant, as it should be.
4. Failure to recognize wind drift or, if recognized, not doing anything about it.
5. Coordination problems. Students sometimes have trouble with this maneuver because they can’t seem to convince themselves that the steepest bank is required when the airplane is headed directly down- wind, as indicated in Figure 16-1.
Suppose an airplane is flying tangent (wings level) to the circle at the positions shown by A, B, C, and D in Figure 16-2. At A, the airplane is moving at its true airspeed plus the wind speed. This results in the high- est relative speed to the reference point of any position around the circle. At C, its relative speed is the lowest because it is moving into a headwind. The arrow (vec- tor) behind each airplane gives a picture of the relative speed at the four positions. The dashed lines show the comparative distances the airplane would be “away”
from the circle for any given interval of time if no turn was made.
Figure 16-2. A comparison of rates of “leaving the circle” for an airplane flying at the same true airspeed at four positions on the circle.
The rate of turn, then, must be greatest at A if it is to
“follow the circle.” Since this is a coordinated maneu- ver, the bank must be greatest at that position (and the bank is most shallow at C). The banks at B and D will be comparable.
Vector Approach to the Maneuver
If you are interested in the mathematics of turns around a point, Figure 16-3 shows wind triangles for the air- plane at eight points around the circle. As noted, the airplane’s true airspeed is 100 K and the wind is from the top of the illustration (North) at 40 K. The solid thin arrow represents groundspeed, or the airplane’s path and speed with respect to the ground. This groundspeed vector varies in size (speed) because of the wind, but at each of the eight points shown (or at any point on the circle) it must be tangent to the circle or else the plane would not be following the prescribed path; so this is the first consideration.
The true airspeed is indicated by the dashed arrows and is always 100 K for this problem. (Disregard slow- ing the airplane in the steeper banks.) The 100 K true airspeed vector, however, must be “pointed” in such a manner that the result of the plane’s heading, plus the wind, makes the airplane’s path tangent to the circle at any position. The wind is a constant velocity and direction.
Maybe you haven’t done any work with the naviga- tion computer yet, but you will, and you can come back to this later.
The circle can be thought of as an “infinite number of short, straight lines,” and the airplane is flying “one leg” of a rectangular course for each one. In order to do this, the plane must be crabbed to fly the line tan- gent to the circle. The reason for the bank is to get the proper heading for the next “leg.” The bank at point 1 must be steepest because the airplane is approaching the next “leg” at the greatest rate. At point 5 the oppo- site is true.
Of course, practically speaking, you fly the airplane and maintain the proper distance from the point by looking at it. But given the true airspeed and wind, you could work out on a navigation computer the required headings for each of the eight points given here. For instance, the course at point 1 is 180°. At point 2 the course would be 135°. At point 3 it would be 090°, etc., and you could find the wind correction angle. The required banks at each point could be obtained math- ematically for the radius of the circle to be flown, using a turn equation similar to that given in Chapter 3 of the Advanced Pilot’s Flight Manual. The maneuver could be theoretically flown “under the hood” once
Chapter 16 / Postsolo Precision Maneuvers 16-3
Figure 16-3. The turns around a point maneuver when seen as a problem in vectors.You may want to come back to this one after you’ve done some work with the computer.
16-4 Part Three / Postsolo Maneuvers