In eights-on-pylons,
the distance from the pylons varies if there is any wind. Instead, the airplane is flown at such a
precise altitude and airspeed that a line parallel to the airplane’s lateral axis, and extending from the pilot’s eye, appears to pivot on each of the pylons. [Figure 6-10] Also, unlike eights around pylons, in the performance of eights-on-pylons the degree of bank increases as the distance from the pylon decreases.
The altitude that is appropriate for the airplane being flown is called the
pivotal altitude and is governed by the groundspeed. While not truly a ground track maneuver as were the preceding maneuvers, the objective
is similar—to develop the ability to maneuver the airplane accurately while dividing one’s attention between the flightpath and the selected points on the ground.
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An explanation of the pivotal altitude is also essential. There is a specific altitude at which, when the airplane turns at a given groundspeed, a projection of the sighting reference line to the selected point on the ground will appear to pivot on that point. Since different airplanes
fly at different airspeeds, the groundspeed will be different. Therefore, each airplane will have its own pivotal altitude. [Figure 6-12] The pivotal altitude does not vary with the angle of bank being used unless the
bank is steep enough to affect the groundspeed.
A rule of thumb for estimating pivotal altitude in calm wind is to square the true airspeed and divide by 15 for miles per hour (m.p.h.) or 11.3 for knots.