CFI-A Lesson 18 (Part 1)

Today I completed the ground instruction portion of Lesson 18. I gave a brief on Eights on Pylons. I didn't complete the flight portion because I've been feeling like I'm coming down with a cold the past 24 hours and haven't slept very soundly. I knew the combination of tired and stuffy-headed wouldn't result in a very sharp performance.

Writing the brief was quite a challenge. Like all others, I had a good source of reference material, but still something was missing. I couldn't quite piece the maneuver together in my head. I knew that if I couldn't fully understand it, then there would be no way for me to successfully describe it to a student. This bothered me all night. This morning, an idea hit me and I raced downstairs to draw up a diagram that explained what I feel is the essence of the concept of pivotal altitude (the key ingredient of Eights on Pylons).

During the brief, I reproduced my diagram, expaining how both airspeed and bank angle effect the radius of a turn, then related this knowledge to the pivotal altitude. If too high, the bank angle must be steeper to maintain a line-of-sight to the pylon, but steeper banks decrease the turn radius (at a given speed), which results in turning too quickly to stay on the pylon. The solution is to increase speed, or decrease altitude. Since it is a constant airspeed maneuver, the only solution is to decrease altitude, which decreases the line-of-sight angle and therefore bank angle, which increases the radius of the turn. There's only one combination of speed, bank, and altitude that will result in maintaining the line-of-sight to the pylon. That said, airspeed may be constant, but ground speed is constantly changing - assuming there's any wind at all, and there always is - so the altitude of the airplane must constantly change to remain on the pivotal altitude.

I thought I described everything well. I went over my time limit by about 15 minutes, but there was a lot to discuss. I still felt miserable when I finished. I couldn't seem to draw my 'student' into the discussion and I read confusion and doubt on his face. The critique was pretty heavy and lasted as long or longer than the brief. Before my next lesson, I will need to prove that I understand all the key elements fully before continuing with the Lesson 18 flight.