Insights

Ground reference maneuver made easy

First, you must have a general idea of pivotal altitude (PA). It equals ground speed in knots squared divided by 11.35. If groundspeed is 100 knots, PA is 881 feet above ground level; if groundspeed is 110 knots, PA is 1,066 feet agl. Those examples show that pivotal altitude is close to traffic pattern altitude, usually 1,000 feet agl. Learn to recognize that altitude without looking at the altimeter; it's critical knowledge for this maneuver and for successful forced landings.

Eights on pylons and view of pylon (inset).

Second, determine your visual reference line, which must be parallel to the airplane's lateral axis. Sit in the pilot's seat and have someone stand beyond the left wing in line with the airplane's lateral axis. Your reference line must be parallel to that line, so note its position in relation to the wing tip.

Third, determine the actual pivotal altitude when in flight. Clear the area for traffic and pick two pylons that meet these requirements: The distance between them is approximately one-half mile, the base of each is at the same elevation, and the line that connects them is perpendicular to the wind, if possible.

Start the maneuver as shown in the illustration using slow cruise airspeed at an altitude that's 200 or 300 feet above traffic pattern altitude. However, before you fly the maneuver as illustrated, determine pivotal altitude by flying one or two circles around the first pylon while descending. When abeam the pylon at point B, reduce power to 14 inches of manifold pressure or 1,400 rpm and start a descending turn. When you reach point D, continue the turn back to point B.

Initially your reference line will point behind the pylon toward the airplane's tail. As you descend, the reference line will move up to the pylon--that's pivotal altitude--and then move ahead of the pylon as you continue the descent. Climb back to the pivotal altitude and start the eights-on-pylon maneuver. As you turn toward point D, watch for the second pylon so that you can roll out of your turn on the proper heading to reach point E. When flying between pylons, point A to B and point D to E, altitude remains constant. The illustration's dotted lines that connect the wing to the pylon represent your visual reference line. While tuning, it must always point at the base of the pylon, which proves that you are maintaining pivotal altitude--the object of the maneuver.

As groundspeed changes, your distance from the pylon will change--which is contrary to most ground-reference maneuvers--and your visual reference line will start to move ahead of or behind the pylon. Therefore, you must adjust the pivotal altitude in order to keep the reference line pointing at the pylon's base. To do that, you climb as groundspeed increases, and descend as groundspeed decreases.

Changing altitude mandates a change in bank angle, not to control ground track, but to keep your reference line pointing at the pylon's base. As you climb, bank angle and turn rate will increase; as you descend, both will decrease. Depending on wind velocity, bank attitude will vary between 30 and 60 degrees.

Yes, eights on pylons are only required for commercial pilot certification, but everyone will benefit from the knowledge and skill that this maneuver generates.

Ralph Butcher, a retired United Airlines captain, is the chief flight instructor at a California flight school. He has been flying since 1959 and has 25,000 hours in fixed- and rotary-wing aircraft. Visit his Web site.